CAREER: Mechanistic Study of Radical Initiations for Aromatic Functionalization

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In this CAREER project, funded by the Chemical Structure, Dynamics & Mechanisms B Program of the Chemistry Division, Professor Ryan Baxter of the Department of Chemistry & Chemical Biology at the University of California, Merced is developing new strategies for initiating radical reactions through single-electron transfers. Because one electron reactions (radical reactions) are traditionally viewed as highly reactive and difficult to control, the goal of this research is to better understand fundamental properties of radical initiations to engineer mild and user-friendly experimental protocols. Many structures that can be accessed via radical chemistry are found in drugs, vitamins, materials and polymers, and so new strategies for radical initiation may have a positive impact on many fields of science that directly benefit society. The project involves monitoring radical reactions in real-time to understand chemical behavior. The resulting reaction data is used to develop educational materials for undergraduate organic chemistry laboratory and lecture courses. In addition, through industrial partnerships, volumes of authentic reaction data is collected and refined to develop a repository of undergraduate/graduate educational materials that are made available to educators throughout the Nation. Arenes and heteroarenes are common structures with many desirable materials. Strategies for their rapid diversification are in demand. Radical carbon-hydrogen functionalization offers the ability to directly modify aromatic carbon hydrogen bonds via either nucleophilic or electrophilic processes, although uncontrolled reactivity is common to intermolecular processes. This project involves two discrete aims to study fundamental physical properties that affect rates of radical initiation for synthetically important reactions. The first focuses on developing catalyst systems that use silver ion, as an oxidant, and exogenous pyridine ligands in a novel way to control the rates of radical initiation for intermolecular nucleophilic functionalization of heteroarenes. Catalyst redox properties are studied electrochemically, and this data is correlated with global reaction rates to inform the development of optimum catalyst/oxidant systems. The second aim involves the iron-catalyzed reduction of nitrogen-oxygen bonds to promote intermolecular radical amination of arenes through an electrophilic process. The electronic properties of various nitrogen-radical precursors are examined to develop efficient strategies that combine mild initiation with reliable rates of initiation.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.