CATALYTIC REDUCTION OF ACETYLENE IN THE PRESENCE OF MOLYBDENUM AND IRON CLUSTERS, INCLUDING FEMO COFACTOR OF NITROGENASE

Acetylene was reduced by zinc amalgam in the presence of three synthet ic polynuclear complexes: { Mg2Mo8O22(OMe)(6)(MeOH)(4)](2-).[Mg(MeOH)( 6)](2+)} 6MeOH (I), (Bu4N)(2)[Fe4S4(SPh)(4)] (II), [Me4N] [VFe3S4Cl3(D MF)(3)]. 2DMF (III) and the iron-molybdenum cofactor of nitrogenase Az otobacter vinelandii MoFe7(S2-)(9).homocitrate, FeMo-co (IV). Thiophen ol was found to greatly facilitate the reaction in the presence of com plexes I, II, IV. The reaction is catalytic and for I and IV proceeds at the amalgam surface. ?Thiophenol seems to increase the adsorption o f the complexes, serving as an electron bridge to transfer electrons t o the catalyst. In the case of II a homogeneous reduction of the subst rate occurs presumably after the cluster reduction at the surface and with III the catalytic reduction proceeds only under the action of sod ium amalgam; no thiophenol cocatalytic action is observed. Relevance t o N-2 enzymatic reduction is discussed. (C) 1998 Elsevier Science S.A.