Tài liệu Reaction mechanisms of inorganic and organometallic systems by robert b. jordan

Reaction Mechanisms of Inorganic and Organometallic Systems TOPICS IN INORGANIC CHEMISTRY A Series of Advanced Textbooks in Inorganic Chemistry Series Editor Peter C. Ford, University of California, Santa Barbara Chemical Bonding in Solids, J. Burdett Reaction Mechanisms of Inorganic and Organometallic Systems, 3rd Edition, R. Jordan Reaction Mechanisms of Inorganic and Organometallic Systems Third Edition Robert B. Jordan OXFORD UNIVERSITY PRESS 2007 OXPORD UNIVERSITY PRESS Oxford University Press, Inc., publishes works that further Oxford University's objective of excellence in research, scholarship, and education. Oxford New York Auckland Cape Town Dar es Salaam Hong Kong Karachi Kuala Lumpur Madrid Melbourne Mexico City Nairobi New Delhi Shanghai Taipei Toronto With offices in Argentina Austria Brazil Chile Czech Republic France Greece Guatemala Hungary Italy Japan Poland Portugal Singapore South Korea Switzerland Thailand Turkey Ukraine Vietnam Copyright © 2007 by Oxford University Press, Inc. Published by Oxford University Press, Inc. 198 Madison Avenue, New York, New York 10016 www.oup.com Oxford is a registered trademark of Oxford University Press All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of Oxford University Press. Library of Congress Cataloging-in-Publication Data Jordan, Robert B. Reaction mechanisms of inorganic and organometallic systems / Robert B. Jordan.—3rd ed p. cm. Includes bibliographical references and index. ISBN 978-0-19-530100-7 1. Reaction mechanisms (Chemistry) 2. Organometallic compounds. 3. Inorganic compounds. I. Title. QD502J67 2006 41'.39—dc25 2006052498 9 8 7 6 5 4 3 2 1 Printed in the United States of America on acid-free paper Preface This book evolved from the lecture notes of the author for a onesemester course given to senior undergraduates and graduate students over the past 20 years. This third edition presents an updating of the material to cover the literature through to the end of 2005, with occasional excursions to early 2006. As a result, the total number of references has increased from about 660 in the second edition to over 1570 in the present one, and 140 pages of text have been added; this seems to be a clear testament to the vitality of the subject area. A new Chapter 9 on kinetics in heterogeneous systems has been added. This area has long been the domain of chemical engineers, but it is of increasing relevance to inorganic kineticists who are studying catalytic processes, such as hydrogenation and carbonylation reactions, where gas/liquid mass transfer is involved. This chapter also covers the kinetic aspects of adsorption and reaction of species on solids, and the question of whether the reaction is really homogeneous or heterogeneous. The overall organization of the first edition has been retained. The first two chapters cover basic kinetic and mechanistic terminology and methodology. This material includes new sections on the analysis of data under second-order conditions, Curtin-Hammett conditions and an expanded discussion of pressure effects. New material has been added at various points throughout Chapters 3 and 4. The coverage of organometallic systems in Chapter 5 has been increased substantially, primarily with material on metal hydrides, catalytic hydrogenation and asymmetric hydrogenation. The inverted region and activation parameters for electron-transfer reactions predicted by Marcus theory have been added to Chapter 6, along with an expanded discussion of intervalence electron transfer. The recently revised assignment of the electronic spectra of metal carbonyls has resulted in substantial revisions to photochemical interpretations in Chapter 7. The coverage of selected bioinorganic systems in Chapter 8 has been extended to include methylcobalamin as a methyl transferase and the chemistry of nitric oxide synthase. Chapter 10 on experimental methods and their applications is largely unchanged. Some new problems for each chapter have been added. There is more material than can be covered in depth in one semester, but the organization allows the lecturer to omit or give less coverage to certain areas without jeopardizing an understanding of other areas. It is assumed that the students are familiar with elementary crystal field v vi Preface theory and its applications to electronic spectroscopy and energetics, and concepts of organometallic chemistry, such as the 18-electron rule, 71 bonding and coordinative unsaturation. For the material in the first two chapters, some background from a physical chemistry course would be useful, and familiarity with simple differential and integral calculus is assumed. It is expected that students will consult the original literature to obtain further information and to gain a feeling for the excitement in the field. This experience also should enhance their ability to critically evaluate such work. Many of the problems at the end of the book are taken from the literature, and original references are given; outlines of answers to the problems will be supplied to instructors who request them from the author. The issue of units continues to be a vexing one in this area. A major goal of this course has been to provide students with sufficient background so that they can read and analyze current research papers. To do this and be able to compare results, the reader must be vigilant about the units used by different authors. Energy units are a special problem, since both joules and calories are in common usage. Both units have been retained in the text, with the choice made on the basis of the units in the original work as much as possible. However, within individual sections the text uses one energy unit. Bond lengths are given in angstroms, which are still commonly quoted for crystal structures. The formulas for various calculations are given in the original or most common format, and units for the various quantities are always specified. The author is greatly indebted to all of those whose research efforts have provided the core of the material for this book. The author is pleased to acknowledge those who have provided the inspiration for this book: first, my parents, who contributed the early atmosphere and encouragement; second, Henry Taube, whose intellectual stimulation and experimental guidance ensured my continuing enthusiasm for mechanistic studies. I am only sorry that I did not finish this edition soon enough for Henry to see that I did make the changes he suggested. Finally and foremost, Anna has been a vital force in the creation of this book through her understanding of the time commitment, her comments, criticisms and invaluable editorial assistance in producing the camera-ready manuscript. However, the inevitable remaining errors and oversights are entirely the responsibility of the author. R.B.J. Edmonton, Alberta June 2006 Contents 1 2 3 4 5 Tools of the Trade, 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 Basic Terminology, 1 Analysis of Rate Data, 3 Concentration Variables and Rate Constants, 12 Complex Rate Laws, 15 Complex Kinetic Systems, 15 Temperature Dependence of Rate Constants, 17 Pressure Dependence of Rate Constants, 21 Ionic Strength Dependence of Rate Constants, 24 Diffusion-Controlled Rate Constants, 25 Molecular Modeling and Theory, 28 Rate Law and Mechanism, 31 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Qualitative Guidelines, 31 Steady-State Approximation, 32 Rapid-Equilibrium Assumption, 34 Curtin-Hammett Conditions, 36 Rapid-Equilibrium or Steady-State?, 37 Numerical Integration Methods, 3 8 Principle of Detailed Balancing, 39 Principle of Microscopic Reversibility, 40 Ligand Substitution Reactions, 43 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 Operational Approach to Classification of Substitution Mechanisms, 43 Operational Tests for the Stoichiometric Mechanism, 44 Examples of Tests for a Dissociative Mechanism, 49 Operational Test for an Associative Mechanism, 54 Operational Tests for the Intimate Mechanism, 57 Some Special Effects, 73 Variation of Substitution Rates with Metal Ion, 83 Ligand Substitution on Labile Transition-Metal Ions, 94 Kinetics of Chelate Formation, 100 Stereochemical Change, 114 4.1 4.2 4.3 4.4 4.5 Types of Ligand Rearrangements, 114 Geometrical and Optical Isomerism in Octahedral Systems, 119 Stereochemical Change in Five-Coordinate Systems, 128 Isomerism in Square-Planar Systems, 130 Fluxional Organometallic Compounds, 130 Reaction Mechanisms of Organometallic Systems, 150 5.1 Ligand Substitution Reactions, 150 5.2 Insertion Reactions, 168 5.3 Oxidative Addition Reactions, 177 vii viii Contents 5.4 5.5 5.6 5.7 6 7 8 9 Reductive Elimination Reactions, 188 Reactions of Alkenes, 188 Catalytic Hydrogenation of Alkenes, 195 Homogeneous Catalysis by Organometallic Compounds, 225 Oxidation-Reduction Reactions, 253 6.1 6.2 6.3 6.4 6.5 6.6 Classification of Reactions, 253 Outer-Sphere Electron-Transfer Theory, 256 Differentiation of Inner-Sphere and Outer-Sphere Mechanisms, 273 Bridging Ligand Effects in Inner-Sphere Reactions, 274 Intervalence Electron Transfer, 281 Electron Transfer in Metalloproteins, 285 Inorganic Photochemistry, 292 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Basic Terminology, 292 Kinetic Factors Affecting Quantum Yields, 294 Photochemistry of Cobalt(III) Complexes, 295 Photochemistry of Rhodium(III) Complexes, 301 Photochemistry of Chromium(III) Complexes, 304 Photochemistry of Ruthenium(II) Complexes, 310 Organometallic Photochemistry, 313 Photochemical Generation of Reaction Intermediates, 327 Bioinorganic Systems, 337 8.1. 8.2 8.3 8.4 8.5 8.6 Basic Terminology, 337 Terms and Methods of Enzyme Kinetics, 338 Vitamin B12, 341 A Zinc(II) Enzyme: Carbonic Anhydrase, 356 Enzymic Reactions of Dioxygen, 361 Enzymic Reactions of Nitric Oxide, 373 Kinetics in Heterogeneous Systems, 391 9.1 Gas/Liquid Heterogeneous Systems, 391 9.2 Gas/Liquid/Solid Heterogeneous Systems, 400 9.3 Where is the Catalyst?, 409 10 Experimental Methods, 422 10.1 10.2 10.3 10.4 10.5 10.6 10.7 Flow Methods, 423 Relaxation Methods, 428 Electrochemical Methods, 431 Nuclear Magnetic Resonance Methods, 435 Electron Paramagnetic Resonance Methods, 446 Pulse Radiolysis Methods, 448 Flash Photolysis Methods, 451 Problems, 457 Chemical Abbreviations, 488 Index, 491 Reaction Mechanisms of Inorganic and Organometallic Systems This page intentionally left blank 1 Tools of the Trade This chapter covers the basic terminology and theory related to the types of studies that are commonly used to provide information about a reaction mechanism. The emphasis is on the practicalities of determining rate constants and rate laws. More background material is available from general physical chemistry texts1,2 and books devoted to kinetics.3-5 The reader also is referred to the initial volumes of the series edited by Bamford and Tipper.6 Experimental techniques that are commonly used in inorganic kinetic studies are discussed in Chapter 9. 1.1 BASIC TERMINOLOGY As with most fields, the study of reaction kinetics has some terminology with which one must be familiar in order to understand advanced books and research papers in the area. The following is a summary of some of these basic terms and definitions. Many of these may be known from previous studies in introductory and physical chemistry, and further background can be obtained from textbooks devoted to the physical chemistry aspects of reaction kinetics. Rate For the general reaction the reaction rate and the rate of disappearance of reactants and rate of formation of products are related by In practice, it is not uncommon to define the rate only in terms of the species whose concentration is being monitored. The consequences that can result from different definitions of the rate in relation to the stoichiometry are described below under the definition of the rate constant. 1 2 Reaction Mechanisms of Inorganic and Organometallic Systems Rate Law The rate law is the experimentally determined dependence of the reaction rate on reagent concentrations. It has the following general form: where k is a proportionality constant called the rate constant. The exponents m and n are determined experimentally from the kinetic study and have no necessary relationship to the stoichiometric coefficients in the balanced chemical reaction. The rate law may contain species that do not appear in the balanced reaction and may be the sum of several terms for different reaction pathways. The rate law is an essential piece of mechanistic information because it contains the concentrations of species necessary to get from the reactant to the product by the lowest energy pathway. A fundamental requirement of an acceptable mechanism is that it must predict a rate law consistent with the experimental rate law. Order of the Rate Law The order of the rate law is the sum of the exponents in the rate law. For example, if m = 1 and n = -2 in Eq. (1.3), the rate law has an overall order of -1. However, except in the simplest cases, it is best to describe the order with respect to individual reagents; in this example, first-order in [A] and inverse second-order in [B]. Rate Constant The rate constant, k, is the proportionality constant that relates the rate to the reagent concentrations (or activities or pressures, for example), as shown in Eq. (1.3). The units of k depend on the rate law and must give the right-hand side of Eq. (1.3) the same units as the left-hand side. A simple example of the need to define the rate in order to give the meaning of the rate constant is shown for the reaction From Eq. (1.2), and assuming the rate is second-order in [A], then If the experiment followed the rate of disappearance of A, then the experimental rate constant would be 2k and it must be divided by 2 to get the numerical value of k as defined by Eq. (1.5). However, if the formation of B was followed, then k would be determined directly from the experiment. Tools of the Trade 3 Half-time The half-time, t1/2, is the time required for a reactant concentration to change by half of its total change. This term is used to convey a qualitative idea of the time scale for the reaction and has a quantitative relationship to the rate constant in simple cases. In complex systems, the half-time may be different for different reagents and one should specify the reagent to which the t1/2 refers. Lifetime The lifetime, T, for a particular species is the concentration of that species divided by its rate of disappearance. This term is commonly used in socalled lifetime methods, such as NMR, and in relaxation methods, such as temperature jump. 1.2 ANALYSIS OF RATE DATA In general, a kinetic study begins with the collection of data of concentration versus time of a reactant or product. As will be seen later, this can also be accomplished by determining the time dependence of some variable that is proportional to concentration, such as absorbance or NMR peak intensity. The next step is to fit the concentration-time data to some model that will allow one to determine the rate constant if the data fits the model. The following section develops some integrated rate laws for the models most commonly encountered in inorganic kinetics. This is essentially a mathematical problem; given a particular rate law as a differential equation, the equation must be reduced to one concentration variable and then integrated. The integration can be done by standard methods or by reference to integration tables. Many more complex examples are given in advanced textbooks on kinetics. 1.2.1 Zero-Order Reaction A zero-order reaction is rare for inorganic reactions in solution but is included for completeness. For the general reaction the zero-order rate law is given by and integration over the limits [B] = [B]0 to [B] and t = 0 to t yields 4 Reaction Mechanisms of Inorganic and Organometallic Systems This predicts that a plot of [B] or [B] - [B]0 versus t should be linear with a slope of k. 1.2.2 First-Order Irreversible System Strictly speaking, there is no such thing as an irreversible reaction. It is just a system in which the rate constant in the forward direction is much larger than that in the reverse direction. The kinetic analysis of the irreversible system is just a special case of the reversible system that is described in the next section. For the representative irreversible reaction the rate of disappearance of A and appearance of B are given by The problem, in general, is to convert this differential equation to a form with only one concentration variable, either [A] or [B], and then to integrate the equation to obtain the integrated rate law. The choice of the variable to retain will depend on what has been measured experimentally. One of the concentrations can be eliminated by considering the reaction stoichiometry and the initial conditions. The most general conditions are that both A and B are present initially at concentrations [A]0 and [B]0, respectively, and that the concentrations at any time are defined as [A] and [B]. For this simple case, the rate law in terms of A can be obtained by simple rearrangement to give Then, integration over the limits [A] = [A]0 to [A] and t = 0 to /, gives and predicts that a plot of In [A] versus t should be linear with a slope of -k\. The linearity of such plots often is taken as evidence of a first-order rate law. Since the assessment of linearity is somewhat subjective, it is better to show that the slope of such plots is the same for different initial concentrations of A and that the intercept corresponds to the expected value of In [A]0. Tools of the Trade 5 The equivalent exponential form of Eq. (1.12) is and it is now common to fit data to this equation by nonlinear least squares to obtain k\. In order to obtain the integrated form in terms of B, it is necessary to use the mass balance conditions. For a 1:1 stoichiometry, the changes in concentration are related by At the end of the reaction, [A] = 0 and [B] = [B]^, and substitution of these values into Eq. (1.14) gives After rearrangement of Eq. (1.14) and substitution from Eq. (1.15), one obtains Then, substitution for [A] from Eq. (1.16) into Eq. (1.10) gives an equation that can be integrated over the limits [B] = [B]0 to [B] and t - 0 to t, to obtain This equation also can be obtained by substitution for [A]0 and [A] from Eq. (1.15) and (1.16) into Eq. (1.12) and predicts that a plot of In ([BL - [B]) versus t should be linear with a slope of -kv The half-time, tm, can be obtained from Eq. (1.12) for the condition [A] = [A] - Xem thêm -