Titanium complexes bearing benzotriazole iminophenolate ligands as efficient catalysts for ring-opening polymerization of cyclic esters

Titanium catalysts incorporated by imino-benzotriazole phenolate (IBTP) ligands (C1NNIBTP, C1FuIBTP and C1NOIBTP) were synthesized and structurally characterized. The reaction of Ti(OiPr)4 with C1NNIBTP-H (1.0 molar equiv.) in toluene produced hexa-coordinated mono-adduct titanium complex [(C1NNIBTP)Ti(OiPr)3] (1). However, six-coordinated bis-adduct Ti complex [(C1FuIBTP)2Ti(OiPr)2] (2) or [(C1NOIBTP)2Ti(OiPr)2] (3) resulted from treatment of Ti(OiPr)4 with C1FuIBTP-H or C1NOIBTP-H in CH2Cl2 using a Ti to ligand precursor ratio of 1:2. Catalytic studies for ring-opening polymerization of ε-caprolactone (ε-CL) or L-lactide utilizing complex 1 were detailedly investigated. Titanium complex 1 was shown to effectively catalyze the ε-CL polymerization not only in a “controlled” fashion but also an “immortal” manner, giving narrowly dispersed polymers having the expected molecular weights.