FUNCTIONAL ANALOGS FOR THE REDUCTION OF CERTAIN NITROGENASE SUBSTRATES - ARE MULTIPLE SITES WITHIN THE FE MO/S ACTIVE-CENTER INVOLVED IN THE 6E(-) REDUCTION OF N-2/

Reactivity studies of clusters that contain the MFe(3)S(4) cores (M = Mo, V) with catecholate, multicarboxylate (or DMF) ligands coordinated to the Mo (or V) atoms, and Cl ligands coordinated to the Fe atoms ha ve been carried out. These studies show the M/Fe/S single cubane clust ers to be effective catalysts in the reduction of nitrogenase substrat es such as hydrazine, acetylene and protons to give ammonia, ethylene and dihydrogen respectively. The same molecules do not activate or cat alyze the reduction of dinitrogen. The results indicate that the obser ved catalyses are occurring at the Mo (V) sites by a process that, in the case of hydrazine, involves substrate protonation prior to reducti on. The facile catalytic reduction of hydrazine by clusters that conta in coordinatively saturated polycarboxylate-bound Mo atoms is rational ized in terms of a possible protonation/proton delivery function of th e coordinated polycarboxylate ligands. The reactivity characteristics of the M/Fe/S clusters (structurally quite similar to the nitrogenase cofactor) have led to the suggestion that the Mo (V) atoms may be invo lved in the reduction of hydrazine in the later stages of dinitrogen r eduction.