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

The incorporation of ${\mathrm{sp}}^3$ -hybridized carbon centers into planar ${\mathrm{sp}}^2$ 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 ${\mathrm{sp}}^2$ 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 ${\mathrm{sp}}^3$ centers into hybrid ${\mathrm{sp}}^3$ ─ ${\mathrm{sp}}^2$ carbon nanostructures, expanding the synthetic toolbox of on-surface chemistry.