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Diisobutylaluminium hydride



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 disclaimer and 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]

Additional recommended knowledge

Contents

Properties

Like most organoaluminum compounds, the compound’s structure is more than that suggested by its empirical formula. It is dimeric, consisting of a pair 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:[2]

(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.[3] 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. ^ Eisch, J. J. Organometallic Syntheses Volume 2, Academic Press: New York, 1981. ISBN 0-12-234950-4.
  3. ^ Galatsis, P. “Diisobutylaluminum Hydride” in Encyclopedia of Reagents for Organic Synthesis John Wiley & Sons: New York, 2001. doi:10.1002/047084289X.rd245
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Diisobutylaluminium_hydride". A list of authors is available in Wikipedia.
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