Amphiphilic ionic palladium complexes for aqueous-organic biphasic Sonogashira reactions under aerobic and CuI-free conditions

The ionic Pd(II)-complexes of 2 (ammonium-[1-(2-hydroxyethyl)-3- methylimidazolium] bis[3-(diphenylphosphino)benzenesulfonate]- dichloropalladium(II) ([(NH₄)(Hemim)][PdCl₂(TPPMS) ₂])) and 3 (bis[1-n-butyl-3-methylimidazolium] bis[3- (diphenylphosphino)benzenesulfonate]-dichloropalladium(II) ([Bmim] ₂[PdCl₂(TPPMS)₂])) were synthesized and fully characterized. The single crystal X-ray diffraction analyses show that 2 and 3 are composed of the imidazolium-based cations and [PdCl₂(TPPMS) ₂]^{2 -} anions. The properties of such imidazolium-based Pd-complexes of 2 and 3, in terms of the aqueous solubilities and the catalytic behaviors in water, could be dramatically varied. When 2 and 3 were applied as the precatalysts for the Sonogashira coupling of iodobenzene with phenylacetylene under aerobic and CuI-free conditions, the much higher yields of 1,2-diphenylethyne were obtained due to their amphiphilicity. The wide generality of 2 was available for aqueous-organic biphasic Sonogashira reactions.