N–N Coupling of Nitrosyl Ligands in a Dinitrosyl Iron Complex Mediated by Exogenous Acids

We disclose the synthesis, characterization, and reactivity profiles of a dinitrosyl iron complex (DNIC) toward exogenous Brønsted and Lewis acids. Treatment of the {Fe(NO)₂}¹⁰ complex (butylNN)Fe(NO)₂ (1) (butylNN = 2-(1-butyl-5(tert-butyl)-1H-pyrazol-3-yl)-6-methylpyridine) with a variety of Brønsted and Lewis acids generates an oxidized {Fe(NO)₂}⁹ species [(butylNN)Fe(NO)₂][PF₆] (2-PF6) and, in the presence of a radical reagent, N₂O. The pathway for N₂O formation is governed by acid additives, and mechanistic studies indicate that the acid promotes electron transfer from the iron center in 1 and facilitates NO lability, providing a pathway for N₂O formation.