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Inorganic Chemistry The Organometallic Chemistry of N‐heterocyclic Carbenes Inorganic Chemistry A Wiley Series of Advanced Textbooks ISSN: 1939‐5175 Editorial Board David Atwood, University of Kentucky, USA Bob Crabtree, Yale University, USA Gerd Meyer, University of Iowa, USA Derek Woollins, University of St. Andrews, UK Previously Published Books in this Series Bioinorganic Chemistry – Inorganic Elements in the Chemistry of Life: An Introduction and Guide, 2nd Edition Wolfgang Kaim, Brigitte Schwederski & Axel Klein; ISBN: 978-0-470-97523-7 Structural Methods in Molecular Inorganic Chemistry David W. H. Rankin, Norbert W. Mitzel & Carole A. Morrison; ISBN: 978‐0‐470‐97278‐6 Introduction to Coordination Chemistry Geoffrey Alan Lawrance; ISBN: 978‐0‐470‐51931‐8 Chirality in Transition Metal Chemistry Hani Amouri & Michel Gruselle; ISBN: 978‐0‐470‐06054‐4 Bioinorganic Vanadium Chemistry Dieter Rehder; ISBN: 978‐0‐470‐06516‐7 Inorganic Structural Chemistry 2nd Edition Ulrich Müller; ISBN: 978‐0‐470‐01865‐1 Lanthanide and Actinide Chemistry Simon Cotton; ISBN: 978‐0‐470‐01006‐8 Mass Spectrometry of Inorganic and Organometallic Compounds: Tools‐Techniques‐Tips William Henderson & J. Scott McIndoe; ISBN: 978‐0‐470‐85016‐9 Main Group Chemistry, Second Edition A.G. Massey; ISBN: 978‐0‐471‐19039‐5 Synthesis of Organometallic Compounds: A Practical Guide Sanshiro Komiya; ISBN: 978‐0‐471‐97195‐5 Chemical Bonds: A Dialog Jeremy Burdett; ISBN: 978‐0‐471‐97130‐6 The Molecular Chemistry of the Transition Elements: An Introductory Course Francois Mathey & Alain Sevin; ISBN: 978‐0‐471‐95687‐7 Stereochemistry of Coordination Compounds Alexander von Zelewsky; ISBN: 978‐0‐471‐95599‐3 For more information on this series see: www.wiley.com/go/inorganic The Organometallic Chemistry of N‐heterocyclic Carbenes Han Vinh Huynh Department of Chemistry National University of Singapore Republic of Singapore This edition first published 2017 © 2017 John Wiley & Sons Ltd 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, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions. The right of Han Vinh Huynh to be identified as the author of this work has been asserted in accordance with law. Registered Offices John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK Editorial Office The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com. Wiley also publishes its books in a variety of electronic formats and by print‐on‐demand. Some content that appears in standard print versions of this book may not be available in other formats. Limit of Liability/Disclaimer of Warranty The publisher and the authors make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of fitness for a particular purpose. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for every situation. In view of ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relat- ing to the use of experimental reagents, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each chemical, piece of equipment, reagent, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. The fact that an organization or website is referred to in this work as a citation and/or potential source of further information does not mean that the author or the publisher endorses the information the organization or website may provide or recommendations it may make. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this works was written and when it is read. No warranty may be created or extended by any promotional statements for this work. Neither the publisher nor the author shall be liable for any damages arising herefrom. Library of Congress Cataloging‐in‐Publication Data Names: Huynh, Han Vinh, 1972– Title: The organometallic chemistry of N-heterocyclic carbenes / Han Vinh Huynh, Department of Chemistry, National University of Singapore. Description: First edition. | Hoboken, NJ : John Wiley & Sons, Inc., 2017. | Series: Inorganic chemistry : a textbook series | Includes bibliographical references and index. Identifiers: LCCN 2016046161 (print) | LCCN 2016046392 (ebook) | ISBN 9781118593776 (cloth) | ISBN 9781118698808 (pdf) | ISBN 9781118698792 (epub) Subjects: LCSH: Organometallic chemistry. | Heterocyclic chemistry. | Carbenes (Methylene compounds) Classification: LCC QD411 .H89 2017 (print) | LCC QD411 (ebook) | DDC 547/.412–dc23 LC record available at https://lccn.loc.gov/2016046161 Cover image: Courtesy of author Cover design by Wiley Set in 10/12pt Times by SPi Global, Pondicherry, India 10 9 8 7 6 5 4 3 2 1 Contents Foreword ix Preface x List of Abbreviations and Definitions xii 1 General Introduction 1 1.1 Definition of Carbenes . .1 1.2 Historical Overview of Carbenes, N‐Heterocyclic Carbenes, and Their Complexes . 3 1.2.1 The Quest for Free Stable Carbenes . .3 1.2.2 The Quest for Carbene Complexes . 11 References. 15 2 General Properties of Classical NHCs and Their Complexes 17 2.1 Stabilization in NHCs (Push‐Pull Effect). 19 2.2 Backbone Differences and Their Implications . 20 2.3 Dimerization of Carbenes. 22 2.4 Nomenclature of N‐Heterocyclic Carbenes. 25 2.5 Electronic Properties of NHCs and Different Electronic Parameters. 29 2.5.1 Tolman’s Electronic Parameter (TEP) and Related Carbonyl Based Systems . 29 2.5.2 Lever’s Electronic Parameter (LEP) . 36 2.5.3 Huynh’s Electronic Parameter (HEP). 38 2.6 Steric Properties of NHCs. 42 2.7 Structural Diversity of NHC Ligands and Their Complexes . 45 2.7.1 Donor‐Functionalized NHCs . 45 2.7.2 Multidentate NHCs . 46 2.7.3 Pincer‐Type NHC Ligands . 47 2.7.4 Tripodal and Macrocyclic Ligands . 48 References. 49 3 Synthetic Aspects 52 3.1 General Routes to Azolium Salts as NHC Precursors . 52 3.1.1 N‐Alkylation of Neutral Azoles. 52 3.1.2 Multicomponent Condensation Reactions . 55 3.1.3 Cyclization of Diamines . 58 3.1.4 Cyclization of Formamidines. 64 3.2 General Routes to Free NHCs. 66 3.2.1 NHCs via Deprotonation of Azolium Salts. 68 3.2.2 NHCs via Reduction of Thiones . 71 3.2.3 NHCs via α‐Elimination of Small Molecules. 73 vi Contents 3.3 General Synthetic Routes to NHC Complexes . 74 3.3.1 Coordination of Free NHCs. 76 3.3.2 Cleavage of Electron‐Rich Entetramines by Transition Metals. 78 3.3.3 In Situ Deprotonation of Azolium Salts in the Presence of Transition Metals. 78 3.3.4 Carbene Transfer Routes . 81 3.3.5 Oxidative Addition of an Azolium Salt to a Low‐Valent Metal Complex . 83 3.3.6 Metal‐Template Synthesis Using Isocyanide Complexes as Precursors . 85 3.3.7 NHC Complexes by Small Molecule Elimination . 89 3.3.8 NHC Complexes by Protonation/Alkylation of Azolyl Complexes . 93 References. 95 4 Group 10 Metal(0)‐NHC Complexes 99 4.1 Nickel(0)‐NHC Complexes. 99 4.1.1 Reactions of Enetetramines and Free NHCs . 99 4.1.2 Reduction of Nickel(II)‐NHC Complexes . 106 4.2 Palladium(0)‐NHC Complexes. 107 4.2.1 Reactions of Free NHCs . 107 4.2.2 Reduction of Palladium(II)‐NHC Complexes. 112 4.3 Platinum(0)‐NHC Complexes. 115 4.3.1 Homoleptic Complexes. 115 4.3.2 Heteroleptic Complexes. 117 References. 120 5 Group 10 Metal(II)‐NHC Complexes 122 5.1 Nickel(II)‐NHC Complexes. 122 5.1.1 Cleavage of Enetetramines and the Free Carbene Route. 122 5.1.2 In Situ Deprotonation of Azolium Salts with Basic Metal Salts . 124 5.1.3 The Silver‐Carbene Transfer Route. 127 5.2 Palladium(II)‐NHC Complexes. 129 5.2.1 Cleavage of Entetramines and the Free Carbene Route. 130 5.2.2 In Situ Deprotonation of Azolium Salts with External Base . 133 5.2.3 The “Palladium Acetate” Route. 135 5.2.4 The Silver‐Carbene Transfer Route. 139 5.2.5 Isomers of Bis(NHC) Palladium(II) Complexes . 143 5.3 Platinum(II)‐NHC Complexes . 150 5.3.1 Cleavage of Entetramines. 151 5.3.2 Cyclization of Isocyanide Complexes. 152 5.3.3 The Oxidative Addition Route . 153 5.3.4 The Free Carbene Route . 157 5.3.5 In Situ Deprotonation of Azolium Salts with External Base . 159 5.3.6 In Situ Deprotonation with Basic Platinum Precursors. 162 5.3.7 Carbene Transfer Reactions. 164 References. 168 6 Group 11 Metal‐NHC Complexes 171 6.1 Copper(I)‐NHC Complexes. 171 6.1.1 The Free Carbene Route . 171 6.1.2 Alkylation of Copper‐Azolate Complexes . 172 Contents vii 6.1.3 In Situ Deprotonation with External Base . 173 6.1.4 In Situ Deprotonation with Basic Copper Precursors. 177 6.1.5 The Silver Carbene Transfer Route. 180 6.1.6 The Copper Powder Route . 182 6.2 Silver(I)‐NHC Complexes . 183 6.2.1 The Free Carbene Route . 183 6.2.2 In Situ Deprotonation with Basic Silver Precursors . 186 6.2.3 Silver‐Carbene Transfer Reactions . 192 6.3 Gold(I)‐NHC Complexes.
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