Synthesis and Characterization of the First Examples of Perfluoroalkyl Substituted Trialkyl-Oxonium Salts, (CH3)2OCF3(+)Sb2F11(-) and (CH3)2OCF(CF3) 2(+) Sb2F11(-).

摘要

In the superacidic HF/SbF5 system, methyl-trifluoromethylether forms at -78 deg C the new tertiary oxonium salt, (CH3)2OCF3(+)Sb2F11(-), that was characterized by Raman and multinuclear NMR spectroscopy and its crystal structure. The same oxonium salt was also obtained by methylation of CH3OCF3 with CH3F and SbF5 in HF solution at -30 to -10 deg C. Replacement of one methyl group in the trimethyloxonium cation by the bulkier and more electronegative trifluoromethyl group increases the remaining O-CH3 bond lengths by 3.7(1) pm and the sum of the C-O-C bond angles by about 4.5 deg. Methylation of CH3OCF(CF3)2 with CH3F and SbF5 in HF solution at -30 deg C in HF solution produces (CH3)2OCF(CF3)2(+)Sb2F11(-). The observed structures and vibrational and NMR spectra are confirmed by theoretical studies at the B3LYP/6-31 l++G(2d, 2p) and the MP2/6-3l l++G(2d,p) levels.