Dinuclear aluminum complexes supported by amino- or imino-phenolate ligands: synthesis, structures, and ring-opening polymerization catalysis of rac-lactide

Abstract

Two series of ligand precursors [2-OH-3-(CH₂NR₂)-5-MeC₆H₂]₂CH₂ (1: NR₂ = NMe₂; 2: NR₂ = N(CH₂)₄; 3: NR₂ = N(CH₂)₅; 4: NR₂ = N(Me)Ph) and [2-OH-3-(CHNR)-5-MeC₆H₂]₂CH₂ (10: R = 2,6-Prⁱ₂C₆H₃; 11: R = p-MeC₆H₄; 12: R = p-ClC₆H₄; 13: R = p-MeOC₆H₄; 14: R = Bu^t) were prepared. These compounds reacted with AlMe₃ to afford corresponding dinuclear aluminum complexes [AlMe₂{2-O-3-(CH₂NR₂)-5-MeC₆H₂}]₂CH₂ (6: NR₂ = NMe₂; 7: NR₂ = N(CH₂)₄; 8: NR₂ = N(CH₂)₅; 9: NR₂ = N(Me)Ph) and [AlMe₂{2-O-3-(CHNR)-5-MeC₆H₂}]₂CH₂ (15: R = 2,6-Prⁱ₂C₆H₃; 16: R = p-MeC₆H₄; 17: R = p-ClC₆H₄; 18: R = p-MeOC₆H₄; 19: R = Bu^t). All the compounds were characterized by ¹H and ¹³C NMR spectroscopy and elemental analyses. Complexes 6 and 16 were additionally characterized by single crystal X-ray diffraction techniques. Catalysis of the aluminum complexes towards the ring-opening polymerization of rac-lactide was evaluated in the presence of benzyl alcohol. All the polymerization reactions proceed in a controlled manner.