Salen, salan and salalen iron(iii) complexes as catalysts for CO2/epoxide reactions and ROP of cyclic esters

A salen ligand and its derivatives salan and salalen, bearing the same substituents on the phenolate rings, have been synthesized and then used for the preparation of the corresponding Fe(iii) complexes. All complexes were characterized by MALDI ToF mass spectroscopy, Evans method, and UV-Vis and IR spectroscopy. Moreover, for the salalen-based iron complex, the X-ray structure was studied. A comparison of their behaviour in the catalysis of CO2 with benchmark epoxide substrates allowed us to individuate an order of reactivity of the different classes of complexes. A salen Fe(iii) complex was prepared with a longer bridge between the two nitrogen atoms of the ligand skeleton in order to evaluate the influence of the flexibility on the activity of the catalyst. Finally, the same complexes were tested as catalysts in the ring-opening polymerization of l-lactide and epsilon-caprolactone.