Stable Antiaromatic [16]Triphyrin(2.1.1) with Core Modification: Synthesis Using a 16π Electrocyclic Reaction

Area of Science:

• * Organic Chemistry
• * Supramolecular Chemistry
• * Materials Science

Background:

• * Antiaromatic porphyrinoids possess unique electronic properties but are challenging to synthesize due to instability.
• * Contracted porphyrinoids with smaller ring sizes are particularly difficult to stabilize.
• * Developing stable antiaromatic systems is crucial for exploring their potential applications.

Purpose of the Study:

• * To report the synthesis and characterization of the first stable antiaromatic contracted porphyrinoid, trioxa[16]triphyrin(2.1.1).
• * To investigate the electronic properties and structural features of this novel compound.
• * To demonstrate the antiaromaticity-aromaticity switching capability of the synthesized system.

Main Methods:

• * Employed a core modification strategy to stabilize the [16]triphyrin(2.1.1) framework.
• * Utilized X-ray crystallography for structural analysis.
• * Conducted electrochemical and chemical oxidation studies to probe electronic properties and reactivity.

Main Results:

• * Successfully synthesized and characterized the stable trioxa[16]triphyrin(2.1.1), a novel 16π antiaromatic contracted porphyrinoid.
• * X-ray crystallography confirmed a nearly planar molecular structure.
• * Electrochemical studies revealed reversible oxidation and a small HOMO-LUMO gap, consistent with antiaromaticity.
• * Chemical oxidation led to an aromatic [14]triphyrin(2.1.1) dication, demonstrating tunable antiaromaticity-aromaticity switching.
• * Identified a key intermediate, dihydrotrioxatriphyrin(2.1.1), formed via a rare 16π electrocyclic reaction.

Conclusions:

• * The core modification approach enables the rational design of stable antiaromatic contracted porphyrinoids.
• * Trioxa[16]triphyrin(2.1.1) exhibits tunable electronic properties and antiaromaticity-aromaticity switching.
• * The discovery of the 16π electrocyclic reaction deepens the understanding of pericyclic reactions.
• * This work provides a foundation for developing novel macrocyclic compounds with tailored properties.