On-Surface Directional C–H Activation of Terminal Alkynes via Intermolecular Radical Transfer

On-surface synthesis of tailored low-dimensional carbon nanomaterials, such as graphdiyne and its derivatives, demands efficient and selective activation of the C(<i>sp</i>)-H bond in terminal alkynes. Recent strategies have shown great promise in the facilitation of C-H activation based on the introduction of extrinsic components, typically like metal atoms, oxygen, and alkynyl halides. However, in these processes, the reaction priority and selectivity of terminal alkynes remain elusive, while the latter case also suffered from released halogen byproducts as well as competing phenyl-phenyl coupling reactions. Herein, we report a directional C-H activation strategy on Ag(111) via intermolecular radical transfer between terminal alkynes and further unravel reaction priority and selectivity of terminal alkynes. By combining scanning tunneling microscopy (STM) imaging with density functional theory (DFT) calculations, we demonstrate that radicals transfer selectively from molecules with a higher radical population to those with a lower one, which was revealed to be driven by their intrinsic reactivity. Our work establishes a fundamental principle for regulating on-surface radical reactions and provides a promising pathway toward the precise construction of diyne-based nanostructures.