Nickel(I) salen-catalyzed reduction of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113): CO2-mediated carbon–fluorine bond cleavage

Abstract

Cyclic voltammetry, controlled-potential (bulk) electrolysis, gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), and high-performance liquid chromatography–electrospray ionization–mass spectrometry (HPLC–ESI–MS) have been used to investigate the direct and nickel(I) salen-catalyzed reduction of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) in both Ar- and CO2-saturated dimethylformamide (DMF) containing 0.10 M tetra-n-butylammonium tetrafluoroborate (TBABF4). Cyclic voltammograms show one irreversible cathodic peak for direct reduction of CFC-113 in CO2-saturated DMF to afford 1-chloro-1,2,2-trifluoroethene (CFC-1113), whereas cyclic voltammograms in Ar-saturated DMF exhibit two irreversible cathodic peaks. Bulk electrolyses of CFC-113 in CO2-saturated DMF at a potential 400 mV more negative than the resolved cathodic peak cause partial reduction of CFC-1113 to yield di-, tri-, and tetrafluoro species. Cyclic voltammograms for reduction of nickel(II) salen in the presence of CFC-113 in CO2-saturated DMF show two cathodic peaks attributable to formation of CFC-1113 and HFC-1123; cyclic voltammograms in Ar-saturated DMF exhibit similar behavior. Bulk electrolyses involving electrogenerated nickel(I) salen in CO2-saturated DMF yield mixtures of HFC-1123, isomers of difluoroethene, and traces of other species. No electrocarboxylation of CFC-113 or its derivatives was seen in the presence of CO2; however, excess CO2 increases the extent of dechlorination of CFC-113 during bulk electrolyses when compared with analogous electrolyses in an Ar-saturated medium. Structural modification of nickel(II) salen during catalytic reduction of CFC-113 in the presence of CO2 was determined with the aid of HPLC–ESI–MS.