Leveraging Polarized Metal-Metal Bonds for Catalytic Hydrodefluorination via Thermal and Photolytic Pathways

Abstract

Organofluorines are pervasive in our everyday lives and found in many commodities and chemicals, including pharmaceuticals, agrochemicals, and lubricants. The utility of organofluorines is due largely to the unique properties imparted from fluorination, with the most notable being the enhanced stability and greatly increased lifetime. However, the increased stability and widespread production of organofluorines has led to widespread environmental contamination, which is especially problematic due to the toxicity of perfluorinated organic molecules. Hence, it is crucial to develop catalysts that are capable of efficiently cleaving the strong C–F bonds in these persistent chemicals. One emerging strategy that has been used to cleave strong bonds is the utilization of bimetallic complexes featuring polarized metal–metal bonds. This dissertation investigates the use of bimetallic complexes comprised of late transition metals (Fe and Rh) supported by Lewis acids, including Ti, Al, Ga, and In, for the hydrodefluorination of fluorinated organics. These complexes were characterized using a suite of spectroscopic, electrochemical, and computational methods to probe the electronic effect that the Lewis acid has on the late transition metals. Overall, it was found that the Rh complexes supported by the group 13 metalloligands were highly active for the cleavage of unactivated aryl C−F bonds using mild heat. Moreover, these same complexes were also found to be highly reducing photoredox catalysts that were capable of reducing and subsequently cleaving unactivated aryl and benzylic C–F bonds using visible light. Overall, this work demonstrates the utility of polarized metal–metal bonds in homogenous defluorination catalysis, welcoming a new paradigm in the activation of the strongest bonds.