On-Surface Friedel-Crafts Alkylation Through a Stabilized Intermediate Complex.

The incorporation of sp 3 -hybridized carbon centers into planar sp 2 carbon nanostructures is a powerful strategy in solution chemistry for tuning their electronic and structural properties. While on-surface synthesis has demonstrated efficient coupling strategies for sp 2 systems, C s p 3 ─ C s p 2 bond formation on surfaces remains largely unexplored. Here, we report the on-surface analogue of Friedel-Crafts alkylation on a metal surface: an intramolecular C s p 3 ─ C s p 2 coupling reaction based on a specifically designed fluorinated aromatic reactant, with the metal surface itself acting as catalyst. Our reactant-catalyst design stabilizes the key intermediate; allowing for direct real-space imaging at the single-molecule level. By integrating high-resolution scanning tunneling microscopy, x-ray photoelectron spectroscopy, and first-principles computations, we elucidate each elementary step of the on-surface Friedel-Crafts alkylation pathway. These results open a new route toward the controlled integration of sp 3 centers into hybrid sp 3 ─ sp 2 carbon nanostructures, expanding the synthetic toolbox of on-surface chemistry.