Racemate resolution via diastereomeric helicates in hydrogen-bonded co-crystals: the case of BINOL-diamine complexes

The structures of a series of co-crystals formed by enantiomers of BINOL (2,2'-dihydroxy-1,1'-binaphthalene) with (R,R)- 1,2-diaminocyclohexane (DACH) and (R,R)-1,2-diamino-1,2-diphenylethane have been determined by X-ray diffraction to investigate the factors responsible for diastereoselective co-crystallization, the process responsible for the highly effective resolution of rac-BINOL by DACH. The absolute configurations of the molecules and directional preferences of the hydrogen bonds in the supramolecular aggregates have been analyzed. The supramolecular aggregation of hydrogen-bonded BINOL and diamines shows considerable distortions from the helical shape, which indicates that cohesion forces other than hydrogen bonds play a significant role in the diastereoselective resolution. (c) 2007 Elsevier Ltd. All rights reserved.