Fe–Fe] hydrogenase models: Iron(I)-carbonyl clusters coupled to alpha- and para-toluenethiolate ligands

Abstract

Two linkage isomers composing of diironhexacarbonyl clusters coupled to α and p-toluenethiolate ligands have been usefully prepared in moderate yields. The composition of both compounds, [(μ2-(p-toluenethiolato))2Fe2(CO)6] (1) and [(μ2-(α-toluenethiolato))2Fe2(CO)6] (2), have been determined by elemental analysis and NMR spectroscopy. A tetrairondodecacarbonyl complex, [μ4-S(μ2-(α-toluenethiolato)Fe2(CO)6)2] (3), was isolated from the reaction mixture of 2. The molecular structures of 2 and 3 determined by X-ray diffraction are discussed. An exploration of the influence of the α- and p-toluenethiolate ligands on the electronic and electrochemical properties of the iron-carbonyl units have been accomplished using infrared spectroscopy, UV–Vis spectroscopy and cyclic voltammetry. In the presence of acetic acid, compounds 1, 2 and 3 catalyze the electrochemical generation of molecular hydrogen. The proton reduction overpotentials for compounds 1 and 2 were determined to be 0.76 V and 0.85V versus Fc/Fc+ respectively in acetonitrile as solvent. Comparatively, compound 1 produces hydrogen at an overpotential 90mV lower than compound 2.