Highly Structure-Selective On-Surface Synthesis of Isokekulene Versus Kekulene

The role of different facets of metal nanoparticles in steering reaction pathways is crucial for the design of heterogeneous catalysts with superior selectivity. As a prominent class of reactions, transition-metal-catalyzed carbon-hydrogen (C─H) bond activation is widely used for the synthesis of base chemicals, modern organic materials, and pharmaceuticals. Here, we report orthogonal selectivity in intramolecular cyclodehydrogenation of a nonplanar cyclic precursor steered by different facets of a copper single crystal. On the Cu(110) surface, the previously unknown cycloarene isokekulene forms with a high selectivity of 92%, whereas reaction on the Cu(111) surface exclusively yields kekulene (>99%). Combining scanning tunneling microscopy with CO-functionalized tips and density functional theory, we identify two adsorption geometries of the precursor, which react to the respective products. Isokekulene adopts two nonplanar adsorption configurations and exhibits strong molecule-substrate interactions, explaining its preferential formation on Cu(110). This combined in-solution and on-surface synthesis approach represents an alternative route for the highly selective synthesis of molecules that are challenging to synthesize and process via conventional methods.