The Orientation of Silver Surfaces Drives the Reactivity and the Selectivity in Homo‐Coupling Reactions. Issue 15 (4th June 2018) - Kalashnyk, Nataliya
Abstract: Original reaction pathways can be explored in the on‐surface synthesis approach where small aromatic precursors are confined to the surface of single crystal metals. The bis‐indanedione molecule reacted with itself on silver surfaces in different ways, through a Knoevenagel reaction or an oxidative coupling, leading to the formation of a variety of new molecular compounds and covalently‐linked 1D or 2D networks. Noteworthy, original reaction products were obtained that cannot be synthesized in traditional solvent‐based chemistry. The lowest activation temperature for the homo‐coupling reactions was found on the Ag(111) surface. The Ag(110) was highly selective in terms of coupling reaction type, while on Ag(100) the temperature could finely control the selectivity. The on‐surface synthesis approach is shown here to be particularly efficient to produce original compounds in mild conditions, using activation temperatures as low as 200 °C. The different structures were characterized by scanning tunnelling microscopy (STM) together with X‐ray photoelectron emission spectroscopy (XPS) and high‐resolution electron energy loss spectroscopy (HREELS). Abstract : Selectivity on a silver platter : A variety of compounds can be synthesised under mild conditions following the on‐surface synthesis approach. Using a silver substrate, indanedione can undergo two distinct homo‐coupling reactions upon thermal activation, a Knoevenagel reaction or oxidative coupling. Fine tuning of reaction products can be achieved through crystallographic orientation of the substrate and/or the activation temperature.