Unravelling the Mechanism of Glaser Coupling Reaction on Ag(111) and Cu(111) Surfaces: a Case for Halogen Substituted Terminal Alkyne

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The mechanisms of Glaser coupling reaction on metal surfaces have been poorly understood. Herein, we propose a reaction pathway toward surface-confined Glaser coupling which is initiated by single-molecule dehydrogenation of terminal alkyne. This is inspired by our experimental observations of alkynyl–Ag–alkynyl and alkynyl–Cu–alkynyl type organometallic intermediates in the coupling reaction of 1,1′-biphenyl,4-bromo-4′-ethynyl (BPBE) on Ag(111) and Cu(111), respectively. Theoretical calculations reveal that the dehydrogenation process of terminal ethynyl of BPBE is most likely catalyzed by a stray H adatom on Ag(111) but by a Cu adatom on Cu(111), followed by the formation of the organometallic intermediates. After the release of interstitial metal adatoms, the final C–C coupling occurs easily on Ag(111) but shows extremely low efficiency on Cu(111), due to the too strong interaction between ethynylene and the Cu(111) substrate.