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.