Photocatalytic Hydrogen Evolution by [FeFe] Hydrogenase Mimics in Homogeneous Solution

To mimic [FeFe] hydrogenases (H(2)ases) in nature, molecular photocatalysts 1a, 1b, and 1c anchoring rhenium(1) complex S to one of the iron cores of [FeFe]-H(2)ases model complex C, have been constructed for H-2 generation by visible light in homogeneous solution. The time-dependence of H-2 evolution and a spectroscopic study demonstrate that the orientation of S and the specific bridge in 1a, 1b, and 1c are important both for the electron-transfer step from the excited S* to the catalytic C, and the formation of unprecedented long-lived charge separation for 1a (780 mu s), 1b, and 1c (>2 ms) in [FeFe]-H(2)ases mimics. The fast forward electron-transfer step from the excited S* to the catalytic C but the slow back electron-transfer step of the charge-recombination in the designed photocatalysts 1a, 1b, and 1c are reminiscent of the behavior of [FeFe]-H(2)ases in nature.