Spectroscopic and electrochemical comparison of [FeFe]-hydrogenase active-site inspired compounds: Diiron monobenzenethiolate compounds containing electron-donating and withdrawing groups

Abstract

The novel compounds [Fe2(μ-SC6H4-p-NO2)2(CO)6] (1), [Fe2(μ-SC6H4-p-tBu)(μ-SC6H4-p-NO2)(CO)6] (2), [Fe2(μ-SC6H4-p-tBu)2(CO)6] (3), [Fe2(μ-SC6H4-p-tBu)(μ-SC6H4-p-CF3)(CO)6] (4) and [Fe2(μ-SC6H4-p-OCH3)(μ-SC6H4-p-CF3)(CO)6] (5) have been characterized by 1H NMR, FTIR, elemental analysis, and cyclic voltammetry. X-ray crystallography of compounds 1 and 2 reveal an anti (ax,eq) S-aryl ligand orientation in the solid state. Carbonyl IR spectra and reduction potentials correlate strongly with Hammett constants of the electron donating/withdrawing groups. Evaluation for electrocatalytic formation of dihydrogen from acetic acid indicates a low overpotential of activity of 0.26 V for compound 5.