Synthesis of Open-Cage Ketolactam Derivatives of Fullerene C60 Encapsulating a Hydrogen Molecule

A novel open-cage fullerene C-60 derivative having a bis(hemiketal) moiety was synthesized by the reaction of C-60-N-MEM-ketolactam (MEM: 2-methoxyethoxymethyl) with N-methylmorpholine N-oxide in the presence of water. The structure was clearly determined by single crystal X-ray analysis. Further enlargement of the opening was performed by treatment with trifluoroacetic anhydride to give the tetraketo derivative having a 15-membered ring opening. For H-2-insertion into the cage, the derivative was exposed to a high pressure of H-2. After the encapsulation, the opening size was reduced to the original one while keeping the hydrogen molecule inside the cage. This compound can be a possible precursor for endohedral azafullerenes encapsulating a hydrogen molecule.