A series of iron complexes ligated by 2-imino-1,10-phenanthrolinyl ligands, LFeCl2 (L = 2-(ArNCR)-1,10-phen), were synthesized and sufficiently characterized by elemental and spectroscopic analysis along with X-ray diffraction analysis. Activated with methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), these iron(II) complexes show high catalytic activities up to 8.95 × 107 g mol-1(Fe) h-1 for ethylene oligomerization. The distribution of oligomers produced follows Schluz−Flory rules with high selectivity for α-olefins. Both the steric and electronic effects of coordinative ligands affect the catalytic activity and the properties of the catalytic products. The parameters of the reaction conditions were also investigated to explore the catalytic potentials of these complexes.