4 Search Results

Copper nitrite reductases (CuNIRs) convert NO₂^– to NO as well as NO to N₂O under high NO flux at a mononuclear type 2 Cu center. While model complexes illustrate N–N coupling from NO that results in symmetric trans-hyponitrite [Cu^II]– ONNO–[Cu^II] complexes, in this work we report NO assembly at a single Cu site in the presence of an external reductant Cp*₂M (M = Co, Fe) to give the first copper cis-hyponitrites [Cp*₂M]{[Cu^II](κ²- O₂N₂)[Cu^I]}. Importantly, the κ¹–N-bound [Cu^I] fragment may be easily removed by the addition of mild Lewis bases such as CNAr or pyridine to form the spectroscopically similar anionmore » {[Cu^II](κ²-O₂N₂)}^–. The addition of electrophiles such as H⁺ to these anionic copper(II) cis-hyponitrites leads to N₂O generation with the formation of the dicopper(II)-bis-μ-hydroxide [Cu^II]₂(μ- OH)₂. One-electron oxidation of the {[Cu^II](κ²-O₂N₂)}^– core turns on H-atom transfer reactivity, enabling the oxidation of 9,10- dihydroanthracene to anthracene with concomitant formation of N₂O and [Cu^II]₂(μ-OH)₂. These studies illustrate both the reductive coupling of NO at a single copper center and a way to harness the strong oxidizing power of nitric oxide via the neutral cis- hyponitrite [Cu](κ²-O₂N₂).« less

Here, a series of β-diketiminate Ni–NO complexes with a range of NO binding modes and oxidation states were studied by X-ray emission spectroscopy (XES). The results demonstrate that XES can directly probe and distinguish end-on vs side-on NO coordination modes as well as one-electron NO reduction. Density functional theory (DFT) calculations show that the transition from the NO 2s2s σ* orbital has higher intensity for end-on NO coordination than for side-on NO coordination, whereas the 2s2s σ orbital has lower intensity. XES calculations in which the Ni–N–O bond angle was fixed over the range from 80° to 176° suggest thatmore » differences in NO coordination angles of ~10° could be experimentally distinguished. Calculations of Cu nitrite reductase (NiR) demonstrate the utility of XES for characterizing NO intermediates in metalloenzymes. This work shows the capability of XES to distinguish NO coordination modes and oxidation states at Ni and highlights applications in quantifying small molecule activation in enzymes.« less

Abstract Nitrosobenzene (PhNO) serves as a stable analogue of nitroxyl (HNO), a biologically relevant, redox‐active nitric oxide derivative. Capture of nitrosobenzene at the electron‐deficient β‐diketiminato nickel(I) complex [ ⁱ Pr ₂ NN _F6 ]Ni results in reduction of the PhNO ligand to a (PhNO) ^./− species coordinated to a square planar Ni ^II center in [ ⁱ Pr ₂ NN _F6 ]Ni(η ² ‐ONPh). Ligand centered reduction leads to the (PhNO) ²⁻ moiety bound to Ni ^II supported by XAS studies. Systematic investigation of structure–reactivity patterns of (PhNO) ^./− and (PhNO) ²⁻ ligands reveals parallels withmore » superoxo (O ₂ ) ^./− and peroxo (O ₂ ) ²⁻ ligands, respectively, and forecasts reactivity patterns of the more transient HNO ligand.« less

Abstract Nitrosobenzene (PhNO) serves as a stable analogue of nitroxyl (HNO), a biologically relevant, redox‐active nitric oxide derivative. Capture of nitrosobenzene at the electron‐deficient β‐diketiminato nickel(I) complex [ ⁱ Pr ₂ NN _F6 ]Ni results in reduction of the PhNO ligand to a (PhNO) ^./− species coordinated to a square planar Ni ^II center in [ ⁱ Pr ₂ NN _F6 ]Ni(η ² ‐ONPh). Ligand centered reduction leads to the (PhNO) ²⁻ moiety bound to Ni ^II supported by XAS studies. Systematic investigation of structure–reactivity patterns of (PhNO) ^./− and (PhNO) ²⁻ ligands reveals parallels withmore » superoxo (O ₂ ) ^./− and peroxo (O ₂ ) ²⁻ ligands, respectively, and forecasts reactivity patterns of the more transient HNO ligand.« less