Bis(imino)-6,7-dihydro-5 H -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 H -quinoline-cobalt(ii) complexes, [2-(ArN = CPh)-8-(NAr)-C 9 H 8 N]CoCl 2 (Ar = 2,6-Me 2 C 6 H 3 Co1, 2,6-Et 2 C 6 H 3 Co2, 2,6-i-Pr 2 C 6 H 3 Co3, 2,4,6-Me 3 C 6 H 2 Co4, 2,6-Et 2 -4-MeC 6 H 2 Co5), have been synthesized in reasonable yield by the template reaction of cobalt(ii) chloride hexahydrate, 2-benzoyl-6,7-dihydro-5 H -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 vs. cyclic) and also the steric properties exerted by the bulky N imine -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 7 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 ( M w / M n range: 1.66-3.28). In particular, the least sterically bulky precatalysts, Co1 and Co4 formed polyethylene waxes ( M w range: 1.94-5.69 kg per mol) with high levels of vinyl unsaturation as confirmed by high temperature 1 H/ 13 C NMR spectroscopy and by IR spectroscopy.