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On-surface synthesis is appearing as an extremely promising strategy to create organic nanoarchitectures with atomic precision. Molecular building blocks holding adequate functional groups are dosed onto surfaces that support or even drive their covalent linkage. The surface confinement and the frequent lack of solvents (most commonly being performed under vacuum conditions) create a completely new scenario fully complementary to conventional chemistry.

In a pedagogical way and based on the most recent developments, this volume presents our current understanding in the field, addressing fundamental reaction mechanisms, synthetic strategies to influence the reactions according to our needs, as well as the ultimate growth and characterization of functional materials.

Verging on chemistry, physics and materials science, the book is aimed at students and researchers interested in nanochemistry, surface science, supramolecular materials and molecular devices.

Chapters "Mechanistic insights into surface-supported chemical reactions", "Reactivity on and of Graphene Layers: Scanning Probe Microscopy Reviels" and "Bottom-up fabrication of atomically precise graphene nanoribbons" of this book are available open access under a CC BY 4.0 license at link.springer.com

Inhaltsverzeichnis

Frontmatter

Open Access

Mechanistic Insights into Surface-Supported Chemical Reactions

Abstract
Its excellent spatial resolution makes scanning probe microscopy a capable method to investigate chemical reactions at the single-molecule level and obtain fascinating and unprecedented insights into the mechanisms of chemical transformations. Particularly exciting are recent advances in atomic force microscopy that allow bond-resolved imaging and thus make the chemical identification of organic molecular reaction intermediates and products possible. In this chapter we will give an overview about recent fundamental research on reaction mechanisms and kinetics of surface-supported reactions by scanning probe microscopy. Particular emphasis will be placed on the stabilization and statistical analysis of intermediates, which provides fundamental understanding of the microscopic driving forces of complex chemical transformations of organic molecules.
Alexander Riss

Kinetic and Thermodynamic Considerations in On-Surface Synthesis

Abstract
In this chapter it will be explained how kinetic and thermodynamic aspects of on-surface reactions may be accounted for by electronic structure theory together with transition state theory. The focus of the chapter is to discuss what free energy contributions, particularly in terms of entropy, we need to account for to properly describe chemical reactions on surfaces. For example, dehydrogenation reactions are often endothermic and their occurrence on surfaces can be explained by the entropy gain of associatively desorbing hydrogen, which make them thermodynamically favorable. In another example, experimentally observed intermediate structures of a bimolecular enediyne coupling were concluded to be stabilized by differences in surface dissipation of excess energy and translational entropy, requiring a quite complex free energy description to understand the reaction. Calculating reaction pathways is becoming a frequent practice within on-surface synthesis, but are often considered at 0 K to reduce computational efforts. The recent advances in describing in particular entropic contributions of on-surface reactions provide important guidelines for how calculations can be refined, and for what kind of scenarios we may expect the necessity for more sophisticated descriptions of kinetics and thermodynamics of reactions.
Jonas Björk

Open Access

Reactivity on and of Graphene Layers: Scanning Probe Microscopy Reveals

Abstract
In this chapter we give an overview of different chemical transformations that can be done on graphene layers and characterized using scanning tunneling (STM) and atomic force microscopies (AFM). We place particular emphasis on the diversity of reactions, systems and synthetic strategies that are now available to surface scientists working in various fundamental and applied research fields. Using imine formation as the model reaction we discuss common principles of building block design and reaction outcomes specific to interfacial synthesis. Then other reactions are briefly overviewed, including: photo- and electrochemically assisted processes, transformations initiated by STM, and finally, reactions involving the covalent modification of graphene layers.
Oleksandr Ivasenko, Steven de Feyter

Dehydrogenative and Dehalogenative Homocoupling Reactions of C–X Groups on Metal Surfaces

Abstract
Surface-assisted synthesis involving hydrocarbons has aroused great attention due to its remarkable potential in constructing novel carbon nanostructures. Particularly, C–C coupling between reactants by cleaving the pre-defined C–X groups (X stands for hydrogen and halogens) followed by forming new carbon-carbon bonds, represents one of the best choices for controllable fabrication of advanced carbon nanostructures. In this chapter, we reviewed the recent achievements of the on-surface reactions of C–X groups activations and C–C couplings, where different carbon species including alkynyl (sp1), alkenyl (sp2), aryl (sp2) and alkyl (sp3) groups are studied.
Liangliang Cai, Qiang Sun, Wei Xu

On-Surface Ullmann Reaction for the Synthesis of Polymers and Macrocycles

Abstract
Compared to organic synthesis in solution, the benefits of on-surface synthesis are apparent especially when it involves insoluble reactants or when in situ characterizations of products with large molecular weight are required. This article covers the on-surface synthesis of hydrocarbon polymers and macrocycles via an Ullmann type reaction of haloarenes on metal single-crystal surfaces. The related formation of stable organometallic reaction intermediates with carbon-metal-carbon bonds is also discussed. Regarding the on-surface synthesis of polymers, deposition onto hot metal surfaces (in contrast to post-annealing) as well as high diffusion rates of the monomers lead to the increase of their chain lengths. To obtain high yields of macrocycles, it is important to enable the ring closure at the stage of the organometallic species with reversible carbon-metal-carbon bonds and to apply high-dilution conditions. In contrast, the formation of macrocycles by cyclisation of polymer chains with only covalent bonds is of low probability due to the particular mechanism of the ring-closure process in two-dimensional confinement.
Qitang Fan, Junfa Zhu, J. Michael Gottfried

Open Access

Bottom-Up Fabrication of Atomically Precise Graphene Nanoribbons

Abstract
Graphene nanoribbons (GNRs) make up an extremely interesting class of materials. On the one hand GNRs share many of the superlative properties of graphene, while on the other hand they display an exceptional degree of tunability of their optoelectronic properties. The presence or absence of correlated low-dimensional magnetism, or of a widely tunable band gap, is determined by the boundary conditions imposed by the width, crystallographic symmetry and edge structure of the nanoribbons. In combination with additional controllable parameters like the presence of heteroatoms, tailored strain, or the formation of heterostructures, the possibilities to shape the electronic properties of GNRs according to our needs are fantastic. However, to really benefit from that tunability and harness the opportunities offered by GNRs, atomic precision is strictly required in their synthesis. This can be achieved through an on-surface synthesis approach, in which one lets appropriately designed precursor molecules to react in a selective way that ends up forming GNRs. In this chapter we review the structure-property relations inherent to GNRs, the synthesis approach and the ways in which the varied properties of the resulting ribbons have been probed, finalizing with selected examples of demonstrated GNR applications.
Martina Corso, Eduard Carbonell-Sanromà, Dimas G. de Oteyza

Aryl–Aryl Covalent Coupling on Rutile TiO2 Surfaces

Abstract
In recent years, enormous progress has been made in developing bottom-up strategies based on the polymerization of specially designed building blocks directly on a supporting surface. So far, selected noble metals have been mostly used as substrates for such on-surface chemical reactions. For the sake of practical applications the semiconductor surfaces clearly represent much more attractive platforms. Especially transition metal oxides exhibiting advantageous optical as well as photo- and electrochemical properties seem to be particularly interesting. In this chapter we describe the strategies for thermally triggered on-surface covalent coupling of aryl halides performed directly on rutile titanium dioxide surfaces. We focus our work on important parameters that need to be considered for understanding and optimization of the polymerization reactions on this model transition metal oxide system.
Marek Kolmer, Jakub S. Prauzner-Bechcicki

On-Surface Synthesis of Two-Dimensional Polymers: Rational Design and Electronic Properties

Abstract
The fabrication of long-range ordered 2D polymers directly on metal surfaces still presents a great challenge in ultra-high vacuum surface science. The structure of the polymer networks is in general predetermined by the coupling chemistry and the symmetry of the molecular precursors. However, the irreversible nature of the C–C coupling reaction readily leads to the formation of defects. Over the last decade, several strategies in the on-surface synthesis have been suggested to improve the structural order. Among them, the programmed hierarchical synthesis through a sequential polymerization proved to be suitable to reduce defects in the formation of 2D polymers. This chapter provides a review on the state-of-the-art structural characterization of surface-supported 2D polymers by established surface science techniques. Further, the chapter focuses on the electronic structure of 2D polymers, which remained experimentally widely unexplored until now.
Sabine Maier

On-Surface Coupling Reactions with Extrinsic Catalysts

Abstract
On-surface coupling reactions have opened a novel route toward synthesizing various organic nanostructures on surfaces. In this chapter, we discuss the catalytic effects of Cu and Pd deposits in the on-surface Ullmann coupling and Sonogashira cross-coupling reactions. The stepwise reaction paths, intermediates, and activation energies are deliberated at a single molecular level using scanning tunneling microscopy (STM). Such studies offer mechanistic insights into the on-surface coupling reactions catalyzed by extrinsic metals.
Wei Zhao, Lei Dong, Ran Zhang, Nian Lin

Addressing Long-Standing Chemical Challenges by AFM with Functionalized Tips

Abstract
In this chapter, we illustrate the great potential of combining organic synthesis with atomic resolution AFM and STM to address relevant and classic issues in chemistry, by summarizing selected examples in which we were involved in recent years. As case studies, the long-standing chemical challenges covered here include the experimental discrimination of bond orders in single molecules, the characterization of extremely insoluble compounds such as nanographenes, the analysis of the individual components of complex mixtures, and the on-surface generation and identification of highly reactive molecules and intermediates.
Diego Peña, Niko Pavliček, Bruno Schuler, Nikolaj Moll, Dolores Pérez, Enrique Guitián, Gerhard Meyer, Leo Gross
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