Mechanistic Insight into Ketone α-Alkylation with Unactivated Olefins via C-H Activation Promoted by Metal-Organic Cooperative Catalysis (MOCC): Enriching the MOCC Chemistry
Mechanistic Insight into Ketone α-Alkylation with Unactivated Olefins via C-H Activation Promoted by Metal-Organic Cooperative Catalysis (MOCC): Enriching the MOCC Chemistry
复制标题
通过金属有机协同催化 (MOCC) 促进的 C-H 活化，深入了解未活化烯烃与酮 α-烷基化反应的机理：丰富 MOCC 化学
DOI：
10.1021/jacs.5b01502
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发表时间：
2015-05-20
影响因子：
15
通讯作者：
Wang, Zhi-Xiang
中科院分区：
文献类型：
--
作者：
Dang, Yanfeng;Qu, Shuanglin;Wang, Zhi-Xiang
金属-有机协同催化(MOCC)通过直接C(sp(2))-H官能化反应成功地催化了烯烃与醛的氢酰化反应。最近，有报道称一个复杂的MOCC体系，包括Rh(I)催化剂和7-氮杂环己烷(L1)助催化剂，甚至可以通过C(sp(3))-H活化催化酮与未活化的烯烃进行α-烷基化反应。在这里，我们提出了密度泛函理论的研究，以了解挑战性的酮α-烷基化反应的机理。转化采用IMesRh(I)Cl(L1)(CH2=CH2)作为活性催化剂，经过7步反应，包括酮与L1缩合，生成烯胺1b；1b与Rh(I)活性催化剂配位，生成Rh(I)-1b中间体；C(sp(2))-H氧化加成，生成Rh(III)-H氢化物；烯烃迁移插入Rh(III)-H键；还原消除，生成Rh(I)-1c(烷基化1b)中间体；1c脱序，释放1c，再生Rh(I)活性催化剂；和1C的水解，提供最终的α-烷基化产物ID并再生L1。在这七个步骤中，还原消除是决定速度的步骤。C-H键通过分子间相互作用的预活化是键活化的关键。这一机制解释了实验谜题：为什么在几个候选人中只有李表现得很好，而其他人都失败了，以及为什么威尔金森的催化剂在MOCC系统中表现不佳。在已有机理的基础上，受其他相关实验反应的启发，我们尝试在计算上丰富MOCC化学，举例说明如何开发新的有机催化剂，并提出L7作为Li的替代品，并展示了将迄今唯一使用的Rh(I)/Rh(III)歧管扩展到Co(0)/Co(II)氧化还原循环在开发MOCC体系中的巨大潜力。
Metal-organic cooperative catalysis (MOCC) has been successfully applied for hydroacylation of olefins with aldehydes via directed C(sp(2))-H functionalization. Most recently, it was reported that an elaborated MOCC system, containing Rh(I) catalyst and 7-azaindoline (L1) cocatalyst, could even catalyze ketone alpha-alkylation with unactivated olefins via C(sp(3))-H activation. Herein we present a density functional theory study to understand the mechanism of the challenging ketone alpha-alkylation. The transformation uses IMesRh(I)Cl(L1)(CH2=CH2) as an active catalyst and proceeds via sequential seven steps, including ketone condensation with L1, giving enamine 1b; 1b coordination to Rh(I) active catalyst, generating Rh(I)-1b intermediate; C(sp(2))-H oxidative addition, leading to a Rh(III)-H hydride; olefin migratory insertion into Rh(III)-H bond; reductive elimination, generating Rh(I)-1c(alkylated 1b) intermediate; decoordination of 1c, liberating 1c and regenerating Rh(I) active catalyst; and hydrolysis of 1c, furnishing the final alpha-alkylation product id and regenerating L1. Among the seven steps, reductive elimination is the rate-determining step. The C-H bond preactivation via agostic interaction is crucial for the bond activation. The mechanism rationalizes the experimental puzzles: why only Li among several candidates performed perfectly, whereas others failed, and why Wilkinson's catalyst commonly used in MOCC systems performed poorly. Based on the established mechanism and stimulated by other relevant experimental reactions, we attempted to enrich MOCC chemistry computationally, exemplifying how to develop new organic catalysts and proposing L7 to be an alternative for Li and demonstrating the great potential of expanding the hitherto exclusive use of Rh(I)/Rh(III) manifold to Co(0)/Co(II) redox cycling in developing MOCC systems.