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

The neutral macrocyclic iron(III) complex Fe(H2O)(LPYA) (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)(Lo-P)] (1)) or by nitro-substituted o-phenylene (K[Fe(H2O)(Lo-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.