Energetics of Organometallic Species NATO ASI Series Advanced Science Institutes Series A Series presenting the results of activities sponsored by the NA TO Science Committee, which aims at the dissemination of advanced scientific and technological knowledge, with a view to strengthening links between scientific communities. The Series is published by an international board of publishers in conjunction with the NATO Scientific Affairs Division A Life Sciences Plenum Publishing Corporation B Physics London and New York C Mathematical Kluwer Academic Publishers and Physical Sciences Dordrecht, Boston and London D Behavioural and Social Sciences E Applied Sciences F Computer and Systems Sciences Springer-Verlag G Ecological Sciences Berlin, Heidelberg, New York, London, H Cell Biology Paris and Tokyo I Global Environmental Change NATO-PCO-DATA BASE The electronic index to the NATO ASI Series provides full bibliographical references (with keywords and/or abstracts) to more than 30000 contributions from international scientists published in all sections of the NATO ASI Series. Access to the NATO-PCO-DATA BASE is possible in two ways: - via online FILE 128 (NATO-PCO-DATA BASE) hosted by ESRIN, Via Galileo Galilei, 1-00044 Frascati, Italy. - via CD-ROM "NATO-PCO-DATA BASE" with user-friendly retrieval software in English, French and German (© WTV GmbH and DATAWARE Technologies Inc. 1989). The CD-ROM can be ordered through any member of the Board of Publishers or through NATO-PCO, Overijse, Belgium. Series C: Mathematical and Physical Sciences - Vol. 367 Energetics of Organometallic Species edited by J. A. Martinho Simoes Departmento de Engenharia Ouimica, Instituto Superior Tecnico, Usbon, Portugal Springer Science+Business Media, B.V. Proceedings of the NATO Advanced Study Institute on Energetics of Organometallic Species Curia, Portugal September 3-13, 1991 Library of Congress cataloging-in-Publication Data NATD Advanced Stuoy Institute an Energetics of Drganometallic Specles (1991 : Cur ia. Portugal) Energetics of organometallic species : proceedings of the NATD Advanced Study Insltute an Energetics of Drganometallic Specles held at Curia. Portugal. September 3-13. 19~1 I edlted by J.A. Martinho Slmăes. p. cm. -- (NATD ASI serles, Serles C. Mathematical and physical sciences ; ne. 367) Includes bibliegraphical references and lneex. ISBN 978-94-010-5088-3 ISBN 978-94-011-2466-9 (eBook) DOI 10.1007/978-94-011-2466-9 1. Organometall ic compounds--Congr~sses. 2. Thermochemlstry- -Congresses, I. Simoes, J. A. Martinhc. II. Title. III. Series. QD410.N355 1991 547'.05'0456--dc20 92-9043 ISBN 978-94-010-5088-3 Printed an acid-free paper AII Rights Reserved © 1992 Springer Science+Business Media Dordrecht Originally published by Kluwer Academic Publishers in 1992 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photo- copying, recording or by any information storage and retrieval system, without written permission from the copyright owner. CONTENTS Foreword vii 1. HISTORICAL PERSPECTIVE OF ORGANOMETALLIC THERMOCHEMISTRY H. A. Skinner 2. COMBUSTION CALORIMETRY OF ORGANOMETALLIC COMPOUNDS G. Pilcher 9 3. ORGANO-f-ELEMENT THERMOCHEMISTRY. IMPLICATIONS FOR REACTIVITY AND BONDING FROM METAL-LIGAND BONDING ENERGETICS M. A. Giardello, W. A. King, S. P. Nolan, M. Porchia, C. Sishta, and T. J. Marks· 35 4. THE ROLE OF BOND ENERGIES IN HYDROCARBON ACTIVATION BY TRANSITION METAL CENTERS W. D. Jones·, R. M. Chin, L. Dong, S. B. Duckett, and E. T. Hessell 53 5. Rh-C BOND DISSOCIATION ENTHALPIES FOR ORGANOMETALLIC DERIVATIVES OF RHODIUM PORPHYRINS B. B. Wayland 69 6. SOLUTION THERMOCHEMISTRY OF ORGANOMETALLIC COMPOUNDS USING PHOTOACOUSTIC CALORIMETRY: ENTHALPIES OF LIGAND EXCHANGE, METAL-LIGAND BONDS, AND METAL-SOLVENT INTERACTIONS T. J. Burkey 75 7. ELECTROCHEMISTRY OF SOME ORGANIC AND ORGANOMETALLIC RADICALS AND THEIR APPLICATION IN THERMOCHEMICAL CYCLES D. D. M. Wayner 95 8. DERIVATIVE CYCLIC VOLTAMMETRY: APPLICATIONS IN THE INVESTIGATION OF THE ENERGETICS OF ORGANOMETALLIC ELECTRODE REACTIONS M. Tilset 109 9. THE USE OF CALORIMETRIC AND SUBLIMATION TECHNIQUES TO STUDY BOND PROPERTIES IN ORGANOMETALLIC COMPOUNDS A. S. Carson 131 10. ESTIMATING ENTHALPIES OF SUBLIMATION OF HYDROCARBONS J. S. Chickos·, D. G. Hesse, and J. F. Liebman 159 vi 11. DERIVATION OF THERMODYNAMIC QUANTITIES FROM KINETIC MEASUREMENTS IN GAS PHASE SILANE CHEMISTRY R. Walsh 171 12. BOND ENTHALPY TRANSFERABILITY - IS IT ACHIEVABLE? J. A. Connor 189 13. ESTIMATES OF THERMOCHEMICAL DATA FOR ORGANOMETALLIC COMPOUNDS J. A. Martinho Simoes 197 14. BONDING AND SOLVATION ENERGETICS FOR ORGANOMETALLIC GAS-PHASE MOLECULES AND IONS: EXPERIMENTAL APPROACHES AND THERMODYNAMIC INSIGHTS D. E. Richardson 233 15. GAS-PHASE ACIDITIES OF TRANSITION-METAL CARBONYL AND TRIFLUOROPHOSPHINE HYDRIDES A. E. Stevens Miller- and T. M. Miller 253 16. BOND STRENGTHS IN TRANSITION METAL CARBONYL ANIONS L. S. Sunderlin and R. R. Squires- 269 17. FUNDAMENTAL GAS PHASE STUDIES OF THE MECHANISM AND THERMOCHEMISTRY OF ORGANOMETALLIC REACTIONS J. L. Beauchamp- and P. A. M. van Koppen 287 18. GUIDED ION BEAM STUDIES OF THE ENERGETICS OF ORGANOMETALLIC SPECIES P. B. Armentrout- and D. E. Clemmer 321 19. A GUIDE TO DENSITY FUNCTIONAL THEORY AND ITS PRACTICAL APPLICATIONS TO THE ENERGETICS OF ORGANOMETALLIC SPECIES T. Ziegler 357 20. THEORETICAL MODELS FOR ORGANOMETALLIC REACTIONS M. R. A. Blomberg-, P. E. M. Siegbahn, M. Svensson, and J. Wennerberg 387 List of Posters and Contributed Oral Presentations 423 List of Participants 425 Subject Index 431 Foreword An overview of modern organometallic thermochemistry, made by some of the most active scientists in the area, is offered in this book. The contents correspond to the seventeen lectures delivered at the NATO ASI Energetics of Organometallic Species (Curia, Portugal, September 1991), plus three other invited contributions from participants of that summer school. These papers reflect a variety of research interests, and discuss results obtained with several techniques. It is therefore considered appropriate to add a few preliminary words, attempting to bring some unity out of that diversity. In the first three chapters, results obtained by classical calorimetric methods are described. Modern organometallic thermochemistry started in Manchester, with Henry Skinner, and his pioneering work is briefly surveyed in the first chapter. The historical perspective is followed by a discussion of a very actual issue: the trends of stepwise bond dissociation enthalpies. Geoff Pilcher, another Manchester thermochemist, makes, in chapter 2, a comprehensive and authoritative survey of problems found in the most classical of thermochemical techniques - combustion calorimetry - applied to organometallic compounds. Finally, results from another classical technique, reaction-solution calorimetry, are reviewed in the third chapter, by Tobin Marks and coworkers. More than anybody else, Tobin Marks has used thermochemical values to define synthetic strategies for organometallic compounds, thus indicating an application of thermochemical data of which too little use has been made so far. Calorimetry is not the only experimental approach to obtain information on the energetics of chemical reactions in solution: equilibrium and kinetic studies have been providing a wealth of important data, as illustrated in chapters 4 and 5. Bill Jones and coworkers, in chapter 4, include a description of the energy profiles of hydrocarbon activation by an unsaturated rhodium complex and discuss the kinetic and thermodynamic selectivities of aromatic C-H activation viii versus ~2-arene coordination. Brad Wayland, in chapter 5, makes a brief survey of the thermochemical results obtained for rhodium (II) porphyrin complexes. One of the highlights of these data is the exothermic carbonyl insertion into a Rh-H bond. The energetics of short-lived species cannot be probed by the traditional calorimetric techniques. Chapter 6, by Ted Burkey, deals with the application of photoacoustic calorimetry to thermochemical studies of transient organometallic unsaturated complexes in solution. Data obtained by the photoacoustic technique can often be coupled to redox potentials of radicals and yield values of heterolytic bond dissociation enthalpies, pK 's, etc.. These relationships are a conveniently summarized in a thermochemical mnemonic included in Dan Wayner's chapter 7. Also included in this chapter are a brief description of photomodulation voltammetry (a technique used to determine redox potentials of transient radicals) and its application to the measurement of bond energies in radical cations. Mats Tilset, in chapter 8, illustrates the use of another electrochemical technique, derivative cyclic voltammetry, to probe the energetics of metal-hydrogen bonds in a number of transition metal-hydride complexes. Ideally, the energetics of chemical bonds should be referred to the perfect gas phase. Solution data are extremely useful, since most important chemical processes occur in solution, and many may provide a good approximation of gas phase data. Unfortunately, in the case of organometallic compounds, the evidence for this last assumption is rather scarce. We know too little about solvation energetics, in particular about sublimation enthalpies. Efforts to measure or to estimate these quantities are addressed in chapters 9 and 10. In chapter 9, by Alexander Carson, the sublimation enthalpies of several organometallic molecules, obtained with a Knudsen cell, are combined with combustion calorimetry results to derive bond enthalpy data. Jim Chickos, Donald Hesse, and Joel Liebman describe, in chapter 10, a method for the estimation of sUblimation enthalpies of hydrocarbons. ix Most results covered by Robin Walsh's contribution, chapter 11, do not require any assumptions regarding solvation enthalpies, since they were obtained in the gas phase. Yet, other assumptions are often necessary to extract thermochemical results from kinetic and equilibrium experiments. A brief description of these methods and hypotheses, illustrated with data for silanes and alkanes, is made in chapter 11. Chapters 12 and 13 are a sort of an interlude in our exploration of organometallic energetics. In chapter 12, Joe Connor introduces and, through a set of selected data, discusses the idea of "bond enthalpy transferability" as appli~d to transition metal organometallic compounds. Although we/~now many of the rules that allow us to predict if two similar bonds in different organic compounds have similar "strengths" (e.g. by comparing the bond orders and the bond lengths), other considerations are required when the exercise is attempted for d-element molecules (e.g. the oxidation state of the metal and the coordination number). The transferability of bond enthalpies is a very relevant issue for predicting the energetics of reactions where no experimental data are available. The estimation of thermochemical data for organometallic compounds is considered in chapter 13, where a critical survey of the methods that have been (or can be) used for that purpose, is made. Several mass spectrometry techniques provided valuable information on metal-ligand bonding energetics in neutral and ionic coordinatively saturated compounds and organometallic fragments. Furthermore, gas phase data such as ionization and electron attachment energies can be compared with their solution counterparts, oxidation and reduction potentials, providing information on solvation energetics. This bridge between gas phase and solution data is analyzed by David Richardson (chapter 14) and illustrated for several organometallic and coordination complexes. It is worth pointing out that Richardson's basic data, ionization and electron attachment energies, were obtained from equilibrium and bracketing studies of ion-molecule reactions in a x Fourier transform ion cyclotron mass spectrometer cell. FTICR, one of the favorite techniques for probing gas phase chemistry and thermochemistry, has also been used by Amy Stevens Miller and Thomas Miller, to determine the gas phase acidities of a number of transition metal-hydride complexes (chapter 15). Trends in these acidities are explained in terms of metal-hydrogen bond dissociation enthalpies and electron affinities of the organometallic fragment radicals. Solvation effects on acidities are also addressed by comparing the gas phase acidities with the solution pK 's of the hydrides. a Some of Amy Stevens Miller's acidity data were obtained by studying ion-molecule reactions in a selected-ion flow tube (SIFT). An apparatus from the same family, a flowing afterglow-triple quadrupole mass spectrometer, was used by Lee Sunderlin and Bob Squires to measure the energy thresholds for CO dissociation in several transition metal carbonyl anions (chapter 16). In some cases, these results were coupled with electron affinity data to yield M-CO stepwise bond dissociation enthalpies in the neutral species. Jack Beauchamp and Petra van Koppen, in chapter 17, review the contribution of several other gas phase techniques (ICR, ion beam and the measurement of kinetic energy release distributions) and theoretical methods to investigate the thermochemistry and the mechanisms of organometallic reactions. The measurement of kinetic energy release distributions is covered in some detail and its application to probe the energetics of large molecules (such as co-enzyme B ) is emphasized. The survey is 1Z illustrated with many examples, and includes a "periodic table" of the trends of atomic metal ion reactivity. Part of the beauty of the experiments by Peter Armentrout and David Clemmer (chapter 18) lies in the simplicity of the systems analyzed. For example, by probing the energetics of "diatomic" species like ML or ML+, they are able to examine the details of M-L lor M+-L) bonding by varying M or L. As many of these species are sufficiently "simple" to be handled by sophisticated theoretical methods, the experimental data can also be used for the calibration of these methods. The guided ion