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

In this study, a series of Al complexes bearing beta-ketiminates and beta-thioketiminates were synthesized and used as catalysts in epsilon-caprolactone (CL) polymerization. S-Pr-Al had the highest catalytic activity among all Al complexes bearing beta-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 degrees C). All Al complexes bearing beta-thioketiminates exhibited higher catalytic activity (2.1- to 24.9-fold) relative to beta-ketiminates. The polymerization results demonstrated that swapping oxygen atoms for sulfur atoms in beta-ketiminate-associated Al complexes improved the catalytic activity of Al complexes for CL ROP.