Figure-eight Octaphyrin Bis-Ge(IV) Complexes: Synthesis, Structures, Aromaticity, and Chiroptical Properties

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Materials Science

Background:

• Highly twisted structures in expanded porphyrins are key to understanding aromaticity and chirality.
• The figure-eight scaffold offers a unique platform for exploring structure-property relationships.

Purpose of the Study:

• To synthesize and characterize bis-Ge(IV) complexes of [38]octaphyrin with figure-eight structures.
• To investigate the relationship between aromaticity, chirality, and chiroptical properties in these complexes.
• To explore the potential of the octaphyrin scaffold for developing novel chiroptical materials.

Main Methods:

• Synthesis of bis-Ge(IV) complexes of [38]octaphyrin.
• Oxidation of [38]octaphyrin complexes to [36]octaphyrin using MnO2.
• Separation of enantiomers using High-Performance Liquid Chromatography (HPLC) with a chiral stationary phase.
• Spectroscopic analysis, including circular dichroism (CD).

Main Results:

• Two isomers of aromatic bis-Ge(IV) [38]octaphyrin with figure-eight structures were synthesized.
• Oxidation yielded a single syn-type isomer of [36]octaphyrin, retaining the figure-eight conformation.
• Enantiomers were successfully separated by chiral HPLC.
• Aromatic [38]octaphyrin complexes exhibited large molar circular dichroism (Δϵ=1500 M⁻¹ cm⁻¹), while weakly antiaromatic [36]octaphyrin complexes showed moderate values (Δϵ=540 M⁻¹ cm⁻¹).

Conclusions:

• The figure-eight octaphyrin scaffold is a versatile platform for creating novel chiroptical materials.
• Tunable aromaticity in these systems influences their chiroptical response.
• The study establishes a link between the molecular structure, aromaticity, and chiroptical properties of expanded porphyrins.