Heterobimetallic cuboidal [Mo3NiS4] and [W3NiS4] cluster diphosphane complexes as molecular models in hydrodesulfurization catalysis

[M3NiS4X3(diphos)3(CH3CN)]+ (M = Mo, W; X = Cl, Br; diphos = dmpe, dppe) clusters have been prepared by addition of [Ni(cod)2] to incomplete cubane-type sulfido clusters [M3S4X3(diphos)3]+. The acetonitrile ligand could be substituted by pyridine, tetrahydrothiophene and carbon monoxide in CH2Cl2 at room temperature modelling the catalytic sites of heterogeneous Ni-MoS2 hydrodesulfurization catalysts. All heterobimetallic [M3NiS4] clusters reported show two quasireversible oxidation processes, the molybdenum complexes being ca. 0.2 V more difficult to oxidize than the tungsten analogues.