Stereoselective On‐Surface Cyclodehydrofluorization of a Tetraphenylporphyrin and Homochiral Self‐Assembly

Abstract

The thermally induced cyclodehydrofluorization of iron tetrakis(pentafluorophenyl)porphyrin proceeded highly stereoselectively to give a prochiral product on a gold surface in an ultrahigh vacuum, whereas dehydrocyclization of the respective iron tetrakisphenylporphyrin did not show such selectivity. Stereoselectivity was predominantly observed for closely packed layers, which is an indication of intermolecular cooperativity and steric constraints induced by adjacent species. Density functional theory identified intermolecular packing constraints as the origin of such selectivity during the reaction. Scanning tunneling microscopy revealed the formation of an enantiomerically pure two‐dimensional self‐assembly as a conglomerate of mirror domains. On‐surface two‐dimensional topochemistry, as reported herein, may open new routes for stereoselective synthesis.

Structures and electronic properties of functional molecules on metal substrates: From single molecule to self‐assemblies

“…For 2H‐TPP, product I is the ground state, and the energy of products II, III, and IV is 0.18, 0.42, and 0.26 eV higher than that of I, respectively 140 . For Fe‐TPFP, product IV has the lowest energy, and the energy of products I, II, and III is 0.56, 0.26, and 0.24 eV higher than IV, respectively 141 . Therefore, if the reaction depends completely on the energy differences, there are only products I in 2H‐TPP and products IV in Fe‐TPFP, respectively.…”

“…140 For Fe-TPFP, product IV has the lowest energy, and the energy of products I, II, and III is 0.56, 0.26, and 0.24 eV higher than IV, respectively. 141 Therefore, if the reaction depends completely on the energy differences, there are only products I in 2H-TPP and products IV in Fe-TPFP, respectively. Besides, the final products of other metal-TPPs such as Co-TPP and Ru-TPP are more likely to be IV, because the structure and symmetry of metal-TPPs are similar to Fe-TPFP.…”

“…(a) A schematic showing four isomers after on-surface intramolecular quadruple ring formation. (b) STM images of 2H-TPP molecules and the products after annealing the surface to 620 K. 140 (c) STM images of Ru-TPP molecules and the products after annealing the surface to 560 K. 140 (d) STM images of Fe-TPFP molecules and the products after annealing the surface to 600 K. 141 lowest energy in step 2 is only 0.03 eV, as shown in Figure 7f, indicating that other products are also very likely to be formed at an annealing temperature of 600 K. These results are in contrast to the fact that there are no other products observed in the self-assembled region of product IV. Furthermore, similar to the case of isolated molecules, the ground state energies of all intermediates considering steric constraints are calculated.…”

“…(c) STM images of Ru‐TPP molecules and the products after annealing the surface to 560 K 140 . (d) STM images of Fe‐TPFP molecules and the products after annealing the surface to 600 K 141 . (e) Histogram of different planar porphyrin derivatives of Ru‐TPP (blue), 2H‐TPP (orange), and Fe‐TPFP (gray).…”

“…(f) Comparison of energies of intermediates along different reaction pathways for free‐standing Fe‐TPFP and Fe‐TPFP/Au(111). Δ I IS , Δ II IS , Δ III IS , and Δ IV IS are energy differences between the lowest and second lowest structures when there is an isolated intermediate, while Δ I SC , Δ II SC , Δ III SC , and Δ IV SC are the energy differences considering steric constraints coming from the neighboring molecules 141 …”