Sulfonated N-heterocyclic carbenes for Pd-catalyzed sonogashira and suzuki-miyaura coupling in aqueous solvents

Article abstract of DOI:10.1002/adsc.200900886

The reactions of the N, N-diarylimidazolium and N, N-diarylimidazolinium salts with chlorosulfonic acid result in the formation of the respective disulfonated N-heterocyclic carbene (NHC) precursors in reasonable yields (46-77%). Water-soluble palladium catalyst complexes, in situ obtained from the respective sulfonated imidazolinium salt, sodium tetrachloropalladate (Na ₂PdCl₄) and potassium hydroxide (KOH) in water, were successfully applied in the copper-free Sonogashira coupling reaction in isopropyl alcohol/water mixtures using 0.2 mol% catalyst loading. The preformed (disulfonatedNHC)PdCl(cinnamyl) complex was used in aqueous Suzuki-Miyaura reactions at 0.1 mol% catalyst loading. The coupling protocol reported here is very useful for Sonogashira reactions of N- and 5-heterocyclic aryl bromides and chlorides with aryl- and alkylacetylenes.