Rational Design of Cycloheptyl‐Fused Bis(arylimino)pyridyl‐cobalt(II) Precatalysts Adorned with Sterically and Electronically Modified N‐Aryls for Enhancing Ethylene Polymerization

Abstract

AbstractThe sterically and electronically modified cycloheptyl‐fused bis(arylimino)pyridine‐cobalt(II) chloride precatalysts [2,3 : 5,6‐{C4H8C(N‐2,4‐(C15H13)‐6‐R‐C6H2}2C5HN]CoCl2 (R=Me (Co1), Et (Co2), i‐Pr (Co3), Cl (Co4), and F (Co5)) have been prepared via one‐pot synthesis approach. All the precatalysts were characterized by elemental analysis, FT‐IR spectroscopy and the single‐crystal X‐ray diffraction for Co2 confirmed distorted‐square‐pyramidal geometry around the cobalt center. On activation with either MAO (methylaluminoxane) or MMAO (modified methylaluminoxane), all the cobalt precatalysts displayed high catalytic activities for ethylene polymerization with peak performance of 3.47×106 g (PE) mol−1 (Co) h−1 at 50 °C using MAO and 4.53×106 g (PE) mol−1 (Co) h−1 at 30 °C with MMAO. The steric and electronic influence of the ortho‐substitutions (R) displayed significant effect on the catalytic activity and molecular weight of the resultant polyethylene. Notably, the precatalyst Co5 (R=F) exhibited high activity, delivering high‐molecular‐weight (558.17 kg mol−1) polyethylene; highlights the beneficial effect of ortho‐substituents (R) alongside with dibenzocycloheptyl groups. In addition, analysis of the obtained polyethylene showed strictly linear structure with saturated and unsaturated (vinyl) end groups.