Search Results (2)

The bis(imino)pyridylcobalt complexes have been finely tuned through using the aniline derivative bearing a meta-chloro substituent, besides its ortho- and para-di(4-fluorophenyl)methyl and ortho-methyl substituents for the series of 2-[1-(3-chloro-4,6-bis((di(4-fluorophenyl)methyl)-2-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridylcobalt(II) chlorides (2,6-Me₂Ph, Co1; 2,6-Et₂Ph, Co2; 2,6-iPr₂Ph, Co3; 2,4,6-Me₃Ph, Co4; and 2,6-Et₂-4-MePh, Co5). The compounds were characterized using elemental analysis, ¹H/¹³C NMR, FT-IR spectroscopy, and the single-crystal X-ray diffraction used in confirming the molecular structures of Co1, Co2, Co4, and Co5. The newly synthesized precatalysts, maintaining steric influences with the addition of an electron-withdrawing meta-chloro group, achieved higher activities along with better thermal stability, and controlled molecular weights of polyethylenes obtained. Upon activation with either MAO or MMAO, all catalysts exhibited remarkable activity for ethylene polymerization, for example, 9.2 × 10⁶ g mol⁻¹ h⁻¹ by Co1 at 70 °C with 30 min and 18.0 × 10⁶ g mol⁻¹ h⁻¹ by Co4 with the first 5 min. Co4 demonstrated exceptionally thermal stability with the peak activity of 8.9 × 10⁶ g mol⁻¹ h⁻¹ at 70 °C and slightly decreased to 7.2 × 10⁶ g mol⁻¹ h⁻¹ at 80 °C, and even maintained an activity of 1.6 × 10⁶ g mol⁻¹ h⁻¹ at 100 °C. More importantly, all resultant polyethylenes were characterized as having vinyl-terminal and high-linear feature along with narrow dispersity; the molecular weights could be adapted in the ranges from 6.4 to 50.0 kg mol⁻¹. In comparison with previous cobalt analogs, the current system performed better thermal stability and polymerization efficiency. Therefore, such robust complex catalysts are potentially considered for the polyethylene industry. Full article

Given the great importance of cobalt catalysts supported by benchmark bis(imino)pyridine in the (oligo)polymerization, a series of dibenzopyran-incorporated symmetrical 2,6-bis(imino) pyridyl cobalt complexes (Co1–Co5) are designed and prepared using a one-pot template approach. The structures of the resulting complexes are well characterized by a number of techniques. After activation with either methylaluminoxane (MAO) or modified MAO (MMAO), the complexes Co1–Co4 are highly active for ethylene polymerization with a maximum activity of up to 7.36 × 10⁶ g (PE) mol⁻¹ (Co) h⁻¹ and produced highly linear polyethylene with narrow molecular weight distributions, while Co5 is completely inactive under the standard conditions. Particularly, complex Co3 affords polyethylene with high molecular weights of 85.02 and 79.85 kg mol⁻¹ in the presence of MAO and MMAO, respectively. The ¹H and ¹³C NMR spectroscopy revealed the existence of vinyl end groups in the resulting polyethylene, highlighting the predominant involvement of the β-H elimination reaction in the chain-termination process. To investigate the mechanism underlying the variation of catalytic activities as a function of substituents, multiple linear regression (MLR) analysis was performed, showing the key role of open cone angle (θ) and effective net charge (Q) on catalytic activity. Full article