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Group 4 metal complexes containing the salalen ligands: Synthesis, structural characterization and studies on the ROP of cyclic esters
Date Issued
15-09-2018
Author(s)
Chakraborty, Debashis
Rajashekhar, Bijja
Mandal, Mrinmay
Ramkumar, Venkatachalam
Abstract
The synthesis of homoleptic salalen ligand supported group 4 complexes and their applications in the ring-opening polymerization (ROP) of ε-caprolactone (ɛ-CL) and lactide (LA) are described. All these complexes of type M(L)2 (LH = (E)-N-(2-(3,5-dibromo-2-hydroxybenzylideneamino)phenyl)-4-methylbenzenesulfonamide: M = Ti (1), M = Zr (4), M = Hf (7); LH = (E)-N-(2-(2-hydroxybenzylideneamino)phenyl)-4-methylbenzenesulfonamide: M = Ti (2), M = Zr (5), M = Hf (8); LH = (E)-N-(2-(3,5-di-t-butyl-2-hydroxybenzylideneamino)phenyl)-4-methylbenzenesulfonamide: M = Ti (3), M = Zr (6), M = Hf (9)) are characterized by various spectroscopic techniques. The single crystal X-ray diffraction analysis confirmed that the metal centres in complexes 6 and 8 adopt distorted dodecahedral geometry. The self-assembly of the complexes in solid state through the molecular interactions demonstrated that the supramolecular network forms molecular channels which act as a host lattice for the assembly of toluene solvent molecules. Complexes (1–9) are effective catalysts for the ROP of ɛ-CL and LA and produced high molecular weight (Mn) polycaprolactone (PCL) and poly (lactic acid) (PLA) respectively with narrow molecular weight distributions (MWDs) in the range of 1.17–1.28. PLA produced from the polymerization of rac-LA is atactic. However, better control over the polymerization process was achieved in the presence of toluene as solvent at 80 °C. All these polymerizations follow first-order kinetics with respect to monomer concentration. MALDI-TOF and NMR spectral analysis suggested that the polymerization proceeds through the coordination-insertion mechanism.
Volume
871