Metalation of 2HTCNPP on Ag(111) with Zn: Evidence for the Sitting atop Complex at Room Temperature

Abstract

We study the interaction and metalation reaction of a free base 5,10,15,20‐terakis(4‐cyanophenyl)porphyrin (2HTCNPP) with post‐deposited Zn atoms and the targeted reaction product Zn‐5,10,15,20‐terakis(4‐cyanophenyl)porphyrin (ZnTCNPP) on a Ag(111) surface. The investigations are performed with scanning tunneling microscopy at room temperature after Zn deposition and subsequent heating. The goal is to obtain further insights in the metalation reaction and the influence of the cyanogroups on this reaction. The interaction of 2HTCNPP with post‐deposited Zn leads to the formation of three different 2D ordered island types that coexist on the surface. All contain a new species with a bright appearance, which increases with the amount of post‐deposited Zn. We attribute this to metastable SAT (“sitting atop”) complexes formed by Zn and the macrocycle, that is, an intermediate in the metalation reaction to ZnTCNPP, which occurs upon heating to 500 K. Interestingly, the activation barrier for the successive reaction of the SAT complex to the metalated ZnTCNPP species can also be overcome by a voltage pulse applied to the STM tip.

Reassessing the Adsorption Behavior and on-Surface Reactivity of a Brominated Porphyrin on Cu(111)

“…This conformation differs from the square symmetry of the conventional “saddle-shaped” configuration in which the two iminic nitrogens are almost parallel to the substrate’s surface. The saddle conformation is typically found in porphyrins on less reactive substrates such as Ag(111). , Our DFT calculations find that the saddle shape is 0.86 eV higher in energy (less stable) than the inverted structure on Cu(111), explaining why our STM images at RT only show rectangular-shaped molecules.…”

“…On Cu(111), however, our STM measurements clearly show that the molecules in the metal–organic framework (MOF) assume the inverted conformation. This finding is interesting because usually porphyrin molecules in 2D networks on metallic surfaces adopt a molecular structure with a low diffusion barrier, ,, and the studies involving porphyrins in inverted conformations reported recently do not present any ordered motifs with the molecule in this configuration. , This demonstrates the importance of this new growth protocol. The 2D hexagonal arrangement shown in Figure b has an experimental lattice angle α ≈ 62 ± 3°.…”

“…The saddle conformation is typically found in porphyrins on less reactive substrates such as Ag(111). 17,39 Our DFT calculations find that the saddle shape is 0.86 eV higher in energy (less stable) than the inverted structure on Cu(111), explaining why our STM images at RT only show rectangular-shaped molecules.…”

Adsorption, self-assembly and self-metalation of tetra-cyanophenyl porphyrins on semiconducting CoO(100) films

“…In the self-assemblies CN-groups are oriented at 90 • angle to the axis of the cyanophenyl ring of a neighboring molecule, as observed on other substrates before [10,32,62,63]. For the stabilization of the supramolecular assembly via the CN-groups [64] hydrogen bonding to the pyrrole group [62] or the phenyl rings [32] has to be considered.…”

Aromatic Ring Fusion to Benzoporphyrin via γ-ortho Cyclodehydrogenation on a Ag(111) Surface

“…As a bottom-up approach, on-surface synthesis has demonstrated its great potentials in constructing low-dimensional molecular nanostructures and materials with atomic precision. , Moreover, recent advances in scanning probe microscopes allows probing on-surface chemical reaction processes at the single chemical bond level. − It has been demonstrated that porphyrins can undergo a number of reactions on the surface to form porphyrinoids and related hybrid nanostructures that are hardly accessible in conventional solution chemistry (Table S1). − Most of these reactions are based on the reactivity at the β- and meso -positions (Figure a). For example, thermal treatment of fluorinated tetraphenylporphyrins on the Au(111) surface can induce intramolecular cyclization of the β-pyrrolic carbon with the ortho -carbon and thus form five-membered rings attached to the molecules.…”