Fused-Pentagon Carbon Cages in Chloro and Trifluoromethyl Derivatives of C₆₀: Non-IPR ¹⁸⁰⁹C₆₀Cl₈, ¹⁸⁰⁶C₆₀(CF₃)₁₄, and Nonclassical C₆₀(NC)Cl₁₄

Abstract

High-temperature chlorination of conventional IPR C 60 can produce chloro derivatives of non-IPR C 60 by skeletal transformations via Stone−Wales rearrangements (SWRs) of the carbon cage. We report the synthesis and structure elucidation of non-IPR 1809 C 60 Cl 8 and nonclassical C 60 (NC)Cl 14 . The present isolation of 1809 C 60 Cl 8 hints at the possibility that the same product in the previously reported chlorine-doped arc-discharge synthesis could have, likewise, resulted from the initially formed IPR C 60 . C 60 (NC)Cl 14 is the first chloride containing a nonclassical carbon cage with one heptagon and 13 pentagons known previously only in a CF 3 derivative. Additionally, trifluoromethylation of non-IPR chlorides revealed the formation of 1806 C 60 (CF 3 ) 14 with a new non-IPR carbon cage and unusual trifluoromethylation pattern. Thereby, the number of different, structurally confirmed non-IPR carbon cages of C 60 now reaches eight.A conventional Kraẗschemer−Huffman arc-discharge process produces fullerene soot which contains extractable fullerenes obeying the Isolated-Pentagon Rule (IPR). 1 Non-IPR fullerenes do not form because of their lower thermodynamic stability. 2 Therefore, the most abundant fullerene, C 60 , is present in the fullerene soot as the only IPR isomer I h -C 60 (or 1812 C 60 according to the spiral algorithm 1b ), whereas 1811 other topologically possible isomeric C 60 cages contain fused pentagons. 1b Generally, exohedral addition rarely changes the carbon cage connectivity. Consequently, the most investigated derivatives of C 60 possess the same IPR connectivity of the carbon cages. 3 Several derivatives of non-IPR fullerenes, including C 60 , were isolated using two different methods. An arc-discharge fullerene synthesis in the presence of chlorine-containing additives (Cl 2 , CCl 4 ) followed by chromatographic separation of the obtained fullerene mixture resulted in the isolation of two non-IPR chlorofullerenes, 1809 C 60 Cl 8 and 1804 C 60 Cl 12 . 4 The authors believe that the addition of chlorine provides the stabilization of non-IPR C 60 cages which are present in hightemperature plasma.The second method consists of high-temperature (400−440 °C) chlorination of IPR 1812 C 60 with SbCl 5 . 5 Under these conditions, cage transformations occur which proceed via Stone−Wales rearrangements (SWRs), i.e., rotations of one or several C−C bonds by 90°and formation of pentagon− pentagon fusions. 6 It was shown by theoretical calculations that the formation of chlorinated pentagon−pentagon junctions is thermodynamically strongly favorable. 5a,7

Chlorination-Promoted Skeletal Transformations in Isolated-Pentagon Rule (IPR) Isomers of Fullerene C86 to Non-IPR Chloro- and Trifluoromethyl Derivatives

“…The C 86 cage connectivity found in the chlorination products is the same as that in the CF 3 derivatives produced by trifluoromethylation of chlorides. The identity of carbon cages was confirmed in this work for the non-IPR #63614 C 86 cage as well as in several other cases of non-IPR isomers of C 60 , , C 76 , and C 82 …”