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In situ transformations of Pd/NHC complexes to colloidal Pd nano-particles studied for N‑heterocyclic carbene ligands of different nature

Abstract

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.

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Publication details

The article was received on 10 Oct 2018, accepted on 05 Dec 2018 and first published on 06 Dec 2018


Article type: Research Article
DOI: 10.1039/C8QI01095A
Citation: Inorg. Chem. Front., 2018, Accepted Manuscript
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    In situ transformations of Pd/NHC complexes to colloidal Pd nano-particles studied for N‑heterocyclic carbene ligands of different nature

    A. Kostyukovich, A. Tsedilin, E. Sushchenko, D. Eremin, A. S. Kashin, M. Nechaev, A. Asachenko, M. Topchiy and V. Ananikov, Inorg. Chem. Front., 2018, Accepted Manuscript , DOI: 10.1039/C8QI01095A

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