Current homogeneous catalysts for the photocatalytic production of H2 are limited by their low activity and/or stability during operation. Here we report iron and nickel pyridyl thiolate complexes as robust catalysts for hydrogen production when coupled with fluorescein as the photosensitizer (PS), and triethylamine (TEA) as the sacrificial electron donor in 1:1 EtOH/H2O. The systems achieve great activities for homogeneous noble-metal-free systems, with over 5500 turnovers after 40 hours of illumination. Under optimized conditions, the rate of H2 production is unabated after 60 hours of irradiation. The photochemical mechanism inviolves electron transfer from the singlet excited state of fluorescein to the catalyst, which avoids the formation of unstable radical anions that degrade other systems. Electrochemical studies suggest that the protonation of the catalyst precedes electron transfer, and that the mechanism may use the pyridine as a proton relay that assists with H-H bond formation. Involvement by a pendant nitrogen base would be reminiscent of the accepted mechanism for [FeFe]-hydrogenase and nickel bis(di-phosphine) catalysts for H2 production.

Iron and nickel thiolate catalysts for the long-lived photocatalytic production of hydrogen from water in noble-metal-free systems

244th National Meeting (2012)

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