A series of penta-coordinated iron complexes with 2,6-bis(imino)pyridine ligands were prepared and used in ethylene polymerization or oligomerization with methylaluminoxane as (MAO) co-catalyst. The activity of the complexes depends strongly on the steric and electronic effects of the ligands, in which the electronic conjugated system plays an important role. N,N′-Bis(α,α-diphenyl) methyl 2,6-bis(imino)pyridine iron complex (1) could not activate ethylene, N,N′-difluorenyl-2,6-bis(imino)pyridine iron complex (2) exhibited high activity for ethylene oligomerization, whilst N,N′-diaryl 2,6-bis(imino)pyridine iron complexes (3–6) performed ethylene polymerization. The results are collected and briefly discussed.© 2002 Society of Chemical Industry