PREDICTIONS AND METHODS OF SEPARATION OF RACEMIC BIDENTATE LIGANDS VIA STEREOSELECTIVE LIGAND-EXCHANGE REACTIONS

The technique of molecular mechanics has been applied to the prediction of isomer distributions of several complexes of chiral quadridentate amine ligands in conjunction with some optically active bidentate substrates. Specifically, the systems reported comprise the cobalt(III) and nickel(II) complexes of N,N'-bis[2(S)-2-pyrrolidinylmethyl]ethane-1,2-diamine (S,S-epm) and N,N'-bis[2(S)-2-pyrrolidinylmethyl]propane-1,3-diamine (S,S-ppm) in combination with the chiral bidentate ligands propane-1,2-diamine, (pn) 2-pyrrolidinylmethanamine (pam), and alanine (ala). Agreement between all predicted and observed isomer ratios was within 5%. The experimentally determined enantiomer ratios were as follows: [Co(S,S-ppm)(pn)]3+, 49/51 R-pn/S-pn; [Ni(S,S-ppm)(pn)]2+, 57/43 R-pn/S-pn; [Ni(S,S-ppm)(pam)]2+, 44/56 R-pam/S-pam; [Ni(S,S-epm)(pn)]2+, 43/57 R-pn/S-pn; [Ni(S,S-epm)(pam)]2+, 70/30 R-pam/S-pam. Various experimental methods are reported for the determination of chiral separation.