Sodium tetraphenylborate is the

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

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 a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

ammonium Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...

rubidium Rubidium is a chemical element; it has Symbol (chemistry), 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 ...

, and

caesium Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has Symbol (chemistry), 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 f ...

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 forms colorless crystals. It is commercially available as a solution in diethyl ether or tetrahydrofuran (THF). Phenylmagnesium bromide i ...

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

Grignard reagent Grignard reagents or Grignard compounds are chemical compounds 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 bromi ...

. 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.

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 class ...

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 good 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 compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

: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 anions 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