Crystal structure of the keto-enamine form of (+) (1S,2S)-2-(2-hydroxybenzylidene)amine-1-phenyl-1,3-propanediol

The title compound crystallizes in the orthorhombic space group P2₁2₁2₁, withZ=4,a=6.068(1)Å,b=10.922(1)Å, andc=21.713(2)Å. The compound is the chiral ligand of a copper complex used as an enantioselective catalyst. It crystallizes from methanol in the keto-enamine form, though the enol-imine isomer predominates in the solution. Most N-salicylideneamines studied by X-ray are enol-imines. The two tautomeric forms may interchange through anintramolecular hydrogen bond and the distances between non-H atoms in the resulting cyclic –O–H...N=C–C=C- or –C=O...H–N–C=C- fragment may be misleading, so that H atom position is the crucial factor for determination of the proper tautomeric form.