Sulfur-driven switching of the Ullmann coupling on Au(111)

Area of Science:

• Surface Chemistry
• Heterogeneous Catalysis
• Organometallic Chemistry

Background:

• The Ullmann coupling reaction is crucial for forming carbon-carbon bonds.
• Controlling surface reactions on metal catalysts like gold (Au) is essential for designing new materials and processes.
• Understanding catalyst deactivation and reactivation mechanisms is key to improving catalytic efficiency.

Purpose of the Study:

• To demonstrate a method for selectively switching the Ullmann coupling reaction of 2,8-dibromodibenzothiophene on a Au(111) surface.
• To investigate the effect of sulfur (S) and hydrogen (H2) on the reactivity of the Au(111) surface in Ullmann coupling reactions.
• To elucidate the mechanism behind the inhibition and reactivation of the Ullmann coupling on sulfur-modified Au(111).

Main Methods:

• Utilizing scanning tunneling microscopy (STM) to observe surface reactions at the atomic level.
• Performing Ullmann coupling reactions on a Au(111) single crystal surface.
• Exposing the Au(111) surface to hydrogen sulfide (H2S) to induce sulfur passivation.
• Treating the sulfur-passivated surface with hydrogen gas (H2) to remove sulfur.

Main Results:

• The Ullmann coupling reaction of 2,8-dibromodibenzothiophene proceeds effectively on the clean Au(111) surface, even at low temperatures.
• Pre-exposure of Au(111) to H2S completely inhibits the Ullmann coupling reaction.
• Sulfur passivation of active gold sites, particularly those emerging from reconstruction sites, is responsible for the reaction inhibition.
• Post-exposure to H2 gas effectively removes the adsorbed sulfur, fully restoring the catalytic activity of the Au(111) surface.

Conclusions:

• Selective switching of the Ullmann coupling reaction on Au(111) is achievable through controlled surface modification.
• Sulfur acts as a reversible inhibitor for the Ullmann coupling on Au(111) by passivating active sites.
• This study provides a pathway for precise control over surface-catalyzed reactions, with implications for catalyst design and surface science.