A novel Bingel monoadduct of La@C82 (mono-A) has been synthesized by the reaction with diethyl bromomalonate in the presence of DBU (Bingel−Hirsch reaction). Its structure has been fully determined by NMR spectroscopic and X-ray crystallographic analyses. The most distinct feature of mono-A is the single bond moiety between the functional group and fullerene cage, which is very different from the cyclopropane moiety in a conventional Bingel adduct of empty fullerenes. Further spectroscopic characterizations and calculations revealed the closed-shell structure of mono-A. Its formation mechanism was discussed according to calculation results.
