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 butylNNFe(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 as [bu-tylNNFe(NO)2][PF6] (2-PF6). We identified two different reaction pathways between 1 and acids: one reaction forms 2, and another O2-promoted reaction produces N2O. This oxygenation pathway for N2O formation is exclusively governed by acid additives, where Brønsted/Lewis acids divert DNIC oxygenation outcomes away from NOx- production, and in-stead, toward N-N coupling. Mechanistic studies indicate the acid promotes electron transfer from the iron center in 1, enabling NO ligand exchange en route to N2O liberation.