银催化端炔类反应机理的研究
发布时间：2019-06-30 21:40
【摘要】：银盐具有催化活性高、路易斯酸特性和价格低廉等优点,且可以有效地避免其他过渡金属催化端炔易于偶联的弊端。因此,银催化端炔类反应成为近年来有机合成的热点研究领域。理论与计算化学在阐明反应、特别是有机反应机理方面发挥着巨大的作用,已成为探究反应历程不可或缺的重要手段。本论文中,我们主要采用密度泛函方法探讨催化剂及实验反应条件(如底物、配体、溶剂及痕量水等)对机理的影响,从而揭示一价银盐独特的催化作用及其高的催化活性本质。主要研究内容如下：1.将密度泛函理论(DFT)与实验结合阐明了异腈-炔环加成的反应机理,详细探究了反应条件对机理的影响。发现该反应是一个新颖的多组分(Ag_2CO_3,溶剂和底物)催化的自由基机理,主要包含异腈自由基的形成,异腈自由基与炔银的环加成,含银五元环的质子化和氢迁移四个过程。第二过程中C2-C4键的形成是反应的决速步,所需活化自由能能垒(△△G(?))为10.2kcal/mol。催化剂Ag_2CO_3在异腈自由基的形成过程中具有双重作用：作拔取异腈Cα原子上质子的碱和形成异腈自由基的引发剂。异腈和溶剂1,4-二氧六烷作质子给体实现含银五元环质子化的同时获得相应的自由基物种,1,4-二氧六烷可以作自由基传递体引发异腈自由基的形成。此外,1,4-二氧六烷作助剂和质子给体/受体,有效地降低氢迁移过程活化能垒而明显增加反应活性。该发现为过渡金属银盐催化含异腈或炔类反应提供新的机理的见解,为银盐催化反应条件的优化提供新思路。2.采用DFT方法探究了利用水和碳酸银共催化端炔的氢叠氮化合成烯基叠氮的详细反应机理。研究发现该反应主要经历Ag_2CO_3与底物TMS-N_3配位促进水与TMS-N_3反应生成HN_3、水协助Ag_2CO_3对端炔去质子化形成炔银、HN_3与炔银的选择性加成和AgHCO_3对端碳原子质子化四个过程形成烯基叠氮产物。第三步中C-N键的形成是该反应的决速步。反应中水作HN_3的氢源和质子传递体。计算结果表明Ag_2CO_3对底物的调控模式包括Ag_2CO_3-配位、Ag_2CO_3-成键及两者的互相转化。该反应的区域选择性遵循马氏规则,很好地解释了实验观测。我们的计算为银-催化端炔的氢叠氮化反应提供合适的机理,为实验研究者提供理论基础。
[Abstract]:Silver salt has the advantages of high catalytic activity, Lewis acid characteristics and low price, and can effectively avoid the disadvantages that other transition metal catalytic terminal alkynes are easy to be coupled. Therefore, silver catalyzed alkynes have become a hot research field in organic synthesis in recent years. Theoretical and computational chemistry plays an important role in illustrating the reaction, especially the mechanism of organic reaction, and has become an indispensable means to explore the reaction process. In this thesis, we mainly use density functional method to investigate the effects of catalysts and experimental reaction conditions (such as substrate, ligands, solvents and trace water, etc.) on the mechanism, so as to reveal the unique catalytic effect of monovalent silver salt and its high catalytic activity. The main research contents are as follows: 1. The density functional theory (DFT) was combined with experiments to clarify the reaction mechanism of isonitrile-alkynes cycloaddition, and the effect of reaction conditions on the mechanism was investigated in detail. It is found that the reaction is a novel free radical mechanism catalyzed by multicomponent (Ag_2CO_3, solvent and substrate), which mainly includes four processes: the formation of isonitrile radical, the cycloaddition of isonitrile radical and silver alkyne, the protonation and hydrogen migration of five-component ring containing silver. In the second process, the formation of C2-C4 bond is the decisive step of the reaction, and the required activation free energy barrier (G (?) It is 10.2 kcal mol. The catalyst Ag_2CO_3 plays a dual role in the formation of isonitrile radical: it is used as an initiator for the extraction of protons on isonitrile C 伪 atom and the formation of isonitrile radical. Isonitrile and solvent 1,4-dioxane were used as proton donors to realize silver pentagonal cycloprotonization at the same time, and the corresponding free radical species were obtained. 1, 4-dioxane can be used as free radical transporter to initiate the formation of isonitrile radical. In addition, 1, 4-dioxane as promoter and proton donor / receptor can effectively reduce the activation energy barrier during hydrogen migration and increase the reaction activity. This finding provides a new idea for the catalytic reaction of isonitrile or alkynes catalyzed by transition metal silver salt, and provides a new idea for the optimization of catalytic reaction conditions of silver salt. 2. The mechanism of hydroazide synthesis of alkenyl azide catalyzed by water and silver carbonate was investigated by DFT. It was found that the reaction was mainly through the coordination of Ag_2CO_3 with substrate TMS-N_3 to promote the reaction of water with TMS-N_3 to form HN_3, water to assist Ag_2CO_3 in the protonation of terminal alkynes to form silver alkynes. The selective addition of HN_3 with acetylene silver and the protonation of AgHCO_3 to terminal carbon atoms formed alkenyl azide products. In the third step, the formation of C 鈮，
本文编号：2508278
[Abstract]:Silver salt has the advantages of high catalytic activity, Lewis acid characteristics and low price, and can effectively avoid the disadvantages that other transition metal catalytic terminal alkynes are easy to be coupled. Therefore, silver catalyzed alkynes have become a hot research field in organic synthesis in recent years. Theoretical and computational chemistry plays an important role in illustrating the reaction, especially the mechanism of organic reaction, and has become an indispensable means to explore the reaction process. In this thesis, we mainly use density functional method to investigate the effects of catalysts and experimental reaction conditions (such as substrate, ligands, solvents and trace water, etc.) on the mechanism, so as to reveal the unique catalytic effect of monovalent silver salt and its high catalytic activity. The main research contents are as follows: 1. The density functional theory (DFT) was combined with experiments to clarify the reaction mechanism of isonitrile-alkynes cycloaddition, and the effect of reaction conditions on the mechanism was investigated in detail. It is found that the reaction is a novel free radical mechanism catalyzed by multicomponent (Ag_2CO_3, solvent and substrate), which mainly includes four processes: the formation of isonitrile radical, the cycloaddition of isonitrile radical and silver alkyne, the protonation and hydrogen migration of five-component ring containing silver. In the second process, the formation of C2-C4 bond is the decisive step of the reaction, and the required activation free energy barrier (G (?) It is 10.2 kcal mol. The catalyst Ag_2CO_3 plays a dual role in the formation of isonitrile radical: it is used as an initiator for the extraction of protons on isonitrile C 伪 atom and the formation of isonitrile radical. Isonitrile and solvent 1,4-dioxane were used as proton donors to realize silver pentagonal cycloprotonization at the same time, and the corresponding free radical species were obtained. 1, 4-dioxane can be used as free radical transporter to initiate the formation of isonitrile radical. In addition, 1, 4-dioxane as promoter and proton donor / receptor can effectively reduce the activation energy barrier during hydrogen migration and increase the reaction activity. This finding provides a new idea for the catalytic reaction of isonitrile or alkynes catalyzed by transition metal silver salt, and provides a new idea for the optimization of catalytic reaction conditions of silver salt. 2. The mechanism of hydroazide synthesis of alkenyl azide catalyzed by water and silver carbonate was investigated by DFT. It was found that the reaction was mainly through the coordination of Ag_2CO_3 with substrate TMS-N_3 to promote the reaction of water with TMS-N_3 to form HN_3, water to assist Ag_2CO_3 in the protonation of terminal alkynes to form silver alkynes. The selective addition of HN_3 with acetylene silver and the protonation of AgHCO_3 to terminal carbon atoms formed alkenyl azide products. In the third step, the formation of C 鈮，
本文编号：2508278
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