Bis(imino)-6,7-dihydro-5H-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-5H-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-5H-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.