Synthesis, redox chemistry, and X-ray structure of the mixed-metal cluster Fe2(CO)6(μ3-S)2Ni(dppf)

The reaction between the dianion [Fe2(CO)6(μ2-S)2]2− and NiCl2(dppf) occurs readily at room temperature to give the mixed-metal cluster Fe2(CO)6(μ3-S)2Ni(dppf) in moderate yield. Fe2(CO)6(μ3-S)2Ni(dppf) was isolated by preparative chromatography and its solid-state structure established by X-ray diffraction analysis. Fe2(CO)6(μ3-S)2Ni(dppf) crystallizes in the monoclinic space group C2/c, a = 20.320(6), b = 13.114(2), c = 15.622(2) Å, β = 110.25(2)°, V = 3905.4(11) Å3, Z = 4, and dcalc = 1.630 g/cm.3 The X-ray structure of Fe2(CO)6(μ3-S)2Ni(dppf) exhibits an Fe2S2Ni arachno polyhedral core, with the pendant dppf ligand attached to an essentially square planar Ni center. The redox chemistry of Fe2(CO)6(μ3-S)2Ni(dppf) was investigated by cyclic voltammetry which showed a reversible, one-electron oxidation localized on the Fe2S2 core along with an irreversible, one-electron reduction that is antibonding with respect to the Fe—Fe and Fe—S bonds. The electrochemical assignments were confirmed by carrying out extended Hückel MO calculations on the model cluster Fe2(CO)6(μ3-S)2Ni(H4-dppf).