Thermally Stable and Highly Efficient N,N,N -Cobalt Olefin Polymerization Catalysts Affixed with N -2,4-Bis(Dibenzosuberyl)-6-Fluorophenyl Groups.

The cobalt(II) chloride N,N,N-pincer complexes, [2-{(2,4-(C₁₅H₁₃)₂-6-FC₆H₂)N=CMe}-6-(ArN=CMe)C₅H₃N]CoCl₂ (Ar = 2,6-Me₂C₆H₃) (Co1), 2,6-Et₂C₆H₃ (Co2), 2,6-i-Pr₂C₆H₃ (Co3), 2,4,6-Me₃C₆H₂ (Co4), 2,6-Et₂-4-MeC₆H₂ (Co5), and [2,6-{(2,4-(C₁₅H₁₃)₂-6-FC₆H₂)N=CMe}₂C₅H₃N]CoCl₂ (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 × 10⁷ 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 [M_w 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. [ABSTRACT FROM AUTHOR]