Transition metal-catalyzed borylation has emerged as a widely utilized approach to the functionalization of C–H bonds for applications in fine chemical synthesis. Precious metal catalysts for this transformation such as the state-of-the-art bipyridine/iridium system are noted for their high activity and sterically-determined site selectivity. Previously, our laboratory reported that bis(phosphino)pyridine (iPrPNP) cobalt complexes are active as catalysts in the borylation of benzene derivatives and five-membered heterocycles. Moreover, these catalysts display rare ortho selectivity in the borylation of fluorinated arenes, even in the presence of functional groups commonly employed as directing groups in iridium-catalyzed C–H borylation. My presentation will focus on a comprehensive experimental and computational investigation into the mechanism of (iPrPNP)Co-catalyzed borylation of fluorinated arenes. Variable time normalization analysis, kinetic isotope effect studies, and deuterium labeling experiments revealed an atypical kinetic regime, wherein C–H oxidative addition was found to be fast and reversible. This kinetic regime, coupled with the stabilization conferred to transition metal aryl complexes by ortho fluorine substituents, results in the observed ortho-to-fluorine regioselectivity. Computational analysis including bond dissociation free energy correlation studies supported the proposed origins of the unique selectivity. Subsequent mechanistic studies revealed that the kinetic regime by which (iPrPNP)Co-catalyzed borylation operates can be perturbed as a function of the arene substrate. This fluidity of kinetic regimes enables selective borylation of sites other than ortho to a fluorine even in cases where C–H bonds ortho to fluorine substituents are sterically accessible.

On the origins of regioselectivity in cobalt-catalyzed C(sp2)–H borylation of fluorinated arenes

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.