Water Oxidation by Mononuclear Ruthenium Complexes with TPA-Based Ligands

The synthesis, characterization, and water oxidation activity of mononuclear ruthenium complexes with tris(2-pyridylmethyl)amine (TPA), tris(6-methyl-2-pyridylmethyl)amine (Me3TPA), and a new pentadentate ligand N,N-bis(2-pyridinylmethyl)-2,2′-bipyridine-6-methanamine (DPA-Bpy) have been described. The electrochemical properties of these mononuclear Ru complexes have been investigated by both experimental and computational methods. Using CeIV as oxidant, stoichiometric oxidation of water by [Ru(TPA)(H2O)2]2+ was observed, while Ru(Me3TPA)(H2O)2]2+ has much less activity for water oxidation. Compared to [Ru(TPA)(H2O)2]2+ and [Ru(Me3TPA)(H2O)2]2+, [Ru(DPA-Bpy)(H2O)]2+ exhibited 20 times higher activity for water oxidation. This study demonstrates a new type of ligand scaffold to support water oxidation by mononuclear Ru complexes.