THE ISOMERISM OF THE (ETHYLENEDIAMINE-N,N'-DIPROPIONATO)(ETHYLENEDIAMINE)-COBALT(III) ION AND ITS STEREOSELECTIVE ISOMERIZATION REACTION

Three isomers (one alpha and two beta) of [Co(eddp)(en)]+ were prepared and optically resolved. The stereochemistry was studied on the basis of absorption, CD and C-13 NMR spectral data. Two beta-isomers, beta(e-1) and beta(e-2), were conformational diastereomers arising from a difference of the chirality around one of the asymmetric N atoms in a coordinated eddp ligand. The beta(e-1) half-arrow-right-over-half-arrow-left beta(e-2) change was an inversion reaction at the asymmetric sec-N atom in the in-plane beta-alaninate ring of the coordinated eddp, and the rate was slow. The alpha half-arrow-right-over-half-arrow-left beta(e-1) or beta(e-2) change (coordination-site exchange reaction) was stereoselective and could be explained by the Co-O bond rupture mechanism proposed for Co(III)-edda complexes.