CAS Number 143-66-8
·
Linear Formula (C6H5)4BNa
·
Molecular Weight 342.22
·
Beilstein Registry
Number 3599783
·
EC Number 205-605-5
·
MDL number MFCD00011494
·
PubChem Substance ID 24900045
Sodium tetraphenylborate is the organic compound with the formula NaB(C6H5)4.
It is a salt, wherein the anion consists of four phenyl rings bonded to boron.
Detailed
description
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.
Synthesis and structure
Sodium tetraphenylborate is synthesized by the
reaction between sodium
tetrafluoroborate and phenylmagnesium
bromide:[1]
NaBF4 + 4 ArMgBr → 2 MgBr2 + 2 MgF2 + NaBAr4 (where Ar = aryl)
A related synthesis involves the use of phenylsodium in
place of the Grignard reagent.[2]
Unlike smaller counteranions, such as nitrate and
the halides, tetraphenylborate confers lipophilicity to its salts. Many
analogues 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.[3]
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 gives
the acylonium salt by precipitating NaCl from the reaction mixture. This method
has a broad scope:[4]
RC(O)Cl + R'3N
+ NaB(C6H5)4 →
[RC(O)NR'3][B(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.[5]
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 {M[P(OCH3)3]5}2+ (Ni, Pd, and Pt) have been prepared as
their tetraphenylborate salts.[6] Similarly, sodium
tetraphenylborate has been used to isolate complexes containing dinitrogen ligands.[7] 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 → [FeH(N2)(diphosphine)2]B(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:[8]
H+ + B(C6H5)4− → B(C6H5)3 + C6H6
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