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Open AccessArticle

Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates

1
Boreskov Institute of Catalysis, Russian Academy of Sciences, Siberian Branch, RU-630090 Novosibirsk, Russian
2
Novosibirsk State University, Pirogova Str. 2, 630090 Novosibirsk, Russian
3
Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, CA 91125, USA
4
Fachbereich Chemie, Universität Konstanz, D-78464 Konstanz, Germany
*
Author to whom correspondence should be addressed.
This article is dedicated to Professor Gerhard Fink on the occasion of his 80th birthday in recognition of his many fruitful contributions to the field of polymerization catalysis.
Polymers 2019, 11(6), 936; https://doi.org/10.3390/polym11060936
Received: 26 April 2019 / Revised: 22 May 2019 / Accepted: 24 May 2019 / Published: 29 May 2019
(This article belongs to the Special Issue Catalytic Polymerization)
Catalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(μ-Me)2AlMe2+ B(C6F5)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)2AlMe2+ by release of AlMe3) by repeated olefin insertions, while the other one is proposed to consist of SBIZr-η3-allyl cations of composition SBIZr-η3-(1-R-C3H4)+ (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-η3-(x-R-(3-x)-pol-C3H3)+ (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 η1- isomer, followed by repeated additional insertions, while the initially formed, less crowded allyl cations, SBIZr-η3-(1-R-C3H4)+ appear to remain unchanged. Implications of these results with regard to the kinetics of zirconocene-catalyzed olefin polymerization are discussed. View Full-Text
Keywords: polymerization catalysis; UV-vis spectroscopy; catalyst speciation; zirconocene-allyl cations; de-activation; re-activation polymerization catalysis; UV-vis spectroscopy; catalyst speciation; zirconocene-allyl cations; de-activation; re-activation
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MDPI and ACS Style

Panchenko, V.N.; Babushkin, D.E.; Bercaw, J.E.; Brintzinger, H.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 . Polymers 2019, 11, 936. https://doi.org/10.3390/polym11060936

AMA Style

Panchenko VN, Babushkin DE, Bercaw JE, Brintzinger HH. Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates . Polymers. 2019; 11(6):936. https://doi.org/10.3390/polym11060936

Chicago/Turabian Style

Panchenko, Valentina N.; Babushkin, Dmitrii E.; Bercaw, John E.; Brintzinger, Hans H. 2019. "Catalyst Speciation during ansa-Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy—Formation and Partial Re-Activation of Zr-Allyl Intermediates " Polymers 11, no. 6: 936. https://doi.org/10.3390/polym11060936

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