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 convent ...

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 as ...

(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 is a substitute for the proper name of a familiar person, place or thing. Commonly used to express affection, a form of endearment, and sometimes amusement, it can also be used to express defamation of character. As a concept, it is ...

d "BARF." The BARF ion is also abbreviated BArF₂₄⁻, to distinguish it from the closely related , C₆F₅)₄Bsup>−. BARF has a tetrahedral geometry around the central boron atom but each of the four surrounding aryl groups is

aromatic In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...

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

hexafluorophosphate Hexafluorophosphate is an anion with chemical formula of . It is an octahedral species that imparts no color to its salts. is isoelectronic with sulfur hexafluoride, , and the hexafluorosilicate dianion, , and hexafluoroantimonate . In this anio ...

, tetrafluoroborate, or

perchlorate A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. Per ...

. Salts 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 Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...

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 Brookhart's acid is the salt of the diethyl ether oxonium ion and tetrakis ,5-bis(trifluoromethyl)phenylorate (BAr′4). It is a colorless solid, used as a strong acid. The compound was first reported by Volpe, Grant, and Brookhart in 1992. Pr ...

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

sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...

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 with the 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 oxide layer ( pas ...

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

iron Iron () is a chemical element with symbol Fe (from la, ferrum) 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, right in f ...

cobalt Cobalt is a chemical element with the 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. The free element, pr ...

, and

nickel Nickel is a chemical element with 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 slow to ...

. They are produced by salt metathesis reactions.

Properties

Non-coordinating anions are anions that interact only weakly with cations, a useful property when studying highly

electrophilic In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carri ...

cations. In

coordination chemistry A coordination complex consists 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 complexing agents. Many ...

, 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 Dioxolane is a heterocyclic acetal with the chemical formula (CH2)2O2CH2. It is related to tetrahydrofuran by interchange of one oxygen for a CH2 group. The corresponding saturated 6-membered C4O2 rings are called dioxanes. The isomeric 1,2-diox ...

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

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

References

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