Quantum chemical studies on substitution effects within silyl group in the silylative coupling of olefins.

In this study quantum chemical calculations based on the density functional theory (DFT) have been carried out to examine the effects of methoxy substituent attached to a silicon atom on the reaction of silylative coupling of olefins. It has been shown, that substituted substrate undergoes the reaction according to the recently proposed insertion-rotation-elimination mechanism. During the rotation around C-C single bond additional stabilization by oxygen-ruthenium interaction was observed. Similarly to the (trimethylsilyl)ethene the rate determining step of the reaction is the insertion of the alkene into Ru-Si single bond. The substitution of SiMe(3) by Si(OMe)(3) decreases the energy span of the reaction by almost 3 kcal mol(-1) that is from 21 kcal mol(-1) to 18 kcal mol(-1). The decrease of the energy barrier of the reaction seems to be the result of the increase of point charge differences between the Ru and Si atoms which increases electrostatic attraction between these atoms. Moreover, for Si(OMe)(3) the rate-determining transition state is closer to the alkene interacting with the Ru centre side of the reaction.