Improvement of the enantioselectivities of Mandyphos‐Pd complexes by introducing groups with different steric and electronic properties

Abstract

BackgroundMandyphos‐Pd has been proven to be a good chiral extractant to enantioseparate 3‐chlorophenylglycine enantiomers with a separation factor of 2.64. However, this extractant is not suitable to enantioseparate other amino acids with separation factors below 2.0. The poor versatility has limited its practical application in chiral extraction.RESULTSMandyphos derivatives with different steric and electronic properties were synthesized and their enantioseparation properties toward amino acid and mandelic acid enantiomers were investigated. The results suggested that the substituent groups with different steric properties affect the extraction properties probably by adjusting the angles of tetra‐coordinated palladium complexes. And the substituent groups with different electronic properties affect the extraction properties mainly by adjusting the π‐π interactions/steric hindrance effects between Mandyphos‐Pd and substrates. After optimization, the highest separation factors for phenylalanine, homophenylalanine, 3‐chloro‐phenylglycine, 4‐nitro‐phenylalanine, mandelic acid and 2‐Cl‐mandelic acid are 2.10, 2.77, 3.51, 2.42, 2.24 and 5.19, respectively. The enantioseparation mechanisms revealed that the coordination interactions between metal ions and ‐COO−/‐NH2, π‐π interactions or steric hindrance effects between aryls are the main acting forces in chiral recognition.CONCLUSIONThe enantioselectivities of Mandyphos‐Pd complexes are improved by introducing groups with suitable steric and electronic properties. Structural modification is a useful method to improve the enantioseparation efficiencies of chiral extractants. The results of this work will supply important theoretical guidance and reference for the design and modification of novel diphosphine ligands in future work.This article is protected by copyright. All rights reserved.