Carbene-Stabilized Monomeric Cyanogen N-Oxide.

Cyanogen N-oxide (NCCNO) is one of the simplest molecules containing carbon, nitrogen, and oxygen, making it an attractive interstellar spectroscopic probe and an intriguing building block in prebiotic chemistry. However, detailed studies of NCCNO are hindered by its high reactivity and propensity for autopolymerization. In this report, monomeric, carbene-stabilized cyanogen N-oxide (1) is synthesized by the unusual complete dehydrogenation of C-H-activated acetonitrile via the addition of "superelectrophilic" nitronium (NO2+). Experimental and computational studies of 1 reveal spectroscopic features supporting its characterization as a trapped form of NCCNO, while novel electronic structure properties distinguish it from closely related organic nitrile oxides. Compound 1 also readily coordinates metal ions (Mg2+ and Fe3+), providing evidence that the NCCNO molecule can display preferential reactivity at the O-terminus over the N-terminus but nevertheless is capable of multiple binding modes. The stabilized NCCNO molecules also undergo reduction to isolable cyanogen N-oxide radical anions─compounds featuring radical localization on the O-terminus with minimal carbene involvement, supporting their assignment as open-shell forms of cyanogen N-oxide. Finally, dehydrogenation conditions were applied to other R-CH3 groups in methyl acetate and nitromethane to synthesize additional small nitrile oxides: methyl cyanoformate N-oxide, which is unknown in its free form, and fulminic acid, the simplest organonitrile. Together, these results showcase a versatile strategy for converting stable carbene C-H activation products to isolable forms of highly reactive carbonaceous small molecules.