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Bis(imino)pyridines fused with 6- and 7-membered carbocylic rings as N,N,N-scaffolds for cobalt ethylene polymerization catalysts

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journal contribution
posted on 22.03.2019, 10:51 by Z Wang, Y Ma, J Guo, Q Liu, GA Solan, T Liang, W-H Sun
The unsymmetrical diketone, 1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-dione, based on a central pyridine unit fused by both 6- and 7-membered rings, has been synthesized via a sequence of reactions including ruthenium-catalyzed coupling cyclization. Templating this diketone with a mixture of cobalt(ii) chloride hexahydrate and the corresponding aniline in acetic acid at reflux afforded five examples of carbocyclic-fused bis(arylimino)pyridine-cobalt(ii) chlorides (aryl = 2,6-Me2Ph Co1, 2,6-Et2Ph Co2, 2,6-i-Pr2Ph Co3, 2,4,6-Me3Ph Co4, 4-Me-2,6-Et2Ph Co5) in good yield. All cobalt complexes have been fully characterized including by 1H NMR spectroscopy which reveals broad but assignable paramagnetically shifted peaks. The molecular structures of Co1, Co3 and Co4 highlight the inequivalency of the two fused rings with the cobalt center adopting a distorted trigonal bipyramidal geometry. Treatment of Co1-Co5 with MAO gave highly active catalysts (up to 5.03 × 106 g PE mol-1 (Co) h-1 at 40 °C, with Co4 > Co5 > Co1 > Co2 > Co3) for ethylene polymerization generating strictly linear vinyl-terminated polymers with low molecular weights (Mw range: 1.53-22.77 kg mol-1). By comparison, polymerizations conducted using Co1-Co5/MMAO were less active and displayed a lower selectivity for unsaturated polymers. Common to both MAO and MMAO, the most sterically hindered precatalyst Co3 gave the highest molecular weight polymer of the series (up to 22.77 kg mol-1) but exhibited the lowest activity.

Funding

This work was supported by the National Natural Science Foundation of China (No. 21871275 and 51861145303) and UCAS Joint PhD Training Program (UCAS[2017]16).

History

Citation

Dalton Trans, 2019, 48, pp. 2582-2591

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Chemistry

Version

AM (Accepted Manuscript)

Published in

Dalton Trans

Publisher

Royal Society of Chemistry

eissn

1477-9234

Acceptance date

10/01/2019

Copyright date

2019

Publisher version

https://pubs.rsc.org/en/Content/ArticleLanding/2019/DT/C8DT04892D#

Notes

The file associated with this record is under embargo until 12 months after publication, in accordance with the publisher's self-archiving policy. The full text may be available through the publisher links provided above.

Language

en

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