Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups
Half-titanocenes are well known to show high activity for ethylene polymerization and good capability for copolymerization of ethylene with other olefins, and the ancillary ligands can crucially affect the catalytic performance. In this paper, the mechanisms of ethylene polymerization catalyzed by t...
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MDPI AG
2021-11-01
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| author | Yang Li Xiaoling Lai Xiaowei Xu Yat-Ming So Yijing Du Zhengze Zhang Yu Pan |
| author_facet | Yang Li Xiaoling Lai Xiaowei Xu Yat-Ming So Yijing Du Zhengze Zhang Yu Pan |
| author_sort | Yang Li |
| collection | DOAJ |
| description | Half-titanocenes are well known to show high activity for ethylene polymerization and good capability for copolymerization of ethylene with other olefins, and the ancillary ligands can crucially affect the catalytic performance. In this paper, the mechanisms of ethylene polymerization catalyzed by three half-metallocenes, (<i>η</i><sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)TiCl<sub>2</sub>(O-2,6-<i><sup>i</sup></i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) (<b>1</b>), (<i>η</i><sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)TiCl<sub>2</sub>(N=C<i><sup>t</sup></i>Bu<sub>2</sub>) (<b>2</b>) and [Me<sub>2</sub>Si(<i>η</i><sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>)(N<i><sup>t</sup></i>Bu)]TiCl<sub>2</sub> (<b>3</b>), have been investigated by density functional theory (DFT) method. At the initiation stage, a higher free energy barrier was determined for complex <b>1</b>, probably due to the presence of electronegative O atom in phenoxy ligand. At the propagation stage, front-side insertion of the second ethylene is kinetically more favorable than back-side insertion for complexes <b>1</b> and <b>2</b>, while both side insertion orientations are comparable for complex <b>3</b>. The energy decomposition showed that the bridged cyclopentadienyl amide ligand could enhance the rigidity of the active species as suggested by the lowest deformation energy derived from <b>3</b>. At the chain termination stage, <i>β-</i>H transfer was calculated to be a dominant chain termination route over <i>β</i>-H elimination, presumably owing to the thermodynamic perspective. |
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| spelling | doaj.art-3b67e17cfd284e26b4056b70b8af021a2023-11-22T22:46:33ZengMDPI AGCatalysts2073-43442021-11-011111139210.3390/catal11111392Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary GroupsYang Li0Xiaoling Lai1Xiaowei Xu2Yat-Ming So3Yijing Du4Zhengze Zhang5Yu Pan6School of Chemical Engineering, Dalian University of Technology, Panjin 124221, ChinaSchool of Chemical Engineering, Dalian University of Technology, Panjin 124221, ChinaSchool of Chemical Engineering, Dalian University of Technology, Panjin 124221, ChinaDepartment of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, ChinaSchool of Chemical Engineering, Dalian University of Technology, Panjin 124221, ChinaSchool of Chemical Engineering, Dalian University of Technology, Panjin 124221, ChinaSchool of Chemical Engineering, Dalian University of Technology, Panjin 124221, ChinaHalf-titanocenes are well known to show high activity for ethylene polymerization and good capability for copolymerization of ethylene with other olefins, and the ancillary ligands can crucially affect the catalytic performance. In this paper, the mechanisms of ethylene polymerization catalyzed by three half-metallocenes, (<i>η</i><sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)TiCl<sub>2</sub>(O-2,6-<i><sup>i</sup></i>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) (<b>1</b>), (<i>η</i><sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)TiCl<sub>2</sub>(N=C<i><sup>t</sup></i>Bu<sub>2</sub>) (<b>2</b>) and [Me<sub>2</sub>Si(<i>η</i><sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>)(N<i><sup>t</sup></i>Bu)]TiCl<sub>2</sub> (<b>3</b>), have been investigated by density functional theory (DFT) method. At the initiation stage, a higher free energy barrier was determined for complex <b>1</b>, probably due to the presence of electronegative O atom in phenoxy ligand. At the propagation stage, front-side insertion of the second ethylene is kinetically more favorable than back-side insertion for complexes <b>1</b> and <b>2</b>, while both side insertion orientations are comparable for complex <b>3</b>. The energy decomposition showed that the bridged cyclopentadienyl amide ligand could enhance the rigidity of the active species as suggested by the lowest deformation energy derived from <b>3</b>. At the chain termination stage, <i>β-</i>H transfer was calculated to be a dominant chain termination route over <i>β</i>-H elimination, presumably owing to the thermodynamic perspective.https://www.mdpi.com/2073-4344/11/11/1392ethylene polymerizationDFThalf-titanocenereaction mechanism |
| spellingShingle | Yang Li Xiaoling Lai Xiaowei Xu Yat-Ming So Yijing Du Zhengze Zhang Yu Pan Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups Catalysts ethylene polymerization DFT half-titanocene reaction mechanism |
| title | Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups |
| title_full | Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups |
| title_fullStr | Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups |
| title_full_unstemmed | Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups |
| title_short | Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups |
| title_sort | theoretical study on ethylene polymerization catalyzed by half titanocenes bearing different ancillary groups |
| topic | ethylene polymerization DFT half-titanocene reaction mechanism |
| url | https://www.mdpi.com/2073-4344/11/11/1392 |
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