Mechanisms of N‑Heterocyclic Carbene Complex Lattice Formation

N-Heterocyclic carbenes (NHCs) that have wingtip groups with low steric bulk, such as 1,3-dimethyl-benzimidazol-2-ylidene (NHC^Me), form bis-complexes with metal atoms when they are deposited onto Au(111) surfaces <i>in vacuo</i>. These complexes self-assemble into three different lattices: a herringbone, a double-herringbone, and a chiral kagome lattice. The static properties of these lattices have been studied with scanning tunneling microscopy and <i>ab initio</i> theoretical methods. Dynamic processes including complex center displacement and hindered monomer motion have also been observed. Our results suggest that in addition to surface hopping, exchange processes are important, providing a facile mechanism for atom exchange between the overlayer and the metal. These dynamic processes are well-known from studies of metal epitaxy but have not previously been discussed in the context of NHC self-assembly.