Highly active and selective ethylene oligomerization catalysts: Asymmetric 2,6-bis(imino)pyridyl iron (II) complexes with alkyl and halogen substitutients

A series of asymmetric 2,6-bis(arylimino)pyridines with alkyl and halogen substitutients on different iminoaryl rings and corresponding iron (II) complexes ([2-(Ar1N = CCH3)-6-(Ar2N = CCH3)C5H3N]FeCl2, 3a–3j) are synthesized and characterized. These Fe(II) complexes are highly active for ethylene oligomerization with high selectivity for linear α-olefins. The oligomer distributions can be tuned by the synergism of alkyl-steric effect and halogen electronic effect, and the production of C6–C16 can reach more than 80% with the highest selectivity being 87.5% for 3 g (Ar1 = 2-ethylphenyl, Ar2 = 2-fluorophenyl), which is 15–30% higher than that catalyzed by their methyl or fluoro-substituted symmetric counterparts.