RUI: Phosphorus-Directed C-H Borylation and Reactivity of Phosphaboronates

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With the support of the Chemical Catalysis Program in the Division of Chemistry, Professor Timothy Clark of the University of San Diego is studying transition metal-catalyzed processes that enable the selective introduction of boron into organic molecules that contain phosphorus. Subsequent reactions that allow for replacement of the boron residue with yet other groups of ultimate interest are also under investigation with the net aim of achieving the manufacture of value-added organophosphorus products. These endeavors are significant because of the fundamental advances to borylation and boron-conversion chemistry that are anticipated and due to the importance of the kinds of organophosphorus products being generated, which have potential applications as pharmaceutical agents, agrochemicals, and other advanced materials of broad utility. Professor Clark works primarily with undergraduate student coworkers at the University of San Diego and, accordingly, the broader impacts of the funded project will extend to the education and training of young people in STEM (science, technology, engineering and mathematics) fields. In addition, a post-doctoral associate working on the project will receive mentoring from the PI to build toward a future career in research and teaching thus further enriching the pool of human resources in science and education.The funded research is focused on significantly expanding recent advances in C–H borylation chemistry to enable efficient new routes to valuable chiral phosphines and phosphonates. Two distinct aims are being pursued that explore this theme in the context of either alkyl or aryl organophosphorus compounds. In Aim 1, iridium-catalyzed C(sp3)–H borylation of alkyl phosphines, phosphonates, and related organophosphorus species, is being investigated in the presence of chiral ligands to achieve an enantioselective synthesis of secondary alkyl boronates. Sequencing this chemistry with the expansive range of reactions that allow for the stereospecific conversion of C–B bonds into C–C or C–X (X = O, N) bonds allows for expedient syntheses of useful enantioenriched chiral phosphines. In Aim 2, biaryl formation from aryl boronates generated by phosphorus-directed ortho borylation of aryl phosphonates, is being explored via novel oxidative copper-catalyzed homo- and hetero-coupling processes. Opportunities for executing this chemistry, which offers a concise route to some important classes of axially chiral bisphosphine ligands, in an enantioselective modality are also under investigation.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.