arylboron

Arylboron refers to organoboron compounds in which a boron atom is bound to an aryl group. This class includes boronic acids (ArB(OH)2), boronate esters (ArB(OR)2, such as ArBpin with pinacol), and related derivatives such as aryltrifluoroborates (ArBF3K). Arylboron reagents are valued in organic synthesis for their versatility in forming carbon–carbon bonds and as intermediates in cross-coupling reactions.

In these compounds, the carbon–boron bond is covalent and the boron center is typically three-coordinate and sp2-hybridized. Boronic acids feature boron bonded to two hydroxyl groups, while boronate esters replace those OH groups with diol ligands (e.g., pinacol), which generally increases stability and handling. Arylboron species can participate in a range of transformations, with stability and reactivity influenced by the boron substituents.

Two principal methods are used to prepare arylboron reagents. Miyaura borylation converts aryl halides into arylboronates (Ar–BPin) using bis(pinacolato)diboron and a palladium catalyst. Iridium-catalyzed C–H borylation directly converts arenes into arylboronates (Ar–BPin) by installing the BPin group onto an arene C–H bond. These routes provide access to versatile Ar–B reagents from readily available arenes or halides.

The most prominent application is the Suzuki–Miyaura cross-coupling, where an arylboron reagent couples with an aryl or vinyl halide to form biaryl or substituted alkenyl products. Other uses include transesterification to form different boronate esters, oxidation to phenols or alcohols, and use as building blocks in medicinal chemistry and materials science. Prominent examples are phenylboronic acid and phenylboronate esters.