Dioxygen superoxo intermediate, kinetic

Mechanisms and rates of dioxygen binding to copper(I) were determined for a series of tripodal complexes that afford end-on superoxo intermediates. Kinetic parameters for a these complexes proved to be rather similar, with activation enthalpies ranging about 3(MK) k.l/mol for reactions in coordinating solvents (nitriles). Activation entropies were relatively small for these processes both small positive and small negative values have been reported.40 This behavior is indicative of... 

Low-spin cobalt(ll) complexes are inherently reactive toward dioxygen due to their d electron configuration. Many of the O2 binding reactions are very fast, therefore, few rate constants have been determined and special techniques such as stopped-flow or flash photolysis had to be employed in kinetic work. The superoxocobalt(III) species formed are in most cases the active intermediates in catalytic reactions, which occur readily with substituted phenol or aniline derivatives, producing quinone type dehydrogenation products. The key step in catalytic cycles is often H-atom abstraction or electron transfer to the superoxo complex from the substrate, which is converted to a free radical, possibly reacting further with cobalt(III)... 

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