Non-IPR Chlorofullerenes

The rule per excellence governing the stability of fullerene cages is the well-known Isolated Pentagon Rule, or IPR. Fullerenes violating the pentagon rule have been obtained in situ through (i) encapsulation of metallic clusters inside the cavity or by (ii) external addition of halogenated species. The endohedral non-IPR cages (type i) appeared in the 2000, with the simultaneous discovery of Sc₂@C₆₆ and Sc₃N@C₆₈;^[1] the halogenated IPR-violating fullerenes (type ii) appeared in 2004 with the characterization of the first empty non-IPR cage C₅₀Cl₁₀.^[2] From then on, the list of non-IPR cages synthesized with any of the two functionalizations has increased significantly. It is important to note that there exists no IPR-violating isomer obtained both as metallo-endohedral and chlorinated fullerene, suggesting that isomers encapsulating metals are not suitable to be obtained with halogen derivatization. The factors that govern the formation of metalloendohedral fullerenes are well-known.^[3] Now, we intend to discover which are the elements that favor the formation of chlorinated species. With this goal, we have analyzed several isomers for C₆₆ and other fullerenes that have been observed as chloro- and endofullerenes in order to unravel the features of the non-IPR isomers that make them suitable to be trapped as halogenated fullerenes. 

(1)    Stevenson, S.; Fowler, P. W.; Heine, T.; Duchamp, J. C.; Rice, G.; Glass, T.; Harich, K.; Hajdu, E.; Bible, R.; Dorn, H. C. Nature 2000, 408, 427.

(2)    Xie, S.-Y.; Gao, F.; Lu, X.; Huang, R.-B.; Wang, C.-R.; Zhang, X.; Liu, M.-L.; Deng, S.-L.; Zheng, L.-S. Science 2004, 304, 699.

(3)    a) Rodriguez-Fortea, A.; Alegret, N.; Balch, A. L.; Poblet, J. M. Nature Chem. 2010, 2, 955; b) Campanera, J. M.; Bo, C.; Poblet, J. M. Angew. Chem., Int. Ed. 2005, 44, 7230.