A series of magnesium complexes containing the tetradentate di and tri anionic amine phenolate backbone were synthesized from the reaction of suitable ligands and diethyl magnesium. All the complexes were completely characterized by different spectroscopic techniques and single crystal X-ray diffraction studies. The single crystal X-ray structure showed that complexes 1 and 5 are dinuclear and trinuclear respectively. All these complexes (1-8) were found to be active towards the bulk the ring opening polymerization (ROP) of lactides in the presence or absence of benzyl alcohol, at 140 °C and it was found that the polymerizations were better controlled in the presence of benzyl alcohol. The kinetics and mechanistic studies associated with these polymerizations have been performed. The complexes have been shown to be highly active toward the copolymerization of cyclohexene oxide (CHO) and propylene oxide (PO) with carbon dioxide. The introduction of a bulky ortho substituent on the phenoxy units of the ligand decreases the catalytic activity of the corresponding magnesium complexes. © 2015 Elsevier Ltd. All rights reserved.