【作者】 张松林；

【导师】 郭庆祥；

【作者基本信息】 中国科学技术大学 ， 有机化学， 2010， 博士

【摘要】 本论文主要工作是量子化学计算方法在过渡金属催化的偶合反应的机理研究中的应用,主要内容如下：第一章介绍了过渡金属催化的偶合反应和基本的金属有机基元步骤。第二章简单介绍了量子计算方法的种类和原理。第三到第七章是我攻读博士学位期间完成的主要工作,其中：第三章报导铜催化的酰胺和卤代芳烃的偶合机理以及配体对催化效率的影响。通过对体系内各种可能的铜物种的相对浓度的估算和对各个铜物种和卤代苯发生氧化加成的研究,我们的结果表明该反应的活性催化剂是中性的L2Cu(amidate),由它出发和卤代芳烃发生决速的氧化加成反应。对该决速步的配体效应的研究结果也和实验观察一致。第四章报导钯催化的脱羧Heck反应的机理,以及各个因素对脱羧步的影响。我们的研究结果表明这一反应的催化循环应该是经历了四个阶段：脱羧、烯烃插入、p-H消除和催化剂再生。脱羧是整个催化循环的决速步,在这一步里羧酸底物上的羧基以CO2形式放出,得到Pd(Ⅱ)-Aryl中间体。Dissociative路径是更加有利的,即脱羧前先离解一分子的DMSO配体。在此基础上,我们研究了一系列影响决速步脱羧能垒的因素,包括负离子效应,中性配体效应,羧酸底物效应和金属中心效应,所有的结果均和实验事实吻合。第五章报导一个新颖的铜催化的、在邻位导向基团存在下,生成meta C-H活化产物的反应机理。通过对几种可能的机理的研究,我们提出了一个不同于原文中建议的,热力学和动力学上更为有利的机理：酰胺基团导向的carbocupration机理。在此机理路径的基础上,预测的产物区域选择性的结果和实验完全一致。更为重要的是,我们提出的反应路径中包含了一个导向基团导向的Cu(Ⅲ)-Ar中间体对双键的顺式加成,这样的反应性还未有报道,它提供了一个研究Cu(Ⅲ)-Ar中间体新的基本反应的可能性,以及它们在催化反应中的应用前景。第六章报导有机铜试剂和烯丙基亲电试剂发生烯丙位取代反应的立体和区域选择性机理。我们的结果表明反应的立体和区域选择性是由早期的氧化加成步决定的,这与钯催化时还原消除决定区域选择性的共识显然不同,因而从理论上提出了一个新的机理图像。氧化加成步中Cu上基团的不同的反位效应是造成反应区域选择性的根源。第七章是对一个新颖的锰催化的二羰基化合物和末端炔烃生成取代苯的反应的机理的研究。我们提出了一个碳金属化/炔烃插入/分子内亲核加成的这样一条路径,它能很好的预测反应的立体和区域选择性。该路径中,产物的区域选择性是由碳金属化和炔烃插入共同决定的。我们对这两步中的电子和立体效应进行了讨论。前面3个课题涉及3个新发展的过渡金属催化的偶合反应的方向；第四个课题是一个古老的,但机理上重要的一类偶合反应,我们提出了新的机理建议；最后一个课题是一个理论与实验相结合的、对一个我们新发现的反应机理的认识的研究。这些研究显示了量子化学方法在过渡金属催化领域的有效性,特别是它能提供很多实验上无法获得的信息,比如一些关键的中间体和过渡态的结构和相对能量信息,以及这些关键的中间体和过渡态中的电子效应和立体效应对整个催化循环的影响等。更多还原

【Abstract】 This dissertation reports a series of mechanistic studies on some representative transition metal-catalyzed cross-coupling reactions by using quantum computational methods. The main contents of this dissertation include the following:Chapter 1 briefly reviews transition metal-catalyzed cross-coupling reactions and relevant primary steps in organometallic chemistry.Chapter 2 aims to give a brief introduction to the category and principles of main quantum computational methods.From Chapter 3 to Chapter 7, five research topics of mechanistic study on cross-coupling reactions, accomplished during my PhD period, have been reported. Chapter 3 describes a study on the mechanism of copper-catalyzed cross-coupling reactions of aryl halides with amides and the impact of ancillary ligands on the catalytic efficiency. Through rough estimate of the relative concentrations of possible catalytic species and examination of oxidative addition of these species with aryl bromide, we suggest that the active copper catalyst is a neutral L2Cu(amidate) species. Oxidative addition of this species with aryl halides constitutes the rate-limiting step of the catalytic cycle. On the basis of the proposed pathway, the effect of several common ligands used in the experiments on the catalytic efficiency is examined, and all the results are in consistent with experimental observations.Chapter 4 reports our study on the mechanism of palladium-catalyzed decarboxylative Heck reactions between carboxylic acids and olefins, and factors controlling the rate-limiting decarboxylation step have been examined. The catalytic cycle is suggested to comprise four steps:decarboxylation, alkene insertion, (3-H elimination and catalyst regeneration. Decarboxylation is the rate-limiting step, in which palladium center dissociates one molecule of neutral DMSO ligand before extruding CO2 to produce an experimentally isolable Pd(II)-Aryl intermediate. The effect of anionic ligands, neutral ligands, carboxylic acids substrate and metal center on the rate-limiting decarboxylation step is examined, providing insightful information for the development of more efficient catalytic decarboxylative reactions.Chapter 5 describes an investigation into the mechanism of a novel copper-catalyzed exclusive meta C-H bond arylation reaction of anilides. A kinetically competent amide-directed carbocupration mechanism, which is distinct from the mechanistic hypothesis in the original report, has been proposed on the basis of examination of several possible reaction pathways. The regioselectivity predicted by this mechanism is in agreement with the experimental observations, favoring meta product exclusively. The critical step of this carbocupration mechanism involves an amide-directed syn addition of Cu(III)-Ph across phenyl C2=C3 bond to generate a C2-cuprated, C3-arylated intermediate. Such reactivity has never been reported in the literature, and thus our results provide the possibility of access of such reactivity experimentally and their application in catalytic reactions.Chapter 6 describes our study on the origin of stereo-and regioselectivity of reaction of organocopper reagents with allylic electrophiles. Our results suggest that the stereo-and regioselectivity of this reaction is controlled by the early oxidative addition step, in contrast to the consensus of related Truji-Trost reaction in which the product regioselectivity is determined by the late-stage reductive elimination step. The regioselectivity of this reaction is caused by different trans effect of the ligands on the copper center.Chapter 7 describes our study on the reaction pathway of a new manganese-catalyzed [2+2+2] annulation reaction of 1,3-dicarbonyl compounds with terminal alkynes, with an emphasis on the origin of the product regioselectivity. A pathway involving carbometalation/alkyne insertion/intramolecular nucleophilic addition sequence has been supported by our results, which can rationally reproduce the stereo-and regioselectivity observed in experiments. The regioselectivity of this reaction is controlled by carbometalation and alkyne insertion step. Electronic and steric factors affecting these two steps have been discussed.The three topics in Chapter 3 to Chapter 5 deal with three new kinds of transition metal-catalyzed cross-coupling reactions; the topic in Chapter 6 represents an old, yet important field of organometallic chemistry and our findings into this topic is also significant; the topic in Chapter 7 demonstrates the ability of theoretical study on the understanding of newly developed transition metal-catalyzed reactions.These studies together demonstrate the powerfulness of quantum computational methods in mechanistic studies of transition metal catalysis. They can provide information that is hard to obtain by experimental means, for example, the structure and energetics of critical intermediates and transition states, and relevant electronic and/or steric effect on the efficiency of the catalytic cycle.更多还原