文献类型：期刊文献

英文题名：Role of 1,2-Dimethoxyethane in the Transformation from Ethylene Polymerization to Trimerization Using Chromium Tris(2-ethylhexanoate)-Based Catalyst System: A DFT Study

作者：Qi, Yuan[1];Dong, Qi[1];Zhong, Lei[1];Liu, Zhen[1];Qiu, Pengyuan[1];Cheng, Ruihua[1];He, Xuelian[1];Vanderbilt, Jeffrey[2];Liu, Boping[1]

机构：[1]E China Univ Sci & Technol, State Key Lab Chem Engn, Shanghai 200237, Peoples R China;[2]Westlake Chem Corp, Longview, TX 75607 USA

年份：2010

卷号：29

期号：7

起止页码：1588

外文期刊名：ORGANOMETALLICS

收录：;EI(收录号：20101612852735);WOS:【SCI-EXPANDED(收录号:WOS:000276215100014)】；

基金：We thank Westlake Chemical Corporation for financial support and permission to publish this work. This work is also financially supported by the Research Program of the State Key Laboratory of Chemical Engineering, Shanghai Pujiang Talent Plan Project (08PJ14032), and the Program of Introducing Talents of Discipline to Universities (B08021). We thank Prof. Sebastian Kozuch from the Institute of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry (Israel) and Prof. Yi Luo from Dalian University of Technology (China) for valuable discussions and suggestions.

语种：英文

外文关键词：Coordination reactions - Chromium compounds - Metals - Dimerization - Density functional theory - Ethylene

摘要：Selective ethylene trimerization into 1-hexene, which is an important comonomer for production of copolymers with high performance, was first commercialized in 2003 using a chromium tris(2-ethylhexanoate) (Cr(EH)(3))-based catalyst. One milestone during the development of this catalyst is the addition of 1,2-dimethoxyethane (DME) to Cr(EH)(3)/partially hydrolyzed tri-isobutyl aluminum (PIBAO) catalyst, resulting in a transformation from ethylene polymerization into trimerization. However, the mechanism of this transformation is unknown. In this work, the role of DME in the switching mechanism from ethylene polymerization to trimerization was investigated by a density functional theory (DFT) method based on the 10 most plausible molecular models for the active species of Cr(EH)(3)/PIBAO catalyst with or without DME coordination. For neutral models (Cr(I)OR; Cr(I)OR/DME; Cr(I)R; Cr(I)R/DME; R refers to isobutyl ligand), those without DME coordination were found to be dominantly ethylene trimerization sites. After DME coordination, both the weak electron-donating effect and steric effect of DME increased the total energy barriers of metallocycle growth, leading to ethylene trimerization with dimerization as a side reaction. So neutral models mainly presented ethylene trimerization with or without DME coordination and were not consistent with experimental evidence of transformation. For cationic models (Cr(I); Cr(I)+/DME; Cr(II)+OR; Cr(II)+OR/DME; Cr(II)R+; Cr(II)R+/DME), metallocycle growth leading to ethylene polymerization occurred on those models without DME. After DME coordination, the strong electron-donating effect of DME was found to facilitate metallocycle expansion, while the dominant role of the steric effect of DME made nine-membered ring formation unfavorable, and thus 1-hexene was liberated from the seven-membered ring. So all the cationic models presented a transformation from ethylene polymerization to trimerization after DME coordination and might be the most plausible active sites for the Cr(EH)(3)/PIBAO catalyst system. The results provided a much deeper understanding of the highly selective trimerization mechanism and for further development of new catalysts with high performance as well.