Gold Makes the Termolecular Assembly Possible: Surface-Catalyzed Conversion of an Aldehyde to Its Cyclic Trimer

Propanal (C2H5CHO) trimerizes to 2,4,6-triethyl-1,3,5-trioxane ring on the (110) face of gold in vacuo. The three-component coupling is not only selective about which crystal plane to react upon but also metal-dependent. Low-coordinated sites, surface-specific morphology, and electronic properties of gold act in concert to construct the cyclic C–O–C linkages. Interplay between metal coordination and molecule–surface and molecule–molecule interactions help gather the reaction components and preorganize them on the surface, promoting an otherwise termolecular reaction to a unimolecular (intracomplex) one and making the cyclization possible.