Unraveling\nChlorite Oxidation Pathways in Equatorially\nHeteroatom-Substituted Nonheme Iron Complexes

The first-coordination sphere of catalysts is known to\nplay a crucial\nrole in reaction mechanisms, but details of how equatorial ligands\ninfluence the reactivity remain unknown. Heteroatom ligated to the\nequatorial position of iron centers in nonheme iron metalloenzymes\nmodulates structure and reactivity. To investigate the impact of equatorial\nheteroatom substitution on chlorite oxidation, we synthesized and\ncharacterized three novel mononuclear nonheme iron(II) complexes with\na pentadentate bispidine scaffold. These complexes feature systematic\nsubstitutions at the equatorial position in the bispidine ligand framework\nwhere the pyridine group is replaced with NMe<sub>2</sub>, SMe, and\nOMe groups. The three iron(II)–bispidine complexes were subjected\nto studies in chlorite oxidation reactions as a model pathway for\noxygen atom transfer. Chlorine oxyanions, which have the halide in\nan oxidation state ranging from +1 to +7, have numerous applications\nbut can contaminate water bodies, and this demands urgent environmental\nremediation. Chlorite, a common precursor to chlorine dioxide, is\nof particular interest due to the superior antimicrobial activity\nof chlorine dioxide. Moreover, its generation leads to fewer harmful\nbyproducts in water treatment. Here, we demonstrate that these complexes\ncan produce chlorine dioxide from chlorite in acetate buffer at room\ntemperature and pH 5.0, oxidizing chlorite through the in situ formation\nof high-valent iron(IV)–oxo intermediates. This study establishes\nhow subtle changes in the coordination sphere around iron can influence\nthe reactivity.