Add time:07/14/2019         Source:sciencedirect.com

A series of cobalt(II) complexes supported by 8-(methylthio)-2-(R-pyrazolyl)quinoline (R = H, CH3, and Ph) ligands (3a–3e) were synthesized and characterized by elemental, FT-IR, and UV–visible analyses. X-ray diffraction analysis revealed that complexes 3b and 3c adopted distorted square pyramidal geometry and trigonal bipyramidal geometry, respectively. Activated by methylaluminoxane (MAO) and ethylaluminum sesquichloride (EASC), the polymerization of 1,3-butadiene with these complexes afforded polymers with high cis-1,4 regularity (ca. 95%) in high yields. The substituent structure on the ligand influenced the catalytic behaviors. Complex 3a without substituent exhibited higher activity than its methyl-substituted counterparts 3b and 3c, while the phenyl-substituted complexes gave polymers in quantitative yields. In particular, even at a high temperature of 100 °C MAO- and EASC- based systems gave polymers in relatively high yields, indicating high thermal stability of the generated active species.

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