Diisobutylaluminium hydride
| Diisobutylaluminium hydride | |
|---|---|
| 300px | |
| 200px | |
| IUPAC name | Diisobutylaluminium hydride |
| Other names | DIBAH; DIBAL; DiBAlH; DIBAL-H; DIBALH |
| Identifiers | |
| CAS number | |
| 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]
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 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.[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
- ↑ 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.
- ↑ 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)3]2: 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.
- ↑ Eisch, J. J. Organometallic Syntheses Volume 2, Academic Press: New York, 1981. ISBN 0-12-234950-4.
- ↑ Galatsis, P. “Diisobutylaluminum Hydride” in Encyclopedia of Reagents for Organic Synthesis John Wiley & Sons: New York, 2001. doi:10.1002/047084289X.rd245
External links
de:Diisobutylaluminiumhydrid Italic text
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