Stereospecific polymerization of 1,3-butadiene catalyzed by cobalt complexes bearing N-containing diphosphine PNP ligands

A series of cobalt complexes bearing N-containing diphosphine PNP ligands has been synthesized and characterized. The nature of the ligand structure affects the binding of the ligand to the cobalt center and determines the coordination geometry of the cobalt complexes. All the complexes have been employed to catalyze the polymerization of 1,3-butadiene, in combination with methylaluminoxane (MAO) or ethylaluminum sesquichloride (EASC) as the cocatalyst. Both the nature of the ligand and the type of cocatalyst had a remarkable influence on the polymerization activity, microstructure and molecular weight of the resulting polymers. The [Co]/MAO catalytic systems resulted in relatively lower conversions of butadiene and cis-1,4 contents in the polymers than the corresponding [Co]/EASC catalytic systems. Upon activation with EASC, the polymerization behaviors of the catalytic systems were also affected by the reaction parameters.

A series of cobalt complexes bearing N-containing diphosphine PNP ligands were synthesized and characterized. EASC was more effective to catalyze the polymerization of butadiene to give high cis-1,4-PBD with high selectivity (>96.6%). In combination with MAO, lower conversions and higher 1,2-vinyl contents (9.0%–20.6%) were obtained.Figure optionsDownload as PowerPoint slideHighlights
► Cobalt complexes bearing N-containing diphosphine PNP ligands were synthesized.
► The [Co]/EASC systems gave high conversion of butadiene and high cis-1,4 selectivity.
► In combination with MAO, the lower activity and higher 1,2-vinyl content were obtained.