Three-Coordinate Boron(III) and Diboron(II) Dications

Area of Science:

• Organometallic Chemistry
• Inorganic Chemistry
• Boron Chemistry

Background:

• Electron-deficient boron species are challenging to stabilize due to their inherent reactivity.
• Low-coordinate boron dications represent a particularly elusive class of compounds.
• Bulky ligands can sterically protect and electronically stabilize reactive metal centers.

Purpose of the Study:

• To exploit the electron-donating capabilities of a bulky bisimino ligand for stabilizing novel boron dication species.
• To synthesize and characterize dicationic mononuclear boron(III) and dinuclear boron(II) complexes.
• To investigate the electronic structure and Lewis acidity of these stabilized boron dications.

Main Methods:

• Synthesis of boron complexes using the bisimino ligand 1,2-(L^Mes N)₂ -C₂ H₄ with PhBBr₂ and (B(Cl)NMe₂ )₂.
• Single crystal X-ray diffraction analysis to determine molecular structures.
• Theoretical computational methods to analyze bonding and charge distribution.
• Hydride transfer reactions to probe Lewis acidity.

Main Results:

• Successful synthesis of a dicationic mononuclear boron(III) complex (4²⁺) and a dicationic dinuclear boron(II) complex (6²⁺).
• X-ray diffraction confirmed the structures of both dicationic complexes.
• Theoretical analysis revealed significant positive charge density delocalization into the ligand system.
• Both dications exhibited Lewis acidity, demonstrated by successful hydride transfer reactions.

Conclusions:

• The bulky bisimino ligand effectively stabilizes highly electron-deficient and low-coordinate boron dications.
• The synthesized boron dications possess unique electronic structures with charge delocalization onto the ligand.
• These findings expand the scope of stable boron compounds and highlight the utility of robust ligands in stabilizing reactive species.