Thermally Resilient Cobalt Ethylene Polymerization Catalysts Under The Joint Influence Of Co-Catalyst, Gem-Dimethyl Substitution And Ortho-Cycloalkyl Ring Size

The N,N,N?-chelated 2-(1-arylimino)ethyl-8-arylimino-7,7-dimethyl-5,6- dihydroquinoline-cobalt (II) chloride complexes, Co1 (aryl = 2-(C5H9)-6-MeC6H3), Co2 (aryl = 2-(C6H11)-6-MeC6H3), Co3 (aryl = 2-(C8H15)-6MeC6H3), Co4 (aryl = 2-(C5H9)-4,6-Me2C6H2), Co5 (aryl = 2-(C6H11)-4,6-Me2C6H2) and Co6 (aryl = 2-(C8H15)4,6-Me2C6H3), have been isolated in reasonable yield using a simple one-pot method. The molecular structures of Co1 and Co5 emphasize not only the gem-dimethyl-substitution present in the carbocyclic-fused tridentate ligand but also the substantial steric properties exerted by the ortho-cycloalkyl groups. Complexes Co1 ? Co6, on interaction with MAO, were highly active catalysts for ethylene polymerization reaching a maximum level of 9.21 ? 106 g PE mol- 1 (Co) h-1 at 70 ?C for cyclopentyl-containing Co1 and Co4. Strictly linear polyethylenes with low molecular weights (Mw range: 9.25?38.5 kg mol- 1) and narrow dispersities were generated with selectivities for vinyl-terminated polymers approaching quantitative levels. By comparison, polymerizations conducted using Co1 ? Co6 with MMAO as co-catalyst proved less thermally stable and less active, with vinyl chainend selectivity proving temperature dependent. Common to both MAO and MMAO, the most sterically hindered precatalyst Co6 incorporating an ortho-cyclooctyl group gave the highest molecular weight polymer of the series.