Diiron and trinuclear NiFe2 dithiolate complexes chelating by PCNCP ligands: Synthetic models of [FeFe]- and [NiFe]-hydrogenases.

ABSTRACT

To further develop the biomimetic chemistry of [FeFe]- and [NiFe]-hydrogenases for catalytic proton reduction to hydrogen (H2), two serials of dinuclear diiron and trinuclear NiFe2 dithiolate complexes with chelating PCNCP ligands, namely, Fe2(µ-edt)(CO)4{κ2-(Ph2PCH2)2NR} (1a-1c) and Fe2(CO)6(µ3-S)2Ni{(Ph2PCH2)2NR} (2a-2c) where edt = SCH2CH2S and PCNCP = (Ph2PCH2)2NR [R = Bui (CH2CHMe2), But (CMe3), and Bun (CH2CH2CH2Me)], have been synthesized in moderate yields. All the new complexes 1a-1c and 2a-2c have been fully characterized by elemental analysis, FT-IR, NMR spectroscopy, and single-crystal X-ray diffraction analysis. More importantly, to explore the influence of transition metal cores (i.e., nickel and iron) on the electrochemical and electrocatalytic properties of hydrogenase-inspired molecular catalysts for H2 evolution, the cyclic voltammetries (CVs) of 1a-1c and 2a-2c are studied and compared in nBu4NPF6/DMF solution without and with acetic acid (HOAc) as a proton source. This finding suggests that (i) complexes 1a-1c and 2a-2c are all found to be active for electrocatalytic H2 evolution, but (ii) they display the distinct redox behaviors and electrocatalytic proton reduction abilities.