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-(CH(2)NR(2))-5-MeC(6)H(2)](2)CH(2) (1: NR(2) = NMe(2); 2: NR(2) = N(CH(2))(4); 3: NR(2) = N(CH(2))(5); 4: NR(2) = N(Me)Ph) and [2-OH-3-(CH=NR)-5-MeC(6)H(2)](2)CH(2) (10: R = 2,6-Pr(2)(i)C(6)H(3); 11: R = p-MeC(6)H(4); 12: R = p-ClC(6)H(4); 13: R = p-MeOC(6)H(4); 14: R = Bu(t)) were prepared. These compounds reacted with AlMe(3) to afford corresponding dinuclear aluminum complexes [AlMe(2){2-O-3-(CH(2)NR(2))-5-MeC(6)H(2)}](2)CH(2) (6: NR(2) = NMe(2); 7: NR(2) = N(CH(2))(4); 8: NR(2) = N(CH(2))(5); 9: NR(2) = N(Me)Ph) and [AlMe(2){2-O-3-(CH=NR)-5-MeC(6)H(2)}](2)CH(2) (15: R = 2,6-Pr(2)(i)C(6)H(3); 16: R = p-MeC(6)H(4); 17: R = p-ClC(6)H(4); 18: R = p-MeOC(6)H(4); 19: R = Bu(t)). All the compounds were characterized by (1)H and (13)C 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.