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···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.