Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States.
Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States.
J Am Chem Soc. 2022 Feb 16;144(6):2735-2746. doi: 10.1021/jacs.1c12111. Epub 2022 Feb 7.
Ag-catalyzed nitrene transfer (NT) converts C-H bonds into valuable C-N bonds. These reactions offer a promising strategy for catalyst-controlled regiodivergent functionalization of different types of reactive C-H bonds, as the regioselectivity is tunable by varying the steric and electronic environments around the Ag nitrene, as well as the identity of the nitrene precursors and the tether length. Therefore, a unified understanding of how these individual factors affect the regioselectivity is key to the rational design of highly selective and regiodivergent C-H amination reactions. Herein, we report a computational study of various Ag-catalyzed NT reactions that indicates a concerted H-atom transfer (HAT)/C-N bond formation mechanism. A detailed analysis was carried out on the effects of the C-H bond dissociation enthalpy (BDE), charge transfer, ligand-substrate steric repulsions, and transition state ring strain on the stability of the C-H insertion transition states with different Ag nitrene complexes. The ancillary ligands on the Ag and the nitrene precursor identity both affect transition state geometries to furnish differing sensitivities to the BDE, tether length, and electronic effects of the reactive C-H bonds. Based on our understanding of the dominant factors that control selectivity, we established a rational catalyst and precursor selection approach for regiodivergent amination of diverse C-H bonds. The computationally predicted regiodivergent amination of β- and γ-C-H bonds of aliphatic alcohol derivatives was validated by experimental studies.
银催化的氮宾转移(NT)将 C-H 键转化为有价值的 C-N 键。这些反应为催化剂控制的不同类型反应性 C-H 键的区域选择性转化提供了一种很有前途的策略,因为通过改变银氮宾周围的空间和电子环境,以及氮宾前体和连接基团的长度,可以调节区域选择性。因此,对这些单个因素如何影响区域选择性有一个统一的理解是合理设计高选择性和区域选择性 C-H 胺化反应的关键。在此,我们报告了对各种银催化的 NT 反应的计算研究,表明存在协同的 H-原子转移(HAT)/C-N 键形成机制。我们对 C-H 键离解焓(BDE)、电荷转移、配体-底物空间排斥以及过渡态环应变对不同 Ag 氮宾配合物的 C-H 插入过渡态稳定性的影响进行了详细分析。Ag 上的辅助配体和氮宾前体的身份都影响过渡态的几何形状,从而对反应性 C-H 键的 BDE、连接基团长度和电子效应表现出不同的敏感性。基于我们对控制选择性的主要因素的理解,我们建立了一种合理的催化剂和前体选择方法,用于不同 C-H 键的区域选择性胺化。通过实验研究验证了我们对脂肪族醇衍生物的β-和γ-C-H 键的计算预测的区域选择性胺化。