Testing the Limits of Proton Coupled Electron Transfer (PCET) from Samarium(II)-Proton Donor Complexes

点击翻译按钮获取中文摘要

The Chemical Structure, Dynamics, and Mechanisms-B Program of the NSF Chemistry Division supports the research of Professor Robert Flowers in the Department of Chemistry at Lehigh University. In this research, Professor Flowers and his students are examining the mechanism of reactions of samarium (II) iodide (SmI2), a widely used reagent in organic synthesis. This project is designed to extend the reactivity of the reagent and to develop new reactions. The research outcome could lead to the development of new organic reactions important for the synthesis of biologically and pharmaceutically relevant compounds. In this project, students are exposed to important areas of contemporary chemistry. The educational experience centers around carrying out research in the context of mechanistic chemistry. Mentoring of high school students provides meaningful research experiences for those interested in scientific careers. In this project, mechanistic studies designed to test the role, advantages, and applications of proton-coupled electron transfer (PCET) in reductions by Sm(II) reagents containing coordinating and chelating proton donors are examined. These investigations are used to study and develop new and synthetically relevant reactions that proceed through PCET from Sm(II)-proton donor complexes to substrates which are typically recalcitrant to electron transfer alone. These studies include the following specific aims: 1) Examination of the relationship between the strength of coordination between proton donors and Sm(II) reagents and its implication on the degree of O-H, N-H, and C-H bond weakening; 2) The use of Sm(II)-proton donor complexes to expand the range of substrates that can be reduced through PCET to refine and develop new reactions; and 3) Examination of the basis of the unusual stability of Sm(II)-proton donor complexes. The mechanistic results of the proposed work lead to the development of new and useful reactions initiated by Sm(II)-proton donor complexes and provide a rationale for the unique reactivity of the reagent system. The protocols developed for the reduction of organic substrates are used as the basis to develop alternative approaches for the direct reduction of molecular nitrogen at room temperature. 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, including high school students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.