Chemistry Reference
In-Depth Information
assignable to [Au
9
(dppe)
5
]
3+
, [Au
11
(dppe)
5
]
3+
, [Au
12
(dppe)
5
Cl]
3+
,
[Au
13
(dppe)
5
Cl
2
]
3+
, and [Au
15
(dppe)
6
ClH]
3+
(Scheme
6
, vide infra) [
75
]. On the
other hand, the same reduction system from the C3-bridged complex
(Au
2
(dppp)
2
Cl
2
)inCH
2
Cl
2
/EtOH (50/50 v/v) affords ESI-mass signals assignable
to higher nuclearity clusters [Au
38
(dppp)
9
Cl
2
]
4+
and [Au
39
(dppp)Cl
3
]
4+
[
76
]. These
results imply that the cluster growth processes are not only governed by the intrinsic
stability of the gold core but also notably affected by the steric and cheating effects
of multidentate ligands and reaction conditions.
3.1.2 Other Methods
Other reducing agents have also been utilized. The utilization of Ti(
-C
6
H
5
CH
3
)
2
developed by Mingos et al. affords [Au
9
(PAr
3
)
8
]
3+
(14, 16) from AuCl(PPh
3
)
(Scheme
2
)[
36
]. The same reduction system from Au(PMe
2
Ph)Cl and Au
(PMePh
2
)Cl) results in the formation of deca-phosphine-coordinated Au
11
cluster
compounds having no Cl ligands on the cluster surface ([Au
11
(PMePh
2
)
10
]
3+
(31)
and [Au
11
(PMe
2
Ph)
10
]
3+
(31
0
)[
34
,
42
]. Recently, [Au
6
(xy-xantphos)
3
]Cl (5·Cl) was
isolated by recrystallization from the reaction mixture of Au(xy-xantphos)Cl and
PhMe
2
SiH [
77
].
HAuCl
4
instead of gold phosphine complex is usable as the starting gold source.
Upon reduction of HAuCl
4
by NaBH
4
in the presence of trioctylphosphine in
aqueous THF, [Au
13
(POct
3
)
8
Cl
4
]
+
is obtained as a minor product
[
76
]. [Au
39
(PPh
3
)
14
Cl
6
]Cl
2
(40·Cl), which is, to date, the largest PGC characterized
by single-crystal X-ray diffraction, was synthesized by the reduction of HAuCl
4
by
NaBH
4
[
78
]. Recently, [Au
24
(PPh
3
)
10
(SC
2
H
4
Ph)
5
X
2
]
+
(38) was synthesized by Jin
et al. through the NaBH
4
reduction of HAuCl
4
based on the Brust's two-phase
method [
79
].
Several other gold sources have also been utilized. [Au
7
(PPh
3
)
7
]
+
(6) can be
prepared by the reaction of gold vapor with PPh
3
in toluene [
31
]. Azido complex
AuN
3
(PPh
3
) is also usable as a precursor, which affords [Au
8
(PPh
3
)
8
]
2+
(8) upon
photolysis in THF [
80
].
η
3.2 Post Synthesis
As noted in Sect.
3.1
,Au
9
and Au
11
clusters are frequently found as the primary
products in the direct PGC synthesis from gold(I) precursors and thus appear to be
relatively stable compounds. However, due to the flexible nature of the cluster
skeletons and lability of Au-Au interactions, they can be easily converted into
different cluster species via post-synthetic aggregation-mediated growth and
degradation-mediated etching processes, thus acting as useful intermediates for a
variety of PGC compounds.
