Functionalised N-Heterocyclic Carbene Complexes

356 Pages·2010·6.444 MB·English

by  Olaf Kuhl(auth.)

Functionalised N-Heterocyclic
Carbene Complexes
Functionalised N-Heterocyclic Carbene Complexes Olaf Kühl
© 2010 John Wiley & Sons Ltd ISBN: 978-0-470-71215-3
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Functionalised
N-Heterocyclic Carbene
Complexes
OLAF KÜHL
Institute for Biochemistry, Ernst-Moritz-Arndt
University of Greifswald, Germany
A John Wiley and Sons, Ltd., Publication
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This edition fi rst published 2010
© 2010 John Wiley & Sons Ltd
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Library of Congress Cataloging-in-Publication Data
Kühl, Olaf.
Functionalised N-heterocyclic carbene complexes / Olaf Kühl.
p. cm.
Includes bibliographical references and index.
ISBN 978-0-470-71215-3
1. Ligands. 2. Heterocyclic compounds. 3. Transition metal complexes. I. Title.
QD474.K825 2009
541'.2242—dc22
2009042558

A catalogue record for this book is available from the British Library.
ISBN: 9780470712153
Set in 10/12 Times Roman by MPS Limited, A Macmillan Company, Chennai, India
Printed and bound in Great Britain by Antony Rowe Ltd, Chippenham, Wiltshire
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Contents
Abbreviations vii
Introduction 1
Chapter 1 The Nature of N-Heterocyclic Carbenes 7
1.1 Synthesis
1.1.1 Synthesis of the Imidazolium Salts
1.1.2 Closing the Ring
1.1.3 Synthesis of the Free Carbenes
1.1.4 Synthesis of Transition Metal Complexes of NHC
1.2 Properties of NHC
1.2.1 The Internal Electronic Structure
1.2.2 Basicity of NHC
1.2.3 Steric Properties
1.2.4 The Carbene-Metal Bond
1.2.5 Decomposition Pathways
References
Chapter 2 Why Functionalisation? 39
2.1 Phosphane Mimic
2.2 Hemilability
2.3 Chirality
2.3.1 Planar Chirality
2.3.2 Axial Chirality
2.4 Ligand Geometry
2.5 Catalysis
2.5.1 Allylic Alkylation
2.5.2 Coupling Reactions
2.5.3 Olefi n Metathesis
2.5.4 Polymerisations
2.5.5 Organocatalysis
References
Chapter 3 N-Heterocyclic Carbenes with Neutral Tethers 55
3.1 Amine Functionalities
3.1.1 Heteroaromatic Functional Groups
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vi Contents
3.1.2 Oxazolines
3.1.3 Imino Functional Groups
3.1.4 Amino Functionalised NHC
3.2 Oxygen-Containing Groups
3.3 Phosphane Functionalities
3.4 Bis-Carbene Ligands
3.5 Tris-N-Heterocyclic Carbene Ligands
3.6 Pincer Carbenes
References
Chapter 4 N-Heterocyclic Carbenes with Anionic Functional Groups 199
4.1 Oxygen-Containing Groups
4.2 Nitrogen-Containing Groups
4.3 NHC Ligands Incorporating Cp Moieties
4.4 Transition Metal NHC Complexes Involved in the Activation of C-H
Bonds
4.5 Immobilisation of the Catalyst
4.6 Sulfur-Containing Functional Groups
References
Chapter 5 Chiral N-Heterocyclic Carbenes 279
References
Chapter 6 Natural Products 309
6.1 Thiazole
6.1.1 Isolation and Stability of Thiazolylidene
6.1.2 Benzothiazoles
6.1.3 Metal Complexes
6.2 Amino Acids
6.3 Purines and Xanthines
6.4 Carbohydrates
6.5 Miscellaneous
References
Index 347
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Abbreviations

acac acetylacetonate
ad adamantyl
ampy 2 - aminomethylpyridine
anti antiparallel orientation
BARF {B[3,5 - (CF ) C H ] } -
3 2 6 3 4
Benz benzyl
BIMCA 3,6 - di - tert - butyl - 1,8 - bis(imidazol - 1 - yl)carbazole
BINAP 1,1 ’ - binaphthylphosphane
BINOL 1,1 ’ - binaphthyldiol
bipy bipyridyl
boc tert - butoxycarbonyl
BoxCarb bisoxazoline carbene
Bun n - butyl
Bu t tert - butyl
CAAC cyclic alkyl amino carbene
cod 1,5 - cyclooctadiene
coe cyclooctene
COMP conjugated organometallic polymer
Cp cyclopentadienyl
Cp* pentamethyl cyclopentadienyl
Cy cyclohexyl
p - cymene p - isopropyl toluene
dba trans , trans - dibenzylideneacetone
DIPP 2,6 - diisopropyl aniline
DMA dimethyl acetamide
DMF dimethyl formamide
DMSO dimethyl sulfoxide
DNA deoxyribonucleic acid
dppe bis - diphenylphosphinoethane
dppf 1,1 ’ - bis(diphenylphosphino)ferrocene
EDA 1,1 - ethanediol diacetate
ee enantiomeric excess
Et ethyl
EWG electron - withdrawing group
fac facial
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viii Abbreviations
Fc ferrocenyl
η hapto, hapticity
Hex hexyl
HOMO highest occupied molecular orbital
IEt 1,3 - diethyl imidazolylidene
IL ionic liquid
Im imidazole, imidazolium
IMes 1,3 - dimesityl imidazolylidene
IPri 1,3 - diisopropyl imidazolylidene
κ kappa
KHMDS potassium hexamethyldisilazane
LDA lithium diisopropylamine
MAC monoaminocarbene
MAO methylaluminoxane
Me methyl
mer meridonal
Mes mesityl
MFILC multi - functionalised ionic liquid composition
nbd norbornadiene
NBS N - bromosuccinamide
NHC N - heterocyclic carbene(s)
NHC - S sulfur functionalised NHC
NMP N - methyl - 2 - piperidone
Np neopentyl
NTf bis(trifl uoromethanesulfonyl)amide
OAc acetate
OTf trifl ate
ox - NHC oxazoline functionalised NHC
PCET proton coupled electron transfer
PHOX phosphino - oxazoline
pr i isopropyl
py pyridyl
pybox pyridyl bisoxazoline
RNA ribonucleic acid
ROMP ring opening metathesis polymerisation
ROP ring opening polymerisation
SHOP Shell Higher Olefi n Process
syn parallel orientation
Taz thiazolylalanine
Tbp trigonal bipyramidal
TEP Tolman Electronic Parameter
thf tetrahydrofuran
tht tetrahydrothiophene
TIME tris - [2 - (3 - alkylmethylimidazolium - 1 - yl)ethyl]methane
TIMEN tris - [2 - (3 - alkylmethylimidazolium - 1 - yl)ethyl]amine
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Abbreviations ix
TOF turnover frequency
Tol tolyl
Tolyl toluenyl
TON turnover number
Tp tris - pyrazolyl borate
TsO tosylate
VE valence electrons
VSEPR valence shell electron pair repulsion
Xyl xylyl
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Introduction
T he chemistry of N-heterocyclic carbenes (NHC) and particularly their transition metal
complexes is considerably older than the isolation of the fi rst free NHC by Arduengo e t al .
in 1991 [1]. In 1968 Ö fele [2] and Wanzlick and Schö nherr [3] independently published
the fi rst transition metal NHC complexes. Whereas Ö fele reacted an imidazolium salt with
a transition metal hydride, Wanzlick and Schö n herr reacted the imidazolium salt with a
transition metal acetate (see Figure I.1 ).
Lappert developed the thermolysis of an electron-rich olefi n in the presence of a tran-
sition metal complex as another way to synthesise these compounds [4]. When, in 1975,
Clarke and Taube published their fi ndings on carbon coordinated purine transition metal
complexes [5], transition metal NHC complexes with functionalised NHC made their debut
in biochemistry. The chemistry of carbenes from natural products became fi rmly estab-
lished following the discovery that the catalytic activity of thiamine (vitamin B1) is based
on the intermediate formation of a carbene derived from thiazole [6 – 9] (see Figure I.2 ).
However, lacking a stable free carbene, the chemistry of transition metal carbene com-
plexes stayed on the very fringes of inorganic chemistry. This changed dramatically after
the publication of the fi rst free stable carbene by Arduengo et al. [1]. Several theoretical
publications describing the electronic and steric properties of the new compound class and
their bonding to transition metals in the long known (over 20 years) complexes appeared
[10– 1 5]. Applications were soon found following Herrmann’ s landmark review concerning
the use of NHC in catalysis [16]. The fi rst catalytic experiments with transition metal NHC
complexes were performed by Lappert e t al . some 10 – 15 years earlier [17].
I n particular, the discovery that NHC were better σ- donors than phosphanes gave the
coordination chemistry of NHC ligands great momentum and many reactions hitherto per-
formed by transition metal phosphane complexes were now reported for their NHC analogues
[16,18 – 20]. Limitations and new opportunities were rapidly appearing. McGuinness e t al .
showed the elimination of the ‘ stable, inert ’ spectator NHC ligand from the transition metal
Functionalised N-Heterocyclic Carbene Complexes Olaf Kühl
© 2010 John Wiley & Sons Ltd ISBN: 978-0-470-71215-3
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2 Introduction
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