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Christoph Elschenbroich

Organometallics

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Christoph Elschenbroich

Organometallics

Translated byJosé OliveiraandChristoph Elschenbroich

Third, Completely Revised and Extended Edition

The Author

Prof. Dr. Christoph ElschenbroichFachbereich ChemiePhilipps-Universität MarburgHans-Meerwein-Str.35043 MarburgGermany

Originally published in the German languageby B.G. Teubner as “Christoph Elschenbroich:Organometallchemie 5. Auflage 2005(5th Edition)”.

© B.G. Teubner Verlag/GWV FachverlageGmbH,Wiesbaden 2005

Cover PictureFrom the disordered liquid or gaseous phase amethane molecule approaches a coordinativelyunsaturated highly reactive metal atom and isabout to form an M...CH4 � complex. Oxidativeaddition to yield a hydrido–metal–methyl uniteventually follows. The low-valent metal atommay either be stabilized by � coordination to anallyl or pentadienyl ligand (the red ribbon) ormay be part of a metal surface (the maroon/blue band pattern). If the northwestern C–Hbond is replaced by a C–C bond that is connec-ted to the ligand, the intermolecular C–H acti-vation described in the scenario above becomesinstead intramolecular C–H activation as en-countered in agostic interactions.

All books published by Wiley-VCH are carefullyproduced. Nevertheless, author and publisher do notwarrant the information contained in these books,including this book, to be free of errors. Readers areadvised to keep in mind that statements, data, illustra-tions, procedural details or other items may inadver-tently be inaccurate.

Library of Congress Card No.:applied for

British Library Cataloguing-in-Publication DataA catalogue record for this book is available from theBritish Library

Bibliographic information published byDie Deutsche BibliothekDie Deutsche Bibliothek lists this publication in theDeutsche Nationalbibliografie; detailed bibliographicdata is available in the Internet at <http://dnb.ddb.de>

© 2006 WILEY-VCH Verlag GmbH & Co. KGaA,Weinheim, Germany

All rights reserved (including those of translation intoother languages). No part of this book may be repro-duced in any form – by photoprinting, microfilm, orany other means – nor transmitted or translated intoa machine language without written permission fromthe publishers. Registered names, trademarks, etc.used in this book, even when not specifically markedas such, are not to be considered unprotected by law.

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Printed in the Federal Republic of GermanyPrinted on acid-free paper

ISBN-13: 978-3-527-29390-2ISBN-10: 3-527-29390-6

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Binding J. Schäffer GmbH, Grünstadt1st Reprint 2011

Preface to the Third Edition

Whereas the Second Edition of this book followed only three years after the first,the Third Edition had to wait 14 years to go into print. In a field as flourishing asthat of organometallic chemistry this time span borders to infinity. Since the formercoauthor Albrecht Salzer reconsidered his priorities, Organometallics, 3rd Ed. hasbecome a single author book, a fact that did not speed up the process of preparingit. If the Third Edition does not look completely alien to the reader this must betraced to the invaluable contributions Albrecht made to previous editions and whichhave kept their place in the most recent version.

Another obvious change is the considerably increased volume of the Third Edi-tion, which appears simultaneously with the Fifth Edition of the German version.This growth reflects the impressive advances made in the field to which, amongothers, Nobel prizes awarded to six leading organometallic chemists during the lastdecade attest. Spectacular new achievements include synthetic masterpieces of fun-damental importance, particularly in main-group organoelement chemistry, in-creased attention to the f-block elements as bonding partners to carbon, and the ela-borate use of organotransition-metal complexes in homogeneous catalysis, servinglaboratory-scale preparations as well as industrial processes. Bioorganometallicchemistry has emerged recently as a fascinating new discipline; the complexity ofthis topic often likens it to searching for a needle in a haystack. These highly dispa-rate endeavors are now aided by access to sophisticated, yet routine, methods ofstructural analysis in solution and in the solid state as well as by the rapidly expand-ing use of computational quantum chemistry. Attempts to convey to the reader a lit-tle bit of all of this without a significant page increase would have been doomed tofailure. Admittedly, the often cited excuse put forward by Blaise Pascal more thanthree centuries ago also applies in the present case: “I have made this a rather longletter because I haven’t had time to make it shorter.”

Organometallics 3rd Edition is thought to contain sufficient material for a one-year course meeting twice a week. Compared to previous editions only Chapter 16,which deals with metal-metal bonds and metal-atom clusters, has remained virtuallyunchanged as no principally new perspectives have turned up and a systematic ap-proach to cluster synthesis does not appear to be in sight.

The selection of citations in the running text is based more on utility considera-tions than on historical fidelity. Often a full paper or a review article is more useful

V

Organometallics. 3rd Ed. C. ElschenbroichCopyright � 2006 WILEY-VCH Verlag GmbH & Co. KGaA,WeinheimISBN: 3-527-29390-6

for the reader than the earlier short communication that protects priority interests.For “milestones” of pivotal importance, however, the appropriate primary referencesare generally given. In view of the vast amount of published work, the choice of arti-cles for further reading collected in Appendix A-4 to some extent reflects “carefularbitrariness”. Notwithstanding, the literature accessible through the author indexshould be fairly representative of modern organometallic chemistry.

I am grateful to numerous colleagues who offered valuable hints. Taking the risk ofincompleteness I would like to name A. Ashe III, A. Berndt, M. Bickelhaupt, G. Boche,M. Brookhart, K.H. Dötz, J. Ellis, R.D. Ernst, H. Fischer, G. Frenking, A. Hafner,J. Heck, G. Herberich, R.W. Hoffmann, P. Jutzi, W. v. Philipsborn, K. Pörschke,Ch. Reichardt, P. Roesky, H. Schwarz, W. Siebert, J. Sundermeyer, R. Thauer, W. Uhl,M. Weidenbruch, H. Werner, and N. Wiberg. To ex-coauthor Albrecht Salzer I am in-debted for the splendid cooperation in the past. New formulae and schemes were drawnwith insight and proficiency by Andrea Nagel; the author and subject indexes were con-verted for the English Edition by José Oliveira. More importantly, it is a pleasure toacknowledge the linguistic contributions of José Oliveira, who translated the new sec-tions from the German Fifth Edition and who commented on those parts which I hadtranslated myself. Cooperation with Project Editor Bettina Bems was both efficient andpleasant. Production Manager Hans-Jochen Schmitt must be commended for creatingan attractive layout and for tolerating several last-minute corrections.

Last but not least I thank those colleagues and students who pointed out errors inprevious editions and made suggestions for improvements. Hopefully, this practicewill continue in future.

Marburg, December 2005 Christoph Elschenbroich

VI Preface to the Third Edition

Preface to the First Edition

The present volume is the translation of the Second Edition (1988) of our text “Or-ganometallchemie – Eine kurze Einführung”; corrections and a few results of veryrecent origin were included but otherwise the body was left unchanged.

Can a 500 page treatise on a branch of chemistry still be called “concise”? Onthe other hand, a section of only 20 pages covering transition-metal olefin com-plexes certainly must be regarded as short. This contrast illustrates the dilemma en-countered if one sets out to portray the whole of organometallic chemistry in a sin-gle volume of tolerable size. The book developed from an introductory course (onesemester, about 30 lectures) on organometallic chemistry for students confrontedwith the field for the first time. The material covered is a mixture of indispensiblebasic facts and selected results of most recent vintage. Attempts to systematize orga-nometallic chemistry by relating molecular structures to the number and nature ofthe valence electrons are presented as are applications of organometallics in organicsynthesis and in industrial processes based on homogeneous catalysis.

An apparent omission is the absence of a chapter specifically dealing with orga-nometallic reaction mechanisms. It is our contention, however, that mechanistic or-ganometallic chemistry has not yet reached the stage which would warrant a shortoverview from which useful generalizations could be drawn by the beginner. Note,for example, that even reactions as fundamental as metal carbonyl substitution arecurrently under active investigation, the intermediacy of 17 or 19 valence electronspecies opening up new possible pathways. Interspersed within the text, however,the reader finds several comments and mechanistic proposals ranging from well es-tablished kinetic studies to catalysis loops which at times have more the character ofmnemotechnic devices than of kinetic schemes based on experimental evidence. De-tailed mechanistic considerations should be deferred to the second act of the studyof organometallic chemistry and several textbooks, mainly concentrating on organo-transition metal compounds, offer a wealth of material with which to pursue thisgoal.

We have structured the text in the traditional way – following the periodic tablefor main-group element organometallics and according to the nature of the ligandfor transition-metal complexes – which we find most suitable for an introduction.Apart from the Chapters 16 and 17 (Metal-metal bonds, clusters, catalysis) some-what more specialized material is presented in sections called “Excursions”. Rigor-

VII


ous scientific referencing would be inappropriate in a text of the present scope. Atthe end, a literature survey (300 odd entries) is given which leads the reader to im-portant review articles and key papers, including several classics in the field.Furthermore, in the running text authors names are linked to the facts describedwhereby the form (Author, year) designates the year of the discovery, usually in ashort communication, and the form (Author, year R) the appearance of the respec-tive full paper or review. The complete citation can then be easily retrieved via con-sultation of Chemical Abstracts. A desired side-effect is to familiarize the studentwith author’s names and their fields of endeavor. The many coworkers, who actuallydid the work, may forgive us that only the name of the respective boss is given.

Among our own coworkers who helped to bring this English Edition to comple-tion, the native speakers Pamela Alean (Great Britain, now a resident of Zürich,Switzerland) and James Hurley (USA; resident of Marburg, Germany) stand out.They went a long way to eliminate our worst excesses of “Gerglish”. The bulk ofthe structural formulae was drawn by one of the authors (A.S.) thereby keepingthings in the right perspective and making the book easy to use. Monika Scheld,Marburg, helped with the preparation of the indexes and by checking the cross refer-ences. We are grateful to the editor Dr. Michael Weller and the production managerBernd Riedel (both of VCH Publishers) for a pleasant form of cooperation and theirtoleration of several last-minute changes. Finally, the authors mutually acknowledgetheir unflagging support during the various stages of the enterprise.

Ch. Elschenbroich March A. SalzerMarburg 1989 ZürichGermany Switzerland

VIII Preface to the First Edition

Contents

Preface to the Third Edition VPreface to the First Edition VII

Introduction

1 Milestones in Organometallic Chemistry 3

2 Organoelement Compounds: Classification and ElectronegativityConsiderations 11

3 Energy, Polarity, and Reactivity of the M–C Bond 153.1 Stability of Main-Group Organometallic Compounds 153.2 Lability of Main-Group Organometallic Compounds 17

Excursion 1: Where does our knowledge of M–C bond energies comefrom? 19

Main-Group Organometallics

4 Overview of Preparation Methods 27

5 Organometallic Chemistry of Alkali Metals (Group 1) 335.1 Organolithium Compounds 33

Excursion 2: 6Li and 7Li NMR Spectroscopy of OrganolithiumCompounds 39

5.2 Organometallic Compounds of the Heavier Alkali Metals 50Excursion 3: EPR Spectroscopy of Organoalkali-Metal Compounds 55

6 Organometallic Compounds of Groups 2 and 12 596.1 Organometallic Compounds of the Alkaline-Earth Metals

(Group 2) 596.1.1 Organoberyllium Compounds 596.1.2 Organomagnesium Compounds 626.1.3 Organocalcium, -strontium, and -barium Compounds 70

IX


6.2 Organometallic Compounds of Zn, Cd, Hg (Group 12) 736.2.1 Organozinc Compounds 736.2.2 Organocadmium Compounds 776.2.3 Organomercury Compounds 78

Excursion 4: Organomercury Compounds in vivo 82

7 Organometallic Compounds of the Boron Group (Group 13) 877.1 Organoboron Compounds 877.1.1 Organoboranes 877.1.2 Organoboron–Transition-Metal Compounds 937.1.3 Boron Heterocycles 947.1.4 Polyhedral Boranes, Carbaboranes, and Heterocarbaboranes 99

Excursion 5: 11B NMR Spectroscopy of Organoboron Compounds 1087.2 Organoaluminum Compounds 1107.2.1 OrganoaluminumIII Compounds 1117.2.2 Subvalent Organoaluminum Compounds 1237.3 Gallium, Indium, and Thallium Organyls 1267.3.1 GaIII, InIII, and TlIII Organyls and their Lewis Base Adducts 1267.3.2 GaII,I, InII,I, and TlII,I Organyls 1297.3.3 Thallium in Organic Synthesis 136

8 Organoelement Compounds of the Carbon Group (Group 14) 1398.1 Organosilicon Compounds 1428.1.1 Silicon Organyls of Coordination Number 4 1428.1.2 Organosilicon Compounds with Coordination Numbers 3, 2, and 1 and

Their Subsequent Products 1538.2 Organogermanium Compounds 1718.2.1 Germanium Organyls of Coordination Number 4 1718.2.2 Organogermanium Compounds with Coordination Numbers 3, 2, and 1

and Their Subsequent Products 1758.3 Organotin Compounds 179

Excursion 6: 119Sn Mössbauer and 119Sn NMR Spectroscopy 1798.3.1 Organotin Compounds with Coordination Numbers 6, 5, and 4 and

Their Subsequent Products 1828.3.2 Organotin Compounds with Coordination Numbers 3, 2, and 1 and

Their Subsequent Products 1918.4 Organolead Compounds 1988.4.1 PbIV Organyls 1998.4.2 PbIII, PbII, and PbI Organyls 203

9 Organoelement Compounds of the Nitrogen Group (Group 15) 2119.1 EV Organyls (E = As, Sb, Bi) 2129.1.1 Pentaorganoelement Compounds R5E 2129.1.2 Organoelement Derivatives RnEX5–n 2159.2 EIII Organyls (E = As, Sb, Bi) 217

X Contents

9.2.1 Trisorganoelement Compounds R3E 2189.2.2 Organoelement Derivatives RnEX3–n 2219.3 Chains and Rings Containing E–E Single Bonds 2249.4 E (P, As, Sb, Bi ) as Partners in Multiple Bonds 2299.4.1 E =C(p�–p�) Bonds 2299.4.2 E�C(p�–p�) Bonds 2329.4.3 E =E(p�–p�) Bonds 2359.4.3 E�E((p�–p�)) Bonds 237

10 Organoelement Compounds of Selenium and Tellurium(Group 16) 239

11 Organometallic Compounds of Copper, Silver, and Gold(Group 11) 249

11.1 Copper and Silver Organyls 24911.2 Gold Organyls 262

Organometallic Compounds of the Transition Metals

12 Introduction 27512.1 The 18 Valence Electron (18 VE) Rule 276

Excursion 7: Can the VSEPR concept be applied to transition-metalcomplexes? 282

12.2 Organometallic Catalysis: Some Fundamental Principles 284

13 �-Donor Ligands 29113.1 Preparation of Transition-Metal–Alkyl and –Aryl Compounds 29213.2 Selected Properties of Transition-Metal �-Organyls 29513.2.1 Thermodynamic Stability versus Kinetic Lability 29513.2.2 Interactions of C–H � Bonds with Transition Metals 29913.2.3 Interaction of C–C � Bonds with Transition Metals 30813.2.4 Transition-Metal Perfluorocarbon � Complexes 31213.3 Transition-Metal Organyls In Vivo 315

14 �-Donor/�-Acceptor Ligands 32914.1 Transition-Metal–Alkenyl, –Aryl, and –Alkynyl Complexes 32914.2 Transition-Metal Carbene Complexes 33314.3 Transition-Metal–Carbyne Complexes 35014.4 Metal Carbonyls 35614.4.1 Preparation, Structure, and Properties 35714.4.2 Variants of CO Bridging 36014.4.3 Bonding Properties and Experimental Evidence 36314.4.4 Principal Reaction Types 37214.4.5 Carbonyl Metalates and Carbonyl Metal Hydrides 37514.4.6 Carbonyl Metal Halides 378

XIContents

14.5 Thio-, Seleno-, and Tellurocarbonyl Metal Complexes 37914.6 Isocyanide Complexes (Metal Isonitriles) 381

Excursion 8: Photochemistry of Organometallic Compounds 383

15 �, �-Donor/�-Acceptor Ligands 39515.1 Olefin Complexes 39515.1.1 Homoalkene Complexes 39515.1.2 Heteroalkene Complexes 41315.1.3 Homo- and Heteroallene Complexes 41515.2 Alkyne Complexes 42415.2.1 Homoalkyne Complexes 42515.2.2 Heteroalkyne Complexes 43515.3 Allyl and Enyl Complexes 43615.3.1 Allyl Complexes 43615.3.2 Dienyl and Trienyl Complexes 445

Excursion 9: NMR Spectroscopy of Organometallic Compounds 45115.4 Complexes of the Cyclic �-Perimeters CnHn 47815.4.1 C3R3

+ as a Ligand 47915.4.2 C4H4 as a Ligand 48015.4.3 C5H5

– as a Ligand 48415.4.3.1 Binary Cyclopentadienyl–Metal Complexes 48615.4.3.2 Cyclopentadienyl Metal Carbonyls 50715.4.3.3 Cyclopentadienyl Metal Nitrosyls 51115.4.3.4 Cyclopentadienyl Metal Hydrides 51215.4.3.5 Cyclopentadienyl Metal Halides and Their Products 51415.4.3.6 Special Applications of Metallocene Derivatives 51815.4.4 C6H6 as a Ligand 52815.4.4.1 Bis(arene)metal Complexes 52815.4.4.2 Arene Metal Carbonyls 53915.4.4.3 Other Complexes of the Type (�6-Arene)MLn 54315.4.4.4 Benzene Cyclopentadienyl Complexes 544

Excursion 10: Organometallic Chemistry of Fullerenes 54615.4.5 C7H7 as a Ligand 54915.4.6 C8H8 as a Ligand 55515.5 Metal–�-Complexes of Heterocycles 56015.5.1 S, Se, and Te Heterocycles 56115.5.2 N Heterocycles 56115.5.3 P and As Heterocycles 56415.5.4 B Heterocycles 57015.5.5 Metallaheterocycles 576

16 Metal–Metal Bonds and Transition-Metal-Atom Clusters 57916.1 Formation of and Criteria for Metal–Metal Bonds 57916.2 Dinuclear Clusters 58416.3 Trinuclear Clusters 587

XII Contents

16.4 Tetranuclear Clusters 588Excursion 11: Structure and Bonding in Clusters – The IsolobalAnalogy 590

16.5 Approaches to Systematic Cluster Synthesis 59516.6 Pentanuclear and Higher Clusters 599

17 Organometallic Chemistry of the Lanthanoids and Actinoids 60917.1 Comparative Considerations 61017.2 Tour of the Ligands 614

18 Organometallic Catalysis in Synthesis and Production 63518.1 Olefin Isomerization 63518.2 C–C Coupling Reactions 63718.2.1 Allylic Alkylation 638

Excursion 12: Asymmetric Allylic Alkylation 64018.2.2 The Heck Reaction 64218.2.3 The Suzuki Reaction 64518.2.4 The Stille Reaction 64918.2.5 The Sonogashira Reaction 65118.2.6 Hydrocyanation 65218.3 C–Heteroatom Coupling 65418.3.1 Amination of Arenes 65418.3.2 Hydroamination 65718.3.3 Hydroboration 65818.3.4 Hydrosilation 65918.4 Olefin Oxidation 66018.5 Water-Gas-Shift and Fischer–Tropsch Reactions 66518.6 Carbonylation of Alcohols 66918.7 Hydrogenation of Alkenes 67018.8 Hydroformylation 67618.9 Reppe Syntheses 67918.10 Alkene and Alkyne Metathesis 68218.10.1 Alkene Metathesis 68218.10.2 Alkyne Metathesis 68818.10.3 Alkene–Alkyne Metathesis 68918.11 Oligomerization and Polymerization of Alkenes and Alkynes 69118.11.1 Oligomerizations 69218.11.2 Olefin Polymerization 69518.11.2.1 Polyethylene 69718.11.2.2 Polypropylene 69918.11.2.3 Homo- and Copolymerization; Functionalized Olefins, Cycloolefins,

and Diolefins 70618.11.2.4 Non-Group 4 Catalysts 70918.11.2.4.1 Lanthanoidocene Catalysts 70918.11.2.4.2 The Iron Age of Olefin Polymerization 710

XIIIContents

Appendix 717A-1 Redox Reagents in Organometallic Chemistry 717A-2 Nomenclature of Organometallic Compounds 721A-3 Abbreviations and Symbols 726A-4 Literature 732

Author Index 761Subject Index 783

XIV Contents

Sir Edward Frankland (1825–1899)pioneer and inventor of the term ‘organometallic’,around 1849, the year he earned his PhDfrom the University of Marburg.[Reproduced with permission from the Royal Societyof Chemistry]

Introduction

1


1Milestones in Organometallic Chemistry

1760 The cradle of organometallic chemistry is a Paris military pharmacy. It isthere that Cadet works on invisible inks based on cobalt salt solutions. Fortheir preparation, he uses cobalt minerals that contain arsenic.

1827 Zeise’s salt, Na[PtCl3C2H4]: the first olefin complex

1840 R. W. Bunsen continues the study of cacodyl compounds, which he names“alkarsines”. The weakness of the As–As bond in molecules of the typeR2As–AsR2 leads to a profusion of derivatives such as (CH3)2AsCN, whosetaste (!) is checked by Bunsen.

1849 E. Frankland, a student of Bunsen at Marburg, attempts the preparation of an“ethyl radical” (cacodyl was also taken to be a radical).

Frankland is admirably skilled in the manipulation of air-sensitive com-pounds. He uses hydrogen gas as a protective atmosphere!

1852 Frankland prepares the important alkylmercury halides:

additionally: (C2H5)4Sn, (CH3)3B (1860).

In the following years, alkyl-transfer reactions with R2Hg and R2Zn servein the synthesis of numerous main-group organometallic compounds.

3


Frankland also introduced the concept of valency (“combining power”) andthe term “organometallic”.

1852 C. J. Löwig and M. E. Schweizer in Zürich first prepare (C2H5)4Pb fromethyl iodide and Na/Pb alloy. In a similar manner, they also obtain(C2H5)3Sb and (C2H5)3Bi.

1859 W. Hallwachs and A. Schafarik generate alkylaluminum iodides:

1863 C. Friedel and J. M. Crafts prepare organochlorosilanes:

1866 J. A. Wanklyn develops a method for the synthesis of halide-freealkylmagnesium compounds:

1868 M. P. Schützenberger obtains [Pt(CO)Cl2]2, the first metal–carbonyl complex.

1871 D. I. Mendeleev uses organometallic compounds as test cases for his periodictable. Example:

Known: Predicted: Found:Si(C2H5)4 Eka-Si(C2H5)4 Ge(C2H5)4 (C.Winkler, 1887)

d = 0.96 d = 0.99Sn(C2H5)4 bp: 160 �C bp: 163.5 �C

1890 L. Mond: Ni(CO)4, first binary metal carbonyl, used in a commercial processfor refining nickel. Mond is the founder of the English company ICI (ImperialChemical Industries) as well as a renowned collector and patron of the arts.

1899 P. Barbier replaces Zn by Mg in reactions with alkyl iodides:

The reaction is explored in more detail by Barbier’s student V. Grignard(Nobel Prize 1912 shared with P. Sabatier). Although less sensitive thanZnR2, RMgX is a more potent alkyl-group-transfer reagent.

1901 L. F. S. Kipping prepares (C6H5)2SiO, suspects its high molecularity, yet callsthe material diphenylsilicone.

4 1 Milestones in Organometallic Chemistry

1909 W. J. Pope: formation of (CH3)3PtI, the first �-organotransition-metalcompound.

1909 P. Ehrlich (developer of chemotherapy, Nobel Prize 1908) introducesSalvarsan for the treatment of syphilis.

1917 W. Schlenk: alkyllithium reagents through transalkylation.

1919 F. Hein synthesizes polyphenylchromium compounds, now known to besandwich complexes, from CrCl3 and PhMgBr.

1922 T. Midgley and T. A. Boyd introduce Pb(C2H5)4 as an antiknock additive ingasoline.

1927 A. Job and A. Cassal prepare Cr(CO)6.

1928 W. Hieber inaugurates his systematic study of metal carbonyls:

1929 F. A. Paneth generates alkyl radicals through pyrolysis of PbR4; radicalidentification by means of their ability to cause the transport of a metallicmirror. Paneth thus reaches the goal set by Frankland in 1849.

1930 K. Ziegler encourages more extensive use of organolithium compounds insynthesis by developing a more simple preparation:

1931 W. Hieber prepares Fe(CO)4H2, the first transition-metal–hydride complex.

1935 L. Pauling provides a valence-bond description of the bonding in Ni(CO)4.

1938 O. Roelen discovers hydroformylation (the oxo process).

1939 W. Reppe starts work on the transition-metal catalyzed reactions of acetylenes.

1943 E. G. Rochow:This “direct synthesis” triggers the large-scale production and use ofsilicones. Preliminary work by R. Müller (Radebeul, near Dresden) wasinterrupted by World War II.

51 Milestones in Organometallic Chemistry

1951 M. J. S. Dewar proposes a bond theory for complexes of alkenes withtransition metals (elaborated on by J. Chatt and L. A. Duncanson, 1953).

1951 P. Pauson (UK) and S. A. Miller (USA) obtain ferrocene, (C5H5)2Fe, thefirst sandwich complex.

1952 H. Gilman prepares LiCu(CH3)2, thereby establishing a now syntheticallyimportant class of compounds, the organocuprates.

1953 G. Wittig develops a new synthesis of olefins from phosphonium ylides andcarbonyl compounds (Nobel Prize 1979).

1955 E. O. Fischer: rational synthesis of bis(benzene)chromium, (C6H6)2Cr.

1955 K. Ziegler, G. Natta: polyolefins from ethylene or propylene in a low-pressure process employing mixed metal (transition-metal halide/AlR3)catalysts (Nobel Prize 1963).

1956 H. C. Brown: hydroboration (Nobel Prize 1979).

1959 J. Smidt, W. Hafner: preparation of [(C3H5)PdCl]2, installation of the field of�-allyl–transition-metal complexes.

1959 R. Criegee: stabilization of cyclobutadiene by complexation in[(C4Me4)NiCl2]2, thereby verifying a prediction by H. C. Longuet-Higginsand L. Orgel (1956).

1960 M. F. Hawthorne prepares the icosahedral closo-borane dianion [B12H12]2–,predicted by H. C. Longuet-Higgins (1955).

1961 D. Crowfood Hodgkins: Based on X-ray crystal-structure analysis,vitamin B12 coenzyme contains a Co–C bond (Nobel Prize 1964).

1963 USA: Reports of the dicarba-closo-borane C2B10H12 are issued by severalindustrial laboratories.

1963 L. Vaska: trans-(PPh3)2Ir(CO)Cl reversibly binds O2.

1964 E. O. Fischer: (CO)5WC(OMe)Me, the first carbene complex.

1965 G. Wilkinson, R. S. Coffey: (PPh3)3RhCl acts as a homogeneous catalyst inthe hydrogenation of alkenes.

1965 R. Petit: Synthesis of (C4H4)Fe(CO)3, stabilization of the antiaromaticcyclobutadiene through complexation.


1965 J. Tsuji discovers the first Pd-mediated C–C coupling.

1967 G. Wilkinson stabilizes the highly reactive carbon monosulfide in therhodium complex (Ph3P)2Rh(Cl)CS.

1968 A. Streitwieser : preparation of uranocene, U(C8H8)2.

1969 P. L. Timms: synthesis of organotransition-metal complexes by means ofmetal-atom–ligand-vapor cocondensation.

1969 A. E. Shilov discovers the PtII-catalyzed H/D exchange of alkenes withsolvent protons in homogeneous solution, thereby laying the foundationfor the now flourishing field of C–H activation.

1970 G. Wilkinson: kinetically inert transition-metal alkyl compounds by blocking�-elimination.

1972 R. F. Heck discovers the palladium-catalyzed substitution of vinylic H atomswith aryl, benzyl, and styryl halides which he subsequently develops intoone of the most important named reactions in organometallic chemistry.

1972 H. Werner : [(C5H5)3Ni2]+, the first triple-decker sandwich complex.

1973 E. O. Fischer: I(CO)4Cr(CR), the first carbyne complex.

1973 Nobel Prize to E. O. Fischer and G. Wilkinson.

1976 Nobel Prize to W. N. Lipscomb: theoretical and experimental clarification ofthe structure and bonding in boranes.

1976 M. F. Lappert opens the field of main-group-element dimetallenes with thesynthesis of [(Me3Si)2CH]2Sn=Sn[CH(SiMe3)2]2.

1979 H. Köpf and P. Köpf-Maier discover the cancerostatic action of titanocenedichloride, (C5H5)2TiCl2.

1980 H. Bock: synthesis and studies of silabenzene C5H5SiH in the gas phase(matrix isolation: G. Maier, 1982).

1981 R. West: (Mes)2Si=Si(Mes)2, the first stable compound with a silicon–silicondouble bond.

1981 Nobel Prize to R. Hoffmann and K. Fukui: semiempirical MO concepts in aunified discussion of the structure and reactivity of inorganic, organic, andorganometallic molecules (isolobal analogy).


1981 G. Becker synthesizes tBu-C�P, the first compound with acarbon–phosphorus triple bond.

1982 R. G. Bergman: intermolecular reactions of organotransition-metalcompounds with alkanes (C–H activation).

1985 W. Kaminsky and H. Brintzinger introduce the “chiral zirconocenedichloride/methyl alumoxane (MAO)” as a new generation of catalysts forthe isotactic polymerization of propene.

1986 R. Noyori develops the catalytic, enantioselective addition of organozincreagents ZnR2 to carbonyl compounds.

1989 P. Jutzi: preparation of decamethylsilicocene, Cp*2Si.

1989 H. Schnöckel synthesizes AlCl(solv), which he uses in the development ofthe organometallic chemistry of monovalent aluminum, for example,Cp*4Al4 (1991).

1991 W. Uhl: synthesis of anionic [i-Bu12Al12]2–, an icosahedral closo-alane.

1993 D. Milstein reports the insertion of Rh into a C–C bond (C–C activation).

1994 S. Harder prepares the lightest metallocene, the lithocene anion[Li(C5H5)2]–.

1995 A. H. Zewail studies M–M and M–CO bond cleavage in Mn2CO10 in amolecular beam on the femtosecond timescale (10–15 s) by means ofa pulsed laser (Nobel Prize 1999).

1995 G. Kubas synthesizes the first �-complex of a silane and studies thetautomerism with the hydridosilyl form:

This observation contributes to the understanding of the mechanism of C–Hactivation.

1996 P. P. Power prepares the first germyne complex with amolybdenum–germanium triple bond.

1997 C. C. Cummins: the C atom as the ultimate ligand in an organometalliccompound: [(R2N)3MoC]–, a “carbon complex”.


1997 G. M. Robinson synthesizes the salt Na2[ArGaGaAr] and postulates agallium–gallium triple bond for the diaryldigallyne anion. (Extreme exampleof the steric protection of a labile structural element!)

1999 W. Ho monitors the dehydrogenation of single ethylene molecules ona Ni(110) surface by means of scanning tunneling microscopy (STM) andinelastic electron tunneling spectroscopy (IETS).

2001 Nobel Prize to K. B Sharpless, W. S. Knowles, and R. Noyori for pioneeringwork in the field of enantioselective catalysis.

2004 E. Carmona reports on decamethyldizincocene Cp*Zn–ZnCp*, the firstmolecule with an unsupported ZnI–ZnI bond.

2005 A. Sekiguchi fully characterizes R–Si�Si–R, the first compound with asilicon–silicon triple bond.

2005 Nobel Prize to Y. Chauvin, R. R. Schrock, and R. H. Grubbs for mechanisticand applications-oriented studies on catalysts active in olefin metathesis.


2Organoelement Compounds:Classification and Electronegativity Considerations

Organometallic compounds (metal organyls, organometallics) are characterized bydirect, more or less polar bonds M�+–C�– between metal and carbon atoms. In manyrespects, the organic chemistry of the elements B, Si, P, As, Se, and Te resemblesthe chemistry of their metallic homologues. Therefore, the term “organoelementcompounds” is used occasionally in order to include the aforementioned non- andsemimetals. A convenient classification of organometallic compounds is based onthe bond type:

In accordance with the similar electronegativities of carbon, EN(C), and hydrogen,EN(H), the ionic/covalent division of organoelement compounds bears a strong re-semblance to the classification of element hydrides.

11


The designations �, �, and � bond are defined as follows:

To evaluate the polarity of a bond, the electronegativity difference between theneighboring atoms is usually employed. The electronegativity values in the table be-low are based on the Pauling thermochemical method of determination.

Electronegativity values according to Pauling

Source: L. Pauling, The Nature of the Chemical Bond, 3rd Ed., 1960, Ithaca; A. L. Allred, J. Inorg. Nucl.Chem. 1961, 17, 215.

The concept of electronegativity is complex, not only with respect to the methodof derivation of the diverse electronegativity scales, but also to the choice of ascale that is suitable for a particular problem (Huheey, 1995). In this section, onlya few aspects that are important for application in organometallic chemistry are dis-cussed.

12 2 Organoelement Compounds: Classification and Electronegativity Considerations

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