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Four-membered ring transition metal silicon ring-opening reaction mechanism studies

Author: ZhaoYanYun
Tutor: BiSiZuo
School: Qufu Normal University
Course: Inorganic Chemistry
Keywords: Four-membered ring Nucleophilic reaction Reaction Mechanism Transition metal Silylene DFT
CLC: O621.25
Type: Master's thesis
Year: 2008
Downloads: 64
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Abstract


In the past few decades, a lot of attention is focused on a M = Si bond silicon metal ene compounds chemically. Alkenyl silicon-metal compound may be an organic silicon compound in a series of conversion reactions, such as hydrogen from the dehydrogenation reaction of the silicon, the silicon atom-substituted rearrangement reaction, silylene other unsaturated organic compounds into the reaction. Silylene compound as the conversion reaction can provide various different information, so that the transition metal compound is prepared silylene synthesis is an important goal. In organometallic compounds Silylene containing silane compound Silylene particularly important. Because these compounds may occur intramolecular 1,3 - group migration, which is considered an organic silicon compound metal-catalyzed rearrangement of substituents key step. Ogino have successfully synthesized a series of intramolecular bridging alkenyl silane silicon transition metal compounds, such as intramolecular four yuan, five yuan, six-membered ring silylene compounds. Tension due to its molecular structure, the special bonding patterns, and reactions of the novelty is attracting people's attention. Although it is based on transition metals or transition metal Silylene silane compounds of theoretical research done a lot of work, but for the intramolecular bridging alkenyl silane silicon theoretical study of transition metal compounds is indeed very small. Since M-Si bond polarity, so that Si atoms easily with a nucleophilic reagent H 2 O, MeOH, HX and other nucleophilic reactions. This is typical of the reaction of such compounds. Therefore, the silicon-containing alkenyl cyclic compounds of transition metal four yuan theoretical study will be a very valuable and instructive subject. In this paper, experiments, based on the study by theoretical calculation of the transition metal compound silylenoids nucleophilic reaction mechanism. We use the density functional theory B3LYP, 6-31G basis set at the level of representation of the corresponding model reaction reaction mechanism, bond lengths, bond angles, etc. are analyzed theoretically. From the structural parameters, kinetics, thermodynamics and other aspects of bond breaking causes. The paper was supported by Shandong Province Natural Science Fund. 1. Density functional theory (DFT), by studying CpRu (CO) (SiMe 2 ) 2 O (Cp = cyclopentadienyl anion) Model Reaction with methanol discussed CpRu (CO) (SiMe 2 ) 2 O and ROH (R = phenyl, alkyl) reaction mechanism of the reaction involved in the analysis of the relevant Compounds of structure and bonding characteristics. Ogino first proposed CpRu (CO) (SiMe 2 ) 2 O and ROH ROH from the side of the mechanism is offensive Ru = Si bond, leaving the four-membered ring-opening RuSiSiO cyclization reaction. We discovered through theoretical calculations attack from the side ROH Ru = Si bond, the President into a stable intermediate, and then after activation energy of the transition state 24.2kcal/mol generate ortho product. The stability of this product is lower than the intermediate. Whether this mechanism is kinetically or thermodynamically unfavorable. We proposed an alternative reaction mechanism that ROH four-membered ring in the middle attack Si-O bond of the reaction mechanism, the first ROH RuSiSiO H atom and an O atom four-membered ring is formed with an intermediate hydrogen, with the ROH O atom attack Si atoms, four-membered ring opening reaction occurs through the activation energy is 23.5 kcal / mol of the transition state, and it generates a bit more than the product of reactants stable 17.4 kcal / mol. ROH attack from the intermediate four-membered rings of Si-O bond in either the reaction mechanism or kinetics are thermodynamically favorable. 2. Through the transition metal catalyzed CC bond activation reactions in organic chemistry active and challenging field. C (R)-CN bond activation reaction of great interest for researchers as alkyl and aryl groups containing double metal cyanide can generate many important intermediate metal-catalyzed reactions. Although the use of a transition metal activated unsaturated nitrile CC bond is often difficult, but some transition metals such as nickel, lead, platinum, molybdenum, rhenium, iridium and iron, an unsaturated nitrile catalyzed CC bond breaking experiments have been reported. In particular, recent reports indicate that some of the organometallic compounds on silicon nitrile CC bond cleavage plays a key role. We studied theoretically Cp * Fe (CO) (= SiMes 2 ) SiMe 3 (1) and the possible reaction mechanism of the reaction of acetonitrile and find out what kind of reaction mechanism in the kinetics and thermodynamics is more reasonable. The reaction mechanism We found there are two possible paths. Path Ⅰ, CN bond occurs first insertion reaction of Fe-Si bond, and then happen oxidative addition reaction of CC bonds. This path is the rate-determining step of the activation energy is required for maximum 17.2 kcal / mol, the product ratio of reactants to stabilize 29.6kcal/mol, explain whether this path is thermodynamically or kinetically is beneficial. And the path of the CC bond Ⅱ addition to the direct oxidation of the transition metal center and complete the required activation energy of 50.7 kcal / mol, which is kinetically unfavorable. This also shows that Si group CC bond activation of such a reaction plays a key role. We compared the calculated and Ru and acetonitrile silylene reaction of the silane compound, is first found reasonable path through CN Ru-Si bond into the reaction, and then CC bond rupture occurs. This reaction is the rate-determining step of the activation energy of 22.0 kcal / mol, than the metal of Fe Silylene silane compound with high activation energy of the reaction of acetonitrile. Silicon metal allyl silane compound Fe acetonitrile CC bond activation on the catalytic effect of slightly better.

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CLC: > Mathematical sciences and chemical > Chemistry > Organic Chemistry > Organic Chemistry general issues > Properties of organic compounds > Chemical properties of organic reactions
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