Issue 2, 2021

Fluorinated cobalt catalysts and their use in forming narrowly dispersed polyethylene waxes of high linearity and incorporating vinyl functionality

Abstract

A family of six bis(arylimino)pyridine-cobalt(II) chloride complexes, [2-{CMeN(2-F-4,6-((4-FC6H4)2CH)2C6H2)}-6-(CMeNAr)C5H3N]CoCl2 (Ar = 2,6-Me2C6H3Co1, 2,6-Et2C6H3Co2, 2,6-i-Pr2C6H3Co3, 2,4,6-Me3C6H2Co4, 2,6-Et-4-MeC6H2Co5) and [2-[CMeN{2-{(4-FC6H4)2CH}-4-{CH(C6H5)ArF}-6-F}]-6-(CMeN(2,6-i-Pr2C6H3))C5H3N]CoCl2 (ArF = (3-(4-FC6H4)2CH-4-NH2-5-F)C6H2) (Co6), each incorporating one ortho-fluoride and one ortho-bis(4-fluorophenyl)methyl group, has been synthesized in good yield from the corresponding unsymmetrical N,N,N′-ligands, L1–L6. All complexes have been well characterized including by 19F NMR spectroscopy; a variable temperature 19F NMR study has also been performed on Co6 to investigate a dynamic isomerization process. The molecular structures of Co1 and Co5 emphasize the variation in steric protection of the metal center imparted by the inequivalent N-aryl groups. In the presence of methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), Co1–Co5 exhibited high activities of up to 11.7 × 106 g of polyethylene (PE) (mol of Co)−1 h−1 at 70 °C, delivering strictly linear, low molecular weight PE waxes (between 924 and 5550 g mol−1) of narrow dispersity and terminated with vinyl functionality. By comparison, Co6, possessing a more extended fluorinated para-CH(C6H5)ArF group, was the least active but afforded the highest molecular weight polyethylene (up to 10 027 mol−1). In addition, DFT studies of the model Co(I)-propyl species, Co1′, Co3′ and Co6′, have been performed in an attempt to explain the favorable formation of the low molecular weight polymers.

Graphical abstract: Fluorinated cobalt catalysts and their use in forming narrowly dispersed polyethylene waxes of high linearity and incorporating vinyl functionality

Supplementary files

Article information

Article type
Paper
Submitted
30 Sep 2020
Accepted
09 Nov 2020
First published
10 Nov 2020

Catal. Sci. Technol., 2021,11, 656-670

Fluorinated cobalt catalysts and their use in forming narrowly dispersed polyethylene waxes of high linearity and incorporating vinyl functionality

Q. Zhang, Z. Li, M. Han, J. Xiang, G. A. Solan, Y. Ma, T. Liang and W. Sun, Catal. Sci. Technol., 2021, 11, 656 DOI: 10.1039/D0CY01917H

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