Disiamylborane

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title: "Disiamylborane" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["alkylboranes", "reagents-for-organic-chemistry"] topic_path: "science/chemistry" source: "https://en.wikipedia.org/wiki/Disiamylborane" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

|Verifiedfields = changed |Watchedfields = changed |verifiedrevid = 399911516 |ImageFile=(isoamyl)2BH dimer.svg |ImageSize=200px |ImageAlt = Skeletal formula of disiamylborane |ImageFile1 = |ImageAlt1 = Ball-and-stick model of the disiamylborane molecule |IUPACName=Bis(1,2-dimethylpropyl)borane |Section1={{Chembox Identifiers |ChemSpiderID_Ref = |ChemSpiderID = 167251 |InChI = 1/C10H23B/c1-7(2)9(5)11-10(6)8(3)4/h7-11H,1-6H3 |InChIKey = HXJFQNUWPUICNY-UHFFFAOYAY |SMILES1 = B(C(C(C)C)C)C(C)C(C)C |StdInChI_Ref = |StdInChI = 1S/C10H23B/c1-7(2)9(5)11-10(6)8(3)4/h7-11H,1-6H3 |StdInChIKey_Ref = |StdInChIKey = HXJFQNUWPUICNY-UHFFFAOYSA-N |CASNo_Ref = |CASNo=1069-54-1 |UNII_Ref = |UNII = 2O6VD8483R |PubChem = 192733 |SMILES=CC(C(C)C)BC(C)C(C)C |Section2={{Chembox Properties |Formula=C10H23B |MolarMass=154.09 g/mol | MeltingPt= 35-40 °C

Disiamylborane (bis(1,2-dimethylpropyl)borane) is an organoborane with the formula (abbreviation: Sia2BH). It is a colorless waxy solid that is used in organic synthesis for hydroboration–oxidation reactions. Like most dialkyl boron hydrides, it has a dimeric structure with bridging hydrides.

Reactions

Disiamylborane is prepared by hydroboration of trimethylethylene with diborane. The reaction stops at the secondary borane due to steric hindrance.

Disiamylborane is relatively selective for terminal alkynes and alkenes vs internal alkynes and alkenes. Like most hydroboration, the addition proceeds in an anti-Markovnikov manner. It can be used to convert terminal alkynes, into aldehydes.

The hydroboration process proceeds via an initial dissociation of the dimer.

Related reagents

9-Borabicyclo[3.3.1]nonane (9-BBN).
Thexylborane ((1,1,2-trimethylpropyl)borane, ThxBH2), a primary borane obtained by hydroboration of tetramethylethylene.

Naming

The prefix disiamyl is an abbreviation for "di*-sec-*isoamyl", where sec-isoamyl ("secondary isoamyl") is an archaic name for the 1,2-dimethylpropyl group (amyl being a obsolescent synonym of pentyl).

References

Eric J. Leopold. (1986). "Selective Hydroboration of a 1,3,7-Triene: Homogeraniol".
(1985). "Hydroboration kinetics. 11. A reinvestigation of the kinetics of hydroboration of representative alkenes with disiamylborane dimer. Conclusive evidence for the dissociation mechanism in the hydroboration of alkenes with dialkylborane dimers". The Journal of Organic Chemistry.

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