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

Abstract

Two [FeFe] hydrogenase mimics, [Fe₂(μ-pdt)(CO)₅L1] (L1 = PPh₂SPhNH₂) (Ph = phenyl) (2) and [Fe₂(μ-pdt)(CO)₅L2] (L2 = PPh₂PhNH₂) (3), and two molecular photocatalysts, [(CO)₅(μ-pdt)Fe₂PPh₂SPhNHCO(bpy)(ppy)₂Ir]PF₆ (bpy = bipyridine, ppy = 2-phenylpyridine) (2a) and [(CO)₅(μ-pdt)Fe₂PPh₂PhNHCO(bpy)(ppy)₂Ir](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 H₂ production using triethylamine (TEA) as a sacrificial electron donor by visible light (>400 nm) in CH₃CN–H₂O solution. The time-dependence of H₂ generation and spectroscopic studies suggest that the activity of H₂ 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.