Sodium tetraphenylborate is the

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...

with the formula NaB(C₆H₅)₄. It is a salt, wherein the anion consists of four phenyl rings bonded to boron. This white crystalline solid is used to prepare other tetraphenylborate salts, which are often highly soluble in organic solvents. The compound is used in inorganic and organometallic chemistry as a precipitating agent for

potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...

ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaterna ...

rubidium Rubidium is the chemical element with the symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have a density higher ...

, and

cesium Caesium (IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that ar ...

ions, and some organic nitrogen compounds.

Synthesis and structure

Sodium tetraphenylborate is synthesized by the reaction between sodium tetrafluoroborate and

phenylmagnesium bromide Phenylmagnesium bromide, with the simplified formula , is a magnesium-containing organometallic compound. It is commercially available as a solution in diethyl ether or tetrahydrofuran (THF). Phenylmagnesium bromide is a Grignard reagent. It is ...

: :NaBF₄ + 4 PhMgBr → 2 MgBr₂ + 2 MgF₂ + NaBPh₄ (where Ph = phenyl) A related synthesis involves the use of

phenylsodium Phenylsodium C6H5Na is an organosodium compound. Solid phenylsodium was first isolated by Nef in 1903. Although the behavior of phenylsodium and phenyl magnesium bromide are similar, the organosodium compound is very rarely used. Synthesis The ...

in place of the

Grignard reagent A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide . ...

. Unlike smaller counteranions, such as nitrate and the halides, tetraphenylborate confers lipophilicity to its salts. Many analogous tetraarylborates have been synthesized, containing both electron-rich and electron-deficient aryl groups. The anhydrous salt adopts a polymeric structure in the solid state consisting of Na⁺-phenyl interactions. As such the salt could be classified as an

organosodium compound Organosodium chemistry is the chemistry of organometallic compounds containing a carbon to sodium chemical bond. The application of organosodium compounds in chemistry is limited in part due to competition from organolithium compounds, which are co ...

Use in chemical synthesis

Preparation of ''N''-acylammonium salts

Addition of sodium tetraphenylborate to a solution of a tertiary amine and an acid chloride in

acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile ( hydrogen cyanide is a simpler nitrile, but the cyanide anion is not clas ...

gives the acylonium salt by precipitating NaCl from the reaction mixture. This method has a broad scope: :RC(O)Cl + R'₃N + NaB(C₆H₅)₄ → C(O)NR'₃B(C₆H₅)₄] + NaCl Sodium tetraphenylborate is also employed as a phenyl donor in palladium-catalyzed cross-coupling reactions involving vinyl and aryl triflates to give arylalkenes and biaryl compounds in good yields and under mild conditions, respectively.

Use in coordination chemistry

Tetraphenylborates are often studied in organometallic chemistry because of their favorable solubility in nonpolar solvents and their crystallinity. For example, the homoleptic trimethylphosphite complexes ²⁺ (Ni, Pd, and Pt) have been prepared as their tetraphenylborate salts. Similarly, sodium tetraphenylborate has been used to isolate complexes containing dinitrogen ligands. In the reaction below, sodium tetraphenylborate allows N₂ to displace the chloride ligand, which is removed from solution as a precipitate of sodium chloride: :FeHCl(diphosphine)₂ + NaB(C₆H₅)₄ + N₂ → eH(N₂)(diphosphine)₂(C₆H₅)₄ + NaCl The use of tetraphenylborate is limited to non-acidic cations. With strong acids, the anion undergoes protonolysis to give triphenylborane and

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...

:Tianshu Li, Alan J. Lough, Cristiano Zuccaccia, Alceo Macchioni, and Robert H. Morris "An acidity scale of phosphonium tetraphenylborate salts and ruthenium dihydrogen complexes in dichloromethane" Can. J. Chem. 84(2): 164–175 (2006). {{doi, 10.1139/V05-236. :H⁺ + B(C₆H₅)₄⁻ → B(C₆H₅)₃ + C₆H₆

Related tetraorganoborates

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 ...

s often are based on tetraarylborates, with electronegative substituents. Examples include B(C₆F₅)₄⁻ and Brookhart's acid containing the tetrakis ,5-bis(trifluoromethyl)phenylorate anion.

References

Sodium compounds Tetraphenylborates