Silaimidazolium and silaimidazolidinium ions.

2-Silaimidazolium ions and 2-silaimidazolidinium ions were synthesized by Lewis acid-base adduct formation between N-heterocyclic silylenes and silyl arenium ions. They were isolated in high yields as their B(C(6)F(5))(4) salts. These salts are stable at room temperature and were characterized by NMR spectroscopy supported by the results of density functional computations of molecular structures and NMR chemical shifts. NICS calculations suggest for the imidazolium ions only a modest degree of aromaticity. Despite the bulkiness of the used substituents R(1) and R(2), silylium ions and behave as classical Lewis pairs and show no unexpected reactivity.