Halogen-Substituted 2,6-Bis(imino)pyridyl Iron and Cobalt Complexes:  Highly Active Catalysts for Polymerization and Oligomerization of Ethylene

Abstract

A series of halogen-substituted 2,6-bis(imino)pyridyl ligands and their iron and cobalt complexes [{2,6-(2,6-X1X2C6H3NCCH3)2C5H3N}MCl2] (X1 = X2 = Br, M = Fe (1), Co (2); X1 = X2 = Cl, M = Fe (3), Co (4); X1 = Cl, X2 = H, M = Fe (5), Co (6); X1 = Br, X2 = H, M = Fe (7), Co (8); X1 = I, X2 = H, M = Fe (9), Co (10)) and [M{2,6-(2,6-X1X2C6H3NCCH3)2C5H3N}2]2+[MCl4]2- (X1 = F, X2 = H, M = Fe (11)) have been synthesized. The molecular structures of complexes 1, 8, 9, 10, and 11 were determined by X-ray diffraction. Crystallographic analyses indicate that 1, 8, 9, and 10 are five-coordinate complexes, while 11 is an ion-pair complex with one six-coordinate iron center and one four-coordinate iron center. These metal coordinative complexes, activated by modified methylaluminoxane (MMAO), lead to highly active ethylene polymerization and/or oligomerization catalysts. The catalyst productivity and product properties crucially depended on the metal center and the halogen substituents on the aryl rings. The catalyst productivities are in the range of (0−73.0) × 106 g/mol of cat·h. The species 11, having ion-pair structure, is inactive. In particular, the product molar masses were changed from high molar mass (M w of 377 000) to low molar mass oligomers by varying the halogen substituents. NMR and thermal analyses reveal the polymer is highly linear. The oligomer products follow a Schulz−Flory distribution with high selectivity for linear α-olefins. The effects of reaction condition on the polymerization and oligomerization have also been studied.

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

“…45, 54 Complexes with only one fluoro substituent at the imino-N aryl ring ortho position had the highest oligomerization activity. The introduction of an electron withdrawing group could increase the electrophilicity of the central metal Fe and the coordination of ethylene, favoring the 60 catalytic activity.…”

Simple Preparation of Halogen-Substituted <i>α</i>-Diimine Nickel Complexes Immobilized into Clay Interlayer as Catalysts for Ethylene Oligo-/Polymerization

“…Another effective strategy is the tuning of the electronic state of the complexes. Qian et al reported that the steric bulk and electro-withdrawing property of the halogen substituents have significant effects on the catalyst activity and the molar mass of the product [15] [16]. The charge control of the metal center in the complex could be achieved by introducing electro-donating groups or electro-withdrawing groups [17] [18] [19].…”

Crystal structure of 1-(6-(1-(perfluorophenylimino)ethyl)pyridin-2-yl)ethanone, C15H9F5N2O

“…The catalytic performances have been greatly improved by introducing halogen atoms into ligands [5,6], and anew method for synthesis of halogen substituted bis(imino)pyridines hasbeen reported [7]. The title compound is in the E conformation.…”