On‐Surface Activation of Trimethylsilyl‐Terminated Alkynes on Coinage Metal Surfaces. Issue 18 (16th July 2019)

• Record Type: Journal Article
• Authors: Zhang, Liding; Zhang, Yi‐Qi; Chen, Zhi; Lin, Tao; Paszkiewicz, Mateusz; Hellwig, Raphael; Huang, Tianjiao; Ruben, Mario; Barth, Johannes V.; Klappenberger, Florian
• Is Part Of: Chemphyschem. Volume 20:Issue 18(2019)
• Page Start: 2382
• Page End: 2393
• Publication Date: 2019-07-16
• Subjects: alkyne -- on-surface reaction -- protecting groups -- scanning tunneling microscopy -- trimethylsilyl; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.201900249
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: The controlled attachment of protecting groups combined with the ability to selectively abstract them is central to organic synthesis. The trimethylsilyl (TMS) functional group is a popular protecting group in solution. However, insights on its activation behavior under ultra‐high vacuum (UHV) and surface‐confined conditions are scarce. Here we investigate a series of TMS‐protected alkyne precursors via scanning tunneling microscopy (STM) regarding their compatibility with organic molecular beam epitaxy (OMBE) and their potential deprotection on various coinage metal surfaces. After in‐situ evaporation on the substrates held in UHV at room temperature, we find that all molecules arrived and adsorbed as intact units forming ordered supramolecular aggregates stabilized by non‐covalent interactions. Thus, TMS‐functionalized alkyne precursors with weights up to 1100 atomic mass units are stable against OMBE evaporation in UHV. Furthermore, the TMS activation through thermal annealing is investigated with STM and X‐ray photoelectron spectroscopy (XPS). We observe that deprotection starts to occur between 400 K and 500 K on the copper and gold surfaces, respectively. In contrast, on silver surfaces, the TMS‐alkyne bond remains stable up to temperatures where molecular desorption sets in (≈600 K). Hence, TMS functional groups can be utilized as leaving groups on copper and gold surfaces while they serve as protecting groups on silver surfaces. Abstract : Substrate dependent leaving or protecting group character of terminal trimethylsilyl moieties : STM investigations of trimethylsilyl‐protected alkyne precursors on coinage metal substrates unravel that the protecting or leaving group character of the terminal functional moieties can be controlled by an appropriate choice of substrates (Cu and Au vs. Ag) and preparation protocols. This affords new possibilities for control over hierarchic reaction pathways and thus expresses potential for future on‐surface synthesis protocols.