Heterolytic Bond Activation by First Row Transition Metals

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This award in the Inorganic, Bioinorganic, and Organometallic Chemistry Program supports research by Dr. Marcetta Y. Darensbourg of the Department of Chemistry, Texas A&M University, on hetrolytic bond activation by first row transition metals. Three projects will be pursued: (1) ligand engineering to activate C-H heterolytic bond cleavage by proximate first row transition metals; (2) mechanism of nickel-thiolate activation of sulfur dioxide to sulfate; (3) homolytic C-S bond cleavage in low-valent nickel complexes in which Ni-H acidity is controlled by ligand structure. In the first study, rigid chelating and tetreadentate ligands will stabilize the metals (Co, Fe, or Ni) and enable a C-H bond to be positioned close to the metal center to promote its activation. In the second investigation, nickel complexes will be used to promote reaction of sulfur dioxide with dioxygen in an unusual reaction in which sulfur dioxide is converted directly to anionic sulfate without formation of a metal-bound sulfate. In the third project, activation of carbon dioxide will also be studied, and the acidity of Ni-H in highly reduced species will be determined. Bond breakage under controlled conditions is critical in many essential chemical reactions. In all the reactions studied with the support of this award, the position of the metal with respect to bonds to be broken will be controlled to order to investiate how to use metals to position other atoms for reaction. Answering this question is important for understanding many biological enzyme reactions and for developing new industrial catalysts. In addition, finding economic means to oxidize sulfur dioxide is vital for pollution abatement, thus adding to the significance of understanding the details of reaction of sulfur dioxide and oxygen.