Efficient [FeFe] hydrogenase mimic dyads covalently linking to iridium photosensitizer for photocatalytic hydrogen evolution

Two [FeFe] hydrogenase mimics, [Fe-2(mu-pdt)(CO)(5)L1] (L1 = PPh2SPhNH2) (Ph = phenyl) (2) and [Fe-2(mu-pdt)(CO)(5)L2] (L2 = PPh2PhNH2) (3), and two molecular photocatalysts, [(CO)(5)(mu-pdt)-Fe2PPh2SPhNHCO( bpy)(ppy)(2)Ir]PF6 (bpy = bipyridine, ppy = 2-phenylpyridine) (2a) and [(CO)(5)(mu-pdt)-Fe2PPh2PhNHCO( bpy)(ppy)(2)Ir](PF6) (3a), have been designed and synthesized, anchoring Ir(ppy)(2)(mbpy) PF6 (mbpy = 4-methyl-4'-carbonyl-2,2'-bipyridine) (PS) to one of the iron centers of complexes 2 and 3 by forming amide bonds. Molecular dyads 2a, 3a and the intermolecular systems 2, 3 with PS have also been successfully constructed for photoinduced H-2 production using triethylamine (TEA) as a sacrificial electron donor by visible light (>400 nm) in CH3CN-H2O solution. The time-dependence of H-2 generation and spectroscopic studies suggest that the activity of H-2 evolution can be tuned by addition of a S atom to the phosphane ligand. The highest turnover numbers (TON) of hydrogen evolution obtained are 127, using 2a as a photocatalyst in a supramolecular system, and 138, based on catalyst 2 in a multi-component system. Density functional theory (DFT) computational studies demonstrate that the S atom in the second coordination sphere makes complex 2 accept an electron more easily than 3 and improves the activity in light-induced hydrogen production.