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 H-1 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.