DYNAMICS OF BOND BREAKING IN ION RADICALS - MECHANISMS AND REACTIVITYIN THE REDUCTIVE CLEAVAGE OF CARBON-FLUORINE BONDS OF FLUOROMETHYLARENES

The reductive cleavage mechanism and reactivity of the carbon-fluorine bonds in fluoromethylarenes are investigated, in liquid ammonia and i n DMF, by means of cyclic voltammetry and/or redox catalysis as a func tion of the number of fluorine atoms and of the structure of the aryl moiety. The reduction of the trifluoro compounds, eventually leading t o complete defluorination, involves the di-and monofluoro derivatives as intermediates. Carbenes do not transpire along the reaction pathway . Application of the intramolecular dissociative electron transfer mod el allows the quantitative rationalization, in terms of driving force and intrinsic barrier, of the variation of the cleavage reactivity of the primary anion radical with the number of fluorine atoms and of the structure of the aryl moiety as well as with the solvating properties of the medium. When, related to the structural factors thus uncovered , the primary anion radical generates the di-and monofluoro intermedia tes far from the electrode surface, their reduction occurs homogeneous ly giving rise to an apparently direct six-electron process according to an internal redox catalysis mechanism. Conversely, with rapid cleav ages, the reduction of the di- and monofluoro intermediates takes plac e at the electrode surface and the stepwise expulsion of the fluorides ions transpire in the cyclic voltammetric patterns.