Peroxo-dicobalt III Complexes

Peroxo-bridged dicobalt(III) complexes are often regarded as models for biological oxygen carriers, and there has been considerable interest in the formation and breakdown of such complexes in aqueous solution. 

The rates of the rapid reversible uptake of SO2 by [Co(tren)(OH2)2] have been studied by stopped-flow techniques over the pH range 3.5-6.6 at various temperatures. The kinetic data obtained are summarized in 

The rate of SO2 uptake by aj8S-[Co(tetren)OH] (23) has also been studied by stopped flow. The rate and activation parameters for SO2 

AS = -21.0 cal moF Retardation by SOs and SO4 is observed and is ascribed to the formation of nonreactive ion pairs. The product of SO2 uptake is the O-bonded sulfito complex. At 10°C the protonated form of such a species a/3S-[Co(tetren)OS02H] [pK = 3.3) eliminates SO2 with k = 550 s , NH = 7.2 kcal mol, and AS = -20.4 cal K mol. The oxygen-bonded sulfito intermediate shows no tendency to undergo internal redox, but slowly isomerizes to its sulfur-bonded analog. 

Kinetic data on complex formation between [Co(NH3)sOOC-C02H] and Fe(III) in acidic solution has been reported. Plots of kobs versus [Fe ]totai are linear with pronounced intercepts. The intercepts are essentially independent of [H ] and the slopes decrease with increasing acidity. A mechanism is proposed in which all possible reactant species are involved 

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The kinetics of formation from and decomposition into Co(II) and 02 of jU-hydroxo-jU-peroxo dicobalt(III) complexes have been studied in detail, and the mechanistic aspects have been discussed in a recent article by Fallab and Mitchell (119). Two different mechanisms have been invoked to explain the kinetics of the first bridge cleavage of L4Co(0H)(02)CoL43+ species. One mechanism involves hydroxo bridge cleavage and formation, as shown in Eq. (71). The parameter values... 

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