Titanium complexes bearing amine bis(phenolate) ligands: Synthesis, structure and catalysis in ring-opening polymerization of lactide

Monomeric bis(isopropoxy) titanium complexes LTi(O i Pr) 2 (L = ─ OC 6 H 2 –4-R 1 –6-R 2 –2-CH 2 N[(CH 2 ) 2 N(R 3 ) 2 ]CH 2 –4-R 4 –6-R 5 -C 6 H 2 O ─ , R 1 = R 2 = t Bu, R 3 = Et, R 4 = R 5 = Cl, (L 1 )Ti(O i Pr) 2 ; R 1 = R 2 = Me, R 3 = Et, R 4 = R 5 = Me, (L 2 )Ti(O i Pr) 2 ; R 1 = R 2 = t Bu, R 3 = Et, R 4 = OMe, R 5 = t Bu, (L 3 )Ti(O i Pr) 2 ; R 1 = R 4 = OMe, R 3 = Et, R 2 = R 5 = t Bu, (L 4 )Ti(O i Pr) 2 ; R 1 = R 2 = t Bu, R 3 = Me, R 4 = OMe, R 5 = t Bu, (L 5 )Ti(O i Pr) 2 ) supported by amine bis(phenolate) ligands were synthesized and characterized using NMR spectroscopy and elemental analysis. The solid-state structure of (L 3 )Ti(O i Pr) 2 was determined using single-crystal X-ray diffraction. (L 1 –5 )Ti(O i Pr) 2 were all found to initiate the ring-opening polymerization of l -lactide and rac -lactide in a controlled manner at 110–160°C. As shown by kinetic studies, (L 1 )Ti(O i Pr) 2 polymerized l -lactide faster than did (L 2 –5 )Ti(O i Pr) 2 . In addition, good number-average molecular weight and narrow polydispersity index (1.00–1.71) of polymers were also obtained. The microstructure of the polymers and a possible mechanism of coordination–insertion of polymerization were evidenced by MALDI-TOF and 1 H NMR spectra of the polylactides.