Bottom-Up Approach for the Synthesis of Contorted Nanographenes by Cp*Co(III)-Catalyzed...

Area of Science:

• Organic Chemistry
• Catalysis
• Materials Science

Background:

• Bottom-up synthesis of polycyclic aromatic hydrocarbons (PAHs) is essential for materials science.
• Regioselective fusion of aromatic moieties onto arene templates is an underexplored synthetic challenge.
• Developing efficient strategies for constructing complex PAHs with unique architectures is crucial.

Purpose of the Study:

• To develop an unprecedented bottom-up strategy for the rapid construction of polycyclic aromatic hydrocarbons (PAHs).
• To explore the regioselective fusion of aromatic moieties using arene-derived ketones and carbon-rich 1,3-diynes.
• To investigate the influence of electronic properties of 1,3-diynes on the cyclization mode and resulting PAH topology.

Main Methods:

• Annulative-π-extension-cyclization cascade reaction.
• First-row Cobalt(III)-catalysis.
• Synthesis and characterization of PAHs, including single-crystal X-ray analysis.
• Density Functional Theory (DFT) studies for mechanistic elucidation and electronic structure analysis (NICS(1)_zz, ACID).

Main Results:

• A novel strategy for rapid PAH synthesis was established using arene-derived ketones and 1,3-diynes.
• Synthesized PAHs exhibit unique, often tilted π-electronic structures, edges, and topologies.
• The electronic nature of 1,3-diynes dictates cyclization pathways, yielding fluorene or phenanthrene moieties via 5-exo-dig or 6-endo-dig cyclizations, respectively.
• Intermediate ethynyl-PAHs were observed with electron-deficient diynes.
• DFT calculations and experimental data confirmed the proposed mechanism and regioselectivity.

Conclusions:

• The developed Co(III)-catalyzed cascade reaction provides an efficient route to diverse PAHs.
• The study highlights the control over PAH topology through the electronic tuning of diyne substrates.
• The synthesized PAHs possess unique structural and electronic properties, with fluorene moieties showing less aromatic character than phenanthrene nuclei.