Investigations on non-classical silylium ions leading to a cyclobutenyl cation

Instead of yielding the desired non-classical silylium ions, the reactions of different alkenes/alkynes with several [Me(3)Si](+) sources mostly led to oligomerization, or – in the presence of Me(3)SiH – hydrosilylation of the alkenes/alkynes. Yet, from the reaction of 2-butyne with ion-like Me(3)Si–F–Al(OR(F))(3) (R(F) = C(CF(3))(3)) the salt of the silylated tetramethyl cyclobutenyl cation [Me(4)C(4)–SiMe(3)](+)[al–f–al](–)1 ([al–f–al](–) = [(R(F)O)(3)Al–F–Al(OR(F))(3)](–)) was obtained in good yield (NMR, scXRD, Raman, and IR). All the experimental and calculated evidence suggest a mechanism in which 1 was formed via a non-classical silylium ion as an intermediate. The removal of the [Me(3)Si](+) moiety from the cation in 1 was investigated as a means to provide free tetramethyl cyclobutadiene (CBD). However, the addition of [NMe(4)]F, in order to release Me(3)SiF and form CBD, led to the unexpected deprotonation of the cation. The addition of 4-dimethylaminopyridine to remove the [Me(3)Si](+) cation as a Lewis acid/base adduct, led to an adduct with the four-membered ring in the direct neighborhood of the Me(3)Si group. By the addition of Et(2)O to a solution of 1, the [F–Al(OR(F))(3)](–) anion (and Et(2)O–Al(OR(F))(3)) was generated from the [al–f–al](–) counterion. Subsequently, the [F–Al(OR(F))(3)](–) anion abstracted the [Me(3)Si](+) moiety from [Me(4)C(4)–SiMe(3)](+), probably releasing CBD. However, due to the immediate reaction of CBD with [Me(4)C(4)–SiMe(3)](+) and subsequent oligomerization, it was not possible to use CBD in follow-up chemistry.