Chemically induzed cagetransformations of fullerenes

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In the course of project KE 489/39-2 (submitted and supported by the DFG from January 2015 up to June 2018) many results have been obtained, which the chemistry of higher fullerenes not only develop but, importantly, open highly promising prospects. The large number of remarkable results in the fullerene chemistry were achieved due to the application of effective and sensitive methods which have been developed during carrying out this project. These include performing the reactions with tiny amounts of substances, effective chromatographic separation, and the use of synchrotron radiation for single crystal X-ray diffraction experiments. The main results include i) the discovery of new isomers of higher fullerenes such as C88, C96, C100, C104, C106, and C108, the latter being so far the highest structurally characterized fullerene, ii) the discovery and theoretical treatment of new cage transformations in the course of chemical reactions. The new skeletal transformations include a new type of Stone-Wales rearrangements (SWR2) in fullerene C100, a new type of cage shrinkage via C2 losses which results in heptagon elimination, and several multistep transformations in C88, C100, and C102, which resulted in chlorides of non-IPR C102 as well as non-classical fullerenes (C84, C96, C98, and C102),iii) a new identification method for skeletal transformations via trifluoromethylation of chlorination products which results in the formation of mixed CF3/F derivatives (Fig. 9 in the main report). This implies a new type of fluorination reaction, the pathway of which is still unknown,iv) our experimental experiences in the field of skeletal transformations supported by theoretical considerations of transformation mechanisms allowed us recently to perform such transformations not only with higher but also with “usual” fullerenes, C60 and C70. The most spectacular result of a transformation of C60, is shown in our report in Figure 10 as an impressive example of a “wonder molecule”, C60Cl20, with five pairs of fused pentagons. Therefore, the remarkable results of the first syntheses of non-IPR C60 and C70 derivatives open a new, highly interesting field of research. In contrast to cage transformations in higher fullerenes, the experiments with C60 and C70 can be performed on a preparative scale. It should be therefore possible to investigate physical and chemical properties of non-IPR C60 and C70. On the basis of the first highly promising results, it seems now necessary to vary the synthesis and separation conditions in order to find optimal methods for obtaining new compounds, thus enabling further structural studies.