PREFACE TO SERIES ............................................ xiii
PREFACE ........................................................ xv
CONTRIBUTORS .................................................. xix
PART 1 PROPERTIES AND REACTIONS OF CARBENES .................... 1
1 Carbene Stability .......................................... 3
Scott Gronert, James R. Keeffe, and Rory A. More
O'Ferrall
1.1 Introduction ............................................... 3
1.2 Background ................................................. 4
1.2.1 Measures of Carbene Stability ....................... 4
1.2.2 Bonding and Orbital Interactions in Carbenes ........ 6
1.2.3 Determining Carbene Stability ....................... 8
1.3 Carbene Stability ......................................... 11
1.3.1 Hydrocarbon-Substituted Carbenes ................... 11
1.3.2 Substituted Phenylcarbenes ......................... 16
1.3.3 Heteroatom-Substituted Carbenes .................... 20
1.3.4 Conjugated Heterocyclic Carbenes ................... 24
1.3.5 Carbenes with Other Electron-Withdrawing Groups .... 27
1.3.6 Carbenes versus Ylides ............................. 29
1.4 Correlations Involving Carbene Stability .................. 30
1.4.1 CSE versus Singlet-Triplet Gap ..................... 30
1.4.2 CSE(Singlet) versus Proton Affinities .............. 31
1.4.3 CSE(Singlet) versus Carbene Reaction Rates ......... 32
1.5 Conclusion and Outlook ..................................... 35
Suggested Reading ......................................... 35
References ................................................ 36
2 Stable Carbenes ........................................... 40
Jonathan P. Moerdyk and Christopher W. Bielawski
2.1 Introduction .............................................. 40
2.2 Types of Stable Carbenes .................................. 41
2.2.1 Push-Push Carbenes ................................. 42
2.2.2 Push-Pull Carbenes ................................. 48
2.2.3 Abnormal Carbenes .................................. 49
2.3 Spectroscopic Characteristics ............................. 50
2.4 Chemical Reactivity ....................................... 52
2.4.1 Heteroallenes/Electrophilic Traps .................. 55
2.4.2 Lewis Acids: Boryl Compounds ....................... 56
2.4.3 Alkenes, Alkynes, and Nitriles ..................... 56
2.4.4 Carbon Monoxide and Isonitriles .................... 59
2.4.5 X-H Activation ..................................... 60
2.4.6 Homodiatomic Bond Activation ....................... 63
2.4.7 Elemental Дtiotropes and other Reactive Species .... 65
2.5 Conclusions and Outlook ................................... 65
Suggested Reading ......................................... 67
References ................................................ 67
3 Acid-Base Chemistry of Carbenes ........................... 75
Ann Marie C. O'Donoghue and Richard S. Massey
3.1 Introduction .............................................. 75
3.2 Solution pKas of the Conjugate Acids of Carbenes .......... 76
3.2.1 Experimental Methods in Aprotic Solvents ........... 77
3.2.2 Experimental Methods in Aqueous Solution ........... 80
3.2.3 Substituent Effects on рКa ......................... 85
3.2.4 Solvent Effects on pKa ............................. 91
3.3 Gas-Phase Basicities and Proton Affinities of Carbenes .... 92
3.3.1 Experimental Methods ............................... 93
3.3.2 Heteroatom-Stabilized Carbenes ..................... 94
3.3.3 Alkyl-and Aryl-Substituted Carbenes ............... 100
3.3.4 Halocarbenes ...................................... 102
3.4 Conclusion and Outlook ................................... 103
Suggested Reading ........................................ 104
References ............................................... 104
4 Computational Methods for the Study of Carbenes and
their Excited States ..................................... 107
Hoi Ling Luk, Shubham Vyas, and Christopher M. Hadad
4.1 Introduction ............................................. 107
4.2 Carbenes ................................................. 109
4.3 Rearrangement in Excited States (RIES) ................... 111
4.4 Advances in Computational Investigations of Carbenes ..... 115
4.4.1 Configuration Interaction ......................... 117
4.4.2 Complete Active Space Self-Consistent Field
(CASSCF) Theory ................................... 118
4.4.3 Coupled-Cluster Theory with Resolution-of-the-
Identity Approximation (RI-CC2) ................... 121
4.4.4 Time-Dependent Density Functional Theory
(TD-DFT) .......................................... 121
4.4.5 Molecular Dynamics (MD) ........................... 123
4.5 Theoretical Studies of the Photochemistry of Carbene
Precursors ............................................... 123
4.6 Conclusion and Outlook ................................... 127
Suggested Reading ........................................ 128
References ............................................... 128
5 Dynamics in Carbene Reactions ............................ 131
Dina C. Merrer, K.N. Houk, and Lai Xu
5.1 Introduction ............................................. 131
5.1.1 Carbenes .......................................... 131
5.1.2 Nonstatistical Reaction Dynamics .................. 133
5.2 Dynamics of Carbene Cycloadditions to Alkenes and
Alkynes .................................................. 136
5.2.1 Carbene Additions to Unstrained Alkenes ........... 136
5.2.2 Carbene Additions to Strained π Systems ........... 144
5.2.3 Carbene Additions to Strained a Systems ........... 152
5.3 Dynamics of Other Carbene-Mediated Reactions ............. 153
5.3.1 Wolff Rearrangement ............................... 153
5.3.2 Photochemical Carbene Formation ................... 156
5.4 Conclusion and Outlook ................................... 159
Suggested Reading ........................................ 159
References ............................................... 160
6 Ultrafast Kinetics of Carbene Reactions .................. 166
Gotard Burdzinski and Mathew S. Platz
6.1 Introduction ............................................. 166
6.2 Ultrafast UV-Vis Studies of the Intermolecular
Reactivity of p-Biphenylylcarbene (BpCH) ................. 167
6.3 Rearrangements in the Excited State of the Carbene
Precursor ................................................ 171
6.4 Dynamics of Carbene Vibrational Cooling and Solvation .... 173
6.5 Influence of Solvent on Carbene Intersystem Crossing
Rates .................................................... 176
6.6 Electronically Excited (Open Shell) Singlet Carbenes ..... 179
6.7 Parent Phenyldiazirine—Mechanistic Aspects of Singlet
Carbene Formation ........................................ 179
6.8 Influence of Halo-Substituent Electron-Donating
Capacity on Diazirine Decay in the First Excited
Singlet State ............................................ 183
6.9 The Influence of Excitation Wavelength on the
Photochemistry of Diazirines ............................. 186
6.10 Conclusion and Outlook ................................... 189
Suggested Reading ........................................ 190
References ............................................... 191
7 Tunneling in the Reactions of Carbenes and Oxacarbenes ... 193
Dennis Gerbig and Peter R. Schreiner
7.1 Introduction: Light- and Heavy-Atom Tunneling ............ 193
7.2 Alkyl- and Halocarbenes .................................. 197
7.2.1 Cyclopropylcarbenes ............................... 197
7.2.2 Ethylidene and Phenylmethylcarbene ................ 200
7.2.3 Methylchlorocarbene and Benzylchlorocarbene ....... 201
7.2.4 tert-Butylchlorocarbene ........................... 202
7.2.5 1-Methylcyclobutylfluorocarbene ................... 202
7.2.6 Noradamantylchlorocarbene ......................... 203
7.3 The Formose Reaction and Hydroxycarbenes ................. 203
7.3.1 Hydroxymethylene .................................. 203
7.3.2 Methylhydroxycarbene and Tunneling Control ........ 205
7.3.3 Arylhydroxycarbenes ............................... 206
7.3.4 Cyclopropylhydroxycarbene ......................... 209
7.4 Conclusion and Outlook ................................... 210
Suggested Reading ........................................ 211
References ............................................... 211
8 Carbodicarbenes .......................................... 216
Gernot Frenking and Ralf Tonner
8.1 Introduction ............................................. 216
8.2 Carbodicarbenes with N-Heterocyclic Ligands C(NHC)2 ...... 218
8.3 Tetraaminoallenes and "Hidden" Carbodicarbenes ........... 225
8.4 Bent Allenes ............................................. 228
8.5 Related Compounds ........................................ 233
8.6 Conclusion and Outlook ................................... 234
Suggested Reading ........................................ 234
References ............................................... 234
9 Catalytic Reactions with N-Mesityl-Substituted
A'-Heterocyclic Carbenes ................................. 237
Jessada Mahatthananchai and Jeffrey W. Bode
9.1 Introduction ............................................. 237
9.1.1 Historical Background ............................. 238
9.1.2 State of the Art Prior to 2004 .................... 238
9.1.3 N-Mesityl Catalysts as the Key Innovation ......... 239
9.2 The N-Mesityl Group: A Mechanistic Aspect ................ 242
9.2.1 Catalytic Generation of Reactive Species via
N-Mesityl NHCs .................................... 242
9.2.2 The Kinetic Effect of the N-Mesityl Group ......... 243
9.3 NHC Catalysis by Class of Reactive Intermediates ......... 246
9.3.1 Acyl Anion Equivalent ............................. 246
9.3.2 Homoenolate Equivalent ............................ 248
9.3.3 Enolate Equivalent ................................ 254
9.3.4 Activated Carboxylate Equivalent .................. 257
9.3.5 α,β-Unsaturated Activated Carboxylate
Equivalent ........................................ 264
9.4 Conclusion and Outlook ................................... 268
Suggested Reading ........................................ 268
References ............................................... 268
10 Supramolecular Carbene Chemistry ......................... 274
Udo H. Brinker, Jean-Luc Mieusset, and Murray
G. Rosenberg
10.1 Introduction ............................................. 274
10.2 Types of Hosts Used in Supramolecular Carbene Chemistry .. 276
10.2.1 Cyclodextrins ..................................... 276
10.2.2 Hemicarcerands .................................... 276
10.2.3 Resorcin[4]arene-Based Cavitands .................. 278
10.2.4 Octa Acid ......................................... 278
10.2.5 Cucurbit[n]urils .................................. 278
10.2.6 Zeolites .......................................... 280
10.3 Choosing the Right Carbene Guest ......................... 283
10.4 Diazirines as Suitable Supramolecular Carbene
Precursors ............................................... 285
10.5 Architecture of the Guest@Host Complex ................... 287
10.6 Case Studies ............................................. 291
10.6.1 Carbenes with Available 1,2-H Shifts .............. 291
10.6.2 (2-[l,3-Dioxolan-2-yl]phenyl)(4-phenylphenyl)-
carbene ........................................... 294
10.6.3 4-Oxocyclohexa-2,5-dienylidene .................... 295
10.6.4 Dichlorocarbene ................................... 296
10.6.5 Adamantylidene .................................... 296
10.6.6 3-Oxobicyclo[3.2.1]octan-8-ylidene ................ 302
10.6.7 endo-3-Hydroxybicyclo[3.2.1]octan-8-ylidene ....... 304
10.6.8 Ring Fragmentation and Expansion .................. 305
10.6.9 Aryl(halo)carbenes ................................ 308
10.6.10 Fluoro(phenoxy)carbene ........................... 312
10.6.11 Persistent Triplet Carbenes ...................... 312
10.7 Conclusion and Outlook ................................... 313
Acknowledgments .......................................... 315
Suggested Reading ........................................ 315
References ............................................... 315
PART 2 METAL CARBENES ........................................ 325
11 Modern Lithium Carbenoid Chemistry ....................... 327
Vita Capriati
11.1 Introduction ............................................. 327
11.2 Structural Features of Lithium Carbenoids ................ 328
11.3 Lithium Halide Carbenoids ................................ 329
11.3.1 Thermal and Kinetic Stability ..................... 329
11.3.2 Configurational Stability and Stereochemistry
of the Coupling Reactions with Electrophiles ...... 331
11.4 Structure-Reactivity Relationships ....................... 342
11.5 Lithium-Oxygen Carbenoids ................................ 344
11.6 Lithium-Nitrogen Carbenoids .............................. 352
11.7 Conclusion and Outlook ................................... 355
Suggested Reading ........................................ 357
References ............................................... 357
12 Rhodium Carbenes ......................................... 363
Huw M.L. Davies and Brendan T. Parr
12.1 Introduction ............................................. 363
12.2 Overview of Rhodium-Carbenoid Intermediates and Chiral
Catalysts ................................................ 364
12.3 Enantioselective Cyclopropanation ........................ 367
12.4 Cascade Sequences Initiated by Rhodium-Catalyzed
Cyclopropanation ......................................... 370
12.5 Enantioselective Cyclopropenation ........................ 373
12.6 C-H Functionalization By Carbenoid-Induced C-H
Insertion ................................................ 375
12.7 Combined C-H Activation/Cope Rearrangement (CHCR) ........ 380
12.8 Formation and Reactions of Rhodium-Bound Ylides .......... 383
12.9 Vinylogous Reactions of Rhodium-Vinylcarbenoids .......... 392
12.10 Conclusions and Future Outlook .......................... 397
Suggested Reading ........................................ 397
References ............................................... 398
13 Ruthenium Carbenes ....................................... 404
Steven T. Diver and Jonathan M. French
13.1 Introduction ............................................. 404
13.2 Improved Mechanistic Understanding ....................... 405
13.2.1 Background ........................................ 406
13.2.2 Identification of Ruthenacyclobutane
Intermediates in Alkene Metathesis ................ 410
13.2.3 Conformational Dynamics "Windshield Wipering" ..... 412
13.3 Catalyst Development ..................................... 413
13.3.1 Development of Phosphine-Free Catalysts ........... 413
13.3.2 Decomposition of the Grubbs' Complex .............. 417
13.4 Achieving Selectivity in Alkene Metathesis ............... 424
13.4.1 Enantioselective Metathesis with Ruthenium
Carbenes .......................................... 424
13.4.2 Site Selectivity Using Relay Ring-Closing
Metathesis ........................................ 426
13.4.3 Z-Selective Alkene Metathesis ..................... 429
13.5 Applications ............................................. 432
13.5.1 Selected Examples of Alkene Metathesis in
the Total Synthesis of Natural Products ........... 432
13.5.2 Applications of Metathesis in Aqueous Systems ..... 438
13.5.3 Applications in Diversity-Oriented Synthesis ...... 441
13.6 Conclusion and Outlook ................................... 444
Suggested Reading ........................................ 445
References ............................................... 446
14 Nucleophilic Carbenes of the Chromium Triad .............. 452
Zachary J. Tonzetich
14.1 Introduction ............................................. 452
14.1.1 Discovery ......................................... 453
14.1.2 Spectroscopic Properties .......................... 455
14.1.3 Metathesis Reactivity ............................. 455
14.2 Chromium Carbenes ........................................ 457
14.2.1 Cr(VI) Carbenes ................................... 457
14.2.2 Nucleophilic Cr(III) Carbenes ..................... 459
14.2.3 Supported Cr(IV) Carbenes ......................... 459
14.3 Molybdenum Carbenes ...................................... 460
14.3.1 Mo(VI) Imido-Alkylidene-bis-Alkoxide Compounds .... 461
14.3.2 Mo(VI) Imido-Alkylidene Pyrrolide Compounds ....... 468
14.3.3 Other Nucleophilic Mo Carbenes .................... 471
14.3.4 Supported Mo Alkylidenes .......................... 473
14.4 Tungsten Carbenes ........................................ 476
14.4.1 W(VI) Imido-Alkylidene-bis-Alkoxide Compounds ..... 476
14.4.2 W(VI) Imido-Alkylidene Pyrrolide Compounds ........ 477
14.4.3 Other Nucleophilic Tungsten Carbenes .............. 480
14.5 Conclusions and Outlook .................................. 484
Suggested Reading ........................................ 485
References ............................................... 485
15 Cobalt-Mediated Carbene Transfer Reactions ............... 491
Xin Cui and X. Peter Zhang
15.1 Introduction ............................................. 491
15.2 Cobalt-Catalyzed Cyclopropanation Reactions .............. 494
15.2.1 Cobalt Dioximato and Cobalt Ketoiminato
Catalysts ......................................... 494
15.2.2 Cobalt Salen Catalysts ............................ 496
15.2.3 Cobalt Porphyrin Catalysts ........................ 501
15.2.4 Cobalt Catalysts with Other Supporting Ligands .... 512
15.2.5 Mechanistic Studies ............................... 514
15.3 Other Cobalt-Catalyzed Carbene Transfer Reactions ........ 517
15.3.1 Cyclopropenation .................................. 517
15.3.2 Carbonylation ..................................... 518
15.3.3 Olefination ....................................... 519
15.4 Conclusion and Outlook ................................... 520
Acknowledgments .......................................... 522
Suggested Reading ........................................ 522
References ............................................... 522
16 Gold Carbenes ............................................ 526
Liming Zhang
16.1 Introduction ............................................. 526
16.2 Nature of the Au-Carbon Double Bond ...................... 528
16.2.1 Experimental Studies .............................. 528
16.2.2 DFT Calculations .................................. 529
16.3 Generation and Reactions of Gold Carbenes ................ 530
16.3.1 Gold Carbenes with Dative or Alkyl Substituents ... 530
16.3.2 Generation and Reactions of α-Oxo Gold Carbenes ... 534
16.3.3 Generation and Reactions of α-Imino Gold
Carbenes .......................................... 542
16.3.4 Generation and Reactivities of Gold Carbenes
via Carbene Transfer .............................. 545
16.3.5 Generation and Reactivities of 1,3-Dipolar
Gold Carbenes from Allenes ........................ 545
16.4 Conclusion and Outlook ................................... 547
Suggested Reading ........................................ 548
References ............................................... 548
Index ......................................................... 552
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