A mesoionic bis(Py-tzNHC) palladium(ii) complex catalyses “green” Sonogashira reaction through an unprecedented mechanism

Abstract

A novel bis(pyridyl-functionalized 1,2,3-triazol-5-ylidene)-palladium(II) complex [Pd(Py-tzNHC)₂]²⁺ catalyses the copper-, amine-, phosphine-, and additive-free aerobic Sonogashira alkynylation of (hetero)aryl bromides in water as the only reaction solvent. The catalysis proceeds along two connected Pd-cycles with homogeneous bis-carbene Pd⁰ and Pd^II species, as demonstrated by electrospray ionization mass spectrometry.