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Issue 37, 2015
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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

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Abstract

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.

Graphical abstract: 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

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Article information


Submitted
15 Jun 2015
Accepted
24 Jul 2015
First published
28 Jul 2015

Dalton Trans., 2015,44, 16280-16293
Article type
Paper
Author version available

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

B. Rajashekhar, S. K. Roymuhury, D. Chakraborty and V. Ramkumar, Dalton Trans., 2015, 44, 16280
DOI: 10.1039/C5DT02267C

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