Mechanistic insights into nitric oxide oxygenation (NOO) reactions of {CrNO} 5 and {CoNO} 8 .

Here, we report the nitric oxide oxygenation (NOO) reactions of two distinct metal nitrosyls {Co-nitrosyl ( S = 0) vs . Cr-nitrosyl ( S = 1/2)}. In this regard, we synthesized and characterized [(BPMEN)Co(NO)] 2+ ({CoNO} 8 , 1) to compare its NOO reaction with that of [(BPMEN)Cr(NO)(Cl - )] + ({CrNO} 5 , 2), having a similar ligand framework. Kinetic measurements showed that {CrNO} 5 is thermally more stable than {CoNO} 8 . Complexes 1 and 2, upon reaction with the superoxide anion (O 2 ˙ - ), generate [(BPMEN)Co II (NO 2 - ) 2 ] (Co II -NO 2 - , 3) and [(BPMEN)Cr III (NO 2 - )Cl - ] + (Cr III -NO 2 - , 4), respectively, with O 2 evolution. Furthermore, analysis of these NOO reactions and tracking of the N-atom using 15 N-labeled NO ( 15 NO) revealed that the N-atoms of 3 (Co II - 15 NO 2 - ) and 4 (Cr III - 15 NO 2 - ) derive from the nitrosyl ( 15 NO) moieties of 1 and 2, respectively. This work represents a comparative study of oxidation reactions of {CoNO} 8 vs. {CrNO} 5 , 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} 8 species, while 4 was unreactive towards NO. Furthermore, the phenol ring nitration test, performed using 2,4-di- tert -butylphenol (2,4-DTBP), suggested the presence of a proposed peroxynitrite (PN) intermediate in the NOO reactions of 1 and 2.