Kinetic Strategies for the Formation of Graphyne Nanowires via Sonogashira Coupling on Ag(111).

The selection of a reaction pathway with high energy barrier in a multipath on-surface reaction system has been challenging. Herein, we report the successful control of the reaction system of 1,1'-biphenyl-4-bromo-4'-ethynyl (BPBE) on Ag(111), in which three coupling reactions (Glaser, Ullman, Sonogashira) are involved. Either graphdiyne (GDY) or graphyne (GY) nanowires can be formed by distinct kinetic strategies. As the energetically favorable pathway, the formation of a GDY nanowire is achieved by hierarchical activation of Glaser (with lowest energy barrier) and Ullman coupling of BPBE. On the other hand, the formation of a GY nanowire originates from the high selectivity of the high-barrier Sonogashira coupling, whose indispensable kinetic parameters are high surface temperature, low molecular coverage, and low precursor evaporation rate, as derived from a series of control experiments. This work achieves the fabrication of GY nanowires via on-surface Sonogashira coupling for the first time and reveals mechanistic control strategies for potential syntheses of other functional nanostructures via cross-couplings on surfaces.