New Mechanistic Insights on the Selectivity of Transition-Metal-Catalyzed Organic Reactions: The Role of Computational Chemistry.
New Mechanistic Insights on the Selectivity of Transition-Metal-Catalyzed Organic Reactions: The Role of Computational Chemistry.
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DOI：
10.1021/acs.accounts.6b00093
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发表时间：
2016-06
影响因子：
18.3
通讯作者：
Xinhao Zhang;L. Chung;Yundong Wu
中科院分区：
文献类型：
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作者：
Xinhao Zhang;L. Chung;Yundong Wu
随着理论方法的新进步和计算能力的增强，计算化学的应用在许多化学领域变得实用和常规。在有机化学中，计算化学在阐明反应机制和各种选择性（例如化学选择性、区域选择性和立体选择性）的起源方面发挥着不可或缺的作用。因此，对机理的理解可以改善合成并有助于新催化剂的合理设计。在本报告中，我们介绍了我们最近的一些工作，以说明计算化学如何为提高几种有机反应的选择性提供新的机制见解。这些例子不仅包括对现有实验观察结果的解释，还包括随后被实验验证的预测。本说明由三个部分组成，讨论三种不同类型的选择性。第一部分讨论主要由 [Cp*Ru(MeCN)3](+) 或 [CpRu(MeCN)3](+) 催化的炔烃氢化硅烷化的区域选择性和立体选择性。计算表明了一种涉及关键钌环丙烯中间体的新机制。这种机制不仅解释了 Trost 及其同事观察到的不寻常的马尔可夫尼科夫区域选择性和反加成立体选择性，而且还激发了进一步的实验研究。新的有趣的实验观察和进一步的理论研究导致了反应机理的扩展。第二部分包括芳基化合物间位选择性C-H活化的三个案例。在铜催化选择性间位C-H活化苯胺的情况下，提出了一种涉及Cu(III)-Ar介导的Heck样过渡态的新机制，其中Ar基团充当亲电子试剂。该机制预测更多缺电子的 Ar 基团具有更高的反应性，这得到了实验的支持。对于 Pd(II) 催化的两种模板介导的间选择性 C-H 键激活，两种模板衍生出不同的机制。一种涉及二聚 Pd-Pd 或 Pd-Ag 活性催化剂，另一种涉及单体 Pd 催化剂，其中单保护氨基酸以二齿方式配位，并作为 C-H 活化的内部碱基。第三部分讨论不对称合成中的去对称策略。刚性骨架的构建对于这些催化剂区分两个前手性基团至关重要。总体而言，计算化学家和实验化学家之间富有成效的合作为这些有用的反应提供了新的、全面的机械理解和见解。
With new advances in theoretical methods and increased computational power, applications of computational chemistry are becoming practical and routine in many fields of chemistry. In organic chemistry, computational chemistry plays an indispensable role in elucidating reaction mechanisms and the origins of various selectivities, such as chemo-, regio-, and stereoselectivities. Consequently, mechanistic understanding improves synthesis and assists in the rational design of new catalysts. In this Account, we present some of our recent works to illustrate how computational chemistry provides new mechanistic insights for improvement of the selectivities of several organic reactions. These examples include not only explanations for the existing experimental observations, but also predictions which were subsequently verified experimentally. This Account consists of three sections discuss three different kinds of selectivities. The first section discusses the regio- and stereoselectivities of hydrosilylations of alkynes, mainly catalyzed by [Cp*Ru(MeCN)3](+) or [CpRu(MeCN)3](+). Calculations suggest a new mechanism that involves a key ruthenacyclopropene intermediate. This mechanism not only explains the unusual Markovnikov regio-selectivity and anti-addition stereoselectivity observed by Trost and co-workers, but also motivated further experimental investigations. New intriguing experimental observations and further theoretical studies led to an extension of the reaction mechanism. The second section includes three cases of meta-selective C-H activation of aryl compounds. In the case of Cu-catalyzed selective meta-C-H activation of aniline, a new mechanism that involves a Cu(III)-Ar-mediated Heck-like transition state, in which the Ar group acts as an electrophile, was proposed. This mechanism predicted a higher reactivity for more electron-deficient Ar groups, which was supported by experiments. For two template-mediated, meta-selective C-H bond activations catalyzed by Pd(II), different mechanisms were derived for the two templates. One involves a dimeric Pd-Pd or Pd-Ag active catalyst, and the other involves a monomeric Pd catalyst, in which a monoprotected amino acid coordinates in a bidentate fashion and serves as an internal base for C-H activation. The third section discusses a desymmetry strategy in asymmetric synthesis. The construction of rigid skeletons is critical for these catalysts to distinguish two prochiral groups. Overall, fruitful collaborations between computational and experimental chemists have provided new and comprehensive mechanistic understanding and insights into these useful reactions.