Fluorinated bis(arylimino)‐6,7‐dihydro‐5H‐quinoline‐cobalt polymerization catalysts: Electronic versus steric modulation in the formation of vinyl‐terminated linear PE waxes

Abstract

Condensation of 2‐benzoyl‐6,7‐dihydro‐5H‐quinolin‐8‐one with an excess of the respective fluorinated aniline in the presence of cobalt (II) chloride has provided an effective one‐flask synthesis of the 2‐(phenyl(arylimino)methyl)‐8‐arylimino‐6,7‐dihydro‐5H‐quinoline‐cobalt (II) chloride complexes, [2‐(ArN=CPh)‐8‐(NAr)‐C9H9N]CoCl2 (Ar = 2‐Me‐4,6‐(CH(p‐FC6H4)2)2C6H2 Co1, 2,6‐Me2‐4‐(CH(p‐FC6H4)2)C6H2 Co2, 2,4‐Me2‐6‐(CH(p‐FC6H4)2)C6H2 Co3, 2‐Et‐4,6‐(CH(p‐FC6H4)2)2C6H2 Co4, 2‐i‐Pr‐4,6‐(CH(p‐FC6H4)2)2C6H2 Co5, 2‐F‐4,6‐(CH(p‐FC6H4)2)2C6H2 Co6). Structural characterization of Co2 and Co4 revealed the unsymmetrical nature of the N,N,N‐chelating ligands and the five‐coordinate geometries around the metal ions. Complexes Co1–Co6 all exhibited high activities as precatalysts for ethylene polymerization when treated with either MAO or MMAO producing highly linear (Tm′s > 118°C) low molecular weight polyethylene (Mw range: 0.69–31.51 kg mol−1) with a variety of dispersities (Mw/Mn range: 2.2–17.5). 2,6‐Dimethyl‐containing Co2 was the most productive precatalyst of the series reaching an exceptionally high activity of 27.06 × 106 g (PE) mol−1 (Co) h−1 at a temperature of 50°C. Additionally, ortho‐fluoride Co6 maintained an impressive level of activity at an operating temperature of 70°C and was able to maintain a long catalytic lifetime. Furthermore, the presence of vinyl end groups (–CH=CH2) in the 1H/13C NMR and IR spectra of their polymers supports the key role played by β‐H elimination in chain transfer.