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1,5-Naphthyl-linked bis(imino)pyridines as binucleating scaffolds for dicobalt ethylene oligo-/polymerization catalysts: exploring temperature and steric effects.

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journal contribution
posted on 2019-05-31, 10:00 authored by Q Chen, H Suo, W Zhang, R Zhang, GA Solan, T Liang, W-H Sun
Six examples of dinuclear bis(imino)pyridine-cobalt(ii) complexes, [1,5-{2-(CMe[double bond, length as m-dash]N)-6-(CMe[double bond, length as m-dash]N(2,6-R12-4-R2-C6H2))C5H3N}2(C10H6)]Co2Cl4 (R1 = Me, R2 = H Co1; R1 = Et, R2 = H Co2; R1 = iPr, R2 = H Co3; R1 = Me, R2 = Me Co4; R1 = Et, R2 = Me Co5; R1 = CHPh2, R2 = Me Co6), have been prepared from the corresponding bis(tridentate) compartmental ligands (L1-L6) in reasonable yields. The molecular structures of Co3 and Co5 revealed two N,N,N-cobalt dichloride units to adopt anti-positions about the 1,5-naphthyl linking unit, with each cobalt center exhibiting a distorted trigonal bipyramidal geometry. On activation with either MAO or MMAO, Co1-Co6 were shown to promote both polymerization and oligomerization of ethylene with high overall activities (up to 1.03 × 107 gPE per·mol(Co) per·h for Co1/MAO at 70 °C). Curiously, on increasing the reaction temperature a larger proportion of polymer was noted, while at lower temperature an enhanced selectivity for oligomer was seen. In general, the oligomeric products displayed Schulz-Flory distributions with high selectivities for α-olefins (>99%). On the other hand, the highly linear polymers displayed narrow dispersities and comprised both fully saturated and unsaturated chain ends with the vinyl content (-CH[double bond, length as m-dash]CH2) found to rise with the reaction temperature. By modulating the steric hindrance exerted by the ortho-R1 substituents in the precatalyst, polyethylenes displaying a remarkably broad range of molecular weights could be obtained [from 4.52 kg mol-1 (R1 = Me) to 246.7 kg mol-1 (R1 = CHPh2)].

Funding

This work was supported by the National Natural Science Foundation of China (51473170 and 21871275). GAS thanks the Chinese Academy of Sciences for a President's International Fellowship for Visiting Scientists.

History

Citation

Dalton Transactions, 2019

Author affiliation

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

Version

AM (Accepted Manuscript)

Published in

Dalton Transactions

Publisher

Royal Society of Chemistry

eissn

1477-9234

Acceptance date

2019-05-07

Copyright date

2019

Publisher version

https://pubs.rsc.org/en/content/articlelanding/2019/DT/C9DT01235D#!divAbstract

Notes

Electronic supplementary information (ESI) available. CCDC 1902895 for L2, 1902896 for Co3, and 1902897 for Co5. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c9dt01235d;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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