Synthesis, characterization and 1,3-butadiene polymerization behaviors of cobalt complexes bearing 2-pyrazolyl-substituted 1,10-phenanthroline ligands

A series of cobalt(II) complexes containing tridentate 2-pyrazolyl-substituted 1,10-phenanthroline ligands (L) with the general formula [LCoCl2] have been successfully synthesized and fully identified by IR spectroscopy, elemental analysis and mass spectroscopy. Cobalt complexes Co4Co8 were further confirmed by X-ray crystallographic analysis, and all the complexes adopted distorted trigonal pyramid geometries around the cobalt center. In combination with methylaluminoxane, the complexes exhibit high cis-1,4-selectivity for 1,3-butadiene polymerization. The catalytic activities of the complexes mainly depend on the nature of the substituent and its position at the pyrazolyl ring of the ligand. Complexes having a bulkier substituent on the pyrazolyl ring of the ligand show lower catalytic activity and the incorporation of electron-withdrawing substituent enhances the activity. Polymerization behaviors were almost not affected with varying [Al]/[Co] ratio, but both activity and the cis-1,4 content decrease slightly as polymerization temperature increasing. Copyright (c) 2013 John Wiley & Sons, Ltd