Redox Properties of Isozazolo[60]fullerenes with Regard to Substituents and Molecular Structure

Abstract

A series of isoxazolo[60]fullerene derivatives 1(a-k), 5 and 6(l-n) have been synthesized by [2+3]cycloadditions of the corresponding nitriloxides to C₆₀. The phenyl-, 1,4- and 1,2-biphenyl substituents are substituted with electron donor groups in different distances and orientations in order to determine their influence on the redox properties of these fullerene derivatives. The redox- behavior was measured by cyclic voltammetry. In compounds 1b-g, 5l-n and 6l-n no significant shift relative to the reference compound la could be found. The insertion of an o-phenylene spacer between the isoxazoline ring and the phenyl ring substituted by donor groups in derivatives lh-k causes a shift of the first reduction potential by 30 mV (1h, 1k) and 60 mV (1i) towards more negative values compared to the reference 1a. Because of the o-phenylene spacer the plane of the donor-phenyl ring is forced into a close and parallel orientation to surface of the fullerene suitable for through-space interaction. This geometry was proven by X-ray structure determination of 1k.