Chemical Photocatalysis (eBook)

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Burkhard König, University of Regensburg, Germany.

List of contributing authors 5
1 Introduction 15
2 Early pioneers of organic photochemistry 17
2.1 References 29
3 Photophysics of Photocatalysts 33
3.1 Setting the Frame 35
3.2 The Experimentalist’s Perspective 38
3.3 The Theoreticians’ Perspective: A Closer Look 45
3.3.1 Transition probabilities 46
3.3.2 Orbitals 50
3.4 References 57
4 Flavin photocatalysis 59
4.1 Introduction 59
4.1.1 General properties 60
4.2 Early examples of flavin photocatalysis 62
4.3 Flavin photocatalysis in synthesis application 65
4.4 Flavin-related compounds in photocatalysis 72
4.5 Photooxidations via singlet oxygen mechanism 73
4.6 Conclusion 75
4.7 References 75
5 Templated Enantioselective Photocatalysis 81
5.1 Introduction 81
5.2 Early studies. Paternò-Büchi cycloadditions of a chiral aromatic aldehyde and cyclic enamines 83
5.3 Enantioselective Norrish-Yang cyclization reaction of prochiral imidazolidinones 83
5.4 Enantioselective photochemical [4+4]-cycloadditions and electrocyclic [4p]-ring closure of 2-pyridones 85
5.5 Enantioselective [6p]-photocyclization of acrylanilides 86
5.6 Enantioselective Diels-Alder reaction of a photochemically generated ortho-quinodimethane 87
5.7 Formal [3+2]-photocycloadditions of 2-substituted naphthoquinones 88
5.8 Intramolecular [2+2]-photocycloadditions of substituted 5,6-dihydro-1H-pyridin-2-ones 88
5.9 Enantioselective radical cyclizations 89
5.9.1 Reductive radical cyclization reactions of 3-(.-iodoalkylidene)-piperidin-2-ones 89
5.9.2 Reductive radical cyclization of 3-(3-iodopropoxy)propenoic acid derivatives 90
5.9.3 Radical cyclization reactions of 4-substituted quinolones 91
5.10 [2+2]-Photocycloaddition reactions of substituted isoquinolones 91
5.11 [2+2]-Photocycloaddition reactions of substituted quinolones 93
5.11.1 Intermolecular [2+2]-photocycloaddition reactions of quinolones 93
5.11.2 Intramolecular [2+2]-photocycloadditions of 4-(2?-aminoethyl)quinolones 93
5.11.3 Intramolecular [2+2]-photocycloadditions of 4-(?-alkenyloxy)-quinol-2-ones 95
5.12 Light-induced enantioselective catalysis 96
5.12.1 Photoinduced electron transfer enantioselective catalytic reactions 98
5.12.2 Catalyzed enantioselective [2+2]-photocycloadditions of 4-substituted quinolones 98
5.13 Conclusion 100
5.14 References 100
6 Photocatalysis with nucleic acids and peptides 105
6.1 Introduction 105
6.2 DNA-assisted enantioselective reactions 105
6.2.1 Photocatalytically active DNA (PhotoDNAzymes) 107
6.2.2 Benzophenone as photosensitizer in DNA for the development of PhotoDNAzymes 108
6.3 Small peptides as organocatalysts 112
6.3.1 Development of peptides for photocatalytic addition to olefins 115
6.4 Conclusion 121
6.5 References 121
7 Visible light photoredox catalysis with [Ru(bpy)3]2+: General principles and the twentieth century roots 125
7.1 Introduction 125
7.2 [Ru(bpy)3]2+ and its photoredox properties 125
7.3 Application of [Ru(bpyb]2+ as catalyst in the twentieth century 127
7.4 Conclusion 143
7.5 Abbreviations 145
7.6 References 145
8 Homogeneous visible light-mediated transition metal photoredox catalysis other than ruthenium and iridium 153
8.1 Introduction 153
8.2 Copper in visible light catalysis 153
8.3 Rhenium and platinum in visible light catalysis 157
8.4 Iron in visible light catalysis 159
8.4.1 Photocatalytic oxidation of hydrocarbons 159
8.4.2 Photocatalytic oxidative decarboxylation 159
8.4.3 Oxidative degradation 160
8.4.4 Isomerization 162
8.5 Conclusion 163
8.6 References 163
9 Synergistic Visible Light Photoredox Catalysis 165
9.1 Introduction 165
9.2 Stabilized iminium ions 167
9.2.1 Secondary amine-catalyzed Mannich reactions 168
9.2.2 Coinage metal-catalyzed alkynylation reactions 170
9.2.3 NHC-catalyzed acylations 172
9.3 Electrophilic carbon-centered radicals 173
9.3.1 Secondary amine-catalyzed a-alkylation of aldehydes 173
9.3.2 Palladium-catalyzed C-H arylation 177
9.3.3 Copper-catalyzed trifluoromethylation of aryl boronic acids 179
9.4 Conclusion 181
9.5 References 181
10 Photoredox catalyzed a-functionalization of amines – Visible light mediated carbon-carbon and carbon-hetero bond forming reactions 183
10.1 Introduction 183
10.2 Aza-Henry Reaction 187
10.3 Addition of malonates 190
10.4 Mannich reaction 191
10.5 Allylation 192
10.6 Cyanation of tertiary amines 192
10.7 Alkynylation 193
10.8 [3+2] cycloaddition reaction 194
10.9 Acylation 194
10.10 C-heteroatom (C-P, C-O, C-N) bond formation 194
10.11 Conclusion 196
10.12 References 197
11 Metal complexes for photohydrogenation and hydrogen evolution 199
11.1 Analysis of construction components of artificial photocatalytic systems 201
11.1.1 Chromophore 201
11.1.2 Electron relay 202
11.1.3 Redox equivalents 202
11.1.4 Reduction catalysts 202
11.1.5 Intramolecular hydrogen evolving photocatalysts 203
11.1.6 Oxidation catalysts 204
11.1.7 Intramolecular oxidation catalysts 205
11.1.8 Comparison of inter- and intramolecular photocatalysis 206
11.2 Intramolecular photocatalysts for hydrogen production and hydrogenation 207
11.2.1 Hydrogen production 208
11.2.2 Photohydrogenation 210
11.2.3 Photophysics 211
11.2.4 Ru(tpphz)Pd-type catalysts as photochemical molecular devices (PMD) 216
11.3 Conclusion 218
11.4 References 219
12 Heterogeneous semiconductor photocatalysis 225
12.1 Inorganic semiconductors 225
12.1.1 General features of a photocatalyst 225
12.1.1.1 Band structure and band gap 225
12.1.1.2 The Fermi level and charge separation 228
12.1.2 How to tune a photocatalyst 231
12.1.2.1 Doping and Co-Catalysts 231
12.1.2.2 Particle size effect 234
12.1.3 Selected examples of photocatalysts and their application to organic synthesis 235
12.1.3.1 TiO2 – an UV active photocatalyst 235
12.1.3.2 Selected examples of visible light active photocatalysts 237
12.2 Organic semiconductors 244
12.2.1 Basic properties of organic semiconductors 245
12.2.1.1 Band structure and band gap 245
12.2.1.2 Photoinduced electron transfer – Exciton generation and dissociation 245
12.2.2 Application of conjugated polymers in photocatalysis 246
12.2.2.1 Linear conjugated polymers 246
12.2.2.2 Conjugated polymers with layered structure 249
12.3 References 253
13 Polyoxometalates in photocatalysis 261
13.1 Introduction 261
13.1.1 Polyoxometalates – Molecular metal oxide clusters 261
13.1.2 Concepts in polyoxometalate photochemistry 262
13.1.3 The basics of POM photochemistry 263
13.1.4 Traditional photooxidation of organic substrates 264
13.2 Recent developments in POM photochemistry 264
13.2.1 Water oxidation by Ru- and Co-polyoxometalates 264
13.2.2 Polyoxoniobate water oxidation 265
13.2.3 Water oxidation by Dawson anions in ionic liquids 266
13.2.4 Photoreductive CO2-activation 267
13.2.5 Photoreductive H2 generation 268
13.3 Optimizing photocatalytic performance of polyoxometalates 268
13.3.1 Structurally adaptive systems 268
13.3.2 Optimized photoactivity by metal substitution 269
13.3.3 Inspiration from the solid-state world 271
13.4 Conclusion 272
13.5 Acknowledgments 272
13.6 References 272
14 Description of excited states in photocatalysis with theoretical methods 277
14.1 Introduction 277
14.2 The concept of potential energy surfaces 278
14.3 Computational methods for excited states 282
14.3.1 QM-Methods 282
14.3.1.1 Time-dependent coupled cluster response 283
14.3.1.2 Time-dependent density functional theory 284
14.3.2 Solvent description via the QM/MM approach 285
14.3.2.1 MM methods 286
14.3.2.2 QM/MM coupling 287
14.4 Procedure 288
14.5 Examples 290
14.5.1 Roseoflavin 291
14.5.2 Benzophenone in dinucleotides 296
14.6 Conclusion 301
14.7 References 302
15 Transient Absorption 309
15.1 Introduction 309
15.2 Experimental Setup 312
15.3 Data Analysis 314
15.3.1 SVD and rank analysis 315
15.3.2 Global lifetime analysis 316
15.3.3 Eliminating invalid data 317
15.3.4 Maximum entropy analysis 317
15.4 Performance 321
15.4.1 RFTA alone 321
15.4.2 Photooxidation of MBA with RFTA 325
15.5 Discussion 329
15.6 Conclusion 330
15.7 Acknowledgments 331
15.8 References 331
16 Time resolved spectroscopy in photocatalysis 333
16.1 UV/Vis absorption spectroscopy: More than just e! 333
16.2 Time-Resolved spectroscopic methods from fs to µs to elucidate photocatalytic processes 337
16.2.1 Transient absorption spectroscopy: Signals, time scales, and data processing 337
16.2.2 Spectroscopy on the fs to ps time scale 340
16.2.3 Spectroscopy on the ns to µs time scale 344
16.2.4 Rate models and the determination of the species associated spectra of the intermediate states 350
16.3 Diffusion limited reactions 360
16.3.1 Diffusion limited excited state quenching with time dependent reaction rate 360
16.3.2 Application of the diffusion fit function to experimental data 365
16.4 Costs of photocatalysis: The reaction quantum yield 371
16.4.1 Requirements for an accurate definition of the quantum yield 371
16.4.2 Determination of the quantity of excited molecules in transient absorption measurements 376
16.4.3 Example of the spectroscopic determination of reaction quantum yields: Flavin photocatalysis 378
16.5 From light absorption to chemistry: Sensitizing mechanisms in homogeneous photocatalysis 383
16.5.1 Sensitization by excitation energy transfer 383
16.5.2 Photoredox catalysis: Requirements on catalyst and substrate 384
16.6 Epilogue 388
16.7 References 390
Index 393