Chloro- and Trifluoromethyl Derivatives of a Pentagon-Fused C: CCl, CCl, and C(CF).

The carbon cage of -C, obeying the isolated-pentagon rule (IPR), can be transformed to the non-IPR -C cage via two successive Stone-Wales rearrangements in the course of high-temperature chlorination of C with SbCl. Two chloro derivatives, -CCl and -CCl, have been isolated by high-performance liquid chromatography (HPLC). High-temperature trifluoromethylation of the chlorination products with CFI, followed by HPLC separation, afforded a non-IPR CF derivative, -C(CF). Structural elucidation of the isolated compounds revealed that all eight sites of pentagon-pentagon fusions on the carbon cage are preferentially occupied by Cl atoms or CF groups. According to density functional theory calculations, chloro and CF derivatives of C are more stable than the isomeric derivatives of C or IPR C, possessing respectively four or no sites of pentagon fusion in their carbon cages.