Ethene Dimerization and Hydrogenation over a Zeolite-Supported Rh(I)-Carbonyl Complex: Mechanistic Insights from DFT Modeling,ACS Catalysis

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Ethene Dimerization and Hydrogenation over a Zeolite-Supported Rh(I)-Carbonyl Complex: Mechanistic Insights from DFT Modeling
ACS Catalysis ( IF 11.3 ) Pub Date : 2018-09-26 00:00:00 , DOI: 10.1021/acscatal.8b02573
Sai V. C. Vummaleti ₁ , Alexander Genest ₁ , Nishamol Kuriakose ₁ , Notker Rösch _{1,

2}

Affiliation

Using DFT calculations within a quantum mechanical/molecular mechanical scheme, we present a model study on a zeolite-supported Rh(I) complex, [Rh(CO)(C₂H₄)]⁺, to rationalize the experimentally observed ethene hydrogenation and dimerization. Our computational results show that the coordination of an ethene to the Rh center of a [Rh(CO)(C₂H₄)]⁺ complex is thermodynamically favorable over H₂ coordination. The diethyl complex [Rh(CO)(C₂H₅)₂]⁺ resulting from hydrogenation acts as a branching point of two catalytic cycles of ethene conversion, to hydrogenation or dimerization. The Rh-acyl complex [Rh(COCH₂CH₃)(C₂H₅)(C₂H₄)]⁺ is the in situ-generated active species initiating the dimerization, as it entails a tremendous lowering of the C–C coupling barrier, by more than 100 kJ mol^–1. Overall, free energy barriers of ethene hydrogenation (89–92 kJ mol^–1) are calculated 4–7 kJ mol^–1 lower than the barrier for dimerization, 96 kJ mol^–1, in qualitative agreement with the experimentally observed selectivity. Finally, a side reaction of the Rh-acyl complex yields a qualitative explanation of the experimentally observed steady increase in butene selectivity.

中文翻译：

沸石负载的Rh（I）-羰基配合物上的乙烯二聚和加氢：从DFT建模的机理见解。

在量子力学/分子力学方案中使用DFT计算，我们对沸石负载的Rh（I）配合物[Rh（CO）（C ₂ H ₄）] ⁺进行模型研究，以合理化实验观察到的乙烯加氢和二聚化。我们的计算结果表明，乙烯与[Rh（CO）（C ₂ H ₄）] ^+配合物的Rh中心的配位在热力学上优于H ₂配位。二乙基络合物[Rh（CO）（C ₂ H ₅）₂ ] ⁺由氢化得到的产物充当乙烯转化为氢化或二聚反应的两个催化循环的分支点。Rh-酰基配合物[Rh（COCH ₂ CH ₃）（C ₂ H ₅）（C ₂ H ₄）] ⁺是原位生成的引发二聚化的活性物质，因为它会大大降低C–C耦合势垒，大于100 kJ mol ^–1。总体而言，氢化乙烯（89-92千焦摩尔的自由能屏障^-1计算）4-7千焦耳摩尔^-1比势垒二聚化降低，96千焦耳摩尔^-1在质量上与实验观察到的选择性一致。最后，Rh-酰基配合物的副反应定性地解释了实验观察到的丁烯选择性的稳定增加。

更新日期：2018-09-26

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