Synthesis of Hydrogen-Bonded Open-[60]Fullerenol Dimers

Two open-[60]fullerenols were synthesized through a selective bond cleavage by reactions with N-oxide or singlet oxygen. Both open-[60]fullerenols having a bis(hemiketal) moiety were aggregated via intra- and intermolecular hydrogen-bondings to show a dimeric configuration in a face-to-face fashion where the hydroxy groups adopt a rhomboidal or chair-like arrangement as confirmed by X-ray diffraction analysis. The dimerization constant of one of the two open-[60]fullerenols was measured to be 22.2±4.7 M^-1 (300 K, CDCl₃ ) which is twice as large as that of a previously-reported open-[60]fullerenol bearing three hydroxy groups. According to theoretical calculations, an averaged interaction energy was estimated to be ca. -1.95 kcal/mol per an H-bonding. By a loss of a water molecule from the bis(hemiketal) moiety, these open-[60]fullerenols are transformed into tetracarbonyl derivatives with a 16-membered-ring orifice. Despite being the same ring-atom count, a larger tilt angle of one of the carbonyl groups reduces the effective orifice size as suggested by theoretical calculations.