Identifying Multinuclear Organometallic Intermediates in On-Surface [2+2] Cycloaddition Reactions.

Area of Science:

• Surface science
• Materials chemistry
• Organic synthesis

Background:

• On-surface reactions offer precise control over molecular assembly and material fabrication.
• Triphenylene derivatives are versatile building blocks for advanced materials.
• Understanding metal-surface interactions is crucial for designing catalytic and self-assembly processes.

Purpose of the Study:

• To investigate the on-surface [2+2] cycloaddition reaction of 2,3,6,7,10,11-hexabromotriphenylene (HBTP).
• To explore the influence of different metal surfaces (Ag(111), Cu(111), Au(111), and Cu-dosed Au(111)) on HBTP reactivity.
• To elucidate the role of organometallic intermediates in directing reaction pathways.

Main Methods:

• Scanning tunneling microscopy (STM) for real-space imaging of surface structures.
• Density functional theory (DFT) simulations for theoretical analysis of reaction mechanisms.
• Controlled thermal treatments to induce and study surface reactions.

Main Results:

• On Ag(111), HBTP forms an organo-silver framework that converts to porous covalent networks via [2+2] cycloaddition above 240°C.
• On Cu(111), a stable organo-copper framework forms, resistant to [2+2] cycloaddition even at 300°C.
• On Au(111), no organo-gold intermediates were observed; however, Cu-dosed Au(111) facilitated [2+2] cycloaddition of partially debrominated HBTP at 140°C.

Conclusions:

• The metal substrate plays a critical role in determining the outcome of the on-surface [2+2] cycloaddition of HBTP.
• Surface-mediated debromination and subsequent framework formation influence the reaction pathway.
• Tailoring surface composition and structure allows for control over the formation of covalent networks and organometallic structures.