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 the generation of catalytically active NHCfree complexes and...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 the generation of catalytically active NHCfree complexes and/or 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 a strong tendency of(NHC)Pd(Ph)(I)DMF complexes bearing various N-heterocyclic carbene(NHC)ligands to undergo Ph-NHC coupling.Calculated energy barriers of these reactions lie in the range of 17.9-25.1 kcal mol^(-1).Ph-NHC coupling is thermodynamically more favorable for the complexes containing unsaturated NHC ligands with bulky substituents.NBO analysis suggests that the process of Ph-NHC formation is similar for different NHC ligands.In order to confirm the results of theoretical studies,a series of ESI-MS reaction monitoring experiments were performed for(NHC)Pd(I)_(2)(Py)and(NHC)Pd(Cl)(η^(3)-1-Ph-C_(3)H_(4))complexes interacting with iodobenzene,where Ph-NHC coupling products were observed in all cases.As direct experimental evidence,the formation of colloidal Pdcontaining nanoparticles was observed in situ for different Pd/NHC complexes in the studied reaction mixtures.展开更多
基金study was supported by the Russian Science Foundation(grant 17-13-01526)。
文摘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 the generation of catalytically active NHCfree complexes and/or 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 a strong tendency of(NHC)Pd(Ph)(I)DMF complexes bearing various N-heterocyclic carbene(NHC)ligands to undergo Ph-NHC coupling.Calculated energy barriers of these reactions lie in the range of 17.9-25.1 kcal mol^(-1).Ph-NHC coupling is thermodynamically more favorable for the complexes containing unsaturated NHC ligands with bulky substituents.NBO analysis suggests that the process of Ph-NHC formation is similar for different NHC ligands.In order to confirm the results of theoretical studies,a series of ESI-MS reaction monitoring experiments were performed for(NHC)Pd(I)_(2)(Py)and(NHC)Pd(Cl)(η^(3)-1-Ph-C_(3)H_(4))complexes interacting with iodobenzene,where Ph-NHC coupling products were observed in all cases.As direct experimental evidence,the formation of colloidal Pdcontaining nanoparticles was observed in situ for different Pd/NHC complexes in the studied reaction mixtures.
