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.