Mechanisms Underlying Enantiomeric Discrimination of Its Structural Analogues with a Diphenylethylenediamine Derivative Revealed by Proton NMR Spectroscopy

A C2-symmetric host (host 1) was synthesized by derivatization of chiral diphenylethylenediamine with phenylisocyanate. High-resolution proton nuclear magnetic resonance (1H NMR) was used to investigate whether the chiral host could be used for enantiomeric discrimination of its structural analogues:α-phenylethylamine (guest 2), α-(p-methoxyphenyl)ethylamine (guest 9) and their derivatives (guests 3~8 and 10~13), and hydrogen-bonding interactions underlying the enantiomeric discrimination. It was observed that the host was able to recognize the urea and amide derivatives of the two primary amines, except for guests 7 and 12 bearing two NO2 groups. The host had stronger hydrogen-bonding interactions with the urea derivatives of guests 2 and 9 than with the corresponding amide derivatives, and high enantiomeric discrimination ability for the CHCH3 groups of the (R)- and (S)-urea derivatives.