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

Abstract

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.