The Fe2(NO)2 Diamond Core: A Unique Structural Motif In Non‐Heme Iron–NO Chemistry

Abstract

Non‐heme high‐spin (hs) {FeNO}8 complexes have been proposed as important intermediates towards N2O formation in flavodiiron NO reductases (FNORs). Many hs‐{FeNO}8 complexes disproportionate by forming dinitrosyl iron complexes (DNICs), but the mechanism of this reaction is not understood. While investigating this process, we isolated a new type of non‐heme iron nitrosyl complex that is stabilized by an unexpected spin‐state change. Upon reduction of the hs‐{FeNO}7 complex, [Fe(TPA)(NO)(OTf)](OTf) (1), the N‐O stretching band vanishes, but no sign of DNIC or N2O formation is observed. Instead, the dimer, [Fe2(TPA)2(NO)2](OTf)2 (2) could be isolated and structurally characterized. We propose that 2 is formed from dimerization of the hs‐{FeNO}8 intermediate, followed by a spin state change of the iron centers to low‐spin (ls), and speculate that 2 models intermediates in hs‐{FeNO}8 complexes that precede the disproportionation reaction.Eine seltene Raute: Der hs‐{FeNO}7‐Komplex 1 wurde durch spektroskopische Methoden und Röntgenkristallographie charakterisiert. Unter reduzierenden Bedingungen wird das Dimer 2 mit rautenförmigem Kern durch Dimerisierung eines hs‐{FeNO}8‐Zwischenprodukts und anschließende Spinzustandsänderung der Eisenzentren zu Low‐Spin (ls) gebildet.