:Pentaborane(11)
{{Chembox
| ImageFile = EntryWithCollCode36283.png
| ImageSize =
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| IUPACName =
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|Section1={{Chembox Identifiers
| CASNo = 18433-84-6
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII = 79Z6OH65UV
| UNII_Ref = {{fdacite|correct|FDA}}
| PubChem =
| ChemSpiderID = 34987102
| EINECS = 242-307-4
| SMILES = [BH3]1[BH2]2[BH]13[BH2]2[BH3]3
| StdInChI = 1S/B5H11/c1-3-4-2-5(1,3)4/h5H,3-4H2,1-2H3
| StdInChIKey = OPSKXWPMAKCNOG-UHFFFAOYSA-N
}}
|Section2={{Chembox Properties
| B=5 | H=11
| Appearance =
| Density =
| MeltingPtC = -123
| MeltingPt_ref =
| BoilingPtC = 63
| BoilingPt_ref =
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|Section3={{Chembox Hazards
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Pentaborane(11) is inorganic compound with the chemical formula B5H11. It is an obscure boron hydride cluster, especially relative to the heavily studied pentaborane(9) (B5H9). With two more hydrogen atoms than nido-pentaborane(9), pentaborane(11) is classified as an arachno- cluster.{{Greenwood&Earnshaw2nd}}
Synthesis
Like many boron hydride clusters, pentaborane(11) was originally obtained from the pyrolysis of diborane. A more systematic synthesis entails treatment of [B4H9]− with boron tribromide. The Lewis acid abstracts hydride to give unstable B4H8, the precursor to B5H11:{{cite journal|title=New, Systematic Syntheses of Boron Hydrides via Hydride ion Abstraction Reactions: Preparation of B2H6, B4H10, B5H11, and B10H14|last1=Toft |first1=Mark A. |last2=Leach |first2=J. B. |last3=Himpsl |first3=Francis L. |last4=Shore |first4=Sheldon G. |journal=Inorganic Chemistry|year=1982|volume=21|issue=5|pages=1952–7|doi=10.1021/ic00135a048 }}
:[B4H9]− + BBr3 → B4H8 + HBBr3−
:2 B4H8 → B5H11 + "B3H5"