Landmarks in Organo-Transition Metal Chemistry Profiles in Inorganic Chemistry

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Landmarks in Organo-Transition Metal Chemistry: A Personal View Helmut Werner

From Coelo to Inorganic Chemistry: A Lifetime of Reactions Fred Basolo

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Landmarks in Organo-Transition Metal Chemistry

A Personal View

13 Helmut Werner Institute of Inorganic Chemistry University of Wu¨ rzburg Germany

ISSN: 1571-036X ISBN: 978-0-387-09847-0 e-ISBN: 978-0-387-09848-7 DOI 10.1007/978-0-387-09848-7

Library of Congress Control Number: 2008940859

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Printed on acid-free paper springer.com To Monika, Andreas, and Annemarie And in Loving Memory of Helga Foreword

Organometallic chemistry has witnessed an exponential growth in the past half decade, and today is represented at its frontiers by the second edition of a multi- volume text, two major journals and a plethora of monographs. Helmut Werner, a pioneer who has contributed extensively to the field, now offers us a personal view of important areas of transition metal chemistry. It is unusual in that it provides an historical perspective on some of the more significant developments in this area. He writes both with a great generosity of spirit and an obvious love of the subject. It is evident that both for him, and now his readers, it is not only the science, but also its protagonists, that are the focus of much attention. The first two chapters provide interesting information on Helmut’s family and scientific background, culminating in his Wu¨ rzburg C4 professorship (since 1975); he has mentored 110 Ph.D. students and 40 postdoctoral and visiting scientists. He continues in Chap. 3 to provide an account of the birth of the subject and its development in the nineteenth century. Subsequent chapters deal with metal carbonyls and derived clusters, the discovery of ‘‘sandwich’’ compounds, triple-decker analogues, metal–ethene complexes and their congeners, metal carbenes and carbynes, and finally metal alkyls and aryls. Each chapter has ample references. Helmut’s account is exceedingly modest; from around 800 citations, less than 20 are to his own contributions. The text is well illustrated with formulae, reaction schemes, biographies and photographs. The work is of very high quality and the author is to be congratulated on having given us a very informative and eminently readable and enjoyable book. He clearly has a profound knowledge of the subject and, as one of its leading practitioners, offers his readers a unique overview. I commend it with confi- dence and much enthusiasm.

July 2008 Michael Lappert

vii Series Preface

A renaissance in the field of inorganic chemistry began in the middle of the twentieth century. In the years following the discoveries of A. Werner and S. M. Jørgensen at the turn of the century, the field was relatively inactive. The publication of Linus Pauling’s Nature of the Chemical Bond in 1938 and World War II shortly thereafter launched this renaissance. The war effort required an understanding of the chemistry of uranium and the synthetic actinide elements that were essential to the production of the atom bomb. There was also a need for catalysts to produce rayon, nylon, synthetic rubber, and other new materials for the war effort. As a result, many gifted chemists applied their talents to inorganic chemistry. Profiles in Inorganic Chemistry explores the roles some of the key contributors played in the renaissance and development of the field. Some of the early leaders in this reawakening are now deceased. Pioneers included John Bailar at the University of Illinois, W. Conard Fernelius, at Pennsylvania State University, and Harold Booth at Western Reserve Univer- sity, who with some others, started the important series entitled Inorganic Syntheses. Several inorganic chemistry journals were born, as were various monograph series including the Modern Inorganic Chemistry series of Springer. Geoffrey Wilkinson, who along with E. O. Fischer was the first inorganic chemist since Werner to win the Nobel prize, started his career at Harvard in about 1950 but later that decade moved to the University of London’s Imperial College. By then, Ron Nyholm already was building a strong inorganic pro- gram at the University of London’s University College. Physical and mathematical concepts including group theory gave inorganic chemists new tools to understand bonding, structure, and dynamics of inorganic molecules. Fischer, Wilkinson, and their contemporaries opened up a new subfield, organometallic chemistry, out of which many metal-based catalysts were developed. It was soon realized that many inorganic minerals play essential roles as catalysts in living systems. As a result, another subfield, bioinor- ganic chemistry, was born. The discipline of inorganic chemistry today includes persons of many different walks of life, some creating new material and catalysts, others studying living systems, many pondering environmental concerns

ix x Series Preface with elements such as tin, mercury, or lead, but all focusing on questions outside the normal scope of organic chemistry. Organic chemistry has enjoyed a long history as a great science, both in Europe and the United States. During the past 15 years or so, many of the U.S. contributors have produced interesting autobiographies as part of an American Chemical Society series entitled Profiles in Inorganic Chemistry. There is also, however, a need to have students and scientists of inorganic chemistry understand the motivating forces that lead prominent living inorganic chemists to formulate their ideas. I am grateful that Springer has undertaken to publish this series. These profiles in inorganic chemistry will portray the interesting and varied personalities of leaders who have contributed significantly to the renaissance of inorganic chemistry.

College Station, TX John P. Fackler, Jr. Preface

In the short period between December 1951 and February 1952, two papers appeared which laid the roots for what a few years later was called by Sir Ronald Nyholm The Renaissance of Inorganic Chemistry. Two research groups, working in completely different fields, reported the isolation of a seemingly simple iron compound of the analytical composition FeC10H10 which quite soon became the flagship of a new chemical discipline. It was not the composition of the new compound but its surprising and absolutely unexpected mole- cular structure that stimulated both experimental and theoretical chemists. While in the nineteenth and even in the first half of the twentieth century, it usually took decades before an epoch-making idea such as the cyclic structure of benzene, the tetrahedral configuration of methane, or Alfred Werner’s concept of coordination compounds has been accepted, the synthesis and structural elucidation of bis(cyclopentadienyl)iron FeC10H10 – later called ferrocene – initiated immediately a research avalanche for which there is almost no pre- cedent. In less than 20 years, not only metal compounds containing planar three-, four-, five-, six-, seven- and eight-membered ring systems were prepared, but at the same time also the chemistry of compounds with metal–carbon double and triple bonds was brought to light. The synthetic techniques together with the newly emerging analytical tools, in particular IR and NMR spectro- scopy, offered the opportunity to follow the course of a chemical reaction and thus to understand the mechanism of the process. This also led to the rebirth of the field of homogeneous catalysis, and it is only fair to say that without the pioneering work in the 1950s and early 1960s on transition metal organometallics a number of important industrial processes such as the oxidation of ethene to acetaldehyde by the Wacker reaction, the synthesis of L-Dopa by the Monsanto process or the stereoselective polymerisation of olefins with the Brintzinger-type ansa-metallocenes as catalysts would not have been developed. When I started writing this book, it was exactly 50 years ago that I became acquainted with organo-transition metal chemistry. As an undergraduate at the University of Jena in the former Deutsche Demokratische Republik (‘‘East Germany’’), I attended a course in preparative inorganic chemistry and a junior colleague of Professor Franz Hein took care of the course. It was at this time, that Professor Ernst Otto Fischer visited Hein’s laboratory to inform him that,

xi xii Preface based on his work at the Technische Hochschule in Mu¨ nchen, he was convinced that the unusual ‘‘polyphenylchromium compounds’’, reported by Hein mainly between 1919 and 1931, were indeed sandwich-type complexes. At first, Hein was irritated but after his coworkers proved that Fischer’s proposal was correct, he accepted the new ideas. Since I had the fortune to work for my Diploma thesis with Hein and for my Ph.D. thesis with Fischer, I became automatically involved in the rapid and breath-taking development of modern organometallic chemistry, and I remained caught and fascinated by this subject ever since. The close personal contacts with Hein and Fischer, together with the fact that from 1968 to 1975 I taught coordination chemistry at the University of Zu¨ rich in the same building as Alfred Werner did, also awakened my interest in the history of ‘‘my’’ discipline, and it became a challenge to discover the links between the beginnings in the nineteenth and early twentieth century and our present research activities. This book is neither a textbook nor an autobiography. If I take into account that in recent years organometallic chemistry has not only grown tremendously but also concerns the chemistry of the majority of the elements of the Periodic Table, it is nearly impossible to cover the historical development of the whole field. Therefore, I limited the content to compounds of the transition metals which also happen to be the most important components in homogeneous catalysis. I did my best to consider all the relevant literature and I apologize if I have missed some of the links. It is, of course, a personal view of the discipline and it may well be that some younger scientists in particular feel that I have over-emphasized what had happened in the past. Thus, I answer with a sentence written by the German author Bernhard Schlink in his novel The Reader: ‘‘Doing history means building bridges between the past and the present, observing both banks of the river, taking an active part on both sides.’’

Wu¨ rzburg, Germany Helmut Werner Acknowledgments

I owe the first and particular debt of gratitude to my friends and colleagues Lutz Gade and Adrian Parkins, who not only corrected and polished my written English but, equally important, also made countless valuable comments regard- ing the content of the Chaps. 3–9 and the list of references. They also pushed me ahead in those moments when I felt exhausted or were near to despair about the bulk of the literature. Moreover, I am grateful to numerous colleagues who provided biographical informations and offered useful hints for the manuscript. Taking the risk of being incomplete, I would like to name Anthony Arduengo, Didier Astruc, Wolfgang Beck, Susanne Becker, Martin Bennett, Robert Bergman, Friedrich Bickelhaupt, Marika Blondel-Me´ grelis, Pierre Braunstein, Hans Brintzinger, Fausto Calderazzo, Ernesto Carmona, (the late) Albert Cotton, John Ellis, Christoph Elschenbroich, John Fackler, (the late) Ernst Otto Fischer, Helmut Fischer, Peter Golitz,¨ William Graham, Malcolm Green, Robert Grubbs, Max Herberhold, Wolfgang Herrmann, Volkan Kisaku¨ rek, Michael Lappert, Jack Lewis, Giuliano Longoni, Peter Maitlis, David Milstein, Ullrich Mu¨ ller-Westerhoff, Luis Oro, Peter Pauson, Martyn Poliakoff, Philip Power, Warren Roper, (the late) Max Schmidt, Richard Schrock, Dietmar Seyferth, Gordon Stone, Rudolf Taube, Jim Turner, Egon Uhlig, Wolfgang Weygand, (the late) Nils Wiberg, and Gu¨ nther Wilke. Most of the formulae and schemes were drawn with insight and proficiency by Sabine Timmroth. I give my sincere thanks to her as well as to Cornelia Walter and my former secretary Inge Bra¨ unert, both of whom proved to be computer experts and helped me extensively. Finally, I am indebted to Kenneth Howard from Springer Publish- ers for the pleasant form of cooperation and his unlimited patience during the time of writing. Last but not least, I hope that the authors of present and future textbooks will not miss the past and tell their students about the roots on which the wonderful field of organo-transition metal chemistry rests.

xiii Contents

1 Prologue...... 1 References ...... 7

2 Biographical Sketch ...... 9 2.1 The Years at Home ...... 9 2.2 The First Move: From Mu¨ hlhausen to Jena ...... 19 2.3 The Second Move: From Jena to Munich ...... 24 2.4 The First Years at Mu¨ nchen ...... 26 2.5 From Mu¨ nchen to Pasadena and Back ...... 31 2.6 Crossing the Border: The Years at Zu¨ rich ...... 41 2.7 Back to Germany ...... 50 Biographies ...... 64

3 The Nineteenth Century: A Sequence of Accidental Discoveries..... 69 3.1 The Beginnings of Organometallic Chemistry ...... 69 3.2 Wilhelm Christoph Zeise and the First Transition Metal -Complex ...... 70 3.3 Edward Frankland’s Pioneering Studies ...... 71 3.4 Victor Grignard: The Father of ‘‘Organometallics for Organic Synthesis’’ ...... 74 3.5 Paul Schu¨ tzenberger and Ludwig Mond: The First Metal Carbonyls ...... 75 Biographies ...... 78 References ...... 83

4 Transition Metal Carbonyls: From Small Molecules to Giant Clusters ...... 85 4.1 A Class of ‘‘Peculiar Compounds’’ ...... 85 4.2 The Giant Work of Walter Hieber...... 89 4.3 Hieber and his Followers ...... 93 4.4 Surprisingly Stable: Multiply Charged Carbonyl Metallate Anions ...... 98 4.5 Metal Carbonyl Cations: Not Incapable of Existence ...... 100

xv xvi Contents

4.6 Highly Labile Metal Carbonyls ...... 102 4.7 The Exiting Chemistry of Metal Carbonyl Clusters...... 105 4.8 Otto Roelen and Walter Reppe: Industrial Applications of Metal Carbonyls...... 110 4.9 Biographies ...... 114 References ...... 119

5 A Scientific Revolution: The Discovery of the Sandwich Complexes ...... 129 5.1 The Early Days: Ferrocene...... 129 5.2 The Rivalry of Fischer and Wilkinson ...... 135 5.3 Fischer’s Star: Bis(benzene)chromium ...... 136 5.4 Hein’s ‘‘Polyphenylchromium Compounds’’ ...... 138 5.5 Zeiss and Tsutsui: Hein’s Work Revisited ...... 140 5.6 Wilkinson’s Next Steps...... 145 5.7 From Sandwich Complexes to Organometallic Dendrimers ...... 146 5.8 The Taming of Cyclobutadiene: A Case of Theory before Experiment ...... 150 5.9 The Smaller and Larger Ring Brothers of Ferrocene...... 152 5.10 Sandwiches with P5 and Heterocycles as Ring Ligands . . . . . 154 5.11 Two Highlights from the 21st Century...... 157 5.12 Brintzinger’s Sandwich-Type Catalysts ...... 159 5.13 Woodward and the Nobel Prize ...... 161 Biographies ...... 163 References ...... 169

6 One Deck More: The Chemical ‘‘Big Mac’’ ...... 177 + 6.1 The Breakthrough: [Ni2(C5H5)3] ...... 177 6.2 The Iron and Ruthenium Counterparts ...... 182 6.3 Arene-bridged Triple-Decker Sandwiches ...... 185 6.4 ‘‘Big Macs’’ with Bridging P5,P6 and Heterocycles as Ligands...... 186 6.5 Tetra-, Penta- and Hexa-Decker Sandwich Complexes . . . . . 189 Notes ...... 191 References ...... 191

7 The Binding of Ethene and Its Congeners: Prototypical Metal p-Complexes ...... 195 7.1 From 1827 to the 1930s: In the Footsteps of Zeise ...... 195 7.2 Reihlen’s Strange Butadiene Iron Tricarbonyl...... 199 7.3 Michael Dewar’s ‘‘Landmark Contribution’’ ...... 200 7.4 The Dewar–Chatt–Duncanson Model ...... 202 7.5 An Exciting Branch: Mono- and Oligoolefin Metal Carbonyls...... 204 Contents xvii

7.6 Schrauzer’s Early Studies on Homoleptic Olefin Nickel(0) Complexes...... 208 7.7 Wilke’s Masterpieces and the ‘‘Naked Nickel’’...... 209 7.8 Stone and the Family of Olefin Palladium(0) and Platinum(0) Compounds ...... 214 7.9 Timms’, Fischer’s and Green’s Distinctive Shares ...... 216 7.10 A Recent Milestone: Jonas’ Olefin Analogues of Hieber’s Metal Carbonylates ...... 219 Biographies...... 221 References ...... 228

8 Metal Carbenes and Carbynes: The Taming of ‘‘Non-existing’’ Molecules ...... 235 8.1 The Search for Divalent Carbon Compounds ...... 235 8.2 From Wanzlick’s and Ofele’s¨ Work to Arduengo’s Carbenes ...... 237 8.3 The Breakthrough: Fischer’s Metal Carbenes ...... 238 8.4 The Next Highlight: Fischer’s Metal Carbynes ...... 241 8.5 Ofele’s,¨ Casey’s and Chatt’s Routes to Metal Carbenes . . . . 242 8.6 Lappert’s Seminal Work on Bis(amino)carbene Complexes . 244 8.7 A Big Step: Schrock’s Metal Carbenes and Carbynes ...... 247 8.8 Fischer and His Followers ...... 253 8.9 Using the Isolobal Analogy: Metal Complexes with Bridging Carbenes and Carbynes ...... 256 8.10 The Seemingly Existing CCL2 and Its Generation at Transition Metal Centers ...... 259 8.11 The Congeners of Metal Carbynes with M:E Triple Bonds ...... 263 8.12 The First and Second Generation of Grubbs’ Ruthenium Carbenes ...... 263 8.13 From Metal Carbenes to Open-Shell Metal Carbyne and Carbido Complexes ...... 268 8.14 The Dotz¨ Reaction and the Use of Metal Carbenes for Organic Synthesis ...... 271 8.15 Olefin Metathesis: A Landmark in Applied Organometallic Chemistry ...... 272 8.16 An Extension: Metal Complexes with Unsaturated Carbenes 274 Biographies...... 276 References ...... 284

9 Metal Alkyls and Metal Aryls: The ‘‘True’’ Transition Organometallics ...... 297 9.1 The Extensions of Frankland’s Pioneering Work ...... 297 9.2 Heteroleptic Complexes with Metal–Alkyl and Metal–Aryl Bonds ...... 299 xviii Contents

9.3 Chatt and His Contemporaries ...... 300 9.4 Lappert, Wilkinson and the Isolation of Stable Metal Alkyls und Aryls ...... 304 9.5 An Apparent Conflict: Metal Alkyls and Aryls Containing - and -Donor Ligands...... 310 9.6 Binary Metal Alkyls with M7M Multiple Bonds ...... 314 9.7 The Recent Highlight: Power’s RCrCrR and the Fivefold Cr7Cr Bonding ...... 315 9.8 Novel Perspectives: Metal Alkyls and Aryls Formed by C7H and C7C Activation ...... 317 9.9 Metal Alkyls and Aryls in Catalysis...... 324 References ...... 325

10 Epilogue ...... 337

Index ...... 341 List of Abbreviations

acac acetylacetonate ACM asymmetric cross-metathesis AROCM asymmetric ring-opening cross-metathesis bpy bipyridyl nBu n-butyl tBu tert-butyl COD 1,5-cyclooctadiene COT cyclooctatetraene Cy cyclohexyl DMSO dimethyl sulfoxide dme 1,2-dimethoxyethane dmpe 1,2-dimethylphosphinoethane dppe 1,2-diphenylphosphinoethane dppm 1,2-diphenylphosphinomethane DQ duroquinone en 1,2-ethylenediamin Et ethyl HMPA hexamethylphosphoric triamide Me methyl Ment mentyl Mes mesityl Naph naphthyl NHC N-heterocyclic carbene Ph phenyl iPr isopropyl py pyridine RCM ring-closing metathesis ROMP ring-opening metathesis polymerization tmeda tetramethylethylenediamine THF tetrahydrofuran Tol tolyl Xyl xylyl

xix Synopsis

‘‘Doing history means building bridges between the past and the present, observing both banks of the river, taking an active part on both sides.’’ This sentence, cited from the novel The Reader by Bernhard Schlink, stands for the content of this book. Since the discovery of ferrocene and the sandwich-type complexes, the development of organometallic chemistry took its course like an avalanche and became one of the scientific success stories of the second half of the twentieth century. Based on this development, the traditional boundaries between inorganic and organic chemistry gradually disappeared and a rebirth of the nowadays highly important field of homogeneous catalysis occurred. It is fair to say that despite the fact that the key discovery, which sparked it all off, was made more than 50 years ago, organometallic chemistry remains a young and lively discipline. The author of this book participated in the success story almost from the beginning. As an undergraduate student, he worked for his Diploma Thesis with Franz Hein, one of the key figures of coordination chemistry in Germany between 1920 and 1960, and obtained his Ph.D. in the laboratory of Ernst Otto Fischer, one of the great heroes of organo-transition metal chemistry in the latter half of the twentieth century. He prepared the first borazine metal complexes, isolated the chemical ‘‘Big Mac’’, promoted the concept of metal basi- city, investigated the chemistry of metallacumulenes and, most recently, discovered a new bonding mode for tertiary phosphines, arsines and stibines. He held academic positions at the Technische Hochschule in Munich, the Uni- versity of Zurich and the University of Wu¨ rzburg, and from 1990 to 2001 was the Chairman of a collaborative research center in organometallic chemistry.

xxi