文献类型：期刊文献

英文题名：Spin Surface Crossing between Chromium(I)/Sextet and Chromium(III)/Quartet without Deprotonation in SNS-Cr Mediated Ethylene Trimerization

作者：Yang, Yun[1];Liu, Zhen[1];Zhong, Lei[1];Qiu, Pengyuan[1];Dong, Qi[1];Cheng, Ruihua[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：2011

卷号：30

期号：19

起止页码：5297

外文期刊名：ORGANOMETALLICS

收录：;EI(收录号：20114114410605);WOS:【SCI-EXPANDED(收录号:WOS:000295347600028)】；

基金：We thank the financial support of the National Natural Science Foundation of China (21004020) and Westlake Chemical Corp. This work was also financially supported by the Research Program of the State Key Laboratory of Chemical Engineering, the Program of Introducing Talents of Discipline to Universities (B08021), and the Fundamental Research Funds for the Central Universities.

语种：英文

外文关键词：Ethylene - Redox reactions - Free energy - Gibbs free energy - Density functional theory - Activation energy - Chromium compounds - Ground state

摘要：Experimentally unsolved problems, including the oxidation states of active species and the occurrence of ligand deprotonation in the SNS-Cr ethylene trimerization system, were studied using the density functional theory (DFT) method. The full catalytic cycle was calculated on the basis of the metallacycle mechanism, and Gibbs free energy surfaces of the trimerization reaction were completely located. A detailed spin state analysis revealed that the ground states of intermediates change along the redox cycle and the spin surface crossing occurring at the minimum energy crossing point (MECP) before metallacyclopentane formation was found to open up a much lower energy pathway by spin acceleration. Formation of metallacycloheptane was identified as the rate-determining step in this system. By comparison of the activation energies of the rate-determining step, Cr(I)/Cr(III) active species bearing nondeprotonated ligands were proposed to be most plausibly responsible for ethylene trimerization. Frontier orbitals and natural population analysis were also determined to further elucidate the reason for high 1-hexene selectivity in this system.