Ethylene polymerization by iron complexes with symmetrical and unsymmetrical ligands

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.