Recently, N-heterocyclic carbenes (NHCs) were introduced as alternative anchors for surface modifications and so offered many attractive features, which might render them superior to thiol-based systems. However, little effort has been made to investigate the self-organization process of NHCs on surfaces, an important aspect for the formation of self-assembled monolayers (SAMs), which requires molecular mobility. Based on investigations with scanning tunnelling microscopy and first-principles calculations, we provide an understanding of the microscopic mechanism behind the high mobility observed for NHCs. These NHCs extract a gold atom from the surface, which leads to the formation of an NHC–gold adatom complex that displays a high surface mobility by a ballbot-type motion. Together with their high desorption barrier this enables the formation of ordered and strongly bound SAMs. In addition, this mechanism allows a complementary surface-assisted synthesis of dimeric and hitherto unknown trimeric NHC gold complexes on the surface.
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Financial support from the Deutsche Forschungsgemeinschaft (DFG) through the SFB 858 (projects B02 and B15), the Transregional Collaborative Research Center TRR 61 (projects B03 and B07), the Ministry of Science and Technology of China (no. 2013CBA01600), the National Natural Science Foundation of China (no. 61390501), the Leibniz award (F.G.) and the Fonds der Chemischen Industrie (J.B.E.) is gratefully acknowledged. We also thank O. Diaz-Arado and H. Mönig (both Westfälische Wilhelms-Universität) for support with the sample preparation for the XPS measurements.
The authors declare no competing financial interests.
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Wang, G., Rühling, A., Amirjalayer, S. et al. Ballbot-type motion of N-heterocyclic carbenes on gold surfaces. Nature Chem 9, 152–156 (2017). https://doi.org/10.1038/nchem.2622
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