Positional Electronic Effects in Iminopyridine‐N‐oxide Nickel Catalyzed Ethylene Polymerization†.

Main observation and conclusion: A series of dibenzhydryl‐based iminopyridine‐N‐oxide ligands bearing a range of electron‐donating or ‐withdrawing substituents (OMe, H, and NO2) and corresponding nickel pre‐catalysts are prepared and characterized. The substituents are installed at different positions on the ligand structure, including 4‐position of the pyridine‐N‐oxide moiety (position X) and 4‐position of the aniline moiety (position Y). These nickel pre‐catalysts are highly active in ethylene polymerization with the addition of very little amount of aluminum cocatalysts, leading to the formation of polyethylenes with molecular weights of well above one million. Electron‐donating substituents make the catalysts sensitive to polymerization temperature. In contrast, the catalysts bearing electron‐withdrawing NO2 substituents show relatively steady performances at different temperatures. Most importantly, we demonstrate that different substituents and different positions both play important roles in determining the properties of nickel catalysts. This provides an alternative strategy for the future design of high‐performance polymerization catalyst. [ABSTRACT FROM AUTHOR]