Lithium-ion-containing [60]fullerene, Li⁺@C₆₀, is a highly electron accepting material, which have been utilized in electron transfer chemistry, supramolecular chemistry, photovoltaics, singlet oxygen generation, and so on. Considering what chemical modification of fullerene has played in, that for Li⁺@C₆₀ would be a significant step for further functionalization of this compound.^[1-7] In addition, chemical modification of Li⁺@C₆₀ can solve this compound's drawback of low solubility in organic solvents due to rock salt packing of [Li⁺@C₆₀][PF₆^–].

Li⁺@C₆₀ was modified with diphenyl(diazo)methane as an easily available diazoalkane to obtain lithium-ion-encapsulated [5,6]- and [6,6]-diphenylmethano[60]fullerenes, Li⁺@C₆₁Ph₂. Successful separation of each [5,6]- and [6,6]-isomer was performed with a positive-ion exchange columns. Both [5,6]-open and [6,6]-closed structures of Li⁺@C₆₁Ph₂ were determined with X-ray crystallographic analysis.