Chiral Discrimination by a Quadridentate Amine: Structural Characterization of Diastereoisomeric Complexes involving Alanine

X-ray structure determinations have shown that two Co(III) complexes, derived from alanine and a chiral quadridentate ligand incorporating three 1R,2R-cyclohexyl moieties, both adopt a Delta -cis-beta (2) configuration. The differences between the complexes arise simply because the alanine configuration is R in one and S in the other. Although the quadridentate is effectively stereospecific in its coordination to Co(III), bound also to a bidentate chelate, the [Co(quadridentate)] unit displays little selectivity in its binding of the amino acid enantiomers.