N-Heterocyclic olefin stabilized boron dication.

Area of Science:

• Organometallic chemistry
• Boron chemistry
• N-heterocyclic carbene chemistry

Background:

• Boron cations are important Lewis acids in various chemical transformations.
• N-heterocyclic olefins (NHOs) are versatile ligands in organometallic chemistry.
• Pentamethylcyclopentadienyl (Cp*) is a common stabilizing ligand in organometallic chemistry.

Purpose of the Study:

• To synthesize and structurally characterize novel boron mono- and di-cations incorporating NHO ligands.
• To investigate the influence of NHO ligands on the Lewis acidity of boron cations.
• To compare the Lewis acidity of boron dications with different NHO substituents.

Main Methods:

• Synthesis of boron dications featuring NHO and Cp* ligands.
• Single-crystal X-ray diffraction for structural characterization.
• Density Functional Theory (DFT) calculations to probe electronic structure and Lewis acidity.

Main Results:

• Successful preparation and structural elucidation of [η(5)-Cp*B-NHO](2+) and [η(5)-Cp*B-IMes](2+).
• Experimental and theoretical data indicate that [η(5)-Cp*B-NHO](2+) is significantly more Lewis acidic than [η(5)-Cp*B-IMes](2+).
• The increased Lewis acidity of [η(5)-Cp*B-NHO](2+) is attributed to the steric congestion imposed by the bent NHO ligand geometry.

Conclusions:

• Novel boron dications with NHO ligands have been successfully synthesized and characterized.
• The Lewis acidity of these boron dications can be tuned by the steric and electronic properties of the NHO ligand.
• The findings provide insights into the design of Lewis acidic boron compounds for catalytic applications.