Proton-Induced Reactivity of NO^– from a {CoNO}⁸ Complex

Research on the one-electron reduced analogue of NO, namely nitroxyl (HNO/NO^–), has revealed distinguishing properties regarding its utility as a therapeutic. However, the fleeting nature of HNO requires the design of donor molecules. Metal nitrosyl (MNO) complexes could serve as potential HNO donors. The synthesis, spectroscopic/structural characterization, and HNO donor properties of a {CoNO}⁸ complex in a pyrrole/imine ligand frame are reported. The {CoNO}⁸ complex [Co­(LN₄^PhCl)­(NO)] (1) does not react with established HNO targets such as Fe^III hemes or Ph₃P. However, in the presence of stoichiometric H⁺ 1 behaves as an HNO donor. Complex 1 readily reacts with [Fe­(TPP)­Cl] or Ph₃P to afford the {FeNO}⁷ porphyrin or Ph₃PO/Ph₃PNH, respectively. In the absence of an HNO target, the {Co­(NO)₂}¹⁰ dinitrosyl (3) is the end product. Complex 1 also reacts with O₂ to yield the corresponding Co^III-η¹-ONO₂ (2) nitrato analogue. This report is the first to suggest an HNO donor role for {CoNO}⁸ with biotargets such as Fe^III-porphyrins.