First examples of stable polyfluorinated bis- and tris-(alkoxy)methyl cations

Stable polyfluorinated bis- and tris-(alkoxy)methyl cations were prepared by the reaction of the corresponding difluoroformals (RfO)2CF2 (Rf = –CH2CF3, –CH(CF3)2, –CH2CF2Cl) with an excess of SbF5. Although the cation (CF3CH2O)2CF+ (1a) is stable at ambient temperature, the chlorinated analog (ClCF2CH2O)2CF+ (3a) can be generated only at low temperature in SO2ClF solvent and rapidly decomposes at ambient temperature. Although the salt [(CF3)2CHO]2CF+SbnF5n+1− (2a) is slightly more stable than the salt of cation 3a, at ambient temperature it undergoes rapid disproportionation with formation of equal amounts of [(CF3)2CHO]3C+SbnF5n+1− (2b) and CF3OCH(CF3)2 (2c). Stable solid salt 2b (n = 2) was isolated and fully characterized by 1H, 19F and 13C NMR spectroscopy and its structure was confirmed by single crystal X-ray diffraction.