Models for the FeMo-Cofactor of Nitrogenase

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The objective of this project in the Inorganic, Bioinorganic and Organometallic Chemistry Program is the synthesis and characterization of compounds consisting of clusters of molybdenum, iron and sulfur atoms. Such clusters are related to the iron-molybdenum cofactor, familiarly known as FeMo-co, of the enzyme nitrogenase. This cofactor, which has a currently unknown structure, constitutes a key portion of the enzyme's active site. Studies of the target compounds are needed in order to assess those aspects of the structural and chemical properties of FeMo-co which are essential to the "fixing" of atmospheric nitrogen through reduction by the enzyme. Nitrogenase catalyzes one of the most complex multi-electron transfer reactions in biology, so that understanding the structure and reactivity of its active site is of fundamental chemical and biochemical importance. Further, a catalytic cluster resembling the active site may be a powerful catalyst for a variety of chemical transformations. Systematic syntheses of high nuclearity Mo-Fe-S clusters will be explored. Emphasis will be placed on controlling the structural reorganizations that occur during oxidative decarbonylation reactions in order to prepare new Mo-S-Fe clusters that may mimic FeMo-co structurally and which will bind small molecules that are nitrogenase substrates or inhibitors in dinitrogen reduction. The synthetic species will be characterized by chemical and physical methods, and their reactivities will be investigated, with emphasis on a systematic examination of the reactivity of the different metal sites within a given cluster.