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 (ТАМ) 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 (3ОРО) system ................ 108
3.8.3 4- and 6-Oxophenalenoxyl (4OPO, 6ОРО)
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
(Me3C)2C=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
[R2N—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 S3N3• .......................................... 320
9.2.3 S3N2•+ 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 Коnu 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 ТАМ 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
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