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 (O2˙-), generate [(BPMEN)CoII(NO2-)2] (CoII-NO2-, 3) and [(BPMEN)CrIII(NO2-)Cl-]+ (CrIII-NO2-, 4), respectively, with O2 evolution. Furthermore, analysis of these NOO reactions and tracking of the N-atom using 15N-labeled NO (15NO) revealed that the N-atoms of 3 (CoII-15NO2-) and 4 (CrIII-15NO2-) derive from the nitrosyl (15NO) moieties of 1 and 2, respectively. This work represents a comparative study of oxidation reactions of {CoNO}8vs. {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.

Exploring the nitric oxide dioxygenation (NOD) reactions of manganese-peroxo complexes.

Here, we report the nitric oxide dioxygenation (NOD) reactions of two MnIII-peroxo (MIII-O22-) complexes, [(3PYENMe)MnIII(O22-)]+ (1) and [(N3PY)MnIII(O22-)]+ (2), bearing pentadentate ligands. Complexes 1 and 2 give MnII-nitrate (MnII-NO3-) complexes (3 and 4) when reacted with nitric oxide (NO), respectively. The mechanistic study explored by using 2,4-di-tert-butylphenol (2,4-DTBP) suggested that the NOD reaction of 1 and 2 occurs via a presumed Mn-peroxynitrite ([Mn-PN]+, [Mn-ONOO-]+) intermediate. Tracking the source of N atoms using 15NO revealed that the N-atoms in MnII-NO3- (3 and 4) are derived from the 15NO moiety. Furthermore, we have explored the MIII-O22- regeneration from NOD products (3 and 4), and we have observed the formation of MIII-O22- complexes (1 and 2) upon treatment with KO2 or H2O2/triethylamine (TEA), respectively.