Non-Heme Transition Metal Complexes of HNO

Abstract

The coordination chemistry of nitroxyl (HNO) with transition metals is described comprising synthetic aspects, structure and reactivity in different modes. HNO is an intermediate in the redox transformations of nitrite to ammonia, and the studies with nonheme systems allow understanding its chemical and biologically relevant properties. Pseudo-octahedral HNO complexes affording low-spin d6 configurations [ML5(NHO)]n (M=Mo, Re, Fe, Ru, Os, Co, Rh, Ir) with ancillary L coligands were prepared in aqueous and nonaqueous media through reduction or oxidation of adequate nitrosyl or nitrogen-hydride precursors. X-ray structures for isolated compounds, diverse spectroscopies (NMR, IR, UV-vis, etc.) in solid state and solution, electrochemistry, theoretical calculations, and kinetic/mechanistic methodologies were used for describing the bonding, stability, and reactivity properties like the formation/dissociation reactions from the metals, acid–base properties generating the NO− anion, and redox reactions of both the HNO/NO−-bound species.