【作者】 徐开来；

【导师】 谢代前；

【作者基本信息】 四川大学 ， 物理化学， 2004， 博士

【摘要】 目前,利用量子化学从头算来研究化学反应,确定化学反应的机理是理论和计算化学的一个重要课题。用量子化学计算方法来研究金属有机反应,将在分子水平上对反应机理有更深刻的理解,为进一步合理地设计合成路线和找寻高性能新催化剂以获取高产率高选择性的化合物提供理论依据。本文采用密度泛函B3LYP方法,对SnCl4作用下烯丙基锡与醛的反应以及GaCl3催化1,6-烯炔成环反应进行了系统的理论研究,优化得到了反应中各反应物、中间体、过渡态和产物的结构和能量,解析了反应路径,探索了反应机理并成功地解释了实验观测到的选择性。在对SnCl4作用下烯丙基锡与醛反应的系列研究中,首先对SnCl4作用下的2-三甲基锡烷基-1,3-丁二烯的金属转移进行了理论研究。研究表明, 反应物2-三甲基锡烷基-1,3-丁二烯在SnCl4作用下通过金属转移首先生成1-三氯锡烷基-2,3-丁二烯,然后再次通过金属转移异构化为2-三氯锡烷基-1,3-丁二烯。第一步金属转移的活化能垒最低,为78.1 kJ.mol-1。我们还考虑了产物与反应物的相互作用,并研究了随后的异构化过程,结果表明SnCl4催化下的1-三氯锡烷基-2,3-丁二烯异构化反应的活化能垒为108.2kJ.mol-1,是所计算的五个异构化反应中最易进行的。随后研究了金属转移的产物1-三氯锡烷基-2,3-丁二烯和2-三氯锡烷基-1,3-丁二烯与甲醛的反应,并用SCRF(PCM)方法在同一水平上对CH2Cl2溶液中的两反应进行了比较研究,计算了两反应在气相和CH2Cl2溶液中的活化能垒、自由能和平衡常数。结果表明, 两反应均有椅式六元环状构型的过渡态,活化能垒也都较低,但两者(G0值相差较大,由(G0<WP=6>计算得到的平衡常数分析表明反应具有很强的选择性,将主要得到1-三氯锡烷基-2,3-丁二烯与甲醛反应的产物,结果和实验事实(Hatakeyama, S. etal. Synlett,1999, 1109)完全吻合。为了在更接近实验条件的情况下进一步探讨反应机理,在上述结果的基础上,我们考虑DMF的配位作用研究了SnCl4作用下1-三氯锡烷基-2,3-丁二烯与甲醛的反应,得到两条反应路径。研究表明,反应仍具有很强的选择性,主要得到DMF作用下1-三氯锡烷基-2,3-丁二烯与甲醛直接反应的产物;DMF的加入降低了活化能垒,促进了反应的进行,并使两反应途径活化能垒相差达60.7 kJ.mol-1,从而增强了反应的选择性。此外, 我们在B3LYP/6-31G*水平上研究了顺-8-三甲基锡烷基-6-辛烯醛分子内环化反应,解析了三条反应途径。结果表明反应具有很强的立体选择性,虽然-OSn(CH3)3和-C2H3基团均处于环的平伏位是最稳定的产物构型,但是主要产物是经过活化能最低,且具有两个椅式六元环的过渡态形成的,该产物中-OSn(CH3)3基团处于环的直立位。与实验一致的立体选择性进一步证实了用六元环状过渡态解析烯丙基锡与醛反应机理的合理性。金属催化的1,n-烯炔成环反应是一个复杂的过程,反应机理目前仍不很清楚。Chatani等人(J. Am. Chem. Soc. 2002, 12, 10294)从实验上研究了GaCl3催化下1,6-烯炔骨架重组生成1-乙烯基环戊烯的反应,猜测产物是通过四元环状的中间体经开环反应而得。我们在B3LYP/6-31G*水平上对该反应的研究却有不同的发现。共找到六条反应途径,计算表明最易发生的不是形成四元环状中间体的反应途径,而是形成含有三中心两电子键的三元环状区域的反应途径。该反应分多步进行,每步的活化能垒都较低,速率控制步骤的活化能垒仅有29.7 kJ(mol-1。反应具有明显的立体选择性,顺式构型的1,6-烯炔将主要生成顺式构型的1-乙烯基环戊烯,结果和实验事实完全吻合。更多还原

【Abstract】 It is of great interest in computational and theoretical chemistry to investigate the chemical reactions and determine the reaction mechanism by using ab initio quantum chemistry calculations recently. Such studies are very useful in understanding mechanism at the molecular level, designing the special synthetic routes, and inventing new higher functional catalysts. In this dissertation, we have investigated the mechanism of reaction of allylic tin with formaldehyde promoted by SnCl4 and cyclization of 1,6-enyne catalyzed by GaCl3 by using B3LYP hybrid density functional method. Electronic structure calculations were performed to identify the stationary structures and energies on the potential energy surfaces. The reaction pathways were characterized and used to explain the selectivity observed by experiments successfully. In the series studies on reaction of allylic tin with formaldehyde promoted by SnCl4, we studied transmetalation of 2-trimethylstannylbuta-1,3-diene with SnCl4 at the B3LYP/6-31G** level at first. Our calculations showed that the reaction between the reactant and SnCl4, which generates 1-trichlorostannylbuta-2,3-diene via transmetalation, has the lowest energy barrier of 78.1kJ.mol-1. The interaction between reactants and product was also involved to study the following isomerization process. It turned out that the isomerization process from 1-trichlorostannylbuta-2,3-diene to 2-trichloro- stannylbuta-1,3-diene via transmetalation with SnCl4 is more energetically <WP=8>favorable than other possible isomerization processes.We have also performed theoretical calculation for two reactions of 1-trichlorostannylbuta-2,3-diene and 2-trichlorostannylbuta-1,3-diene with formaldehyde. The structures and energies of the stationary points were calculated to produce the activation barriers, free energy changes and equilibrium constants. Both reactions in CH2Cl2 solvent at 1atm, 298.2K have also been studied by the SCRF(PCM) method. The results showed that both reactions have a six-membered chair like cyclic transition state and low energy barrier, whereas the free energies are significantly different. It is showed from the calculated the equilibrium constants that the global reaction takes place with high regioselectivity and mainly produce the product of the reaction of the 1-trichlorostannylbuta-2,3-diene with formaldehyde, which is in good agreement with the recent experimental results (Hatakeyama, S. et al. Synlett,1999, 1109).In order to access more closely the experimental conditions, we have studied the mechanism of the reaction of 1-trichlorostannylbuta-2,3-diene with formaldehyde involved both SnCl4 and DMF. Two reaction pathways were obtained and discussed. Our results showed that the global reaction take place with high regioselectivity and mainly produce the product of the reaction of the 1-trichlorostannylbuta-2,3-diene with formaldehyde involved DMF. DMF also reduces the energy barrier and promotes the reaction. Since the difference between energy barriers of two reaction pathways is up to 60.7kJ.mol-1, the regioselectivity of reaction becomes higher when DMF is involved.In addition, we have carried out ab inito calculations for the cyclization of (Z)-8-(trimethylstannyl)oct-6-enal. Three reaction pathways were indentified. Our results showed that the reaction takes place with high stereoselectivity. Among the three reactions, the product in which both -OSn(CH3)3 and –C2H3 moieties are in the equatorial position is the most stable one. However, the mainly product is obtained through the double-six-membered chair like cyclic <WP=9>transition state with the lowest barrier height, in which -OSn(CH3)3 moiety is in the axial position. Stereoselectivity agrees well with experiment, which demonstrates the rationality of the mechanism including the six-membered cyclic transition state. On the other hand, the mechanism of cyclization of 1,n-enynes catalyzed by metals is not very clear till now. Chatani and co-workers(J. Am. Chem. Soc. 2002, 12, 10294)studied the skeletal reorganization更多还原