CAREER: Metal-Free C-C Bond Formation and C-O Bond Cleavage Mediated by Electron-Donor-Acceptor Complexes of Arenes

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With the support of the Chemical Synthesis Program in the Division of Chemistry, Sébastien Laulhé of Indiana University-Purdue University Indianapolis is studying new heavy metal-free processes designed to reduce the environmental footprint of chemical manufacturing. Blue light is employed to activate so-called 'electron-donor-acceptor complexes' enabling them to either mediate the assembly of carbon-carbon bonds or else to break carbon-oxygen bonds. Processes belonging to the first class are useful for the generation of pharmaceutical agents, agrochemicals, and other societally important products, and the approach being pursued may provide an alternative to current technologies reliant on the use of rare and/or toxic metal species. The second type of processes will be deployed to break down biomass-derived molecules, such as lignin, to turn what are typically regarded as agricultural waste streams into renewable and valuable sources of carbon, thereby potentially reducing dependence on fossil-based carbon sources. The broader impacts of the award extend to the benefits accrued to society as Dr. Laulhé and his team of coworkers pursue a range of activities, including the provision of stimulating and educational research experiences, to better prepare undergraduate students for careers in the STEM (science, technology, engineering and mathematics) workforce. The funding secured will also enable Dr. Laulhé to continue to develop an organic chemistry curriculum for visually impaired students, the results of these efforts will be shared with the higher education community.The formation of carbon-carbon bonds through regioselective C(sp3)–H functionalization strategies in the absence of transition-metals remains a challenge. The research being pursued under this project will address this problem by utilizing aryl radical species capable of effecting hydrogen-atom transfer that are released upon visible light-mediated excitation of electron-donor-acceptor (EDA) complexes of readily generated carbanions (e.g., aminoacetate enolates) and haloarenes. A major goal of the research is to apply this principle to access non-canonical amino acid derivatives via site-selective direct C-H functionalization and to render such transformations diastereoselective by manipulation of the transition state for the radical-radical coupling step using specific counter ions and/or the use of chiral organocatalysts. The second part of the funded project will exploit EDA complexes of solvent anions (e.g., dimsyl anion) and arene-containing ethers to promote selective C–O bond cleavages upon irradiation with visible light. In this case, it is expected that tuning of the electronic parameters between electron-donors and electron-acceptors will enable selective debenzylation of complex protected alcohols and depolymerization of lignocellulosic biomass. A number of significant (and heavy metal-free) new methods for both the functionalization of C–H bonds and the cleavage of C–O bonds, are likely emerge from this research program and the pursuit of the aims described will further fundamental knowledge of EDA complex photochemistry.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.