Catalyst Speciation during <i>ansa</i>-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates <xref rid="fn1-polymers-503797" ref-type="fn">†</xref>
Catalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(μ-Me)<sub>2</sub>AlMe<sub>2</sub><sup>+</sup> B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub><sup>&am...
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doaj-0594421cfc3845238b7ffbabf890a32d2020-11-24T21:27:42ZengMDPI AGPolymers2073-43602019-05-0111693610.3390/polym11060936polym11060936Catalyst Speciation during <i>ansa</i>-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates <xref rid="fn1-polymers-503797" ref-type="fn">†</xref>Valentina N. Panchenko0Dmitrii E. Babushkin1John E. Bercaw2Hans H. Brintzinger3Boreskov Institute of Catalysis, Russian Academy of Sciences, Siberian Branch, RU-630090 Novosibirsk, RussianBoreskov Institute of Catalysis, Russian Academy of Sciences, Siberian Branch, RU-630090 Novosibirsk, RussianArnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, CA 91125, USAFachbereich Chemie, Universität Konstanz, D-78464 Konstanz, GermanyCatalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(μ-Me)<sub>2</sub>AlMe<sub>2</sub><sup>+</sup> B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub><sup>−</sup> (SBI = <i>rac</i>-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<sup>+</sup> (formed from SBIZr(μ-Me)<sub>2</sub>AlMe<sub>2</sub><sup>+</sup> by release of AlMe<sub>3</sub>) by repeated olefin insertions, while the other one is proposed to consist of SBIZr-η<sup>3</sup>-allyl cations of composition SBIZr-η<sup>3</sup>-(1-R-C<sub>3</sub>H<sub>4</sub>)<sup>+</sup> (R = n-propyl), formed by σ-bond metathesis between SBIZr-Me<sup>+</sup> 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<sup>3</sup>-(x-R-(3-x)-pol-C<sub>3</sub>H<sub>3</sub>)<sup>+</sup> (pol = <i>i</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<sup>1</sup>- isomer, followed by repeated additional insertions, while the initially formed, less crowded allyl cations, SBIZr-η<sup>3</sup>-(1-R-C<sub>3</sub>H<sub>4</sub>)<sup>+</sup> appear to remain unchanged. Implications of these results with regard to the kinetics of zirconocene-catalyzed olefin polymerization are discussed.https://www.mdpi.com/2073-4360/11/6/936polymerization catalysisUV-vis spectroscopycatalyst speciationzirconocene-allyl cationsde-activationre-activation |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Valentina N. Panchenko Dmitrii E. Babushkin John E. Bercaw Hans H. Brintzinger |
spellingShingle |
Valentina N. Panchenko Dmitrii E. Babushkin John E. Bercaw Hans H. Brintzinger Catalyst Speciation during <i>ansa</i>-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates <xref rid="fn1-polymers-503797" ref-type="fn">†</xref> Polymers polymerization catalysis UV-vis spectroscopy catalyst speciation zirconocene-allyl cations de-activation re-activation |
author_facet |
Valentina N. Panchenko Dmitrii E. Babushkin John E. Bercaw Hans H. Brintzinger |
author_sort |
Valentina N. Panchenko |
title |
Catalyst Speciation during <i>ansa</i>-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates <xref rid="fn1-polymers-503797" ref-type="fn">†</xref> |
title_short |
Catalyst Speciation during <i>ansa</i>-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates <xref rid="fn1-polymers-503797" ref-type="fn">†</xref> |
title_full |
Catalyst Speciation during <i>ansa</i>-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates <xref rid="fn1-polymers-503797" ref-type="fn">†</xref> |
title_fullStr |
Catalyst Speciation during <i>ansa</i>-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates <xref rid="fn1-polymers-503797" ref-type="fn">†</xref> |
title_full_unstemmed |
Catalyst Speciation during <i>ansa</i>-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates <xref rid="fn1-polymers-503797" ref-type="fn">†</xref> |
title_sort |
catalyst speciation during <i>ansa</i>-zirconocene-catalyzed polymerization of 1-hexene studied by uv-vis spectroscopy—formation and partial re-activation of zr-allyl intermediates <xref rid="fn1-polymers-503797" ref-type="fn">†</xref> |
publisher |
MDPI AG |
series |
Polymers |
issn |
2073-4360 |
publishDate |
2019-05-01 |
description |
Catalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(μ-Me)<sub>2</sub>AlMe<sub>2</sub><sup>+</sup> B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub><sup>−</sup> (SBI = <i>rac</i>-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<sup>+</sup> (formed from SBIZr(μ-Me)<sub>2</sub>AlMe<sub>2</sub><sup>+</sup> by release of AlMe<sub>3</sub>) by repeated olefin insertions, while the other one is proposed to consist of SBIZr-η<sup>3</sup>-allyl cations of composition SBIZr-η<sup>3</sup>-(1-R-C<sub>3</sub>H<sub>4</sub>)<sup>+</sup> (R = n-propyl), formed by σ-bond metathesis between SBIZr-Me<sup>+</sup> 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<sup>3</sup>-(x-R-(3-x)-pol-C<sub>3</sub>H<sub>3</sub>)<sup>+</sup> (pol = <i>i</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<sup>1</sup>- isomer, followed by repeated additional insertions, while the initially formed, less crowded allyl cations, SBIZr-η<sup>3</sup>-(1-R-C<sub>3</sub>H<sub>4</sub>)<sup>+</sup> appear to remain unchanged. Implications of these results with regard to the kinetics of zirconocene-catalyzed olefin polymerization are discussed. |
topic |
polymerization catalysis UV-vis spectroscopy catalyst speciation zirconocene-allyl cations de-activation re-activation |
url |
https://www.mdpi.com/2073-4360/11/6/936 |
work_keys_str_mv |
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