Reaktivität von Koordinationsverbindungen, XXIII [1]. Bildung und Zerfall des Sauerstoffadduktes mit N,N′‐Bis‐(4‐(5)‐imidazolylmethyl)‐äthylendiamin‐kobalt (II)‐Ionen

In aqueous solution N, N′‐bis‐(4‐(5)‐imidazolylmethyl)‐ethylenediamine‐cobalt (II) (CoIMEN 2+ ) takes up molecular oxygen giving μ‐dioxygen‐μ‐hydroxo‐bis‐[N, N′‐bis‐(4‐(5)‐imidazolylmethyl)‐ethylenediamine]‐dicobalt (II). (Co IMEN) 2 O 2 (OH) 3+ is exceptionally stable against irreversible autoxydation to Co III species. Its absorption spectrum is very similar to that of the known analogous complex (CoTRIEN) 2 O 2 (OH) 3+ . The kinetics of formation and dissociation of (CoIMEN) 2 O 2 (OH) 3+ are studied by spectrophotometry and with an oxygen specific electrode. The rate of the forward reaction is described by v f = [CoIMEN 2+ ] 2 · [O 2 ] · ( k 1 + k 2 · [OH − ]) with k 1 = 9 · 10 4 M −2 s −1 and k 2 = 1 · 10 12 M −3 S −1 , at 25° and I = 0,2. A mechanism including hydroxylated as well as nonhydroxylated intermediates is proposed. Dissociation is preceeded by protonation of the oxygen adduct. At pH 1–2 the rate of dissociation is independent of [H + ] and follows first order kinetics: v D = k 3 · [(CoIMEN) 2 O 2 (OH) 3+ ] with k 3 = 2.15 · 10 −2 S −1 .