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 AlMe 3 and chiral biaryl Schiff-base NO 2 ligands, 1 H 2 - 7 H 2 , 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 1 H 2 with 1 equiv of AlMe 3 in THF gives the mononuclear complex ( 1 )AlMe(THF) ( 8 ) in 90% yield. While reaction of 2 H 2 , 3 H 2 , 4 H 2 , 5 H 2 , 6 H 2 or 7 H 2 with 1 equiv of AlMe 3 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.