Nonorthogonal Dilithium-1,3-biborataallenes Containing Planar-Tetracoordinate Carbon Atoms

Area of Science:

• Organoboron chemistry
• Main group chemistry
• Organic synthesis

Background:

• 1,3-Diborataallenes are a unique class of compounds featuring a boron-containing allene core.
• Understanding their geometric preferences is crucial for predicting reactivity and designing new molecules.
• Previous studies have explored the electronic and structural properties of related systems.

Purpose of the Study:

• To investigate the structural characteristics of tetraaryl-1,3-diborataallenes in contact-ion triples.
• To elucidate the factors influencing the observed geometries of these organoboron compounds.
• To explore the role of steric and electronic interactions in dictating molecular architecture.

Main Methods:

• Synthesis of tetraaryl-1,3-diborataallenes as lithium contact-ion triples.
• Single-crystal X-ray diffraction analysis to determine molecular structures.
• Computational modeling to assess steric and electronic effects.

Main Results:

• Observed significant deviations (up to 36°) from the expected orthogonal geometry of the allene system.
• Identified steric hindrance between ortho-methyl groups on the aryl substituents as a primary cause.
• Demonstrated the influence of lithium counterion interactions with aryl π-electrons on molecular conformation.
• Noted small intrinsic barriers to planarization for the 1,3-diborataallene core.

Conclusions:

• The geometry of tetraaryl-1,3-diborataallenes is significantly influenced by steric and ion-pairing effects.
• These findings provide insights into the conformational flexibility and stability of boron-containing allenes.
• The study highlights the interplay between substituents, counterions, and the core structure in determining molecular shape.