Elucidating the Binding Modes of N-Heterocyclic Carbenes on a Gold Surface

Abstract

Tuning the binding mode of N-heterocyclic carbenes on metal surfaces is crucial for the development of new functional materials. To understand the impact of alkyl side groups on the formation of NHC species at the Au(111) surface, we combined scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. We reveal two significantly different binding modes depending on the alkyl chain length. In the case of a short alkyl substituent, an up-standing configuration with one Au adatom is preferred, whereas the longer alkyl groups result exclusively in NHC-Au-NHC complexes lying flat on the surface. Our study highlights how well-defined structural modifications of NHCs allow for controlling the local binding motif on surfaces, which is important to design designated catalytic sites at interfaces.

Flexible NO2‐Functionalized N‐Heterocyclic Carbene Monolayers on Au (111) Surface

“…The adsorption energy was increased to −3.36 eV once the NHC was anchored on Au ad‐atom [Au‐ad/Au (111)] (Figure d). The enhanced adsorption energy is a result of stabilization of the bulky molecule on the defected surface . It should be noted that in both adsorption scenarios (with and without ad‐atom) the adsorption geometry was similar; the central NHC ring slightly tilted toward the surface, whereas the bulky NO 2 ‐decorated phenyl rings oriented parallel to the surface.…”

Highly Robust but Surface-Active: N-Heterocyclic Carbene-Stabilized Au25 Nanocluster as a Homogeneous Catalyst

“…30 Several groups have demonstrated that NHCs readily form robust self-assembled monolayer on coinage metal surface and function as a performance-enhancing modifier. [31][32][33][34][35][36] NHCs stabilized Au nanoparticles with excellent water-solubility, thermal stability, and chemical resistance to thiol exchange have also been reported. [37][38] Several coinage metal clusters stabilized by NHCs have been prepared as well.…”

Cooperation of N‐Heterocyclic Carbenes on a Gold Surface

“…Further analysis of the STM results revealed a reduction of the amount of carbene species at the surface to 18 % of the initial coverage after 125 hours, probably due to the formation of IMe‐Au‐IMe complexes, [6h] which might have a lower binding energy compared to the IMe‐Au species. However, the exact desorption process might involve a more complex pathway, which is not in the scope of the current study.…”