Silaimidazolium and silaimidazolidinium ions

Abstract

2-Silaimidazolium ions 7 and 2-silaimidazolidinium ions 8 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(C₆F₅)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 7 only a modest degree of aromaticity. Despite the bulkiness of the used substituents R¹ and R², silylium ions 7 and 8 behave as classical Lewis pairs and show no unexpected reactivity.