2-[1-(2,4-Dibenzhydryl-6-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridylcobalt(ii) dichlorides: Synthesis, characterization and ethylene polymerization behavior

Abstract

A series of cobalt(II) dichloride complexes ligated by 2-[1-(2,4-dibenzhydryl-6-methylphenylimino) ethyl]-6-[1-(arylimino)ethyl]pyridines was synthesized and characterized by FT-IR spectroscopy and elemental analysis. The molecular structure of the representative complex Co4 (R1 = Me, R2 = Me) was confirmed as pseudo square-pyramidal geometry at cobalt by single-crystal X-ray diffraction. Upon treatment with the co-catalysts MAO or MMAO, all cobalt pre-catalysts exhibited high activities up to 1.81 × 107 g PE mol-1(Co) h-1 in ethylene polymerization, and produced polyethylene products with molecular weights in the tens of thousands and narrow molecular weight distributions. The influence of the reaction parameters and nature of the ligands on the catalytic behavior of the title cobalt complexes was investigated

Carbocyclic-fused N,N,N-pincer ligands as ring-strain adjustable supports for iron and cobalt catalysts in ethylene oligo-/polymerization

“…Over the last five years, our group has also been interested in improving the catalytic activity and thermal stability of bis(arylimino)pyridine-iron and -cobalt complexes [43,46,51]. In particular we have found that the introduction of sterically demanding benzhydryl groups and their derivatives into the N,N,N-ligand frame of their iron and cobalt catalysts can be influential (14-30, Figure 14) [70][71][72][73][74][75][76][77][78][79][80][81] for ethylene polymerization (see Table 2).…”

“…By stark contrast, the symmetrical iron complexes 18 and 20 ( Figure 14) bearing two bulky 2,6-dibenzhydrylphenyl groups showed only poor activity with only trace amounts of polymers detectable which has been credited to the presence of too much steric bulk [70,72,73]. Meanwhile, a family of unsymmetrical diphenylmethyl-containing bis(arylimino)pyridine-iron and -cobalt complexes 21 and 22 ( Figure 14) still displayed high activity and thermal stability for ethylene catalysis [75,76]. On treatment with either MAO or MMAO, all the iron pre-catalysts possessed good thermo-stability and exhibited high activities (up to 22.7 × 10 6 g PE mol -1 (Fe) h -1 ) towards ethylene polymerization, producing highly linear polyethylene [75].…”

“…Benzhydryl-substituted bis(arylimino)pyridine-iron and -cobalt complexes 14-31 [70][71][72][73][74][75][76][77][78][79][80][81]…”

Bi- and tri-dentate imino-based iron and cobalt pre-catalysts for ethylene oligo-/polymerization

“…When using cobalt instead of iron, the activity for ethylene polymerization of the pre-catalysts 134, 138, 141, 143, and 145 was one order of magnitude lower than the corresponding iron pre-catalysts. 22,32,[68][69][70][71] In addition, polymers obtained via The 1,8-diimino-2,3,4,5,6,7-hexahydroacridine iron and cobalt complexes 148 and 149 (Scheme 24, left) were prepared via a one-pot synthesis and exhibited high activity for ethylene polymerization when treated with methylaluminoxane. 75 The 50 ortho substituents of the aryl rings and the type of metal employed played a significant role on ethylene activation and specifically on product distribution.…”

Recent progress in immobilization of late-transition-metal complexes with diimine ligands for olefin polymerization

“…In contrast to complexes of early transition-metals, the late-transitionmetal (LTM) complexes reported by Brookhart [4] and Gibson [5] are attracting increasing attention because of the easy preparation and modification of their Schiff base ligands [6][7][8]. Recently, according to different coordination forms, some LTM-based complexes with novel diimine ligands containing Fe [9][10][11][12], Co [13,14], Ni [15][16][17][18][19][20][21], Pd [22,23] are applied to olefin polymerization. The products obtained using such catalysts can be changed from polyethylene (PE) to oligomers by tuning the steric and electronic properties of the ligands [24].…”