Asymmetrically PNP-chelate diiron ethanedithiolate complexes Fe2(μ-edt) (CO)4{κ2-(Ph2P)2NR} as diiron subsite models of [FeFe]-hydrogenases: Structural and electrocatalytic investigation

As a further exploration of the desirable diiron subsite models of [FeFe]-hydrogenases for hydrogen (H-2) evolution, the asymmetrically PNP-chelate diiron ethanedithiolate complexes Fe-2(mu-edt)(CO)(4){kappa(2)-(Ph2P)(2)NR} (1-3) can be synthesized in good yields through the substitution reactions of diiron all-carbonyl complexes Fe-2(mu-edt) (CO)(6) (A, edt = SCH2CH2S) with different PNP ligands (PNP = (Ph2P)(2)NR, R = (CH2)(2)CHMe2, (CH2)(3)OMe, (CH2)(3)SMe) in the presence of Me3NO center dot 2H(2)O as decarbonylating agent. These new complexes 1-3 have been fully characterized by elemental analysis, FT-IR, NMR spectroscopy, and particularly for 1 by X-ray crystallography. Further, the electrochemical and electrocatalytic properties of complexes 1-3 and their precursor A as a reference compound are studied and compared through cyclic voltammetry (CV) in the absence and presence of HOAc as a proton source, suggesting that they are all found to be electrochemically active but show the distinct electrocatalytic abilities for proton reduction to H-2.