Über Reaktionen oxygenierter Kobalt(II)-Komplexe. V. Reaktivität diastereoisomerer μ-Peroxo-μ-hydroxo-dikobalt(III)-Ionen

On Reactions of oxygenated Cobalt(II) Complexes. V. Reactivity of diastereoisomeric μ-peroxo-μ-hydroxo-dicobalt(III) Ions The kinetics of dissociation of μ-peroxo-μ-hydroxo-dicobalt(III) chelates have been reinvestigated using a stopped flow technique. The binuclear cations (trien)Co(O₂, OH) Co(trien)]³⁺, (tren)Co(O₂, OH)Co(tren)]³⁺ and (en)₂Co(O₂, OH)Co(en)₂]³⁺ dissociate on acidifying to Co²⁺ and the protonated ligand and up to 100% of the bound O₂ is evolved. The dissociation is H⁺-catalyzed and first order in complex. The observed rate constants at pH 2 are in the range of 10^?3 to 10^?1 s^?1 (20°). They depend not only on the nature of the ligand and on ligand configuration but also on the diastereoisomeric structure of the binuclear cation. In the case of trien there are 8 possible chemically different isomers. On oxygenation of Co(trien)²⁺ in dilute solution 3 of those isomers seem to be formed preferentially. Their rate constants are separated over a factor of 50. For (en)₂ Co(O₂, OH)Co(en)₂]³⁺ there exist a meso form and a chiral structure. On oxygenation of Co(en)₂²⁺ in dilute solution the meso form and the racemate are formed to about equal amounts. The racemate dissociates about 5 times slower. Of the 3 possible achiral isomers of (tren)Co(O₂, OH)Co(tren)]³⁺ one is formed stereoselectively by oxygenation in solution.