Bimetallic cooperative effect on O-O bond formation: copper polypyridyl complexes as water oxidation catalyst

The performance of water oxidation catalysis by a Cu-based polypyridyl complex, [Cu-II(TPA)(OH2)](2+) (1H; TPA = tris-(pyridylmethyl)amine), has been investigated in neutral aqueous solution by electrochemical methods. Compared with our previously reported binuclear catalyst, [(BPMAN)(Cu-II)(2)(-OH)](3+) (2; BPMAN = 2,7-[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine), mononuclear catalyst 1 has a higher overpotential and lower catalytic activity toward water oxidation under the same conditions. Experimental results revealed that the O-O bond formation occurred via a water nucleophilic attack mechanism in which formal Cu-IV(O) is proposed as a key intermediate for the mononuclear catalyst 1H. In contrast, for the binuclear catalyst, O-O bond formation was facilitated by bimetallic cooperation between the two Cu-III centers.