Optical Resolution of Phosphinates and Phosphine Oxides by Complex Formation with Optically Active 2,2′-Dihydroxy-1,1′-Binaphthyl and Crystallographic Study of two Diastereomeric Complexes with (CH₃)(C₆H₅)(OCH₃)PO

Some [(alkyl-substituted)arene] phosphinates and -phosphine oxides have been resolved efficiently by crystalline complexation with optically active 2,2′-dihydroxy-1, 1′-binaphthyl (1). Two diastereomeric 1:1 complexes of the latter with a representative phosphoric ester (CH₃)(C₆H₆)(CH₃O)P=O (2a) were studied by X-ray diffraction methods in order to characterize the geometric pattern of intermolecular interaction. They form very similar crystal structures in space group P2₁ which consist of continuous chains of hydrogen-bonded species. Along the chains, 2a is located between and bound (through its PO nucleophile) simultaneously to two adjacent molecules of 1, while 1 donates its OH protons to two different molecules of 2a. Steric forces that involve the lipophilic substituents and steric barriers on the interacting components play an important role in determining the crystal packing arrangements and effecting mutual recognition.