Class Silylene Structure And Reaction Theory

Silylenoid (R₁R₂SiMX), silicon analogues of carbenoids, can be species with some silylene-like character. A leaving group X (usually halogens) and a metal atom M (usually alkali metals) are bound to the same silicon atom in a silylenoid. Silylenoids have been confirmed to be existent and to be active intermediates in some organosilicon reactions. Both experimental and theoretical results show that silylenoids have ambiphilic character, nucleophilicity and electrophilicity, and can take part in many reactions. Such reactions as insertion, addition, rearrangement, and polymerization were recognized as important and effective methods for preparation of the new silicon-bonded and heterocyclic silicon compounds. Therefore, further thorough investigations on silylenoids will be of important theoretical and practical values.In contrast to extensive experimental and theoretical studies on carbenoids, there are only a few reports on silylenoids, and knowledge of the structures and reactions of silylenoids is still quite limited. This dissertation is mainly composed of the following parts based on the above research background.In introduction (chapter 1), the research history and current state on silylenoid chemistry have been briefly illustrated. The research methods about ab initio and density functional theory have been introduced.In chapter 2, the theoretical investigation on the structures and reactions of silylenoid H₂SiLiF is performed. Silylenoid H₂SiLiF has four isomers, three-membered ring structure (1), p-complex (2), σ-complex (3), and "classical" tetrahedral structure (4). The thermal stability of these isomers is in order of 2 > 1 > 4 >> 3.1) The insertion reactions of 1 and 2 into XH_n (X = C, Si, N, P, O, S, F, Cl; n = 4, 4, 3, 3, 2, 2, 1, 1) molecules have been studied at G3MP2 level. Two reaction paths for 1 and three paths for 2 are obtained. The reaction mechanism is a concerted manner via a three-center type transition state to obtain the substituted silane H₃SiXH_n-1 and LiF. The insertion reactivity of structure 1 is higher than that of 2.2) The H₂ elimination reactions of 1 with XH_n, H₂SiLiF + XH_n → H_nXSiLiF +...