Nitric Oxide Reactivity of a Cu(II) Complex of an Imidazole-Based Ligand: Aromatic C‑Nitrosation Followed by the Formation of N‑Nitrosohydroxylaminato Complex

A binuclear Cu­(II) complex, 1, [Cu2(L–)2(OAc)]­(OAc) of imidazole-based ligand LH {LH = 2-(bis­(2-ethyl-5-methyl-1H-imidazol-4-yl)­methyl)­phenol} was synthesized and characterized spectroscopically and structurally. Addition of an equivalent amount of nitric oxide (NO) by a gastight syringe to the acetonitrile:methanol (5:1, v/v) solution of complex 1 at room temperature resulted in the reduction of Cu­(II) center to Cu­(I) with concomitant C-nitrosation of the ligand. Spectroscopic characterization of the resulting Cu­(I) complex (1a) of the C-nitrosylated ligand, L′ {L′ = 2-(bis­(2-ethyl-5-methyl-1H-imidazol-4-yl)­methyl)-4-nitroso-phenol} has been done. The Cu­(I) complex, 1a, further reacted with NO to result in the corresponding N-nitrosohydroxylaminato complex, 2, [Cu2(L–ONNO)2]­(OAc)2 through the formation of a Cu­(I)-nitrosyl intermediate. A small fraction of the nitrosyl intermediate decomposed to the corresponding Cu­(II) complex 3, [Cu­(L′)2], and N2O in a parallel reaction.