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首页> 外文期刊>Chemistry: A European journal >The wacker process: Inner- Or outer-sphere nucleophilic addition? New insights from Ab initio molecular dynamics
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The wacker process: Inner- Or outer-sphere nucleophilic addition? New insights from Ab initio molecular dynamics

机译：瓦克过程：内球或外球亲核加成？从头算分子动力学的新见解

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The Wacker process consists of the oxidation of ethylene catalyzed by a Pd~(II) complex. The reaction mechanism has been largely debated in the literature; two modes for the nucleophilic addition of water to a Pd-coordinated alkene have been proposed: syninner- and anti-outer-sphere mechanisms. These reaction steps have been theoretically evaluated by means of ab initio molecular dynamics combined with metadynamics by placing the [Pd-(C_2H _4)Cl_2(H_2O)] complex in a box of water molecules, thereby resembling experimental conditions at low [Cl~-]. The nucleophilic addition has also been evaluated for the [Pd(C _2H_4)Cl_3]~- complex, thus revealing that the water by chloride ligand substitution trans to ethene is kinetically favored over the generally assumed cis species in water. Hence, the resulting trans species can only directly undertake the outersphere nucleophilic addition, whereas the inner-sphere mechanism is hindered since the attacking water is located trans to ethene. In addition, all the simulations from the [Pd(C _2H_4)Cl_2-(H_2O)] species (either cis or trans) support an outer-sphere mechanism with a free-energy barrier compatible with that obtained experimentally, whereas that for the inner-sphere mechanism is significantly higher. Moreover, additional processes for a global understanding of the Wacker process in solution have also been identified, such as ligand substitutions, proton transfers that involve the aquo ligand, and the importance of the trans effect of the ethylene in the nucleophilic addition attack.
机译：Wacker过程由Pd〜（II）络合物催化的乙烯氧化组成。反应机理在文献中已被广泛争论。已经提出了将水亲核加成到Pd配位的烯烃中的两种模式：增效剂和反外层机理。通过将[Pd-（C_2H _4）Cl_2（H_2O）]络合物置于一盒水分子中，从头算分子动力学与元动力学相结合，对这些反应步骤进行了理论上的评估，从而与低[Cl〜- ]。还已经对[Pd（C _2H_4）Cl_3]-络合物的亲核加成进行了评估，因此揭示了通过氯配体取代成乙烯的水在动力学上优于通常假定的顺式物种。因此，所得的反式物种仅能直接进行外球的亲核加成，而内球的机理受到阻碍，因为攻击水位于反式乙烯的位置。此外，所有来自[Pd（C _2H_4）Cl_2-（H_2O）]物种（顺式或反式）的模拟都支持外层机制，其自由能垒与实验获得的能垒兼容，而内层则为内能球机制明显更高。而且，还已经确定了对溶液中的瓦克过程有全局理解的其他过程，例如配体取代，涉及水族配体的质子转移，以及乙烯在亲核加成攻击中的反式作用的重要性。

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