Table Of ContentStable Radicals
Fundamentals and Applied Aspects
of Odd-Electron Compounds
Editor
ROBIN G. HICKS
Department of Chemistry, University of Victoria, Canada
A John Wiley and Sons, Ltd., Publication
Stable Radicals
Fundamentals and Applied Aspects
of Odd-Electron Compounds
Editor
ROBIN G. HICKS
Department of Chemistry, University of Victoria, Canada
A John Wiley and Sons, Ltd., Publication
Thiseditionfirstpublished(cid:1)c 2010
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Stableradicals:fundamentalsandappliedaspectsofodd-electroncompounds/
editor,RobinG.Hicks.
p.cm.
Includesbibliographicalreferencesandindex.
ISBN978-0-470-77083-2(hardback)
1. Radicals(Chemistry)–Stability.2. Electronmobility.I.Hicks,RobinG.
QD471.S732010
(cid:2)
541.224–dc22
2010010754
AcataloguerecordforthisbookisavailablefromtheBritishLibrary.
ISBN978-0-470-77083-2
Typesetin10/12TimesbyLaserwordsPrivateLimited,Chennai,India
PrintedandboundintheUnitedKingdombyAntonyRoweLtd,Chippenham,Wiltshire
Contents
Preface xv
ListofContributors 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
vi Contents
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
Contents vii
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, Franc¸ois 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
viii Contents
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 C) C=NOH 236
3 2
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 N−NR] Group 245
2
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
