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Co‐catalyst effects on the thermal stability/activity of N,N,N ‐Co ethylene polymerization Catalysts Bearing Fluoro‐Substituted N‐2,6‐dibenzhydrylphenyl groups
Author(s) -
Zhang Qiuyue,
Ma Yanping,
Suo Hongyi,
Solan Gregory A.,
Liang Tongling,
Sun WenHua
Publication year - 2019
Publication title -
applied organometallic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 71
eISSN - 1099-0739
pISSN - 0268-2605
DOI - 10.1002/aoc.5134
Subject(s) - chemistry , catalysis , aryl , cobalt , steric effects , ethylene , polymerization , thermal stability , medicinal chemistry , polymer chemistry , stereochemistry , organic chemistry , alkyl , polymer
The unsymmetrical bis (arylimino)pyridines, 2‐[CMeN{2,6‐{(4‐FC 6 H 4 ) 2 CH} 2 –4‐ t ‐BuC 6 H 2 }]‐6‐(CMeNAr)C 5 H 3 N (Ar = 2,6‐Me 2 C 6 H 3 L1 , 2,6‐Et 2 C 6 H 3 L2 , 2,6‐ i ‐Pr 2 C 6 H 3 L3 , 2,4,6‐Me 3 C 6 H 2 L4 , 2,6‐Et 2 –4‐MeC 6 H 2 L5 ), each containing one N‐aryl group bedecked with ortho ‐substituted fluorobenzhydryl groups, have been employed in the preparation of the corresponding five‐coordinate cobalt (II) chelates, LCoCl 2 ( Co1 – Co5 ); the symmetrical comparator [2,6‐{CMeN(2,6‐(4‐FC 6 H 4 ) 2 CH) 2 –4‐ t ‐BuC 6 H 2 } 2 C 5 H 3 N]CoCl 2 (Co6) is also reported. All cobaltous complexes are paramagnetic and have been characterized by 1 H/ 19 F NMR spectroscopy, FT‐IR spectroscopy and elemental analysis. The molecular structures of Co3 and Co6 highlight the different degrees of steric protection given to the metal center by the particular N‐aryl group combination. Depending on the aluminoxane co‐catalyst employed to activate the cobalt precatalyst, distinct variations in thermal stability and activity of the catalyst towards ethylene polymerization were exhibited. In particular with MAO, the resultant catalysts reached their optimal performance at 70 °C delivering high activities of up to 10.1 × 10 6 g PE (mol of Co) −1 h −1 with Co1 > Co4 > Co2 > Co5 > Co3 >> Co6 . On the other hand, using MMAO, the catalysts operate most effectively at 30 °C but are by comparison less productive. In general, the polyethylenes were highly linear, narrowly disperse and displayed a wide range of molecular weights [ M w range: 18.5–58.7 kg mol −1 (MAO); 206.1–352.5 kg mol −1 (MMAO)].