A Molecular Light-Driven Water Oxidation Catalyst

Two mononuclear Ru(II) complexes, [Ru(ttbt)(pynap)(I)]I and [Ru(tpy)(Mepy)2(I)]I (tpy = 2,2′;6,2″-terpyridine; ttbt = 4,4′,4″-tri-tert-butyltpy; pynap = 2-(pyrid-2′-yl)-1,8-naphthyridine; and Mepy = 4-methylpyridine), are effective catalysts for the oxidation of water. This oxidation can be driven by a blue (λmax = 472 nm) LED light source using [Ru(bpy)3]Cl2 (bpy = 2,2′-bipyridine) as the photosensitizer. Sodium persulfate acts as a sacrificial electron acceptor to oxidize the photosensitizer that in turn drives the catalysis. The presence of all four components, light, photosensitizer, sodium persulfate, and catalyst, are required for water oxidation. A dyad assembly has been prepared using a pyrazine-based linker to join a photosensitizer and catalyst moiety. Irradiation of this intramolecular system with blue light produces oxygen with a higher turnover number than the analogous intermolecular component system under the same conditions.