Silylene Insertion Reaction In The Three-dimensional Electronic Effects

This paper selectively takes the insertion reaction between silylene (1-3) (see Sheme 1) and chlorosilanes/silanes with different substituents as model reactions to investigate the reaction mechanism of Si-Cl and Si-H insertion reaction by ab intio quantum chemistry methods. The difference of these two types of reactions, the mainly factors that affect the speed of reaction and selectivity, which aims at revealing the reaction mechanisms of the insertion reaction between silylene and different silanes. At the same time,the reactivity of Si-X(X=F, Cl, Br) insertion of silylene has also been discussed systematically. Experiment was taken using silylene 4 reaction with chlorosilane to validate the theoretical results.The main methods used in this paper are DFT theories(B3LYP) of quantum chemistry implemented in the Gaussian 98/03 package, which have respectively been employed to locate all the stationary points along the reaction pathways at the level of 6-31++G(d;p).By studying on the mechanisms of Si-Cl insertion reactions between dimethylsilylene and monochorosilane, we know that the finely products gained in a concerted mechanism via a three-membered ring transition states. Especially deserveing our attention is that there are distinct relationship between reactivity of insertion reaction and sterelectronic effect of silane. Two types of substiuents in silane, which bearing different geometry characteristic in TSs were found to play different role in affecting the activation energy. On one hand, the substituent, which is in the same plane with the three-membered-ring of TSs was found to have profound effect to the nucleophilic interaction of silylene to silane and electronegative substituent could strongly accelerate the reaction, contrarily, the electron donating would reduce the reactivity of insertion reaction. On the other hand, substituent, which is in the out of plane position, mainly affect the reaction reactivity from the steric effect and remarkable substituent could also reduce the reactivity for both insertion reactions and the influence to Si-Cl is larger than Si-H insertion. Compare the electronic and steric effect to the reactivity, the electronic effect is more distinctly than steric effect.Then we study the effect of substituents of silylene to insertion reaction. By studying on the mechanism of Si-Cl and Si-H insertion reaction between silylene with different steric effect (silylene 1-3) and H3SiCl or H3SiH, the steric effect on silylene also would reduce the kinetics of Si-Cl and Si-H insertion reaction, what is different is, the steric of silylene have comparable effect for both types of insertion, however, the steric of silane have different effect for both, the influence to Si-Cl is larger than Si-H insertion. On the other hand, the electronic effect of silylene to insertion reaction are different with silanes', which the electronic-withdrawing substituent would lowed the reacvity of insertion.Then the Si-X(X=F, Cl, Br) insertion of silylene have been studied systematically and found Si-Br insertion is much favorable than others. If one silane including Si-F, Si-Br and Si-Cl bonds, it would first take Si-Br insertion reaction.At last, the experimental reactions of 2,2,5,5-tetrakis(trimethylsilyl)silacyclopentane-1,1-diyl with different chlorosilanes have been done to validate the theoretical prediction.The research results have not only provided theoretical chemists with theoretical evidence to further study this topic, but also experimental chemists with systemic theoretical evidence to efficiently develop and exploit the insertion reactions of silylene to synthesis of new organosilicon frameworks which have important applied values in the field of material and medicine synthesis science.