Selective Ethylene Oligomerization with Nickel Oxime Complexes

Two nickel-oxime complexes, Ni (2-pyridine aldoxime)2 dichloride (6) and Ni (methyl 2-pyridyl ketone oxime)2 dichloride (7), were prepared and characterized by X-ray crystallography. Both complexes are six-coordinate and have 2-pyridylimines as ligand backbones, where the two nitrogen atoms from each of the oxime ligands coordinate to the metal, but the oxygen atom remains protonated and does not participate in bonding to the metal center. The complexes were found to be selective ethylene dimerization catalysts in the presence of cocatalyst such as methylaluminoxane (MAO) or diethyl aluminum chloride (DEAC). With DEAC, the productivity is considerably higher than with MAO. Under optimum conditions the productivity values are as high as 200 kg/mol catalyst/h/bar (for 6) to 335 kg/mol catalyst/h/bar (for 7). The selectivities toward dimerization under these conditions are 84% and 77%, respectively, with the terminal isomer 1-butene being the only (≥99.5%) C4 product.