Lithium tetrakis(pentafluorophenyl)borate

Lithium tetrakis(pentafluorophenyl)borate
Structural formula of lithium tetrakis(pentafluorophenyl)borate
Ball-and-stick model of the component ions of lithium tetrakis(pentafluorophenyl)borate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.155.284
Properties
C24BF20Li
Molar mass 685.98 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
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. Its anion is closely related to the non-coordinating anion known as BARF.

Structure and properties

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

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.[2]

Reactions

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

References

  1. ↑ A.G. Massey, A.J. Park. "Perfluorophenyl derivatives of the elements : I. Tris(pentafluorophenyl)boron." Journal of Organometallic Chemistry, 1964, 2, 245-250. doi:10.1016/S0022-328X(00)80518-5
  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
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.