Borane dimethylsulfide (BMS) is a complexed borane reagent that is used for

hydroboration In organic chemistry, hydroboration refers to the addition of a hydrogen-boron bond to certain double and triple bonds involving carbon (, , , and ). This chemical reaction is useful in the organic synthesis of organic compounds. Hydroboration p ...

s and reductions. The advantages of BMS over other borane reagents, such as borane-tetrahydrofuran, are its increased stability and higher solubility. BMS is commercially available at much higher concentrations than its tetrahydrofuran counterpart (10 M) and does not require sodium borohydride as a stabilizer, which could result in undesired side reactions. In contrast, borane·THF requires

sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds appli ...

to inhibit reduction of THF to tributyl borate. BMS is soluble in most aprotic solvents.

Preparation and structure

Although usually purchased, BMS can be prepared by absorbing diborane into

dimethyl sulfide Dimethyl sulfide (DMS) or methylthiomethane is an organosulfur compound with the formula (CH3)2S. Dimethyl sulfide is a flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cook ...

: :B₂H₆ + 2 SMe₂ → 2 Me₂SBH₃ It can be purified by bulb to bulb vacuum transfer. Although a structure of BMS has not been determined crystallographically, (pentafluorophenyl)-borane dimethylsulfide (C₆F₅BH₂SMe₂), has been examined by

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

. The boron center adopts a tetrahedral geometry.

Reactions

Hydroborations

Due to the experimental ease of its use, BMS has become common in hydroboration reactions. In hydroborations with BMS, the

dimethylsulfide Dimethyl sulfide (DMS) or methylthiomethane is an organosulfur compound with the formula (CH3)2S. Dimethyl sulfide is a flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cook ...

dissociates ''in situ'', liberating diborane, which rapidly adds to the unsaturated bonds. The resulting organoborane compounds are useful intermediates in organic synthesis. Boranes add to alkenes in an anti-Markovnikov fashion and allow conversion of alkynes to the corresponding cis-alkenes.

Reductions

BMS has been employed for the reduction of many functional groups. Reductions of aldehydes, ketones, epoxides, esters, and carboxylic acids give the corresponding alcohols. Lactones are reduced to diols, and nitriles are reduced to amines. Acid chlorides and nitro groups are not reduced by BMS. Borane dimethylsulfide is one of the most common bulk reducing agents used in the

Corey–Itsuno reduction The Corey–Itsuno reduction, also known as the Corey–Bakshi–Shibata (CBS) reduction, is a chemical reaction in which an achiral ketone is enantioselectively reduced to produce the corresponding chiral, non-racemic alcohol. The oxazaborolidine ...

. The dimethylsulfide ligand attenuates the reactivity of the borane. Activation by the nitrogen of the chiral oxazoborolidine catalyst of the stoichiometric reducing agent allows for asymmetric control of the reagent. In general BMS does not lead to significantly greater enantiomeric selectivities than borane-THF, however its increased stability in the presence of moisture and oxygen makes it the reagent of choice for the reduction.

Safety

Borane dimethylsulfide is flammable and reacts readily with water to produce a flammable gas. It also has an unpleasant smell.

References

{{reflist Boranes Reagents for organic chemistry Foul-smelling chemicals