An unexpected organometallic intermediate in surface-confined Ullmann coupling.

Area of Science:

• Surface science
• Materials chemistry
• Organic synthesis

Background:

• Ullmann coupling is crucial for synthesizing polymers on metal surfaces.
• It typically involves dehalogenation followed by C-C coupling.
• The intermediate organometallic (OM) phase dictates polymer topology.

Purpose of the Study:

• To investigate intermediate phases during poly(para-phenylene) synthesis on Cu(110).
• To explore the formation of novel intermediate structures beyond the known linear OM phase.

Main Methods:

• Utilized X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM).
• Employed near-edge X-ray absorption fine structure (NEXAFS) spectroscopy.
• Performed density functional theory (DFT) calculations for modeling.

Main Results:

• Identified two distinct organometallic (OM) phases during Ullmann coupling.
• Observed a phase reorganization to a 2D 'chessboard-like' OM structure.
• The 2D-OM phase is stabilized by Cu clusters and persists upon cooling.

Conclusions:

• On-surface synthesis mechanisms are more complex than previously understood.
• A novel 2D-OM intermediate phase expands knowledge of Ullmann coupling.
• This discovery offers new insights into controlling polymer topology in surface-confined reactions.