On-Surface Synthesis of Gold Porphyrin Derivatives via a Cascade of Chemical Interactions: Planarization, Self-Metalation, and Intermolecular Coupling

On-surface chemistry in ultrahigh vacuum offers complementary routes for synthesizing molecular complexes that cannot be accessed through standard solution chemistry. The presence of a surface not only imposes spatial two-dimensional restraints but also frequently acts as a source of adatoms actively participating in the chemical reactions. Here we demonstrate the formation of gold porphyrin derivatives via thermally induced chemical transformations of a fluorinated free-base porphyrin, 2H-4FTPP, on a Au(111) surface, which can rarely be accessed via standard solution chemistry protocols. We also provide an accurate description of the mechanisms of on-surface reactions and self-assembly processes, including structural and electronic characterization of intermediates and products using high-resolution scanning probe microscopy with a CO tip supported by a computational study. An initial annealing step at 500 K induces planarization of the adsorbed free base via dehydrogenation and ring-closing reactions that preserve the integrity of the C-F bonds. A second annealing step at 575 K enables metalation, producing unprecedented surface-supported gold-coordinated planarized porphyrins. A final annealing step at 625 K induces C-F and C-H activation, leading to intermolecular C-C coupling between phenyl termini to form planarized porphyrin oligomers. These results open new avenues for engineering in a stepwise manner thermally sensitive on-surface chemical reactions and metal-organic compounds that cannot be accessed in solution chemistry.