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, La2@Ih-C80 and La2@D5h-C80, 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, metal–metal bonding orbital. Accordingly,
the fullerene cage protects the radical center from other reactive
species. Furthermore, we demonstrate that the fullerenyl radical adduct
of La2@Ih-C80 reacts with toluene to afford additional benzylation. Interestingly,
the benzylated derivative is diamagnetic in solution, while it forms
a paramagnetic dimer when crystallized.