Adaptive Aromaticity in 18e Metallapentalenes

Area of Science:

• Inorganic Chemistry
• Theoretical Chemistry
• Quantum Chemistry

Background:

• Adaptive aromaticity, where a molecule exhibits aromaticity in both singlet (S₀) and triplet (T₁) electronic states, is rare.
• Traditional aromaticity rules (Hückel's and Baird's) often predict aromaticity in only one electronic state.
• Previous studies primarily focused on 16-electron metallapentalenes for adaptive aromaticity.

Purpose of the Study:

• To investigate the potential of 18-electron metallapentalenes to exhibit adaptive aromaticity.
• To explore the role of specific ligands in achieving adaptive aromaticity in metallapentalenes.
• To understand the electronic factors governing aromaticity in different electronic states.

Main Methods:

• Density functional theory (DFT) calculations were employed to study model systems.
• A set of aromaticity indices were used to evaluate aromatic character.
• Analysis of metal-carbon bond strength and spin electron localization was performed.

Main Results:

• 18-electron metallapentalenes with nitrido and imido ligands demonstrate adaptive aromaticity.
• Metal-carbon bond strength influences aromaticity in the S₀ state.
• Spin electron localization is key to achieving aromaticity in the T₁ state.

Conclusions:

• The introduction of nitrido and imido ligands enables adaptive aromaticity in 18-electron metallapentalenes.
• This work expands the scope of known compounds exhibiting adaptive aromaticity.
• Findings provide valuable insights for designing novel metallaaromatic compounds.