Polymerization of 1,3-butadiene catalyzed by ion-pair cobalt complexes with (benzimidazolyl)pyridine alcohol ligands

•Ion-pair cobalt complexes with (benzimidazolyl)pyridine alcohols were synthesized.•Ion-pair cobalt complexes were comprised of [CoL2]2+ and [CoCl4]2− ions.•The [Co]/EASC systems afforded high conversion of butadiene and cis-1,4 selectivity.•The catalytic properties were affected by reaction parameters and ligand structure.

A series of ion-pair cobalt complexes (C1–C6) supported by (benzimidazolyl)pyridine alcohol ligands ([NNO]) were synthesized and characterized. The single-crystal X-ray diffraction demonstrated that the ion-pair cobalt complexes formed, consisting of [CoL2]2+ and [CoCl4]2−, in which the cobalt center was surrounded by two [NNO] ligands and adopted distorted octahedronal geometry in the cationic moiety along with [CoCl4]2− as the counterion. The type of cocatalyst had a remarkable influence on the catalytic properties and ethylaluminum sesquichloride (EASC) was proved to be the most efficient cocatalyst for the polymerization of 1,3-butadiene to produce high conversion of butadiene and high cis-1,4 content in the resulting polymers. Upon activation with EASC, all the cobalt complexes (C1–C6) displayed high catalytic activity for the polymerization of 1,3-butadiene to yield cis-1,4-polybutadiene with high selectivity (>95%) under the Al/Cat molar ratio of 50 at 30 °C. The conversion of butadiene, microstructure and properties of the resulting polymers were also affected by the reaction parameters and ligand structure.

Graphical abstractA series of ion-pair cobalt complexes bearing (benzimidazolyl)pyridine alcohol ligands ([NNO]) in the formula of [CoL2] and [CoCl4] were synthesized and characterized. On activation with EASC, all the cobalt complexes displayed high catalytic activity for the polymerization of 1,3-butadiene to yield cis-1,4-polybutadiene with high selectivity (>95%).Figure optionsDownload full-size imageDownload high-quality image (85 K)Download as PowerPoint slide