Open-cage fullerene derivatives suitable for the encapsulation of a hydrogen molecule

The encapsulation of molecular hydrogen into an open-cage fullerene having a 16-membered ring orifice has been investigated. It is achieved by the pressurization of H-2 at 0.6-13.5 MPa to afford endohedral hydrogen complexes of open-cage fullerenes in up to 83% yield. The efficiency of encapsulation is dominantly dependent on both H-2 pressure and temperature. Hydrogen molecules inside the C-60 cage are observed in the range of -7.3 to -7.5 ppm in H-1 NMR spectra, and the formations of hydrogen complexes are further confirmed by mass spectrometry. The trapped hydrogen is released by heating. The activation energy barriers for this process are determined to be 22-24 kcal/mol. The DSC measurement of the endohedral H-2 complex reveals that the escape of H-2 from the C-60 cage corresponds to an exothermic process, indicating that encapsulated H-2 destabilizes the fullerene.