PPh₃/Isocyanide and N₂/Isocyanide Exchange: Pathways to Isolable Alkali Metal Keteniminyl Anions

Keteniminyl anions hold significant promise for advancing ketenimine chemistry, yet their isolation has remained elusive until now. Drawing inspiration from recent advances in ligand exchange reactions at carbon, we report the successful synthesis of a series of isolable alkali metal keteniminyl anions through substitution of the phosphine ligand in metalated ylides or the N₂ ligand in diazomethanides with isocyanides. The exchange reactions were found to proceed more rapidly with aryl isocyanides than with the more electron-rich alkyl-substituted derivatives and were also more efficient when starting from the diazo compounds. The resulting keteniminyl anions exhibit bent geometries, which can be attributed to a donor–acceptor interaction with the isocyanide, giving rise to a carbone-like structure. Electron-withdrawing substituents on the nitrogen enhance backbonding, thus leading to larger bending angles and a more pronounced ynamide character as also evidenced by a blue-shifted ketenimine stretch in the IR spectrum. The keteniminyl anions react efficiently with unsaturated compounds to form a diverse array of heterocycles, highlighting their potential as versatile building blocks in synthetic chemistry.