Diisobutylaluminium hydride

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Diisobutylaluminium hydride
DIBAH.png
DIBAL-3D-balls.png
Identifiers
CAS number 1191-15-7 YesY
ChemSpider 10430352 YesY
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 –80 °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 (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Diisobutylaluminium hydride (DIBALH, DIBAL, DIABLO - III , DIBAL-H or DIBAH, DYE-bal) 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[edit]

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.

DIBALH 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 DIBALH can be purchased commercially as a colorless liquid, it is more commonly purchased and dispensed as a solution in an organic solvent such as toluene or hexane.

Use in organic synthesis[edit]

DIBALH is useful in organic synthesis for a variety of reductions, including converting esters and nitriles to aldehydes. DIBALH 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]. DIBALH 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[edit]

DIBALH, like most alkylaluminium compounds, reacts violently with air and water, potentially leading to fires.

References[edit]

  1. ^ Ziegler, K.; Martin, H.; Krupp, F. (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. ^ Self, M. F.; Pennington, W. T.; Robinson, G. H. (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. (1981). Organometallic Syntheses 2. New York: Academic Press. ISBN 0-12-234950-4. 
  4. ^ Galatsis, P. (2001). "Diisobutylaluminum Hydride". Encyclopedia of Reagents for Organic Synthesis. New York: John Wiley & Sons. doi:10.1002/047084289X.rd245. ISBN 0471936235. 

External links[edit]