Ab initio/IGLO 29Si NMR studies of trisubstituted silicenium and silylated arenium ions. Comparison with experimental data of claimed ions

Abstract

Ab initio/IGLO (individual gauge for localized orbital) 29 Si NMR studies of trisubstituted silicenium and their related arenium ions have been carried out. Comparison of the obtained results with the reported experimental data indicate that to date no free long-lived trisubstituted silicenium cations have been observed in solution. The reported results in π-donor arene solvents clearly indicate the formation of silylated Wheland intermediates (arenium ions), whereas in previously discussed heteroatom n-donor solvents (such as ethers or nitriles) the related silylated onium (such as oxonium or nitrilium) ions are formed. At the same time due to the high electrophilicity of trivalent silicon and its affinity for oxygen, halogen, etc, counter ions, such as perchlorate or fluoroantimonates, are also unsuitable for the observation of long-lived trisubstituted silyl cations.