gem-Dimethyl-substituted bis(imino)dihydroquinolines as thermally stable supports for highly active cobalt catalysts that produce linear PE waxes

Abstract

Six types of 2,8-bis(imino)-7,7-dimethyl-5,6-dihydroquinoline, 2-(ArNCMe)-8-(ArN)-7,7-Me₂C₉H₆N (Ar = 2,6-Me₂C₆H₃L1, 2,6-Et₂C₆H₃L2, 2,6-ⁱPr₂C₆H₃L3, 2,4,6-Me₃C₆H₂L4, 2,6-Et₂-4-MeC₆H₂L5, 2,4,6-^tBu₃C₆H₃L6), distinguishable by their steric and electronic profile, are described that can readily undergo complexation with cobaltous chloride to form their corresponding LCoCl₂ chelates, Co1–Co6. The molecular structures of Co2 and Co3 reveal square pyramidal geometries with ring puckering a feature of the gem-dimethyl section of their unsymmetrical N,N,N′-ligands. On activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all the cobalt complexes exhibited exceptionally high activities for ethylene polymerization with levels reaching up to 1.19 × 10⁷ g PE per mol (Co) per h for mesityl-containing Co4. Significantly, these catalysts exhibited good thermal stability by displaying their optimal performance at temperatures up to 70 °C whilst also maintaining appreciable catalytic lifetimes. With the exception of that obtained using the most sterically hindered Co6 (2,4,6-t-butyl), the polyethylenes are of low molecular weight (M_w ≤16.0 kg mol⁻¹) and of narrow dispersity (M_w/M_n ≤3.4). Moreover, end-group analysis of these highly linear polymer waxes reveals evidence for unsaturated as well as various levels of fully saturated materials highlighting the role of both β-H elimination and chain transfer to aluminum as termination pathways.