Ullmann Coupling Reactions on Ag(111) and Ag(110); Substrate Influence on the Formation of Covalently Coupled Products and Intermediate Metal-Organic Structures

Abstract

On-surface reactions based on Ullmann coupling are known to proceed on coinage-metal substrates (e.g. Au, Ag, Cu), with the chemistry of the surface strongly influencing the reaction progression. In addition, the topography of the surface may be expected to affect the local adsorption geometry of the reactants as well as the intermediate and final structures. Here, we investigate the effect of two different surface facets of silver, Ag(111) and Ag(110) on the formation of organometallic and covalent structures for Ullmann-type coupling reactions. Deposition of 4,4”-diiodo-m-terphenyl molecules onto either Ag(111) or Ag(110) surfaces leads to the scission of C-I bonds followed by the formation of organometallic zigzag structures, consisting of molecules connected by coordination bonds to Ag adatoms. The covalently coupled product is formed by annealing each surface, leading to the removal of Ag atoms and the formation of covalently bonded zigzag poly(m-phenylene) structures. Comparisons of the adsorption model of molecules on each surface before and after annealing reveal that on Ag(111), structures rearrange by rotation and elongation of bonds in order to become commensurate with the surface, whereas for the Ag(110) surface, the similarity in adsorption geometry of the intermediate and final states means that no rotation is required.

Dechlorinated Ullmann Coupling Reaction of Aryl Chlorides on Ag(111): A Combined STM and XPS Study

“…In this study, the DCUC reaction of DCTP on Ag(111) happens without observable side reactions. However, the generated oligophenylenes 2 always exist in shorter chains aggregated in smaller domains, compared with those acquired from debrominated coupling of DBTP or deiodinated coupling of 4,4′′‐diiodo‐1,1′:3′,1′′‐terphenyl (DITP) . On the one hand, the DCTP molecules gradually desorb from Ag(111) prior to the high temperature required for the C−Cl bond cleavage, which results in significant decrease of the molecular coverage and smaller domains of the products.…”

“…On the one hand, the DCTP molecules gradually desorb from Ag(111) prior to the high temperature required for the C−Cl bond cleavage, which results in significant decrease of the molecular coverage and smaller domains of the products. On the other hand, long zig‐zag organometallic intermediate chains can be achieved on Ag(111) at room temperature for DITP, and at 353 K for DBTP . Further ordering occurs before the sample is annealed to the demetalation temperature, leading to that the produced polyphenylene chains self‐assemble into highly ordered islands.…”

The Orientation of Silver Surfaces Drives the Reactivity and the Selectivity in Homo‐Coupling Reactions

“…Here, the different reaction pathways must be considered in detail by taking into account the full system constituted by the supporting surface and the molecular reactants. Indeed, organometallic intermediates are often encountered for surface‐supported reactions,,, and the global reactivity of the substrate is closely related to the epitaxial conditions, the adsorption sites along the reaction pathway and the related stability of the different transition states ,. In particular for the linear coupling mechanism on Ag(111), it is thus expected that there is a favourable epitaxial relationship that lowers the activation energy for this pathway.…”

On‐Surface Synthesis of Porous Carbon Nanoribbons on Silver: Reaction Kinetics and the Influence of the Surface Structure

“…Correspondingly, differences in the organometallic intermediates are expected on the two Ag lattices, if the lattice registry of Ag adatoms drives the structure oft he organometallic overlayers. At present, a majority of on‐surface synthesis reactions on Ag are reported on the (111) facet, although Ullmann‐type coupling also successfully proceeds on Ag(110) and Ag(100) surfaces. Therefore, this study will provide further interesting insights into Ullmann‐type reactions on Ag(100), which has rarely been addressed although the Ullmann‐type reaction is a workhorse in on‐surface synthesis.…”