Mechanism Study Of Transition Metal Catalyzed Chiral Silance Construction

Owing to the potential use of the silicon-stereogenic organosilane in the aspect of chiral auxiliary agent, reagent, resolving agent and the candidate drugs, the high efficiency and high selectivity synthesis of chiral silane gradually began to arouse attention from researchers in recent years. Compared with the well-investigated enantioselective preparation of carbon-stereogenic compounds, the corresponding preparation of silicon-stereogenic compounds is much less established. Undoubtedly, the exploration of new synthesis method with high enantioselectivity remains a challenging task.The asymmetric catalysis of prochiral silane under transition metal-catalyzed is an effective strategy to prepare the silicon-stereogenic organosilane. Despite we have been successfully synthesized various silicon-stereogenic organosilane by this strategy, there are still many drawbacks such as poor applicability of substrate, low chemoselectivity and enantioselectivity and so on. Since the reaction under transition metal-catalyzed involves a lot of unstable intermediates which are hardly detected by experimental means, the mechanism for this reaction is still not clear, which severely restricted the construction and subsequent optimization of new catalytic systems. In recent years, together with the development of quantum chemistry theory, software and computer hardware, quantum chemistry theoretical calculations have become an important research tools to research the mechanism of complex reactions.In this paper, we use the quantum chemistry theoretical calculation as the main research method, and study the reaction mechanism of two types of asymmetric catalysis of prochiral silane under transition metal-catalyzed in details:(1) palladium-catalyzed desymmetrization of silacyclobutanes with alkynes; (2) palladium-catalyzed asymmetric arylation of prochiral dihydrosilane with aryl iodides. The study shows that in the system of desymmetrization of silacyclobutanes with alkynes under Pd0-phosphoramidite composite catalyzed, the whole catalytic cycle was initiated by a π-complex formed with the alkyne, subsequently the oxidative addition of silacyclobutane Si-C bond to the composite formed PdⅣ intermediate, which further inserted to Si-Pd bond formed another PdⅡ intermediate. The following reductive elimination lead to the entire catalytic path. For the asymmetric arylation of prochiral dihydrosilane with aryl iodides under Pd0-phosphoramidite composite catalyzed, the reaction may start with the insertion of complex to C-I bond giving PdⅣ intermediates which is followed by subsequent transmetalation with dihydrosilane Si-H bond through two different ways, and obtained the product of silicon-carbon coupling or reduction. This is an important amendment for the originally recognized mechanism. In addition, we also explored the impact of the reaction paths, the rate-determining step and enantioselectivity-determining step in the aspect of coordination mode of palladium catalyst, the impact of electronic effect and steric effect of ligands.