Pendant bases as proton transfer relays in diiron dithiolate complexes inspired by [Fe–Fe] hydrogenase active site

Three dinuclear iron complexes containing pendant nitrogen bases in phosphine ligands with general formular (μ-pdt) [Fe2(CO)5L] (where pdt is SCH2CH2CH2S, L = PPh2NH(CH2)2N(CH3)2 (5), PPh2NH(2-NH2C6H4) (6), PPh2[2-N(CH3)2CH2C6H4] (7)), were prepared as the models of the [Fe–Fe] hydrogenase active site. The molecular structures of 5–7 were characterized by X-ray crystallography. The secondary amine in 6 has weak intramolecular hydrogen bonding with both the terminal nitrogen and sulfur atom, which may suggest a proton transfer pathway from amine in phosphine ligand to the sulfur atom of active site. Protonation of complexes 5 and 6 only occurred at the terminal nitrogen atom. Electrochemical properties of the complexes were studied in the presence of triflic acid by cyclic voltammetry.