Cobalt complexes bearing pyridine-imino ligands with bulky aryl substituents: Synthesis, characterization, and 1,3-butadiene polymerization behaviors

• Co(II) complexes bearing pyridine-imino ligands with bulky aryl groups were successfully synthesized.
• The complexes afforded polybutadienes with high cis-1,4 contents and high molecular weights.
• The incorporation of bulky substituent enhanced the thermal stability of these complexes.

A series of Co(II) complexes bearing pyridine-imino ligands [2-Ar1-6-(CMe = NAr2)C5H3N]CoCl2 (Ar1 = C6H5, Ar2 = 2,6-i-Pr2C6H3 (3a); Ar1 = 2′-C10H7, Ar2 = 2,6-i-Pr2C6H3 (3b); Ar1 = 2′-C10H7, Ar2 = C6H5 (3c); Ar1 = 2′-C10H7, Ar2 = 4-ClC6H4 (3d); Ar1 = 4′-C6H5–C6H4, Ar2 = 2,6-i-Pr2C6H3 (3e); Ar1 = 4′-C6H5–C6H4, Ar2 = C6H5 (3f); Ar1 = 4′-C6H5–C6H4, Ar2 = 4-ClC6H4 (3g)) with bulky aryl groups were synthesized and characterized. Determined by single-crystal X-ray diffraction, 3a, 3b, and 3e adopted distorted tetrahedron configurations. Activated by ethylaluminum sesquichloride (EASC), these complexes exhibited high cis-1,4 selectivity for 1,3-butadiene polymerization. The steric and electronic properties of substituent of the ligand remarkably influenced catalytic activity. The effects of polymerization parameters such as [Al]/[Co] ratio and temperature on the polymerization were also investigated in details.

Co(II) complexes bearing pyridine-imino ligands with bulky aryl groups were synthesized and polymerized 1,3-butadiene to give polymers with high cis-1,4 contents. The representative system, 3g/EASC, gave polymer in a high yield up to 99% even at 80 °C, indicating the high thermal stability.Figure optionsDownload as PowerPoint slide