A Nonheme Mononuclear {FeNO}⁷ Complex that Produces N₂O in the Absence of an Exogenous Reductant

A new nonheme iron(II) complex, Fe^II(Me₃TACN)((OSi^Ph2)₂O) (1), is reported. Reaction of 1 with NO_(g) gives a stable mononitrosyl complex Fe(NO)(Me₃TACN)((OSi^Ph2)₂O) (2), which was characterized by Mössbauer (δ=0.52 mm s⁻¹, |ΔE_Q|=0.80 mm s⁻¹), EPR (S=3/2), resonance Raman (RR) and Fe K-edge X-ray absorption spectroscopies. The data show that 2 is an {FeNO}⁷ complex with an S=3/2 spin ground state. The RR spectrum (λ_exc=458 nm) of 2 combined with isotopic labeling (¹⁵N, ¹⁸O) reveals ν(N-O)=1680 cm⁻¹, which is highly activated, and is a nearly identical match to that seen for the reactive mononitrosyl intermediate in the nonheme iron enzyme FDPnor (ν(NO)=1681 cm⁻¹). Complex 2 reacts rapidly with H₂O in THF to produce the N-N coupled product N₂O, providing the first example of a mononuclear nonheme iron complex that is capable of converting NO to N₂O in the absence of an exogenous reductant.