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Bis-cycloheptyl-fused bis(imino)pyridine-cobalt catalysts for PE wax formation: positive effects of fluoride substitution on catalytic performance and thermal stability

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Abstract

The α,α′-bis(imino)-2,3:5,6-bis(pentamethylene)pyridyl-cobalt(II) chlorides, [2,3:5,6-{C4H8C(N(2-R1-4-R3-6-R2C6H2))}2C5HN] CoCl2 (R1 = Me, R2 = R3 = CH(p-FPh)2 Co1; R1 = Et, R2 = R3 = CH(p-FPh)2 Co2; R1 = i-Pr, R2 = R3 = CH(p-FPh)2 Co3; R1 = Cl, R2 = R3 = CH(p-FPh)2 Co4; R1 = F, R2 = R3 = CH(p-FPh)2 Co5; R1 = F, R2 = R3 = CHPh2 Co5′′, R1 = R2 = Me, R3 = CH(p-FPh)2 Co6; R1 = R3 = Me, R2 = CH(p-FPh)2 Co7), have been synthesized by a one-pot template reaction of α,α′-dioxo-2,3:5,6-bis(pentamethylene)pyridine, cobalt(II) chloride and the respective aniline in n-butanol. By contrast, the mixed cobalt(II) chloride/acetate complex, [2,3:5,6-{C4H8C(N(2-F-4,6-(CH(p-FPh)2)2C6H2))}2C5HN]CoCl(OAc) (Co5′), was isolated when the corresponding template reaction was carried out in acetic acid. Structural characterization of Co4, Co5 and Co5′′ revealed distorted square pyramidal geometries while six-coordinate Co5′, incorporating a chelating acetate ligand, exhibited a distorted octahedral geometry. On activation with either MAO or MMAO, 2-fluoride-4,6-bis{di(p-fluorophenyl)methyl}-substituted Co5 showed maximum catalytic activity for ethylene polymerization at a high operating temperature of 60 °C (up to 2.1 × 107 g (PE) mol−1 (Co) h−1), producing highly linear (Tms > 121 °C), low molecular weight polyethylene waxes (Mw range: 1.5–5.0 kg mol−1) with narrow dispersity (Mw/Mn range: 1.7–2.9). End-group analysis of the waxes reveals β-H elimination as the dominant chain transfer process.

Graphical abstract: Bis-cycloheptyl-fused bis(imino)pyridine-cobalt catalysts for PE wax formation: positive effects of fluoride substitution on catalytic performance and thermal stability

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Supplementary files

Article information


Submitted
26 May 2020
Accepted
22 Jun 2020
First published
23 Jun 2020

Dalton Trans., 2020, Advance Article
Article type
Paper

Bis-cycloheptyl-fused bis(imino)pyridine-cobalt catalysts for PE wax formation: positive effects of fluoride substitution on catalytic performance and thermal stability

Q. Zhang, N. Wu, J. Xiang, G. A. Solan, H. Suo, Y. Ma, T. Liang and W. Sun, Dalton Trans., 2020, Advance Article , DOI: 10.1039/D0DT01876G

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