Ring-opening polymerization of ε-caprolactone, β-butyrolactone and lactides by β-ketiminate pyrazolonate zinc complexes: Preparation and characterization

Four bidentated iminopyrazolones ((LH)-H-1-(LH)-H-4) were prepared by the reaction of 3-methyl-4-(4-methylbenzoyl)-1-phenyl-1H-pyrazol-5(4H)-one with POCl3 followed by the addition of the corresponding anilines. The reaction of less steric bulky ligands, (LH)-H-1-(LH)-H-3, with ZnEt2 yields homoleptic zinc complexes [L2Zn] (1-3), respectively. However, the most steric bulky ligand, OH reacts with ZnEt2 producing heteroleptic complex [(LZnEt)-Zn-4] which further reacts with benzyl alcohol (BnOH) giving [(LZn)-Zn-4(OBn)](2) (4). All of these complexes were characterized by elemental analyses, NMR spectroscopic study as well as X-ray diffraction. Experimental results indicate that complexes 1-3 are inactive toward the ring opening polymerization CROP) of rac-lactide. On the other hand, complex 4 showed excellent activity in the ROP of cyclic esters such as rac-lactide, epsilon-caprolactone and beta-butyrolactone. (C) 2013 Elsevier B.V. All rights reserved.