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.

Facile and systematic access to the least-coordinating WCA [(RO)Al-F-Al(OR)] and its more Lewis-basic brother [F-Al(OR)] (R = C(CF)).

By reaction of the Lewis acid MeSi-F-Al(OR) with a series of [PF] salts, gaseous PF and MeSi-F are liberated and salts of the anion [F-Al(OR)] ([f-al]; R = C(CF)) can be obtained. By addition of another equivalent of MeSi-F-Al(OR) to [f-al], gaseous MeSi-F is released and salts of the least coordinating anion [(RO)Al-F-Al(OR)] ([al-f-al]) are formed. Both procedures work for a series of synthetically useful cations including Ag, [NO], [PhC] and in very clean reactions with 5 g batch sizes giving excellent yields typically exceeding 90%.