Difluoromethylenation of fullerene C₇₀ provides isomeric diversity and availability of equatorial [5,6]-homofullerene C₇₀(CF₂)

We report synthesis, isolation, and spectroscopic characterization of the novel [5,6]-open C70(CF2) isomer III along with the already known [6,6]-closed and [6,6]-open C70(CF2) isomers I and II. The compounds were obtained in a ratio of I : II : III = 4 : 6 : 1 by means of thermal treatment of C70 fullerene with sodium chlorodifluoroacetate. This product composition is explained with the use of quantum chemical calculations that identify the reaction pathway as a two-stage nucleophilic cyclopropanation rather than the previously postulated carbene addition. We further report the first cyclic voltametric studies for the whole set of isomers of C70(CF2). Together with the DFT data, they demonstrate that the LUMO is stabilized in both isomer II ([6,6]-open) and III ([5,6]-open) by 0.1 eV with respect to the pristine C70, and isomer III has the lowest reorganization energy of all.