An inorganic functional group approach to the systematic synthesis and reactivity studies of binuclear Mo/S and Mo/S/O complexes

Abstract

A number of general reactions, based on molybdenum-coordinated sulphido or polysulphido ligands, can account for the synthesis of many members of the [Mo2V(S)n(S2)6-n]2-, [Mo2V(O)(S)n(S2)5-n]2- and [Mo2V(O)2(S)n(S2)4-n]2- homologous series. These reactions include: (a) sulphur addition and sulphur abstraction reactions; (b) oxidative removal of the Sx2- ligands and their replacement by substitutionally labile ligands; (c) oxidation of coodinated RS- ligands by Sx0 fragments, and in situ generation of Sx2- ligands; (d) oxidative dimerization reactions of molybdenum(IV) complexes; and (e) reductive elimination of Sx0 fragments. The synthesis of the new [(Cp)MoV(O)([mu]-S)2MoV(O)S4]- and [(Cp)MoV(O)([mu]-S)2MoV(O)S2]- anions has alowed the use of 1H NMR spectroscopy to monitor the solution behaviour and reactivity of the MoV(O)S2 group. The existence of the MoV(O)S2+S2aiMoV(O)S4 equilibrium has been unequivocally established. The [(Cp)MoV(O)([mu]-S)2MoV(O)S2]- complex gives a vinyl disulphide derivative by insertion of dicarbomethoxyacetylene, DMA, into the Mo-[eta]2-S2 group. Upon prolonged heating to 70[deg]C the vinyl disulphide ligand is converted quantitatively to a dithiolene ligand. The same conversion takes place swiftly at ambient temperatures when catalytic amounts of S8 are present in the reaction medium. Reaction pathways for both the thermal and catalytic conversions have been suggested by 1H NMR studies. Preliminary studies of the utility of the (Et4N)[Mo2O2S8Cl], [Ni(DMF)6][Mo2O2S8Cl]2, (Et4N)2[Mo4O4S18] and (Ph4P)2[Mo2S6] complexes as catalysts for the hydrodesulphurization of thiophene are reported. The Ni/Mo catalyst obtained from [Ni(DMF)6][Mo2O2S8Cl]2 is at least 10 times more effective than a commercial Co/Mo catalyst.