Di-nuclear zinc complexes containing tridentate imino-benzotriazole phenolate derivatives as efficient catalysts for ring-opening polymerization of cyclic esters and copolymerization of phthalic anhydride with cyclohexene oxide

Zinc catalysts incorporated by imino-benzotriazole phenolate (IBTP) ligands were synthesized and characterized by single-crystal X-ray structure determinations. The reaction of the ligand precursor ((IBTP)-I-C1DMe-H or (IBTP)-I-C1DIP-H) with diethyl zinc (ZnEt2) in a stoichiometric proportion in toluene furnished the di-nuclear ethyl zinc complexes [(-(IBTP)-I-C1DMe)ZnEt](2) (1) and [(-(IBTP)-I-C1DIP)ZnEt](2) (2). The tetra-coordinated monomeric zinc complex [((IBTP)-I-C1Ph)(2)Zn] (3) or [((IBTP)-I-C1Bn)(2)Zn] (4) resulted from treatment of (IBTP)-I-C1Ph-H or (IBTP)-I-C1Bn-H as the pro-ligand under the similar synthetic method with ligand to metal precursor ratio of 2:1. Single-crystal X-ray diffraction of bimetallic complexes 1 and 2 indicates that the (IBTP)-I-C1DMe or (IBTP)-I-C1DIP fragment behaves a NON-tridentate ligand to coordinate two metal atoms. Catalysis for ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL), -butyrolactone (-BL), and lactide (LA) of complexes 1 and 2 was systematic studied. In combination with 9-anthracenemethanol (9-AnOH), Zn complex 1 was found to polymerize epsilon-CL, -BL, and L-LA with efficient catalytic activities in a controlled character. This study also compared the reactivity of these ROP monomers with different ring strains by Zn catalyst 1 in the presence of 9-AnOH. Additionally, Zn complex 1 combining with benzoic acid was demonstrated to be an active catalytic system to copolymerize phthalic anhydride and cyclohexene oxide. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 714-725