This award in the Inorganic, Bioinorganic, and Organometallic Program supports research by Dr. Colin P. Horwitz of the Chemistry Department, Rensselaer Polytechnic Institute, on manganese(II) complexes of Schiff bases. These compounds promote 4-electron reduction of molecular oxygen and form metal complexes which often incorporate one or more of the oxygen atoms. The goal of the research is to investigate the mechanism of reactions of this type, and test the validity of a proposed reaction pathway involving a Mn(III)-molecular oxygen Schiff-base anion. Spectroscopic and electrochemical methods will be used to detect the intermediates and examine the effect of structure on the reactivity of the complexes. The Schiff bases will be modified to provide electronic and structural changes in the metal complex which will help to stabilize the intermediates. %%% A number of mechanisms have been proposed for these reactions, and this study will help to clarify how molecular oxygen binds to manganese and how manganese promotes the cleavage of the O-O bond. The results will increase understanding of the behavior of oxygenase enzymes which contain manganese and assist in the design of Mn-based catalyts capable of partial oxygenation reactions with molecular oxygen.