Graduate Student Nancy Oloyede

"Titanocene Redox Catalysis- A Sustainable System for Organic Radical Transformations"

Titanium (Ti) is non-toxic and is the second most abundant transition metal in the earth’s crust making it an attractive metal for the synthesis of inexpensive and environmentally friendly organotitanium complexes. In the low valent form, Ti complexes have high reducing character and an open site for coordination to ligands and solvent. The most common of these complexes is titanocene dichloride (Cp2TiCl2). Cp2TiCl2 has been implicated in a variety of transformations involving epoxides and carbonyl functional groups with Cp2TiCl2 acting as a pre-catalyst requiring the need for metal reductants to generate the active catalyst. This requirement reduces the overall sustainability and atom economy of the titanocene redox chemistry. A collaborative effort between the Flowers and the Gansäuer research groups demonstrated, for the first time, that the active titanocene complex can be generated in the absence of metal reductants via photoredox catalysis. Excitation of Cp2TiCl2 with green light in the presence of a tertiary amine, results in the oxidation of the amine to an amine radical cation and the generation of the active low valent TiIII intermediate. We were able to apply our method in epoxide reduction and cyclization reactions. Our efforts on the application of titanocenes as photocatalysts in photoredox transformation will be presented. In addition, our research on expanding the chemistry of catalytic titanocenes for applications in N-O bond cleavage in oxime substrates that provides facile access to nitrogen-containing heterocycles, imines, and amines under mild conditions will be described. Finally, our efforts towards developing titanocene-amine proton-coupled electron transfer (PCET) systems for the reduction of challenging substrates will be presented.