Synthesis Of A Novel Type Of Chiral Zirconium Phosphonate And Its Application For Heterogeneous Asymmetric Catalysis

Heterogeneous asymmetric catalysis has received considerable attention in the area of catalysis. The suitable supports for chiral ligand are the key importance for heterogeneous asymmetric catalysis. Various reported supports such as organic polymers, silica or aluminosilicates and dendrimers are available for the immobilization of homogeneous chiral catalysts. In this paper, a readily available (1S, 2R)-(+)-2-amino-1, 2-diphenylethanol and (1R, 2S)-(-)-2-amino-l, 2-diphenylethanol were immobilized on the layered zirconium phosphonates and the hybrid chiral zirconium phosphonates framework by covalent bond to obtain a novel type of supported chiral catalyst.Four zirconium phosphonates, four hybrid zirconium phosphonates, a zirconium ethylphospho-nate and a zirconium phosphate-phosphonate had been synthesized under the atomospheric pressure by hydrothermal method. The composition, structure and surface morphology of the supports and catalysts were characterized by IR, ³¹P NMR, element analysis, TG, XPRD, SEM and AFM. The structure of the catalysts was simulated by the proposed model.The experimental results showed that the type of chiral zirconium phosphonates possessed regular crystalline with the layered structures. The d spacings of the layered compounds were greatly related to the volume and structure of their phosphonates. For the hybrid compounds [Zr(O₃P(?))_2-x(O₃P R)_x·yH₂O, (?) is N-ethyl-2-imino-1, 2-diphenylethanol and R is ethyl group], the d spacings decreased with the x increase from x= 0 to 0.77, 1.72 and 2.0. Due to the hydrogen bond between the moieties of 2-amino-1, 2-diphenylethanol in the framework of zirconium phosphonate, the chiral organic ligands on the surface of zirconium phosphonates lined up regularly and homogeneously. The catalysts showed self-assemble structures detected by AFM. In the addition of Et₂Zn to benzadehyde, the above 90 % yield and 51 % e.e enantioselectivity of optical secondary alcohol were obtained at room temperature for 72 h in tolune as solvent. The enantioselectivity decrease at only 6 % enantiomeric excess lower than the corresponding chiral ligand (1R, 2S)- (-)-35 in homogeneous asymmetric catalysis. The zirconium phosphonate catalysts was easily recovered and reused.