Improvement of durability of an organic photocatalyst in p-xylene oxygenation by addition of a Cu(II) complex.
The catalytic durability of an organic photocatalyst, 9-mesityl-10-methyl acridinium ion (Acr(+)-Mes), has been dramatically improved by the addition of [{tris(2-pyridylmethyl)amine}Cu(II)](ClO(4))(2) ([(tmpa)Cu(II)](2+)) in the photocatalytic oxygenation of p-xylene by molecular oxygen in acetonitrile. Such an improvement is not observed by the addition of Cu(ClO(4))(2) in the absence of organic ligands. The addition of [(tmpa)Cu](2+) in the reaction solution resulted in more than an 11 times higher turnover number (TON) compared with the TON obtained without [(tmpa)Cu(II)](2+). In the photocatalytic oxygenation, a stoichiometric amount of H(2)O(2) formation was observed in the absence of [(tmpa)Cu(II)](2+), however, much less H(2)O(2) formation was observed in the presence of [(tmpa)Cu(II)](2+). The photocatalytic mechanism was investigated by laser flash photolysis measurements in order to detect intermediates. The reaction of O(2)˙(-) with [(tmpa)Cu(II)](2+) monitored by UV-vis spectroscopy in propionitrile at 203 K suggested formation of [{(tmpa)Cu(II)}(2)O(2)](2+), a transformation which is crucial for the overall 4-electron reduction of molecular O(2) to water, and a key in the observed improvement in the catalytic durability of Acr(+)-Mes.
Department of Material and Life Science, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.
Yusuke
Y
Yamada
Kazuki
K
Maeda
Kei
K
Ohkubo
Kenneth D
KD
Karlin
Shunichi
S
Fukuzumi
D000166:Acridines / Q000737:chemistry; D002384:Catalysis; D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D004579:Electron Transport; D007700:Kinetics; D008027:Light; D010100:Oxygen / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry; D013696:Temperature; D014992:Xylenes / Q000737:chemistry*
D000166:Acridines; D056831:Coordination Complexes; D011725:Pyridines; D014992:Xylenes; C431843:tris(2-pyridylmethyl)amine; C031286:4-xylene; D003300:Copper; D010100:Oxygen