Protonation of nitriles: isolation and characterization of alkyl- and arylnitrilium ions

The reactions of acetonitrile, propionitrile, butyronitrile, N,N-dimethylaminoacetonitrile, benzonitrile, o-tolunitrile and 1,4-dicyanobenzene with HF/AsF5 or HF/SbF5 in anhydrous HF result in protonation of the nitrile. The obtained nitrilium ions were isolated as [AsF6](-), [SbF6](-) and [Sb2F11](-) salts and characterized by multinuclear NMR and vibrational spectroscopy, and their X-ray crystal structures.