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Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates †
Catalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(μ-Me)(2)AlMe(2)(+) B(C(6)F(5))(4)(−) (SBI = rac-dimethylsilyl-bis(1-indenyl)) at 23 °C is studied by following the accompanying UV-vis-spectral changes. These indicate that the onset...
Autores principales: | , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
MDPI
2019
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6630943/ https://www.ncbi.nlm.nih.gov/pubmed/31146475 http://dx.doi.org/10.3390/polym11060936 |
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author | Panchenko, Valentina N. Babushkin, Dmitrii E. Bercaw, John E. Brintzinger, Hans H. |
author_facet | Panchenko, Valentina N. Babushkin, Dmitrii E. Bercaw, John E. Brintzinger, Hans H. |
author_sort | Panchenko, Valentina N. |
collection | PubMed |
description | Catalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(μ-Me)(2)AlMe(2)(+) B(C(6)F(5))(4)(−) (SBI = rac-dimethylsilyl-bis(1-indenyl)) at 23 °C is studied by following the accompanying UV-vis-spectral changes. These indicate that the onset of polymerization catalysis is associated with the concurrent formation of two distinct zirconocene species. One of these is proposed to consist of SBIZr-σ-polyhexenyl cations arising from SBIZr-Me(+) (formed from SBIZr(μ-Me)(2)AlMe(2)(+) by release of AlMe(3)) by repeated olefin insertions, while the other one is proposed to consist of SBIZr-η(3)-allyl cations of composition SBIZr-η(3)-(1-R-C(3)H(4))(+) (R = n-propyl), formed by σ-bond metathesis between SBIZr-Me(+) and 1-hexene under release of methane. At later reaction stages, all zirconocene-σ–polymeryl cations appear to decay to yet another SBIZr-allyl species, i.e., to cations of the type SBIZr-η(3)-(x-R-(3-x)-pol-C(3)H(3))(+) (pol = i-polyhexenyl, x = 1 or 2). Renewed addition of excess 1-hexene is proposed to convert these sterically encumbered Zr-allyl cations back to catalytically active SBIZr-σ–polymeryl cations within a few seconds, presumably by initial 1-hexene insertion into the η(1)- isomer, followed by repeated additional insertions, while the initially formed, less crowded allyl cations, SBIZr-η(3)-(1-R-C(3)H(4))(+) appear to remain unchanged. Implications of these results with regard to the kinetics of zirconocene-catalyzed olefin polymerization are discussed. |
format | Online Article Text |
id | pubmed-6630943 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2019 |
publisher | MDPI |
record_format | MEDLINE/PubMed |
spelling | pubmed-66309432019-08-19 Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates † Panchenko, Valentina N. Babushkin, Dmitrii E. Bercaw, John E. Brintzinger, Hans H. Polymers (Basel) Article Catalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(μ-Me)(2)AlMe(2)(+) B(C(6)F(5))(4)(−) (SBI = rac-dimethylsilyl-bis(1-indenyl)) at 23 °C is studied by following the accompanying UV-vis-spectral changes. These indicate that the onset of polymerization catalysis is associated with the concurrent formation of two distinct zirconocene species. One of these is proposed to consist of SBIZr-σ-polyhexenyl cations arising from SBIZr-Me(+) (formed from SBIZr(μ-Me)(2)AlMe(2)(+) by release of AlMe(3)) by repeated olefin insertions, while the other one is proposed to consist of SBIZr-η(3)-allyl cations of composition SBIZr-η(3)-(1-R-C(3)H(4))(+) (R = n-propyl), formed by σ-bond metathesis between SBIZr-Me(+) and 1-hexene under release of methane. At later reaction stages, all zirconocene-σ–polymeryl cations appear to decay to yet another SBIZr-allyl species, i.e., to cations of the type SBIZr-η(3)-(x-R-(3-x)-pol-C(3)H(3))(+) (pol = i-polyhexenyl, x = 1 or 2). Renewed addition of excess 1-hexene is proposed to convert these sterically encumbered Zr-allyl cations back to catalytically active SBIZr-σ–polymeryl cations within a few seconds, presumably by initial 1-hexene insertion into the η(1)- isomer, followed by repeated additional insertions, while the initially formed, less crowded allyl cations, SBIZr-η(3)-(1-R-C(3)H(4))(+) appear to remain unchanged. Implications of these results with regard to the kinetics of zirconocene-catalyzed olefin polymerization are discussed. MDPI 2019-05-29 /pmc/articles/PMC6630943/ /pubmed/31146475 http://dx.doi.org/10.3390/polym11060936 Text en © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). |
spellingShingle | Article Panchenko, Valentina N. Babushkin, Dmitrii E. Bercaw, John E. Brintzinger, Hans H. Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates † |
title | Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates † |
title_full | Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates † |
title_fullStr | Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates † |
title_full_unstemmed | Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates † |
title_short | Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates † |
title_sort | catalyst speciation during ansa-zirconocene-catalyzed polymerization of 1-hexene studied by uv-vis spectroscopy—formation and partial re-activation of zr-allyl intermediates † |
topic | Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6630943/ https://www.ncbi.nlm.nih.gov/pubmed/31146475 http://dx.doi.org/10.3390/polym11060936 |
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