Water Oxidation by Mononuclear Ruthenium Complexes with TPA-Based Ligands

Abstract

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 <i>N</i>,<i>N</i>-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 Ce^IV 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.