(Invited) Chemical Reactions of Ionic Metallofullerenes: An Alternative Route for Exohedral Functionalization

The chemistry of cationic forms of clusterfullerenes remain less explored than that of the corresponding neutral or anionic species. In the present work, M3N@Ih -C80 (M = Sc or Lu) cations were generated by both electrochemical and chemical oxidation methods. The as-obtained cations successfully underwent the typical Bingel-Hirsch reaction that fails with neutral Sc3N@Ih -C80. Two isomeric Sc3N@Ih -C80 cation derivatives, [5,6]-open and [6,6]-open adducts, were synthesized, and the former has never been prepared via a Bingel-Hirsch reaction with neutral clusterfullerenes. Density functional theory (DFT) calculations indicated that the oxidized M3N@Ih -C80 was much more reactive than the neutral compound upon addition of the diethyl bromomalonate anion. The Bingel-Hirsch reaction of M3N@Ih -C80 cations occurred via an unusual outer-sphere single-electron transfer (SET) process from the diethyl bromomalonate anion to the stable intermediate [M3N@C80(C2H5COO)2CBr]•. Remarkably, the diethyl bromomalonate anion was found to act as both a nucleophile and an electron donor. Cationic forms of clusterfullerenes exhibited chemical properties that are different from those of the corresponding neutral and anionic forms. These findings promote a better understanding of EMFs cations and offer a complementary strategy to activate and functionalize EMFs.