Rapid water oxidation electrocatalysis by a ruthenium complex of the tripodal ligand tris(2-pyridyl)phosphine oxide

The tris(2-pyridyl)phosphine oxide (Py(3)PO) complex [Ru(Py(3)PO)(bpy)(OH(2))](2+) (bpy is 2,2′-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 Py(3)PO 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.