Suzuki coupling reactions in ether-functionalized ionic liquids: The importance of weakly interacting cations

Imidazolium- and pyridinium-based ionic liquids with ether/polyether substituents have been evaluated as solvents for palladiurn-catalyzed Suzuki C-C coupling reactions. In general, reactions proceed more efficiently in these solvents compared to other ionic liquids, which is believed to be due to better stabilization of the palladium catalyst, involving weak interactions with the ether groups. The position and the number of oxygen atoms in the ether side chain strongly influence the outcome of the coupling reactions in the imidazolium-based ionic liquids, whereas for the pyridinium-based liquids no influence is observed. Carbene derivatives, generated from the imidazolium-based ionic liquids, are believed to play a role by terminating the catalytic cycle, and representative species have been isolated and characterized from stoichiometric reactions.