Rings, Clusters, and Polymers of the Main Group Elements 9780841208018, 9780841210608, 0-8412-0801-8

Table of contents :
Title Page......Page 1
Copyright......Page 2
ACS Symposium Series......Page 3
FOREWORD......Page 4
PREFACE......Page 5
IN MEMORIAM: Ralph W. Rudolph......Page 6
PdftkEmptyString......Page 0
Background......Page 8
Hydride Abstraction Reactions in the Absence of a Solvent......Page 11
Pentaborane(9): A Raw Material for the Preparation of Boron Hydrides and Boron Hydride Derivatives.......Page 17
Literature Cited......Page 21
2 Coordination and Related Chemistry of Polycyclic Tetraphosphorus Compounds......Page 24
P4 and P4-related Tetrahedral Clusters as Donors.......Page 25
Tetraphosphorus Oxides and Imides as Donors. The Transmission of Electronic and Structural Effects through the Molecular Frame......Page 33
Structural Disorder : a Prominent Feature of Closo-Compounds......Page 40
Trends in P-O and P-N Bond Lengths; Contribution to π-Bonding......Page 42
The Coordination Chemistry of Tetraphosphorus Sulfides : a Deceptive but Open Case......Page 47
Literature Cited......Page 51
3 Cyclic and High-Polymeric Phosphazenes as Carrier Molecules for Carboranyl, Metallo, or Bioactive Side Groups......Page 55
Cyclic Trimers and Tetramers as Reaction Models......Page 56
Modern Objectives in Polymer Synthesis......Page 58
Bioactive Polyphosphazenes......Page 60
Linkage of Transition Metals to Phosphazene Rings and High Polymers......Page 63
Literature Cited......Page 71
4 Polyanionic Clusters in Solids and Their Chemical Reactions......Page 74
Metal Compounds as Sources for Polycyclic Systems......Page 75
Crystalline and Plastic Phases M3P7 and M3P11 (M=alkaline metal)......Page 79
Literature Cited......Page 84
5 Cyclophosphathiazenes Containing Two- or Three-Coordinate Sulfur......Page 86
Cyclophosphathiazenes with Two Coordinate Sulfur......Page 87
Cyclophosphathiazenes with Three Coordinate Sulfur......Page 91
Summary and Conclusions......Page 96
Literature Cited......Page 97
6 Polyatomic Zintl Anions Stabilized Through Crypt Complexation of the Cation Heteroatomic Examples......Page 99
Homopolyatomic Anions......Page 100
Electronic Requirements......Page 104
Heteropolyatomic Anions......Page 106
Acknowledgment......Page 111
Literature Cited......Page 113
7 Multihapto Bonding Between Main Group Elements and Carbocyclic Ligands An Approach to the Bonding in Main Group Cluster Compounds......Page 115
Computational Procedures......Page 116
Qualitative Considerations......Page 117
Six or Eight Interstitial Electrons?......Page 119
Consequences of Increasing the Number of Valence Electrons on the Main-Group Fragment......Page 121
Three-, Four-, and Six-Membered Ring Systems......Page 123
Literature Cited......Page 125
8 Novel Cluster Interactions in Metalloboranes......Page 128
Literature Cited......Page 141
9 Molecular State Fingerprints and Semiempirical Hypersurface Calculations Useful Correlations to Track Short-Lived Molecules......Page 142
Some Hints on the Design of Hypersurface Calculations......Page 144
Representative Examples of Semiempirical Hypersurface Calculations for Medium-Sized Molecules.......Page 149
Concluding Remarks......Page 163
Acknowledgments......Page 165
Literature Cited......Page 166
10 Synthesis of Phosphorus-Nitrogen Polymers by Using Silicon-Nitrogen-Phosphorus Reagents......Page 169
Synthesis of Polyphosphazenes......Page 170
CCI4 Reactions of (Silylamino)phosphines......Page 173
Low-coordinate Phosphorus Systems......Page 174
Literature Cited......Page 177

Citation preview

Rings, Clusters, and Polymers of the Main Group Elements Alan

H.

Cowley, EDITOR

University of Texas at Austin

Based on a symposium sponsored by the ACS Division of Inorganic Chemistry at the 184th Meeting of the American Chemical Society, Kansas City, Missouri, September 12-17, 1982

ACS

SYMPOSIUM

SERIES

232

AMERICAN CHEMICAL SOCIETY W A S H I N G T O N , D. C.

1983

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

Library of Congress Cataloging in Publication Data Rings, clusters, and polymers of the main group elements. (ACS symposium series ISSN 00976156; 232) "Based on a symposium sponsore Division of Inorganic Chemistry at the 184th Meeting of the American Chemical Society, Kansas City, Missouri, September 12-17, 1982." Includes bibliographical references and index. 1. Ring formation (Chemistry)—Congresses. 2. Polymers and polymerization—Congresses. 3. Organometallic compounds—Congresses. I. Cowley, Alan H . II. American Chemical Society. Division of Inorganic Chemistry. III. American Chemical Society. Meeting (184th: 1982: Kansas City, Mo.) IV. Series. QD281.R5R56 1983 ISBN 0-8412-0801-8

547'.5

83-15462

Copyright © 1983 American Chemical Society All Rights Reserved. The appearance of the code at the bottom of the first page of each article in this volume indicates the copyright owner's consent that reprographic copies of the article may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc. for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating new collective work, for resale, or for information storage and retrieval systems. The copying fee for each chapter is indicated in the code at the bottom of the first page of the chapter. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. PRINTED IN T H E U N I T E D STATES O F A M E R I C A

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

ACS Symposium Series M. Joan Comstock, Series Editor

Advisory Board David L. Allara

Robert Ory

Robert Baker

Geoffrey D. Parfitt

Donald D. Dollberg

Theodore Provder

Brian M. Harney

Charles N. Satterfield

W. Jeffrey Howe

Dennis Schuetzle

Herbert D. Kaesz

Davis L. Temple, Jr.

Marvin Margoshes

Charles S. Tuesday

Donald E. Moreland

C. Grant Willson

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

FOREWORD The A C S S Y M P O S I U a medium for publishin format of the Series parallels that of the continuing A D V A N C E S IN CHEMISTRY S E R I E S except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. Papers are reviewed under the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however, verbatim reproductions of previously published papers are not accepted. Both reviews and reports of research are acceptable since symposia may embrace both types of presentation.

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

PREFACE S T U D Y O F T H E M A I N G R O U P E L E M E N T S has consistently promoted ad­ vances in many fields of chemistry. The mainstream of research, though, has been somewhat restricted in the past to the study of relatively small molecules. More recently, the increased knowledge of molecular to­ pology, bonding, and coordination chemistry, coupled with safer and sim­ pler syntheses of reasonable yield, has forged a path for more productive study of the larger ring, Although the puzzles to challenging, the relatively small group of researchers who tackle macromolecular studies perceive the promise of exciting and dramatic ad­ vances in the near future in both fundamental science and technology. The Ralph Rudolph Memorial Symposium on rings, clusters, and poly­ mers of the main group elements embraced a unique array of topics in this diverse field presented by a remarkable group of experts from around the world. Their contributions in this volume establish a long-needed definitive work in this now fast-moving area. The authors outline the realized and potential impact of the advances in their subspecialties—a very valuable perspective—and detail specific examples from their own research. It is hoped that this unprecedented collection will increase interaction among researchers in this area of inorganic chemistry and researchers in organic chemistry, polymer chemistry, and applied material science; the rewards are undeniable.

vii

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

IN M E M O R I A M : Ralph W . Rudolph Adapted from a speech by Robert W. Parry, President of the American Chemical Society, 1982

Ralph W. Rudolph, a brilliant and innovative inorganic chemist, was a proponent of active communication within his field and across related disciplines. Initially his research interest focused fluorophosphines but he continually explore the inorganic community. He used his pioneering expertise to decipher mysteries of compounds having phosphorus-phosphorus bonds, polyboranes and carboranes, and complex cage structures involving various main group elements. He strove to devise classification systems much needed in this undefined area. He wrote, "speaking personally, my re­ search has attracted much more attention and become more fulfilling as it has evolved and diversified from boron clusters to include main group metal clusters, catalysis, etc. Many have suggested that although spe­ cialization has some advantages, creativity usually fluorishes with diver­ sification." Not surprisingly, it was Ralph Rudolph who foresaw the great need for a comprehensive forum in the fast-moving area of rings, clusters, and polymers of the main group elements. The purposes of this symposium were to communicate advances to the inorganic community, to fill the gap for a much needed definitive work in this area, and to spur greater interaction with organic chemistry, transition metal chemistry, and ap­ plied science that is needed to fully develop this field. In response to his proposal for such a unifying symposium, the Inorganic Division requested that he organize the program. He agreed, and things were going well until late in April 1981. At that time, Ralph went into the hospital for a check­ up. He had been suffering from Hodgkin's disease, but his progress seemed wonderful. Then, one week later he became dreadfully ill and passed away in Ann Arbor on May 11, 1981. Thanks to the efforts of Alan Cowley, the distinguished panel of speakers, and those who at­ tended the symposium, the program envisioned by Ralph was a monu­ mental success, a very fitting tribute to this bright and dedicated scientist. Ralph Rudolph was born on July 14, 1940 in Erie, Pennsylvania. In 1962, he was graduated from Pennsylvania State University very near the ix

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

top of his class. He received the Ph.D. from the University of Michigan in 1966. His thesis, which reported the synthesis of P F H , P F , and P F C N , initiated many studies, both theoretical and experimental, in lab­ oratories around the world. Following his graduation from Michigan, he spent three years in Fort Collins, Colorado, at the F. J. Seiler Research Laboratory of the U.S. Air Force. In 1969, he returned to the University of Michigan as a member of the faculty. At the time of his death he was developing a program of research in the chemistry of "naked metal clus­ ters." He will be remembered for his pioneering syntheses in phosphorus chemistry, for his synthesis of thiaborane (a boron cage with a sulfur atom incorporated into the cage), for his inspirational teaching at both the graduate and undergraduate levels, for his strong sense of professional responsibility which is illustrated by the birth of this symposium, and for his many personal attribute was a delightful human achievement. 2

2

2

χ

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4

1 Systematic Approaches to the Preparation of Boron Hydrides and Their Derivatives S. G. SHORE The Ohio State University, Department of Chemistry, Columbus, OH 43210

Classical procedures for boron hydride syntheses are reviewed. The development f principle f synthese is presented an drides and thei One of t h e m a i n d r a w b a c k s t o t h e d e v e l o p m e n t o f t h e c h e m i s t r y of many of t h e b o r o n h y d r i d e s has been t h e a b s e n c e of s y n t h e t i c procedures f o r producing these m a t e r i a l s i n reasonable y i e l d s and q u a n t i t i e s by r e l a t i v e l y s a f e and s i m p l e t e c h n i q u e s . C l a s s i c a l a p p r o a c h e s a r e h e a v i l y dependent upon p y r o l y t i c p r o ­ cedures. A l t h o u g h t h e y have been d e v e l o p e d t o a " f i n e a r t , " t h e y r e q u i r e a h i g h d e g r e e of s k i l l i n o r d e r t o be e m p l o y e d s a f e l y i n o r d i n a r y l a b o r a t o r y environments. Other important c l a s s i c a l methods a r e dependent upon c o n t r o l l e d p r o t o l y s i s r e a c t i o n s , f r e q u e n t l y g i v i n g m i x t u r e s of m a t e r i a l s w h i c h a r e d i f f i c u l t to separate. F o r some t i m e we have been c o n c e r n e d w i t h d e v e l o p i n g r a t i o n a l a p p r o a c h e s t o b o r o n h y d r i d e s y n t h e s e s w h i c h w o u l d be b a s e d upon t h e s y s t e m a t i c a p p l i c a t i o n o f c h e m i c a l p r i n c i p l e s . T h i s a p p r o a c h has p r o v e d t o be s u c c e s s f u l f o r t h e p r e p a r a t i o n o f a number of b o r o n h y d r i d e s . D e s c r i b e d b e l o w i s t h e d e v e l o p m e n t of p r i n c i p l e s of b o r o n h y d r i d e s y n t h e s e s and t h e i r a p p l i c a t i o n s . Background The f i r s t d e f i n i t i v e p r e p a r a t i o n and c h a r a c t e r i z a t i o n of b o r o n h y d r i d e s was r e p o r t e d i n 1912 ( 1 ) . W i t h t h i s w o r k , A l f r e d S t o c k and h i s c o l l a b o r a t o r s i n t r o d u c e d an a r e a of i n o r g a n i c c h e m i s t r y f o r w h i c h t h e r e was no p r e c e d e n t i n terms of s t r u c t u r e and b o n d i n g . Over a p e r i o d o f t w e n t y - f o u r y e a r s t h i s g r o u p i s o l a t e d , i d e n t i f i e d and s t u d i e d t h e c h e m i s t r y of s i x b o r o n hydrides

(B2Hfc,

BifHio,

B5H9,

B5H11,

B6H10,

and

Β 10H. H+) ·

In

that

p a r t i c u l a r t i m e frame ( 1 9 1 2 - 1 9 3 6 ) t h e s e e f f o r t s r e p r e s e n t e d r e m a r k a b l e a c h i e v e m e n t s s i n c e i t was f i r s t n e c e s s a r y t o d e v e l o p t e c h n i q u e s f o r h a n d l i n g , s e p a r a t i n g and p h y s i c a l l y c h a r a c t e r -

0097-6156/83/0232-0001 $06.00/0 © 1983 American Chemical Society

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

2

RINGS, CLUSTERS, A N D

POLYMERS

i z i n g m a t e r i a l s ( f r e q u e n t l y i n l e s s than m i l l i m o l a r q u a n t i t y ) w h i c h f o r t h e most p a r t were v o l a t i l e s u b s t a n c e s t h a t r e a c t violently with a i r (2). The e a r l i e s t s y n t h e s e s of b o r o n h y d r i d e s were g r o s s l y i n e f f i c i e n t , g i v i n g m i x t u r e s of p r o d u c t s o f 4-5% t o t a l y i e l d s . These p r o c e d u r e s were b a s e d upon t h e r e a c t i o n of magnesium boride with hydrochloric a c i d . O n l y much l a t e r were y i e l d s o f 11% o b t a i n e d when 8N p h o s p h o r i c a c i d was u s e d ( 2 ) . Mg3B2 + H3P0i+

•

Boron Hydrides

+

H2

(1)

Β^Ηιο, B 5 H 9 , ,ΒβΗιο,

BioHm(trace)_

D i b o r a n e ( 6 ) was o b t a i n e (2). I n v i e w of t h e r e s t r i c t e t h e use of magnesium b o r i d e i n b o r o n h y d r i d e s y n t h e s e s , d e v e l o p ­ ment of t h e i r c h e m i s t r y p r o c e e d e d s l o w l y e v e n a f t e r t e c h n i q u e s had been a c q u i r e d f o r h a n d l i n g t h e s e m a t e r i a l s . The f i r s t s i g n i f i c a n t improvement i n b o r o n h y d r i d e s y n t h e s e s o c c u r r e d i n 1931 when S c h l e s i n g e r and B u r g ( 3 ) o b t a i n e d B 2 H 6 i n o v e r a l l y i e l d s o f 75%, a l b e i t i n s m a l l amounts, by p a s s i n g B C I 3 and H 2 t h r o u g h a h i g h v o l t a g e d i s c h a r g e . Over a p e r i o d of a p p r o x i m a t e l y t e n y e a r s S c h l e s i n g e r and Burg ( 4 ) , a l o n g w i t h a number of a s s o c i a t e s , c o n t i n u e d t o i m p r o v e upon t h e p r e p a r a t i o n of B 2 H 6 , and t h e y a l s o p i o n e e r e d i n s t u d y i n g the c h e m i s t r y of t h i s h y d r i d e . T h i s work i n c o n j u n c t i o n w i t h t h e d i s c o v e r y of m e t a l b o r o h y d r i d e s ( 5 - 1 2 ) made p o s s i b l e l a t e r l a r g e s c a l e p r e p a r a t i o n s of Β 2 Η 6 · B a s e d upon a h a l i d e - h y d r i d e exchange r e a c t i o n , t h e f i r s t t r u l y p r a c t i c a l s y n t h e s i s of B 2 H 6 was r e p o r t e d by F i n h o l t , Bond, and S c h l e s i n g e r i n 1947 ( 1 3 ) ( R e a c t i o n ( 2 ) ) . Et20 3 L1AIH4 + 4BCI3

•

2 B H 6 + 3LÎC1 + 3 A 1 C 1 3 2

(2)

Y i e l d s of 99% B 2 H 6 were o b t a i n e d . S u b s e q u e n t l y , a number of v i a b l e p r o c e d u r e s were d e v e l o p e d f o r t h e p r e p a r a t i o n o f B 2 H 6 by t h e h a l i d e - h y d r i d e exchange r o u t e ( 1 4 , 1 5 ) . P r o m i n e n t among these i s the f o l l o w i n g r e a c t i o n (16)Γ diglyme 3 NaBHi + 4 B F 3 +

*

2 B H 6 + 3 NaBF4 2

(3)

O t h e r u s e f u l r o u t e s t o B 2 H 6 were a l s o d e l i n e a t e d . Among t h e s e i s t h e r e a c t i o n of NaH w i t h e x c e s s B(OCH3)3 (14,1£,17), t h e r e a c t i o n o f BHi+~ w i t h I 2 ( 1 8 , 1 9 ) , and t h e c o n t r o l l e d " r e a c t i o n o f BHi+~ w i t h H3P0i|(conc) (20) Γ~ I n a l a t e r s e c t i o n of t h i s a r t i c l e t h e r e i s r e p o r t e d a h i g h y i e l d p r e p a r a t i o n o f B 2 H 6 by h y d r i d e a b s t r a c t i o n f r o m BHi+"~ i n t h e a b s e n c e of a s o l v e n t ( 2 1 ) . A t t e m p t s t o d e v e l o p h i g h e n e r g y b o r a n e f u e l s i n t h e 1950's

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

1.

SHORE

Boron Hydrides and Derivatives

e l e v a t e d B2H6 , B 5 H 9 , and B i o H m f r o m the s t a t u s o f l a b o r a t o r y c u r i o s i t i e s t o compounds p r o d u c e d on a tonnage b a s i s . From t h e c o n t r o l l e d p y r o l y s i s of B2H6 , e i t h e r B5H9 o r B10H14. as the d e s i r e d p r o d u c t , was o b t a i n e d ( 2 2 ) . T h i s program spawned i n t e n s e r e s e a r c h a c t i v i t y , l e a d i n g to r a p i d developments i n s y n t h e t i c chemistry (organoboranes ( 2 3 ) , h y d r o b o r a t i o n (24,25), p o l y h e d r a l boranes (26,27), carboranes (27,49), metalloboranes ( 2 7 , 5 0 ) , m e t a l l o c a r b o r a n e s ( 2 7 , 5 0 ) ) and s t r u c t u r a l and t h e o r e t i c a l chemistry (27,28)^ Today, a number of B2H6 d e r i v a t i v e s a r e c o m m e r c i a l l y a v a i l a b l e , and B i o H m s e r v e s as t h e s t a r t i n g m a t e r i a l f o r a l a r g e v a r i e t y of h i g h e r boranes, c a r b o r a n e s , m e t a l l o b o r a n e s , and m e t a l l o c a r b o r a n e s . Uses f o r B5H9 have been p r i m a r i l y c o n c e r n e d w i t h i t s a p p l i c a t i o n as a s t a r t i n g m a t e r i a l i n the p r e p a r a t i o n of s m a l l e r c a r b o r a n e s , m e t a l l o b o r a n e s , and m e t a l l o c a r b o r a n e s . I n the 1950's and 1960' b o r o n h y d r i d e a n i o n s wer e m p h a s i s was p l a c e d upon s t a b l e h i g h e r b o r a n e e n t i t i e s d e r i v e d f r o m B i o H m , s i g n i f i c a n t p r o g r e s s was made i n the p r e p a r a t i o n o f new, s m a l l e r b o r o n h y d r i d e s . U n f o r t u n a t e l y , at t h i s p e r i o d of t i m e , most of t h e s e m a t e r i a l s c o u l d be o b t a i n e d o n l y i n s m a l l amounts. (A c o m p r e h e n s i v e t r e a t m e n t o f a l l b o r o n h y d r i d e s p r e p a r e d t h r o u g h 1978 i s g i v e n i n r e f e r e n c e s (51) and ( 5 2 ) . D u r i n g t h i s p e r i o d of p r o g r e s s , s i g n i f i c a n t p r o c e d u r e s f o r t h e a l r e a d y known l o w e r b o r o n h y d r i d e s Bi+Hio ( 1 5 , 2 9 , 3 0 ) and B 5 H 1 1 ( 3 0 , 3 1 ) were i n t r o d u c e d , but t h e s e posed t e c h n i c a l demands and s a f e t y p r o b l e m s , w h i c h i n g e n e r a l made them u n a t t r a c t i v e as l a b o r a t o r y p r e p a r a t i o n s . Subsequent, r e l a t i v e l y s a f e p r e p a r a t i o n s o f Bi+Hio were a c h i e v e d t h r o u g h the r e a c t i o n o f [N(CH3 [ B 3 H 8 ] w i t h p o l y p h o s p h o r i c a c i d ( 4 0 % y i e l d ) (32) and NaB3H8 w i t h HC1 ( 4 0 % y i e l d ) ( 3 3 ) , but s u f f e r e d f r o m t h e ~ r e q u i r e m e n t of t i m e - c o n s u m i n g and t e d i o u s s e p a r a t i o n p r o c e d u r e s . By the c l o s e of t h e I960's e m p h a s i s had s h i f t e d t o the p r e p a r a t i o n and s t u d y of m e t a l l o b o r a n e s and m e t a l l o c a r b o r a n e s , many of w h i c h were p r e p a r e d f r o m B i o H m and B5H9 ( l e g a c i e s f r o m the h i g h e n e r g y f u e l s p r o g r a m ) . I n t e r e s t i n boron h y d r i d e s w h i c h c o u l d not be r e a d i l y o b t a i n e d o r p r e p a r e d had waned, not b e c a u s e t h e y were i n t r i n s i c a l l y u n i n t e r e s t i n g , but more l i k e l y b e c a u s e o f p r o b l e m s a s s o c i a t e d w i t h o b t a i n i n g . them. At t h i s t i m e , from s t u d i e s of B 5 H 9 , we became i n c r e a s i n g l y aware o f p o s s i b i l i t i e s f o r d e v e l o p i n g r a t i o n a l , s y s t e m a t i c methods f o r p r e p a r i n g some of the r a r e s m a l l e r b o r o n h y d r i d e s i n good y i e l d s and r e a s o n a b l e q u a n t i t i e s . T h i s work e v e n t u a l l y l e d t o the d e v e l o p m e n t of two d i f f e r e n t t y p e s of s y s t e m a t i c a p p r o a c h e s t o boron hydride syntheses (34,21). I t not o n l y r e s u l t e d i n t h e p r e p a r a t i o n of b o r o n h y d r i d e s p r e v i o u s l y not r e a d i l y a c c e s s i b l e , b u t a l s o r e c e n t l y d e m o n s t r a t e d the p o t e n t i a l o f B5H9 as a f e e d s t o c k i n the p r e p a r a t i o n o f B i o H m and o t h e r h i g h e r b o r o n h y d r i d e s y s t e m s and d e r i v a t i v e s . D e s c r i b e d b e l o w a r e the r e s u l t s of t h e s e s t u d i e s .

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

3

4

RINGS, CLUSTERS, A N D

POLYMERS

D e p r o t o n a t i o n and Boraae I n s e r t i o n R e a c t i o n s Many o f t h e b o r o n h y d r i d e s have been shown t o f u n c t i o n as Bro'nsted a c i d s (See 34 f o r r e f e r e n c e s ) . The b r i d g i n g h y d r o g e n s are a c i d i c . Pentaborane(9) i s a monoprotic a c i d i n the presence of a v a r i e t y of bases ( 3 5 , 3 6 , 3 7 ) . An example of s u c h a r e a c t i o n ( 3 8 ) i s g i v e n i n Scheme I , R e a c t i o n ( 4 ) . By r e m o v i n g t h e b r i d g i n g p r o t o n t o g i v e BsHs~, a b o r o n - b o r o n bond i s formed w h i c h i s s u s c e p t i b l e t o i n s e r t i o n of e l e c t r o p h i l l i c a g e n t s . Thus by i n s e r t i n g BH3 i n t o t h i s s i t e , t h e new a n i o n B f c H n " was formed (35,39) (Scheme I , R e a c t i o n ( 5 ) ) . T r e a t m e n t of t h i s a n i o n w i t h HC1 gave B 6 H 1 2 i n 60% y i e l d s ( 3 9 ) (Scheme I , R e a c t i o n (6)). On t h e o t h e r hand by t r e a t i n g B e H i i ^ w i t h an a d d i t i o n a l q u a n t i t y of B 2 H 6 , B 6 H 1 0 was o b t a i n e d i n y i e l d s o f 30% ( 4 0 ) (Scheme I , R e a c t i o n ( 7 ) ) . The p r o c e d u r e s o u t l i n e c i p l e s f o r p r e p a r i n g tw w i t h d i f f i c u l t y i n v e r y s m a l l y i e l d s as a p p a r e n t b y - p r o d u c t s o f reactions. The c o m m e r c i a l a v a i l a b i l i t y o f t h e s t a r t i n g m a t e r i a l B5H9 ( C a l l e r y C h e m i c a l Co., C a l l e r y , PA 16024) enhances t h e u s e f u l n e s s of t h e s e p r e p a r a t i o n s . T h i s a p p r o a c h t o b o r o n h y d r i d e s y n t h e s e s was f u r t h e r a p p l i e d t h r o u g h t h e f o l l o w i n g sequence w h i c h s t a r t e d w i t h B 4 H 1 0 and gave B 5 H 1 1 i n 60% y i e l d s ( 3 9 ) (Scheme I I , R e a c t i o n s ( 8 ) , (9), (10). The p r e p a r a t i o n of B 6 H 1 0 was g r e a t l y i m p r o v e d when b r o m i n a t e d p e n t a b o r a n e ( 9 ) was used as a s t a r t i n g m a t e r i a l ( 4 1 ) . l - B r B H s + KH

>

5

K[l-BrB H ] + V2B 6 H

5

7

2

K[l-BrBsH7] + H2 y

B Hio+KBr 6

(11) (12)

Y i e l d s of ΒβΗχο were 75%. T h i s method d e m o n s t r a t e s t h a t bromide i o n i s a good l e a v i n g group f r o m borane e n t i t i e s . In subsequent s t u d i e s by S c h a e f f e r ( 4 2 ) and by G a i n e s ( 4 3 ) , f u s e d borane and l i n k e d borane cages were p r e p a r e d by t a k i n g a d v a n t a g e of t h i s property. H y d r i d e A b s t r a c t i o n R e a c t i o n s i n t h e Absence

of a S o l v e n t

I n t h e c o u r s e of s t u d y i n g t h e p r e p a r a t i o n o f B 6 H 1 0 f r o m 6 H i i ~ " ( R e a c t i o n ( 7 ) ) , s i g n i f i c a n t q u a n t i t i e s of B 1 0 H 1 4 (up t o 27% y i e l d s ) ( 4 0 ) were o b t a i n e d f r o m r e a c t i o n m i x t u r e s i n e t h e r s m a i n t a i n e d a t o r above room t e m p e r a t u r e . The s o u r c e of B i o H m was b e l i e v e d t o be B 6 H i ] ~ f r o m w h i c h ΒΗι+"~ was a p p a r e n t l y e l i m i n a t e d upon warming t h e s y s t e m . B

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

Boron Hydrides and Derivatives

SHORE

(B H, ) 6

2

SCHEME

I

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

SCHEME II

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

1.

SHORE

K[B5H8]

1

Boron Hydrides and Derivatives +V B2H6

• [ B5 H7 ] + K[ ΒΗΊ+ ]

•K[B6Hll]

2

(13)

i V2 B i o Hii+ The p o s s i b i l i t y was c o n s i d e r e d t h a t i f R e a c t i o n ( 1 3 ) does o c c u r t h r o u g h t h e i n t e r m e d i a t e [ B 5 H 7 ] , t h e n l - B r B s H z " m i g h t be a v e r y good c a n d i d a t e f o r p r e p a r i n g BioHm. i n h i g h y i e l d s , s i n c e B r ~ i s a good l e a v i n g g r o u p . The f o l l o w i n g r e a c t i o n was a t t e m p t e d . K[l-BrB5H7]

+

• [B5H7]

BBr3

+

K[BBri+ ]

(14)

ι V

2

B i o Hi

I t was a f a i l u r e . Althoug i c a l l y , t h e y i e l d was i n s i g n i f i c a n intractable. A s e c o n d a t t e m p t was made a t b r o m i d e i o n a b s t r a c t i o n . In t h i s c a s e , h o w e v e r , the B3H7Br" i o n was u s e d i n t h e hope o f p r e p a r i n g B6H12 t h r o u g h t h e f o l l o w i n g p r o p o s e d r e a c t i o n . [N(n-OtH9)if ] [ B 3 H 7 B r ]

+

BBr3

• [B3H7] +

V

2

[N(r,-C H ) ] [BBr ] 4

B 6 H m - > V B6H12 + V 2

9

2

4

«2

4

(15)

I n t h e s e n s e t h a t B6H12 was n o t p r o d u c e d , t h i s r e a c t i o n was a l s o a f a i l u r e ; however i t d i d p r o d u c e 2-BrBi+H9 and B1+H10 ( e a c h i n 10-15% y i e l d ) . I n f a c t , t h i s i s t h e p r e f e r r e d r o u t e t o 2BrB^Hg. F u r t h e r m o r e , t h i s r e s u l t s u g g e s t e d t h a t t h e H~ i o n as w e l l as B r ~ c a n be a b s t r a c t e d f r o m B 3 H / B r " . Thus i f B 3 H 8 " were u s e d i n p l a c e o f B r B 3 H 7 ~ , t h e y i e l d o f Βι+Ηιο s h o u l d i n c r e a s e . Indeed t h i s p r o v e d t o be t h e c a s e and p r o v i d e d t h e k e y t o e s t a b l i s h i n g a s y s t e m a t i c r o u t e to boron h y d r i d e syntheses to p r o d u c e B 2 H 6 , Βι+Ηιο, B 5 H 1 1 , and B i o H m ( 2 1 ) . The p r o c e d u r e s a r e s i m p l e and g i v e e s s e n t i a l l y s t o i c h i o ­ m e t r i c r e a c t i o n s w h i c h can be c a r r i e d o u t i n t h e a b s e n c e of a solvent. The s y s t e m a t i c n a t u r e o f t h e s e s y n t h e s e s r e l a t e s t o the o b s e r v a t i o n t h a t h y d r i d e i o n c a n be a b s t r a c t e d f r o m c e r t a i n b o r o n h y d r i d e a n i o n s t o g i v e as one o f t h e f i n a l p r o d u c t s a n e u t r a l b o r o n h y d r i d e w h i c h c o n t a i n s one more b o r o n atom t h a n the a n i o n i c s t a r t i n g m a t e r i a l . These r e a c t i o n s a r e d e s c r i b e d below. B2H6 f r o m BHt+~. The s i m p l e s t r e a c t i o n o b s e r v e d i n v o l v e s the a b s t r a c t i o n o f h y d r i d e i o n f r o m ΒΗι+~" by a b o r o n h a l i d e t o g e n e r a t e BH3 u n i t s w h i c h combine t o f o r m B 2 H 6 . R e a c t i o n (16) r e p r e s e n t s the g e n e r a l r e a c t i o n o b s e r v e d .

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

8

RINGS, CLUSTERS, A N D

2 BH4~

+

2 BX3

BH3

+

BH3

•

B2H6

2 BX3

•

B2H6

2 BHi+ The B2H6 that free

+

• 2 BH3

+

POLYMERS

2 HBX ~ 3

+ 2 HBX3

(16)

r e a c t i o n of s o l i d NaBHi+ w i t h BF3 a t room t e m p e r a t u r e g i v e s i n 95% y i e l d . T h i s p r o c e d u r e d i f f e r s from R e a c t i o n ( 3 ) i n h y d r i d e - h a l i d e exchange i s n o t i n v o l v e d and t h e s y s t e m i s of e t h e r s o l v e n t .

Bt+Hip f r o m B 3 H 8 " . T e t r a b o r a n e ( 10) i s o b t a i n e d i n 65% y i e l d ( b a s e d on b o r o n i n B 3 H 8 " ) f r o m t h e r e a c t i o n o f s o l i d [ N ( n Ci*R9 )4 ] [B3He ] w i t h B C I 3 a t room t e m p e r a t u r e . T h i s r e a c t i o n has been s t u d i e d i n d e t a i l viewed i n the f o l l o w i n An i n i t i a l s t e p i n v o l v e s a b s t r a c t i o n of h y d r i d e i o n from B 3 H 8 " to g e n e r a t e the u n s t a b l e i n t e r m e d i a t e [ B 3 H 7 ] . T r a n s f e r of a BH3 u n i t from one [ B 3 H 7 ] m o l e c u l e t o a n o t h e r would g e n e r a t e Bi+Hio and a r e s i d u e of e m p i r i c a l c o m p o s i t i o n ( B H 2 ) · Thus t h e f o l l o w i n g sequence w i t h r e s u l t i n g s t o i c h i o m e t r y (17) i s envisioned. B3H8""

+

BCI3

V [B3H7]

+V [B3H7]

2

B3H8""

•

• V

2

+

BC13 •

[B3H7]

• \

2

+

HBCI3"

B4H10 +

1/χ(ΒΗ ) 2

χ

Bi+HiO + H B C I 3 " + 1/χ(ΒΗ2)

χ

(17)

I n r e a c t i o n ( 1 7 ) , 67% o f t h e b o r o n i n B 3 H e ~ i s c o n v e r t e d t o Bi+Hio. T h i s p e r c e n t c o n v e r s i o n a g r e e s c l o s e l y w i t h e x p e r i m e n t a l yields. I t suggests that the p r e p a r a t i v e procedure i s q u a n t i t a ­ t i v e w i t h r e s p e c t t o the t h e o r e t i c a l amount o f Bi+Hio w h i c h c a n be p r o d u c e d . T h i s i s by f a r t h e s a f e s t r o u t e t o B ^ H ^ Q available. I t i s a l s o a t t r a c t i v e b e c a u s e of the c o m m e r c i a l a v a i l a b i l i t y of [N(CHU)/][Β0Η0] ( A l f a P r o d u c t s , D a n v e r s , MA 01923). B5H11 f r o m Β^Ηθ". P e n t a b o r a n e ( 1 1 ) i s o b t a i n e d i n 60% y i e l d ( b a s e d upon b o r o n i n Bi+H9~~) f r o m t h e r e a c t i o n of s o l i d K[Bi+Hg] w i t h l i q u i d B C I 3 a t -35°C. T h i s r e a c t i o n has been s t u d i e d i n detail. I t i s a n a l o g o u s t o r e a c t i o n s (16) and ( 1 7 ) and i s v i e w e d as f o l l o w s . H y d r i d e a b s t r a c t i o n f r o m Bi+Hg" g e n e r a t e s t h e u n s t a b l e i n t e r m e d i a t e [Bi+He]. F o r m a t i o n o f B5H11 c a n o c c u r i n a s e c o n d s t e p w h i c h i n v o l v e s t r a n s f e r of BH3 f r o m one [Bi+Ηβ] u n i t t o a n o t h e r [ B 4 H 8 ] . The f o l l o w i n g s e q u e n c e w i t h r e s u l t i n g s t o i c h i o ­ m e t r y (18) i s s u g g e s t e d .

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

1.

Bi+Hg"

BCI3

+

•

1

ν [Βι,Η8] + / 2 [ B i H ] 2

Bi+Hg""

+

+

9

Boron Hydrides and Derivatives

SHORE

BCI3

8

[B4H8]

+

HBCl3~ x

^ B s H l l *

B

( V ) ( 3H 5> 2

x

>V2B5H11 + HBCI3" + ( V2X)(B3H5)

(18)

X

I n r e a c t i o n ( 1 8 ) 6 3 % o f t h e b o r o n i n t h e Bi+Hg"~ i s c o n v e r t e d t o B5H11. Thus t h e e x p e r i m e n t a l y i e l d , 6 0 % , i s c l o s e t o t h e t h e o r e t i c a l l i m i t of B5H11 a v a i l a b l e from ( 1 8 ) . This i s t h e safest route to B^H^. B i p H m f r o m BgHm~". D e c a b o r a n e ( 14) i s o b t a i n e d i n 5 0 % y i e l d ( b a s e d upon b o r o n i n BgHm"") f r o m t h e r e a c t i o n o f s o l i d [N(CH3)i+] [ B g H m ] w i t h B C 1 3 a t room t e m p e r a t u r e . This r e a c t i o n has been s t u d i e d i n d e t a i l . I t i s analogous t o Reactions ( 1 6 ) , ( 1 7 ) , and (18) a n d i s b e l i e v e sequence g i v i n g s t o i c h i o m e t r Β9Η11Γ

+ BCI3

V2B9H13 BgHm" +

+

V2B9H13 BCI3

+ [B9H13] ^V BioHm 2

+

HBCl3~" +

V x(B H 2

8

1 0

)

+

x

1/ H 2

2

• V 2 B i o H i i f + V H 2 + HBC1 3 " + 2

( V x)(B8Hl0) 2

x

(19)

I n r e a c t i o n ( 1 9 ) 56% o f t h e b o r o n i n t h e B g H m " i s c o n v e r t e d t o B l O ^ m . The e x p e r i m e n t a l y i e l d o f B i o H m , 5 0 % , s u g g e s t s t h a t t h e t h e o r e t i c a l l i m i t d e f i n e d by R e a c t i o n ( 1 9 ) i s a p p r o a c h e d . I n t h e above p r e p a r a t i o n s o f B i o H m , B 5 H 1 1 , a n d Bi+HlO> a b s t r a c t i o n o f H" f r o m a b o r a n e a n i o n g i v e s a n u n s t a b l e n e u t r a l fragment which i s b e l i e v e d t o o b t a i n a BH3 u n i t from another l i k e fragment t o form t h e d e s i r e d borane p r o d u c t . One h u n d r e d per cent c o n v e r s i o n of t h e s t a r t i n g m a t e r i a l t o the d e s i r e d b o r o n h y d r i d e c a n n o t be a c h i e v e d . On t h e o t h e r hand i f B H 3 c o u l d be " f u n n e l e d " i n t o t h e r e a c t i o n m i x t u r e t o r e a c t w i t h t h e u n s t a b l e i n t e r m e d i a t e , t h e n 100% c o n v e r s i o n c o u l d be a c h i e v e d i n principle. The a b i l i t y o f C I B H 3 " t o f u n c t i o n a s a B H 3 d o n o r was examined i n t h e p r e p a r a t i o n o f Β î o H m . An e q u i v a l e n t o f [ N ( C H 3 ) i t J [ C I B H 3 ] was added t o [N(CH3> 4] [BgHn+] a l o n g w i t h d o u b l e the amount o f B C I 3 n o r m a l l y u s e d t o p r e p a r e B i o H m The p u r p o s e o f t h e e x c e s s B C I 3 was t o e x t r a c t C l ~ f r o m C1BH3~, t h e r e b y r e l e a s i n g BH3 t o r e a c t w i t h t h e [BgHi3] g e n e r a t e d from t h e r e a c t i o n of BgHm~ w i t h B C I 3 . The p r o j e c t e d s t o i c h i o m e t r y i s R e a c t i o n ( 2 0 ) , w i t h complete c o n v e r s i o n of BgH^ ~ t o B ^ Q H ^ 4

BgHm" + C I B H 3 " +2BCI3

y BioHm + H

2

+ HBC1 3 " + BC1 4 " ( 2 0 )

A y i e l d o f 70% Β - ^ Η · ^ ( b a s e d upon t h e b o r o n i n Β^Η·^ and C1BH3~) was o b t a i n e d . T h i s r e s u l t s u p p o r t s t h e proposed sequence f o r

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

10

RINGS, CLUSTERS, A N D POLYMERS

R e a c t i o n ( 1 9 ) and p r e s e n t s a p r o m i s i n g m o d i f i c a t i o n o f t h e synthetic procedure. P e n t a b o r a n e ( 9 ) : A Raw M a t e r i a l f o r t h e P r e p a r a t i o n o f B o r o n H y d r i d e s and B o r o n H y d r i d e D e r i v a t i v e s . P e n t a b o r a n e ( 9 ) i s a p o t e n t i a l l y u s e f u l raw m a t e r i a l f o r t h e p r o d u c t i o n of h i g h e r boron h y d r i d e s . I t i s c o m m e r c i a l l y a v a i l a b l e ( C a l l e r y C h e m i c a l Co.; C a l l e r y , PA 1 6 0 2 4 ) . Close to 100 t o n s i s i n s t o r a g e , l e f t o v e r f r o m t h e h i g h e n e r g y b o r a n e f u e l s program. I t s u s e i n t h e p r e p a r a t i o n o f ΒβΗιο and ΒβΗΐ2 has a l r e a d y been d i s c u s s e d i n t h i s a r t i c l e . O t h e r , p e r h a p s more i m p o r t a n t a p p l i c a t i o n s c a n be made a l s o . The e x a m p l e s g i v e n below r e p r e s e n t a b e g i n n i n g i n the study of such a p p l i c a t i o n s . B i p H m from B5H9 v i p r o c e d u r e has been d e v e l o p e B 5 H 9 w h i c h i s amenable t o a w i d e range o f r e a c t i o n s c a l e s (21). I n one s t e p t h e B 5 H 9 i s c o n v e r t e d t o [ N ( C H 3 ) 4 ] [ Β 9 H m ] , and i n t h e s e c o n d s t e p B g H m " i s c o n v e r t e d t o ΒιοΗ]Λ a c c o r d i n g to t h e p r e p a r a t i o n d i s c u s s e d p r e v i o u s l y ( S e e Scheme I I I ) . The B10H14 i s then sublimed from the r e a c t o r . C o n v e r s i o n of B5H9 to [N(CH3)4][B9H14] i s achieved through t h e r e a c t i o n o f B 5 H 9 w i t h NaH i n 2:1 m o l a r r a t i o i n THF a t room t e m p e r a t u r e i n t h e p r e s e n c e o f one e q u i v a l e n t o f [ N ( C H 3 ) i j C l . An i n i t i a l d e p r o t o n a t i o n s t e p i s i n v o l v e d , as i n R e a c t i o n ( 4 ) , to g e n e r a t e B5H8"" w h i c h t h e n r e a c t s w i t h an e q u i v a l e n t amount o f the r e m a i n i n g B5H9 t o g i v e B9H14"". B 9 H 1 3 L and n-B],8H22 f r o m B 9 H 1 4 " " . Standard syntheses f o r B g H i 4 ~ , B 9 H 1 3 L ( L = L e w i s b a s e ) and n - B i 8 H 2 2 use B 1 0 H 1 4 as a s t a r t i n g p o i n t and i n v o l v e d e g r a d a t i o n o f t h e B i o s k e l e t o n t o a B9 s k e l e t o n . By t a k i n g a d v a n t a g e of t h e s i m p l e - h i g h y i e l d c o n v e r s i o n o f B 5 H 9 t o B9H14"", d e s c r i b e d a b o v e , i t has been p o s s i b l e t o c o n v e r t B 5 H 9 t o B 9 H 1 3 L ( L = R 2 S , N R 3 , P h 3 P ) and n B18^22 * p r a c t i c a l " o n e - p o t " p r o c e d u r e s w h i c h a r e m o d i f i c a t i o n s of e a r l i e r m e t h o d s ( 4 4 ) . The B9H14"" i s c o n v e r t e d t o B 9 H 1 3 L a n d n - B i s H 2 2 a c c o r d i n g t o Scheme IV b e l o w . n

5 , 6 - ( C H 3 ) C 2 B 8 H i Q from B 5 H 9 v i a B 9 H 1 4 " . The c a r b o r a n e 5,6(CH3)2C2B8Hio was p r o d u c e d i n 35% y i e l d ( b a s e d on b o r o n i n B5H9). Scheme V o u t l i n e s t h e s y n t h e s i s . This type of carborane was p r e v i o u s l y p r e p a r e d f r o m a l a r g e r c a r b o r a n e s y s t e m t h r o u g h a d e g r a d a t i o n p r o c e s s ( 4 5 , 4 6 ) and a l s o f r o m t h e r e a c t i o n o f Β3^12 w i t h a l k y n e s ( 4 7 , 4 8 ) . The p r o c e d u r e g i v e n i n Scheme V i s s i m p l e r than t h e s e " e a r l i e r p r e p a r a t i v e methods. 2

Acknowledgments a r e made t o t h e Army R e s e a r c h O f f i c e and t h e N a t i o n a l Science Foundation f o r f i n a n c i a l support.

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

1.

SHORE

11

Boron Hydrides and Derivatives

Να H +

2B H 5

9

+

N(CH ) CI 3

4

(B, H, ) 0

4

SCHEME EE

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

RINGS, CLUSTERS,

NaH

+

2B H 5

THF

Ν0Β Η, + 9

9

HCI

B H OR 9

| 3

4

+

AND

H

POLYMERS

2

R 0 2

2

+ L

(n-B H )

(B^ L)

|8

|3

22

SCHEME 32

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

SHORE

Boron Hydrides and Derivatives

SCHEME Y.

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

14

RINGS, CLUSTERS, AND POLYMERS

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9.

10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.

Stock, A; Massenez, C. Ber. 1912, 45, 3529. Stock, A. "Hydrides of Boron and Silicon," Cornell University Press, Ithaca, New York, 1933. Schlesinger, H. I.; Burg, A. B. J. Am. Chem. Soc. 1931, 53, 4321. Schlesinger, H. I..; Burg, A. B. Chem. Rev. 1942, 31, 1. Schlesinger, H. I. Brown, H. C. J. Am. Chem. Soc. 1940, 62, 3429. Burg, A. B.; Schlesinger, H. I. J. Am. Chem. Soc. 1940, 62, 3425. Schlesinger, H. I.; Sanderson, R. T.; Burg, A. B. J. Am. Chem. Soc. 1939, 61, 536. Schlesinger, H. I.; Sanderson, R. T.; Burg, A. B. J. Am. Chem. Soc. 1940 62, 3421 Schlesinger, H C.; Davidson, N.; , ; , ; Hoekstra, H.; Horvitz, L.; Hyde, Ε. K.; Katz, J. J . ; Knight, J . ; Lad, R. Α.; Mayfield, D. L.; Rapp, L.; Ritter, D. M.; Schwartz, A. M.; Sheft, I.; Tuck, L. D.; and Walker, A. O. J. Am. Chem. Soc. 1953, 75, 186. Schlesinger, Η. I.; Brown, H. C.; Hoekstra, H. R.; Rapp, L. J. Am. Chem. Soc. 1953, 75, 199. Schlesinger, Η. I.; Brown, H. C., Finholt, A. E. J. Am. Chem. Soc. 1953, 75, 205. Schlesinger, Η. I.; Brown, H. C.; Hyde, Ε. K. J. Am. Chem. Soc. 1953, 75, 209. Finholt, A. E.; Bond, A. C.; Schlesinger, Η. I. J. Am. Chem. Soc. 1947, 69, 1199. Adams, R. M. Advan. Chem. Ser. 1961, 33, 60. Parry, R. W.; Walter, M. K. Prep. Inorg. React. 1968, 5, 45. Brown, H. C.; Tierney, P. J. J. Am. Chem. Soc. 1958, 80, 1522. Bush, J. D.; Carpenter, R. Α.; Schechter, W. H., U. S. Pat. 3,014,059; Dec. 19, 1961. Nainan, K. C.; Ryschkewitsch Inorg. Nucl. Chem. Lett. 1970, 6, 765. Freeguard, G. F.; Long, L. M. Chem. Ind. (London) 1965, 11, 471. Duke, B. J.; Gilbert, J. R.; Read, I. A. J. Chem. Soc., London 1964, 50, Toft, Μ. Α.; Leach, J. B.; Himpsl, F. L.; Shore, S. G. Inorg. Chem. 1982, 21, 1952. Holzman, R. T.; Hughes, R. L.; Smith, I. C.; Lawless, E. W., "Production of the Boranes and Related Research," Academic Press, New York, 1967. Onak, T. "Organoboranes," Academic Press, New York, 1975. Brown, H. C., "Hydroboration," Benajmin, New York, 1962.

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

SHORE

25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51.

Boron Hydrides and Derivatives

Brown, H. C. "Boranes in Organic Chemistry," Cornell University Press, Ithaca, New York, 1972. Muetterties, E. L.; Knoth, W. H. "Polyhedral Boranes," Dekker, New York, 1968. Muetterties, E. L . , "Boron Hydride Chemistry," Academic Press, New York, 1975. Lipscomb, W. N. "Boron Hydrides," Benjamin, New York, 1963. Kodama, G., Ph.D., Thesis, University of Michigan, Ann Arbor, 1957, pp. 60-62. Klein, M. J.; Harrison, B. C.; Solomon, I. J. J. Am. Chem. Soc. 1958, 80, 4149. Norman, A. D.; Schaeffer, R. Inorg. Chem. 1965, 4, 1225. Gaines, D. F.; Schaeffer, R. Inorg. Chem. 1964, 3, 438. Schaeffer, R.; Tebbe, F. J. Am. Chem. Soc. 1962, 84, 3974. Shore, S. G. Pur Geanangel, R. Α.; Shore, S. G. J. Am. Chem. Soc. 1967, 89, 6771. Gaines, D. F.; Irons, T. V. J. Am. Chem. Soc. 1967, 89, 3375. Onak, T.; Dunks, G. B.; Searcy, I. W.; Spielman, J. Inorg. Chem. 1967, 6, 1465. Geanangel, R. Α.; Johnson, H. D. II; Shore, S. G. Inorg. Chem. 1970, 9, 908. Remmel, R. J.; Johnson, H. D., II; Jaworiwsky, I. S.; Shore, S. G. J. Am. Chem. Soc. 1975, 97, 5395. Geanangel, R. Α.; Johnson, H. D., II; Shore, S. G. Inorganic. Chem. 1971, 10, 2363. Johnson, H. D., II; Brice, V.T.,; Shore, S. G. Inorg. Chem. 1973, 12, 689. Huffman, J. C.; Moody, D. C.; Schaeffer, R. Inorg. Chem. 1976, 15, 227. Gaines, D. F.; Jorgenson, M. W.; Kulzick, M. A. J. Chem. Soc., Chem. Commun. 1979, 380. Dobson, J . ; Keller, P. C.; Schaeffer, R. Inorgan. Chem. 1968, 7, 399. Stibr, B.; Plesek, J . ; Hermanek, S. Coll. Czech. Chem. Commun. 1873, 38, 338. Plesek, J . ; Hermanek, S. Coll. Czech. Chem. Commun. 1974, 39, 821. Rietz, R. R.; Schaeffer, R. J. Am. Chem. Soc. 1971, 93, 1263. Rietz, R. R.; Schaeffer, R. J. Am. Chem. Soc. 1973, 95, 6254. Grimes, R. "Carboranes," Academic Press, New York, 1970. Grimes, R., "Metal Interactions with Boron Clusters," Plenum Press, New York, 1982. Yamauchi, M.; Shore, S. G., "Gmelin Handbuch der Anorganischen Chemie," Springer-Verlag, Berlin, 1978, Boron Supplement 18, Vol. 52.

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

16

52.

RINGS, CLUSTERS,

A N D POLYMERS

Barton, L., Onak, T., Shore, S. G., "Gmelin Handbuch der Anorganischen Chemie," Springer-Verlag, Berlin, 1979, Boron Supplement 20, Vol. 54.

RECEIVED June 21, 1983

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

2 Coordination and Related Chemistry of Polycyclic Tetraphosphorus Compounds JEAN G. RIESS Laboratoire de Chimie Minérale Moléculaire, Equipe de Recherche Associée au CNRS, Université de Nice, 06034 Nice, France

Polycyclic tetraphosphorus compounds including the Ρ4 molecule mixed derivatives a wide choice of potential donor sites. Their coor­ dination chemistry is described and discussed. The transmission of structural and electronic effects through the molecular frame -i.e. the interdepen­ dence of the phosphorus donor sites - is evident in their chemical behavior, kinetic and thermodynamic differences, spectral and structural data. The in­ terpretation of NMR and X-ray data in terms of chan­ ges in electronic distribution and of π character in bonding, is critically scrutinized. It is con­ cluded that apportioning the observed effects among σ and πelectronic contributions and steric contri­ butions can usually not be achieved in a reliable way. Structural "softness" and disorder in the solid are recognized as prominent features characteristic of tetraphosphorus closo-compounds. The field con­ tains many riddles, and promises new developments, especially in the realm of mixed picnogen/transition metal complexes and clusters. Phosphorus d i s p l a y s a remarkable p r o p e n s i t y t o breed s t a b l e t e t r a p h o s p h o r u s closo-type s t r u c t u r e s i n many o f i t s s i m p l e s t mo­ l e c u l a r c o m b i n a t i o n s , i n c l u d i n g i t s o x i d e s , s u l f i d e s and i m i d e s ( 1 - 6 ) . A l l d e r i v e , a t l e a s t f o r m a l l y , f r o m t h e P4 t e t r a h e d r o n . The o x i d e s ( P 4 0 ) 0 (η = 0 t o 4 ) , t h e r e l a t e d i m i d e s [ P ^ N R ) ^ ] ( N R ) ( n = 0 t o 4 ) , and some o f t h e s u l f i d e s , a d o p t t h e a d a m a n t a n e l i k e b o n d i n g a r r a n g e m e n t (A^B^)C ( n = 0 t o 4 ) shown i n scheme 1. T h i s a r r a n g e m e n t i s a l s o f o u n d i n an i n c r e a s i n g r a n g e o f m i x e d compounds t h a t d e r i v e f r o m t h e f o r m e r by d i v e r s e s u b s t i t u t i o n s i n t h e b r a n ­ c h i n g , b r i d g i n g and t e r m i n a l p o s i t i o n s (scheme 1 ) ; some o f t h e s e were n o t i s o l a t e d , b u t have o n l y been i d e n t i f i e d i n r e d i s t r i b u t i o n 6

n

n

n

0097-6156/83/0232-0017 $09.00/0 © 1983 American Chemical Society

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

18

RINGS, CLUSTERS, AND

POLYMERS

m i x t u r e s . The l o w e r p h o s p h o r u s s u l f i d e s , f o r t h e i r p a r t , f o r m a u n i q u e s e r i e s o f s t r u c t u r e s , g e n e r a l l y o f l e s s e r symmetry, a sam­ p l i n g o f w h i c h i s shown i n scheme 2. A l l t h e s e compounds a r e c l o s e t o s p h e r i c a l i n shape ( s e v e r a l o f them show p l a s t i c - p h a s e b e h a v i o r ) , and a r e l i t e r a l l y c o a t e d w i t h v a l e n c e - s h e l l e l e c t r o n p a i r s , w h i c h make them p o t e n t i a l m u l t i d e n t a t e d o n o r s . A l t h o u g h many o f them have been known f o r o v e r a c e n t u r y , i t was n o t u n t i l 1965 t h a t t h e f i r s t c o o r d i n a t i o n a d d u c t o f a closo-phosphorus s t r u c t u r e , P 4 O 5 [ ( N i ( C 0 ) 3 ] 4 1 ( F i g u r e 1) was r e p o r t e d ( 2 8 ) . S e v e r a l b o o k s and g e n e r a l r e v i e w s a r e a l r e a d y a v a i l a b l e on p h o s p h o r u s r i n g and c a g e * s y s t e m s ( 1 6 ) . T h i s one w i l l f o c u s more s p e c i f i c a l l y on t h e c o o r d i n a t i o n c h e m i s t r y o f m o l e c u l a r t e t r a p h o s p h o r u s - b a s e d closo-compounds, i n c l u d i n g P4 i t s e l f and c l o s e l y r e l a ­ t e d a n a l o g s , and w i l l a l s o i n c l u d e s t r u c t u r a l d a t a on b o t h f r e e and c o o r d i n a t e d s p e c i e s electronic and s t r u c t u r a and o f t h e e x t e n t o f ττ - b o n d i n g , w i l l be c r i t i c a l l y c o n s i d e r e d . Some u n p u b l i s h e d p r e l i m i n a r y o b s e r v a t i o n s , as w e l l as u n r e s o l v e d e n i g m a s , w i l l a l s o be t r e a t e d . P4 and

P 4 ~ r e l a t e d T e t r a h e d r a l C l u s t e r s as

Donors.

T h e o r e t i c a l i n v e s t i g a t i o n s o f t h e P4 m o l e c u l e ( 3 0 , 3 1 ) d e p i c t i t s v a l e n c e s h e l l e l e c t r o n d e n s i t y as b e i n g c o n c e n t r a t e d i n s i d e and on t h e f a c e s o f t h e t e t r a h e d r o n , where i t p l a y s t h e r o l e o f m u l t i c e n t e r m o l e c u l a r b o n d i n g , w i t h l i t t l e o r no ( n u c l e o p h i l i c ) f r e e e l e c t r o n p a i r s l o c a t e d on, and p o i n t i n g out f r o m , t h e i n d i ­ v i d u a l atoms. A t t h e same t i m e t h e t h i r d - r o w - e l e m e n t b a s e d m o l e c u l e i s uns a t u r e d and e x p e c t e d t o d i s p l a y - a c i d c h a r a c t e r . Thus t h e most p r o p i t i o u s c o n d i t i o n s f o r b o n d i n g t o a t r a n s i t i o n m e t a l s h o u l d be t h o s e u n d e r w h i c h t h e m e t a l c a n b o t h a c c e p t and b a c k - d o n a t e e l e c ­ t r o n d e n s i t y t o t h e P4 l i g a n d . The f i r s t t r a n s i t i o n m e t a l a d d u c t s c o n t a i n i n g t h e t e t r a p h o s ­ p h o r u s m o l e c u l e were r e p o r t e d by G i n s b e r g i n 1971 (32 ). They r e s u l t e d indeed from d i r e c t s u b s t i t u t i o n of w h i t e phosphorus f o r phosphane o r a r s a n e l i g a n d s on l o w - v a l e n t r h o d i u m : L RhCl + P 3

4

-—•

L RhCl(P4) + 2

L = PPh , P(m-tolyl)3, P(p-tolyl)3, 3

L AsPh

3

The p r e s e n c e o f t h e P4 m o l e c u l e was i n d i c a t e d by o s m o m e t r i c m o l e c u l a r w e i g h t d e t e r m i n a t i o n s , mass s p e c t r o m e t r y , and by t h e e a s y d i s p l a c e m e n t , e v e n a t -78°C, o f t h e i n t a c t P4 u n i t by c a r b o n m o n o x i d e o r phosphane l i g a n d s . The i n f r a - r e d and Raman s p e c t r a showed bands a t t r i b u t a b l e t o a bound P4 m o l e c u l e u n d e r C or C 3 v

* a m i s l e a d i n g denomination

s i n c e t h e r e i s no room i n t h e

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

s

"cage".

2.

Poly cyclic Tetraphosphorus Compounds

RiESS

A. Q

A

:

BRANCHING SITES P, As, P/N, P/CR, As/CR

Β

:

BRIDGING SITES 0, NR , S , Se a

Β I

?

I

C

PPh , SiMe °, GeMe , SnMe^ 2

A ^ L D ^ A

d

2

S/N" , 0/CH

R

e

2

/

B'

b

C

TERMINAL SITES 0, NPh, S, Se f

f

0/S , 0/Se

Scheme 1. Examples of tetraphosphorusadamantane-type core A B superscripts (when no reference is given, consult Ref. 1-6): A unique non-adamantane P (NR) closo-structure has recently been obtained with R = i-C H (1) and has been shown to convert into the thermodynamically more stable ada­ mantane-type isomer upon heating; as in P S (8), P4S9, and P4S10; Ref 9; in P S N~ (10); in[P 0 (CH )2]0 (\\) or As 0(CH ) (\2); as in (P 0 )0 - S (\3) and[P (NMe)^0 - S (\^). 4

4

6

3

b

4

5

d

8

e

4

7

c

f

4

4

2

4

4

4

4

2

n

2

4

6

4

n

Figure 1. Structure of the (P 0 )[Ni(CO) ] 4

6

3

4

adduct (29).

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

n

n

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

n

3

(see text)

3

SP [Co(co) ]

4

3

P . Cco(co) ]

S

4

+

n

n

3

4

3

4

3

2

3

4

4

3

3

4

06

P. s. Ο (20 4 4 As,S,(22), As.Se, 4 4 44 ct-P,S NPh(23) 4 3 P (PH) (19) 4

4

As (AsR) (19)

4

w

B

/\

A

Β B

0

n

B

Λ

A

P [M] (19)

3

3

4

4

P (PR) , P (SiMe ) P (P") _ (PR) (18-20)

3

P S (15), As S (17) As (As )

4

S e

(P _ As )S (.6)

P

4 3> 4 3 As^S^j As^Se^

P

'/

B

43

NT*

B'

A

\

\

J

S e

5

C (24)

4

As S

5

P (PR) (3)(19-20)

4 5

S

P

4 5

P

^ B

fi •

a

B " ^

4

/

IΤ /

B

¥ 5

P

S

B

'*

B

A A

47

4

6

0

4

2

S

2

?

4 7 P As S (27)

P

c

^ B

A A—I

B ^ y

A Bo_ C _ .

" 4 6 (25, 26)

B

A — I — AA i B' •B

g

A

R B

\ ï / \ï /

B y

D

46

Scheme 2. Sampling of non-adamantane tetraphosphorus and related doso-compounds

n

P Se (15)

3

4

PS

3

V

A s

c

Ai,

2.

RiESS

21

Polycyclic Tetraphosphorus Compounds

symmetry b u t t h e mode o f c o o r d i n a t i o n o f t h e P4 m o l e c u l e c o u l d n o t be d e t e r m i n e d e x a c t l y . I n v i e w o f some o f t h e above t h e o r e t i c a l c o n s i d e r a t i o n s , the h y p o t h e s i s of bonding through a face o f the t e t r a h e d r o n was p r e f e r r e d o v e r t h o s e t h r o u g h a n edge o r a n apex. The f a i l u r e t o o b s e r v e 31p NMR l i n e s due t o P4 s u g g e s t e d t h a t some f a s t i n t e r o r i n t r a m o l e c u l a r exchange p r o c e s s was t a k i n g p l a c e on t h e NMR t i m e s c a l e . S i x y e a r s l a t e r the d i s c r e t e d i a m a g n e t i c complex P4[Fe(C0)4l3 was o b t a i n e d by Schmid and Kempney b y a l l o w i n g P4 t o r e a c t w i t h F e 2 ( C O ) 9 (33 ). I t s i n f r a - r e d s p e c t r u m i n s o l u t i o n i n d i c a t e d t h e p r e s e n c e o f d i s t i n c t F e ( C 0 ) 4 g r o u p s , and t h e M o s s b a u e r s p e c t r u m d e f i n i t e l y showed t h e e x i s t e n c e o f p e n t a - and h e x a - c o o r d i n a t e d i r o n atoms i n a 1:2 r a t i o . The 31p NMR, however, e x h i b i t e d o n l y a s i n g l e l i n e a t 21 ppm a t room t e m p e r a t u r e , w h i c h c a u s e d t h e a u t h o r s t o s u g g e s t a f l u c t u a t i n g s t r u c t u r e i n w h i c h two b r i d g i n g and one apex-bound F e ( C 0 dly i n solution (Figur and t e m p e r a t u r e - s e n s i t i v e , and decomposed w i t h i n h o u r s i n b e n z e n e , t o l u e n e o r THF s o l u t i o n , w i t h e v o l u t i o n o f CO and f o r m a t i o n o f a p o l y m e r [(C0>3Fe02] , w h i c h no l o n g e r c o n t a i n e d t h e P& u n i t . n

Figure 2. Proposed dynamic structure of P4Fe(CO) ] 4

3

(33).

The n i c k e l - P 4 and p a l l a d i u m - P 4 a d d u c t s 3 were p r e p a r e d by S a c c o n i e t a l . , by the f o l l o w i n g r e a c t i o n (34) :

The n i c k e l c o m p l e x was s t a b l e enough t o a l l o w , f o r t h e f i r s t t i m e , a n X - r a y d i f f r a c t i o n a n a l y s i s , w h i c h showed t h a t t h e P4 t e t r a h e d r o n i s bound t o t h e m e t a l t h r o u g h a n apex. The n i c k e l atom i s surrounded by i t s f o u r phosphorus l i g a n d s i n a q u i t e r e g u l a r t e t r a h e d r a l f a s h i o n , t h e n i t r o g e n atom no l o n g e r b e i n g bound t o t h e m e t a l , i . e . r e a c t i o n 2 c a n be d e s c r i b e d a s a s i m p l e l i g a n d e x c h a n g e , w i t h t h e P4 m o l e c u l e p r o v i d i n g t h e m e t a l w i t h t h e two

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

22

RINGS, CLUSTERS,

A N D POLYMERS

e l e c t r o n s i n i t i a l l y d o n a t e d by t h e n i t r o g e n atom. The Ni-CP^.) bond i s t h e s h o r t e s t ( b y 0.25Â) o f t h e f o u r N i - P b o n d s , s u g g e s t i n g a s i g n i f i c a n t d-^-d-p. i n t e r a c t i o n b e t w e e n t h e two atoms, a n d / o r l o w e r s t e r i c r e q u i r e m e n t s f o r t h e P4 m o l e c u l e . A d i s t i n c t s i t u a t i o n i s c r e a t e d when r e a g e n t s t h a t a r e p o t e n t i a l s o u r c e s o f a g r o u p b a s e d on a 1 5 - e l e c t r o n t r a n s i t i o n m e t a l a r e a l l o w e d t o r e a c t w i t h P 4 . Such g r o u p s a r e e l e c t r o n i c a l l y e q u i v a l e n t t o phosphorus, i n the sense t h a t b o t h t h e t r a n s i t i o n m e t a l b a s e d g r o u p and t h e p n i c n o g e n e l e m e n t need 3 e l e c t r o n s i n o r d e r t o r e a c h t h e i r s t a b l e c l o s e d - s h e l l c o n f i g u r a t i o n s o f 18 and 8 e l e c t r o n s r e s p e c t i v e l y ( 3 5 , 3 6 ) . One way t o s a t i s f y t h i s need i s , i n e i t h e r case, f o r the d e f i c i e n t center t o share e l e c t r o n s w i t h t h r e e o t h e r e l e c t r o n i c a l l y a n a l o g o u s g r o u p s o r e l e m e n t s ; hence one has t h e a n a l o g y b e t w e e n t h e s t a b l e P 4 m o l e c u l e and t h e C l r ( C O ) l 4 c l u s t e r . T h i s c o n c e p t c a n be u s e d t o r a t i o n a l i z e t h e e x i s t e n c e o f a series of f a i r l y stabl c l u s t e r s o b t a i n e d by D a h and c o - w o r k e r s , w h i c h c a n t h e n be r e g a r d e d as d e r i v i n g f r o m P 4 o r A S 4 by s t e p w i s e r e p l a c e m e n t o f p h o s p h o r u s o r a r s e n i c atoms by e l e c t r o n i c a l l y e q u i v a l e n t m e t a l l i c g r o u p s , f o r example ( 3 8 ) : 3

P Co(C0) 3

P

4

+

Co (CO) 2

3

P [Co(C0) ] 2

3

2

8

P[Co(C0) ] 3

3

[PCo (C0) ] 3

8

3

The same s e r i e s o f p r o d u c t s was a l s o o b t a i n e d by t h e r e a c t i o n of P C 1 or P B r w i t h C o ( C O ) o r t h a t o f P I w i t h Co(C0)4~ ( 3 8 ) . A r s e n i c a n a l o g s had a l r e a d y b e e n r e p o r t e d ( 3 5 , 3 7 ) by D a h l . 3

3

2

8

3

CO

That t h e s e P 4 ~ r e l a t e d t e t r a h e d r a l c l u s t e r s r e t a i n donor c a p a c i t y t h r o u g h t h e p h o s p h o r u s atoms was i l l u s t r a t e d by t h e i s o l a t i o n of adduct 5 ( t h e parent P [ C o ( C 0 ) ] c l u s t e r i s u n s t a b l e ( 3 8 ) , i n w h i c h t h e P C o c l u s t e r b e h a v e s as a t w o - e l e c t r o n d o n o r t o w a r d s t h e u n s a t u r a t e d 1 6 - e l e c t r o n F e ( C 0 ) 4 m o i e t y . The r a t h e r h i g h CO v i b r a t i o n f r e q u e n c i e s i n the i n f r a - r e d spectrum i n d i c a t e a g a i n that t h e c l u s t e r a l s o has some T T - a c c e p t i n g c a p a c i t y . F u r t h e r m a n i f e s t a t i o n o f t h e d o n o r c h a r a c t e r o f t h i s p h o s p h o r u s atom c a n be s e e n i n i t s t e n d e n c y t o r e a d i l y d i s p l a c e CO f r o m a C o ( C 0 ) m o i e t y 3

3

3

3

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

RiESS

2.

Poly cyclic Tetraphosphorus Compounds

23

t o f o r m t h e r e m a r k a b l e c y c l i c t r i m e r { E3 [ 0 0 ( 0 0 ) 3 ] 2 ECoCCO^] } (Ε = Ρ o r A s ) ( 4 0 ) , w h i c h r e s u l t s f r o m t h e d i s p l a c e m e n t o f one c a r b o n y l l i g a n d on Co by t h e p h o s p h o r u s apex o f t h e n e x t c l u s t e r i n t h e c y c l i c t r i m e r . A s [ 0 0 ( 0 0 ) 3 ] 3 r e a d i l y gave t h e M(C0)5 (M = Or, Mo, W) and A I C I 3 a d d u c t s ( u n s t a b l e i n t h e l a t t e r c a s e ) ( 4 1 ) , and s i m i l a r d e r i v a t i v e s o f t h e a n t i m o n y c l u s t e r S b [ r p C p F e ( 0 0 ) 2 ! 3 have a l s o been r e p o r t e d ( 4 2 ) . The a c t i o n o f L e w i s a c i d s ( o r b a s e s ) on t h e E [ 0 0 ( 0 0 ) 3 ] 4 - n c l u s t e r s c a n however a l s o p r o v o k e the r e d i s t r i b u t i o n of fragments w i t h i n the c l u s t e r ' s core ( 4 3 ) . F o r example : 3

n

As Co(C0) 3

+ Co (CO)

3

2

b y _ • A s [ C o ( C 0 ) 3 ] 2 + (CO) WAs [ C o ( C 0 ) ] 3

8

2

w(co)

5

3

6

+

{As[Co(CO) l [Co(CO)2l}3

I n t h e same v e i n on hybrid clusters 6 : Co (CO) 2

R C l C L i + ECI3

-RC1 C-EC1

2

2

8

2

[Co] [Co] = C o ( C 0 ) ; Ε = P, A s ; R = H (As o n l y ) , Me, Ph, S i M e 3

tCo]

3

6

which i n c o r p o r a t e the t h r e e d i s t i n c t e l e c t r o n i c a l l y e q u i v a l e n t g r o u p s P, RC and 0 0 ( 0 0 ) 3 (4-4). These c l u s t e r s may a l s o be r e g a r d e d as 0 0 2 ( 0 0 ) 5 a d d u c t s o f t h e u s u a l l y u n s t a b l e p h o s p h a and a r s a a c e t y l e n e RC=E l i g a n d s , and a r e t h e r e f o r e r e l a t e d t o t h e t e t r a h e d r a l a c e t y l e n e c o m p l e x e s ( R C = C R ) [ ( 0 0 ) 3 0 0 - 0 0 ( 0 0 ) 3 ] . The d o n o r a b i l i t y o f t h e Ρ ( b u t n o t t h e A s ) atom i s e s t a b l i s h e d by t h e f o r m a t i o n o f ( C 0 ) M P ( C R ) [0ο(00) 1 a d d u c t s (M = Or, Mo, W) when 6 i s a l l o w e d t o r e a c t w i t h M ( C 0 ) 5 ( t h f ) , as w e l l as by t h e i r s l o w c y c l o t r i m e r i s a t i o n t o { (MeC)P[Co(CO) ]CCo(CO) ]}3 ( 4 4 ) . The t e t r a h e d r a l P3ML c l u s t e r s 7, where M = Co, I r , Rh,Pd o r Pt, and L i s a t r i p o d l i g a n d , o b t a i n e d by S a c c o n i e t a l ( 3 4 , 4 5 , 4 7 , 4 9 ) : 5

3

2

3

0ο(Η 0) 2

+ +

2

6

BF " 4

or

[Rh(CO)2Cl]

or

[Rh(C H )2Cll2 2

2

P4

2

4

CH C(CH PPh )3 3

2

2

or I r ( P P h ) ( C O ) C l 3

2

7 c a n be r e g a r d e d , f o r t h e p u r p o s e s o f e l e c t r o n - c o u n t i n g , e i t h e r as c o m p l e x e s i n w h i c h t h e t r i p h o s p h o r u s c y c l e a c t s as a t r i - h a p t o 3 - e l e c t r o n d o n o r t o w a r d s t h e t r a n s i t i o n m e t a l m o i e t y , o r as t e t r a h e d r a l P3M c l u s t e r s whose e x i s t e n c e i s b a s e d on 2 - e l e c t r o n C o v a l e n t bond f o r m a t i o n . X - r a y d i f f r a c t i o n s t u d i e s showed t h e s e compounds t o be i s o m o r p h o u s ( 4 7 ) . A l l c o n t a i n t h e c y c l o t r i p h o s p h o r u s m o i e t y and t h e t r i p h o s p h o r u s t r i p o d l i g a n d , and a l l show an o c t a h e d r a l a r r a n g e m e n t o f t h e s i x p h o s p h o r u s atoms a r o u n d t h e me­ t a l . The M(P3) bonds a r e c o n s i s t e n t l y l o n g e r t h a n t h e o t h e r m e t a l - P

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

24

RINGS, CLUSTERS, A N D

POLYMERS

b o n d s , by 0.10 t o 0.16 Â, w h i l e t h e P-P d i s t a n c e s i n t h e c y c l o - P 3 u n i t a r e s i g n i f i c a n t l y s h o r t e r (2.14 t o 2.16 Â) t h a n i n P4 (2.21Â) o r i n t h e P 3 [ M n ( C 0 ) C p ] 3 a d d u c t (2.26 Â) ( 4 8 ) . T h i s s h o r t e n i n g , as e a r l i e r p r o p o s e d f o r t h e A s 3 C o ( C 0 ) 3 c l u s t e r ( 3 5 ) , has been r a t i o n a l i z e d on t h e b a s i s o f p a r t i a l d e r e a l i z a t i o n o f t h e e l e c t r o n d e n s i t y f r o m t h e p o l a r i z a b l e c y c l o - P 3 f r a g m e n t t o t h e more e l e c t r o n - d e m a n d i n g 0 0 ( 0 0 ) 3 m o i e t y , and c o n s e q u e n t r e l i e f o f i n t e r e l e c t r o n i c r e p u l s i o n s i n the c y c l o - P 3 fragment. In compensation t h e m e t a l d r a i n s l e s s e l e c t r o n d e n s i t y f r o m t h e t r i p o d ' s Ρ atoms, w h i c h d i s p l a y l o n g e r Co-P bonds (by 0.10 t o 0.15 Â) t h a n u s u a l . The s l i g h t i n c r e a s e i n P-P b o n d - l e n g t h s , and c o n c o m i t a n t d e c r e a s e o f t h e PMP a n g l e , f r o m c o b a l t t o r h o d i u m o r i r i d i u m , i s c o n s i s t e n t w i t h t h e i n c r e a s i n g s i z e o f t h e m e t a l atom and c o n s e q u e n t r e d u c t i o n of o r b i t a l o v e r l a p w i t h phosphorus. T h a t t h e s e m i x e d P3M c l u s t e r s s t i l l have e l e c t r o n - d o n o r c a p a c i t y i s i l l u s t r a t e d by 2

-P\

C r

C

p/ °\j/ Ρ

P

(

C 0

) Utriphos)Co(n -P )Cr(C0) 6

3

5

((triphos)Co(n -P ) [Cr(CO) ] 3

3

5

2

8 i n w h i c h t h e p h o s p h o r u s atoms r e a d i l y r e p l a c e CO g r o u p s f r o m C r ( C 0 ) 5 t o g i v e s t a b l e a d d u c t s ( 4 9 ) . The X - r a y s t r u c t u r e a n a l y s i s p e r f o r m e d on 8 showed ( F i g u r e 3) t h e two O r ( 0 0 ) 5 g r o u p s t o be bound t o i n d i v i d u a l p h o s p h o r u s atoms, w i t h C r - P d i s t a n c e s o f 2.42 Â, e q u a l t o t h a t f o u n d i n PtvjP [ C r ( C O ) 5 ] , s u g g e s t i n g t h a t t h e L e w i s base p r o p e r t i e s o f t h e p h o s p h o r u s atoms i n t h e C0P3 u n i t a r e s i m i l a r t o t h o s e o f PPh3. I t i s a l s o n o t e w o r t h y t h a t t h e C0P3 t e t r a h e d r o n r e m a i n s a l m o s t u n a f f e c t e d on b o n d i n g t o t h e two C r ( C 0 ) 5 g r o u p s . The c y c l o - P 3 u n i t c a n a l s o behave as a t h r e e e l e c t r o n b r i d g i n g l i g a n d ( 4 5 ) t o g i v e a v a r i e t y o f homo and h e t e r o m e t a l l i c t r i p l e - d e c k e r sandwich complexes which are t r e a t e d i n a r e c e n t r e v i e w ( 1 0 0 ) . The r e m a r k a b l e i d e a l l y c u b i c m i x e d m e t a l / p n i c o g e n S b [ 0 0 ( 0 0 ) 3 ] 4 ( 5 0 ) , o r P 4 [ S n P h l 4 ( 5 1 ) , and t e t r a g o n a l l y d i s t o r t e d m e t a l / p h o s p h o r u s P4 [CpCo]4 ( 5 2 ) c u b a n e - l i k e c l u s t e r s ( F i g u r e 4 ) , o b t a i n e d by D a h l o r Schumann, may be v i e w e d a l o n g s i m i l a r l i n e s . I n t h e l a t t e r c a s e e a c h 1 4 - e l e c t r o n CpCo g r o u p c o m p l e t e s i t s v a l e n c e - s h e l l by s h a r i n g e l e c t r o n p a i r s w i t h one o t h e r CpCO g r o u p and w i t h t h r e e p h o s p h o r u s atoms, c o n s i s t e n t w i t h i t s d i a m a g n e t i c c h a r a c t e r and w i t h t h e o b s e r v e d geometry. I t i s l i k e l y t h a t many more s u c h m i x e d c l u s t e r s , i n c o r p o r a t i n g b o t h t r a n s i t i o n m e t a l s and m a i n g r o u p e l e m e n t , w i l l be d e v e l o p e d i n t h e f u t u r e . A r a n g e o f p o l y p h o s p h o r u s compounds, many o f w h i c h e x h i b i t r e m a r k a b l e p o l y c y c l i c s k e l e t o n s , i n c l u d i n g s t a b l e compounds t h a t c a n be f o r m a l l y d e r i v e d f r o m t h e P4S3 o r p-P4S5 frames by r e p l a c i n g t h e s u l f u r by P" o r PR b r i d g e s , have b e e n d e v e l o p p e d i n r e c e n t y e a r s , and a r e t r e a t e d i n two f a s c i n a t i n g r e c e n t r e v i e w a r t i c l e s ( 1 9 , 2 0 ) . T h e i r c o o r d i n a t i o n c h e m i s t r y , w h i c h does n o t seem t o have b e e n i n v e s t i g a t e d y e t , s h o u l d p r o v e p r o m i s i n g , e s p e c i a l l y i n view o f the f a c t t h a t s e v e r a l t r a n s i t i o n m e t a l adducts o f m o n o c y c l i c p o l y p h o s p h i n e s have a l r e a d y been r e p o r t e d (53). 4

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

2.

RiESS

Poly cyclic Tetraphosphorus Compounds

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

25

26

RINGS, CLUSTERS, A N D

POLYMERS

T e t r a p h o s p h o r u s O x i d e s and I m i d e s a s D o n o r s . The T r a n s m i s s i o n o f E l e c t r o n i c and S t r u c t u r a l E f f e c t s t h r o u g h t h e M o l e c u l a r Frame The C o o r d i n a t i o n C h e m i s t r y o f P^Oft, P&O7 a n d P&(NMe)fi. The p h o s p h o r u s o x i d e s , i m i d e s , t h e i r d e r i v a t i v e s a n d t h e i r a n a l o g s u s u a l l y have t h e a d a m a n t a n e - t y p e s t r u c t u r e shown i n scheme 1. A l l b e a r numerous l o n e p a i r s on t h e i r p h o s p h o r u s o r a r s e n i c a n d / o r o x y g e n , n i t r o g e n , s u l f u r , e t c . , atoms, w h e t h e r i n b r a n c h i n g , b r i d g i n g o r t e r m i n a l p o s i t i o n s , thus o f f e r i n g a wide c h o i c e of p o t e n t i a l donor s i t e s f o r c o o r d i n a t i o n , π - a c c e p t i n g c h a r a c t e r can a l s o be a n t i c i p a t e d f r o m t h e e l e m e n t s f r o m t h e T h i r d Row o n . No c h e l a t i n g b e h a v i o r c a n be e x p e c t e d , h o w e v e r , f r o m t h e b r a n c h i n g P ( I I I ) o r A s ( l l l ) atoms, i n v i e w o f t h e d i v e r g i n g o r i e n t a t i o n s o f t h e i r l o n e e l e c t r o n p a i r s . The p a r t i c i p a t i o n o f 3d o r b i t a l s i n b o n d i n g i n P4O5 h a s been j u d g e d , f r o m a n LCAO-SCF-CNDO c a l c u l a ­ t i o n , t o be s u b s t a n t i a l even o u t t h e r e l a t i v e charge These e x p e c t a t i o n s were b o r n e o u t f o r e x a m p l e by t h e r e a c t i o n s o f d i b o r a n e a n d o f a s e r i e s o f m e t a l c a r b o n y l s w i t h P4O5 and P4(NMe)£, whose c o o r d i n a t i n g a b i l i t i e s have b e e n t h o r o u g h l y i n v e s ­ t i g a t e d ( 2 8 , 5 5 ) . P4O5, i n c o n t r a s t t o i t s u s u a l b e h a v i o r , w h i c h i s o f t e n c h a r a c t e r i z e d by v i o l e n t r e a c t i o n s i n w h i c h t h e p o l y p h o s p h o r u s s t r u c t u r e i s s h a t t e r e d ( 5 6 ) , r e a c t s s m o o t h l y a t room tem­ p e r a t u r e , w i t h a l a r g e e x c e s s o f N i ( C 0 ) 4 , t o add 1 t o 4 N i ( C 0 ) 3 g r o u p s i n a s e q u e n t i a l manner, a s shown by ^ P NMR m o n i t o r i n g ( 5 5 ) ; 3

3 1

p

NMR

pattern : Ni(CO)

P

A B

3

2

A B

2

singlet

3

4

=r

4°6

AB

( P

4°6 C )

]—^A°6^2

N i

-

Ρ

4

0

6 Μ

3

^ Ρ

0 4

6

[ ^ ] 4

excess, RT I

.

[Ni] =

Ni(CO)

] f

.

3

P

} FAST

4°6

1

-CO slow P 0 /Ni/CO POLYMERS 4

6

When on t h e c o n t r a r y i t i s P4O5 t h a t i s i n e x c e s s , i t c a n r e p l a c e up t o t h r e e c a r b o n y l g r o u p s i n N i ( C 0 ) 4 . When n e i t h e r r e a g e n t i s i n excess, h i g h l y c r o s s - l i n k e d , three-dimensional polymeric networks a r e o b t a i n e d , i n w h i c h t h e n i c k e l atoms a r e b r i d g e d by i n t a c t P4O5 m o l e c u l e s , w h i c h i n t u r n a r e b r i d g e d by n i c k e l atoms ( 5 5 ) . As e x ­ p e c t e d f r o m t h e f o u r - f o l d b r a n c h i n g c h a r a c t e r o f b o t h P4O5 and t h e N i a t o m s , t h e r e a r e two g e l p o i n t s i n t h e s y s t e m , a t N1/P4O5 m o l e ­ c u l a r r a t i o s o f c_a 0.25 and 4. I t i s n o t e w o r t h y t h a t p o l y c o n d e n s a t i o n does n o t o c c u r i m m e d i a t e l y when t h e i s o l a t e d (P4O5)|Ni(C0)3l4 i s a l l o w e d t o r e a c t w i t h P4O5 : t h e i n i t i a l s t e p s o f t h e r e a c t i o n

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

RiESS

2.

27

Poly cyclic Tetraphosphorus Compounds

consist o f the progressive s t r i p p i n g , i n a matter of minutes, o f N i ( 0 0 ) 3 g r o u p s f r o m t h e P4O5 c o r e u n t i l o n l y one i s l e f t , t h u s avoiding, a tthe f i r s t stage, the region of polymeric structures i n which the r e a c t i o n r a t e s decrease r a p i d l y as c r o s s - l i n k i n g i n ­ creases . T e t r a p h o s p h o r u s and t e t r a a r s e n i c h e x a m e t h y l i m i d e s s i m i l a r l y add one t o f o u r N i ( C 0 ) 3 g r o u p s , b u t t h e c o o r d i n a t i o n o f more t h a n one P4(NMe)£ l i g a n d on N i , and hence t h e f o r m a t i o n o f p o l y m e r i c s t r u c t u r e s , a r e n o t observed, presumably f o r s t e r i c reasons ( 5 7 , 58). The N i ( C 0 ) 3 g r o u p s a l w a y s exchange b e t w e e n t h e p h o s p h o r u s do­ n o r s i t e s ; i n t h e c a s e o f t h e a r s e n i c a n a l o g As4(NMe)£, t h i s e x ­ change i s f a s t enough t o p r o v o k e t h e c o a l e s c e n c e o f t h e s i g n a l s i n t h e H NMR ( F i g u r e 5 ) . The r e a c t i o n s o f P4O5 ( a n d P4O7) w i t h i r o n and g r o u p V I c a r b o n y l s have a l s o been i n v e s t i g a t e d p r i n c i p a l l y by M i l l s e t a l (59-61): 1

140° diglyme P 0 4

6

+

- J

I

%

I

5

4

Μ,ΓΡΤ

P

4°6

+

F

e |0-7 •+

Fe(CO) .

9

R

T

t

f i

4

C O

'4

F e

]

( P n

9

P„O diglyme H i o i ™

7

' (">Ve(P 0 ) •

' ['

M

(59) —

χ

(C0KFe(P 0 ) 4 6 2

6

4°6

)

4

c

6

6

+ nM(C0)

iMtCOJm.iln (P4O7)

m

M = C r , Mo, W (60) +

η CO

(61)

M = N i , η = 1-3; M = Fe, η = 1,2; M = Cr,Mo,W, n=l

isolated The t h e r m a l r e a c t i o n o f P4O5 w i t h F e ( C 0 ) 5 l e a d s t o a m i x t u r e o f the mono and d i - i r o n c a r b o n y l s , w h i c h were s e p a r a t e d b y s u b l i m a ­ t i o n ; t h e a c c o m p a n y i n g a u t o x i d a t i o n o f P4O5 t o P4O7 i s p r e s u m a b l y i n d e p e n d e n t o f t h e p r e s e n c e o f t h e i r o n compound, s i n c e i t c o u l d be o b t a i n e d i n h i g h y i e l d s b y s i m p l y h e a t i n g a d i g l y m e s o l u t i o n of P4O5 ( 5 9 ) . The same m e t a l a d d u c t s were o b t a i n e d a t l o w e r tempe­ r a t u r e u n d e r p h o t o c h e m i c a l a c t i v a t i o n ; t h e y were t h e n a c c o m p a n i e d by a n o t h e r u n c o o r d i n a t e d p h o s p h o r u s s p e c i e s , p r o b a b l y P4O9. S i m i l a r b e h a v i o r was f o u n d w i t h F e 2 ( C O ) 9 , and a p p e a r s t o t a k e p l a c e w i t h F e ( C O ) . The P 4 0 [ M ( C O ) l compounds (M = C r , Mo, W) ( 6 0 ) and t h e i r P4O7 a n a l o g s ( 6 1 ) d i s p l a y h i g h c a r b o n y l s t r e t c h i n g f r e q u e n ­ c i e s , consistent with the l i g a n d s having a strong TT-accepting c h a r a c t e r . The i n c r e a s e i n f r e q u e n c y n o t e d when d e s c e n d i n g t h e 3

1 2

6

3

1

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

28

RINGS, CLUSTERS,

!

Figure 5. Variable-temperature H-NMR of a mixture of complexes in CDCl .

A N D POLYMERS

As (NMe) [Ni(CO) ] 4

6

3

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

3

n

2.

Poly cyclic Tetraphosphorus Compounds

RiESS

29

y j t h g r o u p i s an i n d i c a t i o n o f a d e c r e a s e i n t h e I T * c a r b o n y l o r b i t a l p o p u l a t i o n , as e x p e c t e d f r o m t h e d e c r e a s e o f t h e P ( 3 d ) o r b i t a l o v e r l a p w i t h t h e l a r g e r , more d i f f u s e , 4d o r 5d o r b i t a l s o f Mo o r W. The h i g h v a l u e (486 Hz) o f t h e J ( ^ P - W ) c o u p l i n g c o n s t a n t , w h i c h i s a l s o thought t o r e f l e c t the TT-acceptor a b i l i t y o f phosp h o r a n e s , r a n k s P4O5 among t h e s t r o n g l y T T - a c c e p t i n g l i g a n d s . Nôth and T h o r n r e p o r t e d t h e p r e p a r a t i o n o f P 4 ( N H ) f c [ M ( C 0 ) 5 l 4 w i t h M = C r and Mo, by t h e r m a l d e c o m p o s i t i o n o f P ( N H 2 ) 3 M ( C O ) 5 , and o f P 4 ( N H ) £ S 4 , t h r o u g h t h e r e a c t i o n o f Sg on t h e chromium a d d u c t ; t h e m i x e d P 4 ( N H ) £ [ O r ( 0 0 ) 5 ] S 4 _ were i d e n t i f i e d d u r i n g t h e p r o c e s s ( 6 2 ) . S i n c e t h e p a r e n t compound P4(NH)£ i t s e l f i s s t i l l unknown, t h i s e x e m p l i f i e s t h e p o s s i b i l i t y o f o b t a i n i n g new c j o s o _ - s t r u c t u r e s, o r l e s s s t a b l e i s o m e r s o f known o n e s , i n a c o m p l e x e d f o r m . 3

n

1 8 3

n

1

The N o n - i n d e p e n d e n t B e h a v i o r o f t h e f o u r P h o s p h o r u s Atoms. The w e a l t h o f d a t a now a v a i l a b l P4(NMe)fc c o r e p r o v i d e s a e l e c t r o n i c and/or s t e r i c e f f e c t s through the c l o s o - s t r u c t u r e , w h i c h m a n i f e s t s i t s e l f i n many ways - f o r e x a m p l e , i n t h e c o m p o r t ment o f P 4 O 5 and P4(NMe)£ t o w a r d s B 2 H 5 and B F 3 . B o t h l i g a n d s r e a c t r e a d i l y w i t h d i b o r a n e u n d e r one a t m o s p h e r e t o g i v e P 4 E ^ ( B H 3 ) a d d u c t s , w i t h η = 1 t o 3 f o r Ε = 0 , and 1 t o 4 f o r Ε = NMe; c o o r d i n a t i o n o c c u r r e d o n l y on p h o s p h o r u s ; c r y s t a l l i n e Ρ 4 θ 5 ( Β Η 3 ) 2 Ρ 4 θ ( Β Η 3 ) and P 4 ( N M e ) f c ( B H 3 ) 4 were i s o l a t e d ( 6 3 - 6 6 ) . An i n t e r e s ­ t i n g p o i n t , as shown i n F i g u r e 6 f o r P4(NMe)£, i s t h a t t h e c o m p o s i ­ t i o n o f t h e m i x t u r e o f a d d u c t s formed was i n i t i a l l y c l o s e t o t h a t w h i c h w o u l d be e x p e c t e d f r o m random o c c u p a t i o n o f t h e d o n o r s i t e s , b u t t h a t t h i s c o m p o s i t i o n e v o l v e d s l o w l y , as t h e BH3 g r o u p s r e d i s t r i b u t e d t h e m s e l v e s among t h e a v a i l a b l e s i t e s , t o f i n a l l y r e a c h an e q u i l i b r i u m d i s t r i b u t i o n t h a t d e p a r t e d c o n s i d e r a b l y f r o m r a n d o m n e s s . Such r e d i s t r i b u t i o n d a t a r e f l e c t t h e r e l a t i v e thermo­ d y n a m i c s t a b i l i t i e s o f t h e v a r i o u s s p e c i e s i n p r e s e n c e ( 6 7 ) , as w e l l as d i f f e r e n c e s i n e n e r g i e s o f c h e m i c a l l y e q u i v a l e n t bonds ( 6 8 ) . The r e d i s t r i b u t i o n i s f a s t e r among t h e P 4 C 5 ( B H 3 ) adducts, and t h e e q u i l i b r i u m d i s t r i b u t i o n ( F i g u r e 7) d e p a r t s e v e n f u r t h e r from randomness, showing a g a i n t h a t each phosphorus s i t e " s e n s e s " whether the o t h e r s i t e s are c o o r d i n a t e d or not. n

5

6

3

n

The e f f e c t o f t h e o x i d a t i o n o f one p h o s p h o r u s atom on t h e L e w i s b a s i c i t y o f t h e r e m a i n i n g t h r e e , has b e e n a p p r o a c h e d t h r o u g h t h e i n v e s t i g a t i o n o f t h e c o o r d i n a t i o n c h e m i s t r y o f P4O7 ( 6 1 ) , and p r o v e d r e m a r k a b l e . Thus, i n c o n t r a s t t o P 4 O 5 , t e n s i o m e t r i c t i t r a ­ t i o n o f P4O7 w i t h B 2 H 5 a t a m b i e n t t e m p e r a t u r e and n o r m a l p r e s s u r e i n d i c a t e d no r e a c t i o n . On t h e o t h e r h a n d , P4O7 has b e e n r e p o r t e d t o add two e q u i v a l e n t s o f B F 3 ( 6 1 ) , w h i l e P 4 O 5 i n c o m p a r a b l e c o n d i t i o n s i s decomposed by B F 3 . 0 E t 2 t o a m i x t u r e w h i c h i n c l u d e s P F 3 , P F 2 O P F 2 -whose p r e p a r a t i o n by a n o t h e r , s e l e c t i v e , r o u t e was r e p o r t e d by R a l p h R u d o l p h ( 6 9 ) -, P F 2 0 E t and p o l y m e r i c m a t e r i a l s i n w h i c h F 2 B O - and F B O 2 - f r a g m e n t s were i d e n t i f i e d ( 6 4 , 7 0 ) . The p h o s p h o r u s l o n e p a i r s on P4O7 s h o u l d i n d e e d be l e s s p o l a r i z a b l e t h a n t h o s e o f P 4 O 5 , due t o t h e e l e c t r o n - w i t h d r a w i n g e f f e c t o f t h e

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

30

RINGS, CLUSTERS, A N D POLYMERS

P (NMe) .2BH 4

6

3

4days Figure 6. Evolution of the composition of a mixture of P (NMe) (BH ) plexes upon standing (66). 4

6

3

n

com-

Figure 7. Equilibrium distribution of BH groups on P 0 . (Reproduced from Ref. 64. Copyright 1966, American Chemical Society.) 3

4

6

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

2.

Polycyclic Tetraphosphorus Compounds

RIESS

31

e x o c y c l i c o x y g e n . P e r t i n e n t t o t h e argument i s a l s o t h e o b s e r v a t i o n t h a t P 4 O 5 S 2 i s more e a s i l y o x i d i z e d t h a n P 4 O 3 b y P 4 S 1 0 ( 1 3 ) . The l o w e r r e a c t i v i t y o b s e r v e d f o r t h e r e s i d u a l P ( I I l ) s i t e i n P4(NMe)5S3, compared t o P4(NMe)5, u n d e r t h e a c t i o n o f M e l , PI1N3, B2H5 o r N i ( 0 0 ) 4 ( 7 1 ) , c a n a l s o be e x a m i n e d a l o n g t h e s e l i n e s . I t c a n be r a t i o n a l i z e d b o t h i n t e r m s o f t h e e l e c t r o n - w i t h d r a w i n g e f f e c t c a u s e d by t h e p e n t a v a l e n t P's, and i n a d d i t i o n , b y t h e i n c r e a s e d crowding o f t h e P ( I I I ) s i t e , r e s u l t i n g from non-bonding r e p u l s i o n s b e t w e e n t h e s u l f u r atoms and t h e m e t h y l g r o u p s , w i t h no means o f a p p o r t i o n i n g t h e s e two e f f e c t s . The a n a l y s i s o f t h e changes o b s e r v e d i n 31p c h e m i c a l s h i f t s upon s t e p w i s e c o o r d i n a t i o n i n terms o f t r a n s m i s s i o n o f e l e c t r o n i c e f f e c t s i s a t e m p t i n g a p p r o a c h . However, t h i s s h o u l d o n l y be u n d e r ­ taken w i t h extreme c a u t i o n , p a r t i c u l a r l y i n view o f t h e pronounced dependence o f t h e s e s h i f t s on a n g u l a r c h a n g e s ( 6 5 ) , and o f t h e f a c t t h a t closο-structure F i g u r e 8 shows t h a t t h d i n a t e d p h o s p h o r u s atoms a r e i n d e e d a f f e c t e d by s t e p w i s e c o o r d i n a ­ t i o n , b u t i n a r a t h e r p e c u l i a r way, w i t h t h e e f f e c t o f t e n r e a c h i n g a maximum a f t e r one o r two s u b s t i t u t i o n s , and d i m i n i s h i n g a g a i n thereafter. F i r s t i t s h o u l d be c l e a r t h a t t h e a m p l i t u d e o f t h e s e v a r i a ­ t i o n s c a n p r o b a b l y be a c c o u n t e d f o r b y a n g u l a r c h a n g e s o f o n l y a few d e g r e e s ( 6 5 ) . Then, t h e i r u n u s u a l a p p e a r a n c e s h o u l d p r o b a b l y be c o n s i d e r e d t o g e t h e r w i t h t h e change i n symmetry f r o m T^ t o C 3 , t h e n C 2 , and b a c k t o C 3 and T^, d u r i n g t h e c o o r d i n a t i o n s e q u e n c e . The c h e m i c a l s h i f t v a r i a t i o n s may t h e r e f o r e p r i m a r i l y r e f l e c t s t r u c t u r a l d e f o r m a t i o n s and a n g u l a r v a r i a t i o n s , and w i l l p r o b a b l y p r o v e t o be o f l i t t l e h e l p i n a p p r e c i a t i n g d i s p l a c e m e n t s o f e l e c ­ tron density during the c o o r d i n a t i o n process. One o f t h e most o b v i o u s l y d e s i r a b l e a p p r o a c h e s t o t h e q u a n t i ­ t a t i v e a p p r e c i a t i o n o f such t r a n s m i s s i o n e f f e c t s , as w e l l as o f t h e e x t e n t o f m u l t i p l e c h a r a c t e r i n b o n d i n g , w o u l d have b e e n t o p e r f o r m X - r a y d i f f r a c t i o n a n a l y s i s on a c o m p l e t e s e r i e s o f a d d u c t s w i t h 0 t o 4 c o o r d i n a t e d p h o s p h o r u s atoms. T h i s h a s s o f a r b e e n p r e v e n t e d by d i f f i c u l t i e s i n i s o l a t i n g t h e p a r t i a l l y coordinated s p e c i e s , l a r g e l y on a c c o u n t o f t h e i r i n s t a b i l i t y w i t h r e s p e c t t o r e d i s t r i b u t i o n o f t h e L e w i s a c i d s among t h e d o n o r s i t e s . B u t , s i n c e t h e p r o b l e m does n o t change i n n a t u r e when o x y g e n o r s u l f u r a r e s t e p w i s e l y added i n t h e e x o c y c l i c p o s i t i o n s o f t h e c l o s o s t r u c t u r e s , i n s t e a d of the p r e v i o u s l y mentioned Lewis a c i d s , a s e r i e s o f o x y i m i d e s , t h i o i m i d e s and m i x e d o x y t h i o i m i d e s was p r e p a ­ r e d f o r t h i s p u r p o s e , a c c o r d i n g t o f o l l o w i n g scheme. V

V

V

!==a P (NMe) 4

6 4

6

P (NMe) S

\ P (NMe) S0

\ P (NMe) S 0

6

4

• P (NMe) S

4

4

P (NMe) S — 4

or P (NMe) S

* P (NMe) 0 4

6

• P (NMe) S

2

4

6

3

6

4

6

4

4

6

3

4

6

2

2

\ P (NMe) S 0 4

6

P (NMe) 4

3

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

6

32

RINGS, CLUSTERS, AND POLYMERS

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

2.

RiESS

Poly cyclic Tetraphosphorus Compounds

33

A l l f o u r s u l f i d e s formed r e a d i l y , were i s o l a t e d , and gave s i n g l e c r y s t a l s (72); t h e t e t r a s u l f i d e had been p r e p a r e d p r e v i o u s l y by Holmes ( 7 3 ) . On t h e c o n t r a r y , o n l y t h e t e t r a o x i d e , a l o n g w i t h t h e c o m p l e m e n t a r y amount o f u n r e a c t e d s t a r t i n g m a t e r i a l , was o b t a i n e d , i n d e p e n d e n t l y o f t h e s t o i c h i o m e t r y o f t h e smooth o x i d i z i n g a g e n t e m p l o y e d , 0NMe3; no p a r t i a l l y o x i d i z e d i m i d e s were formed e i t h e r upon a t t e m p t e d r e d i s t r i b u t i o n o f t h e p e r i p h e r a l o x y g e n s b e t w e e n P4(NMe)£ and P4(NMe)fc04 ( 1 4 ) . T h i s i s c e r t a i n l y a n o t h e r s t r i k i n g m a n i f e s t a t i o n of the transmission of e l e c t r o n i c e f f e c t s through t h e s t r u c t u r e : t h e c o o r d i n a t i o n o f a f i r s t o x y g e n atom w o u l d i n ­ c r e a s e t h e a f f i n i t y f o r o x y g e n o f t h e r e m a i n i n g ones t o s u c h a n e x t e n t t h a t t h e f u l l y o x i d i z e d s p e c i e s would form. The exchange o f t h e p e r i p h e r a l , f o r m a l l y d o u b l e - b o n d e d s u l f u r atoms, when f o r example P4(NMe)£ i s added t o P4(NMe)£S4, was f o u n d t o o c c u r w i t h o u t l o s s o f t h e i n n e r P4(NMe)£ c o r e ( 7 4 , 7 5 ) . However, i t t a k e s s e v e r a l days a P4(NMe)£S4 m o l e c u l e s ; t h p a r t s s i g n i f i c a n t l y f r o m randomness. The f a c t t h a t t h e t e r m w i t h η = 2 i s l e s s s t a b l e t h a n t h o s e w i t h η = 1 o r 3 c o u l d a l s o be r e ­ l a t e d t o changes i n symmetry r a t h e r t h a n t o e l e c t r o n i c p o l a r i ­ z a t i o n e f f e c t s w h i c h w o u l d be e x p e c t e d t o v a r y i n a monotonous way a s η i n c r e a s e s . The same h o l d s f o r P4S3 - o r (?^Sfr)S2 - w h i c h i s l e s s s t a b l e t h a n b o t h P4S7 and P4S9 (8). S t r u c t u r a l D i s o r d e r : a P r o m i n e n t F e a t u r e o f Closo-Compounds X - r a y s t r u c t u r e d e t e r m i n a t i o n have been p e r f o r m e d on t h e e n t i r e s e r i e s o f compounds P4(NMe)£S (η = 0 - 4 ) and P4(NMe)£04 w i t h t h e a i m o f g a i n i n g some i n s i g h t i n t o t h e e x t e n t o f TT c o n t r i ­ b u t i o n t o t h e i r b o n d i n g and t h e t r a n s m i s s i o n o f e f f e c t s t h r o u g h s t r u c t u r e s (76-80). A c c u r a t e bond d i s t a n c e s were e x p e c t e d , i f o n l y b e c a u s e e a c h t y p e o f P-N bond i s r e p e a t e d , f o r example 12 t i m e s i n m o l e c u l e s o f T^ symmetry - o r e v e n 24 o r 48 t i m e s when two (P4(NMe)£) o r f o u r (P4(NMe)504) c r y s t a l l o g r a p h i c a l l y i n d e p e n d e n t m o l e c u l e s a r e p r e s e n t i n t h e u n i t c e l l - t h u s p r o v i d i n g 12, 24 o r 48 i n d e p e n d e n t measure­ ments o f t h e same m o l e c u l a r q u a n t i t y , f r o m w h i c h an a c c u r a t e a v e r a g e w o u l d o r d i n a r i l y be e x p e c t e d . I n s p i t e o f s o l i c i t o u s e f f o r t s - d a t a b e i n g i n some c a s e s c o l ­ l e c t e d on s e v e r a l c r y s t a l s o r a t d i f f e r e n t t e m p e r a t u r e s ( s e e a l s o r e f . 8 1 ) - o n l y d i s a p p o i n t i n g l y i m p r e c i s e bond d i s t a n c e s were ob­ t a i n e d , j u s t s u f f i c i e n t t o d i s c e r n q u a l i t a t i v e t r e n d s i n bondl e n g t h v a r i a t i o n s upon p r o g r e s s i v e c o o r d i n a t i o n o f t h e c l o s o s t r u c ­ t u r e , b u t i n s u f f i c i e n t t o p e r m i t any v a l i d d i s c u s s i o n o f t h e s e d a ­ t a i n terms o f t h e v a r i o u s c o n t r i b u t i o n s t h a t m i g h t d e t e r m i n e them. T h i s t e n d e n c y t o d i s o r d e r i s i l l u s t r a t e d by a l a r g e s p r e a d i n bond l e n g t h - u s u a l l y o v e r a t e n t h o f an a n g s t r o m - s o t h a t t h e average value c a r r i e s a wide i n t e r v a l o f u n c e r t a i n t y (77). I t a l s o manifests i t s e l f by t h e e x i s t e n c e o f p o l y m o r p h s , m o n o c l i n i c and o r t h o r h o m b i c f o r P4(NMe)£S ( 7 8 ) , a n d , i n t h e c a s e o f P4(NMe)fcS4, o f a g r o s s d i s o r d e r ( F i g u r e 9) o f a p u z z l i n g c h a r a c t e r , w i t h a t 3°C, two p o s s i b l e l o c a t i o n s f o r t h e s u l f u r atoms w i t h o c c u p a n c y n

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

34

RINGS, CLUSTERS,

A N D

POLYMERS

Figure 9. A view of the P (NMe) S molecule with the two locations Sj and S found for the sulfur atoms at 3 °C (11). This disorder is shown on one phosphorus atom only to avoid overcrowding. 4

6

4

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

2

2.

35

Poly cyclic Tetraphosphorus Compounds

RiESS

f a c t o r s c l o s e t o 50% ( t h r e e l i k e l y p o s i t i o n s f o r t h e s e s u l f u r s , w i t h o c c u p a n c y f a c t o r s o f 0.65, 0.28 a n d 0.07%, were f o u n d a t 22°C ( 7 7 ) . The most i n t e r e s t i n g outcome o f t h i s s t u d y l i e s i n f a c t i n the r e c o g n i t i o n t h a t t h i s u n c e r t a i n l y and tendency t o s t r u c t u r a l d i s o r d e r a p p e a r s t o be a common, p r o m i n e n t f e a t u r e i n c l o s o p h o s p h o r u s compounds. T h i s f e a t u r e c a n be u n d e r s t o o d i n t u i t i v e l y on two g r o u n d s : 1) t h e c l o s o - m o l e c u l e s have n o c e n t r a l atom t y i n g t h e atoms t o g e ­ t h e r a c r o s s t h e cage s t r u c t u r e , and hence s h o u l d be e n v i s i o n e d a s r a t h e r s o f t , d e f o r m a b l e e n v e l o p e s ( a l t h o u g h t h e r e i s no room i n s i ­ de t o accommodate s u c h a c e n t r a l a t o m ) , r e m i n i s c e n t o f a d e f l a t e d t e n n i s b a l l , s u b j e c t t o easy d e f o r m a t i o n under t h e a c t i o n o f c r y s ­ t a l p a c k i n g f o r c e s ; a s a r e s u l t t h e e l e c t r o n d i s t r i b u t i o n i s more l i k e l y t o adapt t o , r a t h e r than t o d e t e r m i n e , t h e geometric s t r u c ­ tures . 2) t h e s e m o l e c u l e s a r e w h i c h t e n d s t o f a v o r r o t a t i o n a l d i s o r d e r a n d / o r l i b r a t i o n a l mo­ t i o n o f l a r g e a m p l i t u d e i n t h e c r y s t a l , and, i n t h e extreme c a s e s , l e a d s t o t h e e x i s t e n c e o f a d i s t i n c t p l a s t i c phase c h a r a c t e r i z e d by v i r t u a l l y f r e e r o t a t i o n i n t h e s o l i d . T h e r e f o r e o n l y q u a l i t a t i v e t r e n d s c a n be r e c o g n i z e d a n d d i s c u s s e d ( 7 9 - 8 0 ) . T r e n d s i n P-0 and P-N Bond L e n g t h s ; C o n t r i b u t i o n t o T T - B o n d i n g The bond l e n g t h d a t a c o l l e c t e d f o r ( P 4 0 f c ) and f o r P 4 ( N M e ) 6 S are d i s p l a y e d d i a g r a m m a t i c a l l y below (A) : n

P46

)

P (NMe) 4

)

6

P4U7

1.638(3)1[gas) 1.656(4) (solid) Ρ ( 111 )—Ε P(III) 1.70(1)

) P(III) —Ε

P (NMe) S ) 4

6

48

)

ρ

P(III)-E P (NMe) S \ 4

6

1.593(7) P(V) 1.63(2)

1.63(1)

1.57(2) 1.66(1)

P(V)

1.60(2) 1.65(2)

P(V)

1.70(1)

-P(III)

j

P (NMe) S 4

1.684(7) . 1.645(7) P(IH) 1.70(1) 1.73(2)

2

P4O9 6

p

410

1.67(1)

1.71(2)

)

P (NMe) S | 4

6

r

1.73(1)

1.66(1) P(IH)

3

n

r

1.59(1) 1.692(4)

1.59(1) 1.68(2)

1.60(1) 1.66(1)

E-P(V)

E-P(V)

} n

'

4

(Data from ref. 4, 76-79, 82-85).

In view o f the l a r g e esd's u s u a l l y a s s o c i a t e d w i t h these data, d i f f e r e n c e s among i n d i v i d u a l bond l e n g t h s may n o t a l w a y s be s i g n i ­ f i c a n t . B u t t h e f a c t t h a t p a r a l l e l t r e n d s emerge t h r o u g h o u t b o t h series substantiates their r e a l i t y .

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

36

RINGS, CLUSTERS, AND

POLYMERS

The s h o r t e n i n g o f t h e P-E bonds when Ρ becomes p e n t a v a l e n t i s s u r p r i s i n g l y low and o f t e n n o t s i g n i f i c a n t . Such s h o r t e n i n g was c e r t a i n l y e x p e c t e d on e i t h e r o r b o t h o f two g r o u n d s : f i r s t , t h e i n c r e a s e i n f o r m a l o x i d a t i o n s t a t e o f t h e p h o s p h o r u s atom upon a t ­ t a c h m e n t o f an e x o c y c l i c o x y g e n o r s u l f u r atom s h o u l d l e a d t o a d e c r e a s e i n i t s c o v a l e n t r a d i i ; d a t a a v a i l a b l e on a c y c l i c a n a l o g s s u g g e s t t h a t t h i s mechanism m i g h t a c c o u n t f o r 0.03-0.04 Â o f s h o r t e n i n g ( 7 9 ) . Then t h e i n c r e a s e i n ττ-electron d e n s i t y drawn f r o m t h e n i t r o g e n atoms by t h e more p o s i t i v e p h o s p h o r u s atom c o u l d a l s o c o n t r i b u t e i n s t r e n g t h e n i n g the bond; t h e c o n t r a c t i o n o f t h e d o r b i t a l s s h o u l d i n p a r t i c u l a r enhance the Np-^-Pdyy c o n t r i b u t i o n t o bonding. More i n t e r e s t i n g , and r e v e a l i n g o f a s e c o n d r a n g e e f f e c t , i s t h a t t h e n a t u r e o f the p h o s p h o r u s atom l o c a t e d on t h e o t h e r s i d e o f the b r i d g i n g atom has a c l e a r e f f e c t on t h e P-N- o r P-0- bond l e n g t h . The g e n e r a l t r e n and P4(NMe)£S2 w h i c h c o n t a i P(III)-EP(V)

> P ( I I I ) - E P ( I I I ) > P(V)-EP(V) >

P(V)-EP(III)

The l o n g e s t and the s h o r t e s t bonds a r e b o t h f o u n d i n the P ( I I I ) E - P ( V ) s e q u e n c e . The f i r s t g a i n s £a 0.03 Â, w h i l e t h e s e c o n d l o s e s a c o m p a r a b l e l e n g t h w i t h r e s p e c t t o the "same" bond as f o u n d i n t h e s y m m e t r i c P4E5 and (P4E£)E'4 m o l e c u l e s . The e l e c t r o n s a r e a t t r a c t e d on t h e s i d e o f t h e p e n t a v a l e n t p h o s p h o r u s a t the e x p e n s e o f t h e bond l o c a t e d on t h e o t h e r s i d e o f t h e b r i d g i n g e l e m e n t ; t h i s d i s p l a c e m e n t of e l e c t r o n d e n s i t y can o c c u r t h r o u g h b o t h the σ and t h e π b o n d i n g f r a m e s . X-Ray s t u d i e s on t h e p h o s p h o r u s o x i d e s l e d t o s i m i l a r o b s e r v a ­ t i o n s ( 8 2 - 8 6 ) . P4O7, f o r e x a m p l e , c a n n o t be c o n s i d e r e d as made up o f f r a g m e n t s t a k e n f r o m P4O5 and P4O10 ( 8 5 ) . They a l s o r e v e a l t h e e f f e c t o f p a c k i n g , as w e l l as s i g n i f i c a n t d i f f e r e n c e s b e t w e e n t h e s o l i d and gas phase s t r u c t u r e s ( 8 4 , 8 6 ) . E v i d e n c e f o r N p - P d c o n t r i b u t i o n t o b o n d i n g i n P4(NMe)£S i n c l u d e t h e c l o s e - t o - p l a n a r a r r a n g e m e n t o f t h e bonds a b o u t a l l n i ­ t r o g e n atoms ( d e v i a t i o n s a r e i n t h e d i r e c t i o n e x p e c t e d f r o m s t e r i c e f f e c t s r a t h e r t h a n r e l a t e d t o t h e t y p e o f bonded Ρ a t o m s ) , t h e s i ­ g n i f i c a n t s h o r t e n i n g - by 0.07-0.10 Â - o f t h e P-N b o n d s , w i t h r e s p e c t t o p r o p e r l y r e d e f i n e d P ( l l l ) - N ( s p ) and P ( V ) - N ( s p ) s t a n d a r d s ( t a k i n g i n t o a c c o u n t b o t h the change i n h y b r i d i z a t i o n o f Ν w i t h r e s p e c t t o the u s u a l s t a n d a r d s , and the o x i d a t i o n s t a t e o f phospho­ r u s ( 7 9 ) , t h e h i g h e n e r g y and b r e a d t h o f t h e n i t r o g e n atom's l o n e p a i r a b s o r p t i o n s i n the p h o t o e l e c t r o n s p e c t r a , and, t o a l e s s e r de­ g r e e , some NMR c o u p l i n g d a t a . W i t h an a v e r a g e 1.70 Â, a l l P-N bonds a r e s h o r t e r t h a n w o u l d be e x p e c t e d on the b a s i s o f σ b o n d i n g a l o n e , e v e n a f t e r t h e u s u a l s i n g l e bond r a d i i a r e c o r r e c t e d f o r the change o f t h e n i t r o g e n ' s h y b r i d i z a t i o n from s p to s p . This s h o r t e n i n g would correspond, on the b a s i s o f C r u i c k s h a n k s t r e a t m e n t ( 8 3 ) , t o a b o n d - o r d e r i n t h e r a n g e o f 1.18 t o 1.30 f o r t h e P ( I I I ) — N - P ( l l l ) b o n d s . JT

TT

n

2

3

2

2

1

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

2.

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37

The π c o n t r i b u t i o n t o b o n d i n g may i n f a c t be l a r g e r t h a n w o u l d a p p e a r f r o m t h e bond s h o r t e n i n g . The f a c t t h a t t h e r e i s no s i g n i f i c a n t change i n P-N b o n d - l e n g t h s i n t h e s e r i e s P ^ N M e ) ^ , P4(NMe)£S4 and P4(NMe)^04 may s i g n i f y t h a t p a r t o f t h e bondl e n g t h ' s s h o r t e n i n g , which would n o r m a l l y r e s u l t from a g i v e n π c o n t r i b u t i o n i n a n open s y s t e m , i s a b s o r b e d h e r e i n c o u n t e r a c t i n g i n c r e a s e d Van d e r W a l l s r e p u l s i o n b e t w e e n non-bonded atoms i n t h e c l o s e d , c o n s t r a i n e d , p o l y c y c l i c system. The a b s o r p t i o n o f t h e n i t r o g e n ' s l o n e - p a i r s o f P4(NMe)fc i n t h e p h o t o e l e c t r o n s p e c t r u m l i e s b e t w e e n 8 and 9 eV, w h i l e i t w o u l d have b e e n e x p e c t e d t o be w e l l b e l o w 7 eV f o r a p u r e N2p l o n e p a i r . And t h e b r e a d t h o f t h e bond i n d i c a t e s t h a t t h e s e e l e c t r o n s a r e n o t s i m p l y i s o l a t e d , e q u i v a l e n t lone p a i r s , b u t t h a t they occupy d e l o c a l i z e d o r b i t a l s w i t h b o n d i n g c h a r a c t e r ( 7 6 ) . The a d d i t i o n o f 1 t o 4 e x o c y c l i c s u l f u r atoms p r o v o k e s a r e g u l a r i n c r e a s e i n t h e i o n i ­ s a t i o n e n e r g y o f t h e s e NpT 1 eV f r o m P4(NMe)£ t o P4(NMe)£S4 t r o n s i s c o n s i s t e n t w i t h a s t r e n g t h e n i n g o f t h e Νρττ-Pdn i n t e r a c t i o n , b u t c o u l d a l s o a r i s e i n d i r e c t l y by p o l a r i z i n g t h e N-P bonds s o a s t o c a u s e t h e more p o s i t i v e n i t r o g e n atoms t o b i n d t h e Ρ e l e c t r o n s more s t r o n g l y . I n t h e NMR s p e c t r a , t h e l^C-^-H c o u p l i n g c o n s t a n t s i n c r e a s e f r o m P4(NMe)5 t o P4(NMe)£S4 t o P4(NMe)fc04; t h i s i s c o n s i s t e n t w i t h t h e e x p e c t a t i o n t h a t t h e e x o c y c l i c atoms w i l l draw e l e c t r o n d e n s i ­ t y away f r o m t h e n i t r o g e n atoms, and t h i s t o a g r e a t e r e x t e n t w i t h o x y g e n t h a n w i t h s u l f u r , and a l s o c o n s i s t e n t w i t h i n c r e a s e d NpjyP d b o n d i n g , i n t h e same o r d e r ( 8 0 ) . B u t t h i s i n t e r p r e t a t i o n a g a i n i s not unique, since the a t t r a c t i o n o f e l e c t r o n d e n s i t y can occur e i t h e r t h r o u g h t h e σ s y s t e m o r t h r o u g h t h e π s y s t e m , o r b o t h , and t h e NMR d a t a p r o v i d e no b a s i s f o r d e t e r m i n i n g t h e r e l a t i v e i m p o r ­ t a n c e o f t h e two p a t h w a y s . n

P l a s t i c p h a s e s . P l a s t i c phase b e h a v i o r h a s b e e n r e c o g n i z e d f o r P 4 , P4S3, P " s a l t s , P4S10, P4(NMe)^ and As4(NMe)fc. I t i s e x e m p l i f i e d h e r e by P4(NMe)^ ( 8 7 ) . F i g u r e 10 shows t h e v a r i a t i o n i n l i n e width of the s i g n a l i n the NMR s p e c t r a m e a s u r e d on s o l i d P4(NMe)5 b e t w e e n 40 and 140°C. The f a c t t h a t t h e l i n e w i d t h i s " o n l y " 4700 Hz a t 40°C a l r e a d y s u p p o s e s c o n s i d e r a b l e r a p i d r e o r i e n t a t i o n a l movement i n t h e s o l i d a t t h a t t e m p e r a t u r e . The a b r u p t change t h a t o c c u r s w i t h i n one d e g r e e a t 56°C r e f l e c t s a d r a s t i c change i n m o l e c u l a r f r e e d o m , w h i c h was a s s i g n e d t o a p l a s t i c phase t r a n s i t i o n above w h i c h t h e m o l e c u l e s r o t a t e a l m o s t f r e e l y w h i l e maintaining t h e i r p o s i t i o n a l order i n the s o l i d . This i n t e r p r e t a ­ t i o n i s s u p p o r t e d by d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y ( F i g u r e 1 1 ) , w h i c h shows, a t t h e same t e m p e r a t u r e , a s h a r p , f i r s t - o r d e r t r a n s i ­ t i o n upon h e a t i n g (upon c o o l i n g , t h e t r a n s i t i o n i s f o u n d a t 50.5°C, w h i c h d e n o t e s h y s t e r y s i s , a common f e a t u r e o f p l a s t i c phase t r a n ­ s i t i o n s ( 8 7 ) ) . A t r a n s i t i o n a t 38°C was t e n t a t i v e l y a s s i g n e d t o t h e r o t a t i o n o f t h e m o l e c u l e a b o u t one o f i t s C3 a x e s ; t h e f a c t t h a t t h e p r o c e s s i s h i g h — o r d e r upon h e a t i n g means t h a t t h e o n s e t o f t h e r o t a t i o n i s c o n c e r t e d . The l o w e n t r o p y o f m e l t i n g J

7

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

RINGS, CLUSTERS,

AND

POLYMERS

Hz

50

y

70

90 Plastic

110

y

130

Phase

!

Figure 10. Line-width of the H-NMR signal measured on solid P (NMe) function of temperature. 4

6

as a

(Reproduced with permission from Ref. 88. Copyright 1977, Institut Mondial du Phosphate.)

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

RiESS

Polycyclic Tetraphosphorus Compounds

Figure 11. Differential scanning calorimetry of

P (NMe) . 4

6

(Reproduced with permission from Ref 88. Copyright 1977, Institut Mondial du Phosphate.)

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

40

RINGS, CLUSTERS, AND

POLYMERS

(AS = 4.8 J m o l ^ K ' ) , a t 122°C, i s a l s o c h a r a c t e r i s t i c o f a p l a s t i c c r y s t a l l i n e p h a s e , as i s the s o f t n e s s o f t h e c r y s t a l s and t h e i r s e n s i t i v i t y t o m a c r o s c o p i c m e c h a n i c a l damage. V a r i a b l e temp e r a t u r e X - r a y powder d i f f r a c t i o n shows a change i n p a t t e r n f r o m m o n o c l i n i c t o c u b i c upon h e a t i n g ; t h e d i f f r a c t i o n l i n e s , s h a r p and numerous f o r the " r i g i d c r y s t a l s , become few and l e s s w e l l - d e f i ned f o r t h e p l a s t i c c r y s t a l . I t s h o u l d be n o t e d t h a t the s t r u c t u r a l c r i t e r i a - g l o b u l a r i t y - w h i c h i s u s u a l l y s u f f i c i e n t t o d e t e r m i n e the e x i s t e n c e o f a p l a s t i c phase f o r o r g a n i c compounds, no l o n g e r s u f f i c e s h e r e , s i n c e P4, P4S10 and P4(NMe)fc do e x h i b i t p l a s t i c p h a s e s , w h i l e t h e e q u a l l y g l o b u l a r P4O5 and P4S1Q o f same symmetry do n o t ( 8 9 ) . Sev e r a l f a c t o r s are l i k e l y to c o n t r i b u t e to t h i s d i f f e r e n c e . F i r s t t h e i n t e r m o l e c u l a r h y d r o g e n / h y d r o g e n i n t e r a c t i o n s , w h i c h a r e known t o have a d e t e r m i n i n g i n f l u e n c e on the c r y s t a l p a c k i n g , should c o n t r i b u t e t o the s e p a r a t i o thus favor f r e e r o t a t i o t l y s p h e r i c a l , and l i t e r a l l y c o a t e d w i t h h y d r o g e n atoms, as i s adamantane. On t h e o t h e r h a n d , t h e l o c a t i o n and l o c a l p o l a r i t y o f t h e o x y g e n atoms i n P4O5 and P4O1Q p r o b a b l y c o n t r i b u t e t o i n c r e a s i n g m o l e c u l a r i n t e r l o c k i n g , and t h e r e f o r e h i n d e r the r o t a t i o n . Thus t h e way t h e P4O1Q m o l e c u l e s p a c k t o g e t h e r i s o f much i n t e r e s t : e a c h m o l e c u l e has f o u r s p i k e s and f o u r r e c e s s e s , and t h e s p i k e s o f e a c h m o l e c u l e f i t i n t o the r e c e s s e s o f i t s f o u r n e a r e s t n e i g h b o r s , l e a d i n g t o a c l o s e p a c k i n g w i t h c o n s i d e r a b l e i n t e r l o c k i n g . The s t r u c t u r a l d a t a show t h a t s u c h interpénétration does n o t e x i s t i n 4 10» i t s p e r i p h e r a l s u l f u r atoms t o o l a r g e t o f i t i n t o the n i t c h e s o f the n e i g h b o r i n g m o l e c u l e s , and w i t h s m a l l e r d i p o l a r i n t e r a c t i o n s . These o b s e r v a t i o n s l e d t o t h e d e f i n i n g o f a new s t r u c t u r a l c r i t e r i o n f o r p r e d i c t i n g p l a s t i c phase b e h a v i o r , b a s e d on t h e d e g r e e o f i n t e r m o l e c u l a r i n t e r l o c k i n g ( 8 9 ) . 1

1 1

P

S

w

i

t

n

The C o o r d i n a t i o n C h e m i s t r y o f T e t r a p h o s p h o r u s S u l f i d e s ; t i v e b u t Open Case

a Decep-

The closo-tetraphosphorus sulfides, with their various s t o i c h i o m e t r i c s and u n i q u e s t r u c t u r e s (Scheme 2 ) , e x h i b i t m u l t i p l e and o f t e n d i s t i n c t p o t e n t i a l c o o r d i n a t i o n s i t e s . These s i t e s o f t e n i n v o l v e s e v e r a l d i s t i n c t s e t s of f o r m a l l y non-bonding e l e c t r o n p a i r s a t b o t h p h o s p h o r u s and s u l f u r atoms, and t h e t e t r a p h o s p h o r u s s u l f i d e s c o u l d t h e r e f o r e be e x p e c t e d t o e x h i b i t a w i d e r a n g e o f c o o r d i n a t i o n modes and o r i g i n a l b e h a v i o r t o w a r d s L e w i s a c i d s . But so f a r t h i s has n o t p r o v e d s o . T h i s i s a l l t h e more d i s a p p o i n t i n g , as a t h o r o u g h t h e o r e t i c a l i n v e s t i g a t i o n o f the e l e c t r o n i c s t r u c t u r e o f P4S3, p e r f o r m e d by Χα s c a t t e r e d wave, as w e l l as by t h e e x t e n d e d Hûckel and CNDO m o l e c u l a r o r b i t a l m e t h o d s , l e d t o t h e c o n c l u s i o n t h a t the a p i c a l and t h e b a s a l p h o s p h o r u s atoms c o u l d be e x p e c t e d t o be e q u a l l y good d o n o r s ( 9 0 ) . The e l e c t r o n i c s t r u c t u r e o f the m o l e c u l e i s d e s c r i b e d by a s e t o f l o w e r e n e r g y v a l e n c e - s h e l l l e v e l s h a v i n g h i g h 3s c h a r a c t e r ,

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

2.

41

Poly eye lie Tetraphosphorus Compounds

RiESS

which p r o v i d e i t s main cohesive energy t h r o u g h m u l t i - c e n t e r bond­ ing w i t h i n the and PS^ s u b - u n i t s , and by another set o f h i g h e r , o c c u p i e d n o n - b o n d i n g o r w e a k l y b o n d i n g l e v e l s t h a t have a l a r g e 3p component. C o n t o u r p l o t s show t h e l a t t e r t o have e l e c t r o n d i s t r i ­ butions c h a r a c t e r i s t i c o f d i r e c t e d lone p a i r s both a t the a p i c a l Ρ and b a s a l P3- u n i t . W h i l e t h e a p i c a l p h o s p h o r u s i s p r e d i c t e d t o have d o n o r p r o p e r t i e s s i m i l a r t o t h o s e o f t e r t i a r y p h o s p h a n e s , t h e b a s a l P3 u n i t w o u l d be e x p e c t e d t o behave e s s e n t i a l l y l i k e P4. The h i g h i o n i z a t i o n e n e r g y ( f r o m H e l p h o t o e l e c t r o n s p e c t r o s ­ copy ( 9 0 ) ) a s s i g n e d t o t h e a p i c a l lone p a i r e l e c t r o n s i n d i c a t e s a v e r y weak b a s e . T h i s i s c o n s i s t e n t w i t h t h e l a c k o f r e a c t i v i t y o f P4S3 t o w a r d s BCI3 o r BF3, i t s f a i l u r e t o be q u a t e r n i z e d u n d e r t h e a c t i o n o f MeS03F o r E t 3 0 B F 4 and, i n g e n e r a l , i t s r e s i s t a n c e t o p r o tonation (91). A f i r s t s e r i e s o f t r a n s i t i o n m e t a l a d d u c t s o f P4S3 was o b t a i ­ ned i n 1969 by N i x o n e CSo 2 P4S3

+

C H M(CO)

4

3 P4S3

+

C H M(CO)

3

7

7

8

8

reflux • ^s-(P S ) M(CO)4 M = Or, Mo, W • / ac-(P4S3) M(CO)3 M = Or, Mo 4

3

2

,

3

5

4 P4S3 + ( η - 0 Η ) Ν Ϊ 5

5

2

(P4S ) Ni 3

4 P4S3 + ( n - c H ) N i 3

3

5

2

4

τ ^ Τ ^ ο

o-is and fac s t e r e o c h e m i s t r i e s were p r o p o s e d on t h e b a s i s o f t h e I R s p e c t r a . The ^ P s p e c t r a were r e p o r t e d a s c o n s i s t i n g o f a d o u b l e t and a q u a r t e t i n 3:1 r a t i o , i n d i c a t i n g t h a t ( o n t h e a v e r a g e ) t h e C3 symmetry o f t h e l i g a n d had been r e t a i n e d . B o t h s i g n a l s were s h i f t e d towards lower f i e l d s w i t h r e s p e c t t o those observed f o r f r e e P4S3. As t h e l a r g e s t s h i f t a f f e c t e d t h e q u a r t e t , i t was p r o ­ p o s e d t h a t i t i s t h e a p i c a l p h o s p h o r u s w h i c h i s bound t o t h e me­ t a l . N i ( P 4 S 3 ) 4 was o b t a i n e d by d i s p l a c e m e n t o f b o t h c y c l o p e n t a d i e n y l r i n g s f r o m n i c k e l o c e n e o r , more c o n v e n i e n t l y , f r o m b i s - T T - a l l y l n i c k e l (92). P4S3Mo(CO)5 was p r e p a r e d by C o r d e s e t a l . by r e f l u x i n g equimo l a r amounts o f P4S3 and Μο(00)β i n c y c l o h e x a n e c o n t a i n i n g a s m a l l amount o f d i g l y m e ( 9 3 ) . The y i e l d was i m p r o v e d by p h o t o c h e m i c a l a c t i v a t i o n ; P4S3W(CO)5 was a l s o t h u s o b t a i n e d i n 6 6 % y i e l d ( 9 4 ) . The X-ray c r y s t a l s t r u c t u r e o f the former r e v e a l s t h a t , i n t h e s o l i d , t h e i n t a c t P4S3 m o l e c u l e b e h a v e s as a m o n o d e n t a t e l i g a n d t h r o u g h i a p i c a l p h o s p h o r u s atom ( F i g u r e 12) ( 9 3 ) . The P4S3 c o r e shows s u r p r s i n g l y l i t t l e d e f o r m a t i o n upon c o o r d i n a t i o n : none o f t h e bond a n ­ g l e s n o r t h e b a s a l bond l e n g t h s a r e c h a n g e d a t a l l , and o n l y b a ­ r e l y s i g n i f i c a n t l e n g t h e n i n g o f b o t h t y p e s o f P-S bonds c o u l d be n o t e d . The s h o r t Mo-P d i s t a n c e o f 2 . 4 7 7 ( 9 ) Â, t h e h i g h c a r b o n y l s t r e t c h i n g f r e q u e n c i e s and a n Mo-C bond l e n g t h c o m p a r a b l e t o t h o s e i n Mo(C0)5 and M o ( C 0 ) P F 3 , l e a d t o t h e r a n k i n g o f P4S3 among t h e s t r o n g l y TT-accepting l i g a n d s . 3

V

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

42

RINGS, CLUSTERS, A N D POLYMERS

I n s o l u b l e , p r o b a b l y p o l y m e r i c a d d u c t s , f o r m u l a t e d as P 4 S 3 C U X (X = C l , B r , I ) , have been o b t a i n e d by a l l o w i n g P4S3 t o r e a c t w i t h Cu(l) or C u ( l l ) halides i n CS (95). C o o r d i n a t i o n t h r o u g h t h e b a s a l p h o s p h o r u s atoms h a s so f a r n o t been e s t a b l i s h e d , i n s p i t e o f numerous a t t e m p t s . The 31p NMR s p e c ­ t r a d i s p l a y e d by P 4 S 3 M ( C O ) 5 i s however p u z z l i n g ( 9 4 ) . These s p e c t r a i n d e p e n d e n t o f s o l v e n t ( h e x a n e , t o l u e n e , CH2CI2, C S ) , and m e t a l (Mo, W), e x h i b i t two s e t s o f s i g n a l s h a v i n g ca 3:1 peak a r e a r a t i o , e a c h c o n s i s t i n g o f a d o u b l e t and a q u a d r u p l e t , a l s o i n ca 3:1 r a t i o . The most i n t e n s e o f t h e s e s e t s h a s c h e m i c a l s h i f t s and c o u p l i n g c o n s t a n t s i d e n t i c a l t o those o f f r e e P4S3(6= - 1 2 8 . 4 ( d ) , +62.1(q) ppm, J = 70 H z ) . The s e c o n d , w e a k e r , s e t i s f o u n d a t l o w e r f i e l d , and shows a g r e a t l y r e d u c e d s p l i t t i n g (Mo : δ = - 1 1 1 . 9 ( d ) , +122.5(q) ; J = 33 Hz; W : δ = - 1 1 1 . 3 ( d ) , + 8 4 . 8 ( q ) ppm; J = 30 H z ) . B o t h t h e s o l u t i o n and s o l i d s t a t e i n f r a - r e d s p e c t r a show no v i b r a ­ tions i n the carbonyl regio M(C0)5 m o i e t y . When t h c r y s t a l l i n e a d d u c t c o u l d be r e c o v e r e d . P o s s i b l e c o o r d i n a t i o n by t h e s u l f u r atoms seems t o be e x c l u d e d b y the Mo-P c o u p l i n g c o n s t a n t o b s e r v e d i n t h e M o NMR ( J - P = 140Hz a t δ = +99 ppm) w i t h r e s p e c t t o M o i C O ^ ) . The a d d i t i o n o f f r e e PPI13 had no i n f l u e n c e on t h e p r o c e s s and PPI13 r e m a i n s u n c o o r d i n a t e d i n a s o l u t i o n o f P4S3Mo(CO)5. A d i s s o c i a t i o n t o f o r m a n a p e x - p l u s - b a s e c o o r d i n a t e d P 4 S 3 [M(C0)5] a d d u c t w h i c h w o u l d r e t a i n t h e C 3 symme­ t r y o f P 4 S 3 i s h a r d l y c o m p a t i b l e w i t h t h e peak a r e a r a t i o f o u n d i n the NMR. T h u s , t h e h y p o t h e s i s we f a v o r , on t h e b a s i s o f t h e peak a r e a r a t i o s , w o u l d be a d i s s o c i a t i o n a c c o r d i n g t o : 2

2

9 5

M o

2

4 P S M(CO) 4

3

V

• P4S rM(CO) ]4

5

3

+

5

3 P4S3

i n w h i c h P4S3 w o u l d behave a s a tetvaàentate, apex-plus-base coord i n a t e d l i g a n d ; b u t t h i s r e m a i n s t o be e s t a b l i s h e d . The l i g a n d b e h a v i o r o f t h e a r s e n i c - b a s e d compound 9 ( F i g u r e l 3 ) s t r u c t u r a l l y r e l a t e d t o P4S3, i s o f i n t e r e s t i n t h i s c o n t e x t . I t was shown t h a t 9 r e a c t s w i t h g r o u p V I m e t a l h e x a c a r b o n y l s u n d e r UV i r r a d i a t i o n t o g i v e t h e a d d u c t s [ C H 3 C ( C H A s ) ] M ( C 0 ) 5 _ (N = 1, M = O r , Mo, W; η = 2, M = C r , W) i n w h i c h 9 b e h a v e s a s a monodentat e l i g a n d ( 9 6 ) . An X - r a y d i f f r a c t i o n a n a l y s i s ( n = 1, M = C r ) d e f i ­ n i t e l y p r o v e s t h a t i n t h e s o l i d t h e m e t a l i s l o c a t e d on one o f t h e t h r e e a r s e n i c atoms o f t h e b a s e , r e m i n i s c e n t o f P4 a d d u c t s ( 9 7 ) . P o l y m e r i c s p e c i e s o f f o r m u l a [CH3C(CH As ^ M o i C O ^ ] and [CH3C(CH As)3Mo(CO)3J , for which b r i d g i n g bidentate behavior of the l i g a n d was s u g g e s t e d , were a l s o o b t a i n e d , and a c o b a l t c a r b o n y l n i t r o s y l a d d u c t , C H 3 C ( C H A s ^ C O Î N O ) ( C 0 ) , was b r i e f l y m e n t i o n n e d ( 9 6 ) . R e l a t e d t o t h e c o o r d i n a t i o n c h e m i s t r y o f P4S3 i s t h a t o f CI-P4S3I2,, w h i c h a l s o d i s p l a y s m u l t i p l e p o t e n t i a l c o o r d i n a t i o n s i tes i n a semi-open ( n i d o ) s t r u c t u r e , b u t w i t h fewer s t e r i c const r a i n t s and no P 3 ~ u n i t . The c o o r d i n a t i o n a b i l i t i e s o f (I-P4S3I2., how e v e r , have a l s o p r o v e n r a t h e r l i m i t e d . Baudler eb dl r e p o r t e d a s e r i e s o f molecular low-valent metal adducts o f type M ( a - P 4 S 3 l ) ( C 0 ) _ ( M = N i , F e ; m = 1-3) ( 9 8 ) . I t i s r e m a r k a b l e - and f r u s 2

2

2

3

n

n

n

n

2

2

2

n

m

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

n

2.

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43

44

RINGS, CLUSTERS, A N D POLYMERS

t r a t i n g t h a t t h e l i g a n d a c t e d e x c l u s i v e l y as a monodentate l i gand; w h e t h e r t h i s a r i s e s f r o m s t e r i c h i n d r a n c e o r f r o m e l e c t r o n délocalisation w i t h i n t h e l i g a n d s frame i s n o t c l e a r . D e p e n d i n g on t h e s o l v e n t u s e d , [ C o ( C 0 ) 4 l 2 r e a c t s w i t h CI-P4S3I2 t o g i v e t h e s u b s t i t u t i o n p r o d u c t [Co( C I - P 4 S 3 I 2 ) ( C C O 3 ] 2 o r a n i o n i c c o m p l e x [Co( d - P 4 S 3 l 2 ( C O ) 3 ] [ 0 0 ( 0 0 ) 4 ! " v i a v a l e n c e d i s p r o p o r t i o n a t i o n . P r e l i m i n a r y b u t e n c o u r a g i n g r e s u l t s have b e e n o b t a i n e d w i t h P4S7 ( 9 4 ) . When a l l o w e d t o r e a c t w i t h a n e x c e s s o f M o i C O ) ^ a t r e f l u x i n c y c l o h e x a n e , t h e i n s o l u b l e P4S7 i s c o n v e r t e d i n t o a y e l l o w c r y s t a l l i n e a i r - s e n s i t i v e m a t e r i a l , s o l u b l e i n most s t a n d a r d o r g a n i c s o l v e n t s and w i t h an e l e m e n t a l a n a l y s i s w h i c h p o i n t s t o t h e f o r m u l a t i o n P 4 S 7 [ M o i C O ^ I , η b e i n g 6 o r 7 ! S i n g l e c r y s t a l s were o b t a i n e d f r o m CH2CI2, b u t decomposed w i t h r e l e a s e o f M o i C O ) ^ upon s t a n d i n g , o r u n d e r t h e X - r a y beam. The p r e s e n c e o f Mo(C0)5 g r o u p s (and a b s e n c e o f Mo(CO)£)in t h e a d d u c t was e s t a b l i s h e d by t h e c h a ­ racteristic v(CO) a b s o r p t i o t i o n s , i n the i n f r a - r e d w h i c h e x h i b i t s two s i g n a l s i n 4:1 r a t i o . The P NMR (CHCI3) d i s ­ p l a y s two s h a r p s i g n a l s a t +107.0 and +46.4 ppm w i t h peak a r e a i n 1:3 r a t i o and no d e t e c t a b l e c o u p l i n g , i n c o n t r a s t t o +110.7 and +83.9 ppm i n 1:1 r a t i o ( a l s o w i t h no d e t e c t a b l e c o u p l i n g ) , f o r f r e e P4S7 i n CS2 s o l u t i o n ( 9 9 ) . The 1:3 s i g n a l r a t i o o f t h e new a d d u c t i s no l o n g e r c o m p a t i b l e w i t h t h e i n i t i a l s t r u c t u r e o f P4S7, and c o u l d i n d i c a t e a r e a r r a n g e m e n t i n w h i c h one o f t h e t e r m i n a l s u l f u r atoms w o u l d be i n s e r t e d i n t o t h e a l r e a d y d i s t e n d e d ( 2 . 3 3 Â ) P-P bond o f P4S7. Such a r e a r r a n g e m e n t h a s a l r e a d y b e e n f o u n d t o o c c u r b e t w e e n CI-P4S5 and p - P 4 S 5 (Scheme 2 ) ; f u r t h e r work i s u n d e r way t o e l u c i d a t e t h i s r i d d l e . When P4S9 and P4S1Q were a l l o w e d t o r e a c t w i t h Μο(θθ)^, s u l ­ f u r was r e l e a s e d , and a m i x t u r e o f t h e above P 4 S 7 [ M o i C O ^ ] 6 ( o r 7 ) - f o r m u l a t e d a d d u c t , w i t h a new a d d u c t , ( w h i c h i n t h e ^ l p NMR d i s ­ p l a y s a q u a r t e t and a d o u b l e t a t 80.0 a n d +63.4 ppm r e s p e c t i v e l y , i n 1:3 r a t i o , w i t h J p p = 6 Hz, t e n t a t i v e l y a s s i g n e d t o a P4S9Mo(CO)5 a d d u c t ) was o b t a i n e d ( 9 4 ) . 1

+

η

3 1

Literature Cited 1. 2. 3. 4. 5. 6.

Van Wazer, J.R. "Phosphorus and its Compounds", Vol.I, Interscience : New York, 1958. Haiduc, I. "The Chemistry of Inorganic Ring Systems", Wiley : London, 1970. Armitage, D.A. "Inorganic Rings and Cages"; Arnold : New-York, 1972. Corbridge, D.E.C. "The Structural Chemistry of Phosphorus" : Elsevier : Amsterdam, 1974. Hoffman, H.; Becke-Goehring, M. in "Topics in Phosphorus Chemistry", Vol. 8, Griffith E.J. and Grayson, M. Ed.; Interscience : New York, 1976. Heal, H.G. "The Inorganic Heterocyclic Chemistry of Sulfur, Nitrogen and Phosphorus"; Academic Press : London, 1980.

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RINGS, CLUSTERS, A N D POLYMERS

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Cotton, F.A.; Troup, J.M.; Casabianca, F.; Riess, J.G. Inorg. Chim Acta 1974, 11, L33. Casabianca, J . ; Cotton, F.A.; Riess, J.G.; Rice, C.E.; Stults, B.R. Inorg. Chem. 1978, 17, 3232. Cotton,F.Α.; Riess, J.G.; Rice, C.E.; Stults, B.R. Inorg. Chem. 1978, 17, 3521. Cotton, F.A.; Riess, J.G.; Rice, C.E.; Stults, B.R. Inorg. Chem. 1982, 21, 3123. Cotton, F.A.; Riess, J.G.; Stults, B.R. Inorg.Chem.(submitted). Hunt, G.W.; Cordes, A.W. Inorg.Nucl.Chem.Letters 1974,10,637. Cruickshank, D.W.J. J. Chem. Soc. 1961, 5486. Beagley, B.; Cruickshank, D.W.J.; Hewitt, T.G.; Jost, K.H. Trans. Faraday Soc. 1969, 65, 1219. Jansen, M.; Voss, M.; Deiseroth, H-J. Angew. Chem. Int. Ed. 1981, 20, 965. Jansen, M.; Voss, M Jansen, M.; Möbs, Μ Postel, M.; Casabianca, F.; Riess, J.G. Inorg. Chim. Acta. 1976, 17, L23. Riess, J.G.; Postel, M.; Jeanneaux, F.; Cotton, F.A.; Stultz, B.R.; Rice, C.E. Proceed. Intl. Cong. Phosphorus Compounds (Rabat, Oct. 1977), p. 51. Postel, M.; Riess, J.G. J. Phys. Chem. 1977, 81, 2634. Head, J.D.; Mitchell, K.A.R.; Noodleman, L.; Paddock, N.L. Can. J. Chem. 1977, 55, 669. Le Geyt, M.R. Thesis, U. of British Columbia, Canada, 1974. Jefferson, R.; Klein, H.F.; Nixon, J.F. J. Chem. Soc. Chem. Commun. 1969, 536. Cordes, A.W.; Joyner, R.D.; Shores, R.D.; Dill, E.D. Inorg. Chem. 1974, 13, 132. Bourgund, P.; Brevard, C.; Hubert-Pfalzgraf, L.G.; Riess, J.G. Unpublished results. Ibáñez, W.; Gonzalez, M.; Clavijo, C. Z. Anorg. Allg. Chem. 1977, 432, 253. Ellermann, J.; Lindner, H.A.; Gäbelein, H. J. Organometal. Chem. 1979, 172, 39. Ellermann, J.; Lindner, H.A.; Schössner, H.; Thiele, G.; Zoubek, G. Z. Naturforsch. 1978, 33b, 1386. Baudler, M.; Mozaffar-Zanganeh, H. Z. Anorg. Allg. Chem. 1976, 423, 193. Brevard, C.; Demarcq, M. Chem. Phys. letters 1981, 82, 167. Di Vaira, M.; Sacconi, L. Angew. Chem. Int. Ed. 1982, 21, 330.

RECEIVED

April 8, 1983

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

3 Cyclic and High-Polymeric Phosphazenes as Carrier Molecules for Carboranyl, Metallo, or Bioactive Side Groups H. R. ALLCOCK The Pennsylvania State University, Department of Chemistry, University Park, PA 16802

Cyclic and hig modified by nucleophilic-type substitution reactions to generate a wide range of derivatives. Recent developments include the introduction of bioactive organic residues to yield biologically-active high polymers and the synthesis of transition metal derivatives of phosphazenes. In addition, hybrid phosphazene-carborane compounds have been prepared including examples in which nido-carboranyl units, attached to a phosphazene ring or chain, function as binding sites for transition metal organometallic units. Most i n o r g a n i c r e s e a r c h i n v o l v e s w o r k w i t h s m a l l m o l e c u l e s , and r e l a t i v e l y l i t t l e c o n c e n t r a t e d e f f o r t h a s b e e n d e v o t e d t o t h e macromolecular aspects o f t h e subject. The c o m p l e x i t y o f t h e macromolecular chemistry has undoubtedly c o n t r i b u t e d t o t h i s neglect. However, i t i s c l e a r f r o m r e c e n t w o r k t h a t d r a m a t i c a d v a n c e s i n b o t h f u n d a m e n t a l s c i e n c e and t e c h n o l o g y w o u l d b e p o s s i b l e i f t h e h i g h polymer c h e m i s t r y o f t h e r e p r e s e n t a t i v e e l e m e n t s w e r e t o be s t u d i e d i n d e t a i l . I n d e e d , t h e muchh e r a l d e d r e n a i s s a n c e i n M a i n Group c h e m i s t r y may u l t i m a t e l y depend on a c l o s e r i n v e s t i g a t i o n o f t h e m a c r o m o l e c u l a r a s p e c t s o f t h e field. My p u r p o s e h e r e i s t o i l l u s t r a t e what c a n be a c c o m p l i s h e d w i t h j u s t one i n o r g a n i c m a c r o m o l e c u l a r s y s t e m — i n t h i s c a s e c o n s t r u c t e d f r o m a b a c k b o n e o f p h o s p h o r u s and n i t r o g e n atoms. A l m o s t c e r t a i n l y , o t h e r s y s t e m s b a s e d o n t h e M a i n Group e l e m e n t s can be d e v e l o p e d t o an e q u a l o r g r e a t e r degree. I hope t h a t t h e f o l l o w i n g comments w i l l s t i m u l a t e a n i n c r e a s e d i n t e r e s t i n t h a t direction. I w i l l a l s o attempt t o i l l u s t r a t e the r e l a t i o n s h i p between t h e fundamental c h e m i s t r y and an approach t o s o l v i n g p r a c t i c a l problems.

0097-6156/83/0232-0049 $06.00/0 © 1983 American Chemical Society

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POLYMERS

Guiding P r i n c i p l e s N e a r l y a l l s y n t h e t i c p o l y m e r s a r e s y n t h e s i z e d by t h e p o l y m e r i z a t i o n o r c o p o l y m e r i z a t i o n o f d i f f e r e n t "monomers." The c h a i n g r o w t h p r o c e s s may i n v o l v e t h e a d d i t i o n c h a i n r e a c t i o n s o f unsaturated small molecules, condensation r e a c t i o n s , or r i n g opening chain-coupling processes. In c o n v e n t i o n a l polymer c h e m i s t r y , t h e s y n t h e s i s o f a new p o l y m e r r e q u i r e s t h e use o f a new monomer. This approach i s o f t e n u n s a t i s f a c t o r y f o r i n o r g a n i c s y s t e m s , where r e l a t i v e l y few monomers o r c y c l i c o l i g o m e r s c a n be i n d u c e d to p o l y m e r i z e , at l e a s t under c o n d i t i o n s t h a t have been studied to date. The m a i n e x c e p t i o n t o t h i s r u l e i s t h e c o n d e n s a t i o n - t y p e growth t h a t occurs w i t h i n o r g a n i c d i - h y d r o x y acids. Because the o p p o r t u n i t i e s f o r c o n t r o l l e d c h a i n growth are more r e s t r i c t e d i n i n o r g a n i n a t i v e approach to polyme i n v o l v e s t h e use o f s u b s t i t u t i o n p r o c e s s e s c a r r i e d o u t on a preformed r e a c t i v e polymeric intermediate. I n t h i s way molecular d i v e r s i t y can be i n t r o d u c e d by d i f f e r e n t s u b s t i t u t i o n r e a c t i o n s r a t h e r t h a n by a d i v e r s i f i c a t i o n o f t h e p o l y m e r i z a t i o n p r o c e s s . I f t h i s p r i n c i p l e c a n be a p p l i e d , two p o t e n t i a l p r o b l e m s must be a v o i d e d : t h e s u b s t i t u t i o n r e a c t i o n s must l e a d t o n e i t h e r c h a i n cleavage nor c r o s s l i n k i n g . Simple S u b s t i t u t i o n Reactions

with

Poly(dihalophosphazenes)

Poly(dichlorophosphazene) (II) i s a highly reactive inorganic macromolecule. I t can be p r e p a r e d by t h e c a r e f u l l y c o n t r o l l e d thermal p o l y m e r i z a t i o n of the c y c l i c t r i m e r , h e x a c h l o r o c y c l o t r i phosphazene ( I ) , i t s e l f s y n t h e s i z e d from phosphorus p e n t a c h l o r i d e and ammonium c h l o r i d e . I n s o l u t i o n , t h e c h l o r i n e atoms i n I I can be r e p l a c e d r e a d i l y by r e a c t i o n w i t h a w i d e v a r i e t y o f o r g a n i c n u c l e o p h i l e s (1,2., 3.) (Scheme 1 ) . The r e s u l t a n t p o l y m e r s ( I I I - V ) a r e s t a b l e and d i s p l a y a r a n g e o f p h y s i c a l and c h e m i c a l p r o p e r t i e s d e t e r m i n e d by t h e n a t u r e o f t h e o r g a n i c s i d e g r o u p s . This s y n t h e s i s p r o c e s s has b e e n r e v i e w e d i n d e t a i l e l s e w h e r e (4.-7) . Here i t i s s u f f i c i e n t to n o t e t h a t s e v e r a l hundred p o l y ( o r g a n o p h o s p h a z e n e s ) h a v e b e e n p r e p a r e d by t h i s method. Polymers of t h i s t y p e are a l r e a d y b e i n g used i n t e c h n o l o g y ; t h e y a r e a l s o o f considerable s c i e n t i f i c interest. S i m i l a r s y n t h e s e s have b e e n d e v e l o p e d b a s e d on p o l y ( d i f l u o r o p h o s p h a z e n e ) , (NPF2) (8). n

C y c l i c T r i m e r s and

T e t r a m e r s as R e a c t i o n

Models

From a t h e o r e t i c a l and m e c h a n i s t i c p o i n t o f v i e w , s m a l l m o l e c u l e r i n g s a r e much e a s i e r t o s t u d y t h a n l o n g m a c r o m o l e c u l a r chains. S u b s t i t u t i o n r e a c t i o n s c a r r i e d o u t on m a c r o m o l e c u l a r

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

3.

ALLCOCK

Cyclic and

High-Polymeric Phosphazenes

51

Scheme 1

s u b s t r a t e s may i n v o l v e s i d e r e a c t i o n s t h a t l e a d t o c h a i n c l e a v a g e or c r o s s l i n k i n g . Mechanistic s t u d i e s w i t h macromolecules are d i f f i c u l t to c a r r y out because o f s o l u t i o n v i s c o s i t y e f f e c t s , d i s t r i b u t i o n s i n c h a i n l e n g t h , and t h e p r o b l e m s o f c h a r a c t e r ization. H e n c e , i t i s p r u d e n t t o e x p l o r e p o t e n t i a l new reactions f i r s t w i t h t h e use o f s m a l l m o l e c u l e m o d e l s s u c h as I , V I , and V I I and t h e n t o e x t e n d t h e s e r e a c t i o n s t o t h e h i g h p o l y m e r s .

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

RINGS, C L U S T E R S , A N D P O L Y M E R S

52 CI

CI

F

F

Cl C1-P

Cl = N-

l Ν Il C 1 - P - N

Cl

Cl

Cl

Cl I

VI

VII

Some o f t h e p o l y m e r i c r e a c t i o n s m e n t i o n e d b e l o w a r e s t i l l s t u d y a t t h e m o d e l compound l e v e l . Modern O b j e c t i v e s

P-C1

II N I = P-C1

under

i n Polyme

Polymers have been v a l u e d s i n c e a n t i q u i t y f o r t h e i r s o l i d state properties. By t h i s i s meant t h e i r a b i l i t y t o u n d e r g o c h a i n e n t a n g l e m e n t o r c o - l i n e a r o r i e n t a t i o n and m i c r o c r y s t a l l i zation i n the s o l i d state. T h i s u n d e r l i e s t h e i r use as s t r u c t u r a l m a t e r i a l s , f i l m s , f i b e r s , and e l a s t o m e r s . Such p r o p e r t i e s s t i l l c o n s t i t u t e t h e d r i v i n g f o r c e f o r most p o l y m e r oriented research, e s p e c i a l l y with respect to the synthesis of heat-stable, radiation-stable,or highly f l e x i b l e materials. The e l e c t r i c a l p r o p e r t i e s o f s o l i d p o l y m e r s h a v e a l w a y s b e e n o f interest. However, i n r e c e n t y e a r s a n o t h e r a p p r o a c h t o p o l y m e r c h e m i s t r y has r e c e i v e d i n c r e a s e d emphasis. I n t h i s , macrom o l e c u l e s a r e s t u d i e d i n terms o f t h e i r b e h a v i o r as s i n g l e m o l e c u l e s r a t h e r than as m o l e c u l a r c o n g l o m e r a t e s . In solution, polymer m o l e c u l e s behave d i f f e r e n t l y from s m a l l m o l e c u l e s because the l o n g c h a i n l e n g t h permits e x t e n s i v e c o i l i n g , reduced t r a n s l a t i o n a l m o b i l i t y , and an i n a b i l i t y t o p a s s t h r o u g h s e m i ­ p e r m e a b l e membranes. L i g h t l y c r o s s l i n k e d polymers behave l i k e l i n e a r polymers i n s o l u t i o n except t h a t t h e s w o l l e n m a t r i x has a p h y s i c a l i m m o b i l i t y and an o p e n m a t r i x c h a r a c t e r u n l i k e any o t h e r system. For these reasons, polymers a r e o f great i n t e r e s t as " c a r r i e r molecules" f o r chemotherapeutic drugs o r t r a n s i t i o n metal c a t a l y s t s . F i n a l l y , s i n g l e macromolecules, because o f t h e i r oned i m e n s i o n a l c h a r a c t e r , o f f e r t h e promise o f s e q u e n t i a l s i d e group c o d i n g , i n f o r m a t i o n s t o r a g e , and t e m p l a t e f u n c t i o n i n t h e manner t h a t i s w e l l known i n b i o l o g i c a l p o l y m e r s ( F i g u r e 1 ) . Conventional s y n t h e t i c organic polymers are being s t u d i e d for a l l o f these reasons, b u t t h e g e n e r a l l a c k o f chemical r e a c t i v i t y i n t h e s e systems i s a s e r i o u s drawback. It i s for t h i s reason that polyphosphazenes, w i t h t h e i r s u b s t i t u t i v e

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983. I C

I D

I D

I C

I Β

I A

I A

1 Ά

I

C

Key: a, traditional use of the solid-state, chain entanglement behavior that gives rise to strength or elasticity; b, explor­ atory use as carrier molecules for bioactive agents in controlled-release drug therapy either as targeted macromolecular drugs or as immobilized biodegradable systems; c, use as immobilizing agent for transition metal catalysts for easier manipulation or recovery or to modify the catalytic activity; d, use as electrical conductors or semiconductors (conduction may occur along unsaturated chain sequences or between chains in crystalline domains); e, sequential arrangement of side groups along a linear polymer chain offers the prospect of (I) control of polymer conformation; (2) use as a template for the controlled construction of complementary polymer molecules; and (3) information storage at the molecular level.

Figure 1. Traditional and exploratory uses for polymers.

I Β

I Ά

BIOACTIVE AGENT

C*9

ο •s

I ο ^*

> r r η ο π *

54

RINGS, C L U S T E R S , A N D P O L Y M E R S

method o f s y n t h e s i s , a r e o f c o n s i d e r a b l e i n t e r e s t . In the f o l l o w i n g s e c t i o n s , I w i l l i l l u s t r a t e why t h e p o l y p h o s p h a z e n e s y s t e m i s an a p p e a l i n g s t a r t i n g p o i n t f o r new d e v e l o p m e n t s i n two s p e c i f i c a r e a s — i n c h e m o t h e r a p y and p o l y m e r - b o u n d c a t a l y s t w o r k . Bioactive

Polyphosphazenes

S p e c i f i c i n o r g a n i c macromolecules a r e unusual because they c a n be h y d r o l y z e d t o r e l a t i v e l y i n n o c u o u s p r o d u c t s o r t o s m a l l m o l e c u l e s t h a t c a n be m e t a b o l i z e d . Most c o n v e n t i o n a l o r g a n i c p o l y m e r s do n o t h a v e t h i s a t t r i b u t e . Thus, t h e s e i n o r g a n i c s y s t e m s a r e o f s p e c i a l i n t e r e s t as c a r r i e r m o l e c u l e s i n chemo­ therapy. R e c e n t w o r k i n o u r l a b o r a t o r y h a s shown t h a t c e r t a i n s i d e groups a t t a c h e d to a polyphosphazene c h a i n impart a s e n s i t i v i t y to h y d r o l y t i c chain cleavage solubility. Both of thes chemotherapy. Polyphosphazenes are a l s o v a l u a b l e i n b i o l o g y b e c a u s e two o r more s u b s t i t u t e d g r o u p s c a n be r e a d i l y a t t a c h e d t o t h e same c h a i n . Thus, i n d i v i d u a l s i d e groups t h a t p o s s e s s chemotherapeutic, w a t e r - s o l u b i l i z a t i o n , h y d r o l y t i c - d e s t a b i l i z a t i o n , o r "homing" c h a r a c t e r i s t i c s c a n be c o m b i n e d i n one m o l e c u l e t o form a drug w i t h a s e t o f s y n e r g i s t i c p r o p e r t i e s . P o l y m e r s c o n t a i n i n g t h e r e p e a t i n g u n i t s shown i n V I I I - X I h a v e b e e n shown t o be h y d r o l y t i c a l l y d e g r a d a b l e a n d / o r w a t e r s o l u b l e (9-13). Amino a c i d e s t e r d e r i v a t i v e s ( V I I I ) d e g r a d e t o e t h a n o l , amino a c i d , p h o s p h a t e , and ammonia, w h i c h c a n e i t h e r be metabolized or excreted. Thus, such s i d e u n i t s used t o g e t h e r w i t h chemotherapeutic c o s u b s t i t u e n t groups, provide a f a c i l e drug d e l i v e r y system. I m i d a z o l y l s i d e groups (IX) a l s o c o n f e r h y d r o l y t i c s e n s i t i v i t y , but the biochemical response to the h y d r o l y s i s p r o d u c t s has n o t y e t been e s t a b l i s h e d . Methylamino s i d e g r o u p s (X) p r o v i d e w a t e r - s o l u b i l i t y , as do g l u c o s e r e s i d u e s (XI).

NHCH COOEt I - Ν = Ρ l

! NHCH COOEt 2

VIII

IX

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

3.

ALLCOCK

55

Cyclic and High-Polymeric Phosphazenes CELOH ι ^

H

° J

OH °

H

NHCH„

I

3

Ν = Ρ -

Ν = Ρ

I NHCfi\

CH OH 2

XI

T h e s e p o l y m e r s w e r e s y n t h e s i z e d b y t h e g e n e r a l methods shown i n Scheme 1. T h e i r h y d r o l y s i s b e h a v i o r has been t h e s u b j e c t o f s e v e r a l f u n d a m e n t a l m e c h a n i s t i c s t u d i e s a t t h e m o d e l compound level (10,11). The a t t a c h m e n t o f b i o l o g i c a l l y - a c t i v e s i d e g r o u p s h a s a l s o been e x p l o r e d . At t h e present time s e v e r a l d i f f e r e n t approaches have been developed w h i c h l e a d t o t h e s y n t h e s i s o f polymers such as X I I - X V I I .

o - Ν

Ρ NHCH C00Et 2

XII

OPh XIII

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

N

56

RINGS, C L U S T E R S , A N D P O L Y M E R S

OH

y

OH

Ν = I OPh XVI

o/f \J -λ.

\,/-v,u - C H N NEt E 0

2

I

0

0

Heparin

3

Ν = Ρ 0
^2* y P ~ ^ " c a t i o n s f i l l the remainder of the c e l l (R = 0.075, R = 0.090 f o r data to 2Θ = 45°) (37). The independent anion u n i t shown i n Figure 5 contains two s u r p r i s e s . F i r s t , the potassium atoms have four t i n neighbors at 3.55 to 3.74 Â through b r i d g i n g opposite edges on the waist of the Sng u n i t , with two more t i n atoms at greater d i s t a n c e s of 4.11 or 4.22 Â to produc about each potassium. Ther groups coordinated to e i t h e r of the potassium atoms. Second, the d i s t a n c e s i n the S n g " group are s c a r c e l y a l t e r e d by the presence of the two potassium atoms, as can be as seen by comparison of these r e s u l t s with those f o r the 'naked Sng *" shown i n Figure 1. Judging from K^Sn^ where potassium has 6 to 8 t i n neighbors i n the range 3.70 to 3.85 Â (maximum d e v i a t i o n = 0.03 to 0.05 Â) (39), the potassium-tin i n t e r a c t i o n s found here appear normal except f o r the short p a i r at 3.55 Â about K(4). Within the S n p o r t i o n of the s t r u c t u r e , the s i m i l a r Sn-Sn d i s t a n c e s i n a l l but the square capped face average 2.964 (5) Â i n t h i s compound com­ pared with 2.966 (6) Â i n Sng ". The s t r u c t u r a l data were c o l ­ l e c t e d at -100 and 5°, r e s p e c t i v e l y , so that some expansion of the c l u s t e r i n K S n " would probably be seen i n an isothermal compari­ son. In a d d i t i o n , there appears to be a p e r c e p t i b l e d i s t o r t i o n of the c l u s t e r i n the new potassium s a l t i n that Sn-Sn d i s t a n c e s where both atoms have potassium neighbors are longer by an average of 0.027 Â. Although the charge t r a n s f e r to potassium i s seem­ i n g l y not l a r g e enough to a l t e r the t i n c l u s t e r very much, perhaps i t i s enough to e l i m i n a t e the ( r e l a t i v e l y weak) tendency f o r potassium to coordinate en. The packing of the crypt-K"*" c a t i o n s can not be a s i g n i f i c a n t f a c t o r i n preventing a l l c o o r d i n a t i o n of solvent s i n c e the s h o r t e s t d i s t a n c e between these potassium atoms and the nearest l i g h t atom i n crypt i s 4.27 Â. With these unusual circumstances i t i s somewhat r e a s s u r i n g to f i n d another example of a s s o c i a t i o n of a c l u s t e r with an a l k a l i metal c a t i o n . In R b A s 3 e n the rubidium atoms a l l bridge edges of the anion, with the solvent coordinated to the a l k a l i metal only on the outside of the R b A s 'complex' (40). +

3

3

g

g

1

l

1

S

i

x

c r

t

1

2

w

4

1

1

g

14

3

g

e

3

7

3

7

Acknowledgment T h i s research was supported by the O f f i c e of B a s i c Energy Sciences, M a t e r i a l s Sciences D i v i s i o n . The Ames Laboratory i s operated f o r the U. S. Department of Energy by Iowa State U n i v e r s i t y under c o n t r a c t No. W-7405-Eng-82.

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

108

RINGS, CLUSTERS, AND POLYMERS

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

6.

CORBETT ET A L .

Polyatomic Zintl Anions

109

Literature Cited 1. Joannis, A. C. R. Hebd. Seances Acad. Sci. 1891, 113, 745; 1892, 114, 587. 2. Smyth, F. H. J. Am. Chem. Soc. 1917, 39, 1299. 3. Kraus, C. A. J. Am. Electrochem. Soc. 1924, 45, 175. 4. Zintl, E.; Goubeau, J; Dullenkopf, W. Z. Phys. Chem., Abt. A 1931, 154, 1. 5. Zintl, E.; Harder, A. Z. Phys. Chem., Abt. A 1931, 154, 47. 6. Zintl, E.; Dullenkopf, W. Z. Phys. Chem., Abt. Β 1932, 16, 183. 7. Kummer, D.; Diehl, L. Angew. Chem., Int. Ed. Engl. 1970, 9, 895. 8. Diehl, L.; Khodadedeh, K.; Kummer, D.; Strahle, J. Chem. Ber. 1976, 109, 3404. 9. Corbett, J. D.; Adolphson D. G.; Merryman D J.; Edwards P. A.; Armatis, F 10. Belin, C. Η. E.; Corbett 1977, 99, 7163. 11. Corbett, J. D.; Belin, C. Η. Ε., unpublished research. 12. Corbett, J. D.; Edwards, P. J . Am. Chem. Soc. 1977, 99, 3313. 13. Edwards, P.; Corbett, J. D. Inorg. Chem. 1977, 16, 903. 14. Critchlow, S. C.; Corbett, J. D., to be published. 15. Cisar, Α.; Corbett, J. D. Inorg. Chem. 1977, 16, 2482. 16. Belin, C. H. E. J . Am. Chem. Soc. 1980, 102, 6036. 17. Adolphson, D. G.; Corbett, J. D.; Merryman, D. J . J. Am. Chem. Soc. 1976, 98, 7234. 18. Teller, R. G.; Krause, L. J.; Haushalter, R. C. Inorg. Chem. 1983, 22, in press. 19. von Schnering, H.-G. Angew Chem., Int. Ed. Engl. 1981, 20, 33. 20. Corbett, J . D. Prog. Inorg. Chem. 1976, 21, 129. 21. King, R. B. 1981, private communication. 22. Burns, R. C.; Gillespie, R. J.; Barnes, J . Α.; McGlinchey, M. J . Inorg. Chem. 1982, 21, 806. 23. Rudolph, R. W.; Wilson, W. L.; Parker, F.; Taylor, R. C.; Young, D. C. J. Am. Chem. Soc. 1978, 100, 4629. 24. Rudolph, R. W.; Wilson, W. L.; Taylor, R. C. J. Am. Chem. Soc. 1981, 103, 2480. 25. Rudolph, R. W.; Taylor, R. C.; Young, D. C. in "Fundamental Research in Homogeneous Catalysis", M. Tsutsui, Ed.; Plenum Press: New York, 1979, p. 997. 26. Pons, B. S.; Santure, D. J.; Taylor, R. C.; Rudolph, R. W. Electrochem. Acta 1981, 26, 365. 27. Rothman, M. J.; Bartell, L. S.; Lohr, L. L. J. Am. Chem. Soc. 1981, 103, 2482. 28. Critchlow, S. C.; Corbett, J. D. J . Chem. Soc., Chem. Commun. 1981, 236. 29. Critchlow, S. C.; Corbett, J. D. Inorg. Chem. 1982, 21, 3286.

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110

30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40.

RINGS, C L U S T E R S , A N D P O L Y M E R S

Burns, R. C.; Corbett, J . D. J. Am. Chem. Soc. 1981, 103, 2627. Hensel, F. Adv. Phys. 1979, 28, 589. Corbett, J . D. Inorg. Chem. 1968, 7, 198. Burns, R. C.; Corbett, J . D. J. Am. Chem. Soc. 1982, 104, 2804. Belin, C. H. E.; Charbonnel, M. M. Inorg. Chem. 1982, 21, 2504. Burns, R. C.; Corbett, J . D. Inorg. Chem. 1981, 20, 4433. Krebs, B.; Hinter, H.-V. Z. Anorg. Allg. Chem. 1980, 462, 143. Burns, R. C.; Corbett, J . D., to be published. Rudolph, R. W. 1980, private communication. Hewaidy, I. F.; Busmann, E.; Klemm, W. Z. Anorg. Allg. Chem. 1964, 328, 283. Honle, W.; von Schnering

RECEIVED

April 8, 1983

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

7 Multihapto Bonding Between Main Group Elements and Carbocyclic Ligands An Approach to the Bonding in Main Group Cluster Compounds S. G. BAXTER, A. H. COWLEY, and J. G. LASCH The University of Texas at Austin, Department of Chemistry, Austin, TX 78712

MNDO calculation performe main-group capping moieties for C H , C H , C H , and C H carbocyclic rings. Perhapto bonding is predicted when the number of interstitial electrons (comprising ring-π plus relevant main-group fragment electrons) totals six. Some cases of intermediate hapticity are discussed in the context of the C H ring. 3

6

3

4

4

5

5

6

5

5

The d i s c o v e r y o f t h e t r a n s i t i o n m e t a l s a n d w i c h m o l e c u l e s f e r r o c e n e a n d d i b e n z e n e c h r o m i u m r a n k s a s one o f t h e more i m p o r t a n t c h e m i c a l d i s c o v e r i e s o v e r t h e p a s t t h r e e d e c a d e s . The c h e m i s t r y o f t h e s e a n d o t h e r d- a n d f - b l o c k c a r b o c y c l i c π-complexes h a s been i n v e s t i g a t e d i n t e n s i v e l y i n the ensuing y e a r s . Significant p r o g r e s s h a s a l s o b e e n made t o w a r d u n d e r s t a n d i n g t h e e l e c t r o n i c s t r u c t u r e s and p a t t e r n s o f s t a b i l i t y o f t h e s e i n t e r e s t i n g com­ pounds ( 1 ) . However, compared w i t h t h e d - a n d f - b l o c k e l e m e n t s , much l e s s i s known a b o u t t h e m u l t i h a p t o i n t e r a c t i o n o f t h e m a i n group e l e m e n t s w i t h c a r b o c y c l i c l i g a n d s . M i n k i n a n d M i n y a e v (2) have s u g g e s t e d t h a t a n n u l e n e - c a p p e r h a p t o b o n d i n g w i l l b e f a v o r e d when t h e t o t a l number o f ring-π p l u s m a i n - g r o u p m o i e t y e l e c t r o n s i s e q u a l t o e i g h t , w h i l e S c h l e y e r e t a l . ( 3 ) f a v o r a n optimum number o f s i x i n t e r s t i t i a l e l e c t r o n s ( 4 ) . S e v e r a l m a i n - g r o u p π-complexes h a v e b e e n i n v e s t i g a t e d u s i n g various l e v e l s o f theory. T h u s , C 5 H 5 L 1 (5) a n d C s H s B e H (6) h a v e b e e n computed u s i n g ab i n i t i o m e t h o d s , a n d Dewar a n d R z e p a (7) h a v e e x p l o r e d t h e i n t e r a c t i o n o f BeX m o i e t i e s w i t h c y c l o p e n t a d i e n y l , i n d e n y l , a n d f l u o r e n y l g r o u p s . The MNDO method h a s a l s o b e e n employed f o r t h e i n v e s t i g a t i o n o f v a r i o u s c a r b o c y c l i c b e r y l l i u m d e r i v a t i v e s , (8) a n d t h e PRDDO method has b e e n u t i l i z e d i n c o n j u n c t i o n w i t h C s H s B e R compounds ( 9 ) . The t i n c a t i o n [ C 5 H 5 S n ] has b e e n s t u d i e d w i t h t h e EHMO method, (10) a n d Hoffmann +

0097-6156/83/0232-0111 $06.00/0 © 1983 American Chemical Society

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

112

RINGS, C L U S T E R S , A N D P O L Y M E R S

Z +

e t a l . (11) have examined t h e m o t i o n o f a [ C H ] fragment a c r o s s a IC5H5]" r i n g . The p r e s e n t c o n t r i b u t i o n r e p r e s e n t s a n a t t e m p t t o d e v e l o p f u r t h e r a model f o r t h e m u l t i h a p t o b o n d i n g o f main-group element f r a g m e n t s t o c a r b o c y c l i c r i n g s , ( C H ) (n=3-6) u s i n g t h e MNDO program system (12). One o f t h e a d v a n t a g e s o f t h i s method i s t h a t i t p e r m i t s study o f t h e capping o f c a r b o c y c l i c r i n g s by t h e h e a v i e r main-group elements. E m p h a s i s i s p l a c e d b a s i c a l l y o n two themes: ( i ) whether a s i x - o r e i g h t - e l e c t r o n counting procedure i s more a p p r o p r i a t e , a n d ( i i ) w h e t h e r c o n f o r m i t y w i t h o t h e r c l u s t e r e l e c t r o n counting procedures i s achieved. I t i s on t h e l a t t e r p o i n t t h a t R a l p h R u d o l p h made o n e o f h i s s e m i n a l c o n t r i ­ butions t o inorganic chemistry. I n d e p e n d e n t l y h e ( 1 3 ) a n d Wade (14) a r r i v e d a t a method o f c o u n t i n g s k e l e t a l e l e c t r o n s w h i c h p r o v i d e d m a j o r new i n s i g h t s i n t o t h e s y s t e m a t i c s o f m a i n - g r o u p a n d t r a n s i t i o n metal c l u s t e 2

n

Computational Procedures A l l c o m p u t a t i o n s w e r e c a r r i e d o u t u s i n g t h e MNDO method ( 1 2 ) and p u b l i s h e d p a r a m e t e r s ( 1 5 ) . For the c y c l i c structures, t r a n s i t s o f a p e r p e n d i c u l a r main-group moiety a c r o s s t h e v a r i o u s r i n g s g e n e r a t e η s t r u c t u r e s ( n = l - 6 ) a s shown b e l o w . η

η

1

This approach has been d i s c u s s e d p r e v i o u s l y f o r t h e c y c l o p e n t a d i e n y l r i n g and has been r e f e r r e d t o as a h a p t o t r o p i c s e a r c h (11,6). The g e o m e t r y d e f i n i t i o n s w e r e a s f o l l o w s : Perhapto S t r u c t u r e s . I n a l l s t r u c t u r e s , t h e c a r b o n atoms o f t h e ( C H ) r i n g (n=3-6) w e r e c o n s t r a i n e d a s a r e g u l a r p o l y g o n , b u t i n e a c h c a l c u l a t i o n t h e C-C bond d i s t a n c e s w e r e r e l a x e d . To e n s u r e a p e r h a p t o f i n a l s t r u c t u r e , t h e p o s i t i o n o f t h e c e n t r a l atom, M, was m i n i m i z e d a l o n g t h e p r i n c i p a l a x i s o f t h e r i n g . The h y d r o g e n s w e r e h e l d symmetry - e q u i v a l e n t (_ι.£. a l l C-H bond l e n g t h s a n d a l l C-C-H bond a n g l e s e q u a l ) , b u t w e r e a l l o w e d t o b e n d o u t o f t h e plane o f t h e r i n g . n

Dihapto S t r u c t u r e s . F o r these c a l c u l a t i o n s , t h e r i n g carbon atoms w e r e f r o z e n i n t o t h e g e o m e t r i e s o b t a i n e d i n t h e p e r h a p t o calculations. A g a i n , s y m m e t r y - e q u i v a l e n t h y d r o g e n atoms w e r e c o n s t r a i n e d t o h a v e e q u a l C-H bond l e n t h s a n d C-C-H bond a n g l e s . However, no t o r s i o n a n g l e l i m i t a t i o n s w e r e i m p o s e d . The c e n t r a l atom was m a i n t a i n e d i n a d i h a p t o c o n f i g u r a t i o n b y r e l a x a t i o n o f i t s p o s i t i o n o n a l i n e p e r p e n d i c u l a r t o t h e r i n g p l a n e and w h i c h b i s e c t e d a C-C b o n d .

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

BAXTER

7.

113

Multihapto Bonding

ETA L .

Monohapto S t r u c t u r e s . As i n t h e c a s e o f t h e d i h a p t o s t r u c t u r e s , the geometries o f the r i n g carbons were c o n s t r a i n e d t o those emerging from the perhapto c a l c u l a t i o n s , and symmetry-equivalent h y d r o g e n s were f o r c e d t o m a i n t a i n e q u a l C-H bond l e n g t h s a n d C-C-H bond a n g l e s . M o n o h a p t i c i t y was i m p o s e d b y m i n i m i z i n g t h e p o s i t i o n o f t h e c e n t r a l atom a l o n g a l i n e p e r p e n d i c u l a r t o t h e r i n g p l a n e and p a s s i n g t h r o u g h a r i n g c a r b o n . S t r u c t u r e s w i t h MH M o i e t i e s . For perhapto s t r u c t u r e s t h e h y d r o g e n was c o n f i n e d t o t h e same l i n e as t h e c e n t r a l atom. The d i h a p t o a n d monohapto c a l c u l a t i o n s a l s o u s e d i n p u t s t r u c t u r e s w i t h t h e h y d r o g e n o n t h e same l i n e u s e d t o c o n s t r a i n t h e c e n t r a l atom, b u t h e r e t h e p o s i t i o n o f t h e h y d r o g e n atom was t o t a l l y r e l a x e d . S t r u c t u r e s w i t h MH2 M o i e t i e s . optimized basis. Qualitative

These were h a n d l e d o n a g e o m e t r y -

Considerations

Due t o t h e a v a i l a b i l i t y o f a p p r o p r i a t e o r g a n o m e t a l l i c r e a g e n t s , b y f a r t h e l a r g e s t number o f a n n u l e n e c o m p l e x e s o f t h e main-group elements i n v o l v e t h e c y c l o p e n t a d i e n y l group. L e t us s t a r t the d i s c u s s i o n , t h e r e f o r e , by c o n s i d e r i n g q u a l i t a t i v e l y t h e π-type c o o r d i n a t i o n o f a C5H5 r i n g t o a m a i n - g r o u p e l e m e n t , M. As shown i n F i g u r e l a , b o n d i n g i n t e r a c t i o n s i n symmetry a r e e x p e c t e d between the v a l e n c e s o r b i t a l o f M and t h e t o t a l l y s y m m e t r i c π-ΜΟ o f C 5 H 5 , a n d b e t w e e n t h e d e g e n e r a t e n p and n p AO's o f M a n d t h e e^ MO o f C 5 H 5 . The 2a\ MO r e s u l t s f r o m m i x i n g o f t h e a n t i b o n d i n g component o f t h e laχ MO a n d a b o n d i n g MO w h i c h r e s u l t s from i n t e r a c t i o n between the v a l e n c e p o r b i t a l and the a j r i n g MO. The r e l a t i v e e n e r g i e s o f t h e e j a n d 2a\ M 0 s a r e g o i n g t o depend o n e.g. t h e e n e r g i e s o f t h e v a l e n c e s a n d ρ o r b i t a l s o f M. Somewhat s i m i l a r d i a g r a m s can b e c o n s t r u c t e d f o r t h e i n t e r ­ a c t i o n between a c y c l o p e n t a d i e n y l group and l i g a t e d main-group m o i e t i e s , MI^. T h a t f o r a 05Η ····ΜΗ i n t e r a c t i o n i s i l l u s t r a t e d in Figure l b . O b v i o u s l y , e i g h t e l e c t r o n s c a n b e accommodated i n e i t h e r t h e ( n - C H 5 ) M o r (n -C5H5)MH b o n d i n g scheme. However, t h e q u e s t i o n of whether a s i x - o r e i g h t - e l e c t r o n i n t e r s t i t i a l e l e c t r o n count i s more v a l i d w i l l depend o n (a) w h e t h e r t h e 2a\ MO i s o c c u p i e d , and (b) i f t h e 2 a i MO i s o c c u p i e d w h e t h e r i t i n v o l v e s s i g n i f i c a n t ring-M i n t e r a c t i o n . R e a l i z i n g t h a t t h e b a s i c p a t t e r n o f a and e l i g a n d π MO's p e r s i s t s t h r o u g h o u t t h e c a r b o c y c l i c r i n g s y s t e m s , C H (n=3-6) (16), i t i s c l e a r t h a t t h e i n t e r a c t i o n o f a n s,p b a s i s s e t o f a m a i n - g r o u p e l e m e n t w i t h C 3 H 3 , C 4 H 4 , and CeHe r i n g s s h o u l d p r o d u c e lai, lei, d 2 a i MO s i n a v e r y s i m i l a r f a s h i o n t o t h e c y c l o ­ p e n t a d i e n y l s y s t e m s i l l u s t r a t e d i n F i g u r e 1. x

v

z

T

5

5

5

5

n

a

n

Five-Membered R i n g

n

1

Systems.

I n terms o f h a p t o t r o p i c

searches,

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

ηΡ

χ

y

np

z

X

ν

^

Λ

(a)

5

5

u

\ (Π5 -C „H )M

1

Λ

»

^

\

/

5

C ηH

f\ 5

a

i

"l

2

5

5

^

Ν

A

1

5

^

/

/

^

'

_

/

with a main group

(b)

5

„ MyiU (η -C H )MH / - . ^ Γ ,

Figure 1. Qualitative scheme for the pentahapto interaction ofC H ττ-orbitals element M (left) or an M-H σ-bond (right).

np

e

s

V i _ U M-H

n

σΜ-Η

χ

ηΡ , nP

y

( a

.

i>

,

m


Ζ Ο

Η W

^

η r

oo

*

115

Multihapto Bonding

BAXTER ET A L .

7.

both C 5 H 5 B and C5H5AI adopt η ground s t a t e geometries (Table I ) . Furthermore, the η preference p r e v a i l s f o r both molecules when a complete geometry o p t i m i z a t i o n i s c a r r i e d out. Only minimal d i s t o r t i o n of the r i n g s takes place d u r i n g the geometry o p t i m i z a ­ tion. Both C 5 H 5 B and C H A 1 are unknown molecules; however, the h e a v i e r congeners C H I n and C H T 1 have been known f o r s e v e r a l years. Although C H I n and C H T1 are polymeric i n the s o l i d s t a t e (17), these molecules adopt η s t r u c t u r e s i n the vapor s t a t e (18). Although C H B and C H A 1 both adopt η geometries, i t i s i n t e r e s t i n g to note that the sequence o f MO s d i f f e r s i n the two molecules; i n C H B the HOMO i s o f e symmetry, w h i l e that o f the aluminum analog i s a . A NOCOR MO c a l c u l a t i o n (19) on C H T 1 i n d i c a t e s that the HOMO i s of a i symmetry; however, U V PES s p e c t r a l data ( 2 0 ) and Χα scattered-wave c a l c u l a t i o n s ( 2 1 ) f o r C s H s I n and C 5 H 5 T I suggest that the HOMO i s o f e symmetry We now turn to som i s o e l e c t r o n i c w i t h C5H5 preference f o r the η geometry. T h i s p r e f e r e n c e p e r s i s t s when the geometry i s completely optimized. The c a l c u l a t i o n s on [ C s H s S i ] * were undertaken because the h e a v i e r congeneric c a t i o n f M e s C s S n ] * i s known and has been found t o e x h i b i t a pentahapto s t r u c t u r e on the b a s i s o f X-ray c r y s t a l l o g r a p h y ( 1 0 ) . The MNDO h a p t o t r o p i c search i n d i c a t e s a minimum at η ; moreover, the pentahapto s t r u c t u r e p e r s i s t s w i t h only minor changes o f energy when the geometry i s optimized. The [ C s H s S i ] " * " c a t i o n has a l s o been i n v e s ­ t i g a t e d by ab i n i t i o methods ( 3 c ) . The c a l c u l a t i o n s on [CsHsBH]"*" were undertaken because boron c a t i o n s o f the type [ M e s C s B X ] * (X=C1, Br, I ) are known ( 2 2 ) , and s p e c t r o s c o p i c evidence i n d i c a t e s that the BX* moiety i s pentahapto-bonded t o the MesCsring. Moreover, C s H s B e H , which i s i s o ­ e l e c t r o n i c with [ C 5 H 5 B H ] + has been shown t o possess a n η geometry (23). Our MNDO c a l c u l a t i o n s o n [ C H B H ] + i m p l y t h a t t h e η and η geometries are very c l o s e i n energy. P r e v i o u s l y , i t has been suggested (24) that the a d d i t i o n o f boron Lewis Acids t o C s H s I n causes a change from η t o η attachment. 5

5

5

5

5

5

b

5

5

5

5

5

5

5

5

5

5

5

1

5

5

x

5

5

5

2

5

5

5

5

1

Six o r Eight I n t e r s t i t i a l

Electrons?

For the systems considered i n Table I , a l l e i g h t e l e c t r o n s would be counted a c c o r d i n g t o the Minkin and Minyaev model ( 2 ) . In the model o f Schleyer e t a l . , (3) a main-group element lone p a i r o f C 5 H 5 B , C 5 H 5 A I , [ C H B e ] " , and [ C 5 H S i ] and the B-H σ-bond of [C5H5BH]"*" would be excluded from the count on the b a s i s that they are not i n t e r s t i t i a l e l e c t r o n s . Χα-SW c a l c u l a t i o n s on e.g. ( n - C H 5 ) I n and ( n - C H 5 ) B e X support the views o f Schleyer et a l . (3a). Thus, the 5ai MO o f ( n - C s H 5 ) I n , which i s predominantly lone p a i r c h a r a c t e r , and the 4 a i MO o f (n -CsH )BeX, which i s the Be-X σ-bond, f e a t u r e only minor c o n t r i b u t i o n s from the C5H5 r i n g . I t should a l s o be noted that a s i x - e l e c t r o n r u l e a f f o r d s conformity w i t h the e l e c t r o n counting procedures o f Rudolph (13) +

5

5

5

5

5

5

5

5

5

b

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

RINGS,

CLUSTERS,

A N D POLYMERS

Heats o f Formation ( k c a l / m o l ) , R e l a t i v e Energies ( k c a l / m o l ) , a n d η G e o m e t r i e s (Â) f o r C5H5 Compounds. 5

HAPTICITY 1

n n n optimized

AH

r

(RELATIVE ENERGY

112. 21

η

5

GEOMETRY

(8.29)

B-•C = 1.904

2

5

103. 90

n n n optimized

76.59 76.11 70.98 70.97

(5.61) (5.13) (0.00)

Al- •C = 2.215 C--C = 1.442 C--H = 1.082

1

75.53 75.01 68. 84 68.84

(6.69) (6.17) (0.00)

Be--C = 2.188 C--C = 1.439 C-•H = 1.083

n n n optimized

213.02 205. 05 189. 89 189. 89

(23.13) (15.16) (0.00)

S i - •C = 2.089 C--C 1.453 C--H = 1.086

1

277. 97 268. 18 269. 24 269. 23

(9.79) (0.00) (1.06)

1

2

5

n n n optimized 2

5

1

2

5

n n n optimized 2

5

1.784 B--C C--C = 1.471 C--H = 1.086 B--H = 1.161

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

7.

BAXTER ET A L .

Multihapto

117

Bonding

and Wade (14). According t o these r u l e s , a l l the compounds i n Table I are p r e d i c t e d t o adopt nido s t r u c t u r e s s i n c e each possesses n+2 s k e l e t a l e l e c t r o n p a i r s . Each CH group c o n t r i b u t e s three s k e l e t a l e l e c t r o n s , hence only one valence e l e c t r o n i s r e q u i r e d from B, A l , Be", Si+, or BH"" to achieve a t o t a l o f s i x electrons. 1

Consequences o f Increasing Main-Group Fragment

the Number of Valence E l e c t r o n s on the

A l l the systems considered i n Table I feature a main-group fragment e l e c t r o n count o f three, only one e l e c t r o n o f which i s involved i n i n t e r s t i t i a l bonding. We now explore the consequences of i n c r e a s i n g the t o t a l e l e c t r o n count o f the main-group fragment to f i v e e l e c t r o n s . Two examples o f t h i s e l e c t r o n count are represented by C5H5MH2 energy geometry i s η an 1

Ε = Β C ( 1 )

Ε = Al

C(2) >

C(3)

C(4)

B-C(l) C(l)-C(2) C(2)-C(3) C(3)-C(4) C(4)-C(5) C(l)-C(5)

1.55 1.52 1.36 1.47 1.36 1.53

     Â

Al-C(l) C(l)-C(2) C(2)-C(3) C(3)-C(4) C(4)-C(5) C(l)-C(5)

1.84 1.51 1.37 1.47 1.37 1.52

     Â

exceed the sum of covalent r a d i i f o r Β and C (1.57 Â) o r A l and C (-2.00 Â ) . Previous ab i n i t i o work (25) had i n d i c a t e d a minimum at η ; however the b a r r i e r s between η , η , and η s t r u c t u r e s were found t o be small. An EHMO i n v e s t i g a t i o n (11) of the system [C5H5]"«··[CH2l a l s o i n d i c a t e d an η minimum but no minimum was found a t the η geometry. The experimental data f o r a number o f Group IIIA compounds of the type (C Rs)MXY (R=H, Me; X, Y=alkyl, C 5 H 5 , CI) have been assembled i n Table I I . C o l l e c t i v e l y , these data i n d i c a t e that the energies o f η , n , and η geometries are r a t h e r c l o s e . S i m i l a r conclusions have emerged from MNDO c a l c u ­ l a t i o n s (35) on phosphenium ions o f the type [(MesCs)(R)P] , namely ( i ) that the g l o b a l minimum i s η , ( i i ) η and η s t r u c ­ tures do not correspond to minima, and ( i i i ) the b a r r i e r to circumannular migration o f the RP moiety i n the η s t r u c t u r e s ( v i a an η intermediate) i s very small (

X

=

X

2 +

2 +

6

6

6

6

+

2

b

6

6

6

Acknowled gment The authors are g r a t e f u l to the Petroleum Research Fund f o r generous f i n a n c i a l support.

Literature Cited 1. For reviews, see (a) Mingos, D.M.P. Adv. Organomet. Chem. 1977, 15, 1; (b) Haaland, A. Acc. Chem. Res. 1979, 12, 415. 2. Minkin, V. I.; Minyaev, R. M. Zh. Org. Khim. 1979, 15, 225, 1569. 3. (a) Jemmis, E. D.; Schleyer, P. v. R. J. Am. Chem. Soc. 1982, 104, 4781. For related papers, see (b) Collins, J. B.; Schleyer, P. v. R. Inorg. Chem. 1977, 16, 152 (c) Krogh­ -Jespersen, K.; Chandrasekhar, J.; Schleyer, P. v. R. J. Org. Chem. 1980, 45, 1608. 4. Interstitial electrons have been defined (3b) as electrons which bind π-bonding ligands to a central atom. 5. (a) Janoschek, R.; Diercksen, G.; Preuss, H. Int. Quantum Chem. Symp. 1967, 1, 205 (b) Alexandratos, S.; Streitwieser, Α., Jr.; Schaefer, H. F., III J. Am. Chem. Soc. 1976, 98, 7959. 6. Jemmis, E. D.; Alexandratos, S.; Schleyer, P. v. R.; Streit­ wieser, A. Jr.; Schaefer, H. F., III J. Am. Chem. Soc. 1978, 100, 5695.

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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A N D POLYMERS

7. (a) Dewar, M. J. S.; Rzepa, H. S. J. Am. Chem. Soc. 1978, 100, 777 (b) Dewar, M. J. S.; Rzepa, H. S. Inorg. Chem. 1979, 18, 602. 8. Bews, J. R.; Glidewell, C. J. Organomet. Chem. 1981, 219, 279. See also, Glidewell, C. J. Organomet. Chem. 1981, 217, 273. 9. Marynick, D. S. J. Am. Chem. Soc. 1981, 103, 1328. 10. Jutzi, P.; Kohl, F.; Hofmann, P.; Krüger, C.; Tsay, Y.-H. Chem. Ber. 1980, 113, 757. 11. Anh, N. T.; Elian, M.; Hoffmann, R. J. Am. Chem. Soc. 1978, 100, 110. 12. Dewar, M. J. S.; Thiel, W. J. Am. Chem. Soc. 1977, 99, 4899. For a discussion of the validity of the MNDO method, see Dewar, M. J. S.; McKee, M. L. Inorg. Chem. 1978, 17, 1075. 13. Rudolph, R. W. Acc. Chem. Res. 1976, 9, 446. 14. (a) Wade, K. J. Chem. Soc. Chem. Commun. 1971, 792 (b) Wade, K. Adv. Inorg. Chem 15. (a) Dewar, M. J. S. 4907 (b) Dewar, M. J. S.; McKee, M. L. ibid. 1977, 99, 5231 (c) Dewar, M. J. S.; Rzepa, H. S. J. Am. Chem. Soc. 1978, 100, 58 (d) Davis, L. P.; Guidry, R. M.; Williams, J. R.; Dewar, M. J. S.; Rzepa, H. S. Journal of Computational Chemistry 1981, 2, 433. 16. Cotton, F. A. "Chemical Applications of Group Theory" 2nd. Ed. Wiley-Interscience 1971. 17. Frasson, E.; Menegus, F.; Panattoni, C. Nature 1963, 199, 1087, 18. (a) Shibata, S.; Bartell, L. S.; Gavin, R. Μ., Jr. J. Chem. Phys. 1964, 41, 717 (b) Tyler, J. K.; Cox, A. P.; Sheridan, J. Nature 1959, 183, 1182. 19. Ewig, C. S.; Osman, R.; Van Wazer, J. R. J. Am. Chem. Soc. 1978, 100, 5017. 20. (a) Evans, S., D. Phil. Thesis Oxford University, 1972 (b) Egdell, R. G.; Fragala, I.; Orchard, A. F. J. Electron Spectrosc. and Relat. Phenom. 1978,14, 467 (c) Cradock, S. Duncan, W. J. Chem. Soc. Faraday Trans. 2 1978, 74, 194. 21. Cowley, A. H.; Lattman, M. To be published. 22. Jutzi, P.; Seufert, A. Angew. Chem. Int. Ed. Engl. 1977, 16, 330. 23. Bartke, T.; Bjørseth, Α.; Haaland, Α.; Marstokk, Κ. M.; Møllendal, H. J. Organomet. Chem. 1975, 85, 271. 24. Contreras, J. G.; Tuck, D. G. Inorg. Chem. 1973, 12, 2596. 25. Gropen, O.; Haaland, A. J. Organomet. Chem. 1975, 92, 157. 26. Grundke, H.; Paetzold, P. I. Chem. Ber. 1971, 104, 1136. 27. Drew, D. Α.; Haaland, A. Acta Chem. Scand. 1973, 27, 3735. 28. Stadelhofer, J . ; Weidlein, J . ; Fischer, P.; Haaland, A. J. Organomet. Chem. 1976, 116, 55. 29. Mertz, K.; Zettler, F.; Hausen, H. D.; Weidlein, J. J. Organomet. Chem. 1976, 122, 159. 30. Teclé, B.; Corfield, P. W. R.; Oliver, J. P. Inorg. Chem. 1982, 21, 458.

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

7.

BAXTER ET A L .

Multihapto Bonding

123

31. Schonberg, P. R.; Paine, R. T.; Campana, C. J . Am. Chem. Soc. 1979, 101, 7726. 32. Schonberg, P. R.; Paine, R. T.; Campana, C. F.; Duesler, Ε. N. Organometallics 1982, 1, 799. 33. Einstein, F. W. B.; Gilbert, M. M.; Tuck, D. G. Inorg. Chem. 1972, 11, 2832. 34. Jutzi, P.; Kohl, F.; Krüger, C.; Wolmershäuser, G.; Hofmann, P.; Stauffert, P. Angew. Chem. Int. Ed. Engl. 1982, 21, 70. 35. (a) Baxter, S. G.; Cowley, A. H.; Mehrotra, S. K. J. Am. Chem. Soc. 1981, 103, 5572 (b) Cowley, A. H.; Mehrotra, S. K. J. Am. Chem. Soc. 1983, 105, 2074. 36. See, for example, (a) Soluki, B.; Rosmus, P.; Bock, H.; Maier, G. Angew. Chem. Int. Ed. Engl. 1980, 19, 51 (b) Maier, G.; Mihm, G.; Reisenauer, H. P. Angew. Chem. Int. Ed. Engl. 1980, 19, 52. 37. For a review, see Ashe 153. 38. Cuthbertson, A. F.; Glidewell, C. J. Organomet. Chem. 1981, 221, 19. 39. Cowley, A. H.; Ebsworth, Ε. Α. V.; Mehrotra, S. K.; Rankin, D. W. H.; Walkinshaw, M. D. J. Chem. Soc. Chem. Commun. 1982, 1099. 40. Davison, Α.; Rakita, P. E. Inorg. Chem. 1970, 9, 289. 41. (a) Rossi, A. R.; Hoffmann, R. Inorg. Chem. 1975, 14, 365 (b) Elian, M.; Maynard, M. L.; Chen, D.; Mingos, D. M. P.; Hoffmann, R. Inorg. Chem. 1976, 15, 1148. 42. Maier, G.; Pfriem, S.; Schaefer, U.; Matusch, R. Angew. Chem. Int. Ed. Engl. 1978, 17, 520. 43. (a) Stohrer, W. D.; Hoffmann, R. J. Am. Chem. Soc. 1972, 94, 1661 (b) Kollmar, H.; Smith, H. O.; Schleyer, P. v. R., J. Am. Chem. Soc. 1973, 95, 5834 (c) Dewar, M. J. S.; Haddon, R. C. J. Am. Chem. Soc. 1973, 95, 5836 (d) Hehre, W. J.; Schleyer, P. v. R. J. Am. Chem. Soc. 1973, 95, 5837. 44. (a) Masamune, S.; Sakai, M.; Ona, H.; Jones, A. J. J. Am. Chem. Soc. 1972, 94, 8956 (b) Masamune, S.; Sakai, M.; Kemp­ -Jones, Α. V.; Ona, H.; Venot, Α.; Nakashima, T. Angew. Chem. Int. Ed. Engl. 1973, 12, 769. 45. (a) Luth, H.; Amma, Ε. L. J. Am. Chem. Soc. 1969, 91, 7515 (b) Weininger, M. S.; Rodesiler, P. E.; Gash, A. G.; Amma, E. L. J. Am. Chem. Soc. 1972, 94, 2135 (c) Rodesiler, P. F.; Auel, Th.; Amma, E. L. J. Am. Chem. Soc. 1975, 97, 7405. RECEIVED June 16, 1983

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

8 Novel Cluster Interactions in Metalloboranes NORMAN N. GREENWOOD University of Leeds, Department of Inorganic and Structural Chemistry, Leeds LS2 9JT, England

Metal atoms have fewer valence electrons than orbitals available for bonding and in this they resemble boron examined and i y electronegativities in the range 1.6-2.4 (B = 2.0) can subrogate boron atoms as vertices in poly­ hedral clusters. Such metalloboranes are often much more stable than the parent boranes or borane anions. Not only can metals mimic boron in known cluster geometries but the flexibility thus introduced can lead to novel and previously unsuspected cluster geometries. The construction of macropolyhedral clusters containing 17-20 vertices is also described. R a l p h R u d o l p h made m a j o r c o n t r i b u t i o n s t o o u r u n d e r s t a n d i n g o f t h e s t r u c t u r e and b o n d i n g o f p o l y h e d r a l c l u s t e r compounds a n d he h a d a n a b i d i n g i n t e r e s t i n d e v e l o p i n g a r a t i o n a l e w h i c h w o u l d e n a b l e t h e s t r u c t u r e o f i n d i v i d u a l compounds t o be s y s t e m a t i z e d and r e l a t e d t o e a c h o t h e r . He i n d e p e n d e n t l y a r r i v e d a t a method o f c o u n t i n g s k e l e t a l e l e c t r o n s w h i c h i s now g e n e r a l l y r e f e r r e d t o as Wade's R u l e s , a n d t h i s h a s h a d a d e c i s i v e i n f l u e n c e o n o u r g e n e r a l p e r c e p t i o n s o f p o l y h e d r a l c l u s t e r compounds. R e l a t e d t o t h i s was h i s p r e o c c u p a t i o n w i t h t h e p r o b l e m o f h e t e r o a t o m s s u c h a s s u l f u r , and t h e number o f e l e c t r o n s w h i c h s u c h atoms c o n t r i b u t e to the heteroborane c l u s t e r s . You w i l l r e c a l l t h a t b o r a n e s a r e now c l a s s i f i e d i n t o v a r i o u s s e r i e s a s summarized i n T a b l e I . The f o r m u l a e and s t r u c t u r e s c a n be r a t i o n a l i z e d o n t h e b a s i s o f t h e number o f s k e l e t a l e l e c t r o n s a v a i l a b l e f o r b o n d i n g and e a c h Β atom i s c o n s i d e r e d t o c o n t r i b u t e 2 e l e c t r o n s i n a d d i t i o n t o t h e one u s e d t o f o r m a t e r m i n a l B - H bond. S u p e r n u m e r a r y Η atoms f o r m B-H -B b r i d g e s o r c o m p r i s e t h e endo-U atom i n a BH2 g r o u p : B H H g j ; t h e y o c c u r i n t h e "open f a c e " o f s t r u c t u r e s from which B H groups a r e n o t i o n a l l y m i s s i n g t

u

t

n

0

t

0097-6156/83/0232-0125 $06.00/0 © 1983 American Chemical Society

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

126

RINGS, CLUSTERS,

Table I .

AND

POLYMERS

B o r a n e S t r u c t u r e s - Wade's R u l e s

Series

Parent Formula

Skeletal Electrons

C l u s t e r Geometry ( d e l t a h e d r o n = closed t r i a n g u l a t e d polyhedron)

preoloso-

Β Η η η

2η

(n-1)vertexed deltahedron p l u s 1 c a p p i n g BH

closo-

Β Η η η+2 Β Η , η η+4

2η+2

n-vertexed deltahedron

2η+4

(n+1)deltahedron

(n o c c u p i e d )

2η+6

(n+2)deltahedron

(n o c c u p i e d )

2η+8

(n+3)deltahedro

(

nidoarachnohypho-

Β

η

η+6

Η

ο η+ο

η

conjuncto-

occupied)

Α

Β Η η m

B-B o r BBB b o n d s , o r by s h a r i n g common v e r t i c e s , e d g e s , o r f a c e s

from the parent c l o s e d t r i a n g u l a t e d p o l y h e d r a l s t r u c t u r e i n which a l l v e r t i c e s are o c c u p i e d . I n g e n e r a l the s t r u c t u r e s r e f l e c t the f a c t t h a t b o r o n has one l e s s v a l e n c e e l e c t r o n t h a n a t o m i c o r b i t a l s a v a i l a b l e f o r bonding. Most m e t a l s a l s o have f e w e r v a l e n c e e l e c t r o n s t h a n o r b i t a l s a v a i l a b l e f o r b o n d i n g and some y e a r s ago we i n i t i a t e d a r e s e a r c h p r o g r a m t o d e l i n e a t e t h e e x t e n t t o w h i c h m e t a l s c o u l d a c t as p o l y h e d r a l v e r t i c e s i n métalloborane complexes. I t t u r n s out t h a t v i r t u a l l y a l l m e t a l s except t h e most e l e c t r o p o s i t i v e ones i n Groups I - I I I o f t h e P e r i o d i c T a b l e c a n a c t i n t h i s way as h o n o r a r y b o r o n atoms. Indeed, the m e t a l l o b o r a n e s a r e f r e q u e n t l y v e r y much more s t a b l e t h a n t h e c o r r e s p o n d i n g p a r e n t b o r a n e s and b o r a n e a n i o n s . T h r e e e x a m p l e s f r o m o u r own r e c e n t work w i l l s u f f i c e t o show how c o o r d i n a t e d m e t a l atoms c a n s u b r o g a t e BH u n i t s i n closo-, nido- and avaohno-decaborane. Thus, the b r i g h t r e d n i c k e l a oloso-decaborane eloso-[(PMe Ph) (I-N1B9H7CI2-2,4)] has b e e n s y n t h e s i z e d 0 ) i n w h i c h t h e B m o i e t y i s η^-bonded t o a c a p p i n g L2N1 g r o u p ( F i g u r e 1 ) . The s t r u c t u r a l r e l a t i o n s h i p t o olosoB10H10 "" i s o b v i o u s a n d , as t h e m e t a l c e n t r e f o r m a l l y r e p l a c e s a BH "" g r o u p w h i c h c o n t r i b u t e s 4e t o t h e c l u s t e r , i t c a n be c o n s i d e r e d as N i - ^ . We f i n d , i n g e n e r a l , t h a t p o l y h a p t o b o r a n e l i g a n d s a r e v e r y good a t s t a b i l i z i n g formal high oxidation s t a t e s of m e t a l s . N e x t we c a n m e n t i o n a nido-analogue, n£ = C H HjC

C=C μι H C=C=C 2

HC 3

2

SH HC^_ ... l>C—SH SH

C = C = S H

H C=C

H

2

_

C=S

H

C

H

HC—S _ î

C

C

H

J/]

HC—S

H

I H C-^

C U

2

h 2 (

HC

bc=S

2

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

(2)

9.

149

Molecular State Hypersurface Calculations

BOCK ET AL.

F o r t h e m o l e c u l e s ( 2 ) MNDO h e a t s o f f o r m a t i o n a r e c a l c u l a ­ t e d b y s t a r t i n g f r o m known s t r u c t u r a l d a t a a n d o p t i m i z i n g t h e i r r e s p e c t i v e g e o m e t r i e s v i a t h e D a v i d s o n - F l e t c h e r - P o w e l l p r o g r a m sub­ routine (Figure 2 ) . CH, 0 3 k

CR S k

MNDOA AHfo kcal/Md 104,80

10cH

o

r>-cn,--«»H

2

Ο

42,60

\:

(Me Si) N-P 3

2

N

R

[(Me Si) NPC1 ] — ( 3

2

(

2

RMgX

R (Me Si) N-P^ CI y

3

or

RLi

2

t o 9 0 % a n d q u a n t i t i e s o f 250 t o 300 grams a r e e a s i l y obtained. The use o f P h P C l i n place of PC1 allows for the introduction of phenyl/alkyl s u b s t i t u t i o n at phosphorus · Many s i m p l e oxidation reactions of tertiary alkyl or a r y l p h o s p h i n e s a r e l e s s s t r a i g h t f o r w a r d i n p h o s p h i n e s w i t h s i l y l a m i n o s u b s t i t u e n t s (_3-8). Two such r e a c t i o n s have r e s u l t e d i n p r e c u r s o r s t o phosphazenes. The f i r s t o f t h e s e i s t h e r e a c t i o n o f b r o m i n e w i t h d i s u b s t i t u t e d s i l y l a m i n o p h o s p h i n e s (_7) t o g i v e M e S i B r and P - b r o m o - N - s i 1 y 1 p h o s p h i n i m i n e s ( e q2 ) . 2

3

3

R /R

B r

I

2

(Me Si) N-P 3

~->

2

^R

f

M e S i N = P-Br | R 3

-Me SiBr 3

(2)

1

R, R

1

= Me, E t , j . - P r , CH SiMe , 2

3

Ph , O C H C F , 2

3

CH Ph, 2

CH CH=CH , e t c . 2

2

The p h o s p h i n i m i n e s a r e t h e r m a l l y u n s t a b l e and r e a d i l y eliminate Me SiBr at temperatures of greater t h a n 100°C t o f o r m o n l y c y c l i c p h o s p h a z e n e s ( e q 3 ) . (_7) 3

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

10.

Phosphorus-Nitrogen Polymers

wisiAN-NEiLSON E T A L .

R

R

1

M e S i N = P-Br

1

Δ

Γ Ί ^ Ρ = Ν4η

3

R

169

1

+

Me3SiBr

R

(3)

η = 3 ,4

More i m p o r t a n t l y , t h e P-bromophosphiniraines react s m o o t h l y w i t h C F 3 C H 2 O H i n t h e p r e s e n c e o f ΕίβΝ t o f o r m P - ( t r i f l u o r o e t h o x y ) p h o s p h i n i m i n e s ( e q 4 ) (_7 ) . On h e a t ­ ing i n e i t h e r sealed g l a s s ampoules or a s t a i n l e s s R I M e S i N =P-Br I R»

CF CH OH 3

2

>

3

Et N 3

R I Me3SiN =P-OCH CF3 I R 2

(4)

s t e e l bomb t h e s e p h o s p h i n i m i n e s r e a d i l y eliminate Me3SiOCH2CF3 ( e q 5) and form e x c l u s i v e l y p o l y m e r i c p h o s p h a z e n e s . (_1) R

R

M e S i N =P-OCH2CF3 3

I

Δ

>

R'

-Ρ"Ρ=Ν4Π

+

I

Me3SiOCH2CF3

(5)

R'

R

Me

Et

Ph

Ph

Ph

R'

Me

Et

Me

Et

Ch Ph 2

The p h y s i c a l p r o p e r t i e s o f t h e s e p o l y m e r s vary c o n s i d e r a b l y as t h e s u b s t i t u e n t s a t p h o s p h o r u s a r e changed. Po1 y ( d i m e t h y l p h o s p h a z e n e ) ( M e 2 P N ) i s a white f i l m - f o r m i n g polymer with a weight averaged m o l e c u l a r w e i g h t ( M ) o f 5 0 , 0 0 0 a s d e t e r m i n e d by l i g h t scatter­ ing. I t i s s o l u b l e i n C H 2 C I 2 , C H C I 3 , CH3CH2OH, a n d THF/H2O, a n d h a s a m e l t i n g p o i n t o f 158°C a n d a g l a s s t r a n s i t i o n t e m p e r a t u r e o f -42°C Q ) . The d i e t h y l analog ( E t 2 P N ) , on t h e o t h e r h a n d , i s q u i t e p e r p l e x i n g since i t s v i r t u a l i n s o l u b i l i t y i n a l l s o l v e n t s p r e c l u d e s most c h a r a c t e r i z a t i o n other than e l e m e n t a l a n a l y s i s . In c o n t r a s t t o t h e a l k y l s u b s t i t u t e d p o l y m e r s , t h e P-phenyl compounds, [ P h ( M e ) P N ] and [Ph(Εt)PN] , a r e b r i t t l e , brown c o l o r e d m a t e r i a l s which a r e q u i t e s o l u b l e i n THF a n d a r e r e a d i l y p l a s t i c i z e d by t r a c e amounts o f s o l v e n t . Determination of molecular weight n

w

n

n

n

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

170

RINGS, CLUSTERS, AND

POLYMERS

by g e l p e r m e a t i o n c h r o m a t o g r a p h y f o r [Ph(Me)PN] indicates M t o be 5 4 , 0 0 0 . I t s g l a s s transition t e m p e r a t u r e was f o u n d t o be 37°C Phosphazene copolymers have a l s o been p r e p a r e d by the t h e r m o l y s i s of e q u i m o l a r m i x t u r e s of the p h e n y l / a l k y l and d i a l k y l s u b s t i t u t e d P - t r i f l u o r o e t h o x y phosphinimines. n

n

Ph

R

= Me ,

Et

These m a t e r i a l r u b b e r - l i k e i n a p p e a r a n c e than e i t h e r of the corres­ ponding homopolymers. Such systems i n d i c a t e t h a t i t should be p o s s i b l e t o " c u s t o m d e s i g n " polyphosphazenes by c h o o s i n g p r e c u r s o r s with desirable substituents . I n s u m m a r y , t h i s new and g e n e r a l m e t h o d o f synthe­ s i z i n g b o t h c y c l i c and p o l y m e r i c phosphazenes (eq 6) R

R

1

1

Me SiN = P—X

>

3

R»

Me SiX 3

+

Γ 1 -|jP=N-Jn R

(6)

1

involves properly designed N-si1ylphosphinimines which c o n t a i n a l e a v i n g g r o u p X and the d e s i r e d substituents R and R on p h o s p h o r u s . Such compounds eliminate s u b s t i t u t e d s i l a n e s M e S i X and form c y c l i c or polymeric phosphazenes. When X i s B r o r , as r e p o r t e d earlier ( £ ) , F, o n l y s m a l l r i n g c o m p o u n d s a r e f o r m e d , b u t w h e n X i s CF CH2Û, polymeric phosphazenes r e s u l t . In c o n t r a s t to the u s u a l methods of p r e p a r i n g inorganic polymers v i a ring opening polymerization, t h i s i s an unusual example of a c o n d e n s a t i o n - p o l y m e r i z a t i o n which g i v e s an i n o r g a n i c P-N polymer backbone. This method, t h e r e f o r e , has the advantage of a l l o w i n g the initial c o n s t r u c t i o n of s m a l l m o l e c u l e b u i l d i n g b l o c k s which incorporate desirable side groups. This is p a r t i c u l a r l y u s e f u l f o r the p r e p a r a t i o n of a l k y l and/or aryl substituted polyphosphazenes with direct carbon to phosphorus bonds, a system which i s d i f f i c u l t to a c h i e v e by o t h e r methods. f

3

3

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

10.

wisiAN-NEiLSON E T A L .

CCI4

Reactions of

Phosphorus-Nitrogen Polymers

171

(Silylamino)phosphines

Other N - s i l y l p h o s p h i n i m i n e s which are also s u i t a b l y c o n s t r u c t e d p h o s p h a z e n e p r e c u r s o r s , c a n be p r e p a r e d by a s e c o n d o x i d a t i o n r e a c t i o n o f s i l y l a m i n o phosphines. When t h e s e p h o s p h i n e s r e a c t w i t h c a r b o n t e t r a c h l o r i d e , t w o t y p e s o f P - c h l o r o p h o s p h i m i n i n e s may be f o r m e d b y e s s e n t i a l l y t w o p a t h w a y s ( e q 7 ) ( 8 ) . R

I -CHCI3 >

H-C-SiMe I Me Q S i N = P - R

3

1

I

A CH R 2

( M e S i ) N-P, 3

R

2

I

R'

H-C-H | Me 3 S i N = P - R

-Me3SiCCl3 >

1

I

Β

CI R = S i M e 3 , Me, P h , Η R = C H S i M e 3 , Me, E t , _ i - P r , OCH CF 1

2

2

_t-Bu, Ph , N M e , 2

OMe ,

3

The e l i m i n a t i o n o f C H C I 3 as s h o w n i n p a t h w a y A o c c u r s i n s i m i l a r s y s t e m s w h i c h c o n t a i n a C-H m o i e t y α to p h o s p h o r u s . P r e s u m a b l y , i n i t i a l f o r m a t i o n o f an i o n p a i r i n t e r m e d i a t e ( R3PC 1 )( C C 1 3 ") (j_0) i s f o l l o w e d by a t t a c k o f t h e C C l 3 ~ a n i o n a t t h e h y d r o g e n on t h e α c a r b o n w i t h e l i m i n a t i o n o f CHCI3 g i v i n g y l i d e p r o d u c t s ( eq 8) (^,^_2_). However, i n systems which +

R* I R P-C-R" 2

R' CCI4 >

• / R P-C-R 2

Η

M

CCI3"

R •CHCI3 -> R P = C-R 2

I \

I

Cl

CI

H

contain a silylamino substitu are presumably intermediates [l,3]-silyl shift ( e q 9) ( 4 ) P - c h l o r o p h o s p h i n i m i n e s shown

!f

(8)

e n t , the analogous ylides which rearrange v i aa to give the i n p a t h w a y A.

In Rings, Clusters, and Polymers of the Main Group Elements; Cowley, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

172

RINGS, CLUSTERS, AND

POLYMERS

R

I CHR

H-C-SiMe-3

I (Me-iSi ) N-P-R'

Me 3 S i N =

>

2

I

(9)

ι P-R'

I

CI Cl An a l t e r n a t e p a t h w a y i s p o s s i b l e f o r s y s t e m s c o n t a i n i n g s i l y l a m i n o s u b s t i t u e n t s at p h o s p h o r u s . This most l i k e l y i n v o l v e s a t t a c k of the CCI3" a n i o n at the e l e c t r o p h i 1 i c s i l i c o n r e s u l t i n g i n e l i m i n a t i o n of M e 3 S i C C l 3 a s s h o w n i n p a t h w a y B. In the systems i n v e s t i g a t e d thus f a r , the r e a c t i o n pathway preference a p p e a r s t o be i n f l u e n c e d by: (1) s o l v e n t p o l a r i t y , and ( 2 ) s t e r i c and e l e c t r o n i at p h o s p h o r u s (8). Low-coordinate

Phosphorus

Systems

R e g a r d l e s s o f w h i c h Ν-si1y 1 p h o s p h i n i m i n e products are formed they a l l are p o t e n t i a l p r e c u r s o r s to phosphazenes v i a e l i m i n a t i o n of M e S i C l . Preliminary e v i d e n c e i n d i c a t e s t h a t the t h e r m a l e l i m i n a t i o n does i n d e e d o c c u r i n some c a s e s . The N-si1y 1phosphinimines are a l s o p o t e n t i a l p r e c u r s o r s to a n o t h e r type of novel Si-N-P compound, i . e . t h r e e - c o o r d i n a t e phosphoranes: 3

R-PC

>