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-R(1)-4-R(2)-anilide)-5,6,7-trihydroquinoline (LH) with AlR(3) (R = Me or Et) afforded the aluminum complexes LAlR(2) (Al1–Al5,Al1: R(1) = (i)Pr, R(2) = H, R = Me; Al2: R(1) = Me, R(2) = H, R = Me; Al3: R(1) = H, R(2) = H, R = Me; Al4: R(1) = Me, R(2) = Me, R = Me; Al5: R(1) = Me, R(2) = Me, R = Et) in high yields. All aluminum complexes were characterized by NMR spectroscopy and elemental analysis. The molecular structures of complexes Al4 and Al5 were determined by single-crystal X-ray diffractions and revealed a distorted tetrahedral geometry at aluminum. In the presence of BnOH, complexes Al1–Al5 efficiently initiated the ring-opening homopolymerization of ε-caprolactone (ε-CL) and rac-lactide (rac-LA), respectively, in a living/controlled manner.