New bis(imino)pyridine-iron(II)- and cobalt(II)-based catalysts: synthesis, characterization and activity towards polymerization of ethylene

The synthesis of a new series of iron(II)- and cobalt(II)-based complexes of the general formula M(N∩N∩N)Cl2 (M=Fe; M=Co) bearing 2,6-bis(imin)pyridyl ligands [A–NC–Py–CN–A] that carry bulky, alkyl-free aromatic terminals (A=naphthyl, pyrenyl, 2-benzylphenyl, phenyl) or chiral cycloaliphatic auxiliary moieties (A=((−)-cis-myrtanyl) is described. The Fe(II) complexes are exceptionally active (up to 40800 kg PE/(mol M h) towards the polymerization of ethylene in the presence of methylaluminoxane (MAO) as activator. Varying the steric bulkiness of the aromatic groups in the tridentate ligands affects catalytic productivity, molecular weight and for the first time the microstructure of the resulted material. The Fe(II) precatalysts are an order of magnitude more active than the corresponding Co(II) precatalysts.