Thermally Stable Perfluoroalkylfullerenes with the Skew-Pentagonal-Pyramid Pattern: C₆₀(C₂F₅)₄O, C₆₀(CF₃)₄O, and C₆₀(CF₃)₆

Reaction of C60 with CF3I at 550 °C, which is known to produce a single isomer of C60(CF3)2,4,6
and multiple isomers of C60(CF3)8,10, has now been found to produce an isomer of C60(CF3)6 with the Cs-C60X6 skew-pentagonal-pyramid (SPP) addition pattern and an epoxide with the Cs-C60X4O variation of the
SPP addition pattern, Cs-C60(CF3)4O. The structurally similar epoxide Cs-C60(C2F5)4O is one of the products
of the reaction of C60 with C2F5I at 430 °C. The three compounds have been characterized by mass
spectrometry, DFT quantum chemical calculations, Raman, visible, and 19F NMR spectroscopy, and, in
the case of the two epoxides, single-crystal X-ray diffraction. The compound Cs-C60(CF3)6 is the first [60]fullerene derivative with adjacent Rf groups that are sufficiently sterically hindered to cause the (DFT-predicted) lengthening of the cage (CF3)C−C(CF3) bond to 1.60 Å as well as to give rise to a rare, non-fast-exchange-limit 19F NMR spectrum at 20 °C. The compounds Cs-C60(CF3)4O and Cs-C60(C2F5)4O are
the first poly(perfluoroalkyl)fullerene derivatives with a non-fluorine-containing exohedral substituent and
the first fullerene epoxides known to be stable at elevated temperatures. All three compounds demonstrate
that the SPP addition pattern is at least kinetically stable, if not thermodynamically stable, at temperatures
exceeding 400 °C. The high-temperature synthesis of the two epoxides also indicates that perfluoroalkyl
substituents can enhance the thermal stability of fullerene derivatives with other substituents.