Interactions of Carbenes with Coinage Metal Surfaces: An Electrophilic Reactive Carbene vs. a Nucleophilic Stable Carbene

Abstract

Carbenes are key intermediates in many chemical applications. The properties of carbenes very much depend on substitution and on the chemical environment such as solvent or surface interactions. In this work, we computationally study cyclopentadienylidene (CP), as an archetypical electrophilic reactive carbene, on three metal surfaces: Cu(111), Ag(111), and Au(111). In addition, we investigate the stable nucleophilic N-heterocyclic carbene imidazolidene (IMI) as a structurally analogous counterpart of CP for comparing the behavior of these two drastically different types of carbene species in the presence of metal surfaces. Our study reveals different adsorption geometries: CP adsorbs tilted; IMI adsorbs perpendicularly on the three surfaces. CP has a much higher adsorption energy on metal surfaces compared to IMI. The adsorption energy of CP follows the tendency Ag < Au < Cu. All metal surfaces induced switching of the ground electronic state of CP from triplet to singlet. The nucleophilic IMI acts as electron donor when adsorbed, with net charge transferred from IMI to the metal surface. The electrophilic CP acts as an electron acceptor, withdrawing net charge from the metal surface. Our study can contribute to engineering new classes of on-surface catalytic systems, based on tailored reactivities of surface-bound carbenes.