From closed-shell edge-extended kekulenes to open-shell carbonylated cycloarene diradicaloid

Area of Science:

• Organic Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Cycloarenes, with their fused macrocyclic π-conjugated systems, present synthetic challenges and unique properties.
• Precise synthesis is crucial for exploring their potential in advanced materials.

Purpose of the Study:

• To synthesize novel alkoxyl- and aryl-cosubstituted cycloarenes (kekulene and edge-extended derivatives).
• To investigate the reactivity and structural characteristics of these cycloarenes.
• To explore the formation and properties of a novel carbonylated cycloarene derivative.

Main Methods:

• Convenient synthesis of kekulene and edge-extended kekulene derivatives (K1-K3).
• Bi(OTf)3-catalyzed cyclization reaction with controlled temperature and gas atmosphere.
• Structural confirmation via single-crystal X-ray analysis, NMR spectroscopy, and theoretical calculations.
• Electrochemical analysis using cyclic voltammetry.

Main Results:

• Successfully synthesized and characterized K1-K3 cycloarene derivatives.
• Discovered an unexpected transformation of K3 into a carbonylated derivative (K3-R) under specific reaction conditions.
• Characterized K3-R, revealing remarkable stability, large diradical character, and a small singlet-triplet energy gap.
• Demonstrated K3-R as the first carbonylated cycloarene diradicaloid and a radical-acceptor cycloarene.

Conclusions:

• Developed a controlled synthesis for substituted cycloarenes and a novel carbonylated derivative.
• The unique electronic properties of K3-R open avenues for designing new conjugated macrocyclic diradicaloids and polyradicaloids.
• This work advances the synthesis and understanding of extended kekulene structures and radical-accepting macrocycles.