Proton-coupled electron-transfer in Sm(II)-proton donor reactions

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The Chemical Structure, Dynamics, and Mechanism Program of the NSF Chemistry Division supports the research of Professor Robert Flowers in the Department of Chemistry at Lehigh University. Professor Flowers and his students are examining the mechanism for reactions of samarium (II) iodide (SmI2), a widely used reagent in organic synthesis. The first goal of this project is designed to examine the role of proton donors (alcohols and water) on the reactivity and efficiency of reactions and determine whether electrons and protons are transferred in sequential steps, or whether the process is concerted and occurs through a formal hydrogen atom transfer. The second goal of this project is to use the mechanistic information from studies on SmI2-proton donor systems to develop catalytic reactions. Students at the undergraduate and graduate level receive training in a range of scientific techniques. Outreach to elementary students leads to sustained engagement with the local community. Finally, video recordings of experimental protocols developed during these studies are freely disseminated on the Flowers research group webpage to assist scientists who use reagents based on SmI2. SmI2 is among the most widely employed reagents that reduce substrates and reactive intermediates through single electron transfer. Although most reactions of SmI2 require proton donors, the mechanism of this reagent combination is not fully understood and the current view is that reductions and reductive coupling reactions proceed through a sequential electron-transfer, proton-transfer processes. This work tests the hypothesis that reductions and reductive coupling reactions proceed through a formal hydrogen atom transfer and that the coupled transfer of an electron and proton is responsible for the unique reactivity of Sm(II)-coordinating proton donor reductions of substrates which are typically recalcitrant to reduction through single electron transfer. As mechanistic work on Sm(II)-proton donors systems is performed, data obtained from these studies is used for the development of useful and user-friendly catalytic reactions; a longstanding, but elusive goal in this field. Integration of a range of experimental techniques along with synthetic applications of proton-coupled, electron-transfer in synthesis provides a dynamic intellectual environment for students at all levels of study. The educational plan includes long-term engagement with local elementary schools designed to nurture greater interest in science. Finally, as research is published in peer-reviewed journals, video recordings of all experimental protocols are made to aid scientists who want to repeat the reaction protocols.