Taming the beast: fluoromesityl groups induce a dramatic stability enhancement in boroles

Area of Science:

• Organic Chemistry
• Materials Science
• Photochemistry

Background:

• Boroles are electron-deficient compounds with potential in optoelectronics.
• Previous borole analogues suffered from poor air and thermal stability, limiting their applications.
• Understanding substituent effects on borole stability is key for material development.

Purpose of the Study:

• To synthesize novel, air-stable electron-deficient pentaarylboroles for optoelectronic applications.
• To investigate the influence of bulky aryl groups and ring substituents on borole stability and properties.
• To explore the Lewis acid-base chemistry and electronic characteristics of these new borole compounds.

Main Methods:

• Synthesis of pentaarylborole 1 (using FMes group) and a novel triarylborole 2 (with a bridging -(CH2)3- group).
• Utilized a new general method involving Li[FMesBF3] and divinyldilithium reagents.
• Characterized stability (air, thermal, isomerization) and electronic properties (reduction potentials, UV-Vis absorption).

Main Results:

• Pentaarylborole 1 exhibits significantly enhanced air stability (>600 times) and good thermal stability due to the bulky FMes group.
• Borole 2 showed isomerization under basic conditions, highlighting the impact of ring substituents.
• Both compounds demonstrated reversible Lewis base binding (e.g., pyridine) and strong electron-accepting abilities (low reduction potentials).
• Compound 1 displayed a blue-shifted absorption spectrum, contrary to existing theories.

Conclusions:

• The incorporation of a bulky FMes group dramatically improves borole air and thermal stability without compromising electron-accepting capabilities.
• These stable boroles are promising candidates for developing next-generation optoelectronic materials.
• The study provides new insights into structure-stability relationships in borole chemistry.