Nitric Oxide Oxygenation Reactions of Cobalt-Peroxo and Cobalt-Nitrosyl Complexes.

Here, we report a comparative study of nitric oxide oxidation (NOO) reactions of Co III -peroxo (Co III -O 2 2- ) and Co-nitrosyl ({CoNO} 8 ) complexes bearing the same N 4 -donor ligand (HMTETA) framework. In this regard, we prepared and characterized two new [(HMTETA)Co III (O 2 2- )] + ( 2 , S = 2) and [(HMTETA)Co(NO)] 2+ ( 3 , S = 1) complexes from [(HMTETA)Co II (CH 3 CN) 2 ] 2+ ( 1 ). Both complexes ( 2 and 3 ) are characterized by different spectroscopic measurements, including their DFT-optimized structures. Complex 2 produces Co II -nitrato [(HMTETA)Co II (NO 3 - )] + (Co II -NO 3 - , 4 ) complex in the presence of NO. In contrast, when 3 reacted with a superoxide (O 2 •- ) anion, it generated Co II -nitrito [(HMTETA)Co II (NO 2 - )] + (Co II -NO 2 - , 5 ) with O 2 evolution. Experiments performed using 18/16 O-labeled superoxide ( 18 O 2 •- / 16 O 2 •- ) showed that O 2 originated from the O 2 •- anion. Both the NOO reactions are believed to proceed via a presumed peroxynitrite (PN) intermediate. Although we did not get direct spectral evidence for the proposed PN species, the mechanistic investigation using 2,4-di- tert -butylphenol indirectly suggests the formation of a PN intermediate. Furthermore, tracking the source of the N-atom in the above NOO reactions using 15 N-labeled nitrogen ( 15 NO) revealed N-atoms in 4 (Co II - 15 NO 3 - ) and 5 (Co II - 15 NO 2 - ) derived from the 15 NO moiety.