Synthesis of [59]Fullerenones through Peroxide-Mediated Stepwise Cleavage of Fullerene Skeleton Bonds and X-ray Structures of Their Water-Encapsulated Open-Cage Complexes

Fullerene skeleton modification has been investigated through selective cleavage of the fullerene carbon−carbon bonds under mild conditions. Several cage-opened fullerene derivatives including three [59]fullerenones with an 18-membered-ring orifice and one [59]fullerenone with a 19-membered-ring orifice have been prepared starting from the fullerene mixed peroxide 1, C₆₀(OO^tBu)₆. The prepositioned tert-butyl peroxy groups in 1 serve as excellent oxygen sources for formation of hydroxyl and carbonyl groups. The cage-opening reactions were initiated by photoinduced homolysis of the ^tBu−O bond, followed by sequential ring expansion steps. A key step of the ring expansion reactions is the oxidation of adjacent fullerene hydroxyl and amino groups by diacetoxyliodobenzene (DIB). Aminolysis of a cage-opened fullerene derivative containing an anhydride moiety resulted in multiple bond cleavage in one step. A domino mechanism was proposed for this reaction. Decarboxylation led to elimination of one carbon atom from the C₆₀ cage and formation of [59]fullerenones. The cage-opened [59]fullerenones were found to encapsulate water under mild conditions. All compounds were characterized by spectroscopic data. Single-crystal structures were also obtained for five skeleton-modified derivatives including two water-encapsulated fulleroids.