Facile synthesis of achiral and chiral PCN pincer palladium(II) complexes and their application in the Suzuki and copper-free Sonogashira cross-coupling reactions

Five non-symmetrical PCN pincer palladium(II) complexes [PdCl{C6H3-2-(CHdouble bond; length as m-dashNR)-6-(View the MathML sourceOPR2′)}] (R = m-ClC6H4, R′ = Ph (2a); R = Ph, R′ = Ph (2b); R = i-Pr, R′ = Ph (2c); R = m-ClC6H4, R′ = i-Pr (2d); R = (S)-1-phenylethyl, R′ = Ph (2e)) have been easily prepared in only two steps from readily available m-hydroxybenzaldehyde and characterized by HRMS, 1H NMR, 13C NMR, 31P NMR and IR spectra. The molecular structures of 2a and 2b have been further determined by X-ray single-crystal diffraction. The obtained Pd complexes were found to be effective catalysts for the Suzuki and copper-free Sonogashira cross-coupling reactions which could be carried out in the undried solvent under air.