A mononuclear nonheme {FeNO}6 complex: synthesis and structural and spectroscopic characterization

Abstract

While the synthesis and characterization of {FeNO}^7,8,9 complexes have been well documented in heme and nonheme iron models, {FeNO}⁶ complexes have been less clearly understood. Herein, we report the synthesis and structural and spectroscopic characterization of mononuclear nonheme {FeNO}⁶ and iron(III)–nitrito complexes bearing a tetraamido macrocyclic ligand (TAML), such as [(TAML)Fe^III(NO)]⁻ and [(TAML)Fe^III(NO₂)]²⁻, respectively. First, direct addition of NO_(g) to [Fe^III(TAML)]⁻ results in the formation of [(TAML)Fe^III(NO)]⁻, which is sensitive to moisture and air. The spectroscopic data of [(TAML)Fe^III(NO)]⁻, such as ¹H nuclear magnetic resonance and X-ray absorption spectroscopies, combined with computational study suggest the neutral nature of nitric oxide with a diamagnetic Fe center (S = 0). We also provide alternative pathways for the generation of [(TAML)Fe^III(NO)]⁻, such as the iron–nitrite reduction triggered by protonation in the presence of ferrocene, which acts as an electron donor, and the photochemical iron–nitrite reduction. To the best of our knowledge, the present study reports the first photochemical nitrite reduction in nonheme iron models.