Atropisomerism in Triarylboranes: Lewis Base Assisted Rotation at C-B Stereogenic Axis in Asymmetrical Boron Lewis...

Area of Science:

• Organoboron Chemistry
• Stereochemistry
• Asymmetric Synthesis

Background:

• Atropisomerism in triarylboranes, particularly at the carbon-boron (C-B) bond, remains underexplored.
• Understanding structural requirements for C-B bond atropisomerism is crucial for developing new chiral boron Lewis acids.

Purpose of the Study:

• To report the first series of atropisomeric triarylboranes featuring a naphthyl rotor and a dihydro-9-bora-anthracenyl stator.
• To investigate the mechanisms, rates, and barriers of diastereomerization and enantiomerization in these novel compounds.
• To elucidate the role of Lewis bases in controlling the atropisomeric behavior of triarylboranes.

Main Methods:

• Synthesis of novel atropisomeric triarylborane derivatives.
• Systematic crystallographic, kinetic, and photophysical analyses.
• Quantum chemical calculations to determine reaction mechanisms and energy barriers.

Main Results:

• Successfully synthesized and characterized the first series of atropisomeric triarylboranes with a C-B stereogenic axis.
• Demonstrated high configurational stability due to orthogonal arrangement of bulky substituents, enabling chiral resolution.
• Identified and elucidated a Lewis-base assisted pathway that controls the rotation speed at the C-B axis.

Conclusions:

• The developed triarylboranes exhibit high configurational stability and can be resolved into enantiopure forms.
• The atropisomeric behavior of these boron Lewis acids can be dynamically controlled by external Lewis bases.
• This work provides fundamental insights into C-B bond atropisomerism and offers a new platform for stereoselective catalysis.