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On-surface dehydro-Diels-Alder reaction of dibromo-bis(phenylethynyl)benzeneMarco Di Giovannantonio,1,# Ashok Keerthi,2,3,# José I. Urgel,1 Martin Baumgarten,2 Xinliang Feng,4 Pascal Ruffieux,1 Akimitsu Narita,2,5 Roman Fasel,1,6,* Klaus Müllen2,*1Empa, Swiss Federal Laboratories for Materials Science and Technology, nanotech@surfaces Laboratory, 8600 Dübendorf, Switzerland2Max Planck Institute for Polymer Research, 55128 Mainz, Germany3Department of Chemistry, The University of Manchester, Manchester M13 9PL, UK 4Center for Advancing Electronics Dresden, Department of Chemistry and Food Chemistry, Technische Universit?t Dresden, 01062, Dresden, Germany5Okinawa Institute of Science and Technology Graduate University, Okinawa 904-0495, Japan6Department of Chemistry and Biochemistry, University of Bern, 3012 Bern, SwitzerlandSupporting Information PlaceholderABSTRACT: On-surface synthesis under ultrahigh vacuum conditions is a powerful tool to achieve molecular structures which cannot be accessed via traditional wet chemistry. Nevertheless, only a very limited number of chemical reactions out of the wide variety known from solution chemistry have been reported to proceed readily on atomically flat substrates. Cycloadditions are a class of reactions that are particularly important in the synthesis of sp2-hybridized carbon-based nanostructures. Here, we report on a specific type of [4+2] cycloaddition, namely a dehydro-Diels-Alder (DDA) reaction, performed between bis(phenylethynyl)-benzene precursors on Au(111). Unlike a Diels-Alder reaction, DDA exploits ethynyl groups to achieve the formation of an extra six-membered ring. Despite its extensive use in solution chemistry for more than a century, this reaction has never been reported to occur on surfaces. The specific choice of our precursor molecule has led to the successful synthesis of benzo- and naphtho-fused tetracene and heptacene products bearing styryl groups, as confirmed by scanning tunneling microscopy and noncontact atomic force microscopy. The two products arise from DDA dimerization and trimerization of the precursor molecules, respectively, and their observation opens perspectives to use DDA reactions as a novel on-surface synthesis tool.Polycyclic aromatic hydrocarbons (PAHs) are disc-type conjugated molecules consisting of fused benzene rings, which occur in various shapes and sizes, including coronenes, acenes, and larger PAHs that can be regarded as nanographenes. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"g47rMYZ7","properties":{"formattedCitation":"\\super 1\\uc0\\u8211{}3\\nosupersub{}","plainCitation":"1–3","noteIndex":0},"citationItems":[{"id":872,"uris":[""],"uri":[""],"itemData":{"id":872,"type":"article-journal","container-title":"Chem. Soc. Rev.","DOI":"10.1039/C5CS00183H","ISSN":"0306-0012, 1460-4744","issue":"18","language":"en","note":"Citation Key: Narita2015","page":"6616-6643","source":"CrossRef","title":"New advances in nanographene chemistry","volume":"44","author":[{"family":"Narita","given":"Akimitsu"},{"family":"Wang","given":"Xiao-Ye"},{"family":"Feng","given":"Xinliang"},{"family":"Müllen","given":"Klaus"}],"issued":{"date-parts":[["2015"]]}}},{"id":6203,"uris":[""],"uri":[""],"itemData":{"id":6203,"type":"article-journal","abstract":"The properties of graphene nanoribbons (GNRs) make them good candidates for next-generation electronic materials. Whereas ‘top-down’ methods, such as the lithographical patterning of graphene and the unzipping of carbon nanotubes, give mixtures of different GNRs, structurally well-defined GNRs can be made using a ‘bottom-up’ organic synthesis approach through solution-mediated or surface-assisted cyclodehydrogenation reactions. Specifically, non-planar polyphenylene precursors were first ‘built up’ from small molecules, and then ‘graphitized’ and ‘planarized’ to yield GNRs. However, fabrication of processable and longitudinally well-extended GNRs has remained a major challenge. Here we report a bottom-up solution synthesis of long (>200 nm) liquid-phase-processable GNRs with a well-defined structure and a large optical bandgap of 1.88 eV. Self-assembled monolayers of GNRs can be observed by scanning probe microscopy, and non-contact time-resolved terahertz conductivity measurements reveal excellent charge-carrier mobility within individual GNRs. Such structurally well-defined GNRs may prove useful for fundamental studies of graphene nanostructures, as well as the development of GNR-based nanoelectronics.","container-title":"Nature Chemistry","DOI":"10.1038/nchem.1819","ISSN":"1755-4330","issue":"2","journalAbbreviation":"Nat Chem","language":"en","note":"Citation Key: Narita2014","page":"126-132","source":"","title":"Synthesis of structurally well-defined and liquid-phase-processable graphene nanoribbons","volume":"6","author":[{"family":"Narita","given":"Akimitsu"},{"family":"Feng","given":"Xinliang"},{"family":"Hernandez","given":"Yenny"},{"family":"Jensen","given":"S?ren A."},{"family":"Bonn","given":"Mischa"},{"family":"Yang","given":"Huafeng"},{"family":"Verzhbitskiy","given":"Ivan A."},{"family":"Casiraghi","given":"Cinzia"},{"family":"Hansen","given":"Michael Ryan"},{"family":"Koch","given":"Amelie H. R."},{"family":"Fytas","given":"George"},{"family":"Ivasenko","given":"Oleksandr"},{"family":"Li","given":"Bing"},{"family":"Mali","given":"Kunal S."},{"family":"Balandina","given":"Tatyana"},{"family":"Mahesh","given":"Sankarapillai"},{"family":"De Feyter","given":"Steven"},{"family":"Müllen","given":"Klaus"}],"issued":{"date-parts":[["2014",2]]}}},{"id":1083,"uris":[""],"uri":[""],"itemData":{"id":1083,"type":"article-journal","container-title":"Chemical Society Reviews","DOI":"10.1039/c2cs35211g","ISSN":"0306-0012, 1460-4744","issue":"23","language":"en","note":"Citation Key: Sun2012c","page":"7857","source":"CrossRef","title":"Low band gap polycyclic hydrocarbons: from closed-shell near infrared dyes and semiconductors to open-shell radicals","title-short":"Low band gap polycyclic hydrocarbons","volume":"41","author":[{"family":"Sun","given":"Zhe"},{"family":"Ye","given":"Qun"},{"family":"Chi","given":"Chunyan"},{"family":"Wu","given":"Jishan"}],"issued":{"date-parts":[["2012"]]}}}],"schema":""} 1–3 These materials possess intriguing properties that make them appealing for applications in organic electronics, ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"bc6FE5Hp","properties":{"formattedCitation":"\\super 4\\nosupersub{}","plainCitation":"4","noteIndex":0},"citationItems":[{"id":1217,"uris":[""],"uri":[""],"itemData":{"id":1217,"type":"article-journal","container-title":"Chemical Reviews","DOI":"10.1021/cr068010r","ISSN":"0009-2665","issue":"3","journalAbbreviation":"Chem. Rev.","page":"718-747","source":"ACS Publications","title":"Graphenes as Potential Material for Electronics","volume":"107","author":[{"family":"Wu","given":"Jishan"},{"family":"Pisula","given":"Wojciech"},{"family":"Müllen","given":"Klaus"}],"issued":{"date-parts":[["2007",3,1]]}}}],"schema":""} 4 as well as for more fundamental studies. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"GdXyTydx","properties":{"formattedCitation":"\\super 5\\nosupersub{}","plainCitation":"5","noteIndex":0},"citationItems":[{"id":220,"uris":[""],"uri":[""],"itemData":{"id":220,"type":"article-journal","abstract":"Polycyclic aromatic hydrocarbons (PAHs) are popular research subjects due to their high stability, their rigid planar structure, and their characteristic optical spectra. The recent discovery of graphene, which can be regarded as giant PAH, has further stimulated the interest in this area. For this reason, the relationship between the geometric and electronic structure and the optical spectra of PAHs are reviewed, pointing out the versatile properties of this class of molecules. Extremely stable fully-benzenoid PAHs with high optical gaps are encountered on the one side and the very reactive acenes with low optical gaps on the other side. A huge range of molecular sizes is covered from the simplest case benzene with its six carbon atoms up to disks containing as much as 96 carbon atoms. Furthermore, the impact of non-planarity is discussed as model cases for the highly important fullerenes and carbon nanotubes. The detailed analysis of the electronic structure of PAHs is very important with regard to their application as fluorescent dyes or organic semiconductors. The presented research results shall encourage developments of new PAH structures to exploit novel materials properties. Copyright ? 2010 John Wiley & Sons, Ltd.","container-title":"Journal of Physical Organic Chemistry","DOI":"10.1002/poc.1644","ISSN":"1099-1395","issue":"4","language":"en","page":"315-325","source":"Wiley Online Library","title":"Forever young: polycyclic aromatic hydrocarbons as model cases for structural and optical studies","title-short":"Forever young","volume":"23","author":[{"family":"Rieger","given":"R."},{"family":"Müllen","given":"K."}],"issued":{"date-parts":[["2010"]]}}}],"schema":""} 5 The preparation of PAHs is typically carried out through “planarization” of polyphenylene precursors by photochemical or oxidative cyclodehydrogenation or via metal-catalysed or oxidative annulation of tailor-made building blocks. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"FINXN1oB","properties":{"formattedCitation":"\\super 6\\uc0\\u8211{}9\\nosupersub{}","plainCitation":"6–9","noteIndex":0},"citationItems":[{"id":208,"uris":[""],"uri":[""],"itemData":{"id":208,"type":"article-journal","abstract":"The progress of the metal-catalyzed annulation reactions toward construction of various π-conjugated polycyclic cores with high conjugation extension is described. This article gives a brief overview of various annulation reactions promoted by metal catalysts including C?H bond functionalization, [2+2+2] cycloaddition, cascade processes, ring closing metathesis, electrophilic aromatization, and various cross-coupling reactions. A variety of conjugated polycycles with planar, bowl-shaped, and helical structures have been constructed in high efficiency and selectivity.","container-title":"Chemistry – A European Journal","DOI":"10.1002/chem.201304640","ISSN":"1521-3765","issue":"13","language":"en","page":"3554-3576","source":"Wiley Online Library","title":"Metal-Catalyzed Annulation Reactions for π-Conjugated Polycycles","volume":"20","author":[{"family":"Jin","given":"Tienan"},{"family":"Zhao","given":"Jian"},{"family":"Asao","given":"Naoki"},{"family":"Yamamoto","given":"Yoshinori"}],"issued":{"date-parts":[["2014"]]}}},{"id":207,"uris":[""],"uri":[""],"itemData":{"id":207,"type":"article-journal","abstract":"Does the dehydrogenative coupling of aromatic compounds mediated by AlCl3 at high temperatures and also by FeCl3, MoCl5, PIFA, or K3[Fe(CN)6] at room temperature proceed by the same mechanism in all cases? With the growing importance of the synthesis of aromatic compounds by double C?H activation to give various biaryl structures, this question becomes pressing. Since some of these reactions proceed only in the presence of non-oxidizing Lewis acids and some only in the presence of certain oxidants, the authors venture the hypothesis that, depending on the electronic structure of the substrates and the nature of the “catalyst”, two different mechanisms can operate. One involves the intermediacy of a radical cation and the other the formation of a sigma complex between the acid and the substrate. The goal of this Review is to encourage further mechanistic studies hopefully leading to an in-depth understanding of this phenomenon.","container-title":"Angewandte Chemie International Edition","DOI":"10.1002/anie.201210238","ISSN":"1521-3773","issue":"38","language":"en","page":"9900-9930","source":"Wiley Online Library","title":"Comparison of Oxidative Aromatic Coupling and the Scholl Reaction","volume":"52","author":[{"family":"Grzybowski","given":"Marek"},{"family":"Skonieczny","given":"Kamil"},{"family":"Butensch?n","given":"Holger"},{"family":"Gryko","given":"Daniel T."}],"issued":{"date-parts":[["2013"]]}}},{"id":206,"uris":[""],"uri":[""],"itemData":{"id":206,"type":"article-journal","abstract":"The halo and aryl substituents of the 1,2-disubstituted styryl group of aromatic enynes undergo a 1,2-shift in the aromatization reaction catalyzed by TpRuPPh3(CH3CN)2PF6 (10 mol %) in toluene (110 °C, 6?8 h). The aryl group shifts to the neighboring olefin carbon, and the iodo (or bromo) substituent migrates to the terminal alkyne carbon. The mechanisms of these two migrations have been elucidated by isotope labeling experiments. It indicates that the 1,2-aryl shift arises from 5-endo-dig electrocyclization of a ruthenium?vinylidene species, whereas the 1,2-iodo shift follows a 6-endo-dig pathway.","container-title":"Journal of the American Chemical Society","DOI":"10.1021/ja0379159","ISSN":"0002-7863","issue":"51","journalAbbreviation":"J. Am. Chem. Soc.","page":"15762-15763","source":"ACS Publications","title":"Ruthenium-Catalyzed Aromatization of Aromatic Enynes via the 1,2-Migration of Halo and Aryl Groups:? A New Process Involving Electrocyclization and Skeletal Rearrangement","title-short":"Ruthenium-Catalyzed Aromatization of Aromatic Enynes via the 1,2-Migration of Halo and Aryl Groups","volume":"125","author":[{"family":"Shen","given":"Hung-Chin"},{"family":"Pal","given":"Sitaram"},{"family":"Lian","given":"Jian-Jou"},{"family":"Liu","given":"Rai-Shung"}],"issued":{"date-parts":[["2003",12,1]]}}},{"id":205,"uris":[""],"uri":[""],"itemData":{"id":205,"type":"article-journal","abstract":"Effective band-gap engineering of armchair graphene nanoribbons calls for control over both width and edge structure. Here, the authors report a modular synthesis of narrow N = 6 armchair graphene nanoribbons whose edges can be unsymmetrically modified with heteroarenes, introducing a simple way to tune band gap.","container-title":"Nature Communications","DOI":"10.1038/s41467-018-03747-2","ISSN":"2041-1723","issue":"1","language":"En","page":"1687","source":"","title":"A modular synthetic approach for band-gap engineering of armchair graphene nanoribbons","volume":"9","author":[{"family":"Li","given":"Gang"},{"family":"Yoon","given":"Ki-Young"},{"family":"Zhong","given":"Xinjue"},{"family":"Wang","given":"Jianchun"},{"family":"Zhang","given":"Rui"},{"family":"Guest","given":"Jeffrey R."},{"family":"Wen","given":"Jianguo"},{"family":"Zhu","given":"X.-Y."},{"family":"Dong","given":"Guangbin"}],"issued":{"date-parts":[["2018",4,27]]}}}],"schema":""} 6–9 Cycloaddition reactions are widely used in the synthesis of large PAHs. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"QHrb6Fci","properties":{"formattedCitation":"\\super 10\\nosupersub{}","plainCitation":"10","noteIndex":0},"citationItems":[{"id":6774,"uris":[""],"uri":[""],"itemData":{"id":6774,"type":"article-journal","container-title":"European Journal of Organic Chemistry","DOI":"10.1002/ejoc.201300470","ISSN":"1434193X","issue":"27","language":"en","note":"Citation Key: Perez2013","page":"5981-6013","source":"CrossRef","title":"Aryne Cycloaddition Reactions in the Synthesis of Large Polycyclic Aromatic Compounds: Synthesis of Large Polycyclic Aromatic Compounds","title-short":"Aryne Cycloaddition Reactions in the Synthesis of Large Polycyclic Aromatic Compounds","volume":"2013","author":[{"family":"Pérez","given":"Dolores"},{"family":"Pe?a","given":"Diego"},{"family":"Guitián","given":"Enrique"}],"issued":{"date-parts":[["2013",9]]}}}],"schema":""} 10 In this regard, a specific class of [4+2] cycloaddition, namely Diels-Alder reaction where cycloaddition occurs between diene and dienophile, has served as an extremely versatile synthetic protocol to achieve the formation of extra six-membered rings. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"5apbavKi","properties":{"formattedCitation":"\\super 11,12\\nosupersub{}","plainCitation":"11,12","noteIndex":0},"citationItems":[{"id":214,"uris":[""],"uri":[""],"itemData":{"id":214,"type":"article-journal","abstract":"The Diels–Alder reaction has both enabled and shaped the art and science of total synthesis over the last few decades to an extent which, arguably, has yet to be eclipsed by any other transformation in the current synthetic repertoire. With myriad applications of this magnificent pericyclic reaction, often as a crucial element in elegant and programmed cascade sequences facilitating complex molecule construction, the Diels–Alder cycloaddition has afforded numerous and unparalleled solutions to a diverse range of synthetic puzzles provided by nature in the form of natural products. In celebration of the 100th anniversary of Alder's birth, selected examples of the awesome power of the reaction he helped to discover are discussed in this review in the context of total synthesis to illustrate its overall versatility and underscore its vast potential which has yet to be fully realized.","container-title":"Angewandte Chemie International Edition","DOI":"10.1002/1521-3773(20020517)41:10<1668::AID-ANIE1668>3.0.CO;2-Z","ISSN":"1521-3773","issue":"10","language":"en","page":"1668-1698","source":"Wiley Online Library","title":"The Diels–Alder Reaction in Total Synthesis","volume":"41","author":[{"family":"Nicolaou","given":"K. C."},{"family":"Snyder","given":"Scott A."},{"family":"Montagnon","given":"Tamsyn"},{"family":"Vassilikogiannakis","given":"Georgios"}],"issued":{"date-parts":[["2002"]]}}},{"id":5891,"uris":[""],"uri":[""],"itemData":{"id":5891,"type":"article-journal","abstract":"A new approach for the synthesis of extremely large PAHs in high yield is the oxidative cyclodehydrogenation of suitable oligophenylenes under Kovacic conditions. The synthesis of oligophenylene precursors and their cyclodehydrogenation (figure) are presented, and the supramolecular structures observed for large PAHs are discussed.","container-title":"Chemistry – A European Journal","DOI":"10.1002/(SICI)1521-3765(19981102)4:11<2099::AID-CHEM2099>3.0.CO;2-T","ISSN":"1521-3765","issue":"11","journalAbbreviation":"Chem. Eur. J.","language":"en","note":"Citation Key: Muller1998","page":"2099-2109","source":"Wiley Online Library","title":"Giant Polycyclic Aromatic Hydrocarbons","volume":"4","author":[{"family":"Müller","given":"Markus"},{"family":"Kübel","given":"Christian"},{"family":"Müllen","given":"Klaus"}],"issued":{"date-parts":[["1998",11,2]]}}}],"schema":""} 11,12 An alternative version of the Diels-Alder reaction is the dehydro-Diels-Alder (DDA) reaction where one or both double bonds in the diene component are replaced by a triple bond (Scheme S1). ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"SHuz0Kj1","properties":{"formattedCitation":"\\super 13,14\\nosupersub{}","plainCitation":"13,14","noteIndex":0},"citationItems":[{"id":212,"uris":[""],"uri":[""],"itemData":{"id":212,"type":"article-journal","container-title":"Chemical Reviews","DOI":"10.1021/cr0783986","ISSN":"0009-2665","issue":"6","journalAbbreviation":"Chem. Rev.","page":"2051-2063","source":"ACS Publications","title":"The Dehydro-Diels?Alder Reaction","volume":"108","author":[{"family":"Wessig","given":"Pablo"},{"family":"Müller","given":"Gunnar"}],"issued":{"date-parts":[["2008",6,1]]}}},{"id":211,"uris":[""],"uri":[""],"itemData":{"id":211,"type":"article-journal","abstract":"Arynes (aromatic systems containing, formally, a carbon–carbon triple bond) are among the most versatile of all reactive intermediates in organic chemistry. They can be ‘trapped’ to give products that are used as pharmaceuticals, agrochemicals, dyes, polymers and other fine chemicals. Here we explore a strategy that unites the de novo generation of benzynes—through a hexadehydro-Diels–Alder reaction—with their in situ elaboration into structurally complex benzenoid products. In the hexadehydro-Diels–Alder reaction, a 1,3-diyne is engaged in a [4+2] cycloisomerization with a ‘diynophile’ to produce the highly reactive benzyne intermediate. The reaction conditions for this simple, thermal transformation are notable for being free of metals and reagents. The subsequent and highly efficient trapping reactions increase the power of the overall process. Finally, we provide examples of how this de novo benzyne generation approach allows new modes of intrinsic reactivity to be revealed.","container-title":"Nature","DOI":"10.1038/nature11518","ISSN":"1476-4687","issue":"7419","language":"en","page":"208-212","source":"","title":"The hexadehydro-Diels–Alder reaction","volume":"490","author":[{"family":"Hoye","given":"Thomas R."},{"family":"Baire","given":"Beeraiah"},{"family":"Niu","given":"Dawen"},{"family":"Willoughby","given":"Patrick H."},{"family":"Woods","given":"Brian P."}],"issued":{"date-parts":[["2012",10]]}}}],"schema":""} 13,14 Another distinction of the DDA reaction from the former is that, in most of the studied cases, it proceeds via multiple steps by formation of cyclic allenes and migration of hydrogens.As a complement to conventional synthetic organic chemistry, on-surface synthesis on metal substrates under ultrahigh vacuum conditions has recently emerged as a strong method to achieve novel PAHs that have not been obtained in solution, including e.g. unstable higher acenes, up to undecacene. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"BNZdTqw2","properties":{"formattedCitation":"\\super 1,10,15\\nosupersub{}","plainCitation":"1,10,15","noteIndex":0},"citationItems":[{"id":872,"uris":[""],"uri":[""],"itemData":{"id":872,"type":"article-journal","container-title":"Chem. Soc. Rev.","DOI":"10.1039/C5CS00183H","ISSN":"0306-0012, 1460-4744","issue":"18","language":"en","note":"Citation Key: Narita2015","page":"6616-6643","source":"CrossRef","title":"New advances in nanographene chemistry","volume":"44","author":[{"family":"Narita","given":"Akimitsu"},{"family":"Wang","given":"Xiao-Ye"},{"family":"Feng","given":"Xinliang"},{"family":"Müllen","given":"Klaus"}],"issued":{"date-parts":[["2015"]]}}},{"id":6774,"uris":[""],"uri":[""],"itemData":{"id":6774,"type":"article-journal","container-title":"European Journal of Organic Chemistry","DOI":"10.1002/ejoc.201300470","ISSN":"1434193X","issue":"27","language":"en","note":"Citation Key: Perez2013","page":"5981-6013","source":"CrossRef","title":"Aryne Cycloaddition Reactions in the Synthesis of Large Polycyclic Aromatic Compounds: Synthesis of Large Polycyclic Aromatic Compounds","title-short":"Aryne Cycloaddition Reactions in the Synthesis of Large Polycyclic Aromatic Compounds","volume":"2013","author":[{"family":"Pérez","given":"Dolores"},{"family":"Pe?a","given":"Diego"},{"family":"Guitián","given":"Enrique"}],"issued":{"date-parts":[["2013",9]]}}},{"id":196,"uris":[""],"uri":[""],"itemData":{"id":196,"type":"article-journal","abstract":"On-surface synthesis is appearing as an extremely promising research field aimed at creating new organic materials. A large number of chemical reactions have been successfully demonstrated to take place directly on surfaces through unusual reaction mechanisms. In some cases the reaction conditions can be properly tuned to steer the formation of the reaction products. It is thus possible to control the initiation step of the reaction and its degree of advancement (the kinetics, the reaction yield); the nature of the reaction products (selectivity control, particularly in the case of competing processes); as well as the structure, position, and orientation of the covalent compounds, or the quality of the as-formed networks in terms of order and extension. The aim of our review is thus to provide an extensive description of all tools and strategies reported to date and to put them into perspective. We specifically define the different approaches available and group them into a few general categories. In the last part, we demonstrate the effective maturation of the on-surface synthesis field by reporting systems that are getting closer to application-relevant levels thanks to the use of advanced control strategies.","container-title":"Chemical Reviews","DOI":"10.1021/acs.chemrev.8b00601","ISSN":"0009-2665","issue":"7","journalAbbreviation":"Chem. Rev.","page":"4717-4776","source":"ACS Publications","title":"Controlling a Chemical Coupling Reaction on a Surface: Tools and Strategies for On-Surface Synthesis","title-short":"Controlling a Chemical Coupling Reaction on a Surface","volume":"119","author":[{"family":"Clair","given":"Sylvain"},{"family":"Oteyza","given":"Dimas G.","non-dropping-particle":"de"}],"issued":{"date-parts":[["2019",4,10]]}}}],"schema":""} 1,10,15 Several chemical reactions traditionally used in solution chemistry have been proven to successfully proceed also on surfaces. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"ZrtNBRhX","properties":{"formattedCitation":"\\super 16\\uc0\\u8211{}20\\nosupersub{}","plainCitation":"16–20","noteIndex":0},"citationItems":[{"id":5834,"uris":[""],"uri":[""],"itemData":{"id":5834,"type":"article-journal","abstract":"On-surface synthesis constitutes a rapidly growing field of research due to its promising application for creating stable molecular structures on surfaces. While self-assembled structures rely on reversible interactions, on-surface synthesis provides the potential for creating long-term stable structures with well-controlled properties, for example superior electron transport for future molecular electronic devices. On-surface synthesis holds the promise for preparing insoluble compounds that cannot be produced in solution. Another highly exciting aspect of on-surface synthesis is the chance to discover new reaction pathways due to the two-dimensional confinement of the reaction educts. In this review, we discuss the current state-of-the-art and classify the reactions that have been successfully performed so far. Special emphasis is put on electrically insulating surfaces, as these substrates pose particular challenges for on-surface synthesis while at the same time bearing high potential for future use, for example, in molecular electronics.","container-title":"ChemPhysChem","DOI":"10.1002/cphc.201500161","ISSN":"1439-7641","issue":"8","journalAbbreviation":"ChemPhysChem","language":"en","note":"Citation Key: Lindner2015","page":"1582-1592","source":"Wiley Online Library","title":"On-Surface Reactions","volume":"16","author":[{"family":"Lindner","given":"Robert"},{"family":"Kühnle","given":"Angelika"}],"issued":{"date-parts":[["2015",6,8]]}}},{"id":5645,"uris":[""],"uri":[""],"itemData":{"id":5645,"type":"article-journal","container-title":"J. Phys. D: Appl. Phys.","DOI":"10.1088/0022-3727/44/46/464011","ISSN":"0022-3727, 1361-6463","issue":"46","note":"Citation Key: Lackinger2011","page":"464011","source":"CrossRef","title":"A STM perspective on covalent intermolecular coupling reactions on surfaces","volume":"44","author":[{"family":"Lackinger","given":"M"},{"family":"Heckl","given":"W M"}],"issued":{"date-parts":[["2011",11,23]]}}},{"id":2606,"uris":[""],"uri":[""],"itemData":{"id":2606,"type":"article-journal","abstract":"Creating or connecting together large organic molecules, as polycyclic aromatic hydrocarbons (PAH), by chemical reactions readily on surfaces is the first step to a true advance in the field of molecular electronics. On-surface synthesis can be regarded as an efficient means to build new molecular species by using bottom-up strategies. Recently, a collection of different reactions leading to large tailor-made organic molecules on single-crystal metal surfaces has been reported. The fundamental mechanisms controlling these reactions can be investigated from a surface science perspective. This discipline skillfully combines the use of characterization techniques at the nanoscale, with single-crystal metallic surfaces able to catalyse these reactions. We present a tutorial review that highlights the relevance of the new bottom up strategies and classifies most of the different molecular on-surface reactions involving aromatic organic molecules that have been published up to date.","container-title":"Chemical Society Reviews","DOI":"10.1039/C0CS00161A","ISSN":"1460-4744","issue":"9","journalAbbreviation":"Chem. Soc. Rev.","language":"en","page":"4578-4590","source":"pubs.","title":"On-surface synthesis of cyclic organic molecules","volume":"40","author":[{"family":"Méndez","given":"Javier"},{"family":"López","given":"M. Francisca"},{"family":"Martín-Gago","given":"José A."}],"issued":{"date-parts":[["2011",8,15]]}}},{"id":204,"uris":[""],"uri":[""],"itemData":{"id":204,"type":"article-journal","abstract":"The discovery of graphene has triggered great interest in two-dimensional (2D) nanomaterials for scientists in chemistry, physics, materials science, and related areas. In the family of newly developed 2D nanostructured materials, 2D soft nanomaterials, including graphene, BxCyNz nanosheets, 2D polymers, covalent organic frameworks (COFs), and 2D supramolecular organic nanostructures, possess great advantages in light-weight, structural control and flexibility, diversity of fabrication approaches, and so on. These merits offer 2D soft nanomaterials a wide range of potential applications, such as in optoelectronics, membranes, energy storage and conversion, catalysis, sensing, biotechnology, etc. This review article provides an overview of the development of 2D soft nanomaterials, with special highlights on the basic concepts, molecular design principles, and primary synthesis approaches in the context.","container-title":"Adv. Mater.","DOI":"10.1002/adma.201401857","ISSN":"0935-9648","issue":"3","journalAbbreviation":"Advanced Materials","page":"403-427","source":"onlinelibrary. (Atypon)","title":"Two-Dimensional Soft Nanomaterials: A Fascinating World of Materials","title-short":"Two-Dimensional Soft Nanomaterials","volume":"27","author":[{"family":"Zhuang","given":"Xiaodong"},{"family":"Mai","given":"Yiyong"},{"family":"Wu","given":"Dongqing"},{"family":"Zhang","given":"Fan"},{"family":"Feng","given":"Xinliang"}],"issued":{"date-parts":[["2014",8,25]]}}},{"id":2976,"uris":[""],"uri":[""],"itemData":{"id":2976,"type":"article-journal","abstract":"Abstract Surface-confined polymerization is a bottom-up strategy to create one- and two-dimensional covalent organic nanostructures with a π-conjugated backbone, which are suitable to be employed in real-life electronic devices, due to their high mechanical resistance and electronic charge transport efficiency. This strategy makes it possible to change the properties of the final nanostructures by a careful choice of the monomer architecture (<i>i.e.</i> of its constituent atoms and their spatial arrangement). Several chemical reactions have been proven to form low-dimensional polymers on surfaces, exploiting a variety of precursors in combination with metal (<i>e.g.</i> Cu, Ag, Au) and insulating (<i>e.g.</i> NaCl, CaCO₃) surfaces. One of the main challenges of such an approach is to obtain nanostructures with long-range order, to boost the conductance performances of these materials. Most of the exploited chemical reactions use irreversible coupling between the monomers and, as a consequence, the resulting structures often suffer from poor order and high defect density. This review focuses on the state-of-the-art surface-confined polymerization reactions, with particular attention paid to reversible coupling pathways and irreversible processes including intermediate states, which are key aspects to control to increase the order of the final nanostructure.","container-title":"Journal of Physics: Condensed Matter","DOI":"10.1088/1361-648X/aaa8cb","ISSN":"1361-648X","journalAbbreviation":"J. Phys.: Condens. Matter","language":"en","page":"093001","source":"Institute of Physics","title":"Reversibility and intermediate steps as key tools for the growth of extended ordered polymers via on-surface synthesis","volume":"30","author":[{"family":"Di Giovannantonio","given":"Marco"},{"family":"Contini","given":"Giorgio"}],"issued":{"date-parts":[["2018"]]}}}],"schema":""} 16–20 One of the most utilized reactions is the Ullmann-like coupling, ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"nMEg7fji","properties":{"formattedCitation":"\\super 21,22\\nosupersub{}","plainCitation":"21,22","noteIndex":0},"citationItems":[{"id":6283,"uris":[""],"uri":[""],"itemData":{"id":6283,"type":"article-journal","container-title":"Ber. Dtsch. Chem. Ges.","issue":"2","note":"Citation Key: Ullmann1901","page":"2174–85","title":"Ueber Synthesen in der Biphenylreihe","volume":"34","author":[{"family":"Ullmann","given":"F"},{"family":"Bielecki","given":"J"}],"issued":{"date-parts":[["1901"]]}}},{"id":1349,"uris":[""],"uri":[""],"itemData":{"id":1349,"type":"article-journal","abstract":"Surface-assisted Ullmann coupling is the workhorse of on-surfaces synthesis. Among the various couplings that were successfully transferred from solution to solid surfaces, Ullmann coupling is arguably the most reliable, controllable, and widespread coupling reaction. The basic reaction scheme is straightforward: halogenated precursors are deposited onto solid surfaces, normally of coinage metals. In the adsorbed state the halogen substitutents are split off by virtue of the surface's reactivity, thereby generating acitvated species that subsequently recombine by forming C–C bonds. Ullmann coupling is well suited for reticular synthesis of novel organic nanostructures: ideally, the halogen substitution pattern of the precursor – which becomes the monomer upon dehalogenation – predetermines dimensionality and topology of the covalent nanostructures. Also in many relevant systems, side-reactions do not occur. However, in reality topological defects, competing C–H activation on more reactive surfaces, and reaction intermediates render this seemingly simple coupling reaction not only more complex, but also more interesting for fundamental research. This feature article aims to provide an account of the vast amount of already published work and tries to destill important findings and currents trends in surface-assisted Ullmann coupling.","container-title":"Chemical Communications","DOI":"10.1039/C7CC03402D","ISSN":"1364-548X","issue":"56","journalAbbreviation":"Chem. Commun.","language":"en","page":"7872-7885","source":"pubs.","title":"Surface-assisted Ullmann coupling","volume":"53","author":[{"family":"Lackinger","given":"M."}],"issued":{"date-parts":[["2017",7,11]]}}}],"schema":""} 21,22 or more generally aryl-aryl coupling, which afforded various conjugated polymers as well as two-dimensional covalent organic frameworks on surfaces. This reaction was also combined with intramolecular cyclodehydrogenation to yield atomically precise graphene nanoribbons with varying widths and edge structures, revealing highly intriguing structure-dependent electronic properties. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"u2R1N6jp","properties":{"unsorted":true,"formattedCitation":"\\super 23\\uc0\\u8211{}26\\nosupersub{}","plainCitation":"23–26","noteIndex":0},"citationItems":[{"id":2159,"uris":[""],"uri":[""],"itemData":{"id":2159,"type":"article-journal","abstract":"We provide insight into surface-catalyzed dehalogenative polymerization, analyzing the organometallic intermediate and its evolution into planar polymeric structures. A combined study using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and first-principles calculations unveils the structural conformation of substrate-bound phenylene intermediates generated from 1,4-dibromobenzene precursors on Cu(110), showing the stabilizing role of the halogen. The appearance of covalently bonded conjugated structures is followed in real time by fast-XPS measurements (with an acquisition time of 2 s per spectrum and heating rate of 2 K/s), showing that the detaching of phenylene units from the copper substrate and subsequent polymerization occur upon annealing above 460 ± 10 K.","container-title":"ACS Nano","DOI":"10.1021/nn4035684","ISSN":"1936-0851","issue":"9","journalAbbreviation":"ACS Nano","page":"8190-8198","source":"ACS Publications","title":"Insight into Organometallic Intermediate and Its Evolution to Covalent Bonding in Surface-Confined Ullmann Polymerization","volume":"7","author":[{"family":"Di Giovannantonio","given":"Marco"},{"family":"El Garah","given":"Mohamed"},{"family":"Lipton-Duffin","given":"Josh"},{"family":"Meunier","given":"Vincent"},{"family":"Cardenas","given":"Luis"},{"family":"Fagot Revurat","given":"Yannick"},{"family":"Cossaro","given":"Albano"},{"family":"Verdini","given":"Alberto"},{"family":"Perepichka","given":"Dmitrii F."},{"family":"Rosei","given":"Federico"},{"family":"Contini","given":"Giorgio"}],"issued":{"date-parts":[["2013",9,24]]}}},{"id":2980,"uris":[""],"uri":[""],"itemData":{"id":2980,"type":"article-journal","container-title":"ACS Nano","DOI":"10.1021/nn500322r","ISSN":"1936-0851","issue":"3","journalAbbreviation":"ACS Nano","page":"1969-1971","source":"ACS Publications","title":"Reply to “Comment on ‘Insight into Organometallic Intermediate and Its Evolution to Covalent Bonding in Surface-Confined Ullmann Polymerization’”","volume":"8","author":[{"family":"Di Giovannantonio","given":"Marco"},{"family":"El Garah","given":"Mohamed"},{"family":"Lipton-Duffin","given":"Josh"},{"family":"Meunier","given":"Vincent"},{"family":"Cardenas","given":"Luis"},{"family":"Fagot-Revurat","given":"Yannick"},{"family":"Cossaro","given":"Albano"},{"family":"Verdini","given":"Alberto"},{"family":"Perepichka","given":"Dmitrii F."},{"family":"Rosei","given":"Federico"},{"family":"Contini","given":"Giorgio"}],"issued":{"date-parts":[["2014",3,25]]}}},{"id":4893,"uris":[""],"uri":[""],"itemData":{"id":4893,"type":"article-journal","container-title":"Nature","DOI":"10.1038/nature09211","ISSN":"0028-0836, 1476-4687","issue":"7305","note":"Citation Key: Cai2010","page":"470-473","source":"CrossRef","title":"Atomically precise bottom-up fabrication of graphene nanoribbons","volume":"466","author":[{"family":"Cai","given":"Jinming"},{"family":"Ruffieux","given":"Pascal"},{"family":"Jaafar","given":"Rached"},{"family":"Bieri","given":"Marco"},{"family":"Braun","given":"Thomas"},{"family":"Blankenburg","given":"Stephan"},{"family":"Muoth","given":"Matthias"},{"family":"Seitsonen","given":"Ari P."},{"family":"Saleh","given":"Moussa"},{"family":"Feng","given":"Xinliang"},{"family":"Müllen","given":"Klaus"},{"family":"Fasel","given":"Roman"}],"issued":{"date-parts":[["2010",7,22]]}}},{"id":6094,"uris":[""],"uri":[""],"itemData":{"id":6094,"type":"article-journal","container-title":"Nat. Chem.","DOI":"10.1038/nchem.1242","ISSN":"1755-4330, 1755-4349","issue":"3","note":"Citation Key: Lafferentz2012","page":"215-220","source":"CrossRef","title":"Controlling on-surface polymerization by hierarchical and substrate-directed growth","volume":"4","author":[{"family":"Lafferentz","given":"L."},{"family":"Eberhardt","given":"V."},{"family":"Dri","given":"C."},{"family":"Africh","given":"C."},{"family":"Comelli","given":"G."},{"family":"Esch","given":"F."},{"family":"Hecht","given":"S."},{"family":"Grill","given":"L."}],"issued":{"date-parts":[["2012",1,15]]}}}],"schema":""} 23–26Scheme 1. On-surface reaction of 1,4-dibromo-2,5-bis(phenylethynyl)benzene (1) and obtained dimer and trimer products.Figure 1. (a-d) STM images of the Au(111) surface after deposition of precursor 1 at RT followed by repeated annealing steps at the indicated temperatures. (e-h) Magnified STM images at different reaction steps. (i-l) Molecular schemes of the structures observed in the STM images. Scanning parameters: (a,e) It=70 pA, Vb=0.2 V; (b) It=30 pA, Vb=0.3 V; (c,g) It=30 pA, Vb=1 V; (d) It=10 pA, Vb=1 V; (f,h) It=70 pA, Vb=0.1 V.Ullmann-like coupling reactions obviously also encounter limitations in achieving more complex architectures. For instance, only single C-C bonds can be created, while sometimes the formation of an extra ring would be desirable without having to refer to cyclodehydrogenation. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"eUKi4Ji4","properties":{"formattedCitation":"\\super 27,28\\nosupersub{}","plainCitation":"27,28","noteIndex":0},"citationItems":[{"id":3443,"uris":[""],"uri":[""],"itemData":{"id":3443,"type":"article-journal","abstract":"On-surface synthesis is a successful approach to the creation of carbon-based nanostructures that cannot be obtained via standard solution chemistry. In this framework, we have established a novel synthetic pathway to one-dimensional conjugated polymers composed of indenofluorene units. Our concept is based on the use of ortho-methyl groups on a poly(para-phenylene) backbone. In this situation, surface-assisted oxidative ring closure between a methyl and the neighboring aryl moiety gives rise to a five-membered ring. The atomically precise structures and electronic properties of the obtained indenofluorene polymers have been unambiguously characterized by STM, nc-AFM, and STS, supported by theoretical calculations. This unprecedented synthetic protocol can potentially be extended to other polyphenylenes and eventually graphene nanoribbons, to incorporate five-membered rings at desired positions for the fine-tuning of electronic properties.","container-title":"Journal of the American Chemical Society","DOI":"10.1021/jacs.8b00587","ISSN":"0002-7863","issue":"10","journalAbbreviation":"J. Am. Chem. Soc.","page":"3532-3536","source":"ACS Publications","title":"On-Surface Synthesis of Indenofluorene Polymers by Oxidative Five-Membered Ring Formation","volume":"140","author":[{"family":"Di Giovannantonio","given":"Marco"},{"family":"Urgel","given":"José I."},{"family":"Beser","given":"Uliana"},{"family":"Yakutovich","given":"Aliaksandr V."},{"family":"Wilhelm","given":"Jan"},{"family":"Pignedoli","given":"Carlo A."},{"family":"Ruffieux","given":"Pascal"},{"family":"Narita","given":"Akimitsu"},{"family":"Müllen","given":"Klaus"},{"family":"Fasel","given":"Roman"}],"issued":{"date-parts":[["2018",3,14]]}}},{"id":4073,"uris":[""],"uri":[""],"itemData":{"id":4073,"type":"article-journal","container-title":"Chemical Communications","DOI":"10.1039/C4CC02859G","ISSN":"1359-7345, 1364-548X","issue":"76","language":"en","note":"Citation Key: Liu2014c","page":"11200","source":"CrossRef","title":"Cyclotrimerization of arylalkynes on Au(111)","volume":"50","author":[{"family":"Liu","given":"Jia"},{"family":"Ruffieux","given":"Pascal"},{"family":"Feng","given":"Xinliang"},{"family":"Müllen","given":"Klaus"},{"family":"Fasel","given":"Roman"}],"issued":{"date-parts":[["2014",8,6]]}}}],"schema":""} 27,28 Hence, cycloaddition reactions have appeared as a valid on-surface chemistry tool to expand the spectrum of attainable chemical structures. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"VNEfkRP0","properties":{"formattedCitation":"\\super 29\\uc0\\u8211{}34\\nosupersub{}","plainCitation":"29–34","noteIndex":0},"citationItems":[{"id":5597,"uris":[""],"uri":[""],"itemData":{"id":5597,"type":"article-journal","abstract":"Using scanning tunneling microscopy, we demonstrate that the 1,3-dipolar cycloaddition between a terminal alkyne and an azide can be performed under solvent-free ultrahigh vacuum conditions with reactants adsorbed on a Cu(111) surface. XPS shows significant degradation of the azide upon adsorption, which is found to be the limiting factor for the reaction.","container-title":"Journal of the American Chemical Society","DOI":"10.1021/ja312303a","ISSN":"0002-7863","issue":"6","journalAbbreviation":"J. Am. Chem. Soc.","note":"Citation Key: Bebensee2013","page":"2136-2139","source":"ACS Publications","title":"On-Surface Azide–Alkyne Cycloaddition on Cu(111): Does It “Click” in Ultrahigh Vacuum?","title-short":"On-Surface Azide–Alkyne Cycloaddition on Cu(111)","volume":"135","author":[{"family":"Bebensee","given":"Fabian"},{"family":"Bombis","given":"Christian"},{"family":"Vadapoo","given":"Sundar-Raja"},{"family":"Cramer","given":"Jacob R."},{"family":"Besenbacher","given":"Flemming"},{"family":"Gothelf","given":"Kurt V."},{"family":"Linderoth","given":"Trolle R."}],"issued":{"date-parts":[["2013",2,13]]}}},{"id":3878,"uris":[""],"uri":[""],"itemData":{"id":3878,"type":"article-journal","abstract":"Radialenes have distinct structural, electronic and chemical properties from other hydrocarbons, but their synthesis remains a challenge. Here, the authors report a copper catalyzed one-step synthetic protocol of [4]radialene via the cyclotetramerization of phenylacetylene molecules upon thermal activation.","container-title":"Nature Communications","DOI":"10.1038/s41467-018-05472-2","ISSN":"2041-1723","issue":"1","language":"En","page":"3113","source":"","title":"Self-assembly directed one-step synthesis of [4]radialene on Cu(100) surfaces","volume":"9","author":[{"family":"Li","given":"Qing"},{"family":"Gao","given":"Jianzhi"},{"family":"Li","given":"Youyong"},{"family":"Fuentes-Cabrera","given":"Miguel"},{"family":"Liu","given":"Mengxi"},{"family":"Qiu","given":"Xiaohui"},{"family":"Lin","given":"Haiping"},{"family":"Chi","given":"Lifeng"},{"family":"Pan","given":"Minghu"}],"issued":{"date-parts":[["2018",8,6]]}}},{"id":2744,"uris":[""],"uri":[""],"itemData":{"id":2744,"type":"article-journal","abstract":"Surface-confined synthesis has been offering a wide range of opportunities for the construction of novel molecular nanostructures. Exploring new types of on-surface coupling reactions is considered essential for being able to deliberately tune the materials properties. Here, we report on the formation of a covalent C–C bonding motif, namely 1,3-cyclobutadiene, via surface-confined [2 + 2] cycloaddition between pyrene moieties using low temperature scanning tunneling microscopy (LT-STM) and X-ray photoemission spectroscopy (XPS) measurements. By employing a hydrogen dosing treatment together with low-temperature activation, we were able to both eliminate residual byproducts and obtain covalent 1D polymers through the formation of 1,3-cyclobutadiene units. The resulting C–C bonding motif has so far hardly been explored in surface chemistry and substantial evidence is provided that the hydrogen treatment is crucial towards the removal of byproducts in surface-confined polymerization.","container-title":"Nanoscale","DOI":"10.1039/C7NR06187K","ISSN":"2040-3372","issue":"46","journalAbbreviation":"Nanoscale","language":"en","page":"18305-18310","source":"pubs.","title":"Surface-confined [2 + 2] cycloaddition towards one-dimensional polymers featuring cyclobutadiene units","volume":"9","author":[{"family":"Tran","given":"Bay V."},{"family":"Pham","given":"Tuan Anh"},{"family":"Grunst","given":"Michael"},{"family":"Kivala","given":"Milan"},{"family":"St?hr","given":"Meike"}],"issued":{"date-parts":[["2017",11,30]]}}},{"id":3876,"uris":[""],"uri":[""],"itemData":{"id":3876,"type":"article-journal","abstract":"The on-surface reaction of 2,3-dibromoanthracene molecules is studied on two surfaces, Au(100) and Au(111) that differ in their surface reconstructions and thus atomic-scale structure. After deposition intact molecules are observed, which form highly ordered close-packed islands, with preferential adsorption along the corrugation rows of the substrate in the case of Au(100). Heating the sample at 520?K induced Br dissociation and on-surface oligomerization of the thus activated anthracene moieties. While dimers and trimers are formed on Au(111) where they segregate into different molecular islands, only dimers are generated on Au(100). Hence, the reaction mode can be controlled on Au(100) which clearly favors the [2+2]cycloaddition product whereas the [2+2+2] cycloaddition reaction is suppressed. This high selectivity for forming the linear dimer seems to be caused by the adsorption geometry on the reconstructed Au(100) surface.","collection-title":"Surface Structure and Dynamics – in Honor of Karl-Heinz Rieder","container-title":"Surface Science","DOI":"10.1016/j.susc.2018.05.014","ISSN":"0039-6028","journalAbbreviation":"Surface Science","page":"194-200","source":"ScienceDirect","title":"Steering a cycloaddition reaction via the surface structure","volume":"678","author":[{"family":"Koch","given":"Matthias"},{"family":"Gille","given":"Marie"},{"family":"Hecht","given":"Stefan"},{"family":"Grill","given":"Leonhard"}],"issued":{"date-parts":[["2018",12,1]]}}},{"id":5735,"uris":[""],"uri":[""],"itemData":{"id":5735,"type":"article-journal","container-title":"ACS Nano","DOI":"10.1021/nn4022789","ISSN":"1936-0851, 1936-086X","issue":"10","language":"en","note":"Citation Key: DiazArado2013","page":"8509-8515","source":"CrossRef","title":"On-Surface Azide–Alkyne Cycloaddition on Au(111)","volume":"7","author":[{"family":"Díaz Arado","given":"Oscar"},{"family":"M?nig","given":"Harry"},{"family":"Wagner","given":"Hendrik"},{"family":"Franke","given":"J?rn-Holger"},{"family":"Langewisch","given":"Gernot"},{"family":"Held","given":"Philipp Alexander"},{"family":"Studer","given":"Armido"},{"family":"Fuchs","given":"Harald"}],"issued":{"date-parts":[["2013",10,22]]}}},{"id":2947,"uris":[""],"uri":[""],"itemData":{"id":2947,"type":"article-journal","abstract":"We report on the surface-catalyzed formal [2+2] and [2+2+2] cycloadditions of ortho-activated tetracene species on a Ag(111) substrate under ultrahigh vacuum conditions. Three different products are obtained: tetracene dimers, trimers, and tetramers. The former results from the formation of a four-membered ring while the other two arise from cyclization into six-membered rings. These on-surface reactions have been monitored by scanning tunneling microscopy and rationalized by density functional theory calculations. Our approach, based on the reaction of ortho-dihalo precursor monomers via formal cycloadditions, establishes an additional method for the highly active field of on-surface synthesis and enables the development of novel 1D and 2D covalent carbon nanostructures.","container-title":"Journal of the American Chemical Society","DOI":"10.1021/jacs.7b10026","ISSN":"0002-7863","issue":"48","journalAbbreviation":"J. Am. Chem. Soc.","page":"17617-17623","source":"ACS Publications","title":"On-Surface Cyclization of ortho-Dihalotetracenes to Four- and Six-Membered Rings","volume":"139","author":[{"family":"Sánchez-Sánchez","given":"Carlos"},{"family":"Nicola?","given":"Adrien"},{"family":"Rossel","given":"Frédéric"},{"family":"Cai","given":"Jinming"},{"family":"Liu","given":"Junzhi"},{"family":"Feng","given":"Xinliang"},{"family":"Müllen","given":"Klaus"},{"family":"Ruffieux","given":"Pascal"},{"family":"Fasel","given":"Roman"},{"family":"Meunier","given":"Vincent"}],"issued":{"date-parts":[["2017",12,6]]}}}],"schema":""} 29–34Despite its extensive use in synthetic organic chemistry, the DDA reaction has not been investigated for on-surface processes. During our attempts to synthesize eleven atoms wide armchair GNRs (11-AGNRs) on Au(111) from 1,4-dibromo-2,5-bis(phenylethynyl)benzene (1) ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"6rzPzf39","properties":{"formattedCitation":"\\super 35\\nosupersub{}","plainCitation":"35","noteIndex":0},"citationItems":[{"id":203,"uris":[""],"uri":[""],"itemData":{"id":203,"type":"article-journal","abstract":"A versatile method for the synthesis of complex, fused polycyclic aromatic systems in high chemical yield is described. Construction is achieved using a general two-step synthetic sequence. Pd-catalyzed Suzuki and Negishi type cross-coupling chemistries allow for the preparation of nonfused skeletal ring systems in yields consistently >80%. The critical ring-forming step, which generally proceeds in very high to quantitative yield, utilizes 4-alkoxyphenylethynyl groups and is induced by strong electrophiles such as trifluoroacetic acid and iodonium tetrafluoroborate. The reaction in essence produces phenanthrene moieties which are integrated into extended polycyclic aromatic structures. Fused polycyclic benzenoids as well as benzenoid/thiophene systems may be prepared utilizing this methodology. The scope of the described cross-coupling/cyclization chemistry including mechanistic insights and problematic side reactions are described.","container-title":"Journal of the American Chemical Society","DOI":"10.1021/ja9642673","ISSN":"0002-7863","issue":"20","journalAbbreviation":"J. Am. Chem. Soc.","page":"4578-4593","source":"ACS Publications","title":"Directed Electrophilic Cyclizations:? Efficient Methodology for the Synthesis of Fused Polycyclic Aromatics","title-short":"Directed Electrophilic Cyclizations","volume":"119","author":[{"family":"Goldfinger","given":"Marc B."},{"family":"Crawford","given":"Khushrav B."},{"family":"Swager","given":"Timothy M."}],"issued":{"date-parts":[["1997",5,1]]}}}],"schema":""} 35 as a precursor, we have observed the formation of dimer- and trimer-like molecules instead of 11-AGNRs (Scheme 1). Here, we demonstrate the dimerization and trimerization of 1, forming benzo[fg]naphtho[1,2,3-op]tetracene and acenaphtho[4,3,2,1-a1b1c1d1]dibenzo[fg,uv]naphtho[3,2,1-lm]heptacene, respectively, through unprecedented on-surface DDA reactions (Scheme 1). The precise chemical structures of the dimer and trimer products are revealed by high-resolution scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM). We discuss a plausible mechanism for the formation of the observed products via surface-assisted DDA cycloadditions.To study the coupling of precursor 1, we deposited it onto an Au(111) surface held at room temperature (RT) in ultrahigh vacuum (UHV). Figure 1a shows an overview STM image of the resulting sample, which consists of intact molecules self-assembled into chains. Halogen-hydrogen interactions are most likely stabilizing this assembly (see Figure S1) which remains unaltered upon annealing up to 100 ?C. This observation is in agreement with previous studies where the C-Br bond was found to be stable up to this temperature on Au(111). ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"GN3yxX6O","properties":{"formattedCitation":"\\super 36\\nosupersub{}","plainCitation":"36","noteIndex":0},"citationItems":[{"id":2792,"uris":[""],"uri":[""],"itemData":{"id":2792,"type":"article-journal","abstract":"On-surface synthesis is a powerful route toward the fabrication of specific graphene-like nanostructures confined in two dimensions. This strategy has been successfully applied to the growth of graphene nanoribbons of diverse width and edge morphology. Here, we investigate the mechanisms driving the growth of 9-atom wide armchair graphene nanoribbons by using scanning tunneling microscopy, fast X-ray photoelectron spectroscopy, and temperature-programmed desorption techniques. Particular attention is given to the role of halogen functionalization (Br or I) of the molecular precursors. We show that the use of iodine-containing monomers fosters the growth of longer graphene nanoribbons (average length of 45 nm) due to a larger separation of the polymerization and cyclodehydrogenation temperatures. Detailed insight into the growth process is obtained by analysis of kinetic curves extracted from the fast X-ray photoelectron spectroscopy data. Our study provides fundamental details of relevance to the production of future electronic devices and highlights the importance of not only the rational design of molecular precursors but also the most suitable reaction pathways to achieve the desired final structures.","container-title":"ACS Nano","DOI":"10.1021/acsnano.7b07077","ISSN":"1936-0851","issue":"1","journalAbbreviation":"ACS Nano","page":"74-81","source":"ACS Publications","title":"On-Surface Growth Dynamics of Graphene Nanoribbons: The Role of Halogen Functionalization","title-short":"On-Surface Growth Dynamics of Graphene Nanoribbons","volume":"12","author":[{"family":"Di Giovannantonio","given":"Marco"},{"family":"Deniz","given":"Okan"},{"family":"Urgel","given":"José I."},{"family":"Widmer","given":"Roland"},{"family":"Dienel","given":"Thomas"},{"family":"Stolz","given":"Samuel"},{"family":"Sánchez-Sánchez","given":"Carlos"},{"family":"Muntwiler","given":"Matthias"},{"family":"Dumslaff","given":"Tim"},{"family":"Berger","given":"Reinhard"},{"family":"Narita","given":"Akimitsu"},{"family":"Feng","given":"Xinliang"},{"family":"Müllen","given":"Klaus"},{"family":"Ruffieux","given":"Pascal"},{"family":"Fasel","given":"Roman"}],"issued":{"date-parts":[["2018",1,23]]}}}],"schema":""} 36 After annealing of the sample to 150 ?C, a more disordered assembly of the molecular units appears from the corresponding STM image (Figure 1b). However, some regular moieties are also visible (Figure 1f). The presence of round protrusions between the molecular units suggests the presence of an organometallic structure, as sketched in Figure 1j and S1. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"FXCeWz0A","properties":{"formattedCitation":"\\super 37,38\\nosupersub{}","plainCitation":"37,38","noteIndex":0},"citationItems":[{"id":4772,"uris":[""],"uri":[""],"itemData":{"id":4772,"type":"article-journal","container-title":"Journal of the American Chemical Society","DOI":"10.1021/ja204956b","ISSN":"0002-7863, 1520-5126","issue":"34","language":"en","note":"Citation Key: Wang2011k","page":"13264-13267","source":"CrossRef","title":"Single-Molecule Resolution of an Organometallic Intermediate in a Surface-Supported Ullmann Coupling Reaction","volume":"133","author":[{"family":"Wang","given":"Weihua"},{"family":"Shi","given":"Xingqiang"},{"family":"Wang","given":"Shiyong"},{"family":"Van Hove","given":"Michel A."},{"family":"Lin","given":"Nian"}],"issued":{"date-parts":[["2011",8,31]]}}},{"id":191,"uris":[""],"uri":[""],"itemData":{"id":191,"type":"article-journal","abstract":"Ullmann coupling or, more generally, dehalogenative aryl–aryl coupling, is one of the most widely exploited chemical reactions to obtain one- and two-dimensional polymers on metal surfaces. It is generally described as a two-step reaction: (i) dehalogenation, resulting in the formation of a stable intermediate organometallic phase and subsequent (ii) C–C coupling. The topology of the resulting polymer depends on the number and positions of the halogen atoms in the haloaromatic precursor, although its orientation and order are determined by the structure of the intermediate phase. Hitherto, only one intermediate structure, identified as an organometallic (OM) phase, has been reported for such a reaction. Here we demonstrate the formation of two distinct OM phases during the temperature-induced growth of poly(para-phenylene) from 1,4-dibromobenzene precursors on Cu(110). Beyond the already known linear-OM chains, we show that a phase reorganization to a chessboard-like 2D-OM can be activated in a well-defined temperature range. This new intermediate phase, revealed only when the reaction is carried out at low molecular coverages, was characterized by X-ray photoelectron spectroscopy, scanning tunneling microscopy and near-edge X-ray absorption fine structure spectroscopy, and modeled by density functional theory calculations. Our data show that the 2D-OM remains stable after cooling down the sample and is stabilized by four-Cu clusters at each node. The observation of such unexpected intermediate phase shows the complexity of the mechanisms underlying on-surface synthesis and broadens the understanding of Ullmann coupling, which continues to be astonishing despite its extensive use.","container-title":"Nanoscale","DOI":"10.1039/C9NR00672A","ISSN":"2040-3372","issue":"16","journalAbbreviation":"Nanoscale","language":"en","page":"7682-7689","source":"pubs.","title":"An unexpected organometallic intermediate in surface-confined Ullmann coupling","volume":"11","author":[{"family":"Galeotti","given":"Gianluca"},{"family":"Di Giovannantonio","given":"Marco"},{"family":"Cupo","given":"Andrew"},{"family":"Xing","given":"Sarah"},{"family":"Lipton-Duffin","given":"Josh"},{"family":"Ebrahimi","given":"Maryam"},{"family":"Vasseur","given":"Guillaume"},{"family":"Kierren","given":"Bertrand"},{"family":"Fagot-Revurat","given":"Yannick"},{"family":"Tristant","given":"Damien"},{"family":"Meunier","given":"Vincent"},{"family":"Perepichka","given":"Dmitrii F."},{"family":"Rosei","given":"Federico"},{"family":"Contini","given":"Giorgio"}],"issued":{"date-parts":[["2019",4,23]]}}}],"schema":""} 37,38 Indeed, the measured C-Au distance of 2.4 ± 0.2 ? agrees with previously reported values for organometallic bonding. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"cmg56EnZ","properties":{"formattedCitation":"\\super 39,40\\nosupersub{}","plainCitation":"39,40","noteIndex":0},"citationItems":[{"id":4805,"uris":[""],"uri":[""],"itemData":{"id":4805,"type":"article-journal","container-title":"Small","DOI":"10.1002/smll.201303011","ISSN":"16136810","issue":"7","language":"en","note":"Citation Key: Zhang2014c","page":"1361-1368","source":"CrossRef","title":"Surface Supported Gold-Organic Hybrids: On-Surface Synthesis and Surface Directed Orientation","title-short":"Surface Supported Gold-Organic Hybrids","volume":"10","author":[{"family":"Zhang","given":"Haiming"},{"family":"Franke","given":"J?rn-Holger"},{"family":"Zhong","given":"Dingyong"},{"family":"Li","given":"Yan"},{"family":"Timmer","given":"Alexander"},{"family":"Arado","given":"Oscar Díaz"},{"family":"M?nig","given":"Harry"},{"family":"Wang","given":"Hong"},{"family":"Chi","given":"Lifeng"},{"family":"Wang","given":"Zhaohui"},{"family":"Müllen","given":"Klaus"},{"family":"Fuchs","given":"Harald"}],"issued":{"date-parts":[["2014",4]]}}},{"id":3444,"uris":[""],"uri":[""],"itemData":{"id":3444,"type":"article-journal","abstract":"We report the on-surface formation of Au-directed heptacene organometallic complexes on a Au(111) template in an ultrahigh vacuum environment. Successive thermal annealing steps investigated by means of scanning tunneling microscopy, noncontact atomic force microscopy, temperature-programmed desorption and density functional theory reveal the formation of heptacene organometallic complexes via a selective two-step activation of an α-diketone-protected heptacene precursor. Furthermore, we demonstrate the efficiency of tip-induced deprotection experiments as a complementary strategy in the complex formation. Our results provide perspectives for the on-surface synthesis of larger acenes featuring potential use in the fields of organic electronics, spintronics and nonlinear optics.","container-title":"Journal of the American Chemical Society","DOI":"10.1021/jacs.7b05192","ISSN":"0002-7863","issue":"34","journalAbbreviation":"J. Am. Chem. Soc.","page":"11658-11661","source":"ACS Publications","title":"On-Surface Synthesis of Heptacene Organometallic Complexes","volume":"139","author":[{"family":"Urgel","given":"José I."},{"family":"Hayashi","given":"Hironobu"},{"family":"Di Giovannantonio","given":"Marco"},{"family":"Pignedoli","given":"Carlo A."},{"family":"Mishra","given":"Shantanu"},{"family":"Deniz","given":"Okan"},{"family":"Yamashita","given":"Masataka"},{"family":"Dienel","given":"Thomas"},{"family":"Ruffieux","given":"Pascal"},{"family":"Yamada","given":"Hiroko"},{"family":"Fasel","given":"Roman"}],"issued":{"date-parts":[["2017",8,30]]}}}],"schema":""} 39,40 The first step toward the expected aryl-aryl coupling ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"OMoOuXKx","properties":{"formattedCitation":"\\super 22\\nosupersub{}","plainCitation":"22","noteIndex":0},"citationItems":[{"id":1349,"uris":[""],"uri":[""],"itemData":{"id":1349,"type":"article-journal","abstract":"Surface-assisted Ullmann coupling is the workhorse of on-surfaces synthesis. Among the various couplings that were successfully transferred from solution to solid surfaces, Ullmann coupling is arguably the most reliable, controllable, and widespread coupling reaction. The basic reaction scheme is straightforward: halogenated precursors are deposited onto solid surfaces, normally of coinage metals. In the adsorbed state the halogen substitutents are split off by virtue of the surface's reactivity, thereby generating acitvated species that subsequently recombine by forming C–C bonds. Ullmann coupling is well suited for reticular synthesis of novel organic nanostructures: ideally, the halogen substitution pattern of the precursor – which becomes the monomer upon dehalogenation – predetermines dimensionality and topology of the covalent nanostructures. Also in many relevant systems, side-reactions do not occur. However, in reality topological defects, competing C–H activation on more reactive surfaces, and reaction intermediates render this seemingly simple coupling reaction not only more complex, but also more interesting for fundamental research. This feature article aims to provide an account of the vast amount of already published work and tries to destill important findings and currents trends in surface-assisted Ullmann coupling.","container-title":"Chemical Communications","DOI":"10.1039/C7CC03402D","ISSN":"1364-548X","issue":"56","journalAbbreviation":"Chem. Commun.","language":"en","page":"7872-7885","source":"pubs.","title":"Surface-assisted Ullmann coupling","volume":"53","author":[{"family":"Lackinger","given":"M."}],"issued":{"date-parts":[["2017",7,11]]}}}],"schema":""} 22 is therefore almost complete at this temperature (some of the bromine atoms are still covalently attached to the precursors, red arrows in Figure 1f). Annealing the sample to 200 ?C produces further modifications in the molecular assemblies (Figure 1c,g). The overall appearance of the surface is characterized by large, ill-defined structures, probably originating from aggregation as well as non-selective coupling reactions (e.g. CH activation and lateral fusion) leading to ill-defined oligomers. The formation of the targeted polymer illustrated in Scheme 1, potentially leading to 11-AGNRs, appears to be prevented by steric hindrance between hydrogens (highlighted in red in Scheme 1) and/or unexpected reactions involving the triple bonds that might be activated on the gold surface at 200 °C (vide infra). Nevertheless, we also observe molecular objects which can be assigned to dimers and trimers formed from precursor 1. They possess one or two out-of-plane phenyl rings (green arrows in Figure 1g,k) which are tilted due to the steric hindrance against the planar aromatic cores. Figure 2. STM images of dimer (a) and trimer (d) products observed after annealing precursor 1 to 300 °C on Au(111). (b,e) Laplace-filtered images of constant-height frequency-shift nc-AFM images performed with CO-functionalized tip. See Figure S2 for the raw data. (c,f) Chemical structures of the observed products. Scanning parameters: (a) It=70 pA, Vb=0.1 V; (d) It=100 pA, Vb=–0.02 V.Scheme 2. Proposed reaction pathway on Au(111), based on the observed intermediates and final products. Precursor 1 adsorbs intactly on the substrate held at RT and up to 100 °C. (a) Annealing of the surface to 150 °C yields organometallic structures (T1). (b) Subsequent heating to 200 °C activates a dehydro-Diels-Alder cycloaddition reaction toward the trimer T2. (c) At 300 °C, sequential cyclodehydrogenation and reduction of ethynyl to vinyl take place to form T3 and T4.Some of the molecules reach a (nearly) planar conformation after annealing the sample to 300 ?C (Figure 1d). We identify two molecular products that are selectively formed with apparently well-defined chemical structures (Figure 1h). Bond-resolved nc-AFM imaging unambiguously elucidates their structures to consist of 44 and 66 carbon atoms, having a benzo- and naphtho-fused tetracene and dibenzo- and dinaphtho-fused heptacene backbones, respectively, which extends laterally with styryl pendent groups (Figure 2). These two products originate from the covalent coupling of two and three monomers, respectively, as sketched with different colors in Figure 2c,f. Statistical analysis of ~350 molecules on the surface revealed that 9% of them form dimeric products along with 12% of trimeric products. The remaining 79% of the monomers form side products and larger assemblies, which we could not clearly identify because of their increased non-planarity. However, we tentatively ascribe the side products to a non-complete DDA reaction or to different reactions involving ethynyl groups of two or more monomers. On the other hand, the larger assemblies could be aggregates of the products as well as covalently bonded oligomers/polymers originating from non-selective intermolecular couplings. The out-of-plane parts of the tetracene and heptacene cores (blue arrows in Figure 2) are due to steric repulsion between neighboring hydrogens. In contrast, a five-membered ring is observed on the opposite side of the heptacene backbone (red arrows in Figure 2). In this case, the steric overlap between hydrogens at a cove-edge position promoted surface-assisted cyclodehydrogenation, as previously reported. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"kD1T0xhu","properties":{"formattedCitation":"\\super 41\\nosupersub{}","plainCitation":"41","noteIndex":0},"citationItems":[{"id":2359,"uris":[""],"uri":[""],"itemData":{"id":2359,"type":"article-journal","abstract":"Five-membered carbon rings play a crucial role in determining the geometric structures and electronic properties of carbon-based materials. However, incorporating five-membered rings into low-dimensional carbon nanomaterials with atomic precision is still a challenge. Here, we report on the on-surface synthesis of a one-dimensional conjugated polymer comprising fluoranthene subunits obtained by the surface-assisted aromatic cyclodehydrogenation of 1-phenylnaphthalene moieties within the precursor monomers. By using scanning tunneling microscopy (STM), we investigate the formation of the polymer by thermally induced dehalogenative aryl–aryl coupling and subsequent aromatic cyclodehydrogenation on a Au(111) substrate. The formed five-membered carbon rings are directly observed with atomic resolution by noncontact atomic force microscopy (nc-AFM). Our results show that carefully designed phenyl-substituted polycyclic aromatic hydrocarbons can be used for the rational fabrication of five-membered rings in the bottom-up synthesis of carbon-based nanomaterials and thus add a further tool to the emerging field of on-surface synthesis.","container-title":"The Journal of Physical Chemistry C","DOI":"10.1021/acs.jpcc.6b05495","ISSN":"1932-7447","issue":"31","journalAbbreviation":"J. Phys. Chem. C","page":"17588-17593","source":"ACS Publications","title":"Building Pentagons into Graphenic Structures by On-Surface Polymerization and Aromatic Cyclodehydrogenation of Phenyl-Substituted Polycyclic Aromatic Hydrocarbons","volume":"120","author":[{"family":"Liu","given":"Jia"},{"family":"Dienel","given":"Thomas"},{"family":"Liu","given":"Junzhi"},{"family":"Groening","given":"Oliver"},{"family":"Cai","given":"Jinming"},{"family":"Feng","given":"Xinliang"},{"family":"Müllen","given":"Klaus"},{"family":"Ruffieux","given":"Pascal"},{"family":"Fasel","given":"Roman"}],"issued":{"date-parts":[["2016",8,11]]}}}],"schema":""} 41 Sequential reaction steps leading to the formation of the observed trimer are proposed in Scheme 2 (see Scheme S3 for the dimer). After debromination of 1 on Au(111), organometallic structures are observed, forming short chains on the surface (T1). Upon further annealing, covalent coupling of three activated monomers takes place with two-fold [4+2] cycloadditions for each trimer, which we ascribe to a DDA reaction towards dibenzo[a,h]naphtho[2,3-c]pentaphene T2. Annealing the sample at 300 ?C furnishes dibenzo[a1b1,lm]dinaphtho[1,2,3-fg:1',2',3'-uv]heptacene T3 via the cyclodehydrogenation of out-of-plane phenyls and the reduction of ethynyl groups at the core. ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"0JVJgLEr","properties":{"formattedCitation":"\\super 42\\nosupersub{}","plainCitation":"42","noteIndex":0},"citationItems":[{"id":1763,"uris":[""],"uri":[""],"itemData":{"id":1763,"type":"article-journal","container-title":"Nature Communications","DOI":"10.1038/ncomms12711","ISSN":"2041-1723","page":"12711","source":"CrossRef","title":"Thermal control of sequential on-surface transformation of a hydrocarbon molecule on a copper surface","volume":"7","author":[{"family":"Kawai","given":"Shigeki"},{"family":"Haapasilta","given":"Ville"},{"family":"Lindner","given":"Benjamin D."},{"family":"Tahara","given":"Kazukuni"},{"family":"Spijker","given":"Peter"},{"family":"Buitendijk","given":"Jeroen A."},{"family":"Pawlak","given":"Rémy"},{"family":"Meier","given":"Tobias"},{"family":"Tobe","given":"Yoshito"},{"family":"Foster","given":"Adam S."},{"family":"Meyer","given":"Ernst"}],"issued":{"date-parts":[["2016",9,13]]}}}],"schema":""} 42 We speculate that the availability of atomic hydrogen on the Au surface might have led to reduction of the pendent ethynyl groups into vinyl moieties (see Figure S3 for details). Finally, the steric hindrance between neighboring hydrogens at the cove-edges can result in the occasional formation of five-member rings via intramolecular cyclodehydrogenation, ADDIN ZOTERO_ITEM CSL_CITATION {"citationID":"WAgFhaAv","properties":{"formattedCitation":"\\super 43\\nosupersub{}","plainCitation":"43","noteIndex":0},"citationItems":[{"id":15113,"uris":[""],"uri":[""],"itemData":{"id":15113,"type":"article-journal","abstract":"The synthesis of porous nanographenes is a challenging task for solution chemistry, and thus, on-surface synthesis provides an alternative approach. Here, we report the synthesis of a triporous nanographene with 102 sp2 carbon atoms by combining solution and surface chemistry. The carbon skeleton was obtained by Pd-catalyzed cyclotrimerization of arynes in solution, while planarization of the molecule was achieved through two hierarchically organized on-surface cyclodehydrogenation reactions, intra- and inter-blade. Remarkably, the three non-planar [14]annulene pores of this nanographene further evolved at higher temperatures showing interesting intra-porous on-surface reactivity.","container-title":"Chemical Science","DOI":"10.1039/C9SC03404H","ISSN":"2041-6539","issue":"43","journalAbbreviation":"Chem. Sci.","language":"en","page":"10143-10148","source":"pubs.","title":"Synthesis and reactivity of a trigonal porous nanographene on a gold surface","volume":"10","author":[{"family":"Zuzak","given":"Rafal"},{"family":"Pozo","given":"Iago"},{"family":"Engelund","given":"Mads"},{"family":"Garcia-Lekue","given":"Aran"},{"family":"Vilas-Varela","given":"Manuel"},{"family":"Alonso","given":"José M."},{"family":"Szymonski","given":"Marek"},{"family":"Guitián","given":"Enrique"},{"family":"Pérez","given":"Dolores"},{"family":"Godlewski","given":"Szymon"},{"family":"Pe?a","given":"Diego"}],"issued":{"date-parts":[["2019",11,6]]}}}],"schema":""} 43 leading to e.g. acenaphtho[4,3,2,1-a1b1c1d1]dibenzo[fg,uv]naphtho[3,2,1-lm]heptacene T4 (experimentally imaged). Products larger than trimers appear as non-regular by STM imaging. We ascribe them to lateral fusion via non-selective CH activation. Here, the DDA reaction between activated precursors 1 can afford products up to trimers leading to an heptacene backbone. This behavior is tentatively attributed to the necessity of simultaneous coupling of the radical positions and cycloadditions involving the ethynyl groups, which makes coupling of more than three monomers impossible, thus yielding only dimers and trimers.In conclusion, we have reported DDA reactions between bis(phenylethynyl)benzene precursors on an Au(111) surface. Detailed structural characterization of the products at different temperatures reveals the presence of gold-mediated organometallic assemblies as reaction intermediates. The adsorbates subsequently undergo DDA coupling at 200 ?C, and are finally converted into planar structures at 300 ?C. Heptacene and tetracene core structures are observed on the surface, which is most likely because a simultaneous activation to the radical and the triple bond is required for this on-surface reaction. Our findings demonstrate that the DDA reaction occurs also in two-dimensional space, thus providing an additional tool to the field of on-surface synthesis. ASSOCIATED CONTENT Supporting InformationThe Supporting Information is available free of charge on the ACS Publications website. Experimental methods; additional reaction schemes and experimental data (PDF).AUTHOR INFORMATIONCorresponding Author* roman.fasel@empa.ch* muellen@mpip-mainz.mpg.deAuthor Contributions#These authors contributed equally.NotesThe authors declare no competing financial interests.ACKNOWLEDGMENT This work was supported by the Swiss National Science Foundation under Grant No. 200020_182015, the European Union’s Horizon 2020 research and innovation program under grant agreement number 785219 (Graphene Flagship Core 2), the Office of Naval Research (N00014-18-1-2708), and the Max Planck Society. AK thanks the Ramsay Memorial Fellowships Trust for the award of fellowship. Lukas Rotach is acknowledged for excellent technical support during the experiments. REFERENCES ADDIN ZOTERO_BIBL {"uncited":[],"omitted":[],"custom":[]} CSL_BIBLIOGRAPHY (1) Narita, A.; Wang, X.-Y.; Feng, X.; Müllen, K. New Advances in Nanographene Chemistry. Chem Soc Rev 2015, 44 (18), 6616–6643.(2) Narita, A.; Feng, X.; Hernandez, Y.; Jensen, S. A.; Bonn, M.; Yang, H.; Verzhbitskiy, I. A.; Casiraghi, C.; Hansen, M. R.; Koch, A. H. R.; Fytas, G.; Ivasenko, O.; Li, B.; Mali, K. S.; Balandina, T.; Mahesh, S.; De Feyter, S.; Müllen, K. Synthesis of Structurally Well-Defined and Liquid-Phase-Processable Graphene Nanoribbons. Nat. Chem. 2014, 6 (2), 126–132.(3) Sun, Z.; Ye, Q.; Chi, C.; Wu, J. Low Band Gap Polycyclic Hydrocarbons: From Closed-Shell near Infrared Dyes and Semiconductors to Open-Shell Radicals. Chem. Soc. Rev. 2012, 41 (23), 7857.(4) Wu, J.; Pisula, W.; Müllen, K. Graphenes as Potential Material for Electronics. Chem. Rev. 2007, 107 (3), 718–747.(5) Rieger, R.; Müllen, K. 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