Lithium triethylborohydride is the

organoboron compound Organoboron chemistry or organoborane chemistry studies organoboron compounds, also called organoboranes. These chemical compounds combine boron and carbon; typically, they are organic derivatives of borane (BH3), as in the trialkyl boranes. Or ...

with the formula Li Et₃ BH. Commonly referred to as LiTEBH or Superhydride, it is a powerful

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are common reducing agents include hydrogen, carbon ...

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 Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...

. It is a colorless or white liquid but is typically marketed and used as a THF solution. The related reducing agent

sodium triethylborohydride Sodium triethylborohydride is an organoboron compound with the formula NaBH(C2H5)3. It is a colorless, pyrophoric solid that is commercially available in toluene solution, unlike the related LiBH(C2H5)3 which is typically sold as a THF solution. ...

is commercially available as

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon with the chemical formula , often abbreviated as , where Ph stands for the phenyl group. It is a colorless, water Water is an inorganic compound with the c ...

solutions. LiBHEt₃ is a stronger reducing agent than

lithium borohydride Lithium borohydride (LiBH4) is a borohydride and known in organic synthesis as a reducing agent for esters. Although less common than the related sodium borohydride, the lithium salt offers some advantages, being a stronger reducing agent and ...

and

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

Preparation

LiBHEt₃ is prepared by the reaction of

lithium hydride Lithium hydride is an inorganic compound with the formula Li H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like (ionic) hydride, it has a high melting point, and it is not solub ...

(LiH) and

triethylborane Triethylborane (TEB), also called triethylboron, is an organoborane (a compound with a B–C bond). It is a colorless pyrophoric liquid. Its chemical formula is or , abbreviated . It is soluble in organic solvents tetrahydrofuran and hexane. ...

(Et₃B) in

tetrahydrofuran Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...

(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. 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 may also be called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. They are used as protecting gro ...

. Similarly

lactone Lactones are cyclic carboxylic esters. They are derived from the corresponding hydroxycarboxylic acids by esterification. They can be saturated or unsaturated. Lactones are formed by lactonization, the intramolecular esterification of the corresp ...

s reduce to diols. α,β-Enones undergo 1,4-addition to give lithium

enolate In organic chemistry, enolates are organic anions derived from the deprotonation of carbonyl () compounds. Rarely isolated, they are widely used as reagents in the Organic synthesis, synthesis of organic compounds. Bonding and structure Enolate ...

Disulfide In chemistry, a disulfide (or disulphide in British English) is a compound containing a functional group or the anion. The linkage is also called an SS-bond or sometimes a disulfide bridge and usually derived from two thiol groups. In inorg ...

s reduce to

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

s (via thiolates). LiBHEt₃ deprotonates carboxylic acids, but does not reduce the resulting lithium carboxylates. For similar reasons,

epoxide In organic chemistry, an epoxide is a cyclic ether, where the ether forms a three-atom ring: two atoms of carbon and one atom of oxygen. This triangular structure has substantial ring strain, making epoxides highly reactive, more so than other ...

s 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: :

Acetal In organic chemistry, an acetal is a functional group with the connectivity . Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments n ...

s and

ketal In organic chemistry, an acetal is a functional group with the connectivity . Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments n ...

s are not reduced by LiBHEt₃. It can be used in the reductive cleavage of

mesylates In organosulfur chemistry, a mesylate is any salt or ester of methanesulfonic acid (). In salts, the mesylate is present as the anion. When modifying the international nonproprietary name of a pharmaceutical substance containing the group o ...

and

tosylate In organic chemistry, a toluenesulfonyl group (tosyl group, abbreviated Ts or TosIn this article, "Ts", unless otherwise stated, means tosyl, not tennessine.) is a univalent functional group with the chemical formula . It consists of a tolyl ...

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

pyridine Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...

and

isoquinolines Isoquinoline is an individual chemical specimen - a heterocyclic aromatic organic compound - as well as the name of a family of many thousands of natural plant alkaloids, any one of which might be referred to as "an isoquinoline". It is a struc ...

piperidines Piperidine is an organic compound with the molecular formula (CH2)5NH. This heterocyclic compound, heterocyclic amine consists of a six-membered ring containing five methylene bridges (–CH2–) and one amine bridge (–NH–). It is a colorless ...

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 A substance is pyrophoric (from , , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolithium compounds and triethylb ...

References

{{Lithium compounds Borohydrides Lithium compounds Reducing agents Organoboron compounds Ethyl compounds Hydrides