Allyloxy- and benzyloxy-substituted pyridine-bis-imine iron(II) and cobalt(II) complexes for ethylene polymerization

Abstract

A series of ethylene polymerization catalysts based on tridentate bis-imine ligands coordinated to iron and cobalt was reported. The ligands were prepared through the condensation of sterically bulky anilines with allyloxy-and benzyloxy-substituted 2,6-acetylpyridines. The pre-catalyst complexes were penta-coordinate species of the general formula {[(ArN=C(Me)) 2 (4-RO-C 5 H 3 N)]MCl 2 } (Ar=ortho dialkyl-substituted aryl ring; R=allyl, benzyl; M=Fe, Co). In the presence of ethylene and methyl alumoxane cocatalysts, these complexes were active for the polymerization of ethylene, with activities lower than those of metal complexes of the general formula {[(2-ArN= C(Me)) 2 C 5 H 3 N]MCl 2 } (Ar=ortho dialkyl-substituted aryl ring; M=Co, Fe), containing no substituents in 2,6-acetylpyridine ring. The effects of the catalyst structure and temperature on the polymerization activity, thermal properties, and molecular weight were discussed.

Ethylene Polymerization over Homogeneous and Supported Catalysts Based on Bis(imino)pyridine Co(II) Complex: Data on the Number of Active Centers and Propagation Rate Constant

“…In comparison with the iron complexes, cobalt complexes are less active at ethylene polymerization (about an order of magnitude) and produce polyethylene (PE) with lower molecular weight (MW). [9][10][11][12][13] Homogeneous catalysts based on LFeCl 2 complexes produce PE with a broad molecular weight distribution (MWD). [5,8,9,13] The values of polydispersity depend on the polymerization conditions, structure of ligand, and nature of activator; but in all cases, the M w =M n values noticeably exceed 2, indicating that a set of different active centers forms in these systems.…”

Kinetic study of ethylene polymerization over 2,6-bis(imino)pyridine cobalt complexes with bulky substituents in ligand

“…As it is known, the bulk of the substituents in the aryl rings of the bis(imino)pyridine ligand of cobalt complexes exerts a pronounced effect on their polymerization activity and on the M w characteristics of the produced polyethylene [11,[14][15][16][17]. Using polymerization quenching with radioactive carbon monoxide ( 14 CO), we determined the C P and k P values for the ethylene polymerization over 2-t BuLCoCl 2 and 2,5-t Bu 2 LCoCl 2 with MAO as an activator.…”

“…It was found by 1 H NMR spectroscopy [9,[12][13][14] that the addition of the ethylene to the catalytic systems L'Co(II)Cl 2 + MAO and L'Co(II)Cl 2 + AlMe 3 (L' = 2,6-Me 2 L, 2,4,6-Me 3 L, 2,6-i Pr 2 L, 2-t BuL) results in a rapid reduction of the initially formed complexes of cobalt(II) to cobalt(I) species and formation of the only one type of the intermediate with close structure both with MAO and AlMe 3 activators, determining the single-site character of these catalysts and close catalytic properties. For bis(imino)pyridine cobalt complexes it was shown that the substituents in the o-position of the aryl rings of the ligand have a pronounced effect upon the MW-characteristics of the resulting polymer [11,[14][15][16][17]. Complexes bearing more bulky substituents ( i Pr, t Bu) produce PE with a noticeably higher MW in comparison with the corresponding Me-substituted complex.…”