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

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 Pd-0 and Pd-II species, as demonstrated by electrospray ionization mass spectrometry.