Two, three, and four water chain models for the nucleophilic addition step in the Wacker process
Two, three, and four water chain models for the nucleophilic addition step in the Wacker process
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DOI：
10.1021/jp961327i
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发表时间：
1996-08-29
影响因子：
--
通讯作者：
Siegbahn, PEM
中科院分区：
文献类型：
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作者：
Siegbahn, PEM
使用密度泛函方法和各种化学模型研究了Wacker过程的前两个步骤。这两个步骤是，第一，羟基亲核加成到与二氯化钯配位的乙烯上，第二，β-消除步骤，得到π-配位的乙烯醇络合物。最重要的结果是发现的亲核加成步骤。结果表明，亲核试剂应模拟的水分子链。至少需要三个水分子从烯烃上的攻击点桥接到负氯离子配体。H_5O_2 ~+-Cl ~-离子对是在低势垒的情况下以一种自负的方式发生亲核加成的同时形成的。由于在该步骤中发生电荷分离，溶剂效应是相当重要的。对于发生β消除的过程的第二步也是如此，因为在这一步骤中，负氯化物从正钯原子上移开，以便为氢化物腾出位置。当使用非常大的基组和溶剂的影响占，良好的协议与已知的实验发现。
The first two steps of the Wacker process are studied using a density functional method and a variety of chemical models. These two steps are, first, the nucleophilic addition of an hydroxyl group to an ethylene coordinated to palladium dichloride and, second, the beta-elimination step leading to a pi-coordinated vinyl alcohol complex. The most important result is found for the nucleophilic addition step. It is shown that the nucleophile should be modeled by a chain of water molecules. At least three water molecules are needed to bridge from the point of attack on the olefin to the negative chloride ligand. The H5O2+-Cl- ion pair is formed simultaneously as the nucleophilic addition occurs in a conceited way with a low barrier. Since a charge separation occurs in this step, solvent effects are quite important. This is also true for the second step of the process where beta-elimination occurs, since in this step a negative chloride is moved away from the positive palladium atom in order to make place for the hydride. When very large basis sets are used and solvent effects are accounted for, good agreement with what is known experimentally is found.