Diisobutylaluminium hydride

Diisobutylaluminium hydride, DIBAL, DIBAL-H or DIBAH, is a reducing agent with the formula (i-Bu2AlH)2, where i-Bu represents isobutyl (-CH2CH(CH3)2). This organoaluminium compound was investigated originally as a co-catalyst for the polymerization of alkenes.

Properties
Like most organoaluminum compounds, the compound’s structure is probably more than that suggested by its empirical formula. A variety of techniques, not X-ray crystallography suggest that the compound exists as a dimer and a trimer, consisting of tetrahedral aluminium centers sharing bridging hydride ligands. Hydrides are small and, for aluminium derivatives, are highly basic, thus they bridge in preference to the alkyl groups.

DIBAH can be prepared by heating triisobutylaluminium (itself a dimer) to induce beta-hydride elimination:
 * (i-Bu3Al)2 &rarr;  (i-Bu2AlH)2  +  2 (CH3)2C=CH2|undefined

Although DIBAH can be purchased commercially as a colorless liquid, it is more commonly purchased and dispensed as a solution in organic solvents such as toluene.

Use in organic synthesis
DIBAH is useful in organic synthesis for a variety of reductions, including converting esters and nitriles to aldehydes. By contrast, LiAlH4 reduces esters and acyl chlorides to primary alcohols, and NaBH4 fails to reduce most esters. DIBAH reacts slowly with electron poor compounds, and more quickly with electron rich compounds. Thus, it is an electrophilic reducing agent whereas LiAlH4 can be thought of as a nucleophilic reducing agent.

Safety
DIBAH, like most alkylaluminium compounds, reacts violently with air and water, potentially leading to fires.