Mechanistic insights into nitric oxide generation from nitrite via O-atom transfer in the unsymmetrical ꞵ-diketiminato copper(II) nitrite complex

Abstract

In this study, we employed DFT calculations to elucidate the mechanism of NO generation from nitrite via PPh₃-induced oxygen atom transfer (OAT) in the unsymmetrical ß-diketiminato copper(II), LCu^IIONO. We discovered that the OAT process involves the cooperation of the two PPh₃ and follows the mechanism distinct from that of the symmetrical ß-diketiminato analogue. The ΔG^‡ value, calculated to be 34.8 kcal/mol, closely matches experimental data. The finding is further supported by analyzing the OAT product yields with varying equivalents of PPh₃. The penta-coordinated species 5a, with PPh₃ occupying the axial site, forms in the final stage of the OAT process. The isomerization of 5a and the decoordination of the hemilabile pyridyl arm synergistically reduce Cu(II) to Cu(I), facilitating NO-releasing from the Cu(I) centre. These computational results provide valuable insights for the ligand design of PPh₃-induced OAT reactions to produce NO in Cu(II) nitrite systems.