A series of halogen-substituted 2,6-bis(imino)pyridyl ligands and their iron and cobalt
complexes [{2,6-(2,6-X1X2C6H3NCCH3)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-X1X2C6H3NCCH3)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.
