Name = Lithium triethylborohydride
ImageFile = Lithiumtriethylborohydride.svg
IUPACName = Lithium triethylborohydride
OtherNames = Superhydride
Section1 = Chembox Identifiers
CASNo = 22560-16-3
Section2 = Chembox Properties
Formula = Li(C2H5)3BH
MolarMass = 105.95 g/mol
Appearance = Colorless to yellow liquid
Density = 0.890 g/cm3, liquid
Solubility = reactive
BoilingPt = 66 °C for THF
Section7 = Chembox Hazards
ExternalMSDS = | [http://www.basf.com/inorganics/pdfs/MSDS/Boranes/CalSelect_LT.pdf External MSDS]
MainHazards = highly flammable
NFPA-H = 3
NFPA-R = 2
NFPA-F = 2
NFPA-O = W
RPhrases = 11-14/15-19-34
SPhrases = 16-26-33-36/37/39-43-45
Section8 = Chembox Related
sodium borohydride sodium hydride lithium aluminium hydride
Lithium triethylborohydride (LiEt3BH), commonly abbreviated to LiTEBH or Superhydride, is a powerful and selective
reducing agentused in inorganicand organic chemistry. LiTEBH is far more powerful than lithium borohydrideand more powerful than lithium aluminium hydride(LAH) in many cases. One of the main advantages of LiTEBH is that it is safer than LAH.
LiTEBH rapidly reduces:: 1.
Aldehydes, ketones, acid chlorides and estersto alcohols: 2. Lactonesto diols: 3. Acid anhydrides to alcohols: 4. α,β-enones by 1,4-addition to give lithium enolates: 5. Disulfidesto thiols: 6. Tertiary amidesto an alcohol
Compounds of lithium hydride and sodium hydride with trialkylboranes such as LiTEBH were first discovered in the course of War Research in the period of 1942-45 at the University of Chicago by Professor H.C. Brown and Professor H.I. Schlesinger. [Krishnamurthy, S. "Aldrichim. Acta." 1974, "7," 55.]
LiTEBH is most commonly produced by the reaction between
lithium hydride(LiH) and triethylborane(Et3B) in tetrahydrofuran(THF): LiH + Et3B → LiEt3BH
which gives a very high yield of approximately 99%. The subsequent solution is collected by
filtrationof any excess LiH to give a crystal clear solution. LiTEBH in THF has appeared to be stable indefinitely under an inert atmosphere.
tructure and Chemical Properties
The structure of LiTEBH causes the compound to be a very strong hydride source. Hydrogen is more electronegative than boron which causes the B-H bond to be strongly polarized with boron having a partial positive charge and hydrogen having a partial negative charge. The ethyl groups on the boron also aids to this abnormal polarizability by removing additional electron density from the boron making it even more electropositive. This polarization of the B-Et and B-H bonds causes the hydrogen to be in the (-I) oxidation state instead of its usual (+I) oxidation state which leads to its high reactivity with atoms that can accept electrons to allow the hydrogen to go to its (+I) oxidation state.
Aldehydesand ketonesrapidly utilizes 1 equivalent of LiTEBH to form the alcohol shown respectively in (1) and (2).
LiTEBH can be used to form the alcohol even when these compounds possess sterically hindered substituents as shown with 2,2,4,4-tetramethyl-3-pentanone in (3).
Estersand lactonesrapidly take up 2 equivalents of LiTEBH, undergoing reduction to the alcohol and diol groups respectively. The example shown below involves the reduction of γ-butyrolactone to 1,4-butanediol which formed in a 94% yield in (4). [Brown, H.C.; Kim, S.C.; Krishnamurthy, S. "J. Org. Chem." 1980, "45," 1-12.]
The opening of the
epoxidering with LiTEBH proceeds with exceptional regio- and stereo- selectivity, yielding only the Markovnikovalcohol.  The example shown below is of 1,2-epoxybutane being reduced to give 1-methylcyclohexanol in (5).
acetaland ketalwill not be reduced by LiTEBH. LiTEBH can be used in the reductive cleavage of mesylatesand tosylates. [Baer, H.H.; Mekarska-Falicki, M. "Can. J. Chem." 1985, "63," 3043.] LiTEBH can selectively deprotect tertiary N-acyl groups without affecting secondary amide functionality. [Tanaka, H.; Ogasawara, K. "Tetrahedron Lett." 2002, "43," 4417.] LiTEBH has also shown high reactivity toward ester groups by the selective reduction of the ester group of aromatic carboxylic acids to alcohols as shown in (6) and (7). 
LiTEBH can also effectively reduce
pyridineand isoquinolinesto piperidinesand tetrahydroisoquinolines respectively. [Blough, B.E.; Carroll, F.I. "Tetrahedron Lett." 1993, "34," 7239.]
The reduction of β-hydroxysulfinyl imines with catecholborane and LiTEBH produces "anti-"1,3-amino alcohols shown in (8). [Kochi, T; Tang, T.P.; Ellman, J.A. "J. Am. Chem. Soc." 2002, "124," 6518.]
LiTEBH reacts violently and exothermically with water, alcohols, or acids releasing flammable hydrogen gas which can ignite explosively and the
pyrophoric triethylboranevapor can ignite spontaneously. It can cause severe eye, skin, and respiratory tract burns.
* [http://www.chemetalllithium.com/pdf/Lithium_Triethylborohydride_20_in_THF_C6H16BLi.pdf Technical information about LiTEBH]
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