Tris(perfluorotolyl)borane-A Boron Lewis Superacid

Area of Science:

• Organometallic Chemistry
• Fluorine Chemistry
• Boron Chemistry

Background:

• Tris(pentafluorophenyl)borane (BCF) is a well-known strong Lewis acid.
• There is ongoing research to develop even stronger Lewis acidic compounds for various applications.

Purpose of the Study:

• To synthesize and characterize a novel boron-based Lewis acid, Tris[tetrafluoro-4-(trifluoromethyl)phenyl]borane (BTolF).
• To evaluate and compare the Lewis acidity of BTolF with established strong Lewis acids.

Main Methods:

• Synthesis of BTolF via reaction of boron tribromide with a copper(I) reagent derived from Grignard reagent.
• Lewis acidity assessment using the Gutmann-Beckett method.
• Calculation of fluoride-ion affinities.
• Structural determination by gas-phase electron diffraction and single-crystal X-ray diffraction.

Main Results:

• Tris[tetrafluoro-4-(trifluoromethyl)phenyl]borane (BTolF) was successfully synthesized.
• BTolF demonstrated 9-10% higher Lewis acidity than tris(pentafluorophenyl)borane (BCF).
• BTolF's Lewis acidity surpasses that of antimony pentafluoride (SbF5).
• Molecular structures of BTolF and BCF were elucidated.

Conclusions:

• BTolF represents a new class of exceptionally strong Lewis acids.
• The enhanced Lewis acidity of BTolF opens potential avenues for novel catalytic applications.
• Structural data provides insights into the electronic and steric factors governing Lewis acidity in these compounds.