REACTIVE INTERMEDIATE CHEMISTRY

REACTIVE INTERMEDIATE CHEMISTRY

REACTIVE INTERMEDIATE CHEMISTRY Edited by Robert A.Moss Department of Chemistry Rutgers University New Brunswick, NJ Matthew S. Platz Department of Chemistry Ohio State University Columbus, OH Maitland Jones, Jr. Department of Chemistry Princeton University Princeton, NJ A John Wiley & Sons, Inc., Publication

Copyright # 2004 by John Wiley & Sons, Inc. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. Published simultaneously in Canada. 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, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400, fax 978-750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, e-mail: permreq@wiley.com. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services please contact our Customer Care Department within the U.S. at 877-762-2974, outside the U.S. at 317-572-3993 or fax 317-572-4002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print, however, may not be available in electronic format. Library of Congress Cataloging-in-Publication Data: Reactive intermediate chemistry/ edited by Robert A. Moss, Matthew S. Platz, Maitland Jones, Jr. p. cm. Includes index. ISBN 0-471-23324-2 (cloth : acid-free paper) 1. Chemical reaction, Conditions and laws of. 2. Intermediates (Chemistry) 3. Organic reaction mechanisms I. Moss, Robert A. II. Platz, Matthew, III. Jones, Maitland, 1937- QD502.R44 2004 541 0.394 dc22 2003021188 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1

CONTENTS Preface vii PART 1: REACTIVE INTERMEDIATES 1. Carbocations 3 R.A. McClelland 2. Crossing the Borderline Between S N 1andS N 2 Nucleophilic Substitution at Aliphatic Carbon 41 T.L. Amyes, M.M. Toteva, and J.P. Richard 3. Carbanions 69 S. Gronert 4. Radicals 121 M. Newcomb 5. Non-Kekulé Molecules as Reactive Intermediates 165 J.A. Berson 6. Organic Radical Ions 205 H.D. Roth 7. Singlet Carbenes 273 M. Jones, Jr. and R.A. Moss 8. Stable Singlet Carbenes 329 G. Bertrand 9. Triplet Carbenes 375 H. Tomioka 10. Atomic Carbon 463 P.B. Shevlin 11. Nitrenes 501 M.S. Platz v

vi CONTENTS 12. Synthetic Carbene and Nitrene Chemistry 561 M.P. Doyle 13. Nitrenium Ions 593 D.E. Falvey 14. Silylenes (and Germylenes, Stannylenes, Plumbylenes) 651 N. Tokitoh and W. Ando 15. Strained Hydrocarbons: Structures, Stability, and Reactivity 717 K.B. Wiberg 16. Arynes 741 M. Winkler, H.H. Wenk, and W. Sander PART 2: METHODS AND TEMPORAL REGIMES 17. Matrix Isolation 797 T. Bally 18. Nanosecond Laser Flash Photolysis: A Tool for Physical Organic Chemistry 847 J.C. Scaiano 19. The Picosecond Realm 873 E. Hilinski 20. Reactions on the Femtosecond Time Scale 899 J.E. Baldwin 21. Potential Energy Surfaces and Reaction Dynamics 925 B.K. Carpenter 22. The Partnership between Electronic Structure Calculations and Experiments in the Study of Reactive Intermediates 961 W.T. Borden Index 1005

PREFACE The chemistry of reactive intermediates is central to a modern mechanistic and quantitative understanding of organic chemistry. Moreover, it underlies a significant portion of modern synthetic chemistry, and is frequently integral to a molecular view of biological chemistry. In the early 1980s, several books or series focused on the area, including three volumes of Reactive Intermediates by Abramovitch, three volumes of the same title by Jones and Moss, and Reactive Molecules by Wentrup. These authors and editors attempted to survey the entire panoply of reactive intermediates and to highlight their centrality to mechanistic organic chemistry. Over the past 15 years, however, there has been no major attempt to integrate the subject further. Meanwhile, the field has evolved from a product-driven enterprise, in which the primary information was the analysis of reaction products followed by the deduction of probable mechanisms and intermediates. Today, direct observation of the intermediates themselves is more common. In other words, chemists can now look at the beasts themselves, rather than make inferences based upon their footprints. Two main driving forces were at work in directing this change: advances in spectroscopic techniques, including matrix isolation and laser flash photolytic spectroscopy, and rapid progress in theory and computational methods, including the introduction of powerful ab initio and density functional theory. Spectroscopic tools now permit the visualization of reactive intermediates on the microsecond to femtosecond time scales, while theoretical methods enable us to calculate the energies and spectra of the intermediates, the activation energies of their reactions, and many of the features of the energy surfaces upon which those reactions play out. Meanwhile, the emerging field of reaction dynamics promises to create new paradigms for reactions that occur on relatively flat surfaces. Theory has also evolved from being limited to triatomics in the gas phase to a point at which it can accurately simulate the IR and UV vis spectra of polyatomic intermediates in the gas phase and solution, affording corresponding and useful interaction with the new timeresolved and matrix isolation spectroscopic methods. In fact, evolution might be too timid a term for the past two decades of reactive intermediate chemistry; revolution might be more apt. Reactive Intermediate Chemistry is an attempt to provide an updated survey and analysis of the field. We have adopted a three-dimensional approach. Reactive Intermediates are considered by type (e.g., carbocations, radicals, carbanions, carbenes, nitrenes, arynes, etc.); they are examined according to the kinetic realms that vii

viii PREFACE they inhabit, with special emphasis on rapid processes occurring on the nanosecond, picosecond, and femtosecond time scales; and they are described in historical context, connecting the older, product-based, deductive analyses of their chemistry with the contemporary, direct observational and computational approaches. At the same time, the emerging methods involving dynamics and theory are highlighted. We intend Reactive Intermediate Chemistry to serve as a free-standing resource to be used by the entire chemical community. It should be especially useful for first or second year graduate students, for whom it could form the basis of a course in reactive intermediate chemistry. To that end, each chapter features a concluding section devoted to a summary of the current situation, as well as a roll call of near-term problems and probable research directions. A list of key reviews and suggestions for additional reading accompanies each chapter. We offer this book in the hope that it will soon be outdated, with confidence that progress in the field will shortly require a new, or very different edition. ROBERT A. MOSS New Brunswick, NJ MATTHEW S. PLATZ Columbus, OH MAITLAND JONES, JR. Princeton, NJ