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

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.