Water oxidation catalyzed by a charge-neutral mononuclear ruthenium(iii) complex.

A new charge-neutral Ru(iii) complex RuL(pic)3 (1) (H3L = 3,6-di-tert-butyl-9H-carbazole-1,8-dicarboxylic acid, pic = 4-picoline) was synthesized and fully characterized. This complex promoted chemical and photochemical water oxidation efficiently with turnover frequencies of 0.28 s-1 and 5 min-1, respectively. In particular, for photochemical water oxidation, complex 1 showed excellent stability and good activity. The X-ray crystal structure, electrochemical results, and the detection of the RuIV-OH intermediate by high-resolution mass spectrometry revealed that complex 1 exchanged its 4-picoline ligand with water at the RuIII state to form the authentic water oxidation catalyst. The kinetics studies suggested a reaction mechanism involving nucleophilic attack by a water molecule.