The cobalt(II) chloride
N,N,N-pincer complexes, [2-{(2,4-(C
15H
13)
2-6-FC
6H
2)N=CMe}-6-(ArN=CMe)C
5H
3N]CoCl
2 (Ar
= 2,6-Me
2C
6H
3) (
Co1), 2,6-Et
2C
6H
3 (
Co2), 2,6-
i-Pr
2C
6H
3 (
Co3), 2,4,6-Me
3C
6H
2 (
Co4), 2,6-Et
2-4-MeC
6H
2 (
Co5), and [2,6-{(2,4-(C
15H
13)
2-6-FC
6H
2)N=CMe}
2C
5H
3N]CoCl
2 (
Co6), each containing at least one
N-2,4-bis(dibenzosuberyl)-6-fluorophenyl group, were synthesized in good yield from their corresponding unsymmetrical (
L1–
L5) and symmetrical bis(imino)pyridines (
L6). The molecular structures of
Co1 and
Co2 spotlighted their distorted square pyramidal geometries (
τ5 value range: 0.23–0.29) and variations in steric hindrance offered by the dissimilar
N-aryl groups. On activation with either MAO or MMAO,
Co1–
Co6 all displayed high activities for ethylene polymerization, with levels falling in the order:
Co1 >
Co4 >
Co5 >
Co2 >
Co3 >
Co6. Indeed, the least sterically hindered 2,6-dimethyl
Co1 in combination with MAO exhibited a very high activity of 1.15 × 10
7 g PE mol
−1 (Co) h
−1 at the operating temperature of 70 °C, which dropped by only 15% at 80 °C and 43% at 90 °C. Vinyl-terminated polyethylenes of high linearity and narrow dispersity were generated by all catalysts, with the most sterically hindered,
Co3 and
Co6, producing the highest molecular weight polymers [
Mw range: 30.26–33.90 kg mol
−1 (
Co3) and 42.90–43.92 kg mol
−1 (
Co6)]. In comparison with structurally related cobalt catalysts, it was evident that the presence of the
N-2,4-bis(dibenzosuberyl)-6-fluorophenyl groups had a limited effect on catalytic activity but a marked effect on thermal stability.
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