Palladium(ii) complexes with electron-poor, 4,5-disubstituted diimidazol-2-ylidene ligands: synthesis, characterization and catalytic activity

Diimidazolium salts featuring different bridges between the imidazolium groups, as well as electron-withdrawing groups (chloride, cyanide) at the 4- and 5-position of the heterocyclic rings, have been successfully prepared. The diimidazolium salts serve as convenient precursors of di(N-heterocyclic carbene) ligands, which coordinate in a chelating fashion to palladium(ii) centres. The effect of the newly introduced electron-withdrawing groups on the spectroscopic and structural characteristics of the resulting complexes as well as on their reactivity as catalysts in a model alkyne hydroarylation reaction has been investigated and is discussed herein.