A complex of Ph 3PO with a chiral hydrogen-bond donor: X-ray crystal structures of the complexes with ( RS)-(±)- and ( S)-(−)-1,1′-bi-2,2′-naphthol: homochiral Ph 3PO

Abstract

The first complex of triphenylphosphine oxide (Ph 3PO) with a chiral substrate, formed by crystallising Ph 3PO in the presence of the synthetically important chiral auxiliary S-(−)-1,1′-bi-2,2′-naphthol (BINOL) is reported. The corresponding racemate form has also been prepared and the single-crystal X-ray diffraction structures of both reveal 1(BINOL):2(TPPO) stoichiometry. In the homochiral complex the TPPO molecules apparently exist in one enantiomeric form only. Crystal packing in both is dominated by intermolecular hydrogen bonding between a BINOL hydroxyl group and a TPPO oxygen atom (around 2 1 and 3 1 axes in the racemate and the chiral forms respectively). The crystalline racemate—a racemic compound rather than a conglomerate—is more densely packed than the homochiral form, thus apparently conforming to Wallach's rule.