Chatani Naoto
Department of Applied Chemistry, Faculty of Engineering, and Research Center for Environmental Preservation, Osaka University, 565-0871 Osaka Japan.
Acc Chem Res. 2023 Nov 7;56(21):3053-3064. doi: 10.1021/acs.accounts.3c00493. Epub 2023 Oct 11.
ConspectusThe development of functionalization reactions involving the activation of C-H bonds has evolved extensively due to the atom and step economy associated with such reactions. Among these reactions, chelation assistance has been shown to provide a powerful solution to the serious issues of reactivity and regioselectivity faced in the activation of C-H bonds. The vast majority of C-H functionalization reactions reported thus far has involved the use of precious metals. Kleiman and Dubeck reported the cyclonickelation of azobenzene and NiCp in which an azo group directs a Ni center to activate the ortho C-H bond in close proximity. Although this stoichiometric reaction was discovered earlier than that for other transition-metal complexes, its development as a catalytic reaction was delayed. No general catalytic systems were available for Ni-catalyzed C-H functionalization reactions for a long time. This Account details our group's development of Ni(0)- and Ni(II)-catalyzed chelation-assisted C-H functionalization reactions. It also highlights how the new strategy can be extended to the activation of other unreactive bonds.In the early 2010s, we found that the Ni(0)-catalyzed reaction of aromatic amides that contain a 2-pyridinylmethylamine moiety as a directing group with alkynes results in C-H/N-H oxidative annulation to give isoquinolinones. In addition, the combination of a Ni(II) catalyst and an 8-aminoquinoline directing group was found to be a superior combination for developing a wide variety of C-H functionalization reactions with various electrophiles. The reactions were proposed to include the formation of unstable Ni(IV) and/or Ni(III) species; the generation of such high-valence Ni species was rare at that time, but since then, many papers dealing with DFT and organometallic studies have appeared in the literature in attempts to understand the mechanism. Based on our in-depth considerations of the mechanism with respect to why an N,N-bidentate directing group is required, we realized that the formation of a N-Ni bond by the oxidative addition of a N-H bond to a Ni(0) species or a ligand exchange between a N-H bond and Ni(II) species is the key step. We concluded that the precoordination of the N(sp) atom in the directing group positions the Ni species to be in close proximity to the N-H bond which permits the formation of a N-Ni bond. Based on this working hypothesis, we carried out the reaction using KOBu as a base and found that the Ni(0)-catalyzed reaction of aromatic amides that do not contain such a specific directing group with alkynes results in the formation of the desired isoquinolinone, in which an amidate anion acts as the actual directing group. Remarkably, this strategy was found to be applicable to the activation of various other unreactive bonds such as C-F, C-O, C-S, and C-CN.
概述
由于与碳氢键活化相关的原子经济性和步骤经济性，涉及碳氢键活化的官能团化反应得到了广泛发展。在这些反应中，螯合辅助已被证明是解决碳氢键活化中反应性和区域选择性严重问题的有效方法。迄今为止报道的绝大多数碳氢键官能团化反应都涉及使用贵金属。克莱曼和杜贝克报道了偶氮苯与NiCp的环镍化反应，其中一个偶氮基团引导镍中心活化紧邻的邻位碳氢键。尽管这个化学计量反应比其他过渡金属配合物的反应发现得更早，但其作为催化反应的发展却被推迟了。长期以来，没有通用的催化体系可用于镍催化的碳氢键官能团化反应。本综述详细介绍了我们小组对镍(0)和镍(II)催化的螯合辅助碳氢键官能团化反应的研究进展。它还强调了这种新策略如何能够扩展到其他惰性键的活化。
在21世纪10年代初，我们发现含有2-吡啶基甲胺基团作为导向基团的芳香酰胺与炔烃在镍(0)催化下发生碳氢键/氮氢键氧化环化反应生成异喹啉酮。此外，发现镍(II)催化剂和8-氨基喹啉导向基团的组合是开发与各种亲电试剂进行多种碳氢键官能团化反应的优异组合。这些反应被认为包括不稳定的镍(IV)和/或镍(III)物种的形成；当时这种高价镍物种的生成很少见，但从那时起，许多涉及密度泛函理论(DFT)和有机金属研究的论文出现在文献中，试图理解其反应机理。基于我们对为什么需要N,N-双齿导向基团这一反应机理的深入思考，我们意识到氮氢键向镍(0)物种的氧化加成或氮氢键与镍(II)物种之间的配体交换形成N-Ni键是关键步骤。我们得出结论，导向基团中氮(sp)原子的预配位使镍物种靠近氮氢键，从而允许形成N-Ni键。基于这个工作假设，我们使用叔丁醇钾作为碱进行反应，发现不含这种特定导向基团的芳香酰胺与炔烃在镍(0)催化下反应生成所需的异喹啉酮，其中酰胺阴离子作为实际的导向基团。值得注意的是，该策略被发现适用于各种其他惰性键的活化，如碳氟键、碳氧键、碳硫键和碳氰键。
