Sulfur-driven switching of the Ullmann coupling on Au(111)

Abstract

We demonstrate a method to selectively switch the Ullmann coupling reaction of 2,8-dibromodibenzothiophene on a Au(111) support. The Ullmann coupling reaction is effective already at low temperature, but the complete inhibition of the same reaction can be achieved on Au(111) pre-exposed to H2S. The marked difference in reactivity of pretreated Au(111) is explained by the S-passivation of free Au atoms emerging from reconstruction sites. The inhibited state can be fully lifted by removing the S via hydrogen gas post-exposure.

Molecular Nanowire Bonding to Epitaxial Single‐Layer MoS2 by an On‐Surface Ullmann Coupling Reaction

“…Figure a shows a typical STM image of isolated poly‐DBT nanowires, obtained after deposition of 2,8‐DBDBT onto a clean Au(111) surface held at 150 K and imaged at 110 K 32. Ullmann coupling reactions have been triggered even at this low temperature on Au(111), resulting in DBT molecules self‐assembled into a characteristic chain network (Figure 2b).…”

“…A contributing factor to the low reactivity seen for the pristine sulfided samples is that Ullmann coupling itself seems to be inhibited by residual S on the Au terraces originating from the H 2 S dosed during MoS 2 synthesis. The mobile sulfur species are not imaged directly but the presence of residual sulfur on Au(111) terraces has in previous studies been shown to lead to inhibition of the Ullmann coupling, possibly due to S coordination and passivation of the Au atoms that can catalyze the Ullmann coupling 32. In our case, the presence of S on the surface can sometimes directly be evidenced by increasing the overage of 2,8‐DBDBT (reducing S mobility) where the S overlayers then become visible (Figure S3, Supporting Information).…”

“…The average distance between sulfur atoms located at the 90° bends in the chains is 8.2 ± 0.4 Å. This distance reflects the spacing between the DBT units within the chain, in good agreement with previous studies of similar molecules deposited on Au(111) 19,22,32. The pristine chain networks are observed to be stable until 800 K, where the molecules decompose partly.…”

“…The chains have the same characteristic 90° bends and the distance between S‐S atoms is 8.5 ± 0.4 Å, in agreement with that on bare Au(111), reflecting that the same DBT chain structure forms as on clean Au (Figure 2). In this case, the unreacted sulfur atoms on the terraces seen for the sulfided sample in Figure S3 (Supporting Information) are reacted off by recombination with H 2 , which increases the Ullmann coupling reactivity 32. Interestingly, inspection of the STM images at this early stage of poly‐DBT wire growth shows that almost all of the short nanowires emanate from the MoS 2 and the close proximity thus suggests that the molecules have now successfully reacted with edge sites of MoS 2 .…”

Reaction Selectivity in On‐Surface Chemistry by Surface Coverage Control—Alkyne Dimerization versus Alkyne Trimerization

“…Also protective group strategies that are well established in solutionphasec hemistry have been developed. [30][31][32] In addition, additives have been used to supress acertain reaction [33,34] and preorganization by different self-assembled structures has been shownt oi nfluencet he reactivity. [35,36] Alternatively, one can run the process at different coverages [37][38][39] or temperatures [40] and use these readily varied reactionp arameters for product control.H owever, to date only few exampleso nr eactionc ontrol based on surfacec overage in two-dimensionalc hemistry have been reported.…”