Dinitrite to Dinitrosyl at Manganese: {Mn(NO)₂}⁸ in Redox Transformations of Nitrogen Oxides

Owing to the highly reactive and transient nature of nitric oxide (NO) and nitroxyl (HNO), the identification of reliable NO/HNO sources is of paramount interest for the development of therapeutic strategies and for understanding NO/HNO signaling pathways. We demonstrate here that a mononuclear manganese(II)-dinitrite complex (2-Py) reacts with p-methylbenzenethiol (^MeArSH) to generate the dinitrosyl species 3-Py/3'-Py. The dinitrosyl {Mn(NO)₂}⁸ core in 3'-Py is capable of facile transfer of both NO and NO^- to suitable metal centers. Interestingly, a reaction with pentafluorophenol ^F5ArOH with 2-Py produces a mixture of NO and nitrate via disproportionation of in situ-generated HNO₂. The oxidizing nature of HNO₂ has been intercepted by triphenylphosphine (Ph₃P), leading to bis(triphenylphosphoranylidene)ammonium ([(Ph₃P)₂N]⁺), thereby demonstrating the intermediacy of transient HNO₂ for the reaction between 2-Py and ^F5ArOH. Additionally, monooxygenation of the dinitrite core in 2-Py by iodosylbenzene (PhIO) affords a manganese(II)-dinitrate complex (4-Py), and dioxygenations of the {Mn(NO)₂}⁸ species by PhIO or O₂ have also been observed to yield 4-Py. Single-crystal X-ray diffraction, FTIR analyses of ¹⁴N/¹⁵N-labeled samples, and multinuclear NMR studies provide unambiguous characterization of a complete series of manganese dinitrite, dinitrosyl, and dinitrate complexes that are chemically linked through nitrite reduction, disproportionation, and oxygenation pathways.