Investigations on silylium ions leading to a cyclobutenyl cation.

Instead of yielding the desired silylium ions, the reactions of different alkenes/alkynes with several [MeSi] sources mostly led to oligomerization, or - in the presence of MeSiH - hydrosilylation of the alkenes/alkynes. Yet, from the reaction of 2-butyne with MeSi-F-Al(OR) (R = C(CF)) the salt of the silylated tetramethyl cyclobutenyl cation [MeC-SiMe][--] ([--] = [(RO)Al-F-Al(OR)]) was obtained in good yield (NMR, scXRD, Raman, and IR). All the experimental and calculated evidence suggest a mechanism in which was formed a silylium ion as an intermediate. The removal of the [MeSi] moiety from the cation in was investigated as a means to provide free tetramethyl cyclobutadiene (CBD). However, the addition of [NMe]F, in order to release MeSiF and form CBD, led to the unexpected deprotonation of the cation. The addition of 4-dimethylaminopyridine to remove the [MeSi] cation as a Lewis acid/base adduct, led to an adduct with the four-membered ring in the direct neighborhood of the MeSi group. By the addition of EtO to a solution of , the [F-Al(OR)] anion (and EtO-Al(OR)) was generated from the [--] counterion. Subsequently, the [F-Al(OR)] anion abstracted the [MeSi] moiety from [MeC-SiMe], probably releasing CBD. However, due to the immediate reaction of CBD with [MeC-SiMe] and subsequent oligomerization, it was not possible to use CBD in follow-up chemistry.