Structural Characterization of Hydro‐, Chloro‐ and Fluoroorganylsilanes with Substituents of Varying Electron Withdrawing Character

Abstract

AbstractWe report on the molecular structure of trimethylsilanes Si(CH3)3X in which the substituents X, namely (Z)‐pentafluoropropen‐1‐yl, trifluoropropyn‐1‐yl, pentafluoroethyl, trifluorovinyl, vinyl, propyn‐1‐yl, di‐ and trichloromethyl, display electron withdrawing effects of varying strength. The lengths of the bonds between the silicon and the carbon atoms of X correlate with the hybridization of the respective orbitals and the steric demand of X rather than with the electron withdrawing capability. In case of chlorinated substituents dispersion effects seem to shorten the Si−C bond. Furthermore, a route for generating trifluoropropyn‐1‐yllithium from the cryogen 2,3,3,3‐tetrafluoropropene (HFO‐1234yf) and n‐butyllithium is described. Tetrafluoropropen‐1‐yllithium is slowly formed at −80 °C but even at this temperature spontaneous elimination of LiF occurs. Deprotonation of the formed 3,3,3‐trifluoropropyne requires temperatures of above −60 °C leading to trifluoropropyn‐1‐yllithium which appears as relatively stable at room temperature.