Photocatalytic oxidation of benzene to phenol using dioxygen as an oxygen source and water as an electron source in the presence of a cobalt catalyst

Photocatalytic hydroxylation of benzene to phenol by dioxygen (O(2)) occurs under visible light irradiation of an O(2)-saturated acetonitrile solution containing [Ru(II)(Me(2)phen)(3)](2+) as a photocatalyst, [Co(III)(Cp*)(bpy)(H(2)O)](2+) as an efficient catalyst for both the water oxidation and benzene hydroxylation reactions, and water as an electron source in the presence of Sc(NO(3))(3). The present study reports the first example of photocatalytic hydroxylation of benzene with O(2) and H(2)O, both of which are the most green reagents, under visible light irradiation to afford a high turnover number (e.g., >500). Mechanistic studies revealed that the photocatalytic reduction of O(2) to H(2)O(2) is the rate-determining step, followed by efficient catalytic hydroxylation of benzene to phenol with H(2)O(2), paving a new way for the photocatalytic oxygenation of substrates by O(2) and water.