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.