Rapid water oxidation electrocatalysis by a ruthenium complex of the tripodal ligand tris(2-pyridyl)phosphine oxide† †Electronic supplementary information (ESI) available: Synthetic procedures and characterization data, electrochemical characterization, and crystallographic details. CCDC 1034644. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc00032g Click here for additional data file. Click here for additional data file.

The tris(2-pyridyl)phosphine oxide (Py3PO) complex [Ru(Py3PO)(bpy)(OH2)] 2+ (bpy is 2,20-bipyridine) is a pH-dependent water oxidation electrocatalyst that accelerates dramatically with increasing pH—up to 780 s 1 at pH 10 ( 1 V overpotential). Despite retaining the pentakis(pyridine) ligand arrangement common to previously reported catalysts, the tripodal Py3PO ligand framework supports much faster electrocatalysis. The early stages of the catalytic cycle are proposed to follow the typical pattern of single-site ruthenium catalysts, with two sequential 1H/1e proton-coupled electron transfer (PCET) oxidations, but the pH-dependent onset of catalysis and rapid rates are distinguishing features of the present system.