Photoinduced Terminal Hydride of [FeFe]-Hydrogenase Biomimetic Complexes

The active site of the [FeFe]-hydrogenase ([FeFe]-H2ase) has a bridging carbonyl ligand and a terminal hydride in the key H-cluster intermediate Hhyd. However, nearly all of the synthetic mimics reported, so far, prefer a hydride bridging the two irons, and only few mimics with a terminal hydride were achieved by tuning the steric effects of bulky diphosphine ligands. Moreover, although intermediates with either a terminal hydride or a protonated bridging thiolate ligand were proposed to exist during protonation processes or hydrogen exchange in the [FeFe]-H2ase mimic, [Fe2(μ-pdt)­(μ-H)­(CO)4(PMe3)2]+ (1H + ), only bridging hydrides were observed by time-resolved IR spectroscopy. In this report, FTIR spectroscopy of 1H + , under CO with longer irradiation time, revealed several new photoinduced species. In addition to the CO loss species, many of the photoinduced products can be assigned to 1H + with a terminal hydride by comparison of their CO vibrational frequencies with density functional theory calculations.