Tetrakis ,5-bis(trifluoromethyl)phenylorate is an

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

with chemical formula sub>4Bsup>−, which is commonly abbreviated as Ar^F₄sup>−, indicating the presence of fluorinated

aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used ...

(Ar^F) groups. It is sometimes referred to as ''Kobayashi's anion'' in honour of Hiroshi Kobayashi who led the team that first synthesised it. More commonly it is affectionately

nickname A nickname, in some circumstances also known as a sobriquet, or informally a "moniker", is an informal substitute for the proper name of a person, place, or thing, used to express affection, playfulness, contempt, or a particular character trait ...

d "BARF." The BARF ion is also abbreviated BArF₂₄⁻, to distinguish it from the closely related , C₆F₅)₄Bsup>−. However, for a small group of chemists, the anion is abbreviated as TFPB otherwise, short for Tetrakis ,5-bis(triFluoromethyl)Phenyl''Borate. BARF has a

tetrahedral In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...

geometry around the central boron atom but each of the four surrounding aryl groups is

aromatic In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...

and planar. The motivation for its preparation was the search for an anion that coordinates more weakly than the then-available ions hexafluorophosphate, tetrafluoroborate, or

perchlorate A perchlorate is a chemical compound containing the perchlorate ion, , the conjugate base of perchloric acid (ionic perchlorate). As counterions, there can be metal cations, quaternary ammonium cations or other ions, for example, nitronium cat ...

Salts In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...

of this anion are known as solids and in both aqueous and non-aqueous solutions. BARF can be used in catalytic systems where the active site requires an anion which will not coordinate to the metal centre and interfere with the catalytic cycle, such as in the preparation of polyketones.

Synthesis of BARF compounds

The sodium

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

is the starting point for most BARF derivatives. It is prepared by treating Grignard reagents derived from XC₆H₃-3,5-(CF₃)₂ (X = Br, I) with NaBF₄. A popular method is summarized in the following equation: :NaBF₄ + 4 Ar^FMgBr → 4 MgBrF + NaBAr^F₄ Brookhart's acid is the salt of the BARF anion with the diethyl ether oxonium cation, Et₂O)₂HAr^F₄. It can be formed from the sodium salt in diethyl ether in the presence of

hydrogen chloride The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hyd ...

sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...

is insoluble in diethyl ether, facilitating cation exchange. : NaBAr^F₄ + HCl + 2 Et₂O → Et₂O)₂HAr^F₄ + NaCl BARF salts with hexakis(acetonitrile)metal(II) cations, (CH₃CN)₆sup>2+, are known for

vanadium Vanadium is a chemical element; it has Symbol (chemistry), symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an ...

chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

cobalt Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...

, and

nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...

. They are produced by salt metathesis reactions.

Properties

Non-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 foun ...

s are anions that interact only weakly with cations, a useful property when studying highly electrophilic cations. In

coordination chemistry 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 chemical bond, bound molecules or ions, that are in turn known as ' ...

, the term can also be used to refer to anions which are unlikely to bind directly to the metal centre of a complex. Hexafluorophosphate is a non-coordinating anion in both senses of the term. Three widely used non-coordinating anions are hexafluorophosphate, tetrafluoroborate , and

; of these, the hexafluorophosphate ion has the least coordinating ability and it is deliberately used for this property. BARF was developed as a new non-coordinating anion in the 1990s, and is far less coordinating than even the hexafluorophosphate anion. Extremely Lewis acidic metal centers can, however, cleave the carbon-boron bond in BARF. NaBAr^F₄ can be used in deprotection of acetal or ketal-protected carbonyl compounds. For example, deprotection of 2-phenyl- 1,3-dioxolane to

benzaldehyde Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is among the simplest aromatic aldehydes and one of the most industrially useful. It is a colorless liquid with a characteristic almond-li ...

can be achieved in water in five minutes at 30 °C. ::PhCH(OCH₂)₂ + H₂O -> ce\text] benzaldehyde, PhCHO + HOCH₂CH₂OH

References

{{Reflist, 30em Anions Trifluoromethyl compounds Non-coordinating anions Tetraphenylborates