Synthesis of New Dicationic Azolium Salts and Their Application as NHC Precursors in Suzuki-Miyaura Coupling

Abstract

Novel dicationic azolium salts were developed as N-heterocyclic carbene (NHC) precursors wherein two 1,2,3-triazolium, one 1,2,3-triazolium and one imidazolium, or two imidazolium units, are tethered to each other through alkylene bridges. These dicationic systems were applied as precursors for ligands in palladium-catalyzed Suzuki―Miyaura couplings using different leaving groups. Interestingly, the combination of an imidazolium and a 1,2,3-triazolium unit performed better than either a single azolium salt or than dications where two imidazolium or two 1,2,3-triazolium units are found. Aryl chlorides, iodides and triflates turned out to be the best substrates for this new catalytic system.