meso-Triaryl-Substituted Smaragdyrins: Facile Aromaticity Switching

Area of Science:

• Organic Chemistry
• Macrocyclic Chemistry
• Synthetic Chemistry

Background:

• All-aza smaragdyrin represents a historically significant but previously unobtained pentapyrrolic macrocycle.
• The synthesis and characterization of such complex macrocycles are crucial for advancing organic chemistry.
• Understanding the electronic properties of macrocycles informs their potential applications.

Purpose of the Study:

• To achieve the first-time synthesis and full characterization of all-aza smaragdyrin.
• To explore the chemical reactivity and electronic properties of the synthesized macrocycle.
• To investigate the interconversion between different electronic states (aromatic and antiaromatic) and metal complexation.

Main Methods:

• Synthesis via a 2-fold S_NAr reaction involving dipyrrin and tripyrrane precursors.
• Acid treatment to yield the antiaromatic [20]smaragdyrin.
• Reduction using sodium borohydride (NaBH₄) under inert conditions to obtain the aromatic [22]smaragdyrin.
• Oxidation and reduction cycles to interconvert between different π-electron systems.
• Metal complexation using copper(II) chloride (CuCl₂).

Main Results:

• Successful synthesis and characterization of all-aza smaragdyrin.
• Demonstration of the stable antiaromatic nature of [20]smaragdyrin.
• Isolation of the aromatic [22]smaragdyrin congener, which is sensitive to air oxidation.
• Interconversion between 22π and 20π electron systems was achieved through redox reactions.
• Synthesis of a hetero bimetal complex.

Conclusions:

• The first synthetic route to all-aza smaragdyrin has been established.
• The study provides insights into the stability and electronic properties of aromatic and antiaromatic macrocycles.
• The findings open avenues for further exploration of functionalized smaragdyrins and their metal complexes.