Mechanistic Insight into the Nitric Oxide Dioxygenation Reaction of Nonheme Iron(III)-Superoxo and Manganese(IV)-Peroxo Complexes

Abstract

Reactions of nonheme Fe-III-superoxo and Mn-IV-peroxo complexes bearing a common tetraamido macrocyclic ligand (TAML), namely [(TAML)Fe-III(O-2)](2-) and [(TAML)Mn-IV(O-2)](2-), with nitric oxide (NO) afford the Fe-III-NO3 complex [(TAML)Fe-III(NO3)](2-) and the Mn-V-oxo complex [(TAML)Mn-V(O)](-) plus NO2-, respectively. Mechanistic studies, including density functional theory (DFT) calculations, reveal that M-III-peroxynitrite (M=Fe and Mn) species, generated in the reactions of [(TAML)Fe-III(O-2)](2-) and [(TAML)Mn-IV(O-2)](2-) with NO, are converted into M-IV(O) and CNO2 species through O-O bond homolysis of the peroxynitrite ligand. Then, a rebound of Fe-IV(O) with CNO2 affords [(TAML)Fe-III(NO3)](2-), whereas electron transfer from Mn-IV(O) to CNO2 yields [(TAML)Mn-V(O)](-) plus NO2-.