Reaction Selectivity in On‐Surface Chemistry by Surface Coverage Control—Alkyne Dimerization versus Alkyne Trimerization

This work reports the influence of molecular coverage in on‐surface C−C‐bond formation on reaction outcome. 6‐Ethynyl‐2‐naphthoic acid (ENA) was chosen as organic component and Ag(111) as substrate. The alkyne moiety in ENA can either react by dimerization to ENA dimers (Glaser coupling or hydroalkynylation) or cyclotrimerization to generate a benzene core as connecting moiety. Dimer formation is preferred at high surface coverage whereas trimerization is the major reaction pathway at low coverage. Mechanistic studies are provided. Coverage matters! This communication reports reaction control in on‐surface chemistry as a function of surface coverage. 6‐Ethynyl‐2‐naphthoic acid (ENA) reacts either by alkyne dimerization (hydroalkynylation/alkyne homocoupling) or through alkyne trimerization on Ag(111). It is shown that at high surface coverage dimers are formed in 71% selectivity, whereas at low coverage trimerization is the favored reaction pathway (79%).