Synthesis, characterization and catalytic behavior toward ethylene of 2-[1-(4,6-dimethyl-2-benzhydrylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridylmetal (iron or cobalt) chlorides

Abstract

A series of 2-[1-(4,6-dimethyl-2-benzhydrylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridines was synthesized and used to prepare the iron(II) and cobalt(II) chloride complexes thereof. All organic compounds were fully characterized by elemental analysis, IR and NMR ((1)H/(13)C) spectroscopy, whilst the metal complexes were characterized by elemental analysis and IR spectroscopy as well as by single-crystal X-ray diffraction studies (for two representative cobalt complexes), which revealed that the geometry at the metal was either pseudo-square-pyramidal or trigonal bipyramidal. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all metal complex pre-catalysts exhibited high activities for ethylene polymerization. The iron pre-catalysts show much higher activity than did their cobalt analogues; however, the iron catalytic systems generally produced polyethylene of wide molecular weight polydispersity. At elevated reaction temperature, the polyethylene was of lower molecular weight, but revealed narrow polydispersity.

Correlating net charges and the activity of bis(imino)pyridylcobalt complexes in ethylene polymerization

“…However, there is rarely reported of the study on cobalt complex system. In this regard, this study considers the cobalt complex pre-catalysts, which was recently reported with high catalytic activities with good thermo-stability [22]. Two spin states of cobalt atoms have been considered to get the effective net charge through QEq method as well as Hirshfeld and Mulliken charge approaches for comparison.…”

Quantitative Structure-Thermostability Relationship of Late Transition Metal Catalysts in Ethylene Oligo/Polymerization

“…Three structural parameters were defined and calculated to correlate with the thermal stability for four series of typical late transition metal complexes from our previous reports [30][31][32][33][34][35][36][44][45][46][47]. The results showed that a catalyst's thermal stability has very good relationships with three structural parameters by using multiple linear regression analysis (MLRA).…”

“…In addition, our group reported the nickel complex catalysts containing acenaphthylene ligands (Scheme 1, E), which showed high catalytic activities (10 6 g·mol −1 (Ni)·h −1 ) and high molecular weight of the produced polyethylene (10 6 g·mol −1 ) at temperature of 80 °C [30]. In addition, the iron-based complex catalysts bearing bis(imino)pyridine ligands with bulky substituents (Scheme 1, F) exhibited good thermal stability with catalytic activities of 10 6 g·mol −1 (Fe)·h −1 at 60-80 °C [31][32][33][34][35][36][37].…”

“…In this section, the bis(imino)pyridyliron(cobalt) complexes 1-10 as showed in the Schemes 3 and 4 from previous reports [31][32][33][34][35][36] were selected to study the thermal stability. For the complexes 1-5, the small variations of structures lie in the different substituents within the aryl moiety, while, for the complexes 6-10, the differences are not only the substituents within the aryl moiety, but also the A r group.…”

“…In our previous studies, the relationship between the structure of a catalyst and its catalytic activity was investigated by molecular modeling, which successfully predicted the catalytic activities of late transition metal complex precatalysts toward ethylene oligo/polymerization, through electronic effects [38][39][40][41] or both from electronic and steric effects [42,43]. Regarding the influence of the catalyst structure on its thermal stability, several possible factors were proposed by previous experimental research [19,[24][25][26][29][30][31][32][33][34][35][36]. However, to our best knowledge, there are less detailed works at a molecular level to study the catalyst with thermal stability quantitatively.…”