(Triphenylphosphine)gold(I) chloride, ClAuPPh3, is a well characterized colorless complex[1] with a melting point of 236–240 °C[2] and it is soluble in most common organic solvents. Although it is commercially available,
it is cheaper to prepare it directly from elemental gold in an easy, high-yielding
two-step synthesis. In the first step, gold is dissolved in boiling aqua regia to form the gold(III) intermediate AuCl4 in solution. By adding dimethyl sulfide, the complex ClAuSMe2 precipitates as a white solid in an excellent yield of 93%.[3]
Scheme 1 Preparation of (triphenylphosphine)gold(I) chloride
This precursor complex is dissolved in dichloromethane together with triphenylphosphine
to form immediately the desired complex in a very good yield of 92% after precipitation
by adding methanol.[4] ClAuPPh3 is a useful reagent in various types of reactions. It is often used in gold catalysis
where it can act as co-catalyst or catalyst itself, or it can be used for the formation
of more complex catalytic systems.[5] ClAuPPh3 can also be used for the synthesis of organogold compounds,[6] which can perform cross-coupling reactions in a generally mild manner and with high
tolerance towards functional groups. Herein, some applications of ClAuPPh3 as reactant will be presented.
Table 1 Use of (Triphenylphosphine)gold(I) Chloride
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(A) ClAuPPh3 can be used for the generation of gold nanoparticles. In the first step, gold chloride
reacts with an ethylene glycol silver carboxylate in a transmetallation reaction.
The resulting gold(I) complex generates the gold nanoparticle by thermal induction.
The resulting nanoparticles do not need any further stabilizing or reducing reagents
and have size diameters of 3–6 nm with narrow size distribution.[7]
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(B) Zhang et al. used ClAuPPh3 as catalytic species for the formation of various saturated substituted O- and N-heterocycles.
The homogeneous oxidative functionalization of terminal alkenes leads to a cyclization
reaction that proceeds within short reaction times and under mild reaction conditions.
In mechanistic studies they found that a conversion of C(sp3)-Au bonds into C(sp3)-C(sp2) bonds is catalyzed by an Au(I)/Au(III) system in a cross-coupling manner when using
boronic acids as nucleophiles with Selectfluor as oxidant.[8]
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(C) Pérez-Sestelo and co-workers prepared different aryl-, alkynyl-, alkenyl-, and
alkylgold(I) compounds in very high yields using the corresponding lithiated organic
species and ClAuPPh3 as reagent. The organogold(I) compounds are used as nucleophiles in palladium-catalyzed
cross-coupling reactions with various electrophiles under mild reaction conditions
and in short reaction times.[9]
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(D) Meyer et al. showed that trimethyltin-substituted naphthalene derivatives perform
transmetalation reactions under very mild conditions using ClAuPPh3 as reagent. One example showed the synthesis of a compound containing both a gold(I)
moiety and an iodide function on the same molecule, which cannot be prepared using
organolithium or Grignard reagents in this case.[10]
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(E) Rominger et al. used boronic acid derivatives as precursors for the synthesis
of organogold(I) phosphane complexes. They are prepared in good yields of 82–98% using
ClAuPPh3 as reagent. This method allows a higher tolerance towards functional groups than
using lithiated species as reactants. As vinyl-, aryl- and heteroarylgold compounds
are assumed to be intermediates in homogeneous gold catalysis, Rominger et al. used
the prepared compounds to obtain more information about the mechanism of a catalytic
cycle with gold.[11]
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(F) Blum and co-workers prepared vinyl and aryl organogold(I) compounds by treating
the corresponding vinyl- or arylmagnesium bromides with ClAuPPh3. These simple compounds were used for continuing steps of reactions: First they performed
a regio- and diastereoselective palladium-catalyzed syn-carboauration of alkynes. In a further step, di- and trisubstituted olefins were
synthesized by either performing palladium-catalyzed cross-coupling reactions or electrophilic
trapping reactions. These reactions demonstrate the potential of the combination of
gold and palladium in organic synthesis.[12]
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(G) Keter et al. synthesized phosphinogold(I) dithiocarbamate complexes by using ClAuPPh3 and similar gold(I) precursors and different potassium salts of the corresponding
dithiocarbamates under mild conditions and in short reaction times. The resulting
complexes were tested for their activity against human cerival epithelioid carcinoma
(HeLa) cells, a type of cancer. The P-Au-S moiety seemed to play an important role
for the activity.[13]
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