Lithium tetrakis(pentafluorophenyl)borate is the lithium salt of the
weakly coordinating anion
Anions that interact weakly with cations are termed non-coordinating anions, although a more accurate term is weakly coordinating anion. Non-coordinating anions are useful in studying the reactivity of electrophilic cations. They are commonly found ...
(B(C
6F
5)
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
Electrochemistry is the branch of physical chemistry concerned with the relationship between Electric potential, electrical potential difference and identifiable chemical change. These reactions involve Electron, electrons moving via an electronic ...
. 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.
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
In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R†...
(OEt
2) molecules are bound to the lithium cation, with Li-O bond lengths of approximately 1.95 Ã…. The
i(OEt2)4sup>+ complex is tetrahedral.
Preparation
The salt was first produced in studies on
tris(pentafluorophenyl)boron, a well known
Lewis acid
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any ...
ic 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:
:(C
6F
5)
3B + Li(C
6F
5) →
i(OEt2)3B(C
6F
5)
4]
Since its discovery, many revised syntheses have been described.
Reactions
Lithium tetrakis(pentafluorophenyl)borate is primarily used to prepare cationic
transition metal complex
A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or ...
es:
:LiB(C
6F
5)
4) + ML
nCl → LiCl +
Ln(C
6F
5)
4
LiB(C
6F
5)
4 is converted to the trityl reagent
h3CB(C
6F
5)
4], which is useful activator of Lewis-acid catalysts.
Safety
Lithium tetrakis(pentafluorophenyl)borate will deflagrate on melting (ca. 265 °C) giving thick black smoke, even under nitrogen. The mechanism is unknown. Metal tetrakis(pentafluorophenyl)borates of K and Na decompose vigorously as well.
See also
*
Tetraphenylborate
Tetraphenylborate (IUPAC name: tetraphenylboranuide) is an organoboron anion consisting of a central boron atom with four phenyl groups. Salts of tetraphenylborate uncouple oxidative phosphorylation
Oxidative phosphorylation(UK , US : or ...
References
{{Lithium compounds
Lithium salts
Organoboron compounds
Pentafluorophenyl compounds
Perfluorinated compounds
Catalysts