Lithium triethylborohydride is the organoboron compound with the formula Li Et₃ BH. Commonly referred to as LiTEBH or Superhydride, it is a powerful reducing agent used in

organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

and organic chemistry. It is a colorless or white liquid but is typically marketed and used as a THF solution. The related reducing agent sodium triethylborohydride is commercially available as toluene solutions. LiBHEt₃ is a stronger reducing agent than lithium borohydride and

lithium aluminium hydride Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula Li Al H4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic ...

Preparation

LiBHEt₃ is prepared by the reaction of lithium hydride (LiH) and triethylborane (Et₃B) in tetrahydrofuran (THF): :LiH + Et₃B → LiEt₃BH Its THF solutions are stable indefinitely in the absence of moisture and air.

Reactions

Alkyl halides are reduced to the alkanes by LiBHEt₃. 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 A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol is also called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. The most common industrial diol is e ...

. 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. LiBHEt₃ can selectively deprotect tertiary N-acyl groups without affecting secondary amide functionality. It has also shown to reduce aromatic esters to the corresponding alcohols as shown in eq 6 and 7. : LiBHEt₃ also reduces pyridine and

isoquinolines Isoquinoline is a heterocyclic aromatic organic compound. It is a structural isomer of quinoline. Isoquinoline and quinoline are benzopyridines, which are composed of a benzene ring fused to a pyridine ring. In a broader sense, the term isoquino ...

to piperidines and tetrahydroisoquinolines respectively.
The reduction of β-hydroxysulfinyl imines with catecholborane and LiBHEt₃ produces ''anti-''1,3-amino alcohols shown in (8). :

Precautions

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

References

{{Lithium compounds Borohydrides Lithium compounds Organoboranes Reducing agents