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

Abstract

A new nonheme iron(II) complex, FeII(Me3TACN)((OSiPh2)2O) (1), is reported. Reaction of 1 with NO(g) gives a stable mononitrosyl complex Fe(NO)(Me3TACN)((OSiPh2)2O) (2), which was characterized by Mössbauer (δ=0.52 mm s−1, |ΔEQ|=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 (λexc=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.

A Reactive, Photogenerated High-Spin (S= 2) FeIV(O) Complex via O2Activation

“…27 This complex exhibited a ν(O−O) of 849 cm −1 , which is more activated than that seen for 2. The less activated O−O bond of 2 is surprising given the more negative E 1/2 (Fe III /Fe II ) potential seen for the starting ferrous complex 1 (E 1/2 = −0.90 vs Fc + /Fc) 31 compared with that of the thiolate-ligated ferrous precursor Fe II (Me 3 TACN)(S 2 SiMe 2 ) (E 1/2 = −0.60 V vs Fc + /Fc). 27 for μ-oxo bridged dimers.…”

“…Addition of excess, dry, dioxygen gas to a solution of 1 in THF at 23 °C results in a rapid color change to purple that persists for about 1 s and then gradually turns pale yellow. In contrast, when the same reaction was carried out at −80 °C, the purple species 2 was stabilized, exhibiting features at 350 nm (ε ∼ 5000 M –1 cm –1 per Fe) and 560 nm (ε ∼ 3200 M –1 cm –1 per Fe) in the UV–vis spectrum (Figure ).…”

“…This complex exhibited a ν­(O–O) of 849 cm –1 , which is more activated than that seen for 2 . The less activated O–O bond of 2 is surprising given the more negative E 1/2 (Fe III /Fe II ) potential seen for the starting ferrous complex 1 ( E 1/2 = −0.90 vs Fc + /Fc) compared with that of the thiolate-ligated ferrous precursor Fe II (Me 3 TACN)­(S 2 SiMe 2 ) ( E 1/2 = −0.60 V vs Fc + /Fc) . It has been proposed that the Fe–O–O angle in peroxo­(diiron) complexes can influence the ν­(O–O) and ν­(Fe–O) stretching frequencies, with more obtuse angles favoring a larger ν­(O–O) and smaller ν­(Fe–O) .…”

“…Potassium hydride (KH) in paraffin was purchased from Sigma-Aldrich, washed with diethyl ether and pentane, and dried under vacuum prior to use. H 2 (OSi Ph2 ) 2 O 63 and complex 1 31 were synthesized according to previously reported procedures. All other reagents were purchased from commercial vendors and used without further purification.…”

“…A similar strategy has been attempted by Limberg to model the ferryl intermediate in Fe-ZSM-5. , Although these compounds have the same tetragonal symmetry and all-oxygen coordination environment at Fe as seen in Fe-ZSM-5, an Fe IV (O) species has not yet been observed in these systems. Herein, we report the reactivity of the Fe II complex, Fe II (Me 3 TACN)­((OSi Ph2 ) 2 O) ( 1 ), an analog of Fe II (Me 3 TACN)­(S 2 SiMe 2 ) in which the sulfur donors are replaced with anionic siloxide oxygen donors. Reaction of 1 with dioxygen produces a metastable, peroxo-bridged, diferric species ( 2 ) that can be trapped at −80 °C.…”