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

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.