Synthesis and Electrocatalytic Activity of [FeFe]‐Hydrogenase Model Complexes with Non‐Innocent Chelating Nitrogen‐Donor Ligands

Abstract

To probe the influence of redox non‐innocent ligands on a well‐known class of [FeFe]‐hydrogenase models, three new asymmetrically disubstituted diiron complexes of the general formula (µ‐SRS)[Fe(CO)3][Fe(CO)(N‐N)] {SRS = propane‐1,3‐dithiolate (pdt) or benzene‐1,2‐dithiolate (bdt), and N‐N = 2,2′‐bipyridine (bipy) or 2,2′‐bipyrimidine (bpym)} have been synthesized from their parent hexacarbonyls and characterized. The new complexes, (µ‐pdt)Fe2(CO)4(κ2‐bpym) (2), (µ‐bdt)Fe2(CO)4(κ2‐bipy) (3), and (µ‐bdt)Fe2(CO)4(κ2‐bpym) (4), were fully characterized by spectroscopic and electrochemical techniques, and the results are compared to those of a related complex, (µ‐pdt)Fe2(CO)4(κ2‐bipy) (1). The crystal structures of 2–4 show that, in each complex, the two iron units are in an eclipsed orientation, and the N‐N ligand lies in the basal plane. IR spectra and electrochemical analyses indicate that electron density at the iron centers decreases in the order 1 > 2 > 3 > 4. Furthermore, compound 2 undergoes a ligand‐centered reduction at the same potential that the hexacarbonyl precursor undergoes its first reduction. However, unlike the 2,2′‐bipy derivatives 1 and 3, the 2,2′‐bpym complexes 2 and 4 are not effective catalysts for electrochemical proton reduction from acetic acid.