First Synthesis and Characterization of CH₄@C₆₀

Abstract

Abstract The endohedral fullerene CH 4 @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 1 H 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 CH 4 @C 60 opens a route to endofullerenes incorporating large guest molecules and atoms.