文献类型：期刊文献

英文题名：Unraveling the Effects of H2, N Substituents and Secondary Ligands on Cr/PNP-Catalyzed Ethylene Selective Oligomerization

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

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

年份：2018

卷号：37

期号：21

起止页码：3893

外文期刊名：ORGANOMETALLICS

收录：;EI(收录号：20184105918003);WOS:【SCI-EXPANDED(收录号:WOS:000450374500028)】；

基金：This work was sponsored by the 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. The authors also thank the China Scholarship Council and the National Natural Science Foundation of China (No. 21174037, No. 21304033).

语种：英文

外文关键词：Oligomerization - Gibbs free energy - Chromium - Free energy - Ligands - Catalyst activity - Catalyst selectivity - Oligomers

摘要：The mechanism of ethylene oligomerization catalyzed by Cr/PNP catalysts has been investigated using combined experimental and theoretical methodologies. The effects of hydrogen, N substituents, and secondary ligands were fully explored in order to tune the catalyst with better selectivity and activity. Our DFT calculations revealed that the associating/dissociating interactions of the hydrogen with the chromium center might be a key factor in promoting the activity of the Cr/PNP/H-2 system, the N substituents show an apparent effect on the energy gap between two adjacent spin states (quartet and sextet) of the bis(ethylene)chromium adducts, which mostly leads to a change in the activation barrier in the reaction of oxidation coupling with a two-state reactivity, and the coordination of secondary ligands (phenyl butyl ether and ethyl benzoate) increases the hindrance of the chromium center, resulting in a shift of the rate-limiting step from the oxidative coupling of two coordinated ethylene molecules to metallacycle growth by insertion of a third coordinated ethylene. The turnover frequencies (TOFs) were computed using the energetic span model (ESM) on the basis of the Gibbs free energy profiles. The steric effects of the secondary ligands as well as the N substituents were evaluated using the Sambvca 2.0 software developed by Cavallo et al.