Imidazolium Dicyanomethylides as N-Ylide Precursors of Anionic N-Heterocyclic Carbenes

In the past, the use of nitrogen ylides focused primarily on cycloadditions, where the 1,3-dipole was used as a building block for the formation of heterocycles such as pyrroles or pyrrolinones. In this work, we present a new perspective on imidazolium dicyanomethylides with their synthesis and utilization as anionic N-heterocyclic carbenes (NHCs). The values of relative carbene formation energies (CREF) for a wide range of substituted imidazolium ylides unknown in the literature showed promising properties. In situ trapping reactions of these anionic NHCs with selenium led to anionic, water-soluble compounds that exhibited remarkable coordination behavior according to X-ray structure analyses. In addition, the 77Se shifts of the investigated compounds were measured to draw conclusions about their pi-acceptance. Imidazolium-ylides are conjugated mesomeric betaines with an exocyclic anionic carbon substituent. These ylides were converted by deprotonation into anionic N-heterocyclic carbenes, which can be formulated with two negative charges on the carbene carbon atom due to their origin. Subsequent reaction with selenium gave anionic selenourea compounds. image