Synthesis, crystal structure, solid-state optical property and C–H activation of sp3 carbon of highly-stable 1-(2′,6′-dimesitylphenyl)-2,3,4,5-tetraphenylborole

Abstract

Terphenyl-substituted borole was prepared through the nucleophilic substitution reaction with chloroborole derivative and terphenyl lithium. From recrystallization, two types of pseudo polymorphs as co-crystals with benzene and hexane were obtained. Owing to the extremely high durability of the crystalline sample in open air, not only X-ray crystallography but also optical measurements in the solid state can be executed. From structural analyses, it was proposed that strong electronic intramolecular interaction should be involved, compared to other boroles. Indeed, from the optical measurements, borole has absorption even in the near-infrared (NIR) region, suggesting that this stronger interaction should be inducible to large degree of stabilization of the electronic conjugation, followed by a significant redshift in the absorption band. Moreover, contrary to high durability in the solid state, degradation rapidly proceeds in the solution state. From the characterization of decomposition compounds, an unexpected ring-fused molecule was obtained, indicating that unique C–H bond activation at the sp³ carbon occurs. These data propose that our molecule should be versatile for designing a novel C–H activation reaction as well as obtaining advanced optoelectronic organic devices based on the unique electronic properties of borole.