Transfer Hydrogenation Reactions of Photoactivatable N, N′-Chelated Ruthenium(II) Arene Complexes

We show that the reaction of Ru-II arene chlorido complexes of the type [(eta(6)-arene) Ru(N, N')Cl](+) arene = p-cymene (p-cym), hexamethylbenzene (hmb), indane (ind), N, N' = bipyrimidine (bpm) and 1,10-phenanthroline (phen) with excess sodium formate generates a very stable formate adduct through spontaneous hydrolysis of the Ru-Cl bond at 310 K and pH* = 7.0. The formate adducts are also produced when Ru-II arene pyridine complexes of the type [(eta(6)-arene) Ru(N, N')(Py)](2+) (where Py = pyridine), are irradiated with UVA (lambda(irr) = 300-400 nm) or visible light (lambda(irr) = 400-660 nm) under the same conditions. The Ru-II arene formato adducts do not catalyse the reduction of acetone through transfer hydrogenation. However, all the complexes (except complex 2 which contains phen as the chelating ligand) can catalyse the regioselective reduction of NAD(+) in the presence of formate (25 mol equiv) in aqueous solution to form 1,4-NADH. The catalytic activity is dependent on the nature of the chelating ligand. Most interestingly, the regioselective reduction of NAD(+) to 1,4-NADH can be also specifically triggered by photoactivating a Ru-II arene Py complex.