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.