Nitric Oxide Oxygenation Reactions of Cobalt-Peroxo and Cobalt-Nitrosyl Complexes
Kulbir kulbir, Akshaya Keerthi C. S, Sulthana Beegam, Sandip Das, Prabhakar Bhardwaj, Mursaleem Ansari, Kuldeep Singh, Pankaj Kumar
Abstract
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.