Improvement of durability of an organic photocatalyst in p-xylene oxygenation by addition of a Cu(ii) complex

Abstract

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 2O 2 formation was observed in the absence of [(tmpa)Cu II] 2+, however, much less H 2O 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} 2O 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. This journal is © the Owner Societies.