A DFT study toward the mechanism of chromium-catalyzed ethylene trimerization
A DFT study toward the mechanism of chromium-catalyzed ethylene trimerization
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DOI：
10.1021/om0306269
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发表时间：
2004-02
期刊：
影响因子：
2.8
通讯作者：
W. V. Rensburg;Cronje Grove;J. P. Steynberg;K. Stark;J. Huyser;P. Steynberg
中科院分区：
文献类型：
--
作者：
W. V. Rensburg;Cronje Grove;J. P. Steynberg;K. Stark;J. Huyser;P. Steynberg
用密度泛函理论方法对铬-吡咯基配合物催化乙烯三聚反应机理进行了理论研究。1-己烯的选择性形成通常被认为遵循金属循环机理。详细的自旋态分析表明，三重态自旋态代表了所有驻点的基态自旋态。绘制了完整的吉布斯自由能表面(298.15 K)，分别对应于吡咯的η5-键和σ-键模式，以及剥离的氯离子模型和完整的ClAlMe3阴离子模型。计算结果表明，提出的金属循环机理在能量上是有利的，金属循环增长被认为是决定反应速率的步骤。此外，在所提出的机理中，吡咯在不同的成键阶段优先选择不同的成键方式，有效地说明了吡咯在势能上的最小能量路径上发生了环的滑移。
A theoretical study of a mechanism for ethylene trimerization, catalyzed by Cr-pyrrolyl complexes, is proposed and investigated with density functional theory methods. The selective formation of 1-hexene is generally accepted to follow a metallacycle mechanism. A detailed spin state analysis for active species in the mechanism shows that the triplet spin state represents the ground spin state for all stationary points. Complete Gibbs free energy (298.15 K) surfaces are mapped for both η5- and σ-bonding modes of pyrrole, as well as a stripped-down Cl anion model and a full ClAlMe3 anion model. From the calculated results it is shown that the proposed metallacycle mechanism is energetically favorable, with metallacycle growth identified as the rate-determining step. In addition, it is demonstrated that different bonding modes of pyrrole are preferred at different stages in the proposed mechanism, effectively suggesting that ring slippage of the pyrrole occurs on the minimum energy path on the potential ener...