Electron-Deficient Triborane and Tetraborane Ring Compounds: Synthesis, Structure, and Bonding

Area of Science:

• Inorganic Chemistry
• Materials Science
• Computational Chemistry

Background:

• Electron-deficient boron rings (B3, B4) feature unique delocalized electron systems, avoiding classical two-center-two-electron bonds.
• These boron rings demonstrate tolerance to various skeletal electron numbers, leading to interesting redox chemistry.
• Despite synthesis of stable B3 and B4 compounds, their chemistry remains underdeveloped, primarily limited to protonation and redox reactions.

Purpose of the Study:

• To review experimental and theoretical findings on electron-deficient boron rings.
• To establish a foundation for exploring the chemistry of these unique boron ring systems.
• To guide the integration of B3 and B4 rings into larger molecular architectures for novel materials.

Main Methods:

• Quantum-chemical calculations were employed to evaluate electronic structures.
• Literature review of experimental and theoretical results on B3 and B4 boron rings.
• Analysis of redox chemistry and electronic properties of synthesized boron compounds.

Main Results:

• Stable compounds with B3 and B4 cores and diverse electron counts have been synthesized.
• Unique σ- and π-delocalized electron systems and avoidance of classical bonds confirmed.
• Quantum-chemical calculations elucidated the electronic structures of these boron rings.

Conclusions:

• The unique electronic and redox properties of electron-deficient boron rings are highlighted.
• Linking multiple B3 and/or B4 rings is proposed for creating novel boron-based materials.
• This review provides a basis for future exploration of boron ring chemistry and materials integration.