Ethylenediamine, complexes with cobalt , resolution

Fanali, S., Ossicini, L., Foret, F., and Bocek, R, Resolution of optical isomers by capillary zone electrophoresis study of enantiomeric and distereoisomeric cobalt (III) complexes with ethylenediamine and amino acid ligands, /. Microcol. Sep., 1, 190, 1989. 

Perhaps Wemer s tour de force in the area of polynuclear cobalt(III) complexes was his successful resolution of the hexoP ion (VIII). He prepared this ion and its ethylenediamine analog by heating a basic solution of m-diaquotetramminecobalt(III) sulfate and deduced its structure by observing that the acid cleavage gave back the cis-diaquo complex and cobaltous ion (37). He later resolved the ion into its optical antipodes with d-camphor sulfonic acid and d-bromocamphor sulfonic acid and obtained the D- and l- forms as the bromides (35). His successful resolution... 

Bridged hydroxy complexes (208) of the bisoxalate type have been known for many years. Both a trihydrate and an anhydrous form are known. The trihydrate is isomorphous with the corresponding cobalt(III) complex (Durrant s salt) and the hydrous complex is slowly converted to the hydrate on exposure to moisture. Only a preliminary crystallographic characterization has appeared " it crystallizes as a meso rather than racemic complex. IR and magnetic studies are in accord with the hydroxy-bridged structure. Despite the crystallographic meso structure, the resolution of the complexes has been reported either photochemically or with cis- — )bis(ethylenediamine)dinitrocobalt(III) and leads to optically active complexes with spectra similar to those of the corresponding tris oxalate. 

Tris (ethylenediamine) cobalt (III) chloride was first prepared by Werner.1 Resolution was effected through the chloride d-tartrate which was obtained by allowing the chloride (1 mol) to react with silver d-tartrate (1 mol). The correct ratio of chloride ion to tartrate ion is important and this has meant that it was necessary to isolate the pure solid chloride, the synthesis of which has been described by Work.2 In the present method the less soluble diastereo-isomer is isolated directly and the expensive and unstable silver d-tartrate is replaced by barium d-tartrate. The addition of activated carbon ensures rapid oxidation of the initial cobalt (II) complex and eliminates small amounts of by-products of the reaction. 

The first successful resolution of coordination compounds was reported by Werner in 1911 and involved two series of complexes, the cw-chloroammine-bis(ethylenediamine)cobalt(III) series (with V. L. King) and the m-bromo-amminebis(ethylenediamine)cobalt(III) series (with E. Scholze). Of the two, the bromoammine series is easier to resolve because of the greater difference in solubility between the diastereoisomers that are formed with the resolving agent, silver ( + )-octahedral configuration first postulated by Werner for cobalt(III) in 1893. 

---