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Polyethylene Waxes with Short Chain Branching via Steric and Electronic Tuning of an 8-(Arylimino)-5,6,7-trihydroquinoline-nickel Catalyst

journal contribution
posted on 21.06.2022, 10:31 authored by S Jiang, Y Zheng, M Liu, Z Yu, Y Ma, GA Solan, W Zhang, T Liang, WH Sun
Ten examples of nickel(II) halide complexes [8-{N(2,4-(C15H13)2-6-RC6H2N)}C9H8N]NiBr2 [R = Me (Ni1), Et (Ni2), iPr (Ni3), Cl (Ni4), or F (Ni5)] and [8-{N(2,4-(C15H13)2-6-RC6H2N)}C9H8N]NiCl2 [R = Me (Ni6), Et (Ni7), iPr (Ni8), Cl (Ni9), or F (Ni10)], each incorporating a sterically encumbered N,N-chelating 8-[2,4-bis(dibenzocycloheptyl)-6-R-phenylimino]-5,6,7-trihydroquinoline ligand, are disclosed. Full details for the preparation of these complexes as well as the zinc-mediated synthesis of precursor ligands L1-L5 are given. Structural characterization of Ni3(H2O), Ni6, Ni7(H2O), and Ni8(H2O) reveals halide-bridged dinuclear structures of the type (N,N)NiX(μ-X)2NiX(N,N) with the ortho-substituted dibenzocycloheptyl groups providing steric protection to each metal center. In the presence of ethylaluminum dichloride (EtAlCl2) or methylaluminoxane (MAO), Ni1-Ni10 displayed high activities for ethylene polymerization [≤6.17 × 106 g of PE (mol of Ni)-1 h-1 for Ni6/EtAlCl2 at 20 °C], generating low-molecular weight polyethylene waxes. Notably, catalysts incorporating a 6-alkyl group (Me, Et, or iPr) as the N-aryl substituent proved to be more active than their 6-halide (Cl or F) counterparts and formed relatively higher-molecular weight polymers (Mw range of 9.1-22.9 kg mol-1) with a narrow dispersity. Moreover, analysis of these waxes by 13C nuclear magnetic resonance spectroscopy showed that they typically possessed short chain branching (>83% methyl) with branching densities of 79-90 branches per 1000 Cs. In addition, chain end analysis revealed the presence of both vinyl (-CH=H2) and internal vinylene (-CH=H-) functional groups, highlighting the role of both β-H elimination and isomerization.

History

Citation

Organometallics, 2022, https://doi.org/10.1021/acs.organomet.2c00100

Author affiliation

Department of Chemistry, University of Leicester

Version

AM (Accepted Manuscript)

Published in

Organometallics

Publisher

American Chemical Society (ACS)

issn

0276-7333

eissn

1520-6041

Acceptance date

25/02/2022

Copyright date

2022

Available date

25/04/2023

Language

en