Wang Keke, Xu Hui, Dang Yanfeng
Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Department of Chemistry, School of Science, Tianjin University, Tianjin 300072, China.
Dalton Trans. 2023 Apr 11;52(15):4849-4855. doi: 10.1039/d3dt00165b.
Nickel-catalyzed stereoselective hydroarylation is one of the most efficient methods to access functionalized arenes. Herein, computational studies have been applied to reveal the mechanism and origins of ligand-controlled enantioselectivity of Ni-catalyzed hydroarylation of 1,3-dienes using ethanol as the hydrogen source. DFT calculations show that the hydroarylation of ()-diene takes place concerted hydronickelation aided by boronate leading to an alkylnickel(II) intermediate, which further undergoes transmetallation and C-C reductive elimination to deliver the final chiral alkylarene. The hydronickelation is found to be the rate-determining step and is irreversible. The enantioselectivity is dominated by the transmetallation step, in which the ligand-substrate interactions are analyzed to unveil the source of stereocontrol. Besides, mechanistic studies demonstrate that the ()-diene initially reacts to offer a ()--alkyl-Ni(II) species, which preferably undergoes facile isomerization σ-π-σ-π-σ interconversion to the ()--alkyl-Ni(II) complex rather than the transmetallation step, thus ultimately generating the same ()-alkylarene product as ()-diene. Overall, the mechanistic understanding will be useful for the further advancement of asymmetric hydroarylation of dienes.
镍催化的立体选择性氢芳基化反应是获得官能化芳烃最有效的方法之一。在此，已应用计算研究来揭示以乙醇作为氢源时，镍催化的1,3 - 二烯氢芳基化反应中配体控制对映选择性的机理和起源。密度泛函理论（DFT）计算表明，（） - 二烯的氢芳基化反应在硼酸酯辅助下通过协同质子镍化反应进行，生成烷基镍（II）中间体，该中间体进一步进行金属转移和碳 - 碳还原消除反应，得到最终的手性烷基芳烃。发现质子镍化反应是速率决定步骤且不可逆。对映选择性主要由金属转移步骤决定，在该步骤中分析配体 - 底物相互作用以揭示立体控制的来源。此外，机理研究表明，（） - 二烯最初反应生成（） - - 烷基 - Ni（II）物种，该物种更倾向于通过σ - π - σ - π - σ相互转化进行容易的异构化反应，生成（） - - 烷基 - Ni（II）配合物，而不是进行金属转移步骤，从而最终生成与（） - 二烯相同的（） - 烷基芳烃产物。总体而言，这种机理理解将有助于二烯不对称氢芳基化反应的进一步发展。
