Factors determining the pattern of a hydrogen‐bonding network in the diastereomeric salts of 1‐arylethylamines with enantiopure P‐chiral acids

In order to clarify factor(s) determining the pattern of a hydrogen‐bonding network in the diastereomeric salts of 1‐arylethylamines ( 1 ) with enantiopure P‐chiral acids, three kinds of enantiopure P‐chiral alkylphenylphosphinothioic acids ( 3 ) were synthesized, and their chiral recognition abilities for racemic 1 were examined. The characteristics of the diastereomeric salt crystals of 1 with 3 were then studied on the basis of their X‐ray crystallographic analyses. Statistical analysis on the molecular conformations observed in the diastereomeric salts with 3 as well as those with P‐chiral O ‐alkyl arylphosphonothioic acids ( 2 ), which have a chemical structure similar to that of 3 , and molecular orbital calculations for 2 and 3 in a gas phase revealed that the torsion angle between the aromatic plane and the PO(alkoxy in 2 ) or PC(alkyl in 3 ) plays an important role in determining the pattern of a hydrogen‐bonding network in the diastereomeric salts, either a closed globular cluster or an infinite 2 1 column type. The calculations also indicated that there is a hydrogen‐bonding‐like interaction between the ammonium hydrogen atom of 1‐arylethylammonium cations and the PO(alkoxy) oxygen atom of phosphonothioate anions in the clusters. Chirality, 2008. © 2008 Wiley‐Liss, Inc.