Lithium triethylborohydride

"Superhydride" redirects here. For the class of compounds sometimes known as superhydrides, see Polyhydride.

Lithium triethylborohydride is the organoboron compound with the formula LiEt₃BH. Commonly referred to as LiTEBH or Superhydride, it is a powerful reducing agent used in organometallic and organic chemistry. It is a colorless or white liquid but is typically marketed and used as a THF solution.^[2] The related reducing agent sodium triethylborohydride is commercially available as toluene solutions.

Lithium triethylborohydride

Names
Preferred IUPAC name Lithium triethylboranuide
Other names Superhydride LiTEBH
Identifiers
CAS Number	22560-16-3 Y
3D model (JSmol)	Interactive image
ChemSpider	2006168 Y
ECHA InfoCard	100.040.963
EC Number	245-076-8
PubChem CID	23712863
UNII	Q1ML638JFD Y
CompTox Dashboard (EPA)	DTXSID10897726
InChI InChI=1S/C6H16B.Li/c1-4-7(5-2)6-3;/h7H,4-6H2,1-3H3;/q-1;+1 Y Key: WCJAYABJWDIZAJ-UHFFFAOYSA-N Y
SMILES [Li+].CC[BH-](CC)CC
Properties
Chemical formula	Li(C2H5)3BH
Molar mass	105.95 g/mol
Appearance	Colorless to yellow liquid
Density	0.890 g/cm3, liquid
Boiling point	66 °C (151 °F; 339 K) for THF
Solubility in water	reactive
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	highly flammable corrosive Causes burns Probable Carcinogen
GHS labelling:[1]
Pictograms
Signal word	Danger
Hazard statements	H250, H260, H314, H335
Precautionary statements	P210, P222, P223, P231+P232, P260, P261, P264, P271, P280, P301+P330+P331, P302+P334, P303+P361+P353, P304+P340, P305+P351+P338, P310, P312, P321, P335+P334, P363, P370+P378, P402+P404, P403+P233, P405, P422, P501
NFPA 704 (fire diamond)	3 2 2 W
Safety data sheet (SDS)	External MSDS
Related compounds
Related hydride	Lithium borohydride sodium borohydride sodium hydride lithium aluminium hydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

LiBHEt₃ is a stronger reducing agent than lithium borohydride and lithium aluminium hydride.

Preparation

LiBHEt₃ is prepared by the reaction of lithium hydride (LiH) and triethylborane (Et₃B) in tetrahydrofuran (THF):

LiH + Et₃B → LiEt₃BH

The resulting THF complex is stable indefinitely in the absence of moisture and air.

Reactions

Alkyl halides are reduced to the alkanes by LiBHEt₃.^[3][4][2]

LiBHEt₃ reduces a wide range of functional groups, but so do many other hydride reagents. Instead, LiBHEt₃ is reserved for difficult substrates, such as sterically hindered carbonyls, as illustrated by reduction of 2,2,4,4-tetramethyl-3-pentanone. Otherwise, it reduces acid anhydrides to alcohols and the carboxylic acid, not to the diol. Similarly lactones reduce to diols. α,β-Enones undergo 1,4-addition to give lithium enolates. Disulfides reduce to thiols (via thiolates). LiBHEt₃ deprotonates carboxylic acids, but does not reduce the resulting lithium carboxylates. For similar reasons, epoxides undergo ring-opening upon treatment with LiBHEt₃ to give the alcohol. With unsymmetrical epoxides, the reaction can proceed with high regio- and stereo- selectivity, favoring attack at the least hindered position:

Acetals and ketals are not reduced by LiBHEt₃. It can be used in the reductive cleavage of mesylates and tosylates.^[5] LiBHEt₃ can selectively deprotect tertiary N-acyl groups without affecting secondary amide functionality.^[6] It has also been shown to reduce aromatic esters to the corresponding alcohols as shown in eq 6 and 7.

LiBHEt₃ also reduces pyridine and isoquinolines to piperidines and tetrahydroisoquinolines respectively.^[7]
The reduction of β-hydroxysulfinyl imines with catecholborane and LiBHEt₃ produces anti-1,3-amino alcohols shown in (8).^[8]

Precautions

LiBHEt₃ reacts exothermically, potentially violently, with water, alcohols, and acids, releasing hydrogen and the pyrophoric triethylborane.^[2]