Mechanistic Details of the Sharpless Epoxidation of Allylic Alcohols—A Combined URVA and Local Mode Study
Mechanistic Details of the Sharpless Epoxidation of Allylic Alcohols—A Combined URVA and Local Mode Study
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DOI：
10.3390/catal12070789
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发表时间：
2022-07
期刊：
影响因子：
3.9
通讯作者：
M. Freindorf;E. Kraka
中科院分区：
文献类型：
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作者：
M. Freindorf;E. Kraka
在这项工作中，我们考察了夏普莱斯二聚钛(IV)-酒石酸盐-双酯催化剂对烯丙醇与甲基过氧化氢环氧化反应的催化作用，考虑了钛原子上配位的反应物种的四个不同方向(反应R1-R4)以及非催化反应(反应R0)的模型。作为主要的分析工具，我们应用了URVA(统一反应谷方法)和LMA(局域模式分析)，这两种方法都是基于振动光谱，并辅之以在DFT理论水平上计算的电子密度的QTAIM分析。在DLPNO-CCSD(T)理论水平上对每个反应的能量进行了重新计算。URVA曲率谱确定了所有五个反应的重要化学事件，即在TS之前发生的过氧化氢OO键断裂(即，解释了能垒)和环氧化物CO键的形成以及在TS之后目标CC双键的碳原子的重新杂化。能量分解为反应相贡献相表明，催化剂的主要作用是减弱了非催化反应中要断裂的OO键，并用更有利的能量断裂的TiO键取代了非催化反应中的OO键断裂。在所有固定点上进行的LMA总结了以下研究：(I)量化了氧化性过氧化氢在金属原子上配位时OO键的减弱，(Ii)表明新的CO环氧化物键的形成更加同步，这些键之间的键强度差异较小，以及(Iii)阐明了催化剂和反应物之间形成的三个TiO键的不同作用以及它们在夏普莱斯催化剂的协调下的相互作用。我们希望本文将启发计算界在未来使用URVA与LMA互补，作为一种有效的机械工具来优化和微调现有的夏普莱斯催化剂，并设计用于环氧化反应的新催化剂。
In this work, we investigated the catalytic effects of a Sharpless dimeric titanium (IV)–tartrate–diester catalyst on the epoxidation of allylalcohol with methyl–hydroperoxide considering four different orientations of the reacting species coordinated at the titanium atom (reactions R1–R4) as well as a model for the non–catalyzed reaction (reaction R0). As major analysis tools, we applied the URVA (Unified Reaction Valley Approach) and LMA (Local Mode Analysis), both being based on vibrational spectroscopy and complemented by a QTAIM analysis of the electron density calculated at the DFT level of theory. The energetics of each reaction were recalculated at the DLPNO-CCSD(T) level of theory. The URVA curvature profiles identified the important chemical events of all five reactions as peroxide OO bond cleavage taking place before the TS (i.e., accounting for the energy barrier) and epoxide CO bond formation together with rehybridization of the carbon atoms of the targeted CC double bond after the TS. The energy decomposition into reaction phase contribution phases showed that the major effect of the catalyst is the weakening of the OO bond to be broken and replacement of OH bond breakage in the non–catalyzed reaction by an energetically more favorable TiO bond breakage. LMA performed at all stationary points rounded up the investigation (i) quantifying OO bond weakening of the oxidizing peroxide upon coordination at the metal atom, (ii) showing that a more synchronous formation of the new CO epoxide bonds correlates with smaller bond strength differences between these bonds, and (iii) elucidating the different roles of the three TiO bonds formed between catalyst and reactants and their interplay as orchestrated by the Sharpless catalyst. We hope that this article will inspire the computational community to use URVA complemented with LMA in the future as an efficient mechanistic tool for the optimization and fine-tuning of current Sharpless catalysts and for the design new of catalysts for epoxidation reactions.