This award to Professor Shannon S. Stahl at the University of Wisconsin at Madison will continue work on the selective oxidation of organic chemicals with molecular oxygen using homogeneous palladium catalysts. These reactions proceed by a two-stage mechanism consisting of (1) Pd(II)-mediated oxidation of the organic substrate and (2) reoxidation of the reduced catalyst by molecular oxygen. In order to facilitate palladium-catalyzed oxidation with O2 as the stoichiometric oxidant, the PI will investigate fundamental mechanisms of reactions between dioxygen and well-defined palladium complexes. The viability of three different mechanisms proposed for reoxidation of reduced palladium under catalytic conditions will be assessed, by preparing suitable Pd(0) or Pd(II) precursors and investigating their reactivity under aerobic conditions. Computational studies will elucidate the electronic structural contributions to these reactions. As dioxygen undergoes reversible exchange with electron-deficient alkenes, such as benzoquinone, at diiminecoordinated Pd centers, the kinetic and thermodynamic aspects of these reactions will be investigated in order to gain a better understanding of the relationship between dioxygen and alkene reactions with palladium. These studies, together with the mechanistic characterization of catalytic reactions that employ benzoquinone as the oxidant, should provide insights that will facilitate the replacement of benzoquinone with dioxygen in catalysis. Finally, the ability of benzoquinone and dioxygen to induce oxidative functionalization of Pd(II)-C bonds will be studied.
The mechanistic characterization of reaction pathways will assist the development of improved methods for dioxygen-coupled turnover in palladium oxidation catalysis, which has implications for the future development of aerobic C-H oxidation methods. A collaboration with Prof. John Moore, director of the Institute for Chemical Education at the University of Wisconsin, will be undertaken to develop an Internet resource for junior high and high school science students that presents modern academic research in an accessible and educational format. Undergraduate students from traditionally underrepresented groups will be involved in the proposed research activities through the P.I.'s participation in the Undergraduate Research Scholars Program at UW-Madison.
