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Diisobutylaluminium hydride
IUPAC name	Diisobutylaluminium hydride
Other names	DIBAH; DIBAL; DiBAlH; DIBAL-H; DIBALH
Identifiers
CAS number	[1191-15-7]
Properties
Molecular formula	C16H38Al2 (dimer)
Molar mass	142.22 (monomer)
Appearance	colorless liquid
Density	0.798 g/cm3
Melting point	–18 °C
Boiling point	116–118 °C/1 mmHg
Solubility in water	hydrocarbon solvents
Hazards
Main hazards	ignites in air
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

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.^[1]

Properties

Like most organoaluminum compounds, the compound’s structure is probably more than that suggested by its empirical formula. A variety of techniques, not including X-ray crystallography, suggest that the compound exists as a dimer and a trimer, consisting of tetrahedral aluminium centers sharing bridging hydride ligands.^[2] 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:^[3]

(i-Bu₃Al)₂ → (i-Bu₂AlH)₂ + 2 (CH₃)₂C=CH₂

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. DIBAH efficiently reduces α-β unsaturated esters to the corresponding allylic alcohol.^[4] 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.

References

1. ^ K. Ziegler, H. Martin and F. Krupp (1960). "Metallorganische Verbindungen, XXVII Aluminiumtrialkyle und Dialkyl-Aluminiumhydride Aus Aluminiumisobutyl-Verbindungen". Justus Liebigs Annalen der Chemie 629 (1): 14–19. doi:10.1002/jlac.19606290103. 
2. ^ Mark F. Self, William T. Pennington and Gregory H. Robinson "Reaction of diisobutylaluminum hydride with a macrocyclic tetradentate secondary amine. Synthesis and molecular structure of [Al(iso-Bu)]₂[C₁₀H₂₀N₄[Al(iso-Bu)₃₂: evidence of an unusual disproportionation of (iso-Bu)2AlH" Inorganica Chimica Acta (1990), volume 175, pp. 151-3. doi:10.1016/S0020-1693(00)84819-7.
3. ^ Eisch, J. J. Organometallic Syntheses Volume 2, Academic Press: New York, 1981. ISBN 0-12-234950-4.
4. ^ Galatsis, P. “Diisobutylaluminum Hydride” in Encyclopedia of Reagents for Organic Synthesis John Wiley & Sons: New York, 2001. doi:10.1002/047084289X.rd245

External links

• Example use
• Overview of reduction

Wikipedia content modification information:

• This page was last modified on 1 August 2008, at 15:22.

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