Head‐to‐Tail Oligomerization by Silylene‐Tethered Sonogashira Coupling on Ag(111)

On‐surface synthesis is a powerful method for the fabrication of π‐conjugated nanomaterials. Herein, we demonstrate chemoselective Sonogashira coupling between (trimethylsilyl)ethynyl and chlorophenyl groups in silylethynyl‐ and chloro‐substituted partially fluorinated phenylene ethynylenes (SiCPFPEs) on Ag(111). The desilylative Sonogashira coupling occurred with high chemoselectivity up to 75 %, while the competing Ullmann and desilylative Glaser homocoupling reactions were suppressed. A combination of bond‐resolved scanning tunneling microscopy/atomic force microscopy (STM/AFM) and DFT calculations revealed that the oligomers were obtained by the formation of intermolecular silylene tethers (‐Me2Si‐) through CH3−Si bond activation at 130 °C and subsequent elimination of the tethers at an elevated temperature of 200 °C. A coupling module composed of (trimethylsilyl)ethynyl and chlorophenyl groups selectively accelerated sluggish desilylative on‐surface Sonogashira coupling with homocoupling efficiently suppressed. Bond‐resolved scanning tunneling microscopy/atomic force microscopy (STM/AFM) with a CO‐functionalized tip enabled investigation of this coupling reaction and evaluation of its chemoselectivity (see picture).