Lithium tetrakis(pentafluorophenyl)borate

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 in the catalyst composition for olefin polymerization reactions and in electrochemistry. It is a water-soluble compound. Its anion is closely related to the non-coordinating anion known as BARF. The tetrakis(pentafluorophenyl)borates have the advantage of operating on a one-to-one stoichiometric basis with Group IV transition metal polyolefin catalysts, unlike methylaluminoxane (MAO) which may be used in large excess.

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).
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Infobox references

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 (OEt2) molecules are bound to the lithium cation, with Li-O bond lengths of approximately 1.95 Angstroms. The [Li(OEt2)4]+ complex is tetrahedral.

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 to prepare cationic transition metal complexes:

LiB(C6F5)4) + MLnCl → LiCl + [MLn]B(C6F5)4

LiB(C6F5)4 is converted to the trityl reagent [Ph3C][B(C6F5)4], which is useful activator of Lewis-acid catalysts.[3][4]

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. Cordoneanu, Adina, Drewitt, Mark, Bavarian, Neda, 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
  4. "The Reaction of Cp*2ZrMe2 with [CPh3][B(C6F5)4]: Triphenylethane Does Not form ηn-Arene Complexes with [Cp*2ZrMe]+". Journal of Organometallic Chemistry. 654: 221–223. 2002. doi:10.1016/S0022-328X(02)01319-0.
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