Tang Siyang, Liu Zhen, Zhan Xingwen, Cheng Ruihua, He Xuelian, Liu Boping
State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Meilong Road 130, Shanghai, 200237, People's Republic of China,
J Mol Model. 2014 Mar;20(3):2129. doi: 10.1007/s00894-014-2129-4. Epub 2014 Feb 20.
1-Hexene and 1-octene are important comonomers for the synthesis of high performance polyolefins. Recently, various N-substituted Cr-bis(diphenylphosphino)amine (PNP-Cr) catalysts show the potential as excellent candidates for highly selective ethylene trimerization/tetramerization. In this work, a series of aryl-substituted PNP-Cr catalysts were studied by two-dimensional quantitative structure-property relationship (QSPR) method based on density functional theory (DFT) calculations. The heuristic method (HM) and best multi-linear regression (BMLR) were used to establish the best linear regression models to describe the relationship between selectivities and catalyst structures. Both Cr(I) and Cr(II) active site models for ethylene trimerization/tetramerization were considered. It was found that 1) the relativity and stability of the models were increased by using self-defined descriptors based on DFT calculations; 2) Cr(I)/Cr(III) centers were the most plausible active sites for ethylene trimerization, while Cr(II)/Cr(IV) active sites were most possibly responsible for ethylene tetramerization; and 3) the skeleton structures of the PNP-Cr system with good complanation and symmetry were crucial for achieving excellent catalytic selectivity of 1-octene, while the PNP-Cr backbone with a large steric effect on N atom would benefit ethylene trimerization. Six new PNP ligands with high selectivity toward ethylene trimerization/tetramerization were predicted based on descriptor analysis and the best linear regression models providing a good basis for further development of novel catalyst systems with better performance.
1-己烯和1-辛烯是合成高性能聚烯烃的重要共聚单体。近年来，各种N-取代的铬-双（二苯基膦基）胺（PNP-Cr）催化剂显示出作为高选择性乙烯三聚/四聚优异候选物的潜力。在本工作中，基于密度泛函理论（DFT）计算，采用二维定量结构-性质关系（QSPR）方法研究了一系列芳基取代的PNP-Cr催化剂。使用启发式方法（HM）和最佳多元线性回归（BMLR）建立最佳线性回归模型，以描述选择性与催化剂结构之间的关系。考虑了用于乙烯三聚/四聚的Cr（I）和Cr（II）活性位点模型。结果发现：1）基于DFT计算使用自定义描述符提高了模型的相关性和稳定性；2）Cr（I）/Cr（III）中心是乙烯三聚最合理的活性位点，而Cr（II）/Cr（IV）活性位点最可能负责乙烯四聚；3）具有良好共平面性和对称性的PNP-Cr体系的骨架结构对于实现优异的1-辛烯催化选择性至关重要，而对N原子具有大空间效应的PNP-Cr主链有利于乙烯三聚。基于描述符分析预测了六种对乙烯三聚/四聚具有高选择性的新型PNP配体，最佳线性回归模型为进一步开发性能更好的新型催化剂体系提供了良好基础。
