Solid-state [4+2] cycloaddition of fullerene C60 with condensed aromatics using a high-speed vibration milling technique

The solid-state reaction using a high-speed vibration milling (HSVM) technique has been applied to the [4 + 2] cycloaddition of fullerene C-60 with condensed aromatics such as anthracenes, tetracene, pentacene, and naphtho[2,3-a]pyrene. From the reaction with anthracene, [4 + 2] cycloadduct 1 was obtained in better yield than the reaction in solution. Despite such heterogeneous solid-state reaction conditions, an equilibrium state appears to be attained between the reactants (C-60 and anthracene) and products (mono- and bisadducts) since essentially the same product mixture was obtained starting either from the reactants or from the monoadduct after 30 min of the HSVM reaction. The reaction with pentacene gave double C-60 adduct 4 with two C60 cages attached to a pentacene molecule, which cannot be obtained in the reaction in toluene solution, in addition to symmetrical monoadduct 3. The HSVM treatment of C-60 with 9, 10-dimethylanthracene, tetracene, or naphtho[2,3-a]pyrene also gave the corresponding [4 + 2] cycloadducts in fair yields. The redox properties of these adducts were investigated by the use of cyclic voltammetry.