The Covalent Chemistry of Higher Fullerenes: C70 and Beyond

Abstract

AbstractAlthough higher fullerenes are not yet available in larger amounts, their accessibility, like that of C60, has gradually improved since the early days of fullerence chemistry. Today, many of the soluble larger carben can be purchased either in pure form or as isomeric mixtures. In particular, pure C70 is available in preparative amounts from fullerene soot without the need for tedious separation by high‐performance liquid chromatography; this has had a major impact on the progress of the chemistry of this higher fullerene. Over the last years C70 has been functionalized in many ways, and pure derivatives of even the larger, more complex carbon spheres C76, C84, and recently also C78, have been isolated and characterized. From the collected body of data, first general principles of reactivity and selectivity begin to emerge for these fullerenes, which are all less symmetric than C60. Important information is provided by multiple additions to higher fullerenes, in which certain isomers are formed with a remarkable selectivity that exceedes that observed for C60. A particularly attractive aspect is the chirality of certain allotropes and many derivatives. Although the chirality of fullerene derivatives is not restricted to the larger carbon cages, it was sofar mostly explored through their chemistry and can be related to different structural characteristics. A recently proposed system allows simple specification by a single descriptor of the configuration of chiral fullerenes and fullerene derivatives with a chiral functionalization pattern, including highly branched carbon frameworks with a multitude of possible stereogenic centers.