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 ( Me ArSH) 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 F5 ArOH with 2-Py produces a mixture of NO and nitrate via disproportionation of in situ-generated HNO 2 . The oxidizing nature of HNO 2 has been intercepted by triphenylphosphine (Ph 3 P), leading to bis(triphenylphosphoranylidene)ammonium ([(Ph 3 P) 2 N] + ), thereby demonstrating the intermediacy of transient HNO 2 for the reaction between 2-Py and F5 ArOH. 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 O 2 have also been observed to yield 4-Py . Single-crystal X-ray diffraction, FTIR analyses of 14 N/ 15 N-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.