Nitric oxide generation study of unsymmetrical β-diketiminato copper(ii) nitrite complexes

Abstract

β-Diketiminato copper(II) L₁CuCl–L₄CuCl and their nitrite complexes L₁Cu(O₂N) and L₂Cu(O₂N) have been synthesized and characterized. X-ray analysis of the L₁CuCl–L₄CuCl complexes clearly reveals their mononuclear structure with a four-coordinated Cu(II) center bound by one chloride and three nitrogen atoms of unsymmetrical β-diketiminato ligands. Cyclic voltametric analysis of the Cu(II) complexes shows that the length of the pyridyl arm controls the Cu(II)/Cu(I) redox process. DFT and EPR results confirm that the geometry of the Cu(II) complexes is also controlled by the length of the chelating pyridyl arm. The oxygen atom transfer nitrite reduction of the Cu(II) nitrite complexes leads to the formation of copper(I)–PPh₃ and OPPh₃ which were confirmed by ¹H and ³¹P NMR. The length of the pyridyl arm of the copper(II) nitrite complexes governs the NO-releasing ability. These findings illustrate the important bioinspired behaviour and NO generation from nitrite via oxygen atom transfer of the unsymmetrical β-diketiminato copper(II) complexes as compared to symmetrical β-diketiminato copper(II) complexes.