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N-Heterocyclic Carbenes

BOOK

N-Heterocyclic Carbenes

Silvia Diez-Gonzalez

(2016)

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Book Details

ISBN
978-1-78262-681-7
Edition
2
Language
English
Pages
636
Subjects
Chemistry
Inorganic chemistry
Catalysis
Industrial chemistry & chemical engineering

Abstract

In less than 20 years N-heterocyclic carbenes (NHCs) have become well-established ancillary ligands for the preparation of transition metal-based catalysts. This is mainly due to the fact that NHCs tend to bind strongly to metal centres, avoiding the need of excess ligand in catalytic reactions. Also, NHC‒metal complexes are often insensitive to air and moisture, and have proven remarkably resistant to oxidation. This book showcases the wide variety of applications of NHCs in different chemistry fields beyond being simple phosphine mimics. This second edition has been updated throughout, and now includes a new chapter on NHC‒main group element complexes. It covers the synthesis of NHC ligands and their corresponding metal complexes, as well as their bonding and stereoelectronic properties and applications in catalysis. This is complemented by related topics such as organocatalysis and biologically active complexes. Written for organic and inorganic chemists, this book is ideal for postgraduates, researchers and industrialists.
Silvia Diez-Gonzalez is a Senior Lecturer in the Department of Chemistry at Imperial College London, UK.

Table of Contents

Section Title Page Action Price
Cover Cover
N-Heterocyclic Carbenes From Laboratory Curiosities to Efficient Synthetic Tools 2nd Edition i
Foreword vii
Preface ix
Dedication xiii
Abbreviations and Acronyms xv
Contents xxi
Chapter 1 - Introduction to N-Heterocyclic Carbenes: Synthesis and Stereoelectronic Parameters 1
1.1 Introduction 1
1.2 Electronic Structure and Stabilization of N-Heterocyclic Carbenes 4
1.3 N-Heterocyclic Carbene Ligands 6
1.3.1 Synthesis of NHC Precursors 6
1.3.2 Preparation of Free N-Heterocyclic Carbenes 14
1.4 Comparison of Different Types of N-Heterocyclic Carbenes 16
1.4.1 Carbenes Derived from Four-Membered Heterocycles 16
1.4.2 Carbenes Derived from Five-Membered Heterocycles 17
1.4.2.1 Imidazol-2-ylidenes 17
1.4.2.2 Imidazolin-2-ylidenes 18
1.4.2.3 Benzimidazol-2-ylidenes and Related Benzannulated NHCs 20
1.4.2.4 Triazol-5-ylidenes and Related Compounds 22
1.4.2.5 Thiazol-2-ylidenes and Benzothiazol-2-ylidenes 24
1.4.2.6 Cyclic Alkyl(amino)carbenes and Related Compounds 24
1.4.2.7 P-Heterocyclic Carbenes 27
1.4.3 Heterocyclic Carbenes Containing Boron Within the Heterocycle 29
1.4.4 N-Heterocyclic Carbenes Derived from Six-, Seven-or Eight-Membered Heterocycles 30
1.5 Conclusions and Outlook 31
References 32
Chapter 2 - Synthesis, Activation, and Decomposition of N-Heterocyclic Carbene-Containing Complexes 46
2.1 Introduction 46
2.2 Synthesis of NHC-Containing Metal Complexes 47
2.2.1 Early Investigations 47
2.2.2 Ligand Displacements with Isolated Carbenes 48
2.2.3 Direct Reactions with Imidazolium Salts 49
2.2.3.1 Deprotonation by a Basic Ligand 49
2.2.3.2 Oxidative Addition 50
2.2.4 Carbene Transfer Reactions 52
2.2.4.1 Carbene Transfer from Silver(i) Complexes 52
2.2.4.2 Carbene Transfer from Copper(i) Complexes 53
2.2.5 Syntheses in Ionic Liquids 54
2.2.6 NHC Adducts and Their Applications 55
2.2.7 Templated Synthesis 56
2.2.8 Using Weak Bases to Generate Free Carbenes In situ 57
2.3 Activation of NHC-Containing Metal Complexes 57
2.3.1 Ruthenium–NHC Complexes for Alkene Metathesis 57
2.3.2 Palladium–NHC Complexes 59
2.3.3 Nickel– and Platinum–NHC Complexes 63
2.3.4 Activation by Extraction of Anionic Ligands 65
2.4 Decomposition of NHC-Containing Metal Complexes 66
2.4.1 C–H, C–C and C–N Activation Reactions 66
2.4.2 Reductive Elimination 73
2.4.3 Migratory Insertion 76
2.4.4 Displacement Behaviour 77
2.4.5 Other Decomposition Reactions 79
2.5 Improving the Stability of Metal–NHC Complexes 80
2.5.1 Preventing Reductive Elimination 80
2.5.2 Inhibiting C–H Bond Activation 82
2.5.3 Preventing NHC Dissociation 84
2.6 Conclusions 85
References 86
Chapter 3 - Non-Classical N-Heterocyclic Carbene Complexes 99
3.1 Introduction 99
3.2 Synthesis of Non-Classical NHC Complexes 100
3.2.1 Synthesis of Complexes via Free Carbenes 100
3.2.2 Heterocycle Assembly at the Metal Center 101
3.2.3 Tautomerization Reactions 102
3.2.4 Transmetalation from Silver Complexes 103
3.2.5 Cyclometalation Reactions 104
3.3 Reactivity and Stability 105
3.3.1 Stability and Lability Towards Acids 105
3.3.2 Stability and Lability Under Basic Conditions 107
3.3.3 Carbene Dissociation and Oxidation 108
3.4 Application of Abnormal Carbene Complexes in Catalysis 109
3.4.1 Water Oxidation 109
3.4.2 Oxidation Reactions 111
3.4.3 Cross-Coupling Reactions 112
3.4.4 Olefin Metathesis 114
3.4.5 Reactions Involving Heterocycle Opening or Formation 116
3.5 Conclusions 117
References 117
Chapter 4 - Computational Studies on the Reactivity of Transition Metal Complexes with N-Heterocyclic Carbene Ligands 120
4.1 Introduction 120
4.2 Non-Innocent Behavior of NHCs at TM Centres 121
4.2.1 Reductive Elimination/Oxidative Addition 121
4.2.2 Migratory Insertion 127
4.2.3 Reactivity at the N-Substituents 128
4.3 Binding and Activation of Small Molecules at NHC–TM Complexes 132
4.4 Group 8 137
4.5 Group 9 146
4.6 Group 10 149
4.7 Group 11 159
4.8 Conclusions 165
References 167
Chapter 5 - Main Group Complexes with N-Heterocyclic Carbenes: Bonding, Stabilization and Applications in Catalysis 178
5.1 Introduction 178
5.2 Bonding and Structural Considerations of Carbene–Main Group Element Complexes 179
5.3 Carbene Complexes with Group 1 and Group 2 Elements 180
5.3.1 Carbene Complexes of the Group 1 Elements 181
5.3.1.1 Lithium Carbene Complexes 181
5.3.1.2 Comparison of Carbene Alkali Metal Complexes 183
5.3.1.3 “Abnormal” NHC Complexes of the Group 1 Elements 184
5.3.2 Carbene Complexes of the Group 2 Elements 186
5.3.2.1 Beryllium Carbene Complexes 186
5.3.2.2 Mixed Group 1/Group 2 Carbene Complexes 187
5.3.2.3 Oligomeric Magnesium Carbene Complexes 187
5.3.2.4 Group 2 Metallocene Carbene Complexes 188
5.3.2.5 Carbene-Supported Group 2 (Ca, Sr, or Ba) Amido Complexes 189
5.4 Carbene Complexes with Group 13 Elements 190
5.4.1 Carbene Complexes with Boron 190
5.4.1.1 Carbene Complexes with Boron–Boron Multiple Bonds 190
5.4.1.2 Carbene Borylene Complexes 192
5.4.1.3 Carbene Complexes with Boron-Centered Radicals 195
5.4.1.4 Carbene Complexes with Boron-Centered Nucleophiles 196
5.4.1.5 Other Carbene Complexes with Boron and Potential Applications in Catalysis 198
5.4.2 Carbene Complexes with Aluminium, Gallium, Indium, and Thallium 199
5.4.2.1 Structural Characterization of Carbene Complexes with Heavy Group 13 Elements 199
5.4.2.2 Applications in Small Molecule Activation and Catalysis 202
5.5 Carbene Complexes with Group 14 Elements 203
5.5.1 Carbene Complexes with Group 14 “Allotropes” 203
5.5.2 Carbene Complexes with EII Centers (E = Si, Ge, Sn) 205
5.5.2.1 Carbene EII Halide/Hydride Complexes 205
5.5.2.2 Reactivity of Carbene Complexes with N-Heterocyclic Silylenes 207
5.5.3 Paramagnetic Carbene Complexes with Group 14 Elements 208
5.5.3.1 Carbene-Stabilized Organic Radicals and Radical Ions 208
5.5.3.2 Carbene-Stabilized Silicon Radicals 210
5.6 Carbene Complexes with Group 15 Elements 211
5.6.1 Carbene Complexes with Group 15 “Allotropes” 211
5.6.2 Carbene-Stabilized Pnictinidines (Pn–R, Pn = P, As, or Sb) 213
5.6.3 Carbene-Stabilized Group 15 Cations, Radicals, and Radical Cations 214
5.6.3.1 Carbene-Stabilized Group 15 Cations and Dications 214
5.6.3.2 Carbene-Stabilized Group 15 Radicals and Radical Cations 216
5.6.4 Carbene-Supported Hypervalent Phosphorus Complexes: Catalytic Applications 218
5.7 Carbene Complexes with Group 16 Elements 219
5.7.1 Carbene Chalcone Complexes 219
5.7.2 Carbene Complexes with Chalcogen Halides and Oxides 220
5.8 Carbene Complexes with Group 17 Elements 222
5.9 Conclusions and Outlook 225
References 226
Chapter 6 - Rare Earth Metal Complexes with N-Heterocyclic Carbenes 238
6.1 Introduction 238
6.2 Structural Survey and Typical Syntheses 240
6.2.1 Complexes with Monodentate NHC Ligands 240
6.2.2 Complexes with Multidentate NHC Ligands 241
6.2.2.1 Complexes with Oxygen Anchors 242
6.2.2.2 Complexes with Nitrogen Anchors 245
6.2.2.3 Indenyl- and Fluorenyl-Functionalized NHC Complexes 247
6.2.2.4 Cyclometallated NHCs 248
6.2.3 Bimetallic Complexes with N-Heterocyclic Carbenes 249
6.3 Structure and Bonding 249
6.3.1 General Trends 249
6.3.2 Bonding 250
6.3.3 Distorted Geometries 252
6.4 Reactivity 253
6.5 Catalytic Applications 258
6.5.1 Polymerization Reactions 260
6.5.1.1 Olefin Polymerization 260
6.5.1.2 Ring-Opening Polymerizations 261
6.5.2 Addition of Amines and Terminal Alkynes to Carbodiimides 263
6.5.3 Cross-Dehydrogenative Coupling 264
6.6 Conclusions and Outlook 264
References 265
Chapter 7 - NHC–Iron, Ruthenium and Osmium Complexes in Catalysis 268
7.1 Introduction 268
7.2 NHC–Iron-Catalysed Reactions 269
7.2.1 Polymerisation Reactions 269
7.2.2 C–C Bond Forming Reactions 270
7.2.2.1 Cyclisation Reactions 270
7.2.2.2 Cross-Coupling Reactions 271
7.2.2.3 Allylic Alkylation Reactions 273
7.2.3 C–X Bond Forming Reactions 274
7.2.3.1 Allylic Sulfenylation and Sulfonylation Reactions 274
7.2.3.2 Aziridination and Epoxidation Reactions 274
7.2.4 Organometallic and Electrochemical Reactions 275
7.3 NHC–Ruthenium-Catalysed Reactions 277
7.3.1 Metathesis Reactions 278
7.3.1.1 Scope and Mechanism 278
7.3.1.2 Benzylidene Catalysts 279
7.3.1.3 Oxygen-Chelated Alkylidene Catalysts 280
7.3.1.4 Other Chelated Alkylidene Catalysts 283
7.3.1.5 Indenylidene Catalysts 284
7.3.1.6 Arene Catalysts 285
7.3.2 Non-Metathesis Reactions 286
7.3.2.1 Introduction 286
7.3.2.2 Isomerisation Reactions 286
7.3.2.3 Cycloisomerisation Reactions 287
7.3.2.4 Oligomerisation and Polymerisation Reactions 289
7.3.2.5 C–C Bond Forming Reactions 290
7.3.2.6 Miscellaneous Reactions 291
7.3.3 Tandem Reactions 291
7.4 NHC–Osmium-Catalysed Reactions 292
7.5 Conclusions and Outlook 294
References 294
Chapter 8 - NHC–Cobalt, –Rhodium, and –Iridium Complexes in Catalysis 302
8.1 Introduction 302
8.2 NHC–Cobalt Complexes 303
8.2.1 Reactivity of [(NHC)Co] Complexes: Stoichiometric Activation of Small Molecules and of Inert Bonds 303
8.2.2 Cobalt-Catalysed Cyclisations 305
8.2.3 Activation of Carbon–Halogen Bonds 307
8.2.4 Functionalisation of C–H bonds 310
8.2.5 Miscellaneous Reactions 311
8.2.5.1 Isomerisation of 1-Alkenes 311
8.3 NHC–Rhodium Complexes 312
8.3.1 Arylation of Carbonyl and Related Compounds with Organoboron Reagents 312
8.3.1.1 Synthesis of Diarylmethanol Derivatives from Aldehydes 312
8.3.1.2 1,4-Addition to α,β-Unsaturated Compounds 315
8.3.1.3 Synthesis of Secondary Amines from Imines 317
8.3.2 Hydroformylations 317
8.3.3 Rhodium-Catalysed Cyclisations and Related Reactions 318
8.4 NHC–Iridium Complexes 323
8.4.1 C-, N- and O-Alkylations 323
8.4.1.1 C-Alkylations 324
8.4.1.2 N-Alkylation 325
8.4.1.3 O-Alkylation 326
8.4.2 Hydroamination of Alkenes 327
8.4.3 Miscellaneous Reactions 328
8.5 General Conclusion 329
References 330
Chapter 9 - NHC–Palladium Complexes in Catalysis 336
9.1 Introduction 336
9.2 C–C Bond Formation 337
9.2.1 Mizoroki–Heck Coupling and Related Chemistry 337
9.2.1.1 Imidazol-2-ylidene Type NHC Ligands 337
9.2.1.2 Functionalised Imidazol-2-ylidene NHC Ligands 339
9.2.1.3 Benzimidazol-2-ylidene and Benzothiazol-2-ylidene NHC Ligands 341
9.2.2 Suzuki–Miyaura Cross-Coupling 343
9.2.2.1 Imidazol-2-ylidene NHC Ligands 343
9.2.2.2 Functionalised Imidazol-2-ylidene NHC Ligands 346
9.2.3 Sonogashira Coupling 349
9.2.4 Application of the PEPPSI Protocol in Coupling Reactions 349
9.2.5 Immobilised Catalysts for Coupling Reactions 351
9.2.6 Pd–Allyl Mediated C–C Bond Formation 354
9.2.7 Direct Arylation by C–H Functionalisation 355
9.2.8 α-Carbonyl Arylation 357
9.2.9 Polymerisation and Oligomerisation Reactions 358
9.2.10 Telomerisation of Dienes 359
9.2.11 Miscellaneous C–C Bond-Forming Reactions 360
9.3 C–N Bond Formation 360
9.3.1 Buchwald–Hartwig Aryl Amination 360
9.3.2 Allylic Amination 362
9.3.3 Miscellaneous C–N Bond-Forming Reactions 363
9.4 Other Transformations 364
9.5 Conclusions and Outlook 364
References 365
Chapter 10 - NHC–Nickel and Platinum Complexes in Catalysis 375
10.1 Introduction 375
10.2 General Considerations for NHC–Ni0 and NHC–NiII Complexes 376
10.3 Dehalogenation and Dehydrogenation Mediated by NHC–Ni Complexes 377
10.3.1 Dehalogenation Mediated by NHC–Ni Complexes 377
10.3.2 Dehydrogenation Mediated by NHC–Ni Complexes 379
10.3.3 Dehydrogenative Cross-Coupling Reactions Induced by NHC–Ni Complexes 380
10.4 Activation/Cleavage of C–C, C–S, C–O or C–CN Bonds Mediated by NHC–Ni Complexes 381
10.5 Aryl Amination, Aryl Thiolation and Hydrothiolation Mediated by NHC–Ni Complexes 383
10.5.1 Aryl Amination Mediated by NHC–Ni Complexes 383
10.5.2 Aryl Thiolation Induced by NHC–Ni Complexes 385
10.5.3 Hydrothiolation of Alkynes Mediated by NHC–Ni Complexes 386
10.6 NHC–Ni-Catalyzed Cross-Coupling Reactions 386
10.6.1 NHC–Ni-Catalyzed Corriu–Kumada Cross-Coupling Reactions 387
10.6.2 Alpha-Arylation of Ketones 390
10.6.3 NHC–Ni-Catalyzed Organomanganese Cross-Coupling Reactions 390
10.6.4 NHC–Ni Catalyzed Suzuki–Miyaura Cross-Coupling Reactions 390
10.6.5 NHC–Ni Catalyzed Negishi Cross-Coupling Reactions 392
10.7 Synthesis of Heterocyclic and Polycyclic Compounds by Cycloaddition Reactions 392
10.7.1 Pyrones from Diynes and Carbon Dioxide 393
10.7.2 Pyridones or Pyrimidine-diones from Diynes or Alkynes and Isocyanates 393
10.7.3 Pyridines from Diynes and Nitriles 395
10.7.4 Pyrans from Unsaturated Hydrocarbons and Carbonyl Substrates 395
10.8 Cycloaddition of Alkynes to Unsaturated Derivatives 396
10.9 Ni-Catalyzed Isomerization of Vinylcyclopropanes and Derivatives 397
10.10 Multi-Component Reactions with Aldehydes and Ketones 399
10.11 Reactions of Alkenes Mediated by NHC–Ni Complexes 402
10.12 Dimerization, Oligomerization and Polymerization Mediated by NHC–Ni Complexes 403
10.13 Carboxylation by NHC–Ni complexes 405
10.14 NHC–Pt Species and their Potential Applications 405
10.15 Reactions Mediated by NHC–Pt Complexes 409
10.16 Conclusion and Outlook 411
References 411
Chapter 11 - NHC–Copper, –Silver and –Gold Complexes in Catalysis 421
11.1 Introduction 421
11.2 NHC–Cu in Catalysis 422
11.2.1 Conjugate Additions and 1,2-Additions to Carbonyl Derivatives 422
11.2.2 Allylic Alkylation Reactions 424
11.2.3 Reduction Reactions 425
11.2.4 Boration Reactions 427
11.2.5 Silylation Reactions 429
11.2.6 Cross-Coupling Reactions 430
11.2.7 Miscellaneous Reactions 431
11.3 NHC–Ag in Catalysis 432
11.4 NHC–Au in Catalysis 434
11.4.1 Enyne Cycloisomerization and Related Reactions 434
11.4.2 1,2- and 1,3-Ester Migration Reactions 436
11.4.3 Hydrofunctionalization of π-Bonds 438
11.4.4 Miscellaneous Reactions 439
11.5 Outlook 441
Acknowledgements 442
References 442
Chapter 12 - Oxidation Reactions with NHC Metal Complexes 456
12.1 Introduction 456
12.2 O2 Activation by NHC–Metal Complexes 457
12.3 Alcohol Oxidation 465
12.4 Alkene Oxidation 472
12.5 Alkane and Arene Oxidation 476
12.6 Conclusion 480
References 480
Chapter 13 - Reduction Reactions with NHC-Bearing Complexes 484
13.1 Introduction 484
13.2 Hydrogenation Reactions 484
13.2.1 Hydrogenation of Alkenes, Carbonyl Compounds and Imines 485
13.2.2 Asymmetric Hydrogenation Reactions 489
13.3 Transfer Hydrogenation Reactions 492
13.3.1 Carbonyl and Imine Reductions 492
13.3.2 Asymmetric Transfer Hydrogenation Reactions 500
13.3.3 Borrowing Hydrogen Methodology 502
13.4 Hydrosilylation Reactions 504
13.4.1 Hydrosilylation of Alkenes 504
13.4.2 Hydrosilylation of Alkynes 505
13.4.3 Hydrosilylation of Carbonyl Compounds 509
13.4.4 Asymmetric Hydrosilylation Reactions 515
13.5 Hydroboration Reactions 519
13.5.1 Asymmetric Hydroboration Reactions 521
13.6 Conclusion 523
References 523
Chapter 14 - N-Heterocyclic Carbenes as Organic Catalysts 534
14.1 Introduction 534
14.2 Benzoin and Stetter Reactions 535
14.3 NHC-Catalyzed Transesterification Reactions 536
14.4 Catalytic Generation of Activated Carboxylates 537
14.5 NHC-Catalyzed Oxidative Esterification 540
14.6 NHC-Catalyzed Reactions of α,β-Unsaturated Aldehydes 543
14.6.1 NHC-Catalyzed Generation of Homoenolates 544
14.6.2 NHC-Catalyzed Cyclopentene and Cyclopentane Formations 547
14.6.3 NHC-Catalyzed Generation of Enolates from Enals 549
14.6.4 Enal Surrogates in NHC-Catalyzed Reactions 550
14.7 Enantioselective Annulations with NHC-Bound Enolate Equivalents 552
14.8 Activation of Boryl and Silyl Derivatives Catalyzed by NHCs 553
14.9 Alkylations Catalyzed by NHCs 555
14.10 NHC–CO2 Adducts 556
14.11 Choice of Azolium Pre-catalysts 557
14.12 Conclusions and Outlook 560
References 560
Chapter 15 - Biologically Active N-Heterocyclic Carbene–Metal Complexes 567
15.1 Introduction 567
15.2 Antimicrobial Activity of NHC–Metal Complexes 568
15.2.1 Antimicrobial Activity of NHC–Silver Complexes 568
15.2.2 Antimicrobial Activity of NHC–Gold Complexes 574
15.2.3 Antimicrobial Activity of Complexes with Other Metals 576
15.3 Anticancer Activity of NHC–Metal Complexes 578
15.3.1 Anticancer Activity of NHC–Silver Complexes 580
15.3.2 Anticancer Activity of NHC–Gold Complexes 582
15.3.3 Anticancer Activity of NHC–Platinum Complexes 585
15.3.4 Anticancer Activity of NHC Complexes with Other Metals 587
15.4 Conclusions and Outlook 589
References 590
Subject Index 596

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