文献类型：期刊文献

英文题名：What Triggered the Switching from Ethylene-Selective Trimerization into Tetramerization over the Cr/(2,2′-Dipicolylamine) Catalysts?

作者：Liu, Lin[1];Liu, Zhen[1];Tang, Siyang[2];Cheng, Ruihua[1];He, Xuelian[1];Liu, Boping[3]

机构：[1]East China Univ Sci & Technol, Sch Chem Engn, Shanghai 200237, Peoples R China;[2]Sichuan Univ, Sch Chem Engn, Chengdu 610065, Sichuan, Peoples R China;[3]South China Agr Univ, Coll Mat & Energy, Guangzhou 510642, Guangdong, Peoples R China

年份：2019

卷号：9

期号：11

起止页码：10519

外文期刊名：ACS CATALYSIS

收录：;EI(收录号：20194507616313);WOS:【SCI-EXPANDED(收录号:WOS:000494549700078)】；

基金：The authors thank the China Scholarship Council, the National Natural Science Foundation of China (nos. 21174037, 21304033). This work is also sponsored by Shanghai Pujiang Program (18PJ1402500), and the Open Project of State Key Laboratory of Chemical Engineering (SKL-ChE-18C01) at the East China University of Science and Technology.

语种：英文

外文关键词：ethylene trimerization; ethylene tetramerization; switchable mechanism; effect of methyl substituent; DFT

摘要：The mechanism of switching from ethylene-selective trimerization into tetramerization catalyzed by Cr/(2,2'-dipicolylamine) catalysts has been investigated using a combined density functional theory and a high-level ab initio DLPNO methods. The oxidation states of metal, the steric position of the ligand, and the position of the methyl substituents in the pyridine rings were fully explored to unravel the key factors that trigger the switchable selectivity. The calculations support the metallacycle mechanism for ethylene tri-/tetramerization with the Cr(I)/Cr(III) catalytic cycle. Conformational analysis shows that the conformers of the metallacycloheptane and metallacyclononane intermediates are of crucial importance in understanding the selectivity of ethylene tri-/tetramerization. The out-of-plane models are responsible for ethylene trimerization and tetramerization. NBO charge analysis indicates that the lower charge at the Cr center has a positive effect on the metallacycle expansion. The steric position of the ligand and the chromacycle, and the methyl substituent in the proximal ortho or the distal para position on the aromatic rings significantly changes the energy of two key transition states for metallacycloheptane decomposition and metallacycloheptane expansion, thereby triggering the switchable selectivity between ethylene trimerization and tetramerization.