Formation of N‐Heterocyclic Carbenes by Tautomerization of Mesomeric Betaines: Cyclic Boron Adducts and Palladium Complexes From 2‐(Imidazolium‐1‐yl)phenolates

2‐(Imidazolium‐1‐yl)phenolates are conjugated heterocyclic mesomeric betaines in tautomeric equilibrium with the corresponding N‐heterocyclic carbenes (NHCs), 3‐(2‐hydroxyphenyl)‐imidazol‐2‐ylidenes. The carbene tautomers can be trapped as thiones (X‐ray analysis). Moreover, bis(triphenylphosphine)palladium(II) dichloride in THF trapped the carbene tautomer as a palladium complex without participation of the phenolate group (X‐ray analysis). The corresponding anionic NHCs, 2‐phenolate‐substituted imidazol‐2‐ylidenes, can be trapped by triethylborane or triphenylborane to form 4,4‐diethyl‐ or 4,4‐diphenyl‐4H‐benzoe]imidazo2,1‐c]1,4,2]oxaza‐borininium‐4‐ides, respectively (two X‐ray analyses). These tricyclic systems are the first representatives of a new heterocyclic ring system. The results of DFT calculations concerning the HOMO/LUMO profiles and partial charges are also presented.