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

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 β-diketiminato copper(II), LCu^IIONO. We discovered that the OAT process involves the cooperation of two PPh₃ ligands and follows the mechanism distinct from that of the symmetrical β-diketiminato analogue. The ΔG^‡ value, calculated to be 34.8 kcal mol⁻¹, 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 release from the Cu(I) centre. These computational results provide valuable insights for the ligand design for PPh₃-induced OAT reactions to produce NO in Cu(II) nitrite systems.