An ab initio insight into the Cu(111)-mediated Ullmann reaction

Area of Science:

• Surface Science
• Computational Chemistry
• Catalysis

Background:

• Phenyl radicals are key intermediates in the Ullmann reaction.
• Understanding radical coupling on metal surfaces is crucial for catalysis and molecular self-assembly.
• Copper (Cu)(111) is a model surface for studying such interactions.

Purpose of the Study:

• To investigate the coupling mechanism of phenyl radicals on the Cu(111) surface.
• To elucidate the role of surface diffusion and electronic effects in the reaction.
• To provide insights applicable to broader surface chemistry phenomena.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Simulations explored potential energy surfaces and reaction pathways.
• Analysis focused on intermediate states and transition barriers.

Main Results:

• Attractive interactions between phenyl radicals were observed even at large distances.
• A novel intermediate state involving a "popping-out" surface Cu atom was identified.
• The coupling to biphenyl is governed by electronic mechanisms involving frontier orbitals and the Fermi level, with a calculated barrier of 0.38 eV.

Conclusions:

• The phenyl radical coupling on Cu(111) follows a complex pathway involving surface diffusion and electronic interactions.
• The findings align with experimental observations and Hoffmann's frontier orbital concepts.
• This study offers a mechanistic understanding relevant to molecular self-assembly and surface-catalyzed reactions.