First Synthesis and Characterization of CH4@C60

The endohedral fullerene CH4@C-60, in which each C-60 fullerene cage encapsulates a single methane molecule, has been synthesized for the first time. Methane is the first organic molecule, as well as the largest, to have been encapsulated in C-60 to date. The key orifice contraction step, a photochemical desulfinylation of an open fullerene, was completed, even though it is inhibited by the endohedral molecule. The crystal structure of the nickel(II) octaethylporphyrin/benzene solvate shows no significant distortion of the carbon cage, relative to the C-60 analogue, and shows the methane hydrogens as a shell of electron density around the central carbon, indicative of the quantum nature of the methane. The H-1 spin-lattice relaxation times (T-1) for endohedral methane are similar to those observed in the gas phase, indicating that methane is freely rotating inside the C-60 cage. The synthesis of CH4@C-60 opens a route to endofullerenes incorporating large guest molecules and atoms.