Pyridine–oxazoline and quinoline–oxazoline ligated cobalt complexes: Synthesis, characterization, and 1,3-butadiene polymerization behaviors

•Co(II) complexes bearing bidentate oxazoline-containing ligands were synthesized.•The complexes displayed high activity for 1,3-butadiene polymerization.•The addition of PPh3 could switch the selectivity from cis-1,4 to 1,2-manner.

A series of cobalt complexes supported by pyridine–oxazoline (Pyox) and quinoline–oxazoline (Quox) were synthesized. Determined by single crystal X-ray crystallography, complexes 6a and 7c adopted distorted octahedron and trigonal bipyramid geometries, respectively, while complex 6b existed as an ion pair comprised of [CoL2]2+ and [CoCl4]2−, in which the cationic and anionic moieties displayed distorted octahedron and tetrahedral geometries, respectively. Upon activation with ethylaluminium sesquichloride (EASC), these cobalt complexes exhibited high catalytic activity and cis-1,4-selectivity toward 1,3-butadiene polymerization. The selectivity of the catalytic system could be switched from cis-1,4 to 1,2-fashion via the addition of PPh3. The effects of ligand environment, polymerization temperature, and [Al]/[Co] ratio on the polymerization were investigated in detail.

Graphical abstractCobalt complexes supported by pyridine–oxazoline (Pyox) and quinoline–oxazoline (Quox) were synthesized and polymerized 1,3-butadiene to give polymers with high cis-1,4 contents. The selectivity of the catalytic system could be switched from cis-1,4 to 1,2-fashion via the addition of PPh3.Figure optionsDownload full-size imageDownload as PowerPoint slide