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

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. Two serials of dinuclear Fe2 and trinuclear NiFe2 dithiolate complexes 1a-1c and 2a-2c with chelating PCNCP (i.e., (Ph2PCH2)2NR) ligands are prepared and compared, aiming to explore the influence of transition metal cores (i.e., nickel and iron) on molecular structures and electrocatalytic properties for synthetic models of [FeFe]- and [NiFe]-hydrogenases. [Display omitted] •Diiron and trinuclear NiFe2 dithiolate complexes 1a-1c and 2a-2c were prepared.•These complexes with chelating PCNCP (i.e., (Ph2PCH2)2NR) ligands are characterized.•Their molecular structures and electrocatalytic properties are studied and compared.•The first carbonyl IR bands of 2a-2c are shifted to higher energy relative to 1a-1c.•Trinuclear NiFe2 complexes 2a-2c exhibit good stability and fast catalysis.