Molecular mechanisms of C–C-coupling reactions: A microscopic view of on-surface chemical bond formation processes

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The bottom-up construction of complex functional molecules has undoubtedly been a guiding vision of researchers in the nanosciences, ever since Feynman’s famous declaration that “there is plenty of room at the bottom”. In the past centuries chemists have established a solid basis of mechanistic models for the course of various reactions to construct molecules. Recently it was demonstrated that CO-functionalized AFM-tips allow imaging molecular structures with atomic resolution and unambiguous chemical bond identification became possible. Since then scientists can clearly distinguish even subtle structural changes as they are occurring in on-surface synthesis and finally understand different reaction pathways. The key in assembling organic (aromatic) structures on-surface is in controlling the formation and reactivity of radical intermediates. Therefore, the main objective of this project is to study the stability and reactivity of aromatic radicals on the basis of a suitable on-surface model reaction. This involves the formation (cleavage of the C–leaving group bond), potential stabilization by the surface and/or an organic intermediate, and further reactions, such as insertion reactions, migration or rearrangement reactions. These elementary processes are the key to understand the reactions, to optimize them and to establish general rules, how to conduct organic synthesis directly on surfaces. To address these issues a simple model reaction has been chosen: The cyclization of a 1-phenylnaphthalene derivative to fluoranthene. A key factor to achieve the project goals is the ability to follow and understand each individual step in a reaction pathway, from dehalogenation and intermediate-formation to diffusion. We combine the expertise of an organic chemist for synthesis, a scanning probe expert for imaging as well as manipulating individual organic molecules on metal surfaces, as well as a theoretician to compare to ab-initio simulations. The final goal is to unravel the complete reaction dynamics of the C-C coupling for a representative organic molecule, including different halogenations, radical formation, isomeric effects, and understanding competing processes with respect to thermal activation.