phenalenyls, cyclopentadienyls, and other carbon-centered radicals<
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"This is a worthwhile and insightful anthology and leaves the reader with the impression that novel prospects and discoveries could surface at any moment from junctions on the stable radical chemical topology." (Angewandte Chemie, 2011)
Table of Contents
Preface xv
List of Contributors xvii
1. Triarylmethyl and Related Radicals 1
Thomas T. Tidwell
1.1 Introduction 1
1.1.1 Discovery of the triphenylmethyl radical 1
1.1.2 Bis(triphenylmethyl) peroxide 3
1.2 Free radical rearrangements 4
1.3 Other routes to triphenylmethyl radicals 5
1.4 The persistent radical effect 7
1.5 Properties of triphenylmethyl radicals 8
1.6 Steric effects and persistent radicals 9
1.7 Substituted triphenylmethyl radicals and dimers 9
1.8 Tris(heteroaryl)methyl and related triarylmethyl radicals 12
1.9 Delocalized persistent radicals: analogues of triarylmethyl radicals 14
1.10 Tetrathiatriarylmethyl (TAM) and related triarylmethyl radicals 16
1.11 Perchlorinated triarylmethyl radicals 20
1.12 Other triarylmethyl radicals 23
1.13 Diradicals and polyradicals related to triphenylmethyl 24
1.14 Outlook 28
Acknowledgements 28
References 28
2. Polychlorotriphenylmethyl Radicals: Towards Multifunctional Molecular Materials 33
Jaume Veciana and Imma Ratera
2.1 Introduction 33
2.2 Functional molecular materials based on PTM radicals 35
2.2.1 Materials with magnetic properties 37
2.2.2 Materials with electronic properties 53
2.2.3 Materials with optical properties 65
2.3 Multifunctional switchable molecular materials based on PTM radicals 69
2.3.1 Photo switchable molecular systems 69
2.3.2 Redox switchable molecular systems 70
2.4 Conclusions 75
References 76
3. Phenalenyls, Cyclopentadienyls, and Other Carbon-Centered Radicals 81
Yasushi Morita and Shinsuke Nishida
3.1 Introduction 81
3.2 Open shell graphene 82
3.3 Phenalenyl 84
3.4 2,5,8-Tri-tert-butylphenalenyl radical 86
3.5 Perchlorophenalenyl radical 92
3.6 Dithiophenalenyl radicals 94
3.7 Nitrogen-containing phenalenyl systems 97
3.7.1 Molecular design and topological isomers 97
3.7.2 2,5,8-Tri-tert-butyl-1,3-diazaphenalenyl 97
3.7.3 Hexaazaphenalenyl derivatives 102
3.7.4 β-Azaphenalenyl derivatives 103
3.8 Oxophenalenoxyl systems 106
3.8.1 Molecular design and topological isomers 106
3.8.2 3-Oxophenalenoxyl (3OPO) system 108
3.8.3 4- and 6-Oxophenalenoxyl (4OPO, 6OPO) systems 110
3.8.4 Redox-based spin diversity 114
3.8.5 Molecular crystalline secondary battery 115
3.8.6 Spin-center transfer and solvato-/thermochromism 117
3.9 Phenalenyl-based zwitterionic radicals 119
3.10 π-Extended phenalenyl systems 122
3.10.1 Triangulenes 122
3.10.2 Trioxytriangulene with redox-based spin diversity nature 125
3.10.3 Bis- and tris-phenalenyl system and singlet biradical characters 125
3.11 Curve-structured phenalenyl system 130
3.12 Non-alternant stable radicals 131
3.12.1 Cyclopentadienyl radicals 131
3.12.2 Cyclopentadienyl radicals within a larger π-electronic framework 135
3.13 Stable triplet carbenes 136
3.14 Conclusions 139
Acknowledgements 139
References 140
4. The Nitrogen Oxides: Persistent Radicals and van der Waals Complex Dimers 147
D. Scott Bohle
4.1 Introduction 147
4.2 Synthetic access 149
4.3 Physical properties 149
4.4 Structural chemistry of the monomers and dimers 150
4.4.1 Nitric oxide and dinitrogen dioxide 150
4.4.2 Nitrogen dioxide and dinitrogen tetroxide 152
4.5 Electronic structure of nitrogen oxides 153
4.6 Reactivity of nitric oxide and nitrogen dioxide and their van der Waals complexes 155
4.7 The kinetics of nitric oxide’s termolecular reactions 156
4.8 Biochemical and organic reactions of nitric oxide 158
4.9 General reactivity patterns 160
4.9.1 Oxidation 160
4.9.2 Reduction 161
4.9.3 Coordination 162
4.9.4 Addition of nucleophiles 162
4.9.5 General organic reactions 165
4.9.6 Reactions with other nucleophiles 165
4.10 The colored species problem in nitric oxide chemistry 166
4.11 Conclusions 166
References 166
5. Nitroxide Radicals: Properties, Synthesis and Applications 173
Hakim Karoui, François Le Moigne, Olivier Ouari and Paul Tordo
5.1 Introduction 173
5.2 Nitroxide structure 174
5.2.1 Characteristics of the aminoxyl group 174
5.2.2 X-ray structures of nitroxides 175
5.2.3 Quantum mechanical (QM), molecular dynamics (MD) and molecular mechanics (MM) calculations 177
5.2.4 Influence of solvent polarity on the EPR parameters of nitroxides 180
5.3 Nitroxide multiradicals 181
5.3.1 Electron spin–spin exchange coupling 182
5.3.2 Miscellaneous aspects of di- and polynitroxides 184
5.4 Nitronyl nitroxides (NNOs) 185
5.4.1 Synthesis of nitronyl nitroxides 186
5.4.2 Nitronyl nitroxide as a nitric oxide trap 186
5.4.3 Nitronyl nitroxides as building blocks for magnetic materials 188
5.5 Synthesis of nitroxides 191
5.5.1 Oxidation of amines 191
5.5.2 Oxidation of hydroxylamines 191
5.5.3 Chiral nitroxides 191
5.5.4 Nitroxide design for nitroxide mediated polymerization (NMP) 193
5.6 Chemical properties of nitroxides 196
5.6.1 The Persistent Radical Effect 197
5.6.2 Redox reactions 197
5.6.3 Approaches to improve the resistance of nitroxides toward bioreduction 198
5.6.4 Hydrogen abstraction reactions 199
5.6.5 Cross-coupling reactions 200
5.6.6 Nitroxides in synthetic sequences 200
5.7 Nitroxides in supramolecular entities 206
5.7.1 Interaction of nitroxides with cyclodextrins 207
5.7.2 Interaction of nitroxides with calix[4]arenes 209
5.7.3 Interaction of nitroxides with curcubiturils 210
5.7.4 Interaction of nitroxides with micelles 211
5.7.5 Fullerene-linked nitroxides 212
5.8 Nitroxides for dynamic nuclear polarization (DNP) enhanced NMR 213
5.8.1 DNP for biological NMR and real-time metabolic imaging 213
5.8.2 Nitroxides as polarizing agents for DNP 214
5.9 Nitroxides as pH-sensitive spin probes 216
5.10 Nitroxides as prefluorescent probes 217
5.11 EPR-spin trapping technique 217
5.11.1 Immuno spin trapping 219
5.11.2 Conclusion 219
5.12 Conclusions 220
References 220
6. The Only Stable Organic Sigma Radicals: Di-tert-Alkyliminoxyls 231
Keith U. Ingold
6.1 Introduction 231
6.2 The discovery of stable iminoxyls 232
6.2.1 Synthesis of di-tert-butyl ketoxime 233
6.2.2 Synthesis of di-tert-butyliminoxyl 234
6.2.3 Stability of di-tert-butyliminoxyl 235
6.3 Hydrogen atom abstraction by di-tert-butyliminoxyl 236
6.3.1 The O−H bond dissociation enthalpy (BDE) in (Me 3 C) 2 C=NOH 236
6.3.2 Oxidation of hydrocarbons with di-tert-butyliminoxyl 237
6.3.3 Oxidation of phenols with di-tert-butyliminoxyl 238
6.3.4 Oxidation of amines with di-tert-butyliminoxyl 239
6.3.5 Oxidation of di-tert-butylketoxime with di-tert-butyliminoxyl 239
6.4 Other reactions and non-reactions of di-tert-butyliminoxyl 241
6.5 Di-tert-alkyliminoxyls more sterically crowded than di-tert-butyliminoxyl 241
6.6 Di-(1-Adamantyl)iminoxyl: a truly stable σ radical 242
References 243
7. Verdazyls and Related Radicals Containing the Hydrazyl [R 2 N−NR] Group 245
Robin G. Hicks
7.1 Introduction 245
7.2 Verdazyl radicals 246
7.2.1 Synthesis of verdazyls 246
7.2.2 Stability, physical properties and electronic structure of verdazyls 250
7.2.3 Verdazyl radical reactivity 256
7.2.4 Inorganic verdazyl analogues 264
7.3 Tetraazapentenyl radicals 265
7.4 Tetrazolinyl radicals 266
7.5 1,2,4-Triazolinyl radicals 268
7.6 1,2,4,5-Tetrazinyl radicals 269
7.7 Benzo-1,2,4-triazinyl radicals 270
7.8 Summary 273
References 273
8. Metal Coordinated Phenoxyl Radicals 281
Fabrice Thomas
8.1 Introduction 281
8.2 General properties of phenoxyl radicals 282
8.2.1 Electronic structure and stabilization 282
8.2.2 Electrochemistry of phenoxyl radicals 283
8.2.3 Structure of non-coordinated phenoxyl radicals 284
8.2.4 UV-Vis spectroscopy 284
8.2.5 EPR spectroscopy 284
8.3 Occurrence of tyrosyl radicals in proteins 285
8.4 Complexes with coordinated phenoxyl radicals 287
8.4.1 General ligand structures 287
8.4.2 Vanadium complexes 290
8.4.3 Chromium complexes 291
8.4.4 Manganese complexes 292
8.4.5 Iron complexes 294
8.4.6 Cobalt complexes 297
8.4.7 Nickel complexes 299
8.4.8 Copper complexes 303
8.4.9 Zinc complexes 310
8.5 Conclusions 313
8.6 Abbreviations 313
References 313
9. The Synthesis and Characterization of Stable Radicals Containing the Thiazyl (SN) Fragment and Their Use as Building Blocks for Advanced Functional Materials 317
Robin G. Hicks
9.1 Introduction 317
9.2 Radicals based exclusively on sulfur and nitrogen 319
9.2.1 NS• and SNS• 319
9.2.2 S3 N3• 320
9.2.3 S3 N2•+ and related radical cations 320
9.2.4 Poly(thiazyl), (SN)X 322
9.3 “Organothiazyl” radicals 323
9.3.1 Thioaminyl radicals 323
9.3.2 1,2,3,5-Dithiadiazolyl radicals 329
9.3.3 1,3,2,4-Dithiadiazolyl radicals 336
9.3.4 1,3,2-Dithiazolyl radicals 339
9.3.5 1,2,3-Dithiazolyl radicals 342
9.3.6 Bis(1,2,3-dithiazole) and related radicals 345
9.3.7 1,2,4-Thiadiazinyl radicals 348
9.3.8 1,2,4,6-Thiatriazinyl and -selenatriazinyl radicals 349
9.3.9 Larger cyclic thiazyl radicals 355
9.4 Thiazyl radicals as “advanced materials” 355
9.4.1 Charge transport properties of thiazyl radicals 356
9.4.2 Thiazyl radical-based charge transfer salts 360
9.4.3 Magnetic properties of thiazyl radicals 364
9.5 Conclusions 373
References 373
10. Stable Radicals of the Heavy p-Block Elements 381
Jari Konu and Tristram Chivers
10.1 Introduction 381
10.2 Group 13 element radicals 382
10.2.1 Boron 382
10.2.2 Aluminum, gallium, and indium 384
10.3 Group 14 element radicals 388
10.3.1 Cyclic group 14 radicals 389
10.3.2 Acyclic group 14 radicals 391
10.4 Group 15 element radicals 395
10.4.1 Phosphorus 395
10.4.2 Arsenic, antimony, and bismuth 400
10.5 Group 16 element radicals 400
10.5.1 Sulfur 400
10.5.2 Selenium and tellurium 401
10.6 Group 17 element radicals 402
10.7 Summary and future prospects 403
References 404
11. Application of Stable Radicals as Mediators in Living-Radical Polymerization 407
Andrea R. Szkurhan, Julie Lukkarila and Michael K. Georges
11.1 Introduction 407
11.2 Living polymerizations 408
11.2.1 Living-radical polymerization background 408
11.3 Stable free radical polymerization 409
11.3.1 Background of the work performed at the Xerox Research Centre of Canada 409
11.3.2 General considerations and mechanism 410
11.3.3 Unimolecular initiators 411
11.3.4 Persistent radical effect 413
11.3.5 Requirements of stable radicals as mediating agents 413
11.3.6 Nitroxides as mediating agents 414
11.3.7 Nitroxides and their ability to moderate polymerizations 414
11.3.8 Rate enhancement of stable free radical polymerization through the use of additives 416
11.4 Non-nitroxide-based radicals as mediating agents 416
11.4.1 Triazolinyl radicals 416
11.4.2 Verdazyl radicals 417
11.4.3 Other radicals as mediators 418
11.5 Aqueous stable free radical polymerization processes 420
11.5.1 Living-radical miniemulsion polymerization 421
11.5.2 Emulsion polymerization 422
11.5.3 Other aqueous polymerization processes 423
11.6 The application of stable free radical polymerization to new materials 423
11.6.1 Statistical copolymers 423
11.6.2 Block copolymers 424
11.7 Conclusions 425
List of abbreviations 425
References 425
12. Nitroxide-Catalyzed Alcohol Oxidations in Organic Synthesis 433
Christian Brückner
12.1 Introduction 433
12.2 Mechanism of TEMPO-catalyzed alcohol oxidations 434
12.3 Nitroxides used as catalysts 435
12.3.1 Monomeric nitroxides 435
12.3.2 Ionic liquid nitroxides 436
12.3.3 Supported nitroxides 436
12.4 Chemoselectivity: oxidation of primary vs secondary alcohols 437
12.5 Chemoselectivity: oxidation of primary vs benzylic alcohols 438
12.6 Oxidation of secondary alcohols to ketones 439
12.7 Oxidations of alcohols to carboxylic acids 439
12.7.1 Oxidations leading to linear carboxylic acids 439
12.7.2 (Diol) oxidations leading to lactones 443
12.8 Stereoselective nitroxide-catalyzed oxidations 444
12.9 Secondary oxidants used in nitroxide-catalyzed reactions 446
12.9.1 Elemental halogens 446
12.9.2 Sodium hypochlorite (bleach) 446
12.9.3 Bis(acetoxy)iodobenzene (BAIB) 447
12.9.4 Oxygen (air) 448
12.9.5 Peroxides 449
12.9.6 Other organic secondary oxidants 450
12.9.7 Anodic, electrochemical oxidation 451
12.10 Use of nitroxide-catalyzed oxidations in tandem reactions 451
12.11 Predictable side reactions 453
12.11.1 Oxidations of sulfur 453
12.11.2 Oxidations of nitrogen 453
12.11.3 Oxidations of carbon 454
12.12 Comparison with other oxidation methods 454
12.13 Nitroxide-catalyzed oxidations and green chemistry 455
Acknowledgements 456
References 456
13. Metal–Nitroxide Complexes: Synthesis and Magnetostructural Correlations 461
Victor Ovcharenko
13.1 Introduction 461
13.2 Two types of nitroxide for direct coordination of the metal to the nitroxyl group 462
13.2.1 Complexes containing only >N−•O as a coordinating group 462
13.2.2 Complexes containing >N−•O and other functional groups as donor fragments 464
13.3 Ferro- and ferrimagnets based on metal–nitroxide complexes 465
13.3.1 Molecular magnets based on 1-D systems 470
13.3.2 Molecular magnets based on 2-D systems 474
13.3.3 Molecular magnets based on 3-D systems 480
13.4 Heterospin systems based on polynuclear compounds of metals with nitroxides 483
13.4.1 Reactions whose products retain both the multinuclear fragment and nitroxide 484
13.4.2 Transformation of polynuclear fragments in reactions with nitroxides 487
13.4.3 Transformation of both the polynuclear fragment and the starting nitroxide 489
13.5 Breathing crystals 490
13.6 Other studies of metal–nitroxides 494
13.6.1 Analytical applications 494
13.6.2 NMR spectroscopy 494
13.6.3 Stabilization of nitroxides with β-hydrogen atoms 496
13.6.4 Increased reactivity 496
13.6.5 Hidden exchange interactions 497
13.6.6 Contrast agents 499
13.7 Conclusions 500
References 500
14. Rechargeable Batteries Using Robust but Redox Active Organic Radicals 507
Takeo Suga and Hiroyuki Nishide
14.1 Introduction 507
14.2 Redox reaction of organic radicals 508
14.3 Mechanism and performance of an organic radical battery 509
14.4 Molecular design and synthesis of redox active radical polymers 512
14.4.1 Poly(methacrylate)s and poly(acrylate)s 512
14.4.2 Poly(vinyl ether)s and poly(allene)s 514
14.4.3 Poly(cyclic ether)s 514
14.4.4 Poly(norbornene)s 514
14.4.5 Poly(acetylene)s 514
14.4.6 Poly(styrene)s 515
14.4.7 Combination of radicals with biopolymers and ionic liquids 515
14.5 A totally organic-based radical battery 515
14.6 Conclusions 517
References 518
15. Spin Labeling: A Modern Perspective 521
Lawrence J. Berliner
15.1 Introduction 521
15.2 The early years 522
15.3 Advantages of nitroxides 523
15.4 Applications of spin labeling to biochemical and biological systems 524
15.4.1 Stoichiometry and specificity: proteins and enzymes 524
15.4.2 The reporter group approach: who makes the news? 525
15.5 Distance measurements 526
15.5.1 Metal–spin label distance measurements 526
15.5.2 Spin label–spin label distance measurements 526
15.5.3 Example of strong dipolar interactions 527
15.5.4 Multiple-quantum EPR and distance measurements 528
15.6 Site directed spin labeling (SDSL): how is it done? 529
15.6.1 The SDSL paradigm 530
15.6.2 SDSL parameters 530
15.7 Other spin labeling applications 531
15.7.1 pH sensitive spin labels 532
15.7.2 Spin labeled DNA – structure, dynamics and sequence analysis 532
15.8 Conclusions 534
References 534
16. Functional in vivo EPR Spectroscopy and Imaging Using Nitroxide and Trityl Radicals 537
Valery V. Khramtsov and Jay L. Zweier
16.1 Introduction 537
16.2 Nitroxyl radicals 538
16.3 Triarylmethyl (trityl) radicals 539
16.4 In vivo EPR oximetry using nitroxyl and trityl probes 539
16.4.1 Magnetic resonance approaches for in vivo oximetry 540
16.4.2 Nitroxide probes for EPR oximetry 540
16.4.3 TAM oximetric probes 545
16.5 EPR spectroscopy and imaging of pH using nitroxyl and trityl probes 547
16.5.1 pH-sensitive nitroxyl radicals 547
16.5.2 Dual function pH- and oxygen-sensitive trityl radicals 553
16.6 Redox- and thiol-sensitive nitroxide probes 556
16.6.1 Nitroxides as redox-sensitive EPR probes 556
16.6.2 Disulfide nitroxide biradicals as GSH-sensitive EPR probes 558
16.7 Conclusions 562
Acknowledgements 563
References 563
17. Biologically Relevant Chemistry of Nitroxides 567
Sara Goldstein and Amram Samuni
17.1 Introduction 567
17.2 Mechanisms of nitroxide reactions with biologically relevant small radicals 569
17.3 Nitroxides as SOD mimics 571
17.4 Nitroxides as catalytic antioxidants in biological systems 573
17.5 Conclusions 576
Acknowledgements 576
References 576
Index 579
