Optimizing bidentate N-heterocyclic carbene ligands for the modification of late transition metal surfaces - new insights through theory.

The functionalization of metal surfaces with N-heterocyclic carbenes (NHCs) has gained much interest in the past decade, since the modified materials are highly suitable for the development of specialized applications, for example in heterogeneous catalysis. More recently, multidentate NHC-ligands have been utilized to further improve the properties of the modified materials. However, the influence of the linker, which connects the NHC units, on the adsorption behavior of multidentate NHC-ligands has not been investigated so far. This knowledge is essential in order to access the full potential of applications. Here, we provide a thorough computational study, which compares the performance of bidentate NHC-ligands with twelve different linkers on the Cu(111), Pd(111) and Au(111) surfaces. It is shown that, on the Cu(111) and Au(111) surfaces, linkers should most importantly allow for a favorable arrangement of all NHC units, while aromatic linkers lead to stronger adsorption than aliphatic ones on Pd(111) surfaces. As a consequence, bidentate NHCs with aromatic linkers on Pd(111) surfaces tolerate larger deviations from the optimum single-NHC adsorption mode.