Elimination of Ethene from 1,2-Diiodoethane Induced by N-Heterocyclic Carbene Halogen Bonding

Abstract

The attempted synthesis of N-heterocyclic carbene (NHC)-stabilised dicarbon (C2) fragments via nucleophilic substitution at 1,2-diiodoethane is reported. Rather than the expected SN2 pathway, clean elimination of ethene and formation of an iodoimidazolium cation was observed. The resistance towards nucleophilic substitution piqued interest, and subsequent investigation determined NHC-halogen bonding as the source. This is in contrast to reactions between NHCs and other alkyl halides, where substitution or elimination pathways are reported. A detailed theoretical study between these cases highlights the importance of iodine as a halogen bond donor compared with other halogens, and shows that NHCs are excellent halogen bond acceptors. This reactivity suggests potential for application of the halogen bonding interaction between NHCs and organic compounds.