Knight Shift in p>13p>C NMR Resonances Confirms the Coordination of N-Heterocyclic Carbene Ligands to Water-Soluble Palladium Nanoparticles

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• 作者：M. Sc. Juan M. Asensio ; Dr. Simon Tricard ; Dr. Yannick Coppel ; Dr. Rom&aacute ; n André ; s ; Prof. Dr. Bruno Chaudret and Prof. Dr. Ernesto de Jesú ; s
• 刊名：Angewandte Chemie
• 出版年：2017
• 出版时间：January 16, 2017
• 年：2017
• 卷：129
• 期：3
• 页码：883-887
• 全文大小：757K
• ISSN：1521-3757

文摘

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 p>13p>C 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 Pdp>IIp> complex. NMR studies after p>13p>CO adsorption established that the KS shifts the p>13p>C 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 p>13p>C-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.