NO Coupling at Copper to -Hyponitrite: NO Formation via Protonation and H-Atom Transfer.

Copper nitrite reductases (CuNIRs) convert NO to NO as well as NO to NO under high NO flux at a mononuclear type 2 Cu center. While model complexes illustrate N-N coupling from NO that results in symmetric -hyponitrite [Cu]-ONNO-[Cu] complexes, we report NO assembly at a single Cu site in the presence of an external reductant CpM (M = Co, Fe) to give the first copper -hyponitrites [CpM]{Cu[Cu]}. Importantly, the κ-N-bound [Cu] fragment may be easily removed by the addition of mild Lewis bases such as CNAr or pyridine to form the spectroscopically similar anion {Cu}. The addition of electrophiles such as H to these anionic copper(II) -hyponitrites leads to NO generation with the formation of the dicopper(II)-bis-μ-hydroxide Cu. One-electron oxidation of the {Cu} core turns on H-atom transfer reactivity, enabling the oxidation of 9,10-dihydroanthracene to anthracene with concomitant formation of NO and Cu. 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 hyponitrite Cu.