Stable Mesoionic N‐Heterocyclic Olefins (mNHOs)

We report a new class of stable mesoionic N‐heterocyclic olefins, featuring a highly polarized (strongly ylidic) double bond. The ground‐state structure cannot be described through an uncharged mesomeric Lewis‐structure, thereby structurally distinguishing them from traditional N‐heterocyclic olefins (NHOs). mNHOs can easily be obtained through deprotonation of the corresponding methylated N,N′‐diaryl‐1,2,3‐triazolium and N,N′‐diaryl‐imidazolium salts, respectively. In their reactivity, they represent strong σ‐donor ligands as shown by their coordination complexes of rhodium and boron. Their calculated proton affinities, their experimentally derived basicities (competition experiments), as well as donor abilities (Tolman electronic parameter; TEP) exceed the so far reported class of NHOs. Highly charged: A new class of mesoionic N‐heterocyclic olefins is described featuring a highly ylidic double bond. The compounds can be utilized as ligands in main‐group and transition metal chemistry. Their donor properties exceed previously reported traditional N‐heterocyclic olefins.