THE EFFECT OF N2-MONOMETHYLATION AND DIMETHYLATION ON THE CRYSTAL-STRUCTURES OF BIS[(S)-PHENYLALANINAMIDATO]COPPER(II) COMPLEXES

(S)-phenylalaninamide, N2-methyl-(S)-phenylalaninamide, and N2,N2-dimethyl-(S)-phenylalaninamide co-ordinate to copper(II) as amidates, giving rise to trans bis(phenylalaninamidato) copper(II) complexes CuL2H-2 respectively (1), (2), and (3). Their crystal structures were determined by X-ray crystallography. The striking feature is that in bis[N2-methyl-(S)-phenylalaninamidato]copper(II) complex (2), both methyl groups are on the axial positions and on the same side of the co-ordination plane. The knowledge of the crystal structures of complexes (1), (2), and (3) which are used successfully as chiral selectors in HPLC (reversed phase), provides very useful information on the stereochemical features of enantioselective species.