We describe the synthesis, characterization, aqueous behavior, and catalytic activity of a new generation of FeIII-TAML (TetraAmido Macrocycle Ligand) activators of peroxides (>2), variants of (>2d), which have been designed to be especially suitable for purifying water of recalcitrant oxidizable pollutants. Activation of H2O2 by >2 (kI) as a function of pH was analyzed via kinetic studies of Orange II bleaching. This was compared with the known behavior of the first generation of FeIII-TAMLs (>1). Novel reactivity features impact the potential for oxidant activation for water purification by >2d and its aromatic ring substituted dinitro (>2e) and tetrachloro (>2f) derivatives. Thus, the maximum activity for >2e occurs at pH 9, the closest yet to the EPA guidelines for drinking water (6.5–8.5) allowing >2e to rapidly activate H2O2 at pH 7.7. In water, >2e has two axial water ligands with pKas of 8.4 and 10.0 (25 °C). The former is the lowest for all FeIII-TAMLs developed to date and is key to >2e’s exceptional catalytic activity in neutral and slightly basic solutions. Below pH 7 >2d was found to be quite sensitive to demetalation in phosphate buffers. This was overcome by iterative design to give >2e (hydrolysis rate >2d > 100×>2e). Mechanistic studies highlight >2e’s increased stability by establishing that to demetalate >2e at a comparable rate to which H2PO4− demetalates >2d, H3PO4 is required. A critical criterion for green catalysts for water purification is the avoidance of endocrine disruptors, which can impair aquatic life. FeIII-TAMLs do not alter transcription mediated by mammalian thyroid, androgen or estrogen hormone receptors, suggesting that >2 do not bind to the receptors and reducing concerns that the catalysts might have endocrine disrupting activity.
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