Study of 1-metalated-2-(trimethylsilyl)vinyl cations: An examination of the β-effect for silyl, germyl and stannyl groups

Abstract

<p>The ability of silicon, germanium and tin elements (group 14) to stabilize a vinyl cation intermediate was investigated upon proton addition to metalated (trimethylsilyl)acetylene compounds to lead, after demetalation, to monometalated acetylenes. The reactions were followed by ¹H NMR spectroscopy. A bimolecular addition mechanism is obtained and nucleophilic participation in the reaction is observed. The reaction rates showed that vinyl cations are stabilized by hyperconjugation of the carbon-metal bond (β-effect) in the order of magnitude Sn (10⁸) > Ge (500) > Si (1). The magnitude of the β-effect on vinyl cation is altered to a degree by the groups born by the metal. The vinyl cations are stabilized, in a lower extent, by inductive effects of the metalated group to the electron-deficient carbon (α-effect).</p>