Geometric Effects on C-C Coupling of Aryl-Carbenes under 2D Confinement.

It is well established that the confinement of reactants to two dimensions influences their reactivity. However, such confinement is often dominated by charge transfer effects between the reactants and the confining walls, in particular if the walls are conductive. Also, the reactivity of carbenes on metal surfaces is significantly affected by the charge transfer between the carbene and the metal, rendering the carbene more nucleophilic or electrophilic. Here, we investigate the geometrical effects of 2D confinement without an influence of the supporting metal for a photoinduced reaction of an aryl carbene on an ionic decoupling layer. We demonstrate the decoupling concept for the C-C coupling of 3-methoxy-9-fluorenylidene (CHO) on a NaBr(100) bilayer on Ag(111). We combine scanning tunneling microscopy with infrared reflection absorption spectroscopy to follow the photoinduced C-C coupling of the carbene from its diazo-protected precursor in two dimensions. Our study demonstrates that the NaBr decoupling bilayer efficiently suppresses the effects of the metal surface, facilitating carbene chemistry under geometrical confinement.