Sulfonated N-Heterocyclic Carbenes for Pd-Catalyzed Sonogashira and Suzuki–Miyaura Coupling in Aqueous Solvents

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Abstract

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 (Na2PdCl4) 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 S-heterocyclic aryl bromides and chlorides with aryl- and alkylacetylenes.

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