Effects of Aluminum Complexes Bearing β‑Thioketiminate and β‑Ketiminates on ε‑Caprolactone Ring-Opening Polymerization Reactivity

In this study, a series of Al complexes bearing β-ketiminates and β-thioketiminates were synthesized and used as catalysts in ε-caprolactone (CL) polymerization. S Pr –Al had the highest catalytic activity among all Al complexes bearing β-thioketiminates and was more active than O Pr –Al (2.8 times as high for CL polymerization) ([CL]/[S Pr –Al]/[BnOH] = 100:1:2, [S Pr –Al] = 0.02 M, conversion = 96% after 20 min at 25 °C). All Al complexes bearing β-thioketiminates exhibited higher catalytic activity (2.1- to 24.9-fold) relative to β-ketiminates. The polymerization results demonstrated that swapping oxygen atoms for sulfur atoms in β-ketiminate-associated Al complexes improved the catalytic activity of Al complexes for CL ROP.