Transformations of Pd/(N-Heterocyclic Carbene) Molecular Complexes into a Nanosized Catalyst System in the Mizoroki-Heck Reaction

The mechanism of formation of catalytic sites in the important Mizoroki-Heck reaction used in modern fine organic synthesis has been studied. It was found that the catalysts based on palladium complexes with N-heterocyclic carbene ligands transform into a "ligand-free" form under the conditions of the Mizoroki-Heck reaction. Molecular modeling performed using quantum-chemical methods showed that these processes compete with the target reaction at three of the six stages of the catalytic cycle. The presence of catalyst transformation products in the reaction system was confirmed by nuclear magnetic resonance and mass spectrometry. Important mechanistic data were obtained for rational design of catalyst systems for cross-coupling reactions.