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Ballbot-type motion of N-heterocyclic carbenes on gold surfaces


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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Figure 1: Investigated NHCs and STM images of NHCs on Au surfaces.
Figure 2: STM topography images of IPr–Au.
Figure 3: Densely packed film of IMe–Au on the Au(111) surface and the DFT results.
Figure 4: Dimeric and trimeric gold complexes.


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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.

Author information




F.G. and H.F. initiated the project. F.G., H.F., G.W., A.R., S.A., N.D., M.K., J.B.E. and H.-Y.G. designed the experiments and coordinated the study. A.R., J.B.E. and C.R. synthesized the molecules. G.W. and M.K. performed the STM measurements. S.A. and N.D. performed DFT calculations. F.G., H.F., G.W., A.R., S.A., N.D., M.K., J.B.E., H.-J.G., H.-Y.G. and C.R. interpreted data. A.T. did the XPS experiments. H.F. and F.G. wrote the manuscript together with G.W., A.R., S.A. and N.D. All the authors read and commented on the manuscript.

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Correspondence to Frank Glorius or Harald Fuchs.

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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).

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