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

Abstract

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···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.