Synthesis and characterization of a novel type of self-assembled chiral zirconium phosphonates and its application for heterogeneous asymmetric catalysis

Abstract

A readily available (1 S,2 R)-(+)-2-amino-1,2-diphenylethanol and (1 R,2 S)-(−)-2-amino-1,2-diphenylethanol were immobilized on the layered zirconium phosphonates and the hybrid chiral zirconium phosphonates framework had been synthesized for the first time. The solid catalysts were characterized by IR, AFM, TG, XRD and elemental analysis. AFM showed that the self-assembled structure of chiral organic ligands on the surface of zirconium phosphonates 4 lined up regularly and homogeneously at 1.1 nm distance. XRD data indicated that zirconium phosphonate 4 was semi-crystalline with the interlayer space 20.11 Å. Zirconium phosphonates 4 enantioselectively catalysized the addition of Et 2Zn to benzaldehyde to afford optical secondary alcohol in >90% yield and 51% e.e. which only decrease at 6% enantiomeric excess lower than the corresponding chiral ligand (1 R,2 S)-(−)- 2 in homogeneous asymmetric catalysis.