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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.
- Source :
-
Dalton Transactions: An International Journal of Inorganic Chemistry . 6/21/2019, Vol. 48 Issue 23, p8264-8278. 15p. - Publication Year :
- 2019
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Abstract
- Six examples of dinuclear bis(imino)pyridine-cobalt(ii) complexes, [1,5-{2-(CMe=N)-6-(CMe=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=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)]. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 14779226
- Volume :
- 48
- Issue :
- 23
- Database :
- Academic Search Index
- Journal :
- Dalton Transactions: An International Journal of Inorganic Chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 136921101
- Full Text :
- https://doi.org/10.1039/c9dt01235d