Organoborane

Organoboranes are organoboron compounds that contain carbon–boron bonds. They form a broad class that includes simple alkylboranes such as trialkylboranes (R3B), dialkylboranes (RB2H), and alkylboranes (RBH2), as well as boron derivatives such as boronic esters (RB(OR')2) and boronic acids (RB(OH)2). The boron center is typically electron-deficient, often trigonal or nearly planar, and many organoboranes are moisture- or air-sensitive.

Preparation and sources: The most common route is hydroboration of alkenes or alkynes using borane reagents such as borane–tetrahydrofuran complex (BH3·THF), B2H6, or specialized partners like 9-BBN, catecholborane, and pinacolborane (HBpin). These reagents form C–B bonds efficiently with syn addition. The resulting boron species can be converted into more stable boronic esters by complexation with diols (e.g., pinacol) for use in further transformations such as cross-coupling.

Reactions and transformations: A central utility of organoboranes is hydroboration–oxidation, where treatment with hydrogen peroxide–sodium hydroxide affords primary or secondary alcohols with anti-Markovnikov regiochemistry. Organoboron compounds are also key partners in Suzuki–Miyaura cross-coupling, enabling formation of C–C bonds from boronic acids or esters with palladium catalysts and base. Other transformations include oxidation, transmetalation, and various functional-group interconversions that exploit the C–B bond.

Applications: Organoboranes are widely used in organic synthesis for stereocontrolled alcohol synthesis, construction of biaryl motifs, and as intermediates in the preparation of complex natural products and pharmaceuticals. Safety notes: many borane reagents are air- or moisture-sensitive and some are pyrophoric; appropriate inert-atmosphere handling is common.