CHIRAL METAL-COMPLEXES .44. ENANTIOMERIC DISCRIMINATION IN TERNARY COBALT(III) COMPLEXES OF N,N'-DIMETHYL-N,N'-DI(2-PICOLYL)-1S,2S-DIAMINOCYCLOHEXANE AND ALPHA-AMINO-ACIDS - INCLUDING THE CRYSTAL-STRUCTURE OF THE S-PROLINATO COMPLEX

When the C-2-symmetrical complex A-alpha-[Co(S,S-picchxnMe(2))Cl-2](+) (S,S-picchxnMe(2) is N,N'-dimethyl-N,N'-di(2-picolyl)-1S,2S-diaminocyclohexane) is reacted with the alpha-amino acids proline (proH), alanine (alaH) or 2-amino-2-methylpropandioic acid (AMMAH(2)), the two chloride ions are replaced by the O,N-bidentates with retention of configuration at the metal centre, The steric environment generated by the metal complex is shown to enantiospecifically discriminate in favour of S-proline from a racemic mixture due to the steric requirements of this amino acid. With the less bulky alanine and AMMAH, ligands there is no enantiomeric preference observed upon their coordination. When the mixed diastereoisomeric Lambda-alpha-[Co(S,S-picchxnMe(2))(AMMAH)](2+) precursors are decarboxylated under warm acidic conditions, neither hand of alanine is found to predominate in the product. The crystal structure of the Lambda-alpha-[Co(S,S-picchxnMe(2))(S-pro)](ClO4)(2) . H2O salt of the sole S-prolinate product was determined by X-ray diffraction methods. Crystal data: C25H28N5O11Cl2Co is orthorhombic, space group P2(1)2(1)2(1), with a=11.082(3), b=13.838(4), c=19.387(5) Angstrom and Z=4. The structure was refined by least-squares methods to R=0.033 for 2672 diffractometer data. The Co atom is six-coordinate with the N-4-tetradentate and the O,N-bidentate amino acidate comprising the octahedral coordination sphere. The average Co-N(pyridine) and Co-N(tert-amine) distances are 1.96 and 2.00 Angstrom, respectively.