New iron-based bis(imino)pyridine complexes 6, 7 and the acetyliminopyridine complex 8a are active catalysts together with the co-catalyst MAO for the oligomerization of ethylene. The ligands 1-4 with electron donating methoxy- and electron withdrawing trifluoromethyl-substituents react with FeCl2 (thf)(2) to the Fe(II) complexes 6-8a. Especially p-methoxy substituents in 6b increase the selectivity in the production of alpha-olefins. The distribution of oligomers obtained in the catalyzed ethylene oligomerization with 5-8a follows Schulz-Flory rules for oligomers >C-4. The probability of chain propagation ot is increased by lowering the reaction temperature, while higher pressure of the ethylene gas in the reaction has nearly no effect on the ce-values. (C) 2003 Elsevier B.V. All rights reserved.