Chemistry of Higher Fullerenes

For origins of fullerene chirality and definitions of configurational description factors fC and fA (f = fullerene, C = clockwise, A = anticlockwise), see C. Thilgen, A. Herrmann, F. Diederich, The Covalent Chemistry of Higher Fullerenes C70 and Beyond , Angew. Chem Int. Ed. Engl. 1997,36,2269-2280. 

Just by comparing the number of publications on fullerenes (5500 until 1994 and 21500 between 1994 and now) it was immediately clear that the whole literature even that focussing on fullerene chemistry cannot be covered in a single monograph. We had to carefully select and condense the material, refer to the many excellent reviews of specific subjects such as chemistry of higher fullerenes and supramolecular chemistry of fullerenes. 

C. Thilgen, A. Herrmann and F. Diederich (1997) Angewandte Chemie, International Edition in English, vol. 36, p. 2268 - The covalent chemistry of higher fullerenes C70 and beyond . 

In general, the chemistry of higher fullerenes is very similar to that of Ceo- This is particularly true for highly pyramidalized regions, like the pole caps of C70. Here the bonds (Figure 1) are the most reactive ones. The pyramidalization of the g bonds within C70 as well as the bond lengths are almost the same as that of the [6,6]-bonds within Ceo (Tables 1 and 2). The equatorial belt of C70 consisting of the a, b, and c bonds is much less reactive. 

It is a considerable challenge to isolate a pure adduct. One of the unique features of fullerene chemistry is the large number of products that sometimes result from addition of even one mole eqivalent of reagent. Owing to its relatively high abundance, most fully characterized complexes are for C60, but the behavior of higher fullerenes is broadly similar. The availability of only small amounts of higher fullerenes, coupled with the inequivalency of some of the double bonds, introduces additional complications. 

Apart from these, a number of reactions, e.g. ozonation [150], hydrogenation [151], fluorination [152], and the formation of methylene adducts by reaction with THF [153], have led to various mixtures of higher fullerene derivatives. Finally, as the methods for production and purification of endohedral fullerene derivatives are being improved, the exohedral functionalization of Qq [70, 73, 74] and C70 [73] cages containing noble gas atoms, and of endohedral metallo-fullerenes [64,154] emerge as new fields of fullerene chemistry. 

Amsharov, K. Y., Jensen, M. (2008). A Cyg Fullerene precursor Toward the direct synthesis of higher fullerenes. Journal of Organic Chemistry, 73, 2931-2934. 

The chemistry of Ceo and that of a series of higher fullerenes has been intensively Investigated m the last 10 years. Various areas of fullerene chemistry as well as principles of fullerene reactivity were summarized in a variety of reviews. Here we... 

Ceo and higher fullerenes are distinguished from other allotropes of carbon, diamond and graphite, in that they exist as discrete molecules. The spherical or ellipsoidal nature of the monotropes opens up the possibility of intriguing new areas of chemistry. Here we are only interested in the hydrogen (or muonium) adducts, although this study has important implications to the very vigorous and extensive research in fullerene chemistry. 

Following the discovery of a bulk fullerene preparation process in 1990, the covalent chemistry of these carbon allotropes has developed at a phenomenal pace. Frontier orbital (LUMO) and tether-directed functionalization concepts have been successfully applied to the regio- and stereoselective preparation of multiple covalent adducts of C60. These have found increasing applications in the construction of functional supramol-ecules. More recently, the sequence of Bingel reaction - retro-Bingel reaction has provided an elegant access to isomerically pure higher fullerenes and, in particular, to pure carbon enantiomers. 

Like CgQ most of the characterized higher fullerenes can be considered as electron-deficient polyenes. They exhibit similarities in their chemical behavior [1-3]. Preferred primary addition reactions are, for example, addition of nucleophiles, as well as cycloadditions at the bonds adjacent to two six-membered rings ([6,6]-bonds). The most important difference from the chemistry of Cgg is due to the less symmetrical cages of the higher fullerenes, which exhibit a broad variety of bond environments with unequal reactivity towards addition reactions. Consequently... 

Comparable alternations between the [6,6]- and [5,6]- bond lengths are observed in many fullerene adducts and higher fullerenes. Moreover, from the evaluation of many exohedral transformation of fullerenes, in particular Cjq, an important principle of fullerene chemistry can be deduced, namely minimization of[5,6]-douhle bonds in the lowest energy Kekule structure. Minimization of [5,6]-double bonds is... 

The chemistry of the higher fullerenes has developed at a slower pace than that... 

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