Departamento de Química Orgánica y Química Inorgánica, Universidad de Alcalá, Campus Universitario, 28871, Alcalá de Henares, Spain.
Laboratoire de Physique et Chimie des Nano-Objets, INSA, CNRS, Université de Toulouse, 135, Avenue de Rangueil, 31077, Toulouse, France.
Angew Chem Int Ed Engl. 2017 Jan 16;56(3):865-869. doi: 10.1002/anie.201610251. Epub 2016 Dec 9.
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 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 Pd complex. NMR studies after CO adsorption established that the KS shifts the 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 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.
氮杂环卡宾（NHC）配体与 3.7nm 钯纳米颗粒（PdNPs）表面的配位可以通过观察卡宾碳原子的 C 共振的奈特位移（KS）来明确确定。为了验证这种配位，通过热分解或 CO 还原二甲基 NHC Pd 配合物制备了粒径从 1.3nm 到 4.8nm 的 PdNPs。CO 吸附后的 NMR 研究表明，只有当颗粒超过约 2nm 的临界尺寸时，KS 才会将化学吸附分子的 C 共振移至高频率几百 ppm。最后，报道了与粒径为 3.7nm 的 PdNPs 结合的 C 标记 NHCs 的卡宾碳原子的共振被奈特位移至 600ppm。通过使用 Car-Purcell-Meiboom-Gill（CPMG）回波串采集 NMR 实验，促进了对这些非常宽的 KS 共振的观察。
