Ionic Lewis Superacids in the Gas Phase. Part 3. Reactions of Gaseous CF3+ with Nitrogen Bases

The results of a Fourier-transform ion cyclotron resonance mass spectrometric study of the gas-phase reactions of CF3+ ions toward a number of amines are reported and compared with those of the preceding paper. As with alcohols, the CF3+ ion exclusively attacks the n-center of the amine giving the corresponding excited onium intermediate that, at variance with that from alcohols, undergoes fragmentation via preferential HF elimination. This process is overwhelmed by simple electron transfer within the collision complex, when thermochemically allowed. With azetidine, pyrrolidine, and piperidine, a cycloreversion reaction in the corresponding adducts with CF3+ is observed as well. The reactivity pattern of CF3+ towards amines has been contrasted with that of SiF3+. The different behavior of the two electrophiles toward n-bases is ascribed to the much larger heterolytic bond dissociation energies of Si-X (X = F, O, or N) compared to those of C-X. According to its reactivity properties, the CF3+ ion can be ranked as a gaseous ''Lewis superacid'' but much weaker than SiF3+.