DOI: 10.1002/cctc.201300299 2 D Self-Assembly and Catalytic Homo-coupling of the Terminal Alkyne 1,4-Bis(3,5-diethynyl-phenyl)butadiyne- 1,3 on Ag(111) Borja Cirera, [a] Yi-Qi Zhang, [a] Svetlana Klyatskaya, [b] Mario Ruben, [b, c] Florian Klappenberger,* [a] and Johannes V. Barth* [a] Introduction Novel carbon-based two-dimensional materials such as gra- phene, graphyne or graphdiyne have attracted enormous in- terest in the past years due to their outstanding properties. [1] While graphene seems to have advanced towards technologi- cal applications, [2] the production of high-quality samples of the latter two materials and their derivatives remains largely elusive. [3] Currently, there is an emerging research domain pro- viding new tools which could help to overcome this problem: the formation of molecular nano-architectures using templated covalent reactions carried out under ultra-high vacuum condi- tions (UHV) on well-defined metal surfaces. [4] This approach al- ready proved to be successful for the production of novel or- ganic species and various one-dimensional structures with atomic precision, [5] and of two-dimensional networks. [6] More- over, under the on-surface conditions, different reaction path- ways and even novel reactions become possible as a result of the influence of a catalytic support. [7] Recently, we have introduced the surface-assisted homo- coupling of terminal alkynes on a noble metal surface as a new tool for covalent bottom-up construction. [8] The em- ployed functional moiety represents a highly versatile building block in 3 D supramolecular chemistry due to its capability to establish C H···p hydrogen bonds in which it acts as proton acceptor and donor at the same time. [9] On noble metal surfa- ces the ethynyl groups remain decisive for the low-tempera- ture self-assembly of three-fold symmetric 1,3,5-triethynyl-ben- zene (TEB), as well as its extended derivative 1,3,5-tris-(4-ethy- nylphenyl)benzene (Ext-TEB). [10] Upon thermal activation, both species selectively dimerize covalently on the Ag(111) surface at 300 to 330 K while avoiding polymerization. [8] At higher an- nealing temperatures (T = 400 K), reticulated polymer networks evolve that lack the targeted regularity and porosity. In the present work we aim at gaining a better understand- ing of the previously encountered hierarchic reaction pathway and general aspects of homo-coupling reactions using the di- meric reaction intermediate from scratch. [8] To this end, we syn- thesized the compound 1,4-bis(3,5-diethynylphenyl)butadiyne- 1,3 (1, Scheme 1) and explored its 2 D self-assembly and on- surface covalent reactions on the Ag(111) surface with scan- ning tunneling microscopy (STM). After adsorption and sponta- The covalent linking of terminal alkynes is a promising ap- proach for the bottom-up fabrication of novel, carbon-rich or all-carbon materials, which was recently extended towards in- terfacial architectures. Here we report the synthesis of a novel organic species (1,4-bis(3,5-diethynylphenyl)butadiyne-1,3) and employ it to engineer self-assembled supramolecular layers and covalent networks on the Ag(111) surface. Samples are prepared in-situ under ultra-high vacuum conditions and ex- amined at the molecular level with scanning tunneling micros- copy. After evaporating the two-fold symmetric molecule onto the substrate at temperatures below 300 K and subsequent cooling to 5 K we find highly regular supramolecular phases commensurate with the underlying silver surface and stabilized mainly by weak, non-covalent interactions originating from the terminal ethynyl moieties. Annealing at temperatures between 350 and 500 K triggers catalytic conversions with the pertain- ing covalent coupling reactions resulting in small aggregates or irregular polymeric networks. Our detailed analysis of the binding motifs demonstrates that two competing reaction pathways dominate the covalent linking processes. The first is the Glaser–Hay-type homo-coupling of two alkyne termina- tions leading to a linear butadiyne bridge. The second is the connection of a butadiyne group to a laterally attacking termi- nal alkyne, converting the attacked ethyne to ethene moieties, which presents a major obstacle for the production of regular networks. [a] B. Cirera, Dr. Y.-Q. Zhang, Dr. F. Klappenberger, Prof. J.V. Barth Physik Department E20 Technische UniversitätMünchen James-Franck-Straße, 85748 Garching (Germany) Fax: (+ 49) 89-28912338 E-mail : florian.klappenberger@tum.de jvb@ph.tum.de [b] Dr. S. Klyatskaya, Prof. M. Ruben Institute of Nanotechnology Karlsruhe Institute of Technology 76344 Eggenstein-Leopoldshafen (Germany) [c] Prof. M. Ruben IPCMS-CNRS UniversitØ de Strasbourg 23 Rue de Loess, 67034 Strasbourg (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201300299.  2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemCatChem 2013, 5, 3281 – 3288 3281 CHEMCATCHEM FULL PAPERS