Lithium tetrakis(pentafluorophenyl)borate

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Lithium tetrakis(pentafluorophenyl)borate
Lithium-tetrakis(pentafluorophenyl)borate-2D-skeletal.png
Identifiers
CAS number 371162-53-7 (etherate) YesY
PubChem 9896287
ChemSpider 8071952, 9160766 (etherate)
Jmol-3D images Image 1
Properties
Molecular formula C24BF20Li
Molar mass 685.98 g mol−1
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Lithium tetrakis(pentafluorophenyl)borate is the lithium salt of the weakly coordinating anion (B(C6F5)4)-. Because of its weakly coordinating abilities, lithium tetrakis(pentafluorophenyl)borate makes it commercially valuable in the salt form for the starting material in polymerization reactions and electrochemistry. It is a water-soluble compound. The salt has only been obtained as the etherate, [Li(OEt2)3][B(C6F5)4].

Structure and properties[edit]

The anion is tetrahedral with B-C bond lengths of approximately 1.65 Angstroms. The salt has only been obtained as the etherate, and the crystallography confirms that four ether molecules are bound to the lithium cation, with Li-O bond lengths of approximately 1.95 Angstroms. This structure gives the Lithium ion a coordination number of 4 with a tetrahedral geometry.

Preparation[edit]

The salt was first produced in studies on tris(pentafluorophenyl)boron, a well known Lewis acidic compound. Combining equimolar ether solutions of pentafluorophenyllithium and tris(pentafluorophenyl)boron gives the lithium salt of tetrakis(pentafluorophenyl)borate, which precipitates as a white solid [1] as the etherate:

(C6F5)3B + Li(C6F5) → [Li(OEt2)3][B(C6F5)4]

Since its discovery, many revised syntheses have been described, including an ether-free method.[2]

Reactions[edit]

Lithium tetrakis(pentafluorophenyl)borate is primarily used in its salt form as a precursor to cationic transition metal complexes. They are capable of forming highly reactive metal catalysts. Lithium tetrakis(pentafluorophenyl)borate is used for its bulky size in primarily polymerization reactions and electrochemistry. (B(C6F5)4)- is a weakly coordinating anion, which is compatible with strong electrophiles. This property is essential for the activation of Ziegler-Natta and Metallocene olefin polymerization catalysts. For example, polymerization by zirconocene catalysts can be initiated with the (B(C6F5)4)- salt of the trityl carbocation [Ph3C]+ : Borate salts of dimethyl annilinium and triethyl ammonium have also been reported to act as successful cocatalysts/activators.[3]

In such cases, the required lithium salt of (B(C6F5)4)- is prepared from Li(B(C6F5)4) and [Ph3C][B(C6F5)4].[4] Another use is in the creation of (η5-pentamethylcyclopentadienyl)tin tetrakis(pentafluorophenyl)borate. This cation is then applied as an efficient Ziegler-Natta α-olefin cocatalyst for the polymerization of alkenes.[5]

See also[edit]

References[edit]

  1. ^ A.G. Massey, A.J. Park, and FGA Stone, "Tris(pentafluorophenyl)boron." Proceedings of the Chemical Society, 1963, 212
  2. ^ Martin, Eddy, Hughes, David, and Lancaster, Simon. "The composition and structure of lithium tetrakis(pentafluorophenyl)borate diethyletherate." Inorganica Chimica Acta, 2010, 363, 275-278 doi:10.1016/j.ica.2009.09.013
  3. ^ Carnahan, E. M., et al, PCT Int. Appl. WO 97/19959, 1997
  4. ^ Cordoneanu, Adina, Drewitt, Mark, Bavarian, Neda, and Baird, Michael. "Synthesis and characterization of weakly coordinating anion salts of a new, stable carbocationic reagent, the dibenzosuberenyl (dibenzotropylium) ion." New Journal of Chemistry, 2008, 32, 1890-1898. doi:10.1039/b804868a
  5. ^ Rhodes, B., Chien, James, Rausch, Marvin. "(η5-Pentamethylcyclopentadienyl)tin(II) Tetrakis(pentafluorophenyl)borate: A New Cocatalyst for the Polymerization of α-Olefins." Organometallics, 1998, 10, 1931-1933. doi:10.1021/om980153j