INVESTIGATIONS OF BIOMIMETIC NITROGEN FIXATION

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Delineating the mechanism of biological nitrogen fixation is a contemporary problem of major importance. As the world's population continues to increase the health and well-being of the people depend upon the availability of sufficient food with protein as an absolutely essential dietary requirement. The long term goals of this research are to elucidate the mechanism of ammonia formation in the biomimetic reduction of N2 and develop catalytic systems for the production of both ammonia and hydrazine. To achieve these goals this research will investigate the mechanism of ammonia formation in a biomimetic system involving dinitrogen (N2) complexes of molybdenum. In addition the mechanism of hydrazine formation in this same system will be studied. These reactions of N2 involve a series of acid-base and redox reactions. The specific aims of this research proposal are four. First, a hypothesis that in the reactions of N2 complexes of molybdenum hydrazine is formed at a single molybdenum center whereas ammonia formation requires intermolecular electron transfer between at least two molybdenum centers will be tested. To do this, molybdenum nitrogen complexes will be attached to solid macroreticular supports in order to prevent any intermolecular interaction between molybdenum centers. Second, isolation of intermediates in the reduction of N2 beyond the (NNH2) stage will be carried out. Initially the (NHNH2) moiety will be specifically targeted. Third, the range of N2 complexes of molybdenum will be extended by using S-, O-, and N-containing ligands. Variations of coordinating atoms can be expected to lead to changes in redox properties, stability of intermediates, and reaction pathways. Fourth, complexes of N2 containing more than one redox active metal will be synthesized in an effort to improve the efficiency of which N2 reduction occurs. From these biomimetic studies a coherent mechanism for the reduction of N2 to ammonia may be proposed, against which data obtained from studies of nitrogenase can be compared.