Photochemistry and Photophysics of Coordination Compounds

More documents

Recommendations

Info

182 S. Campagna et al. tained in the dark or when one of the key components (the Ru(II) chromophore, the Pd catalyst, or the particular bridging ligand) is missing. Interestingly, the same compound where the bridging ligand between the two metal sites is a bipyrimidine unit does not evolve molecular hydrogen. It is also reported that the amount of photocatalytically formed hydrogen depends strongly on the TEA concentration and the exposure time, and chloride ions inhibit the reaction. The amount of hydrogen produced increases steadily and levels off after 1200 min. After about 1800 min no more hydrogen is produced. The rate of hydrogen formation increases with increasing TEA concentration for low TEA concentration, but becomes independent at a TEA concentration > 0.86 mol L –1 , where it is about 1600 nmol min –1 . Although detailed mechanistic data are not available, the authors suggest as a first step of the process a twofold photoinduced reduction of the compound by TEA, analogously to what was reported for the related photoinduced electron collection system 51. Probably reduction is concomitant with proton extraction from TEA oxidation products: TEA should therefore be the proton source. The successive step should be reduction of the protons at the nearby Pd center. This latter step probably passes through a temporary chloride loss. The same paper also reports the photocatalyzed selective hydrogenation of tolane to cis-stilbene, accomplished by the same compound. Analogously to 60, the Ru(II) chromophore of 61 acts as the light harvester/photosensitizer (which also contains in its structure the electron acceptor subunit, that is, the phenazine moiety of the bridging ligand), while the role of the catalytic unit is here played by the Pd(II) center. Molecular hydrogen evolution under visible light irradiation has also been reported for trimetallic species like 53 [348]. Mechanistic details are not available. 5.8.2 Other Photocatalytic Systems The catalytic potential of heterometallic species containing Ru(II) and Re(I) chromophores for the conversion of CO2 to CO has been recently shown [349]. Compound 62 is one of the species in this regard. This investigation highlighted the fact that the photocatalytic activity is deeply influenced by the nature of both the bridging ligand and the peripheral ligands at the light-harvesting Ru(II) chromophore. The proposed mechanism is that upon light irradiation (λ > 480 nm) in DMF/triethanolamine (TEOA, acting as base) with 1-benzyl- 1,4-dihydronicotinamide (BNAH) as sacrificial donor, the initially produced Ru-based MLCT state is reduced by BNAH. Then intrabridging ligand electron transfer occurs, with formation of the reduced rhenium subunit. This latter speciesisknowntoreactwithCO2 upon Cl ligand loss [350, 351]. The reduction of CO2 is bielectronic, so it is assumed that the second electron transfer follows a similar route. The most efficient species of this series of compounds, which is exactly 62, exhibits a turnover number of 170.
Photochemistry and Photophysics of Coordination Compounds: Ruthenium 183 Two other dinuclear species (63 and 64) have been reported to show photocatalytic activity for specific reactions. The Ru–Pd dimer 63 is active for the photocatalytic dimerization of 1-methylstyrene [352], and the turnover numbers of the photocatalyzed reaction (> 90 within 4 h) and the high selectivity compete well with thermal catalytic systems. Compound 64 is active for the conversion of trans-4-cyanostilbene to its cis form [353]. Other aspects of the last mentioned works and of similar systems are also commented on in a very recent paper [354]. Photocatalytic processes based on photoelectrochemical cells in which the Ru chromophores are physically interfaced to electrodes or other solid systems are reported later. 5.9 Photoactive Molecular Machines Able to Perform Nuclear Motions In the last 10 years there has been great interest in designing molecular machines [280]. As machines of the macroscopic world, even molecular machines need energy to operate, and a suitable form of energy to power
Page 1 and 2:
280 Topics in Current Chemistry Edi
Page 3 and 4:
Photochemistry and Photophysics of
Page 5 and 6:
Volume Editors Prof. Vincenzo Balza
Page 7 and 8:
Topics in Current Chemistry Also Av
Page 9 and 10:
X Preface nation Compounds. The ven
Page 11 and 12:
Contents Photochemistry and Photoph
Page 13 and 14:
Top Curr Chem (2007) 280: 1-36 DOI
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Top Curr Chem (2007) 280: 37-67 DOI
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
70 N. Armaroli et al. (e.g. catenan
Page 83 and 84:
72 N. Armaroli et al. can be classi
Page 85 and 86:
74 N. Armaroli et al. Fig. 2 Qualit
Page 87 and 88:
76 N. Armaroli et al. Fig. 3 Theblu
Page 89 and 90:
78 N. Armaroli et al. In the CuA mi
Page 91 and 92:
80 N. Armaroli et al. pseudo-rotaxa
Page 93 and 94:
82 N. Armaroli et al. Fig. 11 Relat
Page 95 and 96:
84 N. Armaroli et al. Fig. 13 Absor
Page 97 and 98:
86 N. Armaroli et al. leading to a
Page 99 and 100:
88 N. Armaroli et al. Fig. 18 Trans
Page 101 and 102:
90 N. Armaroli et al. Fig. 20 Ligan
Page 103 and 104:
92 N. Armaroli et al. Fig. 22 Ligan
Page 105 and 106:
94 N. Armaroli et al. tionalized de
Page 107 and 108:
96 N. Armaroli et al. Fig. 24 Absor
Page 109 and 110:
98 N. Armaroli et al. prisingly, PP
Page 111 and 112:
100 N. Armaroli et al. A different
Page 113 and 114:
102 N. Armaroli et al. Cuprous clus
Page 115 and 116:
104 N. Armaroli et al. Fig. 32 Sche
Page 117 and 118:
106 N. Armaroli et al. Fig. 34 A te
Page 119 and 120:
108 N. Armaroli et al. which are va
Page 121 and 122:
110 N. Armaroli et al. Acknowledgem
Page 123 and 124:
112 N. Armaroli et al. 58. Miller M
Page 125 and 126:
114 N. Armaroli et al. 123. Armarol
Page 127 and 128:
Top Curr Chem (2007) 280: 117-214 D
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142: Photochemistry and Photophysics of
Page 191: Photochemistry and Photophysics of
Page 225 and 226: Top Curr Chem (2007) 280: 215-255 D
Page 243 and 244:
Page 245 and 246:
Page 247 and 248:
Page 249 and 250:
Page 251 and 252:
Page 253 and 254:
Page 255 and 256:
Page 257 and 258:
Page 259 and 260:
Page 261 and 262:
Page 263 and 264:
Page 265 and 266:
Page 267 and 268:
258 Author Index Volumes 251-280 Be
Page 269 and 270:
260 Author Index Volumes 251-280 Er
Page 271 and 272:
262 Author Index Volumes 251-280 Je
Page 273 and 274:
264 Author Index Volumes 251-280 Me
Page 275 and 276:
266 Author Index Volumes 251-280 Sa
Page 277 and 278:
268 Author Index Volumes 251-280 Vi
Page 279 and 280:
Subject Index Alkyne bridges 148 An
Page 281:
Subject Index 273 Rh(III) cyclometa
show all

Photochemistry and Photophysics of Coordination Compounds

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?