PREPARATION AND STEREOCHEMISTRY OF THE MIXED-LIGAND COMPLEX, AMMINE(ETHYLENEDIAMINE)(ETHYLENEDIAMINE-N-ACETATO)COBALT(III)

Four geometrical isomers for [Co(edma)(NH3)(en)]2+ (edma=ethylenediamine-N-acetate) were prepared for the first time; isomers with the facially chelated edma ligand were optically resolved. Geometrical structures were assigned on the basis of the absorption, H-1 NMR, C-13 NMR, and CD spectral data; the crystal structure of one of these isomers was determined by an X-ray diffraction method. The crystal is orthorhombic, space group P2(1)2(1)2(1), a=8.345(1), b=21.054(2), c=7.914(1) angstrom, V=1390.6(3) angstrom3, Z=4, and R=0.047 for 1985 independent reflections [F(o)>3-sigma(F(o))]. The cobalt atom is octahedrally surrounded by one ammine, the bidentate en, and the facially chelated edma ligands. The ammine ligand occupies the trans position of the secondary nitrogen atom in the edma, trans (N(c), NH3) geometry. This cation, which shows a positive CD sign at 519 nm, takes a LAMBDA-DELTA configuration around the cobalt atom and an S configuration around the secondary nitrogen atom. The absolute configurations of the other optically active isomers with the facially chelated edma ligand were assigned based on the stereospecific deuteration for the methylene protons of the glycinate ring in the edma ligand in a basic D2O solution.