Synthesis and structural characterization of aluminum complexes supported by NNO-tridentate ketiminate ligands: Efficient catalysts for ring-opening polymerization of L-lactide

Abstract

Four NNO-tridentate ketiminate derivatives (L-H-H, L-F-H, L-OMe-H and L-tBu-H) were prepared through the condensation reaction of 1-(4-chlorophenyl)-4-(4-X-benzoyl)-3-methyl-1H-pyrazol-5(4H)-one (X = H, F, OMe, Bu-t) with N,N-dimethylenediamine (1.1 molar equiv) under reflux condition. Further reaction of AlMe3 (1.2 molar equiv) with L-H-H, L-F-H, L-OMe-H and L-tBu-H, respectively, affords penta-coordinated mono-adduct aluminum complexes [(L-H)AlMe2] (1), [(L-F)AlMe2] (2). [(L-OMe)AlMe2] (3), and [(L-tBu)AlMe2] (4) in high yield. Experimental results indicate complexes 1-4 are active catalysts for ring-opening polymerization of L-lactide (L-LA) in the presence of benzyl alcohol (BnOH). Al complex 2 catalyzes efficiently not only in a "living" fashion but also an "immortal" manner, giving polymers with the expected molecular weights and narrow PDIs. (C) 2012 Elsevier B.V. All rights reserved.