Metal Interactions with Boron Clusters MODERN INORGANIC CHEMISTRY Series Editor: John P. Fackler, Jr. Texas A&M University METAL INTERACTIONS WITH BORON CLUSTERS Edited by Russell N. Grimes A Continuation Order Plan is available for this series. A continuation order will bring delivery of each new volume immediately upon publication. Volumes are billed only upon actual shipment. For further information please contact the publisher. Metal Interactions with Boron Clusters Edited by Russell N. Grimes University of Virginia Charlottesville, Virginia SPRINGER SCIENCE+BUSINESS MEDIA. LLC Library of Congress Cataloging in Publication Data Main entry under title: Metal interactions with boron clusters. (Modern inorganic chemistry) Includes bibliographies and index. I. Borane. 2. Metal-metal bonds. 3. Reactivity (Chemistry) I. Grimes, Russell N., 1935- . II. Series. QD181.BIM47 1982 546'.67159 82-9068 ISBN 978-1-4899-2156-7 ISBN 978-1-4899-2154-3 (eBook) AACR2 DOI 10.1007/978-1-4899-2154-3 © 1982 Springer Science+Business Media New York Originally published by Plenum Press, New York in 1982 Softcover reprint of the hardcover 1st edition 1982 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher To the memory of our friend and colleague, Ralph Rudolph Contributors Silvana Bresadola • Istituto di Chimica, Universita di Trieste, Trieste, Italy, and CNR-Centro di Studio sulla Stabilita e Reattivita dei Composti di Co ordinazione, Padova, Italy Donald F. Gaines • Department of Chemistry, University of Wisconsin, Madi son, Wisconsin William E. Geiger, Jr. • Department of Chemistry, University of Vermont, Burlington, Vermont Norman N. Greenwood • Department of Inorganic and Structural Chemistry, University of Leeds, Leeds LS2 9JT, England Russell N. Grimes • Department of Chemistry, University of Virginia, Charlottes ville, Virginia Steven J. Hildebrandt • Minerals and Chemicals Division, Engelhard Minerals and Chemicals Corporation, Edison, New Jersey John D. Kennedy • Department of Inorganic and Structural Chemistry, Univer sity of Leeds, Leeds LS2 9JT, England Marion E. O'Neill • Chemistry Department, Durham University, South Road, Durham OHI 3LE, England Lee J. Todd • Department of Chemistry, Indiana University, Bloomington, Indiana Kenneth Wade • Chemistry Department, Durham University, South Road, Dur ham OH 1 3LE, England vii Preface Molecular clusters, in the broad sense that the term is commonly understood, today comprise an enormous class of species extending into virtually every important area of chemistry: "naked" metal clusters, transition metal carbonyl clusters, hydrocarbon cages such as cubane (C8H8) and dodecahedrane (C20H20), organometallic cluster complexes, enzymes containing Fe S or MoFe S 4 4 3 4 cores, high polymers based on carborane units, and, of course, the many kinds of polyhedral borane species. So large is the area spanned by these diverse classes that any attempt to deal with them comprehensively in one volume would, to say the least, be ambitious-and also premature. We are presently at a stage where intriguing relationships between the various cluster families are becoming apparent (particularly in terms of bonding descriptions), and despite large dif ferences in their chemistry an underlying unity is gradually developing in the field. For example, structural changes occurring in Fe S cores as electrons are 4 4 pumped in and out, in some measure resemble those observed in boranes and carboranes. The cleavage of alkynes via incorporation into carborane cages and subsequent cage rearrangement, a sequence familiar to boron chemists, is a thermodynamically favored process which may be related to the behavior of unsaturated hydrocarbons on metal surfaces; analogies of this sort have drawn attention from theorists and experimentalists. The perception of such relationships between boranes and other cluster types arises partly from new discoveries, but is also largely a matter of tying to gether facts that have been around for some time. Yet most chemists today are specialists; few are expert in separate fields as seemingly disparate as, for ex ample, metal carbonyl clusters and metallaboranes. Bridges, therefore, are much in need, and the present volume is a modest attempt in that spirit. This book deals with the interface between metal chemistry and the prototype cluster family, the boranes. In labeling the boranes and their derivatives "prototype", I rest partly on the historic truth that the cage-like boron hydrides discovered by Alfred Stock early in this century were the first true discrete, covalent cluster species (though their structures were not elucidated until some years later). I ix X Preface also draw attention to the fact that, as Kenneth Wade has noted, the boranes are "pattern-makers" for clusters in general. The widely cited electron-counting rules for polyhedral cages were inspired by the boron systems; moreover, the boranes, carboranes, and their metal complexes form by far the most extensive and structura1y varied class of molecular clusters in existence, ranging over dozens of different cage geometries and thousands of individual compounds. No other cluster family is really comparable, either in terms of extensively developed chemistry or in the central role occupied by the boron clusters in the theory of bonding in electron-delocalized polyhedra. The selection of topics for this book was conducted with two things in mind: first, to provide selective and up-to-date coverage of the fascinating chem istry that results when polyhedral boron compounds and metal reagents get together, and second, to deal explicitly with certain aspects of this field that have not previously been reviewed per se. To my knowledge there has been no specific treatment of B3H8 --metal complexes, metallaborane and metallacar borane electrochemistry, polyhedral boranes with metal-hydrogen bonds, or metallaboron compounds of the main group metals; until now, anyone interested in any of these important topics has had to comb the literature for scattered references. The subjects of the three remaining chapters, dealing with cluster bonding, a-bonded metal complexes of boranes and carboranes, and transition metal metallaboranes, have been reviewed before but not recently; the present treatments are intended to bring the reader abreast of these rapidly developing areas. Finally, it is important to stress the interface aspect of this book; the content is as much "metal chemistry" as "boron chemistry". It is to be hoped that the contribution of this volume to both fields will be significant. Russell N. Grimes Charlottesville, Virginia Contents 1. Structural and Bonding Features of Metallaboranes and Metallacarboranes Marion E. O'Neill and Kenneth Wade 1. Introduction ................ . 2. Structures and Bonding of Boranes and Their Metalla Derivatives . . . . . 2 2.1. The Borane-Carborane Structural Pattern. . . . . . . . . . . . . . . . . . 2 2.2. The Significance of the Numbers of Skeletal Bond Pairs. . . . . . . . . 4 2.3. Isolobal Relationships between Cluster Units ................ 13 3. Related Cluster Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3 .1. Metal-carbonyl Clusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.2. Metal-Hydrocarbon 'IT-Complexes. . . . . . . . . . . . . . . . . . . . . . . 19 3.3. Other Related Main Group Cluster Systems. . . . . . . . . . . . . . . . . 24 4. Some Specific Metallacarborane Structural Types. . . . . . . . . . . . . . . . 26 4.1. Commo Complexes [M(C2B9H11 )2] n-4 with Slipped Structures, and Related Systems . . . . . . . . . . . . . . . . . . . . . . . . 26 4.2. Multidecker Sandwich Metallacarboranes . . . . . . . . . . . . . . . . . . 30 4.3. Further Systems with Apparently Anomalous Electron Numbers. . . 33 5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2. Transition-Metal Derivatives of Nido-Boranes and Some Related Species Norman N. Greenwood and John D. Kennedy 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2. Monoboron and Diboron Compounds . . . . . . . . . . . . . . . . . . . . . . . 44 3. Triboron Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 4. Tetraboron Compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 5. Pentaboron Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 5.1. Direct Reaction of B5H9 with Metal Atoms ................ 56 5.2. Direct Reaction of B5H9 with Metal Compounds ............. 57 xi