Regioselective Dehydrogenation Coupling via Out-of-Plane Flipping on Metal Surfaces

Selective dehydrogenation coupling plays a vital role in on-surface synthesis for achieving high-yield target nanostructures. Most dehydrogenation reactions are based on in-plane movement-induced reactant coupling, while the feasibility and selectivity of reactant cyclodehydrogenation through out-of-plane flipping have rarely been explored. Here, we report a regioselective dehydrogenation coupling reaction achieved through reactant flipping on two-dimensionally confined metal substrates. The yields of target reactants obtained by out-of-plane flipping of three benzofluoranthrene derivatives with different masses on the Au(111) surface are higher than 99%. By combining scanning tunneling microscope characterization and density functional theory calculations, we visualize the reaction process of reactant flipping and cyclization. By comparing the results on Au(111) with those on Ag(111) and Cu(111), we summarize that the main factors determining the out-of-plane flipping-induced cyclodehydrogenation reaction of benzofluoranthrene derivatives on a metal surface are their own mass and the interaction with the underlying substrate. Our work provides a new strategy for achieving regioselective surface dehydrogenation coupling reactions and offers a new research paradigm for the synthesis of conjugated carbon nanostructures.