Coverage‐ and Temperature‐Dependent Metalation and Dehydrogenation of Tetraphenylporphyrin on Cu(111)

Abstract

Using temperature-programmed desorption, supported by X-ray photoelectron spectroscopy and scanning tunneling microscopy, a comprehensive overview of the main reactions of 5,10,15,20-tetraphenyl-21H,23H-porphyrin (2HTPP) on Cu(111) as a function of coverage and temperature is obtained. Three reactions were identified: metalation with Cu substrate atoms, stepwise partial dehydrogenation, and finally complete dehydrogenation. At low coverage the reactions are independent of coverage, but at higher coverage metalation becomes faster and partial dehydrogenation slower. This behavior is explained by a weaker interaction between the iminic nitrogen atoms and the Cu(111) surface in the high-coverage checkerboard structure, leading to faster metalation, and the stabilizing effect of T-type interactions in the CuTPP islands formed at high coverage after metalation, leading to slower dehydrogenation. Based on the amount of hydrogen released and the appearance in STM, a structure of the partially dehydrogenated molecule is suggested.

Self-assembly and coverage dependent thermally induced conformational changes of Ni(ii)-meso-tetrakis (4-tert-butylphenyl) benzoporphyrin on Cu(111)

“…45 A similar explanation is also applicable to our experimental results. Because of the comparably weak molecule-substrate interaction, Ni-TTBPBP molecules are very mobile on Cu surface (note the required reduced STM acquisition temperature in Fig.…”

“…45 Based on the overall similarity of 2H-TPP and Ni-TTBPBP, and the very similar changes in the STM images, we suggest that the change of intramolecular conformation for Ni-TTBPBP on Cu(111) after annealing is mainly induced by the dehydrogenation of neighbouring carbon atoms (in the same molecule) along with the formation of new intramolecular C-C bonds. Fig.…”

“…A similar square structure was also reported for 2H-TPP on Cu(111) after partial dehydrogenation. 23,45 There, in the course of the dehydrogenation reaction of 2H-TPP, one phenyl group fuses with only one neighboring pyrrole ring in a specific fashion. We propose a similar dehydrogenative intramolecular aryl-aryl coupling reaction.…”

“…Furthermore, assuming that the dehydrogenation is catalysed by the Cu substrate, a reduced substrate C-H bond distance, which is certainly easier realized in the dynamic situation of the 2D-gas phase, promotes the reaction. 45 …”

Evidence for a precursor adcomplex during the metalation of 2HTPP with iron on Ag(100)

“…By metalating the porphyrins in situ, on the surface, such ligands can be avoided [15]. Recent investigations of the self-metalation of 2HTPP on Cu(1 1 1) with copper substrate atoms provide unprecedented new insights in the metalation mechanism [16,17], but still the process is not fully understood. Based on Xray photoelectron spectroscopy (XPS) measurements, the present study further expands our general understanding of the metalation reaction, by showing the presence of an Fe-2HTPP adcomplex as a precursor for metalation.…”