物理化学学报 >> 2019, Vol. 35 >> Issue (9): 940-953.doi: 10.3866/PKU.WHXB201810052

所属专题: 碳氢键活化

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过渡金属参与C―H键切断模式的理论研究进展

单春晖1,*(),白若鹏2,蓝宇2,3,*()   

  1. 1 重庆大学生物医学工程博士后流动站,重庆 4013312
    2 重庆大学化学化工学院与理论与计算化学重庆市重点实验室,重庆 401331
    3 郑州大学化学与分子工程学院,郑州 450001
  • 收稿日期:2018-10-23 录用日期:2018-11-21 发布日期:2018-11-27
  • 通讯作者: 单春晖,蓝宇 E-mail:chunhui.shan@cqu.edu.cn;lanyu@cqu.edu.cn
  • 作者简介:单春晖,生于1985年。2017年在重庆大学获得博士学位,目前在重庆大学从事博士后研究。研究方向为过渡金属催化C―H键官能团化反应|蓝宇,重庆大学化学化工学院教授,1981年生。2008年在北京大学获博士学位;2009–2012年在美国UCLA从事博士后研究;2012年4月加入重庆大学。研究方向为有机化学理论和理论有机化学
  • 基金资助:
    国家自然科学基金(21822303);国家自然科学基金(21772020);中央高校基本科研业务费(2018CDXZ0002);中央高校基本科研业务费(2018CDPTCG0001/4);重庆市博士后科研项目(XmT2018085)

Theoretical Advances of Transition Metals Mediated C―H Bonds Cleavage

Chunhui SHAN1,*(),Ruopeng BAI2,Yu LAN2,3,*()   

  1. 1 Postdoctoral Station of Biomedical Engineering, Chongqing University, Chongqing 401331, P. R. China
    2 School of Chemistry and Chemical Engineering, and Chongqing Key Laboratory of Theoretical and Computational Chemistry, Chongqing University, Chongqing 401331, P. R. China
    3 College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, P. R. China
  • Received:2018-10-23 Accepted:2018-11-21 Published:2018-11-27
  • Contact: Chunhui SHAN,Yu LAN E-mail:chunhui.shan@cqu.edu.cn;lanyu@cqu.edu.cn
  • Supported by:
    The project was supported by the National Natural Science Foundation of China(21822303);The project was supported by the National Natural Science Foundation of China(21772020);Fundamental Research Funds for the Central Universities, China (Chongqing University)(2018CDXZ0002);Fundamental Research Funds for the Central Universities, China (Chongqing University)(2018CDPTCG0001/4);Chongqing Postdoctoral Science Special Foundation, China(XmT2018085)

摘要:

过渡金属催化活化C―H键来构建新共价键因具有原子经济和合成简捷的特点,已成为合成化学中最为有效策略之一。本文中,我们总结了过渡金属参与的C―H键切断的理论研究进展,并系统性提出了C―H键切断的相关模式,包括:C―H键对金属的氧化加成、碱协助的去质子化、σ-复分解、Friedel-Crafts型亲电芳香取代、α-或β-氢消除以及夺氢活化等。理论计算表明,当使用还原性较强的零价金属催化剂时,反应可按照氧化加成模式进行。当使用金属羧酸盐作为催化剂时,通常以协同金属化-去质子化机理模式实现C―H键切断。当使用阳离子金属催化剂,富电子芳烃比缺电子芳烃优先反应时,C―H键切断则会经历碱协助的内部亲电取代模式。σ-复分解是协同金属化-去质子化机理的另一种模式。如果亲电体对芳烃进行加成时,则可按照Friedel-Crafts型亲电芳香取代方式活化C―H键。α-或β-氢消除也是比较常见的活化C―H键模式。此外,夺氢活化可通过自由基过程实现C―H键活化。本文通过对过渡金属参与的C―H键活化模式的论述旨在为实验提供理论指导。

关键词: 过渡金属, C―H键切断, 理论计算, 反应机理, 协同金属化-去质子化

Abstract:

Transition-metal-catalyzed C―H bond activation, which has been widely applied to construct new covalent bonds, has emerged as one of the most effective strategies in synthetic chemistry due to atom economy and simple procedure. In this review, we have summarized the recent reports on the theoretical mechanistic study of transition-metal-catalyzed C―H bond cleavage. Based on these comprehensive theoretical studies, we have systematically discussed the general modes of C―H bond activation, which involves oxidative addition, base-assisted deprotonation, σ-metathesis, Friedel-Crafts-type electrophilic aromatic substitution, α- or β-hydrogen elimination, and hydrogen atom abstraction. From a mechanistic point of view, C―H bond activation by oxidative addition generally involves a zero-valent transition metal catalyst with strong reducibility, which requires a low activation barrier. The concerted metalation-deprotonation (CMD)-type C―H bond cleavage often occurs via a six-membered cyclic transition state using transition metal carboxylate as the catalyst with a directing group, which is a common mechanism for transition metals with high oxidation states. Base-assisted internal electrophilic substitution (BIES)-type C―H bond activation is commonly performed in the presence of cationic transition metal catalysts, in which electron-rich arenes react preferentially compared to electron-deficient arenes. In some other cases, outer-sphere base-assisted deprotonation can also result in C―H activation, which is dependent on the strength of the base used. The stronger the base used, the lower the energy barrier, and thus, the easier it is to protonate. The σ-metathesis pathway, which could occur via a four-membered cyclic transition state, is often considered an alternative for concerted metalation-deprotonation. If the aromatic hydrocarbon is attacked by electrophiles, the C―H bond can be activated by Friedel-Crafts-type electrophilic aromatic substitution. Elimination of α- or β-hydrogen is also frequently proposed for transition-metal-catalyzed C―H functionalization. Hydrogen atom abstraction could achieve C―H bond activation via a free radical process. Moreover, the C―H bonds of hydrocarbons can be considered weak nucleophiles because the electronegativity of carbon is higher than that of hydrogen, and they could be converted to strong nucleophiles (C―M) in the presence of transition metal catalysts via the different pathways mentioned above. It enables further functionalization with electrophiles or nucleophiles to construct complex molecular skeletons. Summarizing the general modes of C―H bond activation will increase our understanding of the associated chemical mechanism and will pave the way for new synthetic strategies. This review aims to offer theoretical guidance for experimental studies and inspire new reaction design by summarizing the modes of transition-metal-catalyzed C―H bond activation.

Key words: Transition metal, C―H bond cleavage, Theoretical study, Mechanism, Concerted metalation-deprotonation