| Diisobutylaluminium hydride | |
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| IUPAC name |
Diisobutylaluminium hydride
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| 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 |
| (what is this?) (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| 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 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:.
- ^ 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: 151–3. doi:.
- ^ 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
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