Hiding and Recovering Electrons in a Dimetallic Endohedral Fullerene: Air-Stable Products from Radical Additions

Fullerenyl radicals can be generated by addition of a free radical to a fullerene surface, by nucleophilic addition followed by one-electron oxidation, or by thermal dissociation of singly bonded fullerene dimers. However, fullerenyl radicals are usually very reactive and generally cannot be isolated. On the contrary, we have found that the reactions of the dimetallic endofullerenes, La-2@I-h-C-80 and La-2@D-5h-C-80, with 3-chloro-5,6-diphenyltriazine resulted in mono-addition of the triazinyl radical to the fullerene cages to yield isolable fullerenyl radicals. The unusual stability of these fullerenyl radicals arises from the confinement of the unpaired electron to an internal, metalmetal bonding orbital. Accordingly, the fullerene cage protects the radical center from other reactive species. Furthermore, we demonstrate that the fullerenyl radical adduct of La-2@I-h-C-80 reacts with toluene to afford additional benzylation. Interestingly, the benzylated derivative is diamagnetic in solution, while it forms a paramagnetic dimer when crystallized.