Gold/Isophorone Interaction Driven by Keto/Enol Tautomerization

The binding behavior of isophorone (C9H14O) to Au adatoms and clusters deposited on MgO/Ag(001) thin films is investigated by scanning tunneling microscopy (STM) and density functional theory (DFT). The STM data reveal the formation of various metal/organic complexes, ranging from Au1/isophorone pairs to larger Au aggregates with molecules bound to their perimeter. DFT calculations find the energetically preferred keto-isophorone to be unreactive toward gold, while the enol-tautomer readily binds to Au monomers and clusters. The interaction is governed by electrostatic forces between the hydroxyl group of the enol and negative excess charges residing on the ad-gold. The activation barrier between keto- and enol-isophorone is calculated to be 0.76 eV, rendering tautomerization feasible at room temperature. Our study provides evidence of an enol-driven chemical reaction of an organic molecule whose thermodynamic equilibrium lies far on the keto-side.