Integrating Ring-Size Adjustable Cycloalkyl and Benzhydryl Groups as the Steric Protection in Bis(arylimino)trihydroquinoline-Cobalt Catalysts for Ethylene Polymerization

Combined condensation and complexation of 2-acetyl-5,6,7-trihydroquinolin-8-one, cobalt(II) chloride and the corresponding aniline has been employed as an effective one-pot route to the 2-(1-(arylimino)ethyl)-8-arylimino-5,6,7-trihydroquinoline-cobalt(II) chlorides (aryl=2-Me-4-(CHPh2)-6-(C5H9)C6H2 Co1, 2-Me-4-(C5H9)-6-(CHPh2)C6H2 Co2, 2-(C5H9)-4-Me-6-(CHPh2)C6H2 Co3, 2-(C5H9)-4,6-(CHPh2)2C6H2 Co4, 2-(C6H11)-4,6-(CHPh2)2C6H2 Co5, 2-(C8H15)-4,6-(CHPh2)2C6H2 Co6, 2-F-4,6-(CHPh2)2C6H2 Co7, 2-Cl-4,6-(CHPh2)2C6H2 Co8, 2-Me-4,6-(CHPh2)2C6H2 Co9). All complexes have been well characterized including by single crystal X-ray diffraction for Co3. On activation with either MAO or MMAO, Co1 was the most active for ethylene polymerization with the MAO-activated precatalyst reaching a peak level at 60 °C (up to 13.66×106 g (PE) mol−1(Co) h−1). By varying the electronic and steric properties of the ortho- and/or the para-substituents of the N-aryl groups, excellent control over molecular weight could be achieved with values falling in the range 0.97–101.63 kg mol−1 obtainable. Notably, with a benzhydryl group positioned on the ortho-position of the N-aryl group, a significant enhancement of the molecular weight was observed, while the least bulky ortho-cyclopentyl substituent led to increased catalytic activity. As a final point, distinctive microstructural characteristics of the polyethylenes were observed with Co1/MAO producing near quantitative levels of vinyl end groups.