Cover

Table of Contents

Cover

Title page

Copyright page

DEDICATION

FOREWORD TO THE FIRST EDITION

PREFACE TO THE SECOND EDITION

PREFACE TO THE FIRST EDITION

1 INTRODUCTION: GENERAL ASPECTS

1.1. AIMS AND OBJECTIVES

1.2. SOME DEFINITIONS

1.3. STRUCTURES OF SOME TYPICAL HYPERCARBON SYSTEMS

1.4. THE THREE-CENTER BOND CONCEPT: TYPES OF THREE-CENTER BONDS

1.5. THE BONDING IN MORE HIGHLY DELOCALIZED SYSTEMS

1.6. REACTIONS INVOLVING HYPERCARBON INTERMEDIATES

2 CARBON-BRIDGED (ASSOCIATED) METAL ALKYLS

2.1. INTRODUCTION

2.2. BRIDGED ORGANOALUMINUM COMPOUNDS

2.3. BERYLLIUM AND MAGNESIUM COMPOUNDS

2.4. ORGANOLITHIUM COMPOUNDS

2.5. ORGANOCOPPER, SILVER, AND GOLD COMPOUNDS

2.6. SCANDIUM, YTTRIUM, AND LANTHANIDE COMPOUNDS

2.7. TITANIUM, ZIRCONIUM, AND HAFNIUM COMPOUNDS

2.8. MANGANESE COMPOUNDS

2.9. OTHER METAL COMPOUNDS WITH BRIDGING ALKYL GROUPS

2.10. AGOSTIC SYSTEMS CONTAINING CARBON–HYDROGEN–METAL 3c–2e BONDS

2.11. CONCLUSIONS

3 CARBORANES AND METALLACARBORANES

3.1. INTRODUCTION

3.2. CARBORANE STRUCTURES AND SKELETAL ELECTRON NUMBERS

3.3. LOCALIZED BOND SCHEMES FOR CLOSO BORANES AND CARBORANES

3.4. MO TREATMENTS OF CLOSO BORANES AND CARBORANES

3.5. THE BONDING IN NIDO AND ARACHNO CARBORANES

3.6. METHODS OF SYNTHESIS AND INTERCONVERSION REACTIONS

3.7. SOME CARBON-DERIVATIZED CARBORANES

3.8. BORON-DERIVATIZED CARBORANES: WEAKLY BASIC ANIONS [CB11H6X6]

3.9. METALLACARBORANES

3.10. SUPRAICOSAHEDRAL CARBORANE SYSTEMS

3.11. CONCLUSIONS

4 MIXED METAL–CARBON CLUSTERS AND METAL CARBIDES

4.1. INTRODUCTION

4.2. COMPLEXES OF CnHn RING SYSTEMS WITH A METAL ATOM: NIDO-SHAPED MCn CLUSTERS

4.3. METAL COMPLEXES OF ACYCLIC UNSATURATED LIGANDS, CnHn+2

4.4. COMPLEXES OF UNSATURATED ORGANIC LIGANDS WITH TWO OR MORE METAL ATOMS: MIXED METAL–CARBON CLUSTERS

4.5. METAL CLUSTERS INCORPORATING CORE HYPERCARBON ATOMS

4.6. BULK METAL CARBIDES

4.7. METALLATED CARBOCATIONS

4.8. CONCLUSIONS

5 HYPERCOORDINATE CARBOCATIONS AND THEIR BORANE ANALOGS

5.1. GENERAL CONCEPT OF CARBOCATIONS: CARBENIUM VERSUS CARBONIUM IONS

5.2. METHODS OF GENERATING HYPERCOORDINATE CARBOCATIONS

5.3. METHODS USED TO STUDY HYPERCOORDINATE CARBOCATIONS

5.4. METHONIUM ION (CH5+) AND ITS ANALOGS

5.5. HOMOAROMATIC CATIONS

5.6. HYPERCOORDINATE (NONCLASSICAL) PYRAMIDAL CARBOCATIONS

5.7. HYPERCOORDINATE HETEROCATIONS

5.8. CARBOCATION–BORANE ANALOGS

5.9. CONCLUSIONS

6 REACTIONS INVOLVING HYPERCARBON INTERMEDIATES

6.1. INTRODUCTION

6.2. REACTIONS OF ELECTROPHILES WITH C–H AND C–C SINGLE BONDS

6.3. ELECTROPHILIC REACTIONS OF π-DONOR SYSTEMS

6.4. BRIDGING HYPERCOORDINATE SPECIES WITH DONOR ATOM PARTICIPATION

6.5. CONCLUSIONS

CONCLUSIONS AND OUTLOOK

Index

Title page

In Memory of the Late Professor William N. Lipscomb

FOREWORD TO THE FIRST EDITION

The periodic nature of the properties of atoms and the nature and chemistry of molecules are based on the wave property of matter and the associated energetics. Concepts including the electron-pair bond between two atoms and the associated three-dimensional properties of molecules and reactions have served the chemist well, and will continue to do so in the future.

The completely delocalized bonds of π-aromatic molecules, introduced by W. Hückel, also provided a basis for a rational description of molecular orbitals in these systems. An extended Hückel theory allowed a study of molecular orbitals throughout chemistry at a certain level of approximation.

The localized multicenter orbital holds a certain intermediate ground, and is particularly useful when there are more valence orbitals then electrons in a molecule or transition state. First widely used in the boron hydrides and carboranes, these three-center and multicenter orbitals provide a coherent and consistent description of much of the structure and chemistry of the upper left side of the periodic table, and of the interactions of metallic ions with other atoms or molecules.

Skeletal electron counts (the sum of the styx numbers), first proposed by Wade, Mingos, and Rudolph, have also provided a guide for synthesis, and have given a basis for filled bonding description of polyhedral species and their fragments. Together with the isolobal concept, diverse areas of chemistry have thereby been unified.

In this book, one sees the remarkable way in which these ideas bring together structure and reactivity in a great diversity of novel carbon chemistry and its relationship with that of boron, lithium, hydrogen, the metals, and others. The authors are to be congratulated.

Rather than ask why it has taken some 30 years for these concepts to become widely known, one can be amazed that the background for this fine book developed at all. It is due in no small part to the reluctance of chemists to adapt to the dynamic changes of chemistry. One can also hope that chemistry will recover from the recent neglect of support of research in mechanistic organic chemistry and synthesis of compounds of the main group elements. In addition, much of the molecular structure determination that is so central to these arguments had to await the newer methods of X-ray diffraction and nuclear magnetic resonance, and the theory had to await the modern development in methods and computers. Thus, the emergence of the depth and breadth of these concepts in this book is a tribute to the dedication of the authors and to the vitality of the ideas themselves.

WILLIAM N. LIPSCOMB

May 1986

PREFACE TO THE SECOND EDITION

More than 20 years have passed since the publication of our book on hypercarbon chemistry. The book became out of print and much progress has since been made in the field. Hypercarbon chemistry has continued to grow, and indeed has become an integral part of the chemistry of carbon compounds usually referred to as high coordination compounds. Hence, it seems warranted to provide a comprehensively updated review and discussion of the field with literature coverage until mid-2009. Les Field was no longer available to help revise our book. However, our friend and colleague Árpád Molnár joined us as a coauthor during a sabbatical year in Los Angeles, and should be credited for his outstanding effort to make the new edition possible, which we hope will be of use to the chemical community. Our publisher is thanked for arranging the new updated edition.

GEORGE A. OLAH

G. K. SURYA PRAKASH

KENNETH WADE

ÁRPÁD MOLNÁR

ROBERT E. WILLIAMS

November 2009

PREFACE TO THE FIRST EDITION

Organic chemistry is concerned with carbon compounds. Over 6 million such compounds are now known, and their number is increasing rapidly. They range from the simplest compound methane, the major component of natural gas, to the marvelously intricate macromolecules that nature uses in life processes.

Within such a rich and diverse subject, it is difficult for someone deeply familiar with one area to keep abreast of developments in others. This can hinder progress if discoveries in one field that can have significant impact on others are not recognized in a timely fashion. For example, developments in the chemistry of carbohydrates, proteins, or nucleotides are traditionally exploited by biochemists and biologists more than by organic chemists. Developments in organometallic chemistry, while increasingly attracting the attention of inorganic chemists, are not as well appreciated by mainstream organic chemists.

In this book we have attempted to alleviate this problem by pooling our diverse experience and backgrounds but centering on a common interest in the fascinating topic of hypercarbon chemistry. The book centers on the theme that carbon, despite its firmly established tetravalency, can still bond simultaneously to five or more other atoms. We refer to such atoms as hypercarbon atoms (short for hypercoordinated atoms), since four valency [hence four coordination, using normal two-center, two-electron type bonds] is the upper limit for carbon (being a first-row element, it can accommodate no more than eight electrons in its valence shell). Since their early detection in bridged metal alkyls, where they helped advance the concept of the three-center, two- electron bond (and later, the four-center, two-electron bond), hypercarbon atoms have now become a significant feature of organometallics, carborane, and cluster (carbide) chemistry, as well as acid-catalyzed hydrocarbon chemistry and the diverse chemistry of carbocations.

First, we survey the major types of compounds that contain hypercarbon. The relationships that link these apparently disparate species are demonstrated by showing how the bonding problems they pose can be solved by the use of three- or multicenter electron-pair bond descriptions or simple MO treatments. We also show the role played by hypercoordinated carbon intermediates in many familiar reactions (carbocationic or otherwise). Our aim here is to demonstrate that carbon atoms in general can increase their coordination numbers in a whole range in reactions.

In our original plans for the book, we were privileged to have our friend and colleague Paul v. R. Schleyer participate, and we regret that other obligations have made it impossible for him to continue. We gratefully acknowledge his many suggestions and thank him for his continued encouragement. We have mainly focused our attention on experimentally known hypercarbon systems and are not discussing only computationally studied ones (these are reviewed by Paul Schleyer elsewhere).

Most chemists’ familiarity with chemical bonding evolved in electron-sufficient systems, where there are enough electrons not only for (2c–2e) bonds but also for nonbonded electron pairs. Hypercarbon atoms are generally found in electron-deficient systems where electrons are in short supply and thus have to be spread relatively thinly to hold molecules or ions together. A relative deficiency of electrons is not uncommon in chemistry, particularly in the chemistry of the metallic elements. The (3c–2e) and multicenter bonding concept of boranes and carboranes, pioneered by Lipscomb, further emphasizes this point. Thus, it is not surprising that the concept of hypercarbon bonding was accepted by inorganic and organometallic chemists earlier than by their organic colleagues. The well-publicized spirited debate over the classical–nonclassical nature of some carbocationic systems preceded their preparation and their spectroscopic study under long-lived stable ion conditions, which unequivocally established their structures. Debate, and even controversy, is frequently an essential part of the “growing pains” of a maturing field, and they should be welcomed as they help progress in finding answers. The importance of hypercoordination in carbocations and related hydrocarbon is now firmly established. At the same time, hypercoordinate carbocations are but one aspect of the much wider field of hypercarbon chemistry.

It is significant to note that almost all carbocations have known isoelectronic and isostructural neutral boron analogs. Boron compounds also provide useful models for many types of intermediates (transition states) of electrophilic organic reactions.

The field of hypercarbon chemistry is already so extensive that it is impossible to give an encyclopedic coverage of the topic. Instead, we have taken the liberty of organizing our discussion around selected topics with representative examples to emphasize major aspects. Our choices were arbitrary and we apologize for inevitably omitting much significant work.

Multiauthor books frequently lack the uniformity that a single-author book is able to convey. Our close cooperation, made possible by the Loker Hydrocarbon Research Institute, has helped us give a homogeneous presentation that merges our individual viewpoints to reflect our common goal. If we had succeeded in calling attention to the ubiquitous presence of hypercarbon compounds, breaching the conventional boundaries of chemistry, and arousing the interest of our readers, then we shall have achieved our purpose.

We thank Ms. Cheri Gilmour for typing the manuscript and our editor, Dr. Theodore P. Hoffman, for helping along the project in his always friendly and efficient way. Many friends and colleagues offered helpful comments and suggestions and we are grateful to them all.

GEORGE A. OLAH

G.K. SURYA PRAKASH

ROBERT E. WILLIAMS

LESLIE D. FIELD

KENNETH WADE

October 1986