Bis(imino)pyridines Incorporating Doubly Fused Eight-Membered Rings as Conformationally Flexible Supports for Cobalt Ethylene Polymerization Catalysts

Abstract

Five distinct α,α′-bis(arylimino)-2,3:5,6-bis(hexamethylene)pyridine-cobalt(II) chloride complexes, [2,3:5,6-{C5H10C(NAr)}2C5HN]CoCl2 (Ar = 2,6-Me2C6H3, Co1; 2,6-Et2C6H3, Co2; 2,6-i-Pr2C6H3, Co3; 2,4,6-Me3C6H2, Co4; 2,6-Et2-4-MeC6H2, Co5), have been synthesized by one-pot template reaction of α,α′-dioxo-2,3:5,6-bis(hexamethylene)pyridine with the corresponding aniline and cobalt(II) chloride in acetic acid. The molecular structures of Co2 and Co3 reveal distorted square pyramidal geometries with two conformationally flexible eight-membered rings, a feature of the ligand manifold. On activation with either methylaluminoxane (MAO) or modified MAO (MMAO), all five complexes displayed high catalytic activities for ethylene polymerization (up to 3.62 × 106 g PE mol–1 (Co) h–1) generating strictly linear polyethylenes with the activity decreasing in the orders: Co4 > Co5 > Co1 > Co2 > Co3 (MAO) and Co1 > Co4 > Co2 > Co5 > Co3 (MMAO). Moreover, the nature of the aluminoxane cocatalyst employed had a marked effec...