Group 4 metal complexes of Trost's semi-crown ligand: synthesis, structural characterization and studies on the ring-opening polymerization of lactides and ε-caprolactone.
The synthesis of titanium(IV), zirconium(IV) and hafnium(IV) complexes of Trost's semi-crown ligand is described. All complexes were fully characterized by 1H and 13C NMR and mass spectroscopy. The molecular structures of the representative complexes 2, 3 and 4 were determined by single-crystal X-ray diffraction studies. The X-ray diffraction studies reveal that complexes 2, 3 and 4 crystallized in an orthorhombic crystal system. Complexes 2 and 3 have a monomeric structure in the solid state with distorted octahedral geometry around the metal center, whereas complex 4 was found to crystallize in a trimeric structure bridging with an oxygen atom, where the geometry around the titanium is distorted trigonal bipyramidal. The activities and stereoselectivities of these complexes toward the ring-opening polymerization (ROP) of lactides (L-LA and rac-LA) and ε-caprolactone (CL) have been investigated. Complexes 1–4 were found to be efficient single-component initiators for the ring-opening polymerization of cyclic esters and yielded high molecular weight polymers (Mn) with narrow molecular weight distributions (MWD).The microstructure of the resultant polylactides (PLAs) from rac-LA was determined. Complexes 2 and 3 afforded isotactic-enriched PLA (Pm = 0.78–0.71) with narrow MWD (1.07–1.04), on the other hand complexes 1 and 4 produced atactic PLA. Kinetic and post polymerization studies confirm that the polymerization proceeds through the coordination–insertion mechanism.
Department of Chemistry, Indian Institute of Technology Madras, Chennai-600 036, Tamil Nadu, India. dchakraborty@iitm.ac.in dc@iitp.ac.in.
Bijja
B
Rajashekhar
Sagnik K
SK
Roymuhury
Debashis
D
Chakraborty
Venkatachalam
V
Ramkumar
D002208:Caproates / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D003442:Crowns; D018360:Crystallography, X-Ray; D004146:Dioxanes / Q000737:chemistry*; D006195:Hafnium / Q000737:chemistry; D007783:Lactones / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008670:Metals / Q000737:chemistry*; D008968:Molecular Conformation; D058105:Polymerization; D011108:Polymers / Q000737:chemistry; D011789:Quantum Theory; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014025:Titanium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
D002208:Caproates; D056831:Coordination Complexes; D004146:Dioxanes; D007783:Lactones; D008024:Ligands; D008670:Metals; D011108:Polymers; C121056:caprolactone; C091880:dilactide; D015040:Zirconium; D014025:Titanium; D006195:Hafnium