This award from the Inorganic, Bioinorganic and Organometallic Chemistry Program is in the area of transition metal chemistry. The goal of the project is the synthesis of molecules which have two binding sites for transition metals, one of which will enclose the metal completely, and the other of which will hold the metal firmly but still leave it able to bind an additional small molecule, such as dioxygen. The resulting new metal complexes are expected to act as catalysts for oxidation reactions, and will serve as useful models for important respiratory enzymes. The focus of the project is the synthesis of binucleating ligands for the generation of homo- and heterobimetallic complexes of the first transition series. These ligands are designed so that one metal resides in a coordinatively saturated site, whereas the other contiguous metal is coordinatively unsaturated. These complexes are expected to bind dioxygen and oxo groups at the exposed metal, and the metal in the encapsulated site should serve to provide electrons to the neighboring site. Such systems could lead to intramolecular four-electron reduction of dioxygen and possibly serve as catalysts for the direct use of dioxygen for oxidations. The binding of oxygen to these bimetallic complexes will be studied in order to determine which complexes reduce oxygen and which combinations of metals lead to four-electron reduction of oxygen. Metal oxo complexes, which are the possible products of reaction with oxygen, will be prepared and their reactivity as oxidants toward a variety of reducing agents will be studied.
