Reactions of Surface-Confined Terminal Alkynes Mediated by Diverse Regulation Strategies

Abstract

Terminal alkynes, characterized by sp-hybridized carbon atoms at the molecular termini, possess high electron density and exceptional chemical reactivity. These properties make them ideal candidates for the synthesis of one-dimensional molecular wires and two-dimensional networks. Advances in nanoscale characterization techniques, such as scanning tunneling microscopy and atomic force microscopy, have enabled the real-space visualization of molecular assembly and chemical reactions of terminal alkynes and in situ atomic-level manipulations under surface-confined conditions. In addition, through the combination of spectroscopic measurements, physicochemical properties of and information about resulting nanostructures have been achieved. Moreover, density functional theory calculations provide deeper insights into the underlying reaction pathways and mechanisms. From this perspective, this review summarizes recent progress in the assembly and chemical transformations of terminal alkynes on noble metal surfaces. It discusses strategies for structural modulation and reaction selectivity control, including direct incorporation of heteroatoms or functional groups into precursors, the selection of metal surfaces, the introduction of extrinsic components into molecular systems, and atomic-scale manipulations using scanning probes.

Keywords: low-dimensional nanostructure; on-surface synthesis; scanning probe microscopy; terminal alkyne.

Scheme 1

Illustration of the assembly and reactions of terminal alkynes on surfaces mediated by diverse regulation strategies.

Figure 1

Supramolecular self-assembly of terminal alkynes on surfaces. (a) Clockwise (C) and anticlockwise (A) chiral adsorption configuration of hexamers aggregated by six phenylacetylene molecules through C–H∙∙∙π interactions. (b) DFT-calculated structural model and bonding analysis of NBO. Arrow color indicates electron donor (blue) or electron acceptor (red) behavior. Copyright 2012 American Chemical Society [63]. (c) Binding energy of different triethynyltriazine derivatives. Blue, grey, and red solid lines represent hcp, X₃-synthon, and X₆-synthon, respectively. Grey dashed lines indicates dense X₃-synthon. Copyright 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co., KGaA [51]. (d–r) STM images along with their magnified views and structural models corresponding to low-temperature deposition, RT annealing for 15, 40, 60 min, and RT deposition, respectively. Structural motifs are highlighted by red dashed circles, and blue parallelograms denote the unit cells of Ag adatoms. Copyright 2016 The Royal Society of Chemistry [64].

Figure 2

Reactions of terminal alkynes on different Ag surfaces. (a) DEBPB reaction pathway regulated by Ag(111), Ag(110), and Ag(100). (b,c) Quantifying lattice commensurability between organometallic chain along different directions and substrate lattices. The colored arrows mark directions where the lattice constants show a relatively good match with the organometallic chain’s periodicity. The brighter the (m,n) square, the better the degree of lattice matches. Copyright 2015 American Chemical Society [71]. (d) Chemical bond formation and identification from DEBP on Ag(111). Copyright 2021 American Chemical Society [72]. (e) Identification of post-400K-annealed products of Ext-TEB on Ag(111). (i–iv) STM images, AFM images, enlarged AFM images, and chemical structures. The white arrows indicate a particular structure at approximately 90 degrees. Copyright 2024 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH [73].

Figure 3

Reactions of terminal alkynes on Au(111). (a) Cyclotrimerization of diyne monomer. The black solid circles and blue dashed circles respectively represent two connection modes. Copyright 2014 American Chemical Society [80]. (b) Thermal activation reaction pathway of 1,2-bis(2-ethynylphenyl)ethyne and electronic structure of its isolated building block 2 and an individual oligomer chain. The blue arrows point out the monomer LUMO and an electronic resonance, respectively. Copyright 2014 American Chemical Society [81].

Figure 4

Reactions of terminal alkynes regulated by precursor design. (a) Different reaction pathways of halogen-functionalized versus unfunctionalized terminal alkynes on Au(111). Copyright 2021 American Chemical Society [76]. (b–f) Highly selective formation of graphdiyne chains from nitrogen-doped terminal alkynes on Au(111). Copyright 2023 American Chemical Society [91]. (g) Reaction scheme of AEB 1 and STM characterization of 1,4-regioisomer 2 and persistent ternary non-covalent monomer assembly. Copyright 2013 American Chemical Society [90].

Figure 5

Reactions of terminal alkynes regulated by tip manipulation. (a) Conformational reversal induced by tip manipulation. The lower panel represents “T”, “U”, “M” encoded 8-bit ASCII values, respectively. Scale bars are 10 Å. (b) Flexibility of nanowires characterized through tip manipulation. The scale bars in upper and lower panels are 50 Å and 100 Å, respectively. The white arrows indicate the displacement of the tip during manipulation. Copyright 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weiheim [101]. (c) Schematic illustration of tip-induced Glaser coupling. (d) Conformations of precursor 1 and product 2. (e–g) AFM images of precursor 1 in different conformations. Scale bars are 5 Å. (h,i) AFM images of product 2 obtained at different tip heights. Scale bars are 5 Å. Copyright 2020 The Authors. Published by Wiley-VCH GmbH [102].

Figure 6

Reactions of terminal alkynes mediated by extrinsic components. (a) Schematic of reactions mediated by oxygen. (b) Large-scale STM image showing micro-scale organometallic network with LEED pattern. Copyright 2019 American Chemical Society [106]. (c) Schematic of the radical transfer reaction pathway. Scale bars are 2 nm. (d) DFT calculation of radical transfer reaction complemented with TPD spectra of H₂ [40].