Bis(imino)-6,7-dihydro-5-quinoline-cobalt complexes as highly active catalysts for the formation of vinyl-terminated PE waxes; steps towards inhibiting deactivation pathways through targeted ligand design.

A set of five related bis(imino)-6,7-dihydro-5-quinoline-cobalt(ii) complexes, [2-(ArN = CPh)-8-(NAr)-CHN]CoCl (Ar = 2,6-MeCHCo1, 2,6-EtCHCo2, 2,6-i-PrCHCo3, 2,4,6-MeCHCo4, 2,6-Et-4-MeCHCo5), have been synthesized in reasonable yield by the template reaction of cobalt(ii) chloride hexahydrate, 2-benzoyl-6,7-dihydro-5-quinolin-8-one and the corresponding aniline. The molecular structures of Co1 and Co4 highlight both the differences in the two imino-carbon environments (phenyl-capped chain cyclic) and also the steric properties exerted by the bulky -aryl groups. On pre-treatment with either modified methylaluminoxane (MMAO) or methylaluminoxane (MAO), all complexes proved productive catalysts for the polymerization of ethylene. In particular, Co1/MAO was the most active reaching a very high level of 1.62 × 10 g PE per mol (Co) per h over a 30 minute run time. Owing to the presence of the imino-phenyl substituent, Co1-Co5 were able to exhibit good thermal stability by displaying appreciable catalytic activity at temperatures between 50 and 80 °C, generating polyethylenes with narrow dispersities ( / range: 1.66-3.28). In particular, the least sterically bulky precatalysts, Co1 and Co4 formed polyethylene waxes ( range: 1.94-5.69 kg per mol) with high levels of vinyl unsaturation as confirmed by high temperature H/C NMR spectroscopy and by IR spectroscopy.