γ-Silyl-stabilized tertiary ions? Solvolysis of 4-(trimethylsilyl)-2-chloro-2-methylbutane

Article abstract of DOI:10.1002/(SICI)1099-1395(199907)12:7<564::AID-POC164>3.0.CO;2-2

Rate constant, isotope-effect, and product studies of the solvolysis of 4-(trimethylsilyl)-2-chloro-2-methylbutane, 11, and its carbon analog, 2-chloro-2,5,5-trimethylhexane, 10, in aqueous ethanol and aqueous 2,2,2-trifluoroethanol (TFE) indicate very little participation of the γ-silyl substituent. These results are in sharp contrast to earlier reports on secondary γ-silyl substituted systems, in which the back lobe of the silicon-carbon bond has been shown to overlap with the carbocation p-orbital to form a so-called 'percaudally' stabilized intermediate. While the solvolytic behaviors of 11 and 10 are nearly identical in ethanol, differences in the TFE lead to the conclusion that there is a minor amount of participation by the silyl substituent in that solvent. Interestingly, this observation lends credence to an earlier suggestion that TFE is better than ethanol at stabilizing more highly delocalized ions. Copyright