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 (MO: (S),(S&_,)'-, (Mob,,_,)'- and (Mo3l(C?),(S),(S,),_Jl- homologous series. These reactions include : (a) sulphur addition and sulphur abstraction reactions ; (b) oxidative removal of the Sz- ligands and their replacement by substitutionally labile ligands ; (c) oxidation of coodinated RS- ligands by S, fragments, and in situ generation of S,'- ligands ; (d) oxidative dimerization reactions of molybdenum(IV) complexes ; and (e) reductive elimination of S, fragments. The synthesis of the new ((C~)MO~(O)(~-S)~MO~(O)S~)- and ((Cp)MoV(0)(p-S),MoV(0)S2)- anions has alowed the use of 'H NMR spectroscopy to monitor the solution behaviour and reactivity of the MoV(0)S2 group. The existence of the MoV(0)S2 + S2 F? MoV(0)S4 equilibri? has been unequivocally established. The ((Cp)Mo' (O)(p-S),Mov(0)S2)- complex gives a vinyl disulphide derivative by insertion of dicar- bomethoxyacetylene, DMA, into the MO-q2-S2 group. Upon prolonged heating to 70°C the vinyl disulphide ligand is converted quantitatively to a dithiolene ligand. The same con- version takes place swiftly at ambient temperatures when catalytic amounts of Ss are present in the reaction medium. Reaction pathways for both the thermal and catalytic conversions have been suggested by 'H NMR studies. Preliminary studies of the utility of the (J%N)(Mo2W&U, ~i(~~~)61~02~2~~~~1~, (EWdMa@.&l and (Phd%(Mo&l complexes as catalysts for the hydrodesulphurization of thiophene are reported. The Ni/Mo catalyst obtained from ~i(DMF)6)(Mo202S,Cl)2 is at least 10 times more effective than a commercial CO/MO catalyst. The binary, MO/S, or tertiary, MO/S/O, thiomolyb- date complexes1-4 are characterized by a remark- able complexity in structure and by interesting reactivity characteristics. The vast majority of these complexes are anionic species and can be described in terms of various combinations of the 02-, S2-, S:- and S$- ligands coordinated to molybdenum(IV), -(V) or -(VI) ions. At times, the deceivingly simple procedures that