2D Zn(II) Coordination Polymer Containing a Quinalizarin Ligand as a Novel Catalyst for Ring-Opening Polymerization of ε-Caprolactone

A novel 2D zinc(II) coordination polymer (complex 1), which comprises quinalizarin and acetate ligands that coordinate Zn(II) centers in both penta- and hexacoordinate geometries, was synthesized. This coordination polymer represents the first reported structure of a quinalizarin-based coordination of any metal complex. Its molecular structure was elucidated through single-crystal and powder X-ray diffraction, UV–Vis spectroscopy, thermogravimetric analysis, and 1H NMR. Complex 1 was investigated as a catalyst for the bulk polymerization of ε-caprolactone (ε-CL) using benzyl alcohol as an initiator at 170 °C. The resulting poly-ε-caprolactone was characterized by 1H NMR, matrix-assisted laser desorption/ionization-time-of-flight, and gel permeation chromatography analyses. The results demonstrate that the zinc coordination polymer effectively catalyzes the ring-opening polymerization of ε-CL with a conversion of 99%, predominantly yielding open-chain polymers featuring hydroxyl terminal groups with molecular weights greater than 5 kDa.