Six-coordinate ruthenium water oxidation catalysts bearing equatorial polypyridinedicarboxylato and axial phosphine ligands

Abstract

Ruthenium catalysts for water oxidation combining multidentate ligands [2,2′:6′,2″-terpyridine]-6,6″-dicarboxylato (tda) and 2,2′-bipyridine-6,6′-dicarboxylato (bda) with apical phosphine ligands have been prepared. These new complexes were fully characterized by standard spectroscopic and single-crystal X-ray crystallography analyses, and their redox properties were evaluated by electrochemistry. Specifically, [RuII(tda)(tris(2-furyl)phosphine)2] displayed two reversible redox waves that were assigned to the RuII/III and RuIII/IV transitions, respectively. The number of turnovers in CeIV-driven water oxidation reached 258 for the bda analog, and for the tda analog, early reaction rates were first order in initial catalyst concentration. The effects of adding fractional equivalents of CeIV were studied using UV–vis spectroscopy. Steric and electronic changes in the axial phosphine ligand can exert their effects on the properties and catalytic activity of the resulting complexes, which may be useful when exploring other chemistry of these complexes.