One-electron reduced non-heme ferrous nitrosyl complexes (referred to as iron nitroxyl complexes, or {FeNO}8 in the Enemark-Feltham notation) have been proposed as intermediates in bacterial nitric oxide reductases (NORs). In addition, non-heme iron enzymes may be involved in the generation and sensing of nitroxyl (NO-/HNO) in biological systems via formation of {FeN(H)O}8 intermediates. Despite their significance, non-heme {FeN(H)O}8 complexes have remained elusive, and little is known about their properties and reactivity. In order to model such complexes, we have synthesized the high-spin non-heme {FeNO}7 complex [Fe(TMG3tren)(NO)](OTf)2. In contrast to other reported high-spin non-heme {FeNO}7 complexes which decompose upon reduction, this species can be reduced chemically or electrochemically to generate the first stable high-spin non-heme {FeNO}8 model complex. Whereas low-spin {FeNO}8 complexes in hemes are diamagnetic, our data show that this complex is high-spin (S=1). Experimental and computational results demonstrate that the reduction is metal-centered, causing a relatively small downshift in ?(N-O) and a decrease in Fe-NO covalency. Additionally, whereas the {FeNO}7 complex is stable in the presence of acid, the {FeNO}8 is basic and can be protonated at low temperature to form an {FeNHO}8 compound. Taken together, these results suggest that in biological systems, reduction may serve as a method to activate stable non-heme {FeNO}7 units towards protonation and other reactivity, for example N-N coupling in NORs.

Characterization of a non-heme {FeN(H)O}<sup>8 </sup>complex: Implications for the reactivity of iron nitroxyl species in biology

248th National Meeting (2014)

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Characterization of a non-heme {FeN(H)O}8 complex: Implications for the reactivity of iron nitroxyl species in biology

Characterization of a non-heme {FeN(H)O}⁸complex: Implications for the reactivity of iron nitroxyl species in biology