Zirconacyclopentadiene-Annulated Polycyclic Aromatic Hydrocarbons

Area of Science:

• Organic Chemistry
• Materials Science

Background:

• Synthesizing large polycyclic aromatic hydrocarbons (PAHs) and graphene nanostructures requires efficient methods for fusing numerous aromatic rings, but such techniques are limited.
• Existing methods often lack selectivity and efficiency in creating complex, fused aromatic systems.

Purpose of the Study:

• To introduce a novel and efficient method for the synthesis of large PAHs and graphene nanostructures.
• To demonstrate the capability of this new method in constructing complex PAH topologies through selective ring fusion.

Main Methods:

• Employing quantitative intramolecular reductive cyclization of oligo(diyne) precursors using a low-valent zirconocene reagent.
• Utilizing the resulting zirconacyclopentadiene (ZrPAH) intermediates for further structural elaboration and characterization.

Main Results:

• Achieved a high-yielding fivefold intramolecular coupling, forming a helical ZrPAH with 16 fused rings from a precursor with no fused rings.
• Successfully synthesized various other complex PAH topologies.
• Isolated and characterized PAHs with appended ortho-quinodimethane (o-QDM) structures via protodemetalation of ZrPAHs, revealing their potential for further reactions.

Conclusions:

• The reported zirconocene-mediated reductive cyclization offers a powerful and efficient strategy for constructing large, complex polycyclic aromatic hydrocarbons and graphene nanostructures.
• The ability to isolate reactive intermediates like o-QDM-appended PAHs opens new avenues for Diels-Alder reactions and the synthesis of even more elaborate molecular architectures.