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)(2)CF2 (R-f = -CH2CF3, -CH(CF3)(2), -CH2CF2Cl) with an excess of SbF5. Although the cation (CF3CH2O)(2)CF+ (1a) is stable at ambient temperature, the chlorinated analog (ClCF2CH2O)(2)CF+ (3a) can be generated only at low temperature in SO2ClF solvent and rapidly decomposes at ambient temperature. Although the salt [(CF3)(2)CHO](2)CF+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)(2)CHO](3)C+SbnF5n+1- (2b) and CF3OCH(CF3)(2) (2c). Stable solid salt 2b (n = 2) 2b (n = 2) was isolated and fully characterized by H-1, F-19 and C-13 NMR spectroscopy and its structure was confirmed by single crystal X-ray diffraction. (C) 2005 Elsevier B.V. All rights reserved.