Synthesis and properties of [Co(NH3)2(AB)2]Cl complexes and their possible role in the formation of tris(amino-acidato)cobalt(III) isomers studied through reaction stereochemistry

Abstract

The preparation is described and the electronic absorption 1H NMR, and CD spectral patterns are reported for [Co(NH3)2(AB)2]Cl complexes, where AB is glycine (4 isomers of the complex), (S)-alanine (5 isomers), or(S)-valine (2 isomers). The isomers are intermediate products in the substitution reaction [Co(NH3)6]3+ → Co(NH3)2(AB)2]+ → [Co(AB)3] and undergo activated charcoal-catalyzed disproportionation [Co(NH3)2(AB)2]+ → [Co(NH3)4(AB)]2 +[Co(AB)3], and in the presence of amino acid, also substitution resulting in a preferential formation of mer-[Co(AB)3] isomers. The Δ isomers yield predominantly Δ[Co(AB)3]. Due to the disproportionations, and also isomerizations, of the [Co(NH3)2(AB)2]+ complexes, no straightforward relation exists between the geometry of these complexes and the mer-to-fac ratio of the final [Co(AB)3]compounds.