Dery Shahar, Berg Iris, Kim Suhong, Cossaro Albano, Verdini Alberto, Floreano Luca, Toste F Dean, Gross Elad
Institute of Chemistry and the Center for Nanoscience and Nanotechnology , The Hebrew University , Jerusalem 91904 , Israel.
Department of Chemistry , University of California, Berkeley , Berkeley , California 94720 , United States.
Langmuir. 2020 Jan 28;36(3):697-703. doi: 10.1021/acs.langmuir.9b02401. Epub 2019 Dec 10.
Fundamental understanding of the correlation between the structure and reactivity of chemically addressable N-heterocyclic carbene (NHC) molecules on various surfaces is essential for the design of functional NHC-based self-assembled monolayers. In this work, we identified the ways by which the deposition of chemically addressable OH-NHCs on Au(111) or Pt(111) surfaces modified the anchoring geometry and chemical reactivity of surface-anchored NHCs. The properties of surface-anchored NHCs were probed by conducting X-ray photoelectron spectroscopy and polarized near-edge X-ray absorption fine structure measurements. While no preferred orientation was identified for OH-NHCs on Pt(111), the anchored molecules adopted a preferred flat-lying position on Au(111). Dehydrogenation and aromatization of the imidazoline ring along with partial hydroxyl oxidation were detected in OH-NHCs that were anchored on Au(111). The dehydrogenation and aromatization reactions were facilitated, along with partial decomposition, for OH-NHCs that were anchored on Pt(111). The spectroscopic results reveal that stronger metal-adsorbate interactions increase the reactivity of surface-anchored OH-NHCs while decreasing their molecular orientational order.
深入理解化学可寻址的氮杂环卡宾（NHC）分子在各种表面上的结构与反应性之间的关联，对于设计基于NHC的功能性自组装单分子层至关重要。在这项工作中，我们确定了化学可寻址的羟基氮杂环卡宾（OH-NHC）在金（111）或铂（111）表面上的沉积改变表面锚定NHC的锚定几何结构和化学反应性的方式。通过进行X射线光电子能谱和偏振近边X射线吸收精细结构测量来探测表面锚定NHC的性质。虽然在铂（111）上未发现OH-NHC有择优取向，但锚定分子在金（111）上采取了择优的平躺位置。在锚定在金（111）上的OH-NHC中检测到咪唑啉环的脱氢和芳构化以及部分羟基氧化。对于锚定在铂（111）上的OH-NHC，脱氢和芳构化反应以及部分分解都得到了促进。光谱结果表明，更强的金属 - 吸附质相互作用会增加表面锚定的OH-NHC的反应性，同时降低其分子取向有序度。
