N-heterocyclic carbene ligated oximes: Exploring the electronic structure and properties

Compounds with (NHC) -> E coordination bond represent a family of chemical species with significant interest and their chemistry is being explored over the past 15 years, where NHC and E represent N-heterocyclic carbene and main group elements, respectively. NHOs (N-heterocyclic olefins) are special among these because of the (NHC) -> CR2 interaction. NHOs carry nucleophilic exocyclic carbon and many interesting reactions of NHOs are due to this character. Alkylated imidazole oximes (cationic, found useful in medicinal chemistry) [(NHC) -> C(H) = N-OH](+) carry NHC unit as a functional group. Similarly, the corresponding nitroso-N-heterocyclic olefins [(NHC) -> C(R)-N=O] also carry NHC as a functional unit. It is important to establish the interactions between the NHC unit and the rest of the molecule in these species. Density functional theory (DFT) was employed to explore the electronic structure details of a series of oximes and nitroso NHOs. The results indicate that a structure with (NHC) -> C coordination interaction can be considered as one of the resonance structures of these species.