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 synthetic polynuclear complexes: { [Mg2Mo8O22(OMe)(6)(MeOH)(4)](2-).[Mg(MeOH)(6)](2+)} 6MeOH (I), (Bu4N)(2)[Fe4S4(SPh)(4)] (II), [Me4N] [VFe3S4Cl3(DMF)(3)]. 2DMF (III) and the iron-molybdenum cofactor of nitrogenase Azotobacter vinelandii MoFe7(S2-)(9).homocitrate, FeMo-co (IV). Thiophenol was found to greatly facilitate the reaction in the presence of complexes I, II, IV. The reaction is catalytic and for I and IV proceeds at the amalgam surface. ?Thiophenol seems to increase the adsorption of the complexes, serving as an electron bridge to transfer electrons to the catalyst. In the case of II a homogeneous reduction of the substrate occurs presumably after the cluster reduction at the surface and with III the catalytic reduction proceeds only under the action of sodium amalgam; no thiophenol cocatalytic action is observed. Relevance to N-2 enzymatic reduction is discussed. (C) 1998 Elsevier Science S.A.