Boron-Boron One-Electron Sigma Bonds versus B-X-B Bridged Structures

Area of Science:

• Inorganic Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• The concept of one-electron B-B sigma bonds is frequently invoked in chemical literature.
• Understanding the precise nature of these bonds is crucial for predicting molecular stability and reactivity.

Purpose of the Study:

• To investigate the existence and characteristics of one-electron B-B sigma bonds in different chemical systems.
• To analyze the factors influencing the formation and strength of these bonds.

Main Methods:

• Electron density analysis using Quantum Theory of Atoms in Molecules (QTAIM), Electron Localisation Function (ELF), Non-Covalent Interaction Plot (NCIPLOT), and Natural Bond Orbital (NBO) approaches.
• Theoretical investigation of [B2X6](-) radical anions and 1,8-disubstituted naphthalene derivatives.

Main Results:

• One-electron B-B sigma bonds are confirmed in [B2X6](-) radical anions, with bond strength increasing with substituent electronegativity.
• In 1,8-disubstituted naphthalene derivatives, two types of structures were observed: those with B-B sigma bonds and those with B-X-B bridges.
• The presence of phenyl groups on boron atoms prevents the formation of B-B sigma bonds due to electron delocalization.

Conclusions:

• The generic label 'one-electron sigma bond' oversimplifies the diverse bonding situations in boron compounds.
• Boron chemistry offers unique systems analogous to proton sponges, capable of stabilizing electrons.
• Computational methods are essential for accurately characterizing novel bonding phenomena in inorganic molecules.