Self-metalation of a free-base porphyrin on a metal oxide surface mediated by extended defects: Insight from ab initio molecular dynamics simulations

An important pathway for functionalization of porphyrin-based organic-inorganic structures is the metalation of porphyrins. Recently, the porphyrin metalation was demonstrated on different metal oxide surfaces, however, the underlying mechanisms regarding the role of the surface morphology, the substituted metal, and ligands are still under investigation. Here we address the adsorption and self-metalation of H2TPP on a MgO(001) surface with low-coordinated sites. We employ ab initio molecular dynamics simulations around room temperature to provide insight into dynamic steric effects. We observe that H2TPP is mobile on the pristine surface as the steric hindrance by phenyl rings prevents the physisorption of the macrocycle at a specific site. In contrast, step edges or kink sites provide anchor points exposing low-coordinated, reactive oxygen-sites to hydrogens of the mac rocycle. We report a spontaneous proton transfer at these sites forming an intermediate complex before the metalation occurs. The energetics of the self-metalation reaction is modeled.