Stereoselectivity in the reactions of cobalt(III) complexes of meso- and dl-2,3-diaminobutanetetraacetic acid with aliphatic diamines

Abstract

Several salts containing the complex anion M(DIMEDTA) − (where M = Ni, Co( II), Cu(II); H 4DIMEDTA = 2,3-diaminobutanetetraacetic acid) have been prepared. The optically stable ion (+) 5461Co ( meso-DIMEDTA) − obtained from the racemic salt K[Co( meso-DIMEDTA)] .2H 2O was shown to react stereoselectively with 50% aqueous ethylenediamine (en), dl-1,2-diaminopropane (pn) and meso-2,3-diaminobutane ( meso-bn) to give (+) Coen 3 3+, (+) Copn 3 3+ and (+) Co( meso- bn) 3 3+ as the predominant isomers. The reaction between aqueous ethylenediamine and Co( dl-DIMEDTA) − resembled that of Co(EDTA) − in following first-order kinetics, but is faster. That with Co( meso-DIMEDTA) − is still faster but does not follow first-order kinetics and there is a definite induction period. In no case does the reaction go to completion; complementary experiments indicate that the reactions of Co(EDTA) − are more complicated that previously reported and that the published rate constants must be incorrect.