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

Two series of ligand precursors [2-OH-3-(CH2NR2)-5-MeC6H2](2)CH2 (1: NR2 = NMe2; 2: NR2 = N(CH2)(4); 3: NR2 = N(CH2)(5); 4: NR2 = N(Me)Ph) and [2-OH-3-(CH=NR)-5-MeC6H2](2)CH2 (10: R = 2,6-(Pr2C6H3)-C-i; 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}](2)CH2 (6: NR2 = NMe2; 7: NR2 = N(CH2)(4); 8: NR2 = N(CH2)(5); 9: NR2 = N(Me)Ph) and [AlMe2{2-O-3-(CH=NR)-5-MeC6H2}](2)CH2 (15: R = 2,6-(Pr2C6H3)-C-i; 16: R = p-MeC6H4; 17: R = p-ClC6H4; 18: R = p-MeOC6H4; 19: R = Bu-t). All the compounds were characterized by H-1 and C-13 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.