Synthesis of open-cage ketolactam derivatives of fullerene C60 encapsulating a hydrogen molecule.

Abstract

A new open-cage C60 fullerene derivative bearing a bis(hemiketal) unit was obtained through reaction of C60-N-MEM-ketolactam (MEM: 2-methoxyethoxymethyl) with N-methylmorpholine N-oxide in the presence of water, with the structure confirmed by single-crystal X-ray diffraction. The orifice was subsequently expanded to a 15-membered ring by treatment with trifluoroacetic anhydride, yielding a tetraketo derivative. Exposure of this compound to high-pressure H2 gas allowed encapsulation of a single hydrogen molecule within the cage. Following encapsulation, the opening was contracted back to its original dimensions while retaining the H2 inside. The resulting compound represents a potential precursor for the preparation of endohedral azafullerenes that contain an encapsulated hydrogen molecule.

Mechanism

High-pressure H2 gas was used to insert a hydrogen molecule through an enlarged 15-membered ring orifice of an open-cage C60 derivative; subsequent chemical reduction of the opening size trapped the H2 molecule inside the fullerene cage.