Chelate control in the nickel-complex catalysed homogeneous oligomerization of ethylene

The impact of various k²-P⌢O chelate ligands on nickel catalysed ethylene oligomerization has been investigated. The ligands 4-8 and 14, 15 were reacted with bis(π-methallyl)nickel yielding seven new complexes, 9-13 and 16, 17 in which the k²-P⌢O chelate ring size was altered and in which methyl substituents were introduced into the k²-P⌢O chelate. These complexes served as precursor complexes leading to active ethylene oligomerization catalysts. Increasing the chelate ring size from a five-membered to a six or seven-membered ring diminishes catalytic activity dramatically. However, by introducing double bonds or an aromatic ring into the six-membered nickelaheterocycle yielded very active ethylene oligomerization systems. Introducing methyl groups into Ph₂PCH(CH₃)COOH (14) and Ph₂PC(CH₃)₂COOH (15) also leads to a significant increase in activity.