Tải bản đầy đủ

Titanium and zirconium in organic synthesis 2002 marek

Titanium and Zirconium in Organic Synthesis. Edited by Ilan Marek
Copyright c 2002 Wiley-VCH Verlag GmbH & Co. KGaA
ISBNs: 3-527-30428-2 (Hardback); 3-527-60067-1 (Electronic)

Titanium and Zirconium
in Organic Synthesis
Edited by Ilan Marek


Titanium and Zirconium in Organic Synthesis. Edited by Ilan Marek
Copyright c 2002 Wiley-VCH Verlag GmbH & Co. KGaA
ISBNs: 3-527-30428-2 (Hardback); 3-527-60067-1 (Electronic)

Further Reading from Wiley-VCH

Ricci, A. (Ed.)

Modern Amination Methods
2000. ISBN 3-527-29976-9

Krause, N. (Ed.)


Modern Organocopper Chemistry
2001. ISBN 3-527-29773-1

Yamamoto, H. (Ed.)

Lewis Acids in Organic Synthesis
A Comprehensive Handbook in Two Volumes
2000. ISBN 3-527-29579-8

Beller, M., Bolm, C. (Eds.)

Transition Metals for Organic Synthesis
Building Blocks and Fine Chemicals
1998. ISBN 3-527-29501-1


Titanium and Zirconium in Organic Synthesis. Edited by Ilan Marek
Copyright c 2002 Wiley-VCH Verlag GmbH & Co. KGaA
ISBNs: 3-527-30428-2 (Hardback); 3-527-60067-1 (Electronic)

Titanium and Zirconium
in Organic Synthesis
Edited by Ilan Marek


Titanium and Zirconium in Organic Synthesis. Edited by Ilan Marek
Copyright c 2002 Wiley-VCH Verlag GmbH & Co. KGaA
ISBNs: 3-527-30428-2 (Hardback); 3-527-60067-1 (Electronic)

Editor:
Prof. Ilan Marek
Department of Chemistry
Technion ± Israel Institute of Technology
Haifa 32000
Israel

This book was carefully produced. Nevertheless, editor, authors and publisher
do not warrant the information contained
therein to be free of errors. Readers are


advised to keep in mind that statements,
data, illustrations, procedural details or
other items may inadvertently be inaccurate.

Library of Congress Card No.: applied for
A catalogue record for this book is available
from the British Library.
Die Deutsche Bibliothek ±
CIP Cataloguing-in-Publication-Data
A catalogue record for this publication is
available from Die Deutsche Bibliothek.
c WILEY-VCH Verlag GmbH,
D-69469 Weinheim
(Federal Republic of Germany), 2002
All rights reserved (including those of
translation in other languages). No part of
this book may be reproduced in any form ±
by photoprinting, microfilm, or any other
means ± nor transmitted or translated into
machine language without written permission from the publishers. Registered names,
trademarks, etc. used in this book, even
when not specifically marked as such, are
not to be considered unprotected by law.
Printed in the Federal Republic of Germany.
Printed on acid-free paper.
Typesetting Hagedorn Kommunikation,
Viernheim, Germany
Printing Strauss Offsetdruck GmbH,
MoÈrlenbach
Bookbinding J. SchaÈffer GmbH & Co. KG,
GruÈnstadt
ISBN

3-527-30428-2


Titanium and Zirconium in Organic Synthesis. Edited by Ilan Marek
Copyright c 2002 Wiley-VCH Verlag GmbH & Co. KGaA
ISBNs: 3-527-30428-2 (Hardback); 3-527-60067-1 (Electronic)

Foreword
The time is apt for synthetic chemists to fully enter the world of organozirconium
and organotitanium chemistry. While Pd, Cu, and Ni catalyzed reactions have been
embraced by synthetic practitioners and the long-standing hydrogenation catalysts,
Rh and Ru, are being increasingly accepted for other uses, Zr and Ti reagents,
with, of course, the notable exceptions of the polymerization catalysts, have not
broken the barrier to widespread application for small molecule synthesis, especially in industry. Aside from reagent availability and sensitivity, perhaps part of
the explanation lies in the inability of the chemist trained in the Corey retrosynthetic analysis mold to adapt their thinking to what are, compared to more classical
paths, the less rational dissection based on organozirconium and organotitanium
reactions. This volume, edited with dedication to content and care in presentation
by Ilan Marek and encompassing forefront topics by the most active researchers in
the field will, with reading and revisit, provide persuasion to irreversibly change
this perspective and to traverse the borders to new exciting synthetic chemistry.
In a masterly introductory chapter, Negishi and Huo set the stage for zirconocene chemistry, providing historical aspects which chronologically attribute the various discoveries by numerous chemists in this field, including the major contributions from the Negishi laboratories and the systematic studies of hydrozirconation
by Schwartz and his students, since the first report in 1954 of the structure of
Cp2ZrCl2 by Wilkinson. In a innovative series of tabulated highlights, Negishi
and Huo teach the generalizations and reactivity patterns of Zr(IV) and Zr(II),
the most synthetically useful species, and provide X-ray structural and mechanistic
insight wherever available. They also delineate what is currently feasible with Zr
reagents (e. g. transmetallation) and where additional work may lead to new synthetic value (e. g. radical and photochemical reactions). The defined subsections
(e. g. p-Complexation, Carbonylation, s-Bond Metathesis) allow the reader, both expert and novice, to quickly focus on given areas and easily pursue the relevant
chapter for details. The discussion is concise, mechanistically friendly to the synthetic organic chemist, and, whenever appropriate, comparative (e.g effect of Li,
Mg, Zn, and Al in Zr-catalyzed cyclic carbometallation) thus providing a most useful overview of the topics in this volume.
Takahashi and Li (Chapter 2) focus on the preparation and reactions of zirconacyclopentadienes which, for a quarter of a century since their discovery in 1974 by

V


VI

Foreword

Watt and Drummond, were considered to be inert for C-C bond forming reactions.
However, by the expedient of transmetallation to Cu, Ni, Zn, Li, and Al, methodologies for the stereoselective synthesis of olefins and dienes, as well as unusual heterocycles, aromatics and their ring-annulated products are now available which are
beginning to make impact on material science, e. g. synthesis of pentacenes and
polyphenylenes. Takahashi and Li provide evidence that, with further developments in transmetallation and handling the zirconacycles outside of the Schlenk
tube techniques, synthetic utility will increase and new catalytic reactions will be
developed.
In a fascinating chapter (Chapter 3) with considerable promise for synthetic
chemists, Dixon and Whitby describe the insertion of carbenoids (a-halo-a-lithio
species) into organozirconocenes. Setting the appropriate background of the mechanistically analogous rapid insertion of the isoelectronic carbon monoxide and
alkylisonitrile (which complements the Pauson-Khand reaction), the authors systematically review the status of various halocarbenoids from which result synthetic
methods for functionalized olefins, dienes, dienynes, among other organic molecules. The focus on the most extensively studied insertion of allyl carbenoids
into zirconacycles leads to illustrations of tandem processes with initial demonstration of application to natural product synthesis. Appropriate mechanistic speculation on very new processes suggests that this area offers a promising future for
synthesis.
Lipshutz, Pfeiffer, Noson, and Tomioka (Chapter 4) assume the formidable task
of providing a seven-year update of the advances in the hydrozirconation±transmetallation sequence in organic synthesis. At the outset, as expected from an experimental organic group, a discussion of practical aspects of the commercial
CpZr(H)Cl (Schwartz reagent) are presented and, similarly graciously, the difficulties of control of its reactions in appropriate air- and moisture-free atmosphere are
stressed. Similarly expected is the emphasis on synthetic utility of the reactions,
which involve acyl- and allylzirconocenes and, most prominently, the cross-coupling reactions following transmetallation to Cu, Zn, B, and Ni. This survey invites
the chemist to view anew various processes which were learned retrosynthetically
by more traditional pathways, e. g. carbocyclization, equivalency of acylzirconocenes
as acyl anions and demonstrates in instructive schemes the impact that not only
zirconium chemistry but other transition metal-catalyzed reactions have made on
bioactive molecule and natural product synthesis. More specialized systems, e. g.
vinyl tellurides, selenides, and phosphonates, are also effectively prepared. Recent
reports (e. g. reduction of tertiary amide to aldehyde using the Schwartz reagent)
and the promise of catalytic hydrozirconation will continue to fuel this area in
the future.
In useful and minor overlap with Chapters 3 and 4, the review (Chapter 5) on
progress in acylzirconocene chemistry by Hanzawa points to the extensive mechanistic investigation of this class of Zr reagents but lack of synthetic application.
Following discussion of the stability and ease of handling of the RCOZr(Cl)Cp2
reagent, its umpolung reactivity is delineated in general synthetic procedures for
a-ketols, a-aminoketones (including Bronsted acid catalysis), selective 1,2-addition


Foreword

products of enones (including the first results of demonstration of enantioselectivity). The closing sections on Pd- and Cu- catalyzed reactions of acylzirconocenes to
give ketones appear to promise scope and the use of unsaturated acylzirconocenes
as ketone a,b-dianion equivalents offer stimulus that the promise of this area may
be imminent.
With Chapter 6 by Hoveyda concerned with a critical review of chiral Zr catalysts
in enantioselective synthesis, synthetic utility goes into high gear. A plethora of
successful or highly promising asymmetric reactions (inter alia, inter- and intramolecular alkylations, kinetic resolution of unsaturated exocyclic allylic ethers,
hydrocyanation, Strecker, aldol, Mannich, and cycloaddition reactions) attest to
the excitement in this young area of research. Synthetic applications abound
already from simple functionalized chiral pieces to heterocycles and complex
macrocyclic natural products. Connections to other modern protocols, e. g. ringclosing metathesis, provide additional innovative synthetic value. In a unique
feature of this chapter, Hoveyda makes the admirable effort to delineate, for
each topic, comparison with catalytic asymmetric reactions, which are promoted
by non-Zr catalysis. Thus the preparation of optically pure acyclic allylic (Sharpless
epoxidation) and homoallylic (Yamamoto, Keck, Tagliavini protocols) alcohols are
contrasted and compared. A provocative section on Zr-catalyzed enantioselective
C-H bond formation closes this review of a field for which more practical and
rapid developments are anticipated.
gem-Metallozirconocenes, a field that sprung forth from the discovery of the
Tebbe reagent and was fueled by the bimetallic Al ± Zr (Schwartz) and Zn ± Zr
(Knochel) contributions is reviewed (Chapter 7) by Dembitsky and Srebnik with
the major concentration being given to the chemistry of bimetallic Al, B, Li, Ga,
Ge, Sn, Zn, and Zr species. An early section on the preparation of stable planar
tetracoordinate carbon Zr/Al compounds sets the tone for this review in which
availability of structural information of Zr derivatives rather than as yet synthetic
application is recognized. In the latter aspect, the use of gem-borazirconocene species for the construction of dienes, trienes, and allenes appears to be in a developed
state and incorporates a useful method for a-aminoboronic ester synthesis. In addition, their application to the preparation of simple natural products and heterocycles invites further study to achieve a more general status. Other gem-bimetallic
species, e. g. Ga-Zr, lead to structurally interesting but unusual systems while the
application of Zn-Zr derivatives provide simple organic molecules, which may be
readily obtained by more standard methods. This statement is not meant to detract
from undertaking further studies of scope and limitations in this evolving area.
Cationic zirconocenes, especially as they find significant value in glycoside bond
formation, are reviewed (Chapter 8) by Suzuki, Hintermann, and Yamanoi. With
an acknowledgement to the value of the rich mechanistic background of this
area due to cationic zirconocene polymerization catalysis, the authors focus on
the Cp2ZrCl2/AgX combination as reagent, intermediate, and catalyst. In turn, glycosylations of simple sugars, terpenes, and nucleosides, are discussed, culminating
in a major section dealing with the construction of highly complex glycosylphosphatidylinositols, constituting plasma membrane anchors on the cell walls of

VII


VIII

Foreword

parasitic protozoa which effect parasite survival and infectivity. A useful section on
the generation, modification, and tuning of the Cp2ZrCl2/AgX reagent is included.
Simpler cationic Zr- mediated reactions, inter alia, addition to aldehydes and epoxides, the generation of ortho-quinodimethides, Diels-Alder, Mukaiyama, and an intriguing dioxolenium ion alkylation and epoxy ester to orthoester rearrangement
are presented which augers well for the future of this promising area.
Sato and Urabe introduce their chapter (Chapter 9) on the use of Ti(II) alkoxides
in synthetic chemistry by a useful table of available reagents and a classification of
the reactions of the combination Ti(OiPr2)-iPrMgX into four categories. Utility is
evidenced in the synthesis (some stereoselective) of tetrasubstituted alkenes, allenyl
alcohols, b-alkylidenecycloalkylamines, allylic and homoallylic alcohols and
amines, aromatics (metallative Reppe reaction), among other functionalized organics. Particularly unique appears to be the intramolecular nucleophilic acyl substitution mediated by Ti(OiPr2)-iPrMgX which leads to bicyclo[3.1.0]hexane systems,
furans, and fused heterocycles, including an alkaloid total synthesis. Another,
equally intriguing reaction which can be equated with Pauson-Khand and the stoichiometric metallo-ene process is the intramolecular alkene±acetylene coupling, a
reaction which also has found application in natural product synthesis. The development of the inexpensive and easily operational Ti(OiPr2)-iPrMgX reagent in
many interesting selective reactions which cannot be carried out with conventional
metallocene reagents suggests that new transformations of synthetic value will be
forthcoming.
In Chapter 10, Rosenthal and Burlakov summarize recent work on the specific
reactions of titanocenes and zirconocenes with bis(TMS)acetylene. Similar to the
classes of Zr derivatives reviewed by Dembitsky and Srebnik (Chapter 7), the
potential of the derived complexes in organic synthesis is at an early stage of development. Thus the reagents, of the type Cp2M(L)(h2 -TMSC2TMS), prepared with
Schlenk tube techniques, undergo reactions with acetylenes, alkenes, diacetylenes,
conjugated and unconjugated dienes, carbonyl compounds, imines, among others
to give metallocyclopentadiene and other, structurally intriguing, complexes. The
main synthetic organic application appears to be in polymerization reactions and
the synthesis of unusual poly-enes, -ynes, and diyne thiophenes. The advantages
of Cp2M(L)(h2 -TMSC2TMS) over the widely used Cp2ZrCl2/n-BuLi system should
stimulate further research on the reactions of the former type reagents.
The discovery in 1989 by Kulinkovich of the reaction of in situ generated alkenetitanium complexes with esters leading, by a two carbon-carbon bond forming process, to cyclopropanols has spawned a new area of low-valent titanium chemistry
which is summarized in Chapter 11 for the active synthetic chemist by de Meijere,
Kozhushkov, and Savchenko. Using extensive tabular surveys, the review begins
with the scope and limitations of the cyclopropanol synthesis from esters, diesters,
and lactones, the authors emphasize the significance of ligand exchange of the initially derived alkenetitanium complex to derive different substitution on the cyclopropane ring, selective cyclopropanations of dienes and trienes, enantioselective
synthesis of bicyclo[3.1.0]hexane systems, and applications in the context of heterocycles. The discovery in the de Meijere laboratories of the low-valent Ti amide to


Foreword

cyclopropylamine variant is elaborated in the other main section of this chapter,
showing scope in terms of cyclopropane ring substitution, enantioenrichment
using Ti bis(TADDOLate) reagents, and other reactions some of which parallel
the ester to cyclopropanol conversion. Variation by replacement of Grignard by organoZn reagent, and addition of metal alkoxides gave rise a promising variant. The
review closes with sections on applications to natural product and materials synthesis and useful transformations of the synthetized cyclopropanols and cyclopropylamines. Although stoichiometric or semi-catalytic in Ti(OiPr)4 (5-10 mol%), these
reactions appear to be operationally simple, use low-cost reagents, proceed in good
yields and with high chemo- and stereo-selectivity, and therefore appear primed for
new synthetic applications.
As reviewed in Chapter 12 by GansaÈuer and Rinker, the general context of the
emerging area of reagent-controlled radical reactions, titanocene complexes are
most promising systems for epoxide opening processes. Originating with the
work of Nugent and RajanBabu who demonstrated the concept of electron-transfer
opening the strained epoxide reductively with stoichiometric amounts of low-valent
metal complexes, this field is evolving to provide new methods for deoxygenation,
reductive opening to alcohols, and 3-exo and 5-exo carbocyclizations. In recent
work, especially in the authors' laboratories, a protocol has been devised involving
protonation of Ti-O and Ti-C bonds allowing reasonable catalytic turnover. This
leads to the development of preparative chemistry for tandem epoxide-opening±
a,b-unsaturated carbonyl trapping, including intramolecular versions, to give initial
indications of diastereo- and enantio±selective control of these radical processes.
This work clearly constitutes the beginning of another new area of titanocene
chemistry.
In Chapter 13, Szymoniak and Moise summarize the progress in the area of allyltitanium reagents in organic synthesis, an area pioneered by the work of Seebach and Reetz. This review delineates, following the historic and convenient
grouping for allyltitaniums into three classes according to ligands (with two Cps;
with one Cp, and without Cps), achievements of the last 10-15 years. As a highlight
in the first category, while the addition to h3 -allyltitanocenes to aldehydes and ketones to give homoallylic alcohols in excellent yields and (for aldehydes) with high
anti stereoselectivity is now well appreciated, other reactions such as intramolecular reactions to cyclobutanes and carboxy alkylation and amidation of cycloheptatriene appear to be of unique synthetic value. Furthermore, combinations of allylTi
and Mukaiyama-aldol or aldol-Tishchenko reactions constitute new diastereoselective routes to polypropionates. The contrast between the useful h3 -allylTi derivatives, the corresponding h1-species, although readily available, have not enjoyed
wide application nor are their enantioselective reactions known. In the one Cp ligand group, the work of Hafner and Duthaler of highly enantioselective and practical asymmetric allyltitanation using tartrate-derived (TADDOL) ligands and their
application to prepare useful chiral building blocks and natural products is summarized. AllylTi reagents without Cp ligands, in spite of being very reactive, are
chemo- and highly diastereoselective in reactions with aldehydes and ketones allowing the development of diastereo- and enantio-selective homoaldol additions.

IX


X

Foreword

Based on the Kulinkovich reagent (Ti(OiPr)4/iPrMgCl), a new route to allyltitaniums has been devised by Sato and coworkers and this has allowed the synthesis
of chiral allylTi reagents which, by reaction with aldehydes and imines provide diverse polyfunctional chiral building blocks. Thus, while a number of versatile and
dependable Ti-based allyl-transfer reagents are now available, the development and
employment of chiral allyltitaniums appears to be poised for new application.
Perhaps appropriately in view of the current high profile of Grubbs metathesis
chemistry, the topic of titanium-based olefin metathesis by Takeda constitutes
the last chapter (Chapter 14) for the volume. The report in 1979 by Tebbe of the
first olefin metathesis between titanocene-methylidene and simple olefins was,
in retrospect, less significant for synthetic chemists than its reaction with esters.
Nevertheless, early tandem carbonyl olefination-olefin metathesis sequences in
complex molecule synthesis appeared, as documented by Takeda. Following
discussion of limitations due to steric effects and unavailability of higher homologues of titanocene-methylidene, potentially useful reactions of thioacetals with
Cp2Ti[P(OEt)3]2 and subsequent metathesis (apparently via titanacyclobutane intermediates) to carbo- and hetero-cyclic products are described and tabulated. Possibly
related reactions (e. g. reaction of 6,6-dihalo-1-alkenes with Ti(II) species to afford
bicyclo[3.1.0]hexanes offer new grounds for exploration while carbonyl, especially
ester, thioesters, and lactone, olefination constitutes an established synthetic
method. Ti-based reagents generated by reduction of gem-dihalides with low-valent
metals for alkylidenation of carbonyl compounds (a half-McMurry reaction), also
noted as a general methodology has, as judged from the synthetic literature,
reached full potential. Similarly, reactions with alkynes and nitriles offer early indications of new routes to dienes and pyridine and diimines, respectively. Perhaps
with further definition of conditions, new synthetic tools from Ti-based olefin metathesis chemistry will be developed.
Sixty years ago, organic chemists were struggling with the preparation and observation of properties of organolithiums; today, metallation chemistry is routinely
executed on gram and multi-ton scale. Since chemists are recognized for their intense level of curiosity and pride in experimental achievement, the real or apparent
intricacies associated with the preparation and use of Zr and Ti reagents that appear to be bizarre, unavailable, and/or relegated to the Schlenk tube will be overcome. May this volume be a hallmark in this quest.
Victor Snieckus
Queen's University
Kingston, ON, Canada


Titanium and Zirconium in Organic Synthesis. Edited by Ilan Marek
Copyright c 2002 Wiley-VCH Verlag GmbH & Co. KGaA
ISBNs: 3-527-30428-2 (Hardback); 3-527-60067-1 (Electronic)

Contents
Foreword V
Preface XXI
List of Contributors XXIII
1

1.1
1.2
1.3
1.3.1
1.3.2
1.3.3
1.3.4
1.4
1.4.1
1.4.1.1
1.4.1.2
1.4.1.3
1.4.2
1.4.3
1.4.3.1
1.4.3.2
1.4.3.3
1.4.4
1.4.5

Synthesis and Reactivity of Zirconocene Derivatives 1

Ei-ichi Negishi and Shouquan Huo
Introduction and Historical Background 1
Fundamental Patterns of Transformations of Zirconocene
Derivatives 3
Synthesis of Organic Derivatives of ZrCp2 8
Transmetallation 8
Hydrozirconation 10
Oxidative Addition 11
p-Complexation (Oxidative p-Complexation) 12
Reactivity of Organylzirconocene Compounds 14
Formation of CarbonÀHydrogen and CarbonÀHeteroatom
Bonds 15
Protonolysis and deuterolysis 15
Halogenolysis 15
Oxidation 16
Formation of CarbonÀMetal Bonds by Transmetallation 16
Formation of CarbonÀCarbon Bonds 18
Polar carbonÀcarbon bond-forming reactions 18
Carbonylation and other migratory insertion reactions 23
Carbozirconation and related carbometallation reactions 26
s-Bond Metathesis of Zirconacycles 40
Ionic Reactions of Organozirconates 44
References 45

XI


XII

Contents

2

2.1
2.2
2.2.1
2.2.2
2.2.3
2.2.4
2.3
2.3.1
2.3.1.1
2.3.1.2
2.3.1.3
2.3.1.4
2.3.1.5
2.3.1.6
2.3.2
2.3.2.1
2.3.2.2
2.3.2.3
2.3.2.4
2.3.2.5
2.3.2.6
2.3.3
2.3.3.1
2.3.3.2
2.3.3.3
2.3.3.4
2.3.3.5
2.3.3.6
2.3.4
2.3.5
2.3.6
2.3.6.1
2.3.6.2
2.3.7
2.4

Zirconacyclopentadienes in Organic Synthesis 50

Tamotsu Takahashi and Yanzhong Li
Introduction 50
Preparation and Reaction of Zirconacyclopentadienes 50
Preparation of Zirconacyclopentadienes 50
Hydrolysis 53
Halogenolysis 55
Formation of Heterocycles by Substitution Reactions 57
CarbonÀCarbon Bond Formation 59
Transmetalation 59
Transmetalation to copper 59
Transmetalation to nickel 60
Transmetalation to lithium 60
Transmetalation to zinc 61
Transmetalation to aluminum 61
Transmetalation to other metals 62
Coupling Reactions 62
Coupling with allyl halides 62
Coupling with benzyl halides 63
Coupling with alkynyl halides 63
Coupling with alkenyl halides 65
Coupling with aryl halides 66
Combination of coupling reactions 66
Addition Reactions to CarbonÀCarbon Triple Bonds 67
1,1-Addition to carbonÀcarbon triple bonds 68
1,2-Addition to carbonÀcarbon triple bonds: Formation of benzene
derivatives 68
Benzene formation from three different alkynes 70
Applications of benzene formation 72
Addition of azazirconacyclopentadienes to carbonÀcarbon triple
bonds 74
Addition to carbonÀcarbon double bonds 75
Insertion Reactions of Carbon Monoxide and Isonitriles 76
CarbonÀCarbon Bond Cleavage Reactions 77
Elimination Reactions 79
Elimination of an alkoxy group or halogen 79
Reductive elimination 80
Rearrangement 81
Conclusion 82
References 83


Contents

3

3.1
3.1.1
3.2
3.2.1
3.2.2
3.3
3.3.1
3.3.1.1
3.3.1.2
3.3.1.3
3.3.1.4
3.3.1.5
3.3.2
3.3.2.1
3.3.2.2
3.3.3
3.3.3.1
3.3.3.2
3.3.4
3.3.5
3.3.5.1
3.3.5.2
3.3.5.3
3.3.5.4
3.3.6
3.3.6.1
3.3.6.2
3.3.7
3.4

Elaboration of Organozirconium Species by Insertion of Carbenoids 86

Sally Dixon and Richard J. Whitby
Introduction 86
Formation of Zirconacycles 87
Carbonylation and Isonitrile Insertion 88
Acyclic Organozirconocenes 88
Zirconacycles 89
Insertion of 1-Halo-1-lithio Species into Organozirconocenes 90
Insertion of 1-Halo-1-lithioalkenes into Acyclic Organozirconocene
Chlorides 91
Insertion of 1-chloro-1-lithio-2,2-disubstituted alkenes 91
Insertion of 1-chloro-1-lithio-2-monosubstituted alkenes 92
Further elaboration of carbenoid insertion products 93
Insertion of 1-lithio-1,2-dihaloalkenes into acyclic organozirconocene
chlorides 93
Insertion of 1-halo-1-lithioalkenes into zirconacycles 94
Insertion of Allenyl Carbenoids 94
Insertions into acyclic organozirconocene chlorides 94
Insertions into zirconacycles 95
Insertion of Allyl Carbenoids into Organozirconium Species 96
Insertion into acyclic organozirconocene chlorides 96
Insertions into zirconacycles 96
Insertion of Propargyl Carbenoids into Zirconacycles 98
Insertion of a-Substituted Alkyl Carbenoids 98
Insertions into acyclic alkenylzirconocene chlorides. A convergent
route to functionalized allylzirconocenes 99
Insertions into zirconacycles 100
Insertion of benzyl carbenoids into zirconacycles 101
Insertion of halo-substituted carbenoids into zirconacycles 102
Insertion of Metalated Epoxides into Organozirconium Species 103
Insertion of 1-nitrile-1-lithio epoxides into acyclic organozirconocene
chlorides 103
Insertion of 1-silyl-, 1-nitrile, and 1-aryl-1-lithio epoxides into
zirconacycles 104
Regiochemistry of Carbenoid Insertion into Zirconacycles 104
Conclusion 106
References and Notes 108

4

Hydrozirconation and Further Transmetalation Reactions 110

4.1
4.2
4.3
4.4
4.5

Bruce H. Lipshutz, Steven S. Pfeiffer, Kevin Noson, and Takashi Tomioka
Introduction 110
Hydrozirconation/Quenching 112
Hydrozirconation: Ring-Forming and Ring-Opening Reactions 115
Acyl Zirconocenes 116
Allylic Zirconocenes 119

XIII


XIV

Contents

4.6
4.7
4.8
4.9
4.10
4.11

5

5.1
5.2
5.3
5.3.1
5.3.2
5.3.2.1
5.3.2.2
5.4
5.4.1
5.4.2
5.4.3
5.4.3.1
5.4.3.2
5.4.4
5.4.4.1
5.4.4.2
5.4.4.3
5.4.4.4
5.4.4.5
5.4.4.6
5.4.5
5.5
5.6

6

6.1
6.2
6.2.1
6.2.1.1

Cross-Coupling Reactions 121
Zirconium to Copper 127
Zirconium to Zinc 132
Zirconium to Boron 137
Zirconium to Nickel 138
Summary and Outlook 139
References 146
Acylzirconocenes in Organic Synthesis 149

Yuji Hanzawa
Introduction 149
Synthesis and Stability of Acylzirconocene Complexes 149
Reactions of Acylzirconocene Complexes 150
Historical Background 150
Conversion to KetoneÀ and KeteneÀZirconocene Complexes and
Reactions Thereof 151
KetoneÀzirconocene complexes 151
KeteneÀzirconocene complexes 153
Reactions of Acylzirconocene Chlorides as ªUnmaskedº Acyl Group
Donors 154
Introductory Remarks 154
Reaction with Aldehydes 155
Reactions with Imines 157
Yb(OTf)3/TMSOTf-catalyzed reactions 157
Brùnsted acid-catalyzed reactions with imines 159
Reactions with a,b-Unsaturated Ketones 161
1,2- and 1,4-Selective additions to a,b-enone derivatives 161
Enantioselective 1,2-selective addition to a,b-enone derivatives 163
1,4-Selective addition to a,b-ynone derivatives 165
Pd-catalyzed coupling reactions 168
Cu-catalyzed cross-coupling reactions 170
Generation of seleno- and telluroesters 173
Cationic Acylzirconocene Complexes 173
Reactivity of a,b-Unsaturated Acylzirconocene Chlorides toward
Nucleophiles 174
Conclusion 176
References and Notes 178
Chiral Zirconium Catalysts for Enantioselective Synthesis 180

Amir H. Hoveyda
Introduction 180
Zr-Catalyzed Enantioselective CÀC Bond-Forming Reactions 180
Zr-Catalyzed Enantioselective Alkylation of Alkenes with Grignard
Reagents 181
Intermolecular catalytic asymmetric alkylations 181


Contents

6.2.1.2
6.2.2
6.2.3
6.2.4
6.2.5
6.2.6
6.2.7
6.2.8
6.2.9
6.2.10
6.2.11
6.2.11.1
6.2.11.2
6.2.12
6.2.13
6.3
6.4
6.5

7

7.1
7.2
7.2.1
7.3
7.3.1
7.3.2
7.3.3
7.3.4
7.3.5
7.3.6
7.3.7
7.3.8
7.3.9
7.3.10
7.4
7.5
7.5.1

Intramolecular catalytic asymmetric alkylations 186
ZrÀCatalyzed Kinetic Resolution of Unsaturated Heterocycles 188
Zr-Catalyzed Kinetic Resolution of Exocyclic Allylic Ethers 191
Zr-Catalyzed Enantioselective Alkylation of Alkenes with
Alkylaluminum Reagents 194
Zr-Catalyzed Enantioselective Allylation of Aldehydes 197
Zr-Catalyzed Enantioselective Imine Alkylations with
Alkylzinc Reagents 199
Zr-Catalyzed Enantioselective Cyanide Addition to Aldehydes 202
Zr-Catalyzed Enantioselective Cyanide Additions to Imines
(Strecker Reactions) 204
Zr-Catalyzed Enantioselective Aldol Additions 207
Zr-Catalyzed Enantioselective Mannich Reactions 209
Zr-Catalyzed Enantioselective Cycloadditions 212
Cycloadditions with carbonyl dienophiles 212
Cycloadditions with imine dienophiles 215
Zr-Catalyzed Enantioselective Alkene Insertions 217
Zr-Catalyzed Enantioselective Additions to Meso Epoxides 217
Zr-Catalyzed Enantioselective CÀN Bond-Forming Reactions 218
Zr-Catalyzed Enantioselective CÀH Bond-Forming Reactions 219
Summary and Outlook 223
References 224
gem-Metallozirconocenes in Organic Synthesis 230

Valery M. Dembitsky and Morris Srebnik
Introduction 230
1,1-Aluminiozirconocene Complexes 231
Synthesis of Stable Planar Tetracoordinate Carbon Zr/Al
Compounds 233
1,1-Boriozirconocene Complexes 237
gem-1,1-Boriozirconocene Alkanes 237
Use of gem-Borazirconocene Alkanes in Regioselective Synthesis 239
Halogenation of gem-Boriozirconocene Complexes 241
Diastereoselective Hydrozirconation 244
Preparation of Diborabutadienes by Zirconocene-Mediated
Coupling 247
Amination of Boriozirconocene Complexes 247
(E)-1,1-Bimetallic Boriozirconocene Alkenes 249
Hydrolysis of (Z)-1-Alkenylboronates 250
Synthesis of Cyclic Boriozirconocenes 252
Bimetallic Boriozirconocene Complexes with Planar Tetracoordinate
Carbon 253
1,1-Lithiozirconocene Reagents 256
1,1-Stanniozirconocene Reagents 256
gem-Stanniozirconocene Alkanes 256

XV


XVI

Contents

7.5.2
7.5.3
7.5.4
7.5.5
7.5.6
7.6
7.6.1
7.7
7.8
7.8.1
7.9
7.10

8

8.1
8.1.1
8.1.2
8.1.3
8.1.4
8.1.5
8.2
8.2.1
8.2.2
8.2.2.1
8.2.2.2
8.2.2.3
8.2.2.4
8.2.2.5
8.2.2.6
8.2.3
8.3
8.3.1
8.3.1.1
8.3.1.2
8.3.2
8.3.3

Transmetalation Reactions 257
Preparation of Halogenated Alkenes 259
Bicyclization of Enynes 262
Zirconium-Promoted Bicyclization of Stannylenyne Derivatives 263
Bicyclization of Diynes 264
1,1-Galliozirconocene Complexes 265
Exchange Reactions of Galliozirconocene Complexes 268
1,1-Germaniozirconocene Complexes 269
1,1-Zinciozirconocene Reagents 269
Preparation of Polyfunctionalized Alkenes 270
1,1-Dizirconocene Complexes 273
Conclusion 276
References 277
Cationic Zirconocene Species in Organic Synthesis 282

Keisuke Suzuki, Lukas Hintermann, and Shigeo Yamanoi
General Introduction 282
Definition of Cationic Zirconocenes in this Review 282
Conditions for the Generation of Cationic Zirconocene 283
Structure and Reactivity of Cationic Zirconocenes 283
Availability 285
Reactions Involving Cationic Zirconocenes 285
Glycosylations with Cp2ZrCl2/Silver Salt Activators 286
Cp2ZrCl2/Silver Salt as a New Activator of Glycosyl Fluorides 286
Applications in Synthesis 287
Application to glycoside and nucleoside synthesis 287
Application to glycosylphosphatidylinositol (GPI) anchor and inositol
phosphoglycan (IPG) synthesis 289
Diverse oligosaccharide syntheses 292
Cycloglycosylation 294
Glycoconjugate synthesis 295
Conclusions on the use of the zirconocene/silver perchlorate activator:
Modification and tuning of the reagent 296
Activation of Glycosyl Sulfoxides 296
Nucleophilic Additions to Aldehydes and Epoxides 297
Silver-Mediated 1,2-Addition of Alk(en)ylzirconocene Chlorides to
Aldehydes [48] 297
1,3-Diene synthesis from aldehydes 299
Homologation of aldehydes 300
Nucleophilic Ring-Opening of Epoxides by Alkylzirconocene
Chlorides 300
Nucleophilic Reactions of Organozirconocene Chlorides with
Epoxides 300


Contents

8.4
8.4.1
8.4.1.1
8.4.1.2
8.4.1.3
8.4.1.4
8.4.2
8.5
8.5.1
8.5.2
8.5.3
8.5.4
8.5.5
8.5.6
8.6
8.7

9

9.1
9.2
9.3
9.4
9.5
9.6

10

10.1
10.1.1
10.1.2
10.1.3
10.2
10.2.1
10.3

Carbometalation of Alkynes and Alkenes 302
Carbometalation of Alkynes 303
Methylalumination 303
Other alkylaluminations 303
Allylzirconation 304
Alkylzirconation 305
Carbometalation of Alkenes 306
Cationic Zirconocene Complexes as Lewis Acid Catalysts 308
Epoxy Ester to Orthoester Rearrangement 308
Epoxide to Aldehyde Rearrangement 310
DielsÀAlder Reaction 310
Cationic DielsÀAlder Reaction 312
Catalytic Mukaiyama Aldol Reaction 313
Silyl Ketene Acetal to a-Silyl Ester Isomerization 314
Miscellaneous Reactions 314
Conclusion 315
References 317
Titanium(II) Alkoxides in Organic Synthesis 319

Fumie Sato and Hirokazu Urabe
Introduction 319
Generation of (h2 -alkyne)Ti(OiPr)2 and its Utilization in
Organic Synthesis 320
Preparation of Allyl- and Allenyltitanium Reagents and their
Synthetic Utility 331
Intramolecular Nucleophilic Acyl Substitution (INAS)
Mediated by 1 337
Intramolecular Coupling of Alkenes and Acetylenes 342
Concluding Remarks 350
References 351
Organometallic Chemistry of Titanocene and
Zirconocene Complexes with Bis(trimethylsilyl)acetylene as the
Basis for Applications in Organic Synthesis 355

Uwe Rosenthal and Vladimir V. Burlakov
Introduction 355
Established Titanocene and Zirconocene Sources 355
Novel Titanocene and Zirconocene Reagents with
Bis(trimethylsilyl)acetylene 356
Mechanistic Considerations 358
Reactions of Titanocene and Zirconocene Sources 358
Acetylenes ÀCaCÀ 359
Alkenes iCˆCI 361

XVII


XVIII

Contents

10.4
10.4.1
10.4.2
10.5
10.5.1
10.5.2
10.6
10.6.1
10.6.2
10.7
10.7.1
10.7.2
10.7.3
10.7.4
10.7.5
10.7.6
10.7.7
10.8
10.9

Diacetylenes 363
Non-Conjugated CaCÀXÀCaC 363
Conjugated CaCÀCaC 364
Dialkenes 371
Non-Conjugated CˆCÀXÀCˆC 371
Conjugated CˆCÀCˆC 371
Double Bonds to Heteroatoms iCˆX(À) 371
Carbonyl Compounds CˆO 371
Imines CˆN 372
Selected Combinations of Functional Groups 372
CaCÀCˆC 373
CaCÀCˆO 373
CaCÀCˆN 373
CˆCÀCˆO 374
CˆCÀCˆN 375
NˆCÀCˆN 376
CˆNÀNˆC 376
Miscellaneous 377
Summary and Outlook 383
References 387

11

Titanium-Mediated Syntheses of Cyclopropanols and
Cyclopropylamines 390

11.1
11.2
11.3
11.3.1
11.3.2
11.4
11.4.1
11.4.2
11.4.3
11.5
11.5.1
11.5.2
11.5.3
11.6

Armin de Meijere, Sergei I. Kozhushkov, and Andrei I. Savchenko
Introduction 390
Reaction Modes of Titanium Alkyl Derivatives Possessing b-Hydrogen
Atoms 391
Preparation of Cyclopropanols 392
From Organomagnesium Precursors 392
Via Ligand-Exchanged Titanium±Alkene Complexes 398
Preparation of Cyclopropylamines 405
From Organomagnesium Precursors 405
Via Ligand-Exchanged Titanium±Alkene Complexes 410
From Organozinc Precursors 415
Applications in Natural Product Syntheses and Syntheses of
Compounds with Potentially Useful Properties 417
Transformations of Cyclopropanols with Retention of the
Cyclopropane Ring 418
Transformations of Cyclopropanols with Cleavage of the
Cyclopropane Ring 419
Transformations of Cyclopropylamines 422
Conclusion 425
References 430


Contents

12

12.1
12.2
12.3
12.3.1
12.3.2
12.3.3
12.3.4
12.3.5
12.4

13

13.1
13.2
13.2.1
13.2.1.1
13.2.1.2
13.2.1.3
13.2.2
13.3
13.4
13.4.1
13.4.2
13.5

14

14.1
14.2
14.2.1
14.2.2
14.2.3
14.2.4
14.2.5

Titanocene-Catalyzed Epoxide Opening 435

Andreas GansaÈuer and BjoÈrn Rinker
Introduction 435
Stoichiometric Opening of Epoxides by Electron Transfer 435
Titanocene-Catalyzed Epoxide Opening 439
Titanocene-Catalyzed Reductive Epoxide Opening to
Alcohols 439
Titanocene-Catalyzed Additions to a,b-Unsaturated Carbonyl
Compounds 442
Titanocene-Catalyzed 5-exo Cyclizations 443
Titanocene-Catalyzed Radical Tandem Reactions 444
Catalytic Enantioselective Epoxide Opening 445
Conclusion 448
References 449
Synthesis and Reactivity of Allyltitanium Derivatives 451

Jan Szymoniak and Claude MoõÈse
Introduction 451
Allyl Bis(cyclopentadienyl)titanium Reagents 452
Preparation and Properties of h3 -Allyltitanocenes 452
Reactions with aldehydes and ketones 453
Other electrophiles and diene precursors 454
Asymmetric reactions with h3 -allyltitanocenes 458
Preparation and Reactions of h1-Allyltitanocenes 459
Allyl Mono(cyclopentadienyl)titanium Reagents 460
Allyltitanium Reagents without Cyclopentadienyl Groups 464
Synthesis by Transmetallation and Selective Allylation Reactions 464
Allyltitaniums from Allyl Halides or Allyl Alcohol Derivatives
and Ti(II) and their Synthetic Utility 467
Conclusion 469
References 473
Titanium-Based Olefin Metathesis and Related Reactions 475

Takeshi Takeda
Introduction 475
Reactions of Titanium Carbene Complexes with CarbonÀCarbon
Double Bonds 475
Olefin Metathesis 475
Formation of Titanocene-Methylidene and its Reaction with Olefins 476
Formation of Titanocene-Alkylidenes and their Application to Olefin
Metathesis 479
Preparation of Titanocene-Alkylidenes from Thioacetals and their
Application to Olefin Metathesis 480
Other Transformations of Titanacyclobutanes 485

XIX


XX

Contents

14.3
14.3.1
14.3.2
14.4
14.4.1
14.4.2
14.5

Reactions of Titanium Carbene Complexes with CarbonÀOxygen
Double Bonds 487
Methylenation of Carbonyl Compounds 487
Alkylidenation of Carbonyl Compounds 488
Reactions of Titanium Carbene Complexes with Triple Bonds 493
Reaction of Titanium Carbene Complexes with Alkynes 493
The Reaction of Titanium Carbene Complexes with Nitriles 495
Conclusion 497
References 498
Index

501


Titanium and Zirconium in Organic Synthesis. Edited by Ilan Marek
Copyright c 2002 Wiley-VCH Verlag GmbH & Co. KGaA
ISBNs: 3-527-30428-2 (Hardback); 3-527-60067-1 (Electronic)

Preface
Although more than a century has passed since the first preparation of titanium
and zirconium species, modern organic synthesis continues to benefit from the
unique versatility of these organometallic derivatives.
This special feature arises from the combination of the transition metal behavior
such as the coordination of a carbon-carbon multiple bond, oxidative addition,
reductive elimination, b-hydride elimination, addition reactions and the behavior
of classical s-carbanion towards electrophiles.
My primary purpose in editing this book was to bring together, in a single
volume, the remarkable recent achievements of organo- titanium and zirconium
derivatives and to give a unique overview on the many possibilities of these two
organometallic compounds such as reagents and catalysts, which are characteristic
for their enduring versatility as intermediates over the years.
In this multi-authored monograph, fourteen experts and leaders in the field
bring the reader up to date in these various areas of research. A special emphasis
was placed on the practical value of this book by the inclusion of key synthetic
protocols.
I gratefully acknowledge the work done by all authors in presenting their recent
and well-referenced contributions. Without their effort, this volume would not have
been possible. It is their expertise that will familiarize the reader with the essence
of the topic. Finally, I express my great gratitude to my wife, Cecile, whose persistence, encouragement and comprehension made possible the editing of this
book.
Technion-Israel Institute of Technology
April 2002

Ilan Marek

XXI


Titanium and Zirconium in Organic Synthesis. Edited by Ilan Marek
Copyright c 2002 Wiley-VCH Verlag GmbH & Co. KGaA
ISBNs: 3-527-30428-2 (Hardback); 3-527-60067-1 (Electronic)

List of Contributors
Dr. Vladimir V. Burlakov
Institut fuÈr Organische
Katalyseforschung
UniversitaÈt Rostock
Buchbinderstraûe 5À6
18055 Rostock
Germany

Prof. Yuji Hanzawa
School of Pharmacy
Tokyo University
1432-1 Horinouchi
Hachioji
Tokyo 192-0392
Japan

Dr. Valery M. Dembitsky
Department of Medicinal Chemistry
and Natural Products
School of Pharmacy
P. O. Box 12065
The Hebrew University of Jerusalem
Jerusalem 91120
Israel

Dr. Lukas Hintermann
Department of Chemistry
Tokyo Institute of Technology
O-okayama
Meguro-Ku
Tokyo 152-8551
Japan

Dr. Sally Dixon
Department of Chemistry
University of Southampton
Hants SO17 1BJ
United Kingdom
Prof. Andreas GansaÈuer
KekuleÂ-Institut fuÈr Organische Chemie
und Biochemie
Gerhard-Domagk-Straûe 1
53121 Bonn
Germany

Prof. Amir H. Hoveyda
Department of Chemistry
Merkert Chemistry Center
Boston College
Chestnut Hill
Massachusetts 02467
USA
Dr. Shouquan Huo
Department of Chemistry
Purdue University
West Lafayette
Indiana 47907-1393
USA

XXIII


XXIV

List of Contributors

Dr. Sergei I. Kozhushkov
Institut fuÈr Organische Chemie
Georg-August-UniversitaÈt
Tammannstraûe 2
37077 GoÈttingen
Germany

Dr. Kevin Noson
Department of Chemistry
and Biochemistry
University of California Santa Barbara
California 93106-9510
USA

Dr. Yanzhong Li
Catalysis Research Centre
and Graduate School
of Pharmaceutical Sciences
Hokkaido University and CREST
Sapporo 060 811
Japan

Dr. Steven S. Pfeiffer
Department of Chemistry
and Biochemistry
University of California Santa Barbara
California 93106-9510
USA

Prof. Bruce H. Lipshutz
Department of Chemistry
and Biochemistry
University of California Santa Barbara
California 93106-9510
USA

Dr. BjoÈrn Rinker
KekuleÂ-Institut fuÈr Organische Chemie
und Biochemie
Gerhard-Domagk-Straûe 1
53121 Bonn
Germany

Prof. Armin de Meijere
Institut fuÈr Organische Chemie
Georg-August-UniversitaÈt
Tammannstraûe 2
37077 GoÈttingen
Germany

Prof. Uwe Rosenthal
Institut fuÈr Organische
Katalyseforschung
UniversitaÈt Rostock
Buchbinderstraûe 5À6
18055 Rostock
Germany

Prof. Claude MoõÈse
Laboratoire de SyntheÁse et
d'ElectrosyntheÁse OrganomeÂtalliques
associe au CNRS
Faculte des Sciences
6, Bd Gabriel
21000 Dijon
France

Prof. Fumie Sato
Department
of Biomolecular Engineering
Tokyo Institute of Technology
4259 Nagatsuta-cho, Midori-ku
Yokohama
Kanagawa 226-8501
Japan

Prof. Ei-ichi Negishi
Department of Chemistry
Purdue University
West Lafayette
Indiana 47907-1393
USA

Dr. Andrei I. Savchenko
Institut fuÈr Organische Chemie
Georg-August-UniversitaÈt
Tammannstraûe 2
37077 GoÈttingen
Germany


List of Contributors

Prof. Morris Srebnik
Department of Medicinal Chemistry
and Natural Products
School of Pharmacy,
P. O. Box 12065
The Hebrew University of Jerusalem
Jerusalem 91120
Israel
Prof. Keisuke Suzuki
Department of Chemistry
Tokyo Institute of Technology
O-okayama
Meguro-ku
Tokyo 152-8551
Japan
Prof. Jan Szymoniak
UniversiteÁ de Reims
CNRS UMR 6519
Groupe SyntheÁse par voie
OrganomeÂtallique
B.P. 1039 Reims Cedex 2
France
Prof. Tamotsu Takahashi
Catalysis Research Center
and Graduate School
of Pharmaceutical Sciences
Hokkaido University and CREST
Kita-ku
Sapporo 060 811
Japan

Prof. Takeshi Takeda
Department of Chemistry
Tokyo University of Agriculture
and Technology
Koganei
Tokyo 184-8588
Japan
Dr. Takashi Tomioka
Department of Chemistry
and Biochemistry
University of California Santa Barbara
California 93106-9510
USA
Dr. Hirokazu Urabe
Department
of Biomolecular Engineering
Tokyo Institute of Technology
4259 Nagatsuta-cho, Midori-ku
Yokohama
Kanagawa 226-8501
Japan
Prof. Richard J. Whitby
Department of Chemistry
University of Southampton
Hants SO17 1BJ
United Kingdom
Dr. Shigeo Yamanoi
Department of Chemistry
Tokyo Institute of Technology
O-okayama
Meguro-Ku
Tokyo 152-8551
Japan

XXV


Titanium and Zirconium in Organic Synthesis. Edited by Ilan Marek
Copyright c 2002 Wiley-VCH Verlag GmbH & Co. KGaA
ISBNs: 3-527-30428-2 (Hardback); 3-527-60067-1 (Electronic)

1

1
Synthesis and Reactivity of Zirconocene Derivatives
Ei-ichi Negishi and Shouquan Huo
1.1

Introduction and Historical Background

Zirconium (Zr) occurs in the lithosphere to the extent of 0.022 % [1]. Although it is much
less abundant than Ti (0.63 %), it is roughly as abundant as C. Despite some technical difficulties in the production of pure Zr compounds, requiring separation of Hf-containing
contaminants, it is one of the least expensive transition metals. Some of its fundamental
properties are listed in Table 1.1
The most common oxidation state for zirconium compounds is ‡4, as suggested by the
electronic configuration of Zr. There are, however, a significant number of Zr(II) compounds, such as Cp2Zr(CO)2 and Cp2Zr(PMe3)2 [2], where Cp ˆ h5 -C5H5. Alkene- and alkyne-ZrCp2 complexes are often viewed as Zr(II) complexes, although they can also be
considered as zirconacyclopropanes and zirconacyclopropenes, respectively, in which Zr
is in the ‡4 oxidation state. It appears best to view them as resonance hybrids of 1 and 2
and to use 1 and 2 interchangeably, as deemed desirable (Generalization 1).

Atomic Number

40

Atomic Weight

91.22

Electronic Configuration

[Kr]4d25s2

Isotopic Composition

90

Zr (51.46 %),

91

Zr (11.23 %),

94

Zr (17.40 %),

96

Zr (2.8 %)

92

Zr (17.11 %)

Magnetic Property

91

Electronegativity

1.4 (Paulinga), 1.22 (Sandersonb)

a

b

Zr (I ˆ 5/2)
The others are magnetically inactive.

Pauling, L., The Nature of the Chemical Bond, 3rd Ed., Cornell
University Press, Ithaca, N. Y., 1960, p. 93.
Sanderson, R. T., Inorganic Chemistry, Van Nostrand-Reinhold,
New York, 1967, p. 72.

Table 1.1. Some fundamental

properties of Zr


Tài liệu bạn tìm kiếm đã sẵn sàng tải về

Tải bản đầy đủ ngay

×