title: Knight Shift in13C NMR Resonances Confirms the Coordination of N-Heterocyclic Carbene Ligands to Water-Soluble Palladium Nanoparticles.
abstract: The coordination of N-heterocyclic carbene (NHC) ligands to the surface of 3.7 nm palladium nanoparticles (PdNPs) can be unambiguously established by observation of Knight shift (KS) in the13C resonance of the carbenic carbon. In order to validate this coordination, PdNPs with sizes ranging from 1.3 to 4.8 nm were prepared by thermal decomposition or reduction with CO of a dimethyl NHC PdIIcomplex. NMR studies after13CO adsorption established that the KS shifts the13C resonances of the chemisorbed molecules several hundreds of ppm to high frequencies only when the particle exceeds a critical size of around 2 nm. Finally, the resonance of a carbenic carbon is reported to be Knight-shifted to 600 ppm for13C-labelled NHCs bound to PdNPs of 3.7 nm. The observation of these very broad KS resonances was facilitated by using Car-Purcell-Meiboom-Gill (CPMG) echo train acquisition NMR experiments.
authors.affiliation: Departamento de Química Orgánica y Química Inorgánica, Universidad de Alcalá, Campus Universitario, 28871, Alcalá de Henares, Spain.
authors.forename: Juan M
authors.initials: JM
authors.lastname: Asensio
authors.affiliation: Laboratoire de Physique et Chimie des Nano-Objets, INSA, CNRS, Université de Toulouse, 135, Avenue de Rangueil, 31077, Toulouse, France.
authors.forename: Simon
authors.identifier: 0000-0002-0061-8578
authors.initials: S
authors.lastname: Tricard
authors.affiliation: Laboratoire de Chimie de Coordination (LCC), CNRS, 205 route de Narbonne, BP44099, 31077, Toulouse Cedex 4, France.
authors.forename: Yannick
authors.initials: Y
authors.lastname: Coppel
authors.affiliation: Departamento de Química Orgánica y Química Inorgánica, Universidad de Alcalá, Campus Universitario, 28871, Alcalá de Henares, Spain.
authors.forename: Román
authors.initials: R
authors.lastname: Andrés
authors.affiliation: Laboratoire de Physique et Chimie des Nano-Objets, INSA, CNRS, Université de Toulouse, 135, Avenue de Rangueil, 31077, Toulouse, France.
authors.forename: Bruno
authors.identifier: 0000-0001-9290-6421
authors.initials: B
authors.lastname: Chaudret
authors.affiliation: Departamento de Química Orgánica y Química Inorgánica, Universidad de Alcalá, Campus Universitario, 28871, Alcalá de Henares, Spain.
authors.forename: Ernesto
authors.identifier: 0000-0001-8101-1358
authors.initials: E
authors.lastname: de Jesús
keywords: N-heterocyclic carbenes; metal nanoparticles; palladium; solid-state NMR spectroscopy; surface characterization