Highly-selective metalation of porphyrin enabled by distinct aromatic ring-fused structures

Metalation is an effective strategy for tuning the optical, magnetic, and other physical properties of porphyrins, which play an important role in material synthesis and biological activities. Multiple aromatic ring-fused structures (ARFSs) can be formed by cyclodehydrogenation from a single porphyrin compound. Understanding the various bonding forms and bond strengths of aromatic allotropes with metals remains as an intriguing area. The role of ARFSs in porphyrin metalation is yet unknown. Herein, we demonstrate highly selective metalation of porphyrin enabled by the distinctive ARFSs derived from a single precursor on Ag(111). ARFS-A is self-metalated with a high yield (∼100%) on Ag(111), setting one Ag atom in its molecular central cavity. ARFS-B is barely metalated until full molecular desorption from the substrate. The selectivity is attributed to the differences in metalation energy barriers originated from the different dehydrocyclization structures and adsorption configurations of porphyrin allotropes on the surface. By exposing the relationship between the ring-fused structures and porphyrin metalation, this work offers insights into how to design aromatic ring-fused porphyrins structurally and shows how to control the occurrence and selectivity of porphyrin metalation.