A series of N, P-based ancillary ligands have been synthesized, and the corresponding catalysts, formed in situ by mixing one of the N, P-ligands, Cr (acac) 3 and MAO, have been tested for ethylene oligomerization. Under standard ethylene oligomerization conditions (30 bar ethylene, 60° C, methylcyclohexane solvent), all of the in situ-formed complexes show catalytic activity, producing oligomers together with varying amounts of polyethylene (PE). ...