Synthesis, structure, and catalytic activity of organoaluminum complexes with chiral biaryl Schiff-base ligands

Abstract

A new series of organoaluminum complexes have been prepared by alkane elimination in good yields from AlMe3 and chiral biaryl Schiff-base NO2 ligands, 1H2-7H2, which are derived from (S)-2-amino-2′-hydroxy-1,1′-binaphthyl or (S)-2-amino-2′-hydroxy-6,6′-dimethyl-1,1′-biphenyl, respectively. However, solvent plays an important role in the formation of the aluminum complexes. For example, treatment of ligand 1H2 with 1 equiv of AlMe3 in THF gives the mononuclear complex (1)AlMe(THF) (8) in 90% yield. While reaction of 2H2, 3H2, 4H2, 5H2, 6H2 or 7H2 with 1 equiv of AlMe3 in benzene gives the binuclear complexes {(2)AlMe}2 (9), {(3)AlMe}2 (10), {(4)AlMe}2 (11), {(5)AlMe}2 (12), {(6)AlMe}2 (13) and {(7)AlMe}2 (14), respectively, in good yields. Complexes 8–14 have been characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses. The complexes 8–14 are active catalysts for the polymerization of rac-lactide in the presence of isopropanol, leading to the heterotactic-rich polylactides.