Bis(amido)titanium complexes having chelating diaryloxo ligands bridged by sulfur or methylene and their catalytic behaviors for ring-opening polymerization of cyclic esters

A series of bis(dialkylamido) titanium complexes coordinated by O-E-O (E = S, CH2) chelating bis(aryloxo) ligands, Ti[E(4-Me-6-'BuC6H2O)(2)](NR2)(2) (1: E = S, R = Me; 2: E = S, R = Et; 3: E = CH2, R = Me; 4: E = CH2, R = Et), were synthesized by the reaction of Ti(NR2)(4) (R = Me, Et) with 2,2'-E(4-Me-6-'BuC6H2OH)(2) (E = S, CH2). The crystal structures of complexes 2 and 4 were determined by X-ray diffraction study. Complex 2 has a trigonal bipyramidal structure with the sulfur and nitrogen atom in trans positions and complex 4 has a tetrahedral structure. The complex 2 was found to initiate the controlled polymerization of epsilon-caprolactone in toluene at 100 degreesC affording poly(epsilon-caprolactone) and poly(L-lactide) with relatively narrow molecular weight distributions. The complex 4 showed higher activity for the polymerization of epsilon-caprolactone to give a polymer with a broader molecular weight distribution in comparison with complex 2. (C) 2003 Elsevier B.V. All rights reserved.