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

Abstract

AbstractTwo 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.