Alkylboranes

Alkylboranes are organoboron compounds in which carbon–boron bonds link boron to one or more alkyl groups. The most common members are dialkylboranes (R2BH) and trialkylboranes (R3B). They are typically prepared by hydroboration of alkenes using borane reagents such as BH3·THF or bulky hydroboration reagents like 9-BBN, often allowing formation of mono-, di-, or tri-substituted boranes depending on stoichiometry and conditions.

In terms of structure and reactivity, the C–B bond in alkylboranes is a versatile handle for subsequent transformations. Hydroboration of alkenes followed by oxidative workup (commonly hydrogen peroxide in base) converts alkylboranes into alcohols with anti-Markovnikov selectivity. This sequence, the hydroboration–oxidation, is a standard route to primary and secondary alcohols from alkenes. Alkylboranes can also undergo halodeboronation to give alkyl halides, or be converted to boronate esters for use in cross-coupling and other boron-mediated transformations. Triethylborane and related trialkylboranes are notable reagents in radical chemistry, including as air–moisture-sensitive initiators for certain polymerizations.

Applications and handling considerations are closely tied to their reactivity. Alkylboranes serve as important intermediates in organic synthesis, enabling anti-Markovnikov alcohol formation and enabling various boron‑based transformations. They are typically air- and moisture-sensitive, especially higher-order boranes, and are handled under inert atmosphere to minimize hazards such as ignition upon exposure to air.