Stable N-Heterocyclic Carbenes: N-Alkyl-N′-phosphanylbenzimidazol-2-ylidenes

Three original approaches to the synthesis of N-alkyl-N′-phosphanylbenzimidazolium salts, which are precursors of the corresponding carbenes, were developed. New stable N-alkyl-N′-phosphanylbenzimidazol-2-ylidenes were prepared in good yields. X-ray analysis of a carbene was made and the chemical properties of the carbenes were studied. The reactions with O-, N-, and C-nucleophiles were found to proceed with or without cleavage of the P–N bond. Thermal rearrangement of the carbenes afforded 2-phosphorylated benzimidazoles.