Ionic Lewis Superacids in the Gas Phase. Part 2. Reactions of Gaseous CF3+ with Oxygen Bases

The reactivity of the CF3+ cation toward some oxygen bases, i.e. H2O, CH3OH, CH3CH2OH, and FCH2CH2OH, has been investigated by Fourier-transform ion cyclotron resonance mass spectrometry. The CF3+ ion, while inert toward H2O, displays a high affinity for the n-center of the selected bases, yielding the corresponding excited onium intermediate that undergoes fragmentation by predominant O-alkyl bond cleavage, leading to CF3OH and the alkyl cation. When the alkyl moiety is CH3, a rapid F- transfer from the CF3OH to CH3+ takes place in the fragmentation complex prior to collapse into products. A comparison between the gas-phase reactivity of CF3+ and of the SiF3+ analogue is presented and the factors governing their different behavior toward the selected oxygen bases discussed.