Dynamic Four-Membered Rings with 2π Aromaticity

Area of Science:

• Computational chemistry
• Aromaticity studies
• Materials science

Background:

• Achieving structural dynamism in aromatic systems presents significant challenges.
• Previous research has not fully explored the dynamic potential of 2π aromatic compounds.

Purpose of the Study:

• To investigate the structural preferences and dynamic behavior of four-membered rings (4MRs) isoelectronic to cyclobutadiene dication (CBD).
• To explore the impact of isoelectronic replacements and substituents on the dynamism of these 4MRs.

Main Methods:

• Density functional theory (DFT) calculations with CCSD(T) and DLPNO-CCSD(T) energy corrections.
• Investigation of various substituents and their effect on structural dynamism.
• Molecular dynamics simulations at room temperature.

Main Results:

• Several 4MRs with the molecular formula A₂X₂ (A=B, Al, Ga; X=Si, Ge) were identified.
• Si₂Al₂ exhibited the lowest transition barrier for structural changes, with transition state aromaticity significantly influencing dynamism.
• Molecular dynamics confirmed the structural dynamism of these compounds.

Conclusions:

• 2π aromatic compounds can achieve significant structural dynamism.
• The aromaticity of transition states is a critical factor in controlling dynamic behavior.
• Si₂X₂ compounds favor cyclic isomers, while Ge₂X₂ compounds show comparable stability between cyclic and open structures.