Narrow dispersed linear polyethylene using cobalt catalysts bearing cycloheptyl-fused bis(imino)pyridines; probing the effects of ortho-benzhydryl substitution.

Graphical abstract Highlights • Bis(imino)-2,3:5,6-bis(pentamethylene)pyridines and their cobalt complexes. • Highly active precatalysts for ethylene polymerization. • Linear polyethylenes with narrow dispersities and vinyl end-groups. • Modulation of molecular weight through ortho -benzhydryl substitution. Abstract The cycloheptyl-fused cobalt(II) chloride complexes, [2,3:5,6-{C 4 H 8 C(N(2-R1-4-R2-6-(CHPh 2)C 6 H 2))} 2 C 5 HN]CoCl 2 (R1 = R2 = Me Co1 , R1 = Me, R2 = CHPh 2 Co2 , R1 = Et, R2 = CHPh 2 Co3 , R1 = i -Pr, R2 = CHPh 2 Co4 , R1 = Cl, R2 = CHPh 2 Co5 , R1 = CHPh 2 , R2 = i -Pr Co6 , R1 = CHPh 2 , R2 = t -Bu Co7 , R1 = CHPh 2 , R2 = F Co8), have been prepared by a one-pot template approach. The molecular structures of Co1 , Co6 and Co8 highlight the varying degrees of steric protection of the metal center imposed by the ortho -benzhydryl/-R1 group pairing. On activation with either MAO or MMAO, Co1–Co5 collectively displayed high activity (up to 2.87 × 106 g (PE) mol−1 (Co) h−1 at 40 °C) affording highly linear low molecular weight polyethylene (M w range: 12.8–59.4 kg mol−1) with narrow polydispersities (M w / M n range: 1.4–2.7). End-group analysis of the polymers highlights the importance of both β-H elimination and chain transfer to aluminum as termination pathways. In relative terms, MMAO proved a marginally more effective activator than MAO with the catalytic activity, in either case, falling in the order: Co1 > Co5 > Co2 > Co3 > Co4. In marked contrast, the 2,6-(CHPh 2) 2 -substituted precatalysts, Co6 , Co7 and Co8 gave, in the presence of the same aluminoxane activators, only trace amounts of polyethylene. [ABSTRACT FROM AUTHOR]