Steering Surface Reaction Dynamics with a Self-Assembly Strategy: Ullmann Coupling on Metal Surfaces

Area of Science:

• Surface science
• Chemical kinetics
• Materials chemistry

Background:

• The Ullmann coupling reaction is crucial for forming carbon-carbon bonds.
• Understanding surface-mediated reactions is key to designing efficient catalytic processes.
• Organometallic intermediate formation significantly impacts reaction outcomes.

Purpose of the Study:

• To investigate the role of organometallic intermediate formation in the Ullmann coupling of 4-bromobiphenyl on Ag(111), Cu(111), and Cu(100) surfaces.
• To elucidate how surface structure and intermediate self-assembly influence reaction pathways and dynamics.
• To demonstrate the potential of self-assembly strategies in controlling surface reactions.

Main Methods:

• Scanning tunneling microscopy (STM) for in-situ surface analysis.
• Theoretical calculations to complement experimental observations.
• Thermal catalysis on Ag(111), Cu(111), and Cu(100) metal surfaces.

Main Results:

• Initial formation of organometallic intermediates occurs as self-assembled or sparsely dispersed species.
• Self-assembled intermediates at full coverage lead to a direct, single-barrier coupling pathway.
• Sparsely dispersed intermediates at low coverage follow a double-barrier pathway via novel clover-shaped intermediates.
• Surface structure and intermediate arrangement critically determine the reaction mechanism.

Conclusions:

• Surface self-assembly of organometallic intermediates is a key factor controlling Ullmann coupling reaction pathways.
• The arrangement of intermediates (self-assembled vs. dispersed) dictates whether a single or double barrier process occurs.
• Self-assembly offers a powerful strategy to steer surface reaction dynamics and product formation.