Green Chemistry for Valorization of Commodity Chemicals via pi-Allylmetal Intermediates

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With the support of the Chemical Synthesis Program in the Division of Chemistry, Professor Michael J. Krische of the University of Texas at Austin is developing catalytic methods for the conversion of abundant chemical feedstocks to value-added products that are relevant to the pharmaceutical and agrochemical industries. A prominent feature of the research is that it will include the generation of so-called 'chiral' compounds in an enantioselective manner, i.e. with high levels of control of the 'handedness' of the molecule. Whereas large volumes of waste often accompany the preparation of structurally complex compounds, the proposed methods minimize byproduct generation, thus reducing chemical waste at the source. Education, training, and career development activities for students from the undergraduate to graduate levels are proposed and these activities are anticipated to foster the participation of individuals belonging to groups traditionally underrepresented in STEM (science, technology, engineering and mathematics). As part of a longstanding collaboration, graduate student trainees involved in the funded project will participate in summer internships at Genentech, thus benefiting from career development experiences in both academic and industrial settings. To further extend the broader impacts of this award, and because women remain significantly underrepresented in pharmaceutical and agrochemical sciences, Professor Krische will continue to organize the biennial “Women in Catalysis and Synthetic Chemistry” symposium, a popular event that attracts a diverse cohort of scientists.Under this award at the University of Texas-Austin, the Krische lab aims to further extend the chemical space accessible to functionally distinct chiral pi-allyliridium and pi-allylruthenium catalysts previously developed in the laboratory. While nearly all enantioselective allylic substitutions exploit low-pKa pronucleophiles, the pi-allyliridium-C,O-benzoate catalysts of interest here are base-tolerant at high temperatures enabling direct use of high-pKa pronucleophiles in combination with inexpensive inorganic carbonate bases. alpha-Olefins are abundant feedstocks (100 M tons produced per year), yet their atom-efficient conversion to useful chiral products often requires mass-intensive oxidants (e.g., benzoquinone) or photochemical promotion. By contrast, hydrogen auto-transfer reactions catalyzed by novel iodide-bound pi-allylruthenium complexes holds promise for atom-efficient allylic C-H functionalizations of alpha-olefins to form enantiomerically enriched products. In addition, related ruthenium and iron catalysts will be used in byproduct-free hydrofunctionalizations of butadiene (12 M tons produced per year). The proposed catalysts are chiral-at-metal-and-ligand, and a special feature of the catalyst design resides in defining metal-centered stereogenicity for optimal asymmetric induction. The project has the potential to yield fundamental advances in the practice and theory of transition metal-catalyzed transformations that are likely to benefit the sustainable manufacture of societally-relevant materials from simple chemical feedstocks.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.