Addition of nitrosobenzene to β‐diketiminato and tris(pyrazolyl)borate copper complexes [[Me2NNF6]Cu(NCMe)] (2) and [iPr2TpCu(NCMe)] (3) gives the corresponding nitrosobenzene adducts [[Me2NNF6]Cu(η2‐ONPh)] (5) and [iPr2TpCu{κ1‐N(O)Ph}] (6). Backbonding to the nitrosoarene is strongest via the η2‐ON binding mode, which is sterically inaccessible for the tris(pyrazolyl)borate complexes. The strength of the interaction is judged by the N–O bond length, the νNO stretching frequencies observed for 5 and 6, as well as by the DFT LUMO energies of 5‐η2‐ON, 5‐κ1‐N, 6‐κ1‐N, which range from highest to lowest. Nitrosoarene complexes 5 and 6 are also produced upon reaction of [[Me2NNF6]Cu(NCMe)] (2) and [iPr2TpCu(NCMe)] (3) with 2 equiv. N‐phenylhydroxylamine (PhNHOH), though a considerable amount of the azoxybenzene PhN=N(O)Ph is observed along with 6. The addition of slight excess of NO to 5 and 6 results in the formation of copper(II) diazeniumdiolates [[Me2NNF6]Cu(κ2‐O2N2Ph)] (7) and [iPr2TpCu(κ2‐O2N2Ph)] (8), which exhibit square‐planar and square‐pyramidal geometries, respectively. These findings give insight into PhNO and PhHNOH reactivity at copper(I) and foreshadow possible transformations of considerably more reactive nitroxyl (HNO) and hydroxylamine (H2NOH) analogues.

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