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

Abstract

Stable polyfluorinated bis- and tris-(alkoxy)methyl cations were prepared by the reaction of the corresponding difluoroformals (R fO) 2CF 2 (R f = –CH 2CF 3, –CH(CF 3) 2, –CH 2CF 2Cl) with an excess of SbF 5. Although the cation (CF 3CH 2O) 2CF + ( 1a) is stable at ambient temperature, the chlorinated analog (ClCF 2CH 2O) 2CF + ( 3a) can be generated only at low temperature in SO 2ClF solvent and rapidly decomposes at ambient temperature. Although the salt [(CF 3) 2CHO] 2CF +Sb n F 5 n+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 [(CF 3) 2CHO] 3C +Sb n F 5 n+1 − ( 2b) and CF 3OCH(CF 3) 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.