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 ((IBTP)-I-C1NN, (IBTP)-I-C1Fu and (IBTP)-I-C1NO) were synthesized and structurally characterized. The reaction of Ti(OPr)(4) with (IBTP)-I-C1NN-H (1.0 molar equiv.) in toluene produced hexa-coordinated mono-adduct titanium complex ((IBTP)-I-C1NN)Ti((OPr)-Pr-i)(3)] (1). However, six-coordinated bis-adduct Ti complex [((IBTP)-I-C1Fu)(2)Ti((OPr)-Pr-i)(2)] (2) or [((IBTP)-I-C1NO))(2)Ti((OPr)-Pr-i)(2)] (3) resulted from treatment of Ti((OPr)-Pr-i)(4) with (IBTP)-I-C1Fu-H or (IBTP)-I-C1NO-H in CH2Cl2 using a Ti to ligand precursor ratio of 1:2. Catalytic studies for ring-opening polymerization of epsilon-caprolactone (epsilon-CL) or L-lactide utilizing complex 1 were detailedly investigated. Titanium complex 1 was shown to effectively catalyze the epsilon-CL polymerization not only in a "controlled" fashion but also an "immortal" manner, giving narrowly dispersed polymers having the expected molecular weights. (C) 2018 Elsevier B.V. All rights reserved.