Synthesis of benzoxazolylpyridine nickel complexes and their efficient dimerization of ethylene to alpha-butene.

A series of new nickel complexes bearing benzoxazolylpyridines was synthesized and characterized by FT-IR spectroscopic and elemental analysis. The molecular structures of two representative complexes were determined by single-crystal X-ray diffraction. The complex [NiCl2[2-(2-benzoxazolyl)-6-methylpyridine]] (5) is a centrosymmetric dinuclear compound with two penta-coordinated Ni(II) centers, whereas the complex [NiCl2[2-(5-methyl-2-benzoxazolyl)-6-methylpyridine}] (6) is mononuclear exhibiting a distorted octahedral-coordination geometry around the nickel atom. Upon activation with diethylaluminium chloride (Et2AlCl), all the complexes exhibited moderate to good catalytic activity for ethylene oligomerization (27-415 g mmol(-1)(Ni) h(-1) bar(-1)) with high selectivity for ethylene dimerization to form alpha-butene. The observed variance in the catalytic activities of the complexes is attributed to the different ligand environments and effects of reaction parameters.