Mechanistic insights into nitric oxide oxygenation (NOO) reactions of {CrNO} and {CoNO}.

Here, we report the nitric oxide oxygenation (NOO) reactions of two distinct metal nitrosyls {Co-nitrosyl ( = 0) . Cr-nitrosyl ( = 1/2)}. In this regard, we synthesized and characterized [(BPMEN)Co(NO)] ({CoNO}, 1) to compare its NOO reaction with that of [(BPMEN)Cr(NO)(Cl)] ({CrNO}, 2), having a similar ligand framework. Kinetic measurements showed that {CrNO} is thermally more stable than {CoNO}. Complexes 1 and 2, upon reaction with the superoxide anion (O˙), generate [(BPMEN)Co(NO)] (Co-NO, 3) and [(BPMEN)Cr(NO)Cl] (Cr-NO, 4), respectively, with O evolution. Furthermore, analysis of these NOO reactions and tracking of the N-atom using N-labeled NO (NO) revealed that the N-atoms of 3 (Co-NO) and 4 (Cr-NO) derive from the nitrosyl (NO) moieties of 1 and 2, respectively. This work represents a comparative study of oxidation reactions of {CoNO} {CrNO}, showing different rates of the NOO reactions due to different thermal stability. To complete the NOM cycle, we reacted 3 and 4 with NO, and surprisingly, only 3 generated {CoNO} species, while 4 was unreactive towards NO. Furthermore, the phenol ring nitration test, performed using 2,4-di--butylphenol (2,4-DTBP), suggested the presence of a proposed peroxynitrite (PN) intermediate in the NOO reactions of 1 and 2.