Zirconocene-Catalyzed Polymerization of α-Olefins: When Intrinsic Higher Activity Is Flawed by Rapid Deactivation
Year: 2019
Type: article
Abstract: Kinetic studies of homogeneous 1-hexene polymerization have been used for determining the propagation rates and active sites concentrations of industrially relevant zirconocene catalytic systems incorporating {SBI}- and {Cp/Flu}- ancillaries: { rac -Me 2 Si(2-Me-Benz[ e ]Ind) 2 }ZrCl 2 ( {SBI}-1 ), { rac -Me 2 Si(2-Me-4-Ph-Ind) 2 }ZrCl 2 ( {SBI}-2 ), {Me 2 C(3,6- t Bu 2 -Flu)(2-Me-4- t Bu-Cp)}ZrCl 2 ( {Cp/Flu}-1 ), {Ph(H)C(3,6- t Bu 2 -Flu)(2-Et-4- t Bu-Cp)}ZrCl 2 ( {Cp/Flu}-2 ), {Ph 2 C(2,7- t Bu 2 -Flu)(2-Me-4- t Bu-Cp)}ZrCl 2 ( {Cp/Flu}-3 ), {Ph(H)C(2,7- t Bu 2 -Flu)(2-Me-4- t Bu-Cp)}ZrCl 2 ( {Cp/Flu}-4 ). The influence of different activation parameters, such as aging time and nature of coactivator (MAO vs boraluminoxane), has been investigated. It was found that the activation efficiency of {Cp/Flu}-type precatalysts by MAO is similar (1–12% at 30 °C) to that of the {SBI}-type precatalysts (4–18%). Moreover, the propagation rates for the {Cp/Flu}-based systems appeared to be superior to those obtained with the {SBI}-type congeners. Deactivation processes, arising from monomer 2,1-misinsertions and resulting in dormant M– sec -alkyl species, were demonstrated to occur for both types of catalytic systems. While the {SBI}-type systems are capable to undergo further regular 1,2-insertions of 1-hexene into the M– sec -alkyl (or undergo regeneration of an active species through β-H elimination), the {Cp/Flu}-type congeners are apparently reluctant to further enchainement; this is proposed to account for the observed overall lower productivity of the latter {Cp/Flu}-type systems. Dormant M– sec -alkyl species with the {Cp/Flu} ancillaries can be efficiently reactivated by introduction of small molecules (H 2 or ethylene).
Source: Organometallics
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
Funder: Total
OpenAlex ID: W2954548481