N-Heterocyclic Carbene Conjugated with Poly(ethylene glycol) for Palladium-Catalyzed Suzuki–Miyaura Coupling in Aqueous Solvents

Here we report a type of N -heterocyclic carbene (NHC)- and phosphine-chelated palladium catalysts with poly(ethylene glycol) (PEG) chain for Suzuki–Miyaura cross-coupling reactions. 1-(2-Diphenylphosphinoferrocenyl)-ethyl-3-imidazolium iodides conjugated with MeO–PEG 400 and MeO–PEG 750 , respectively, have been synthesized and characterized. It was demonstrated that the salts bearing with PEG chain could act as NHC precursors successfully under the catalytic condition to form NHC-supported palladium complexes joined by phosphine. The formed palladium complexes are highly efficient for Suzuki–Miyaura coupling of aryl bromides with phenylboronic acid at the palladium loading of 0.1 mol% in both organic and aqueous solvents. Graphical Abstract A type of N -heterocyclic carbene (NHC)- and phosphine-chelated palladium catalysts with different length of poly(ethylene glycol) (PEG) chain has been developed and shown to be highly efficient for Suzuki–Miyaura cross-coupling reactions.