期刊
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
卷 56, 期 3, 页码 865-869出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.201610251
关键词
metal nanoparticles; N-heterocyclic carbenes; palladium; solid-state NMR spectroscopy; surface characterization
资金
- Ministerio de Economia y Competitividad [CTQ2014-55005-P]
- Agence Nationale de la Recherche [ANR-11-INTB-101]
- Ministerio de Educacion [AP2012-4745]
- European Commission [PCIG11-GA-2012-317692]
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 the C-13 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 PdII complex. NMR studies after (CO)-C-13 adsorption established that the KS shifts the C-13 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 for C-13-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.
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