Aromaticity in Fully π-Conjugated Open-Cage Molecules.

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Aromaticity in 2D π-conjugated systems is well-established.
• Aromaticity in 3D π-conjugated molecular cages remains underexplored due to synthetic difficulties.
• Triphenylamine derivatives are key building blocks in π-conjugated materials.

Purpose of the Study:

• To report the facile synthesis of a novel 3D π-conjugated molecular cage.
• To investigate the aromaticity and electronic properties of the cage and its oxidized derivatives.
• To compare the aromaticity of the cage with related macrocyclic trimers.

Main Methods:

• Platinum-mediated assembly of a pinacol borate trisubstituted dimethylmethylene-bridged triphenylamine (DTPA) derivative.
• Reductive elimination to form the π-conjugated molecular cage.
• Oxidation of the cage and model compounds, followed by experimental measurements and theoretical calculations (e.g., DFT).

Main Results:

• A π-conjugated molecular cage (1) with an open-cage structure was successfully synthesized.
• Neutral cage 1 exhibits localized aromaticity in its benzene rings.
• Dication 1^2+ shows bicyclic (anti)aromaticity with both aromatic (38π) and antiaromatic (28π) macrocycles.
• Tetracation 1^4+ displays dominant 2D Hückel antiaromaticity (36π) in one macrocycle.
• Model compounds 2 and 3 show global antiaromatic and nonaromatic properties, respectively, in their dicationic forms.
• Several oxidized species exhibit open-shell singlet ground states with diradical character, while one adopts a triplet ground state.

Conclusions:

• The study presents a facile synthetic route to a 3D π-conjugated molecular cage.
• The cage and its derivatives demonstrate complex 2D and 3D aromaticity and antiaromaticity.
• This work expands the understanding of aromaticity in three-dimensional π-conjugated systems.