On-Surface Cyclization of ortho-Dihalotetracenes to Four- and Six-Membered Rings.

We report on the surface-catalyzed formal [2+2] and [2+2+2] cycloadditions of ortho-activated tetracene species on a Ag(111) substrate under ultrahigh vacuum conditions. Three different products are obtained: tetracene dimers, trimers, and tetramers. The former results from the formation of a four-membered ring while the other two arise from cyclization into six-membered rings. These on-surface reactions have been monitored by scanning tunneling microscopy and rationalized by density functional theory calculations. Our approach, based on the reaction of ortho-dihalo precursor monomers via formal cycloadditions, establishes an additional method for the highly active field of on-surface synthesis and enables the development of novel 1D and 2D covalent carbon nanostructures.