Transfer Hydrogenation Reactions of Photoactivatable N,N’-Chelated Ruthenium(II) Arene Complexes
Keywords:Ruthenium, arene, pyridine, hydride, NAD /NADH, photoactivation
AbstractWe show that the reaction of RuII arene chlorido complexes of the type [(η6-arene)Ru(N,N’)Cl]+ arene = p-cymene (pcym), 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 RuII arene pyridine complexes of the type [(η6-arene)Ru(N,N’)(Py)]2+ (where Py = pyridine), are irradiated with UVA (λirr = 300-400 nm) or visible light (λirr = 400-660 nm) under the same conditions. The RuII 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 RuII arene Py complex.
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