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Highly branched unsaturated polyethylenes achievable using strained imino-cyclopenta[b]pyridyl-nickel precatalysts

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journal contribution
posted on 23.03.2017, 15:52 by Youfu Zhang, Chuanbing Huang, Xinxin Wang, Qaiser Mahmood, Xiang Hao, Xinquan Hu, Cun-Yue Guo, Gregory A. Solan, Wen-Hua Sun
A new family of strained imino-cyclopenta[b]pyridines, 7-(ArN)-6-Me2C8H5N (Ar = 2,6-Me2Ph (L1), 2,6-Et2Ph (L2), 2,4,6-Me3Ph (L3), 2,6-Et2-4-MePh (L4), 2,6-i-Pr2Ph (L5)), have been synthesized in reasonable yield by a sequence of reactions from 2-chloro-cyclopenta[b]pyridin-7-one. Treatment of L1 and L3 with NiCl2·6H2O generates mononuclear bis-ligated [7-(ArN)-6-Me2C8H5N]2NiCl2 (Ar = 2,6-Me2Ph (Ni1), 2,4,6-Me3Ph (Ni3)), while with L2 and L4, the chloride-bridged binuclear complexes [7-(ArN)-6-Me2C8H5N]2Ni2(μ-Cl)2Cl2 (Ar = 2,6-Et2Ph (Ni2), 2,6-Et2-4-MePh (Ni4)), have been isolated; no apparent reaction occurred with L5. On activation with either MAO or MMAO, Ni1-Ni4 exhibited high activities towards ethylene polymerization with Ni3 the most active (5.02 × 106 g PE per mol Ni per h at 20 °C); rapid regeneration of the active species (3096-5478 h-1 at 20 °C) is a feature of their catalytic performance. A detailed microstructural analysis of the polyethylenes reveals the presence of vinyl and higher levels of internal vinylene groups indicative of high rates of chain isomerization, e.g., the ratio of (-CHCH-) to (H2CCH-) groups is 2.2 : 1 using Ni3/MAO at 60 °C. Agostic interactions involving γ-, δ- and higher-hydrogens are inferred in addition to β-hydrogen elimination to account for the vinylene groups and the longer chain alkyl branches. The molecular structures of Ni1 and Ni2·2MeOH are also reported.

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Citation

Polymer Chemistry, 2017, 8 (6), pp. 995-1005

Author affiliation

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

Version

AM (Accepted Manuscript)

Published in

Polymer Chemistry

Publisher

Royal Society of Chemistry

issn

1759-9954

eissn

1759-9962

Acceptance date

16/01/2017

Copyright date

2017

Available date

16/01/2018

Publisher version

http://pubs.rsc.org/en/Content/ArticleLanding/2017/PY/C6PY02089E#!divAbstract

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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