Аннотация:R–NHC coupling was previously considered as a process of degradation of M/NHC species, however recent studies have
pointed out that it may be responsible for generation of catalytically active NHC-free complexes or/and metallic
nanoparticles. Therefore, a detailed and systematic study of R-NHC coupling for various carbene ligands is an important
topic. In the present article this process has been studied for reactive aryl iodide coupling partners by a combination of
quantum chemical calculations and continuous reaction monitoring via pressurized sample infusion electrospray ionization
mass spectrometry (PSI-ESI-MS). DFT calculations revealed strong tendency of (NHC)Pd(Ph)(I)DMF complexes bearing
various N-heterocyclic carbene ligands (NHC) to undergo Ph–NHC coupling. Calculated energy barriers of these reactions
lie in the range of 17.9 – 25.1 kcal/mol. Ph–NHC coupling is thermodynamically more favorable for the complexes
containing unsaturated NHC ligands with bulky substituents. NBO analysis has suggested that the process of Ph–NHC
formation is similar for different NHC ligands. In order to confirm theoretical studies, a series of ESI-MS reaction
monitoring experiments was performed for (NHC)Pd(I)2(Py) and (NHC)Pd(Cl)(η3-1-Ph-C3H4) complexes interacting with
iodobenzene, where Ph–NHC coupling products were observed in all cases. As a direct experimental evidence, formation
of colloidal Pd-containing nanoparticles was observed in situ for different Pd/NHC complexes in the studied reaction
mixtures.