Tris(pentafluorophenyl)boron
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{{Chembox new
| Name = Tris(pentafluorphenyl)boron
| ImageFile = Tris(pentafluorophenyl)boron-3D-vdW.png
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| ImageName = Tris(pentafluorphenyl)boron
| IUPACName = Tris(pentafluorophenyl)boron
| OtherNames = Perfluorotriphenylboron
| Section1 = {{Chembox Identifiers
| SMILES =
| CASNo = 1109-15-5
| RTECS =
}}
| Section2 = {{Chembox Properties
| Formula = (C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>B<br /> C<sub>18</sub>F<sub>15</sub>B
| MolarMass = 511.98 g/mol
| Appearance = colorless solid
| Density =
| Solubility = forms adduct
| MeltingPt = 126-131 °C
| BoilingPt =
| Viscosity =
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| Section3 = {{Chembox Structure
| MolShape = trigonal planar
| Dipole = 0 [[Debye|D]]
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS =
| MainHazards =
| RPhrases = 36/37/38
| SPhrases = 26-36
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| Section8 = {{Chembox Related
| OtherCpds = Triphenylboron (C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>B<br />[[Boron trifluoride|BF<sub>3</sub>]]
}}
}}
'''Tris(pentafluorophenyl)boron''' is the [[chemical compound]] (C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>B. The molecule consists of three pentafluorophenyl groups attached in a "paddle-wheel" manner to a central [[boron]] atom; the BC<sub>3</sub> core is planar. It has been described as the “ideal [[Lewis acid]]” because of its versatility and the relative inertness of the B-C bonds. Related fluoro-substituted boron compounds, such as those containing B-CF<sub>3</sub> groups, decompose with formation of B-F bonds.
==Preparation==
(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>B is prepared using a [[Grignard reagent]]:
:3C<sub>6</sub>F<sub>5</sub>MgBr + BCl<sub>3</sub> → (C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>B + 3MgBrCl
Originally the synthesis employed C<sub>6</sub>F<sub>5</sub>Li, but this reagent can detonate with elimination of LiF.<ref>Piers, W. E.; Chivers, T. “Pentafluorophenylboranes: from Obscurity to Applications” Chemical Society Reviews volume 26, pages 345-354 (1997)</ref>
==Lewis acidity==
The most noteworthy property of this molecule is its strong [[Lewis acid]]ity: stronger than BF<sub>3</sub> but weaker than BCl<sub>3</sub>. This property indicates that the [[electronegativity]] of the C<sub>6</sub>F<sub>5</sub> group and a halide are similar. An most important application of (C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>B is that it forms [[noncoordinating anion]]s by removing anionic ligands from metal centers.<ref>Fuhrmann, H.; Brenner, S.; Arndt, P.; Kempe, R. “Octahedral Group 4 Metal Complexes That Contain Amine, Amido, and Aminopyridinato Ligands: Synthesis, Structure, and Application in α-Olefin Oligo- and Polymerization” Inorganic Chemistry 1996, 35, 6742-6745.</ref> Illustrative is a reaction that give rise to [[Ziegler-Natta catalyst|alkene polymerization]] catalyst:
:(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>B + (C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>Zr(CH<sub>3</sub>)<sub>2</sub> → [(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>ZrCH<sub>3</sub><sup>+</sup>][ C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>BCH<sub>3</sub><sup>−</sup>]
In this process, the strongly coordinating methyl group transfers to the boron to expose a reactive site on zirconium. Alkenes can bind to this site, whereupon they couple to the remaining methyl [[ligand]] to give a propyl ligand, thereby starting the growth of a chain of polyethylene.
(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>B is also capable of abstracting hydride to give [(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>BH]<sup>−</sup>, and it catalyzes [[hydrosilylation]] of aldehydes. Otherwise (C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>B binds to a wide range of Lewis bases, even weak ones.<ref>Erker, G. "Tris(pentafluorophenyl)borane: A Special Boron Lewis Acid for Special Reactions" Dalton Transactions (2005), 1883-1890.</ref> The compound is hygroscopic, forming the trihydrate [(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>BOH<sub>2</sub>](H<sub>2</sub>O)<sub>2</sub>, wherein one water in coordinated to boron and the other two waters are hydrogen-bonded to the coordinated water.
Related compounds are Pentafluorophenylboron halides.<ref>Chivers, T. “Pentafluorophenylboron halides: 40 years later” Journal of Fluorine Chemistry (2002), volume 115, page 1-8.</ref>
==Other reactions==
(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>B was used to prepare a compound containing a Xe-C bond:
:(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>B + XeF<sub>2</sub> → [C<sub>6</sub>F<sub>5</sub>Xe<sup>+</sup>][(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub>BF<sub>2</sub><sup>−</sup>]
One study<ref>''Reversible, Metal-Free Hydrogen Activation'' Gregory C. Welch, Ronan R. San Juan, Jason D. Masuda, Douglas W. Stephan [[Science|Science (journal)]] 17 November '''2006''': Vol. 314. no. 5802, pp. 1124 - 1126 {{DOI|10.1126/science.1134230}}</ref> reported a [[nucleophilic aromatic substitution]] on one of the pentafluorinephenyl rings by [[organophosphorus chemistry|dimesityl phosphane]]:
:[[Image:PhosphinoboraneSynthesis.png|500px|Phosphino-borane Synthesis Welch 2006]]
The bulky [[mesityl]] groups prevent the phosphorus atom from coordinating directly to boron and instead the ring is attacked. When the fluorine atom on boron is replaced by hydrogen with [[organosilicon chemistry|dimethylchlorosilylhydride]], the resulting phosphazenium borate is capable of reversible [[hydrogen storage]]<ref>See also [[Hydrogen storage#Research|hydrogen storage]]</ref>
==References==
{{reflist}}
[[Category:Boron compounds]]
[[Category:Fluorides]]
[[Category:Inorganic carbon compounds]]
[[cs:Tris(pentafluorofenyl)boran]]