Table Of ContentMechanisms of Reactions of Metal Complexes in Solution
Mechanisms of Reactions of
Metal Complexes in Solution
By
Debabrata Banerjea
Calcutta University, India
Email: [email protected]
and
M. K. Bharty
Banaras Hindu University, India
Email: [email protected]
Print ISBN: 978-1 - 83916- 186- 5
PDF ISBN: 978- 1- 83916-3 60- 9
EPUB ISBN: 978- 1- 83916- 361- 6
A catalogue record for this book is available from the British Library
© Debabrata Banerjea and M. K. Bharty 2023
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Preface
Mechanisms of reactions of metal complexes attracted the attention of
Alfred Werner, who, based on qualitative observations, proposed an intramo-
lecular mechanism of racemization of tris-chelate complexes of metals that
involves opening and closing of a chelate ring, but studies on the kinetics of
reactions of metal complexes were first started by Lamb and co-w orkers early
in the last century. However, during the first half of the twentieth century,
many stalwarts in inorganic chemistry did not consider such investigations
worth pursuing. In the early 1940s, a young Fred Basolo, after listening to a
lecture delivered by the German chemist Walter Hieber on some reactions
of metal carbonyls, asked him if he had any idea as to how such reactions
occur, namely their mechanisms. Professor Hieber replied, “Young man, we
are interested in chemistry, not the philosophy of chemistry”. However, since
the late 1940s, the field has started to attract the attention of several groups,
mainly in the UK and USA, and in other countries research schools in this
field developed in the following years. During the period 1980–2010, publica-
tions on the mechanisms of reactions of metal complexes comprised about
15% of the total publications in inorganic chemistry.
In the six decades from the 1950s, there has been an explosive growth in
this field, significantly more than in any other area of inorganic chemistry,
and particularly since the 1960s with the development of several techniques
for following fast reactions.
Most of the early developments were well covered in the book Mechanisms
of Inorganic Reactions: A Study of Metal Complexes in Solution by Fred Basolo
and Ralph G. Pearson, the first edition of which was published in 1958 and
the second edition in 1967, with a reprint in 1972. A few other books and
reviews covering the field, specifically of different individual classes of reac-
tions, have been published, some of them in the latter part of the last cen-
tury, such as the book The Study of Kinetics and Mechanism of Reactions of
Mechanisms of Reactions of Metal Complexes in Solution
By Debabrata Banerjea and M. K. Bharty
© Debabrata Banerjea and M. K. Bharty 2023
Published by the Royal Society of Chemistry, www.rsc.org
v
vi Preface
Transition Metal Complexes by Ralph G. Wilkins, the first edition being pub-
lished in 1974 and the second edition in 1991.
In this book, we have attempted to highlight the major progress and devel-
opments in this area, up to the second decade of the present century. The
coverage is much more exhaustive than in previously published books, and
includes reactions of some s and p block elements also. However, profuse
literature compelled us to be selective according to our discretion and we
apologise for any omissions.
We acknowledge the help received from Dr V. K. Jain, former Head of
the Chemistry Division, Bhabha Atomic Research Centre, Mumbai, and
Dr S. Goswami, Assistant Professor of Chemistry, Calcutta University, in
preparing the drafts of some of the chapters in Word format from the PDF
versions prepared by the senior author, and the co- author prepared one
chapter in Word format and made all necessary corrections in the drafts of
all the chapters before submission to the publisher.
Our thanks are also due to Drew Gwilliams and staff at the Royal Society of
Chemistry for the publication of this book.
D. Banerjea
M. K. Bharty
Contents
Chapter 1 Reactions of Metal Complexes 1
1.1 Introduction 1
1.2 Molecularity and Order of a Reaction 5
1.3 General Mechanism of Ligand Replacement
Reactions 8
1.4 Experimental Evidence for Mechanisms 16
1.5 Methods for the Characterization of Reactive
Intermediates 18
1.6 Order of Reaction and Reaction Mechanisms 21
1.7 Lability of Complexes 26
1.7.1 Ligand Field Theory 30
References 52
Chapter 2 Techniques for Following Reactions and Factors
that Affect Rates 59
2.1 Techniques for Evaluating Rates of Reactions 59
2.1.1 Direct Chemical Analysis 59
2.1.2 Spectrophotometric Methods 60
2.1.3 Electrometric Methods 63
2.1.4 Polarimetric Methods 66
2.1.5 Use of Isotropic Tracers 67
2.2 Special Techniques for Studying Fast Reactions 67
2.2.1 Flow Methods 67
2.2.2 Electrochemical Methods 69
2.2.3 Relaxation Methods 70
2.2.4 Flash Photolysis 71
Mechanisms of Reactions of Metal Complexes in Solution
By Debabrata Banerjea and M. K. Bharty
© Debabrata Banerjea and M. K. Bharty 2023
Published by the Royal Society of Chemistry, www.rsc.org
vii
viii Contents
2.2.5 Nuclear Magnetic Resonance (NMR) and
Electron Paramagnetic Resonance (EPR)
Methods 71
2.2.6 Studies of Exchange Rates by NMR
Spectroscopy 72
2.2.7 Electron Paramagnetic Resonance (EPR)
Spectroscopy 75
2.2.8 Application of Ultrasonic Absorption
and Pulse Radiolysis 76
2.3 Rate Constants in Some Complex Systems 76
2.4 Factors that Affect Rates of Reactions 80
2.4.1 Effect of Temperature 80
2.4.2 Effect of External Pressure 84
2.4.3 Effect of Ionic Strength 87
2.4.4 Influence of Solvent 89
2.5 Nucleophilicity and Rate 89
2.6 Relative Nucleophilicities 90
2.7 Hammett Relationship 94
2.8 Taft Relationship 96
2.9 Linear Free Energy Relationship (LFER) 97
2.10 Isotope Effects 97
References 99
Chapter 3 Ligand Replacement Reactions of Metal Complexes
of Coordination Number Four and Higher 105
3.1 Square- planar Complexes 105
3.1.1 Complexes of Platinum(ii) 105
3.1.2 trans Effect Theories 107
3.1.3 π- Bonding Theory of the trans Effect 121
3.1.4 Mechanism of Reaction 125
3.1.5 Energy Profile for Reactions of Square- planar
Complexes 154
3.2 trans Effect in Platinum(iv) Complexes 155
3.3 Other Square- planar Metal Complexes 155
3.3.1 Palladium(ii) Complexes 156
3.3.2 Gold(iii) Complexes 161
3.4 Further Comments on trans-and cis Effects 163
3.4.1 trans Effect in Terms of Discrimination 164
3.4.2 cis- Labilizing Effect 165
3.4.3 cis Effect in Terms of Discrimination 165
3.5 Square- planar Complexes of Nickel(ii) and
Copper(ii) 167
3.6 Reactions of Tetrahedral Complexes 172
3.7 Complexes of Coordination Number Five 177
3.8 Complexes of Higher Coordination Number 182
References 183
Contents ix
Chapter 4 Ligand Replacement Reactions of Octahedral
Complexes 194
4.1 Aquation/Solvolysis, Anation/Formation
and Ligand Exchange Reactions 194
4.1.1 Effect of Leaving Ligand 194
4.1.2 Effect of Charge on Reaction Rate 198
4.1.3 Steric and Structural Effects of Spectator
Ligands 200
4.1.4 Electronic Effects of Spectator (Non- leaving)
Ligands 206
4.1.5 Stereochemical Change Accompanying a
Ligand Replacement Process 207
4.1.6 Other Evidence 211
4.1.7 Activation Parameters and Reaction
Mechanism 218
4.1.8 Solvent Effect 223
4.1.9 Comparison of the Rate of Replacement
of a Metal- bound Aqua Ligand in a Metal
Complex With the Rate of Exchange of the
Bound Water With the Water in the Solvent 226
4.1.10 Stoichiometric Mechanisms 228
4.2 Base Hydrolysis 231
4.3 Ligand Replacement Reactions of [M(CO) ] 246
6
4.4 Reactions of s- and p- Block Metals 247
References 248
Chapter 5 Catalysed Reactions and Formation Reactions 255
5.1 Electrophilic and Nucleophilic Catalysis 255
5.1.1 Acid Catalysis 256
5.1.2 Electrophilic Catalysis by Metal Ions 276
5.1.3 Nucleophilic Catalysis 282
5.1.4 Electron Transfer Mechanism of Reactions
of Metal Complexes 285
5.2 Formation Reactions 286
References 335
Chapter 6 Isomerization, Optical Inversion and Racemization
Reactions 347
6.1 Linkage Isomerization 347
6.2 Geometrical Isomerization 350
6.2.1 Square- planar Complexes 351
6.2.2 Octahedral Complexes 353
6.3 Other Types of Structural Isomerization 360
6.4 Optical Inversion 362
6.5 Optical Isomerization (Racemization) 364
6.5.1 Intermolecular Mechanism 365
x Contents
6.5.2 Intramolecular Mechanism 367
6.5.3 Isomerization and Racemization of Tris
Chelates of Unsymmetrical Chelating Ligands 372
6.6 Structural Changes in Complexes of Terdentate
Ligands of the Type M(L′)(L″) 376
6.7 Structural Changes in Four- coordinate Complexes 377
6.8 Optical Isomerism in Tetrahedral Complexes 377
6.9 Configurational Changes in Some Planar
Complexes 378
References 380
Chapter 7 Electron Transfer Reactions 386
7.1 Introduction 386
7.2 Outer- sphere Mechanism 388
7.3 The Marcus Equation: Marcus Cross- relation and
Its Applications 388
7.4 Inner- sphere Mechanism 394
7.4.1 Atom (or Group) Transfer Processes 395
7.5 Comproportionation 411
7.6 Mixed Outer- and Inner- sphere Reactions 412
7.7 Estimation of Redox Rate Constants for
Inner- sphere Reactions 412
7.8 Electron Transfer Reactions in Heterogeneous
Systems 413
7.9 Solvated Electrons 416
7.10 Oxidative Addition Reactions 419
7.10.1 Mechanisms of Oxidative Addition 422
7.10.2 Five- coordinate Eighteen- electron
Substrates 424
7.10.3 Four- coordinate Sixteen- electron
Substrates 426
7.10.4 Four- coordinate Eighteen- electron
Substrates 426
7.11 Reductive Elimination 427
References 429
Chapter 8 Activation of Molecules by Coordination and Reactivity
of Coordinated Ligands 435
8.1 Introduction 435
8.2 Activation of Some Diatomic Molecules 435
8.2.1 Activation of Dihydrogen by Coordination 435
8.2.2 Activation of Dioxygen by Coordination 441
8.2.3 Activation of Dinitrogen by Coordination 445
8.3 Reactivity of Coordinated Ligands 449
8.3.1 Reaction of Metal- bound CO Ligand 449
8.3.2 Reactions of Coordinated CO and SO 450
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