A Supramolecular Separation Process for Regioisomeric Fullerene Bisadducts Using a Tetrahedral Zinc(II) Coordination Capsule

Separation of fullerene bisadduct regioisomers remains a significant challenge because conventional functionalization of fullerene generally affords complex mixtures of compounds with similar physicochemical properties. Here, we demonstrate regioisomer-selective recognition and separation of C60 bis(N-methylpyrrolidine) adducts using a tetrahedral Zn(II) coordination capsule. The capsule readily encapsulated a C60 monoadduct, and variable-temperature 1H NMR spectroscopy revealed dynamic reorientation of the guest within the cavity. In contrast, the trans-4 bisadduct formed a more conformationally restricted host–guest complex, for which no coalescence of the host or guest signals was observed even at 343 K. NOESY measurements showed distinct intermolecular correlations between the two N-methylpyrrolidine moieties and different sets of inward-facing host protons, supporting a binding geometry in which the two addends are directed toward different vertices of the tetrahedral capsule. When a crude mixture of fullerene bisadduct regioisomers was subjected to capsule formation, the encapsulated fraction was enriched in the trans-4 isomer. Although the equatorial isomer was initially more abundant than trans-4, the recovered fraction contained trans-4 and equatorial isomers in a 71:29 ratio. These findings demonstrate preferential recognition of the trans-4 regioisomer and suggest that geometric complementarity between the guest substitution pattern and the tetrahedral host cavity may contribute to the observed selectivity.