Asymmetric Epoxidation of Alkenes Catalyzed by a Cobalt Complex,Journal of the American Chemical Society

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Asymmetric Epoxidation of Alkenes Catalyzed by a Cobalt Complex
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2023-07-05 , DOI: 10.1021/jacs.3c05476
Qianwen He ₁ , Mao-Ping Pu ₁ , Zheng Jiang ₁ , Hongyu Wang ₁ , Xiaoming Feng ₁ , Xiaohua Liu ₁

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Asymmetric epoxidation of alkenes catalyzed by nonheme chiral Mn–O and Fe–O catalysts has been well established, but chiral Co–O catalysts for the purpose remain virtually undeveloped due to the oxo wall. Herein is first reported a chiral cobalt complex to realize the enantioselective epoxidation of cyclic and acyclic trisubstituted alkenes by using PhIO as the oxidant in acetone, wherein the tetra-oxygen-based chiral N,N′-dioxide with sterically hindered amide subunits plays a crucial role in supporting the formation of the Co–O intermediate and enantioselective electrophilic oxygen transfer. Mechanistic studies, including HRMS measurements, UV–vis absorption spectroscopy, magnetic susceptibility, as well as DFT calculations, were carried out, confirming the formation of Co–O species as a quartet Co(III)-oxyl tautomer. The mechanism and the origin of enantioselectivity were also elucidated based on control experiments, nonlinear effects, kinetic studies, and DFT calculations.

中文翻译：

钴配合物催化烯烃的不对称环氧化

非血红素手性 Mn-O 和 Fe-O 催化剂催化的烯烃不对称环氧化反应已经成熟，但由于氧壁的原因，用于此目的的手性 Co-O 催化剂实际上尚未开发出来。本文首次报道了一种手性钴配合物，以PhIO为氧化剂，在丙酮中实现环状和无环三取代烯烃的对映选择性环氧化，其中具有位阻酰胺亚基的四氧基手性N,N'-二氧化物起到了关键作用。在支持 Co-O 中间体的形成和对映选择性亲电氧转移中发挥作用。进行了机理研究，包括 HRMS 测量、紫外可见吸收光谱、磁化率以及 DFT 计算，证实 Co-O 物种形成为四重 Co(III)-氧基互变异构体。基于控制实验、非线性效应、动力学研究和DFT计算，还阐明了对映选择性的机制和起源。

更新日期：2023-07-05

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