Abstract
New enantiopure crown ethers containing either an ethyl diarylphosphinate moiety [(S,S)-4 to (S,S)-7] or a proton-ionizable diarylphosphinic acid unit [(S,S)-8 to (S,S)-11] have been synthesized. Electronic circular dichroism (ECD) studies on the complexation of these new enantiopure crown ethers with the enantiomers of alpha-(1-naphthyl)ethylammonium perchlorate (1-NEA) and with alpha-(2-naphthyl)ethylammonium perchlorate (2-NEA) were also carried out. These studies showed appreciable enantiomeric recognition with heterochiral [(S,S)-crown ether plus either (R)-1- or (R)-2-NEA] preference. Theoretical calculations found three significant intermolecular hydrogen bonds in the complexes of (S,S)-9. Furthermore, preference for heterochiral complexes was also observed, in good agreement with ECD results. Complex formation constants were determined by NMR titration for four selected crown ether/NEA pairs.