Homo-coupling of terminal alkynes on a noble metal surface

Abstract

The covalent linking of acetylenes presents an important route for the fabrication of novel carbon-based scaffolds and two-dimensional materials distinct from graphene. To date few attempts have been reported to implement this strategy at well-defined interfaces or monolayer templates. Here we demonstrate through real space direct visualization and manipulation in combination with X-ray photoelectron spectroscopy and density functional theory calculations the Ag surface-mediated terminal alkyne C sp À H bond activation and concomitant homo-coupling in a process formally reminiscent of the classical Glaser-Hay type reaction. The alkyne homo-coupling takes place on the Ag(111) noble metal surface in ultrahigh vacuum under soft conditions in the absence of conventionally used transition metal catalysts and with volatile H 2 as the only by-product. With the employed multitopic ethynyl species, we demonstrate a hierarchic reaction pathway that affords discrete compounds or polymeric networks featuring a conjugated backbone. This presents a new approach towards on-surface covalent chemistry and the realization of two-dimensional carbon-rich or allcarbon polymers.

Unraveling the Mechanism of the Covalent Coupling Between Terminal Alkynes on a Noble Metal

“…17 The generality of this approach was demonstrated by its application to different organic building-blocks [17][18][19] and on the differently reactive surfaces Ag(111), 17,18 Au(111) 18 and Cu(111). 18,19 The reaction takes place under mild and clean conditions, with hydrogen as only byproduct released from the surface.…”

Dirac Cones in two-dimensional conjugated polymer networks

“…Solution-based monoand few-layer sheets can now be produced at micron diameters, highly crystalline 18 and largely defect-free 19 . These materials demonstrate the incredible capability of modern chemistry to create 'bottom-up' uniform repeatable 2D networks from customdesigned monomers [20][21][22] . However, while 2D COFs appear a promising route to create hexagonal organic monolayers, these materials are wide gap semiconductors 23,24 .…”

Recent Progress in the Fabrication of Low Dimensional Nanostructures via Surface-Assisted Transforming and Coupling

“…Meanwhile, dynamic mechanism of whole reaction systems has also been explored deeply by DFT theory, including the phase transforming during reaction [28,91]. However, side-reactions still exist for surface-assisted coupling; topological defects remain the most severe issue.…”

“…Moreover, the effect of metal substrate was also tested: Ag substrate is comparably suited for Glaser coupling [25,26], and Glaser coupling can be used highly efficiently to generate linear oligomer/polymer along the step-edges of the noble metal vicinal surface while inhibiting a variety of side-reactions resulting in irregularly branched polymeric networks [27]. Likewise, the defined -conjugated two-dimensional network was realized after the optimization of the 2D Glaser coupling [28], while the precursor with more than 3 terminal alkynes is a determined factor. Actually, polymerization reaction is not limited in the C-H bond, and it also occurs in other types of bonds like N-H bond [29,30].…”