High Turnover in a Photocatalytic System for Water Reduction to Produce Hydrogen Using a Ru, Rh, Ru Photoinitiated Electron Collector

Covalent coupling of Ru-II light absorbers to a Rh-III electron collecting site through polyazine bridging ligands affords photocatalytic production of H-2 in the presence of visible light and a sacrificial electron donor. A robust photocatalytic system displaying a high turnover of the photocatalyst has been developed using the photoinitiated electron collector [{(bpy)(2)Ru(dpp)}(2)RhBr2](5+) (bpy = 2,2'-bipyridine; dpp = 2,3-bis(2-pyridyl)-pyrazine) and N,N-dimethylaniline in DMF/H2O. Studies have shown that increased [DMA], the headspace volume, and the use of DMF solvent improves the systems performance and stability providing mechanistic insight into the deactivation routes of the photocatalytic system. Photolysis of the system at 460 nm generates 20 mL of H-2 in 19.5 h with a maximum Phi = 0.023 based on H-2 produced and an overall Phi = 0.014 and 280 turnovers of the photocatalyst. The photocatalytic system also displays long-term photostability with 30 mL of H-2 generated and 420 turnovers in 50 h under the same conditions. Prolonged photolysis provides 820 mol H-2 per mole of catalyst.