Polymerization of 1,3-butadiene catalyzed by pincer cobalt(II) complexes derived from 2-(1-arylimino)-6-(pyrazol-1-yl)pyridine ligands

Authors: Dirong Gong, Weiguo Jia, Tao Chen, Kuo-Wei Huang

Abstract:
A new class of air stable and structurally well-defined cobalt complexes with unsymmetrical pincer type ligands ([2-(ArN=CMe)-6-(Py)C₅H₃N]CoCl₂) (Ar = C₆H₅, Py = pyrazol-1-yl, 5a; Ar = 2,4,6-Me₃C₆H₂, Py = pyrazol-1-yl, 5b; Ar = 2,6-ⁱPr₂C₆H₃, Py = pyrazol-1-yl, 5c; Ar = C₆H₅, Py = 3,5-Me₂pyrazol-1- yl, 5d; Ar = 2,4,6-Me₃C₆H₂, Py = 3,5-Me₂pyrazol-1-yl, 5e; Ar = 2,6-ⁱPr₂C₆H₃, Py = 3,5-Me₂pyrazol-1- yl, 5f; Ar = 2,6-ⁱPr₂C₆H₃, Py = 3,5-ⁱPr2pyrazol-1-yl, 5g and [2-(O CMe)-6-(3,5-diphenylpyrazol-1- yl)C5H3N]CoCl₂ 5h) were prepared and the molecular structures of 5a, 5c and 5f were determined by single crystal X-ray crystallography. Upon activation by methylaluminoxane (MAO) in toluene at room temperature, all complexes initiate polymerization of 1,3-butadiene (polymer yields: 65–99%), affording polybutadiene with excellent cis-1,4 regularity (97.5–98.7%). The polymer yields and properties in terms of molecular weight and distribution are well controlled by the substituents on iminoaryl rings and pyrazole rings. Selectivity switch from cis-1,4 to syndio-1,2 was also achievable by adding phosphine as microstructure regulator.

Keywords:
Cobalt(II) complexes
2-(1-Arylimino)-6-(pyrazol-1-yl)pyridine
1,3-Butadiene
Selectivity
Polybutadiene

Published in: Applied catalysis A: General  (Volumes 464–465, Pages 1-384, 15 August 2013)

Publisher: Elsevier  

ISSN Information: 0926-860X

Polymerization of 1,3-butadiene catalyzed by pincer cobalt(II) complexes derived from 2-(1-arylimino)-6-(pyrazol-1-yl)pyridine ligands

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