Cage Complexes of Carbenium and Silylium Cations with an Aromatic Base. Is the η<sup>6</sup> Coordination Type Realizable?

The cage cations [E­((CH<sub>2</sub>)<sub>3</sub>)<sub>3</sub>C<sub>6</sub>R<sub>3</sub>]<sup>+</sup> (E = C (<b>1</b>), Si (<b>2</b>); R = H (<b>a</b>), Li (<b>b</b>), F (<b>c</b>)) were studied theoretically using the MP2/6-311++G­(d,p) approach. The migration of the electrophilic center E and a proton around the perimeter of the arene ring in the cations [E­((CH<sub>2</sub>)<sub>3</sub>)<sub>3</sub>C<sub>6</sub>H<sub>3</sub>]<sup>+</sup> was considered. Our results are indicative of the π type of E←arene coordination in the intramolecular complexes [E­((CH<sub>2</sub>)<sub>3</sub>)<sub>3</sub>C<sub>6</sub>R<sub>3</sub>]<sup>+</sup>. The cation [Si­((CH<sub>2</sub>)<sub>3</sub>)<sub>3</sub>C<sub>6</sub>H<sub>3</sub>]<sup>+</sup> (<b>2a</b>), which corresponds to a peak (M – CH<sub>3</sub>)<sup>+</sup> at <i>m</i>/<i>z</i> 229 in the mass spectrum of methylsilacyclophane, exists in a firmly established η<sup>1</sup>π form, as opposed to the case for the known complexes of the trivalent silicon atom with aromatic bases. The species [C­((CH<sub>2</sub>)<sub>3</sub>)<sub>3</sub>C<sub>6</sub>F<sub>3</sub>]<sup>+</sup> (<b>1c</b>), as well as <b>4a</b>, obtained by connecting the equatorial carbon atoms in [Si­((CH<sub>2</sub>)<sub>3</sub>)<sub>3</sub>C<sub>6</sub>H<sub>3</sub>]<sup>+</sup> by a methylene bridge, are the first representatives of stable “face” complexes of carbenium and silylium cations with a benzene ring. The process of deprotonation of the complexes [C­((CH<sub>2</sub>)<sub>3</sub>)<sub>3</sub>C<sub>6</sub>H<sub>3</sub>]<sup>+</sup>, [Si­((CH<sub>2</sub>)<sub>3</sub>)<sub>3</sub>C<sub>6</sub>H<sub>3</sub>]<sup>+</sup>, and <b>4a</b> was found to be energetically unfavorable, even in the presence of a strong base such as NEt<sub>3</sub>. The effect of the counterions BX<sub>4</sub><sup>–</sup> (X = F, C<sub>6</sub>F<sub>5</sub>) and the polarity of solvents on the structure of the above cations was investigated using the examples of toluene and DMSO.