Chloride Tuning of the Pka-Controlled Reactivity of the NewTAML Activator [Feiii{4-No2c6h3-1, 2-(Ncocme2nso2)2chme}(oh< Sub>2)]-

The kinetics of oxidation catalysis by TAML activators of peroxides [LFeIII(OH2)](-) (TAML = tetraamido macrocyclic ligand) in water can be typically quantified by a mechanism comprised of two key steps: catalyst activation to the reactive state with rate constant k(I), followed by substrate oxidation with rate constant k(II). Usually, k(I) << k(II) and the overall catalytic activity is limited by the first step. The second-order rate constant k(I) can be enhanced by changing structural features in the TAML macrocycle that make the iron site more electrophilic. Chemical interventions beyond changes at the catalyst itself should also be able to change k(I). In examining potentially useful interventions, the effect of chloride on k(I) was explored and an intriguing fact was found. For the NewTAML catalyst, [Fe-III{4-NO2C6H3-1,2-(NCOCMe2NSO2)(2)CHMe}(OH2)](-), increasing chloride concentration reduces the rate constant k(I) when the pH is below the pK(a) of the catalyst ([LFeIII(OH2)](-) -><- [LFeIII(OH)](2-) + H+), but increases k(I) when the pH > pK(a). Mechanisms of the observed deceleration/acceleration effects are discussed. A linear dependence between K-Cl and pK(a) for iron(III) TAMLs is established: logK(Cl) = 16 +/- 2 - (1.6 +/- 0.2) x pK(a).