Chelating C4-bound imidazolylidene complexes via oxidative addition of imidazolium salts to palladium(0)

Oxidative addition of donor-functionalised 4-iodoimidazolium salts to palladium(0) provides a selective route for the preparation of chelating abnormal N-heterocylic carbene complexes and enables the introduction of a variety of donor groups. The activation of the C4 position does not necessitate the imidazolium C2 position to be protected, leaving this site available for further modification. While metallation of the unsubstituted C2 position of the N-heterocyclic carbene ligand was unsuccessful when palladium was bound to the C4 carbon, sequential metallation of first the C2 position via transmetallation followed by C4–I oxidative addition afforded a dimetallic complex comprising two palladium centres bridged by a single NHC ligand.