Charged Macromolecular Rhenium Bipyridine Catalysts with Tunable CO₂ Reduction Potentials

Abstract

A series of polymeric frameworks with functional assemblies were designed to alter the catalytic activity of covalently bound Re^I electrocatalysts. Norbornenyl polymers containing positively charged quaternary ammonium salts, neutral phenyl, or negatively charged trifluoroborate groups were end-labelled with a Re^I fac-tricarbonyl bipyridine electrocatalyst via cross metathesis. Electrochemical studies in acetonitrile under an inert atmosphere and with saturated CO₂ indicate that the quaternary ammonium polymers exhibit a significantly lower potential for CO₂ reduction to CO (ca. 300 mV), while neutral polymers behave consistently with what has been reported for the free, molecular catalyst. In contrast, the trifluoroborate polymers displayed a negative shift in potential and catalytic activity was not observed. It is demonstrated that a single catalytically active complex can be installed onto a charged polymeric framework, thereby achieving environmentally tuned reduction potentials for CO₂ reduction. These materials may be useful as polymer-based precursors for preparing catalytic and highly ordered structures such as thin films, porous catalytic membranes, or catalytic nanoparticles.