Preparation, structures and electrochemical property of phosphine substituted diiron azadithiolates relevant to the active site of Fe-only hydrogenases

Mono- and di-phosphine diiron azadithiolate complexes [{(μ-SCH2)2N(4-NO2C6H4)}Fe2(CO)5(PMe3)] (2), [{(μ-SCH2)2N(4-NO2C6H4)}{Fe(CO)2L}2] (3, L = PMe3; 4, PMe2Ph) and the μ-hydride diiron complex [3(FeHFe)]+[PF6]− were prepared as biomimetic models of the active site of Fe-only hydrogenases. The complexes 2-4 and [3(FeHFe)]+[PF6]− were characterized by IR, 31P, 1H and 13C NMR spectra and their molecular structures were determined by single crystal X-ray analyses. The PMe3 ligand in complex 2 lies on the basal position. The PMe3-disubstituted complex 3 exists as two configuration isomers, transoid basal/basal and apical/basal, in the crystalline state, while two PMe2Ph ligands of 4 are in an apical/basal orientation. The variable temperature 31P NMR spectra of 2 and 3 were made to have an insight into the existence of the possible conformation isomers of 2 and 3 in solution. The [3(FeHFe)]+ cation possesses the sole transoid ba/ba geometry as other reported μ-hydride diiron analogues. The electrocatalytic property of {(μ-SCH2)2NC6H5}[Fe(CO)2PMe3]2 (5) was studied for proton reduction in the presence of HOAc.