Silver Surface-Assisted Dehydrobrominative Cross-Coupling between Identical Aryl Bromides.

Cross-coupling reactions represent an indispensable tool in chemical synthesis. An intriguing challenge in this field is to achieve selective cross-coupling between two precursors with similar reactivity or, to the limit, the identical molecules. Here we report an unexpected dehydrobrominative cross-coupling between 1,3,5-tris(2-bromophenyl)benzene molecules on silver surfaces. Using scanning tunneling microscopy, we examine the reaction process at the single-molecular level, quantify the selectivity of the dehydrobrominative cross-coupling, and reveal the modulation of selectivity by substrate lattice-related catalytic activity or molecular assembly effect. Theoretical calculations indicate that the dehydrobrominative cross-coupling proceeds via regioselective C-H bond activation of debrominated TBPB and subsequent highly selective C-C coupling of the radical-based intermediates. The reaction kinetics plays an important role in the selectivity for the cross-coupling. This work not only expands the toolbox for chemical synthesis but also provides important mechanistic insights into the selectivity of coupling reactions on the surface.

Formation of positionally ordered but orientationally disordered molecular organization on surface.

Positionally ordered but orientationally disordered molecular structures are commonly found in materials like liquid crystals and molecular glasses. Understanding these structures and their phase transitions helps in designing materials with a wide range of applications. Herein, we report the formation of positionally ordered but orientationally disordered structures via adsorption and organization of 2,4,6-tri([1,1'-biphenyl]-2-yl)-1,3,5-triazine (TBTA) molecules on different coin metal surfaces. It is found that deposition of TBTA molecules on Au(111), Ag(111), and Cu(111) surfaces leads to similar hexagonal lattices, differing in molecular orientation. The molecules have two orientations on Au(111) and Ag(111) surfaces, giving birth to positionally ordered but orientationally disordered molecular structures. The regularity of the structures on Ag(111) is slightly better than that on Au(111). On Cu(111) surface, however, all molecules exhibit the same orientation, resulting in a long-range ordered hexagonal assembly. The density functional theory calculations demonstrate that the matching between the substrate lattice and the hexagonal lattice of molecular structure is responsible for the different molecular organizations.