Topics in Organic Electrochemistry

306 Pages·1986·24.59 MB·English

by  Albert J. Fry (auth.), Albert J. Fry, Wayne E. Britton (eds.)

Topics in
Organic
Electrochemistry
Topics in
Organic
Electrochemistry
Edited by
Albert J. Fry
Wesleyan University
Middletown, Connecticut
and
Wayne E. Britton
The University of Texas at Dallas
Richardson, Texas
SPRINGER SCIENCE+BUSINESS MEDIA, LLC
Library of Congress Cataloging in Publication Data
Main entry under title:
Topics in organic electrochemistry.
Includes bibliographical references and index.
1. Electrochemistry. 2. Chemistry, Physical organic. I. Fry, Albert J. Il. Britton,
Wayne E.
QD555.5.T66 1986 547.1'37 85-28178
ISBN 978-1-4899-2036-2 ISBN 978-1-4899-2034-8 (eBook)
DOI 10.1007/978-1-4899-2034-8
© 1986 Springer Science+Business Media New York
Originally published by Plenum Press, New York in 1986
Softcover reprint of the hardcover 1s t edition 1986
Ali 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
Contributors
Wayne E. Britton e Department of Chemistry, University of Texas at
Dallas, Richardson, Texas
Marye Anne Fox e Department of Chemistry, University of Texas at
Austin, Austin, Texas
Albert J. Fry e Department of Chemistry, Wesleyan University,
Middletown, Connecticut
Masamichi Fujihira e Department of Chemical Engineering, Tokyo
Institute of Technology, Tokyo, Japan
John C. Kotz e Chemistry Department, State University of New York,
Oneonta, New York
Vernon D. Parker e Norwegian Institute of Technology, University of
Trondheim, Trondheim, Norway
v
Preface
Organic electrochemistry is a remarkably diverse science. Many study it for
its own sake. Such individuals have traditionally been interested primarily
in the mechanisms of reactions of organic substances at electrode surfaces,
in developing new synthetic applications, or in electrochemical methods
for analyzing mixtures of organic substances. In recent years, however, the
field has attracted the attention of individuals with a wider variety of research
interests. Physical organic chemists have learned that electrochemistry can
afford valuable thermodynamic and structural information on organic sys
tems, and that there exists a wealth of electrochemical methods which can
be employed to measure the rates and mechanisms of fast organic reactions
occurring at electrodes. Organometallic chemists are beginning to discover
and this is still almost virgin territory-the wide range of reaction mech
anisms which can take place upon electrochemical oxidation or reduction
of organometallic substrates. Physical chemists are attempting to understand
the complex processes which occur at the surfaces of semiconductors, and
when light impinges on an electrode surface. Others are studying the ways
in which the composition of the electrode surface affects the course of
electrode processes, and are devising ways to modify the chemical structure
of electrode surfaces to achieve specific purposes. The range of contexts in
which electrochemistry is now being used in some way in organic research
is truly impressive.
The very pace and breadth of developments in these areas have created
problems of their own. A number of important areas in organic elec
trochemistry, we felt, were at that stage in their development where they
were ripe for a critical review. Some of the topics in this volume have not
been reviewed in some time, and others not at all. This alone would argue
for their presence here. In addition, however, we felt the need for a collection
of reviews addressed to the general organic chemical community, who may
vii
viii Preface
not be aware of how extensive recent developments in some of these areas
have been. The nature of some of these problems is such that frequently
they can benefit from insights which organic chemists are uniquely suited
to contribute. We hope in this set of authoritative and critical reviews not
only to summarize developments in a number of important areas of organic
electrochemistry at a level useful to investigators in the respective fields,
but also to make this information available in a format accessible to organic
chemists not previously familiar with it. We hope thereby to promote some
useful interactions between what would otherwise be very disparate con
stituencies.
A brief survey of the subjects covered in this volume will serve to
illustrate the remarkably wide range of subjects studied by modem organic
electrochemistry. (We have not included here synthetic electrochemistry,
which has been adequately reviewed recently in a number of formats,
including the large multi-author work of Baizer and Lund.) Parker discusses
the use of electrochemical techniques, including recently developed
methods for analysis of the data, for extracting from electrochemical systems
information on the rates and mechanisms of organic reactions occurring at
electrodes. In chapters also directed toward elucidation of information of
interest in physical organic chemistry, Fry examines the electrochemical
behavior of nonbenzenoid aromatic hydrocarbons and Britton discusses the
effects of conformational change upon electrochemical behavior in a variety
of flexible systems, including cyclooctatetraenes and cyclohexanes. Kotz
presents a schema for rationalizing the wide variety of reaction mechanisms
observed upon electrochemical oxidation or reduction of organometallic
substances. Fox reviews the variety of phenomena involved when light,
organic substances, and electrode surfaces interact, an area of far-reaching
practical implications in an era of diminishing energy resources. Fujihara
takes up another subject of great current interest, the effects of experimental
conditions, including chemical modifications of many kinds, upon the nature
of electrode surfaces and processes occurring there. The ambitious but not
unrealistic hope of workers in this field is of course to be able to create
new s~rfaces which are able to effect highly selective transformations. The
breadth of subjects covered by the authors is impressive, yet all retain the
characteristic orientation of the organic chemist. We hope that we have
been successful in making better known the excitement and the many
successes and challenges of modem physical organic electrochemistry.
Albert J. Fry Wayne E. Britton
Middletown, Connecticut Dallas, Texas
Contents
Chapter 1
The Electrochemistry of Nonbenzenoid Hydrocarbons
Albert J. Fry
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Benzenoid Hydrocarbons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Annulenes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. [ 4] Annulene (Cyclobutadiene) . . . . . . . . . . . . . . . . . . . . . . 8
3.2. [8] Annulene (Cyclooctatetraene) . . . . . . . . . . . . . . . . . . . . 11
3.3. [10] Annulene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.4. [12] Annulene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.5. [14] Annulene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.6. [16] Annulene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.7. Larger Annulenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4. Homoaromaticity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5. Fused-Ring Hydrocarbons................................ 25
5.1. Pentalene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.2. Heptalene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.3. Octalene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.4. Azulene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
References.............................................. 32
Chapter 2
Electrochemical Applications in Organic Chemistry
Vernon D. Parker
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
ix
x Contents
2. Chemical Reactions Coupled to Charge Transfer . . . . . . . . . . . . 37
2.1. Equilibrium Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.2. Kinetic Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3. Direct Electrochemical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.1. Cyclic and Derivative Cyclic Voltammetry............. 42
3.2. Double Potential Step Chronoamperometry. . . . . . . . . . . . 47
3.3. Other Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4. Indirect Electrochemical Methods . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.1. Linear Sweep Voltammetry (LSV) . . . . . . . . . . . . . . . . . . . . 51
4.2. Convolution Potential Sweep Voltammetry (CPSV) . . . . . 53
4.3. Normalized Potential Sweep Voltammetry (NPSV) . . . . . 54
4.4. Linear Current-Potential Analysis (LCP) . . . . . . . . . . . . . . 55
5. The "Reaction Order Approach".......................... 56
5.1. Applied to Direct Methods.......................... 57
5.2. Applied to Linear Sweep Voltammetry . . . . . . . . . . . . . . . . 61
5.3. Determination of Activation Energies................. 62
5.4. Determination of Kinetic Isotope Effects . . . . . . . . . . . . . . 63
6. Putting It All Together, Practical Examples . . . . . . . . . . . . . . . . . 63
6.1. Reactions of 9-Diazofluorene Anion Radical........... 63
6.2. Reactions of 4-Methoxybiphenol Cation Radical . . . . . . . 66
6.3. The Anion Radical-Proton Donor Complex Reactions 68
6.4. Dimerization of 9-Substituted Anthracene Anion Radicals 69
6.5. Dimerization of Benzaldehyde Anion Radical . . . . . . . . . . 72
6.6. The Protonation of Anthracene Anion Radical by Phenol 74
7. Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Chapter 3
The Electrochemistry of Transition Metal Organometallic Compounds
John C. Kotz
1. Electrochemistry of the Metallocenes, ( 715 -C5H5hMXn . . . . . . . 83
1.1. The Simple Metallocenes, ( 715-C HshM............... 84
5
1.2. Decamethylmetallocenes, ( 715- C5Me5hM . . . . . . . . . . . . . . 87
1.3. General Conclusions Regarding Metallocene Electro-
chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
1.4. Bent Metallocenes, ( 715-C H hMXn . . . . . . . . . . . . . . . . . . 90
5 5
1.5. Substituent Effects in Metallocene Derivatives . . . . . . . . . 95
1.6. Organometallic Mixed Valence Compounds: The Electro-
chemistry of Multi-Metal Compounds . . . . . . . . . . . . . . . . 100
Coatents xi
2. Other "Sandwich" Compounds of Pi Donor Ligands . . . . . . . . 109
2.1. Symmetrical Bis-Arene Complexes: (ArenehM......... 109
2.2. (1J6-Arene)(1J5-C5H5)M Complexes................... 111
2.3. ( 115 -Cyclopentadienyl)(Olefin) Metal Complexes . . . . . . . 113
2.4. Complexes of Metals with Heterocyclic Rings . . . . . . . . . 114
2.5. Other Sandwich Compounds . . . . . . . . . . . . . . . . . . . . . . . . 116
3. The Binary Metal Carbonyls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
4. Metal Carbonyl Derivatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
4.1. Metal Carbonyls with Sigma Donor Ligands M(CO)xLy 121
4.2. Compounds with Pi Donor Substituents . . . . . . . . . . . . . . . 130
4.2.1. Compounds with Olefin and Allyl Ligands . . . . . . 130
4.2.2. Cyclopentadienyl Metal Carbonyls and Related
Compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
4.2.2a. Monomeric Complexes . . . . . . . . . . . . . . . 132
4.2.2b. Dimeric Complexes . . . . . . . . . . . . . . . . . . 135
4.2.3. Arene Metal Carbonyls. . . . . . . . . . . . . . . . . . . . . . . 139
4.2.4. Other Pi Donor Ligands...................... 141
5. Electrochemically Induced Reactions . . . . . . . . . . . . . . . . . . . . . . 142
5.1. Electrochemically Induced Structural Changes . . . . . . . . . 142
5.1.1. Isomerization of Six-Coordinate Complexes..... 143
5.1.2. Isomerization of a Pi Donor Ligand............ 144
5.2. Redox-Induced Ligand Substitution . . . . . . . . . . . . . . . . . . 147
5.2.1. Substitution of Neutral Sigma Donor Ligands . . . 148
5.2.1a. Anodically Induced Substitutions . . . . . . 148
5.2.1b. Cathodically Induced Substitutions . . . . 149
5.2.2. Substitution of Anionic Sigma Donor Ligands:
M-R and M-X Bond Breaking . . . . . . . . . . . . . . . . 150
5.3. Reactions at Coordinated Ligands.................... 160
5.4. The Formation of Metal-Carbon Bonds............... 164
6. Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
References.............................................. 167
Chapter 4
Organic Photoelectrochemistry
Marye Anne Fox
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
1.1. The Photoelectrochemical Cell . . . . . . . . . . . . . . . . . . . . . . . 177
1.2. Electron Transfer in the Excited State . . . . . . . . . . . . . . . . 178
1.3. The Photoelectrochemical Experiment . . . . . . . . . . . . . . . . 179