It is clear that while Ce(IV)-based reagents are a potentially important component in the arsenal of synthetic chemists, very little is known about their mechanism of action under reaction conditions utilized by synthetic organic chemists. As a result, full utilization of Ce(IV) is limited. In order to understand the reactivity of Ce(IV) reagents at a basic level, it is important to determine the relative stabilities of the reactants, and the rate limiting transition structures on the solvent medium. Under the proposed research, we will address the following questions: 1) how is the rate of oxidation by Ce(IV) influenced by solvent, ligands, and reagent structure? 2) To what degree do substrates and Ce(IV) interact along the reaction coordinate? and 3) Can the side-products commonly present in many Ce(IV) mediated oxidations be prevented by understanding the mechanistic factors responsible for their formation? To address these questions, the rates of oxidation and reaction order of a series of organic substrates including enamines, amines, enolates, silylenol ethers, inorganic ions and cyclopropanols by Ce(IV) complexes will be measured by stopped-flow spectrophotometry, ReactIR, and other methods. The preliminary data obtained from these studies will be used to investigate the mechanism of a number of important reactions including: 1) Rates of oxidation of enamines and secondary amines important in SOMO activation, 2) Oxidative heterocoupling of enolates, and 3) Radical cation addition to olefins. Since many of the substrates examined in these studies can be oxidized to radical cations (or radicals) and can also act as radicophiles, the relative rates of oxidation of obtained in these experiments will aid in the design of heterocoupling reactions initiated through single electron oxidation by Ce(IV) reagents.
The mechanistic and synthetic studies as proposed herein will extend the scope and utility of Ce(IV)-based oxidants and potentially provide alternative approaches to the synthesis of biologically important molecules.
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