Ensemble Effects on Allylic Oxidation within Explicit Solvation Environments
Ensemble Effects on Allylic Oxidation within Explicit Solvation Environments
复制标题
显式溶剂化环境中烯丙基氧化的整体效应
DOI：
10.1039/d1dt00785h
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发表时间：
2021
影响因子：
4
通讯作者：
Hung M. Le, Mariano Guagliardo
中科院分区：
文献类型：
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作者：
Hung M. Le, Mariano Guagliardo
采用伞形采样密度泛函理论分子动力学（DFT-MD）研究了Cu（II）7-氨基-6-（（2-羟基苯亚甲基）氨基）喹喔啉-2-醇配合物在乙腈中催化环己烯烯丙基氧化生成环己烯酮和水的全催化循环.在初始H原子提取步骤之后，已经鉴定了两种不同的反应途径，其通过在催化剂回收过程中烷基氢过氧化物（称为“开放”循环）与甲醇副产物（称为“封闭”循环）的参与来区分。重要的是，这两种途径都涉及脱氢和再氢化的-NH 2基团结合到Cu-网站-一个功能，这是揭示了从合奏采样的配置的反应性物种，稳定在明确的溶剂环境的模拟。根据实验转换频率估算的能量跨度在350 K时约为22.7 kcal mol−1。而闭合循环值预计为26.2 kcal mol−1，开放循环值为16.5 kcal mol−1。这两种途径进一步与先前观察到的Cu（II）和Cu（III）之间的平衡一致。与先前的静态DFT计算相比，溶质和溶剂配置的集合有助于揭示支撑整个催化循环的过程的广度，从而更全面地理解自由基反应和催化回收的重要性。
Umbrella-sampling density functional theory molecular dynamics (DFT-MD) has been employed to study the full catalytic cycle of the allylic oxidation of cyclohexene using a Cu(II) 7-amino-6-((2-hydroxybenzylidene)amino)quinoxalin-2-ol complex in acetonitrile to create cyclohexenone and H2O as products. After the initial H-atom abstraction step, two different reaction pathways have been identified that are distinguished by the participation of alkyl hydroperoxide (referred to as the “open” cycle) versus the methanol side-product (referred to as the “closed” cycle) within the catalyst recovery process. Importantly, both pathways involve dehydrogenation and re-hydrogenation of the –NH2 group bound to the Cu-site – a feature that is revealed from the ensemble sampling of configurations of the reactive species that are stabilized within the explicit solvent environment of the simulation. Estimation of the energy span from the experimental turnover frequency yields an approximate value of 22.7 kcal mol−1 at 350 K. Whereas the closed cycle value is predicted to be 26.2 kcal mol−1, the open cycle value at 16.5 kcal mol−1. Both pathways are further consistent with the equilibrium between Cu(II) and Cu(III) that has previously been observed. In comparison to prior static DFT calculations, the ensemble of both solute and solvent configurations has helped to reveal a breadth of processes that underpin the full catalytic cycle yielding a more comprehensive understanding of the importance of radical reactions and catalysis recovery.