Iron and cobalt complexes of tridentate N-donor ligands in ethylene polymerization: Efficient shielding of the active sites by simple phenyl groups

摘要

Tridentate 2,6-bis[3(5)-pyrazolyl]pyridines and 2,6-bis(4-pyrimidinyl)pyridine were synthesized and characterized spectroscopically and by single-crystal X-ray structure analysis. The derived complexes with FeCl2 and CoCl2 were investigated for their activity in the ethylene polymerization in the presence of methylalumoxane (MAO). Iron and cobalt catalysts bearing the ligand 2,6-bis[5-butyl-1-(4-nitrophenyl)pyrazol-3-yl)pyridine showed moderate catalytic activity and gave PE with high molecular weight, although the aryl substituents are not equipped with additional bulky side chains in the 2,6-positions to shield the metal centre. This can be explained by the geometric parameters of the pyrazole units, which provide efficient shielding of the active site, even with unsubstituted aryl groups. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).