Effective Enantioselective Recognition by Chiral Amino-Phosphonium Salts*.

The research on chiral recognition and selection is not only fundamental in deciding the mystery of homochirality, but also informative in terms of substrate recognition in biological processes and asymmetric catalysis. We report an enantiomeric pair of phosphonium salts having chiral (R and S) amino substituents that are utilized towards the enantioselective recognition of a variety of chiral compounds having functional groups, such as carboxylic acid, amine, and alcohol. These simple phosphonium salts are found to exhibit a high enantiomeric discrimination for 1-cyclohexylethylamine (CY). A remarkable guest selectivity (ξ) value of 5.3×10 is achieved for the enantiomer of R-CY over S-CY by using the R-isomer of the phosphonium salt. Such high binding selectivities and discrimination capabilities is attributed to multiple non-covalent interactions between the host and guest molecules as inferred from the DFT optimized structures of the host-guest pairs.