:Borane dimethylsulfide
{{Chembox
| ImageFile = BH3SMe2improve.svg
| ImageSize = 150px
| ImageAlt =
| IUPACName =
| OtherNames = BMS, Borane-dimethyl sulfide
|Section1={{Chembox Identifiers
| CASNo = 13292-87-0
| CASNo_Ref = {{cascite|correct|CAS}}
| ChemSpiderID = 28533982
| EINECS = 236-313-6
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 6AVE9SRR08
| PubChem = 12423031
| StdInChI=1S/C2H6S.BH3/c1-3-2;/h1-2H3;1H3
| StdInChIKey = RMHDLBZYPISZOI-UHFFFAOYSA-N
| SMILES = [BH3-][S+](C)C }}
|Section2={{Chembox Properties
| Formula = {{chem2|BH3*S(CH3)2}}
| MolarMass = 75.96 g/mol
| Appearance = colorless liquid
| Density = 0.801 g/mL
| MeltingPt =
| BoilingPt =
| Solubility = }}
|Section3={{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt = }}
}}
Borane dimethylsulfide (BMS) is a chemical compound with the chemical formula {{chem2|BH3*S(CH3)2}}. It is an adduct between borane molecule ({{chem2|BH3}}) and dimethyl sulfide molecule ({{chem2|S(CH3)2}}). It is a complexed borane reagent that is used for hydroborations and reductions. The advantages of BMS over other borane reagents, such as borane-tetrahydrofuran, are its increased stability and higher solubility.{{cite journal | doi = 10.1080/00304948109356130 | title = Utility and Applications of Borane Dimethylsulfide in Organic Synthesis. A Review | year = 1981 | last1 = Hutchins | first1 = Robert O. | last2 = Cistone | first2 = Frank | journal = Organic Preparations and Procedures International | volume = 13 | issue = 3–4 | pages = 225}} 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–tetrahydrofuran requires sodium borohydride to inhibit reduction of THF to tributyl borate ({{chem2|B(OCH2CH2CH2CH3)3}}).{{cite journal | author = Kollonitisch, J. | title = Reductive Ring Cleavage of Tetrahydrofurans by Diborane | journal = J. Am. Chem. Soc. | year = 1961 | volume = 83 | pages = 1515 | doi = 10.1021/ja01467a056 | issue = 6| bibcode = 1961JAChS..83.1515K }} BMS is soluble in most aprotic solvents.
Preparation and structure
Although usually purchased, BMS can be prepared by absorbing diborane into dimethyl sulfide:{{cite journal | author1 = Braun, L. M. | author2 = Braun, R. A. | author3 = Crissman, R. | author4 = Opperman, M. | author5 = Adams, R. M. | title = Dimethyl Sulfide-Borane. A Convenient Hydroborating Reagent | journal = J. Org. Chem. | year = 1971 | volume = 36 | pages = 2388–2389 | doi = 10.1021/jo00815a047 | issue = 16}}
:{{chem2|B2H6 + 2 S(CH3)2 → 2 BH3*S(CH3)2}}
It can be purified by bulb to bulb vacuum transfer. Although a structure of BMS has not been determined crystallographically, (pentafluorophenyl)-borane dimethylsulfide ({{chem2|C6F5BH2*S(CH3)2}}), has been examined by X-ray crystallography.{{cite journal | doi = 10.1021/om100152v | title = Synthesis and Structure of the Dimethyl Sulfide Adducts of Mono- and Bis(pentafluorophenyl)borane | year = 2010 | last1 = Fuller | first1 = Anna-Marie | last2 = Hughes | first2 = David L. | last3 = Lancaster | first3 = Simon J. | last4 = White | first4 = Callum M. | journal = Organometallics | volume = 29 | issue = 9 | pages = 2194}} The boron atom adopts a tetrahedral molecular geometry.
Reactions
=Hydroborations=
Due to the experimental ease of its use, BMS has become common in hydroboration reactions.{{OrgSynth|author=Atsushi Abiko |year=1925|title=Dicyclohexylboron Trifluoromethylsulfonate |volume=79|pages=103|collvol=10|collvolpages=273|prep=CV10P0273}} In hydroborations with BMS, the dimethylsulfide 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 are not reduced by BMS.
Borane dimethylsulfide is one of the most common bulk reducing agents used in the Corey–Itsuno reduction. The dimethylsulfide ligand attenuates the reactivity of the borane. Activation by the nitrogen of the chiral oxazaborolidine{{cln|reason=What on this Earth is "oxazaborolidine"??? Please, clear this jargon for an average mortal human being.|date=August 2023}} catalyst of the stoichiometric reducing agent allows for asymmetric control of the reagent.{{cln|reason=What on this Earth is "asymmetric control of the reagent"??? Please, clear this jargon for an average mortal human being.|date=August 2023}} 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.{{cite journal | author1 = Corey, E.J. | author2 = Helal, C. J. | title = Reduction of Carbonyl Compounds with Chiral Oxazaborolidine Catalysts: A New Paradigm for Enantioselective Catalysis and a Powerful New Synthetic Method | journal = Angew. Chem. Int. Ed. | year = 1998 | volume = 37 | pages = 1986–2012 | doi = 10.1002/(SICI)1521-3773(19980817)37:15<1986::AID-ANIE1986>3.0.CO;2-Z | issue = 15| pmid = 29711061 }}
Safety
Borane dimethylsulfide is flammable and reacts readily with water to produce a flammable gas. It also has an unpleasant smell.{{cite web|title=Sigma-Aldrich Material Safety Data Sheet|url=http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=CA&language=en&productNumber=179825&brand=ALDRICH&PageToGoToURL=http%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fproduct%2Faldrich%2F179825%3Flang%3Den|website=www.sigmaaldrich.com/|accessdate=29 November 2014}}