Synthesis of Aluminum Complexes Bearing 8-Anilide-5,6,7-trihydroquinoline Ligands: Highly Active Catalyst Precursors for Ring-Opening Polymerization of Cyclic Esters

The stoichiometric reactions of 8-(2,6-R1-4-R2-anilide)-5,6,7-trihydroquinoline (LH) with AlR3(R = Me or Et) afforded the aluminum complexesLAlR2(Al1–Al5,Al1: R1=iPr, R2= H, R = Me;Al2: R1= Me, R2= H, R = Me;Al3: R1= H, R2= H, R = Me;Al4: R1= Me, R2= Me, R = Me;Al5: R1= Me, R2= Me, R = Et) in high yields. All aluminum complexes were characterized by NMR spectroscopy and elemental analysis. The molecular structures of complexesAl4andAl5were determined by single-crystal X-ray diffractions and revealed a distorted tetrahedral geometry at aluminum. In the presence of BnOH, complexesAl1–Al5efficiently initiated the ring-opening homopolymerization ofε-caprolactone (ε-CL) andrac-lactide (rac-LA), respectively, in a living/controlled manner.Keywords:aluminum complexes;crystal structures;ring-opening polymerization;biodegradable polyesters