Iron (II) complexes with hyperbranched salicylaldimine ligands: Synthesis, characterization and ethylene oligomerization

A series of novel hyperbranched salicylaldimine iron (II) complexes have been synthesized and characterized with IR, UV, MS and TG. These iron coordinative complexes, activated with methylaluminoxane (MAO), exhibited moderate activities in ethylene oligomerization (TOF   =   2.62–9.19   ×   10 4   g/mol   Fe·h), giving higher selectivity (7.37–24.44%) for higher carbon number olefins (C 10+ ). As reaction temperature increased, the catalytic activities firstly increased and then decreased, but the product distributions were almost independent on the temperature. With the increase of the Al/Fe molar ratio and the ethylene pressure, the catalytic activity increased rapidly and the selectivity of higher carbon number olefins increased at first and then decreased. In addition, the nature of solvent and co-catalyst, as well as the structure of catalyst significantly affected both the catalytic activities and product compositions of the resultant catalysts. Under optimized conditions ([Fe]   =   7   μmol, 25   °C, Al/Fe   =   500, 0.5   MPa ethylene), pre-catalyst Fe1 led to catalytic activity of 6.91   ×   10 4   g/mol   Fe·h and 20.48% selectivity for higher carbon number olefins.