Charged Macromolecular Rhenium Bipyridine Catalysts with Tunable CO2 Reduction Potentials

5 years ago

Charged Macromolecular Rhenium Bipyridine Catalysts with Tunable CO2 Reduction Potentials

Po Ling Cheung, Swagat Sahu, Nathan C. Gianneschi, Steven A. Chabolla, Charles W. Machan, Clifford P. Kubiak

A series of polymeric frameworks with functional assemblies were designed to alter the catalytic activity of covalently bound ReI electrocatalysts. Norbornenyl polymers containing positively charged quaternary ammonium salts, neutral phenyl, or negatively charged trifluoroborate groups were end-labelled with a ReI 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. Charges matter: A series of norbornenyl polymers containing positively charged quaternary ammonium salts, neutral phenyl, or negatively charged trifluoroborate groups were end-labelled with a ReI fac-tricarbonyl bipyridine electrocatalyst via cross metathesis. Electrochemical studies indicate that the quaternary ammonium polymers exhibit a significantly lower potential for CO2 reduction, while neutral polymers behave consistently with what has been reported for the free, molecular catalyst. In contrast, no catalytic activity was observed for the trifluoroborate polymers.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701901