Diisobutylaluminium hydride

Diisobutylaluminium hydride
IUPAC name

Diisobutylaluminum hydride
Other names

DIBAH; DIBAL; DiBAlH; DIBAL-H; DIBALH
Identifiers
CAS number 1191-15-7 Y
ChemSpider 10430352 Y
Jmol-3D images Image 1
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
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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]

Contents

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 nitriles to primary amines [use Feiser work-up procedure]. 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 (1990). "Reaction of diisobutylaluminum hydride with a macrocyclic tetradentate secondary amine. Synthesis and molecular structure of [Al(iso-Bu)]2[C10H20N4][Al(iso-Bu)3]2: evidence of an unusual disproportionation of (iso-Bu)2AlH". Inorganica Chimica Acta 175 (2): 151–153. 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