Synthesis and Structure of Palladium 1,2,3-Triazol-5-ylidene Mesoionic Carbene PEPPSI Complexes and Their Catalytic Applications in the Mizoroki-Heck Reaction

New mono- and bimetallic 1,2,3-triazol-5-ylidene mesoionic carbene (MIC) complexes of Pd have been synthesized, isolated, and characterized. We have described the synthesis of a bis(MIC) complex via transmetalation from a Ag-MIC complex and two PEPPSI-type complexes which are directly available from their respective triazolium salts by treatment with PdCl2 in pyridine. The X-ray structures are reported for all complexes described herein. Interestingly, each complex described exhibits various secondary noncovalent interactions in the solid state of the general type C-H center dot center dot center dot Cl, which appear to be important for the stabilization of the solid-state structure of the complexes. We further demonstrated the utility of the new PEPPSI complexes in the Mizoroki-Heck reaction. In the case of aryl iodides and electron-deficient bromides, high conversion is observed with methyl acrylate. Hg poisoning tests suggest that, even with an easily dissociated ligand, the reaction likely proceeds via Pd nanoparticles.