Radicals anions of F-alkyl substituted fluoro-olefins

Abstract

In this communication we present the results of an EPR and electrochemical investigation on free radicals produced by electrochemical reduction, at controlled potential, of the following alkyl substituted perfluoro-olefins: R 1R 2CCR 3R 4 1. R 1R 2R 3R 4Me 2. R 1R 3Me, R 2R 4Et 3. R 1R 2i-Prop, R 3Me, R 4F 4. R 1R 2Me, R 3i-Prop, R 4Et All the olefins studied present, in acetonitrile, a chemically reversible one-electron reduction step in the range 0.4–0.8 V vs. Ag/AgCl, corresponding to the formation of the radical anion. The latter is some cases can be accumulated by macroscale electrolysis at low temperature (0 to −30 °C). At more negative potentials, the radical anions are reduced to the corresponding dianions, which are very unstable because of a fast fragmentation process. The EPR spectra are characterized by very large hyperfine coupling constants of the unpaired electron with 19F nuclei directly bonded to the unsaturated carbon atom, with the β 19F nuclei of the alkyl groups and additional couplings to γ 19F nuclei, indicating a significant contribution of the fluorine orbitals to the molecular orbital occupied by the unpaired electron. The spectra show a strong dependence on the temperature which is fully described by a restricted rotation of the perfluoro-alkyl groups, including perfluoro-methyls, about the single bonds.