Dinuclear Intermediates - Indirect Evidence

Labile Dinuclear Intermediates— Indirect Evidence.—In the reaction of cytochrome c peroxidase(ii) [an iron(iv) complex] with cytochrome deviation from the Marcus equation has been interpreted in terms of differing stabilities of precursor and successor complexes, though these were not directly detected. In several other systems, dinuclear complexes have been inferred from the rate law. The reaction of [Co(NH3)5(SCN)] + with Ti obeys the rate law (33), consistent with the mechanism shown in equations (34) and (35). Comparison of the rate with that of the [Co(NH3)5Ng] +-Ti system implies an inner-sphere mechanism, and the dinuclear complex is presumably the precursor species with oxidation states Co . .. TP.  

In the thiocyanate case, base catalysis is reminiscent of other Ti reactions in which TiOH + is the effective reagent. In the salicylate case, the authors write the dinuclear complex as a chelate with the phenolic hydroxy-group deprotonated. It will be noted. 

The reaction [PtCl5(HaO)]-+[PtCl4] has the stoicheiometry (38) [in effect, a platinum(ii)-catalysed anation reaction] and the rate law (39). °  

The mechanism suggested is shown, in condensed form, in equation (40), where 1 

Alternative explanations of a denominator term of the form shown in equation (39) would be various mechanisms involving a labile pre-equilibrium which reaches appreciable saturation in the concentration range studied  

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