The Preparation and Characterization of Radical Cation Salts Derived from Perfluorobenzene, Perfluorotoluene, and Perfluoronaphthalene

Article abstract of DOI:10.1021/ja00276a039

The salts C6F6⁺AsF6^- (yellow), C6F5CF3^- (lime green), and C10F8⁺AsF6^- (dark green) may be prepared by electron oxidation of the appropriate perfluoro aromatic molecule with O2⁺AsF6^-.Other O2⁺ salts can be similarly employed as can the more strongly oxidizing transition-metal hexafluorides, but salts of the latter are more labile than their AsF^- relatives.C6F6⁺AsF6^- is a convenient electron oxidizer (C6F6AsF6+C10F8 -> C10F8AsF6+C6F6) since that which remains from the reaction decomposes at room temperature to volatile products (2C6F6AsF6 -> C6F6+1,4-C6F8+2AsF5).Magnetic susceptibilities for C6F6AsF6 and C10F8AsF6 approximate to Curie law behavior, and g values are close to free-electron values.X-ray diffraction data (single crystal) show C6F6AsF6 to be primitive rhombohedral with a₀=6.60 (1) Angstroem, α=106.0 (1) deg, V=246.1 Angstreom³, Z=1, probable space group R3, and (powder data) C10F8AsF6 to be tetragonal with a₀=8.27 (5) Angstroem, c₀=18.57 (s) Angstroem, V=1270 Angstoem³, Z=4.Salts derived from the monocyclic perfluoro aromatics are thermally unstable but can be kept below -15 deg C.The perfluoronapthalene salts are indefinitely stable at room temperatures.All hydrolyze rapidly.The products of thermal decomposition of the hexafluoroarsenates of the monocyclic cation salts parallel the products of the attack by F^-.The latter reaction products are in the molar ratios indicated by the following equations: 2C6F6⁺ 2F^- -> C6F6+ 1,4-C6F8; 2C6F5CF3⁺ ->2F^- -> C6F5CF3+1,3-C6F7CF3.The 1,3-C6F7CF3 isomerizes to a 1:1 mixture with 1,4-C6F7CF3 over several days in the presence of fluoro acids.Mechanisms for the formation of the dienes are discussed.