Synthesis and crystal structure determination of Mn(II) Schiff base complexes and their performance in ethene polymerization

Mn(II) complexes 1–10, of which eight are novel, were prepared in high yields by reacting MnCl2 with bidentate N,N′-imine-pyridine and N,N′-imine-quinoline-type donor ligands having different kinds of chemical modifications. The complexes were fully characterized by elemental analysis, mass spectrometry and IR spectroscopy. Crystal structures of 6, 7 and 9 were determined by X-ray crystallography and the results showed that 6 has a dimeric square-pyramidal geometry, whereas 7 and 9 have distorted octahedral structures. Magnetic studies on the high spin complexes 6 and 9 showed that the former exhibits a weak intramolecular antiferromagnetic interaction through the chloride-bridging ligands with a magnetic exchange coupling J = −0.46(6) cm−1, whereas the latter, as expected for its mononuclear structure, only shows very weak intermolecular interactions and/or zero-field splitting effects. All the complexes were activated with methylaluminoxane and investigated under low pressure (5 bar) for ethene polymerization at 60 °C. Complexes 1 and 6–10 showed catalytic activity. The prepared polyethenes exhibited high molar masses (296 000–399 000 g/mol) and high melting temperatures (133–140 °C). The low molar mass distribution values of 2.15–2.55 indicated single-site polymerization behavior.

Ten Mn(II) complexes with bidentate N,N′-imine-pyridine and N,N′-imine-quinoline-type donor ligands were synthesized and applied to ethene polymerization at 60 °C with MAO activation.Figure optionsDownload as PowerPoint slide