Reaktivität von Koordinationsverbindungen XXII [1]. Zur Kinetik der O2-Aufnahme von Kobalt(II)-Chelaten 3-zähniger Amine und Amide

The kinetics of the interaction between molecular oxygen and the Co²⁺-complexes of the three terdentate ligands Z, N-(2-picolyl)-ethylenediamine (PEN), N-(2-picolyl)-oxamide (POA) and diethylenetriamine (DIEN) have been studied spectrophotometrically and using an O₂ specific Clark electrode. Starting from the respective 1:1- and 1:2-complexes, the binuclear species ZCoO₂(OH)CoZ and Z₂CoO₂CoZ₂ are formed with each ligand. The existence of the former product shows that a minimum of three chelating nitrogen donors is sufficient to make a Co²⁺-complex reactive towards O₂. As derived from the empirical rate laws the same general reaction mechanism must be valid for all three systems. In the case of PEN- and DIEN-complexes the oxygen adducts are metastable intermediates and formed in stoichiometric quantities. With POA irreversible formation of cobaltic species is rapid, and O₂-adducts are present in steady state concentrations only, except in strongly basic solutions.