CHIRAL METAL-COMPLEXES .44. ENANTIOMERIC DISCRIMINATION IN TERNARY COBALT(III) COMPLEXES OF METHYL-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 ethyl-N,N'-di(2-picolyl)-1S,2S-diaminocyclohexan e) is reacted with the alpha-amino acids proline (proH), alanine (alaH ) or 2-amino-2-methylpropandioic acid (AMMAH(2)), the two chloride ion s are replaced by the O,N-bidentates with retention of configuration a t the metal centre, The steric environment generated by the metal comp lex is shown to enantiospecifically discriminate in favour of S-prolin e from a racemic mixture due to the steric requirements of this amino acid. With the less bulky alanine and AMMAH, ligands there is no enant iomeric preference observed upon their coordination. When the mixed di astereoisomeric Lambda-alpha-[Co(S,S-picchxnMe(2))(AMMAH)](2+) precurs ors are decarboxylated under warm acidic conditions, neither hand of a lanine is found to predominate in the product. The crystal structure o f the ambda-alpha-[Co(S,S-picchxnMe(2))(S-pro)](ClO4)(2) . H2O salt of the sole S-prolinate product was determined by X-ray diffraction meth ods. 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 267 2 diffractometer data. The Co atom is six-coordinate with the N-4-tetr adentate 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.