Bridged Imidazolium Salts Used as Precursors for Chelating Carbene Complexes of Palladium in the Mizoroki-Heck Reaction

A variety of chiral and achiral imidazolium salts is synthesized. Methylene-, ethylene-, propylene- and pyridinyl-bridged bis(imidazolium) halides are used to generate the respective free chelating carbenes. The synthesis of palladium complexes of general formula [cis-CH2{NC(H)=C(H)N(R)C}2PdX2] with these chelating N-heterocyclic carbene ligands is reported. Structural proofs of complexes 28 and 46 are represented by X-ray diffraction studies. Catalytic applications in the Mizoroki-Heck reaction are presented.