A Macrocyclic Iron Complex with Pyridinium Amidate, Amidate, and Sulfonamidate N-Donor Atoms as Oxidation Catalysts

The neutral macrocyclic iron(III) complex Fe(H₂O)(L_PYA) (3) is a homogeneous catalyst for the oxidation of organic micropollutants with hydrogen peroxide. The macrocyclic ligand incorporates two hybrid pyridinium amidate/amidate (hybrid PYA/A) N-donors and two sulfonamidate N-donors with an -N(CH₃)- group bridging the two sulfonamidate functions. Anionic analogues of 3 in which the pyridinium group is replaced by o-phenylene (K[Fe(H₂O)(L_o-P)] (1)) or by nitro-substituted o-phenylene (K[Fe(H₂O)(L_o-P*)] (2)) were also synthesized. Complexes 1-3 were investigated as potential catalysts for the oxidative destruction by hydrogen peroxide of persistent micropollutants that remain in wastewater after conventional treatment regimens. Complexes 1-3 catalyzed the oxidation of the surrogate micropollutants Orange II and Safranine O, and kinetic parameters for these reactions were obtained. 3 also catalyzed the oxidation of carbamazepine (CBZ), which is an actual persistent micropollutant under conditions that are relevant for practical applications ([3] 50 nM, [CBZ] 50 μM, [H₂O₂] 250 μM, i.e., 8.5 ppm, 25 °C, pH 7.0). Complex 3 catalyzed the oxidation of each of the above substrates at rates three to four times greater than those of the benchmark homogeneous catalyst for reactions of this type.