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

Names
Preferred IUPAC name Lithium tetrakis(pentafluorophenyl)boranuide
Identifiers
CAS Number	371162-53-7 (etherate) Y
3D model (JSmol)	Interactive image
ChemSpider	8071952 N 9160766 (etherate) N
ECHA InfoCard	100.155.284
PubChem CID	9896287
InChI InChI=1S/C24BF20.Li/c26-5-1(6(27)14(35)21(42)13(5)34)25(2-7(28)15(36)22(43)16(37)8(2)29,3-9(30)17(38)23(44)18(39)10(3)31)4-11(32)19(40)24(45)20(41)12(4)33;/q-1;+1 N Key: WTTFKRRTEAPVBI-UHFFFAOYSA-N N InChI=1/C24BF20.Li/c26-5-1(6(27)14(35)21(42)13(5)34)25(2-7(28)15(36)22(43)16(37)8(2)29,3-9(30)17(38)23(44)18(39)10(3)31)4-11(32)19(40)24(45)20(41)12(4)33;/q-1;+1 Key: WTTFKRRTEAPVBI-UHFFFAOYAW
SMILES [Li+].Fc1c(c(F)c(F)c(F)c1F)[B-](c2c(F)c(F)c(F)c(F)c2F)(c3c(F)c(F)c(F)c(F)c3F)c4c(F)c(F)c(F)c(F)c4F
Properties
Chemical formula	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 YN ?) 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 Å. 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 the etherate as a white solid:^[1]

(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) + ML_nCl → LiCl + [ML_n]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]

Safety

Lithium tetrakis(pentafluorophenyl)borate will deflagrate on melting (ca. 265 °C) giving thick black smoke, even under nitrogen.^[5] The mechanism is unknown. Metal tetrakis(pentafluorophenyl)borates of K and Na decompose vigorously as well.^[6][7]

See also

• Tetraphenylborate