Dipa Mandal
Indian Institute of Technology Madras, India
Title: Group IV complexes of tridentate salicylaldiminato ligands and their catalytic activity in ring-opening polymerizations of ε-caprolactone, lactides and epoxides
Biography
Biography: Dipa Mandal
Abstract
Biodegradable polymers have various biomedical and environmental applications and the preferred method for producing these polymers is ring-opening polymerizations (ROP) of ε-caprolactone (ε-CL) and lactides. Particularly group IV complexes are found to be most efficient and stereoselective as catalysts for the ROP. New Ti(IV), Zr(IV) and Hf(IV) complexes containing tridentate [NNO]-type salicylaldiminato ligands (L1 and L2) have been synthesized by reacting metal alkoxides with the ligands via alcohol elimination. In the solid state, Zr and Hf complexes are monomeric whereas, the Ti complexes are dimeric, where both Ti atoms are connected through mono-µ-oxo bridge formation due to controlled hydrolysis. During the complexation with L1 in situ intramolecular Meerwein–Ponndorf–Verley (MPV) type reduction of the imine moiety happened and the amine got deprotonated. In contrast, the ligand L2 has produced imine complexes under similar conditions. DFT calculations were carried out to investigate the activation energies of MPV type reduction. These complexes are found to be active catalysts for the ROP of ε-CL and rac-LA with narrow MWDs of the produced polymers in a living manner through coordination-insertion mechanism. Also, these complexes initiate the polymerization in a stereoselective manner to produce heterotactic-rich PLA from rac-LA with Pr value upto 0.84. In addition, these complexes are quite active for the catalytic ROP of epoxides such as rac-cyclohexene oxide, rac-styrene oxide and rac-propylene oxide.