Novel neutral arylnickel(II) phosphine catalysts containing 2-oxazolinylphenolato N–O chelate ligands for ethylene oligomerization and propylene dimerization

A series of new neutral arylnickel(II) phosphine complexes 1 bearing 2-oxazolinylphenolato ligands [2-(4-R1-5-R2-C3H2NO)–C6H4O]Ni(2-R4-4-R3-C6H3)(PPh3) were synthesized by reactions of sodium salts of 2-(4,5-dihydro-2-oxazolyl)phenol derivatives with trans-Ni(Ar)(Cl)(PPh3)2 or by direct reactions of the ligands with trans-Ni(Ar)(Cl)(PPh3)2 in the presence of NEt3. These neutral Ni(II) complexes 1 exhibited high activities and selectivities in ethylene oligomerization and propylene dimerization. The catalytic activities and the product distributions were dependent on the selection of various organoaluminum cocatalysts and phosphine scavenger (Ni(COD)2). The effects of various reaction conditions on ethylene oligomerization were also examined. The highest activity of 5.51 × 105 g oligomers/(mol Ni · h) and 83% selectivity of C6 internal olefins were obtained in 1a/MAO catalytic system in ethylene oligomerization. The oligomers consisted mainly of lower carbon olefins in the range of C4–C8. Complexes 1 showed the moderate tolerance of polar additives in ethylene oligomerization. The highest activity of 1a/MAO in propylene dimerization reached to 1.32 × 105 g oligomers/(mol Ni · h).