Second Coordination Sphere Effects in an Evolved Ru Complex Based on a Highly Adaptable Ligand Results in Rapid Water Oxidation Catalysis

A new Ru complex containing the deprotoanted 2,2':6',2''-terpyridine,6,6''-diphosphonic acid (H4tPa) and pyridine (py) of general formula, [RuII(H3tPa--N3O)(py)2]+, 2+, has been prepared and thoroughly characterized by means of spectroscopic, electrochemical techniques, X-ray diffraction analysis and with DFT calculations. Complex 2+, presents a dynamic behavior in solution that involves the synchronous coordination and the decoordination of the dangling phosphonic groups of the tPa4- ligand. However, at oxidation state IV complex 2+, becomes seven coordinated with the two phosphonic groups now bonded to the metal center. Further at this oxidation state at neutral and basic pH, the Ru complex undergoes coordination of an exogenous OH- group from the solvent that leads to an intramolecular aromatic O-atom insertion into the CH bond of one of the pyridyl groups forming the corresponding pheoxoxo-phosohonate Ru complex [RuIII(tPaO--N2OPOC)(py)2]2, 42, where tPaO5- is 3-hydroxo-[2,2':6',2''-terpyridine]-6...