Phenylboronate

Phenylboronate refers to boron-containing organic compounds bearing a phenyl substituent on boron, typically in a boronate form with three hydroxyl-related groups. In common usage it describes the conjugate base of phenylboronic acid, PhB(OH)3−, formed when phenylboronic acid loses a proton under basic conditions: PhB(OH)2 + OH− ⇌ PhB(OH)3−. The neutral form, phenylboronic acid, has the structure PhB(OH)2 and acts as a Lewis acid that forms cyclic boronate esters with cis-diols.

In aqueous solution, the boron center can shift between a planar, sp2-hybridized form in the neutral acid and a tetrahedral boronate form upon deprotonation or ester formation. Phenylboronates readily form esters with diols, a property exploited in sensing, saccharide recognition, and materials chemistry where boronate-diol linkages enable reversible crosslinking.

Applications in organic synthesis are prominent, especially in Suzuki–Miyaura cross-coupling reactions. Arylboron reagents, including phenylboronates and protected derivatives, serve as versatile partners for transmetalation with palladium catalysts to form new carbon–carbon bonds.

Preparation methods include hydroboration of phenylacetylene followed by oxidation to yield phenylboronic acids, which can equilibrate to boronate forms, and direct palladium- or copper-catalyzed borylation of arenes. Phenylboronates are widely used as building blocks in medicinal chemistry, materials science, and catalysis, with handling typically requiring moisture control and standard safety practices for boron-containing compounds.

See also boronic acid, boronate, Suzuki coupling.