Addition of CF2 group to endohedral fullerene Sc3N@Ih-C80

Abstract

We report the first successful synthesis of a CF₂ derivative of the stable endohedral fullerene Sc₃N@I_h-C₈₀. Reaction with CF₂ClCOONa yields a single C_s-symmetric Sc₃N@C₈₀(CF₂) adduct where the CF₂ group is inserted into a [6,6]-bond and opens it to 2.3 Å between the bridgehead carbon atoms. As evidenced by absorption and fluorescence spectroscopy as well as cyclic voltammetry, both the HOMO and the LUMO level of Sc₃N@C₈₀(CF₂) are slightly (ca. 0.1 eV) downshifted with respect to the parent Sc₃N@I_h-C₈₀, so the HOMO–LUMO gap remains essentially unchanged. The DFT calculations suggest that the reaction mechanism is not the previously assumed [2 + 1]-cycloaddition of :CF₂ carbene but rather nucleophilic addition of CF₂Cl⁻ anion followed by elimination of Cl⁻ and closing of the CF₂ bridge via intramolecular nucleophilic substitution. Selective formation of the [6,6]-Sc₃N@C₈₀(CF₂) turns out to be kinetically controlled and promoted by a particular orientation of the endohedral Sc₃N cluster with respect to the CF₂Cl⁻ addition site. In its turn, the CF₂ addend partly hampers the rotation of Sc₃N the endohedral cluster compared to its quasi-free reorientations in the parent Sc₃N@I_h-C₈₀.