Formation of Organometallic Intermediate States in On‐Surface Ullmann Couplings

TLDR

The study investigates possible origins of organometallic intermediate formation in on‑surface Ullmann couplings using STM and DFT. The authors model iodobenzenes on Cu, Ag, and Au surfaces, employing ab initio molecular dynamics and climbing‑image nudged elastic band DFT to show that metal atoms can be extracted from the surface to form organometallic species. Experimental STM shows surface vacancies and metal adatoms, and computational results reveal that metal atoms can be extracted from the surface to form organometallic intermediates, while thermally activated adatom formation is energetically unfavorable.

Abstract

Abstract Possible origins of the formation of organometallic intermediates in on‐surface Ullmann couplings have been investigated by surface tunneling microscopy (STM) and density functional theory (DFT) calculations. We consider the case of iodobenzenes on the coinage metals copper, silver, and gold. We found experimental evidence for the formation of surface vacancies and the presence of metal adatoms in these coupling reactions, which are taken as a hint for the reactive extraction of surface atoms by adsorbates. In a second step, we demonstrate by ab initio molecular dynamics calculations for aryl–iodides on copper that metal atoms can be pulled out of the surface to form metal‐organic species. By contrast, a thermally activated provision of a metal atom from the surface to form an adatom is energetically unfavorable. Finally, we investigate the mechanism and energetics of the reactive extraction of surface metal atoms by means of (climbing‐image) nudged elastic band density‐functional theory calculations for iodobenzene on copper, silver, and gold, and analyze our results in the light of the experimental findings.