Ruthenium Hydride Complex Supported on Gold Nanoparticle Cored Triazine Dendrimers for C-C Coupling Reactions

Article abstract of DOI:10.1021/acs.organomet.6b00163

In this work, the unusual ability of a ruthenium hydride catalyst, [RuHCl(PPh₃)₃CO], supported on gold nanoparticle cored triazine dendrimers in the Suzuki-Miyaura cross-coupling reaction and also in the synthesis of diaryl ketones is reported. [Ru-H@AuNPs-TD] was characterized by Fourier transform infrared spectroscopy, CHNS, TEM, SEM, ICP, and TGA analyses. The ruthenium hydride catalyst was used as a heterogeneous catalyst for the C-C coupling reactions of aryl halides with phenylboronic acids, and the biphenyl derivatives were produced in good to excellent yields. On the other hand, this catalytic system was applied for synthesis of diaryl ketones by the reaction of phenylboronic acids with substituted benzaldehydes. Moreover, this catalyst can be well-dispersed in the reaction medium, conveniently separated from the reaction mixture, and reused several times without significant loss of its activity.

Full text of DOI:10.1021/acs.organomet.6b00163

Article
pubs.acs.org/Organometallics
Ruthenium Hydride Complex Supported on Gold Nanoparticle Cored
Triazine Dendrimers for C−C Coupling Reactions
Anahita Daneshvar, Majid Moghadam,* Shahram Tangestaninejad,* Valiollah Mirkhani,
Iraj Mohammadpoor-Baltork, and Akram Khalili
Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-73441, Iran
*
S Supporting Information
ABSTRACT: In this work, the unusual ability of a ruthenium
hydride catalyst, [RuHCl(PPh ) CO], supported on gold
3
3
nanoparticle cored triazine dendrimers in the Suzuki−Miyaura
cross-coupling reaction and also in the synthesis of diaryl
ketones is reported. [Ru-H@AuNPs-TD] was characterized by
Fourier transform infrared spectroscopy, CHNS, TEM, SEM,
ICP, and TGA analyses. The ruthenium hydride catalyst was
used as a heterogeneous catalyst for the C−C coupling
reactions of aryl halides with phenylboronic acids, and the
biphenyl derivatives were produced in good to excellent yields.
On the other hand, this catalytic system was applied for
synthesis of diaryl ketones by the reaction of phenylboronic acids with substituted benzaldehydes. Moreover, this catalyst can be
well-dispersed in the reaction medium, conveniently separated from the reaction mixture, and reused several times without
significant loss of its activity.
INTRODUCTION
■
Dendrimers are treelike, hyperbranched, highly symmetrical
polymeric structures and have emerged as promising supports for
catalysis. The regular branched structure, monodispersity, and
desired solubility in organic/aqueous media are three main
advantages that make these compounds a bridge between
Figure 2. Synthesis of AuNPs and their stabilization with thiols.
1
−5
homogeneous and heterogeneous catalytic systems.
Metal-containing dendrimers are a class of materials that have
attracted much attention in recent years. Dendrimer-encapsu-
lated nanoparticles (DENs), dendrimer-stabilized nanoparticles
9
stabilized by a variety of ligands bearing thiol groups. For
example, Astruc et al. investigated the synthesis of gold
nanoparticles with both dodecanethiolate and the dendronized
thiolate either by the ligand-substitution procedure or by direct
(
DSNs), and nanoparticle-core dendrimers (NCDs) are three
general categories of metal ion containing dendrimers (Figure
6
,7
10
1).
synthesis from mixtures of functional and nonfunctional thiols.
AuNPs can be synthesized by the reduction of HAuCl with
NCDs with a gold nanoparticle core and thiol-functionalized
4
9
NaBH and stabilized by thiols (Figure 2).
dendrons at the focal point were synthesized by the Brust−
4
9
The Brust−Schiffrin method for AuNP synthesis allowed the
facile synthesis of heat- and air-stable AuNPs with a narrow
particle size distribution for the first time. Afterward, more
investigations opened an avenue to the synthesis of AuNPs
Schiffrin method. However, this approach required a large
excess of dendrons and had poor control of the nanoparticle core
dimension. Therefore, a new synthesis methodology is highly
desirable for a basic understanding of the structure/property
11
relationships of these nanostructures.
In an alternative synthetic method, the synthesis of monolayer-
protected nanoparticles is followed by building the dendrimer
architecture on functionalized nanoparticles. A high surface to
volume ratio of the nanoparticles and surface effects increase the
10,12
catalytic efficiency of these catalysts.
The development of catalytic reactions that use transition-
metal complexes as catalysts under neutral and mild reaction
8
Received: February 26, 2016
Figure 1. Metal-containing dendrimers.
©
XXXX American Chemical Society
A
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Article
conditions is particularly important, and catalysis with metal-
lodendritic complexes has attracted much attention in recent
years.
Scheme 1. C−C Coupling Reactions Catalyzed by [Ru-H@
AuNPs-TD]
Ruthenium-based complexes are generally considered to be
efficient catalysts due to their high activity and electron transfer
1
3
features. Among these complexes, ruthenium hydride catalysts
have received considerable attention due to their ability in the
1
4
catalysis of reductive carbon−carbon bond formations,
postpolymerization functionalization of conjugated polyisoper-
1
5
16
ene, synthesis of (E)-styryl ketones from styrene, and
1
7
conversion of dialdehydes and keto aldehydes to lactones.
Recently, we reported the catalytic activity of ruthenium
under an oxygen flow at a uniform heating rate of 20 °C min−1 in the
1
8
complexes in the alkylation of 1,3-dicarbonyl compounds,
range of 25−600 °C. Scanning electron microscope measurements were
carried out on a Hitachi S-4700 field emission-scanning electron
microscope (FE-SEM). Transmission electron microscopy (TEM) was
carried out on a Philips CM10 transmission electron microscope
operating at 100 kV. The Ru content of [Ru-H@AuNPs-TD] was
determined by a Jarrell−Ash 1100 ICP analysis. The complex
19,20
direct oxidation of alcohols to carboxylic acids, 23epoxidation
2
1,22
of alkenes,
and catalytic C−C bond formation.
In organic chemistry, the C−C coupling reaction refers to a
variety of reactions in which two hydrocarbon fragments are
coupled with the aid of a metal catalyst. The Heck, Suzuki−
Miyaura, Sonogashira, Stille, and Buchwald−Hartwig reactions
are different common reactions that are catalyzed by transition
metals and are widely used in the synthesis of pharmaceuticals,
biologically active molecules, natural products, and polymeric
[
RuHCl(CO)(PPh ) ] was prepared according to the method reported
3 3
34
in the literature. The substances were identified and quantified by gas
chromatography (GC) on an Agilent GC 6890 instrument equipped
with a 19096C006 80/100 WHP packed column and a flame ionization
detector (FID).
2
4,25
materials.
The Suzuki−Miyaura cross-coupling reaction,
Synthesis of Triazine Dendrimers Supported on Gold
Nanoparticles. Preparation of Gold Nanoparticles Modified by 4-
Aminothiophenol. A solution of HAuCl ·H O (500 mg) in CH OH
which is an increasingly popular method for the synthesis of
unsymmetrical biaryl compounds, is largely dominated by
palladium phosphine complexes. Therefore, the development
of new catalytic systems using other transition-metal species such
4
2
3
(
62.5 mL) was added to a solution of 4-aminothiophenol (0.4687 mg) in
3
CH OH (62.5 mL), and the mixture was stirred for 20 min. Then, a
freshly prepared solution of sodium borohydride (0.356 mg) in
deionized water (30 mL) was added to the vigorously stirred reaction
mixture. Stirring was continued for 1 h. Finally, the AuNPs stabilized
2
6,27
28,29
as nickel
and gold
is of great importance. Chang and co-
workers reported their investigations on the Suzuki-type cross-
coupling reactions of aryl iodides with phenylboronic acids using
with 4-aminothiophenol, AuNPs-ATP, were separated by centrifugation
3
0
35
Ru/Al O3 as catalyst. In another example, a ruthenium-grafted
and purified by successive washing with CH Cl and deionized water.
2 2
2
Preparation of AuNPs-ATP-CC . AuNPs-ATP (1 g) was added to a
triazine functionalized mesoporous polymer was reported as an
1
3
1
solution of cyanuric chloride (0.29 g, 1.57 mmol) and N,N-diisopropyl-
N-ethylamine (DIPEA, 1 mL) in THF (5 mL). The reaction mixture was
stirred at 0 °C for 18 h. The solid was separated by centrifugation,
efficient catalyst in Suzuki−Miyaura cross-coupling reactions.
In two other examples, biphenylene-substituted ruthenocenyl
3
2
33
phosphine and ruthenium phosphido complexes as support-
ing ligands for palladium-catalyzed Suzuki−Miyaura cross-
coupling reactions were reported.
25
washed with ethanol several times, and then dried in a vacuum oven.
Preparation of the First-Generation Dendrimer (G ). To a slurry of
1
AuNPs-ATP-CC (1 g) in DMF (10 mL) were added diethylenetri-
1
Cross-coupling reactions of aryl aldehydes with arylboronic
acids in Rh-, Pd-, and Pt-catalyzed reactions have already been
reported as an approach to access diaryl ketones. In 2011,
Fukuyama and co-workers reported [RuHCl(CO)(PPh ) ] to
amine (DETA, 1 mL) and DIPEA (1.4 mL). The reaction mixture was
stirred at 85 °C for 16 h. The solid part of the reaction mixture was
separated by centrifugation, washed with ethanol several times, and then
2
5
dried in a vacuum oven.
Preparation of AuNPs-ATP-CC . G (1 g) was added to a solution of
3
3
be an efficient homogeneous catalyst for the coupling reaction of
2
1
cyanuric chloride (1.28 g) and DIPEA (1.56 mL) in THF (10 mL). The
reaction mixture was stirred at 0 °C for 18 h. The solid was separated by
centrifugation, washed with ethanol several times, and then dried in a
arylboronic acids with aryl aldehydes to give the corresponding
1
4
diaryl ketones.
By combination of the advantages of CNDs and the
RuHCl(PPh ) CO] complex, herein we wish to report the
25
vacuum oven.
[
3
3
Preparation of the Second-Generation Triazine Dendrimer (G2).
preparation and characterization of a new thermally stable,
reusable, and efficient ruthenium hydride catalyst supported on
gold nanoparticles functionalized with dendrimers. In this
manner, a gold nanoparticle cored triazine dendrimer bearing
thiol groups as surface ligands was prepared and [RuHCl-
To a slurry of AuNPs-CC (1 g) in DMF (12 mL) were added 2-
2
aminoethanethiol (9.2 mmol, 0.71 g) and DIPEA (1.4 mL). The
reaction mixture was agitated at 85 °C for 16 h, and then the solid was
separated by centrifugation, washed with ethanol several times, and
2
5
dried in a vacuum oven.
Preparation of the [RuHCl(CO)(PPh ) ] Catalyst Supported on a
3
3
(
PPh ) CO] was attached to the thiol groups. The catalytic
3 3
Gold Nanoparticle Cored Dendrimer, [Ru-H@AuNPs-TD]. A mixture
activity of this new heterogeneous catalyst was investigated in
Suzuki−Miyaura C−C coupling reactions and also in the
synthesis of diaryl ketones (Scheme 1).
of [RuHCl(CO)(PPh ) ] (650 mg, 0.74 mmol) and the gold
3
3
nanoparticle supported triazine dendrimer G2 (1 g) in toluene (15
mL) was refluxed for 72 h, and then the solid was filtered, washed with
2
3
toluene, and dried under vacuum.
General Procedure for Suzuki−Miyaura Cross-Coupling
Reactions Catalyzed by [Ru-H@AuNPs-TD]. In a screw-capped
test tube, a mixture of aryl halide (1 mmol), phenylboronic acid (1.1
mmol), K CO (1.5 mmol), and the [Ru-H@AuNPs-TD] catalyst
EXPERIMENTAL SECTION
■
The chemicals used in this work were purchased from Fluka and Merck.
1
FT-IR spectra were recorded on a Jasco 6300 spectrophotometer. H
2
3
and 13C NMR (400 and 100 MHz) spectra were recorded on a Bruker
(0.011 mmol, based on the amount of Ru as determined from the ICP
Avance 400 MHz spectrometer using CDCl as solvent. Elemental
value of 0.293 mmol of Ru/g of [Ru-H@AuNPs-TD]) in toluene/H O
3
2
analysis was performed on a LECO CHNS-932 analyzer. Thermogravi-
(2/1) was prepared. The test tube was purged with argon and sealed.
metric analysis (TGA) was carried out on a Mettler TG50 instrument
The reaction mixture was stirred at 80 °C. The reaction progress was
B
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Scheme 2. Preparation of the [Ru-H@AuNPs-TD] Catalyst
monitored by GC. After completion of the reaction, the reaction mixture
was cooled to room temperature, and [Ru-H@AuNPs-TD] was
separated by centrifugation and washed with EtOH. The solvent was
evaporated under reduced pressure, and the residue was recrystallized
from ethyl acetate and ether (1/3) to afford the pure product. In all
cases, the isolated yields matched well with GC yields with only 2−7%
difference.
The solvent was evaporated under reduced pressure, and the residue was
purified by chromatography on a silica gel plate (petroleum ether/ethyl
acetate 20/1) to give the desired product.
Catalyst Recycling Procedure. The reusability of [Ru-H@AuNPs-
TD] was checked using sequential Suzuki−Miyaura cross-coupling
reactions of 4-iodoanisole with phenylboronic acid and the reaction of 4-
nitrobenzaldehyde with phenylboronic acid in the synthesis of diaryl
ketones. The reaction procedures were as described above. After the
reaction was completed, [Ru-H@AuNPs-TD] was easily recovered
from the reaction mixture by centrifugation, washed with EtOH, and
dried at 40 °C. The filtrates were used for the determination of Ru
leached by ICP analysis, and the recovered [Ru-H@AuNPs-TD]
catalyst was used in the next catalytic cycle using fresh 4-iodoanisole and
phenylboronic acid in the Suzuki−Miyaura cross-coupling reaction and
General Procedure for Synthesis of Diaryl Ketones Catalyzed
by [Ru-H@AuNPs-TD]. In a screw-capped test tube, a mixture of
phenylboronic acid (1 mmol), aryl aldehyde (2 mmol), [Ru-H@
AuNPs-TD] (0.023 mmol, based on the amount of Ru as determined
from the ICP value of 0.293 mmol of Ru/g of [Ru-H@AuNPs-TD]),
toluene (3 mL), K CO (2 mmol), and H O (1 mmol) was prepared.
2
3
2
The test tube was purged with argon and sealed. The reaction mixture
was stirred at 110 °C for 8 h. After the reaction was completed, [Ru-H@
AuNPs-TD] was separated by centrifugation and washed with EtOH.
C
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in the reaction of 4-nitrobenzaldehyde and phenylboronic acid in the
synthesis of diaryl ketones in the presence of K CO as base.
The surface morphology of the nanocatalyst [Ru-H@AuNPs-
TD] was directly visualized by FE-SEM (Figure 3). As can be
seen, [Ru-H@AuNPs-TD] particles are aggregated and have
formed a porous structure.
2
3
RESULTS AND DISCUSSION
■
Synthesis and Characterization of the Ruthenium
Hydride Catalyst Supported on a Gold Nanoparticle
Cored Triazine Dendrimer, [Ru-H@AuNPs-TD]. The prep-
aration route for the [Ru-H@AuNPs-TD] catalyst is shown in
Scheme 2. First, the AuNPs were prepared by reduction of
35
HAuCl with NaBH and then coated with 4-aminothiophenol.
4
4
The reaction of cyanuric chloride (CC) with the amines of the
AuNPs-ATP led to substitution of one chlorine atom in cyanuric
chloride. Then, AuNPs-ATP-CC was reacted with diethylenetri-
1
amine, to give G , which in turn converted to AuNPs-CC upon
1
2
reaction with cyanuric chloride. Finally, AuNPs-ATP-CC was
2
reacted with 2-aminoethanethiol to produce the gold nano-
particle cored triazine dendrimer (G or AuNPs-TD) as support.
2
These processes were monitored by FT-IR, elemental, and
thermogravimetric analyses (TGA).
The presence of bands in the FT-IR spectra at 1563−1608
−
1
−1
cm (CN) and 1408 and 2932 cm (C−H ) confirms the
aliph
−1
synthesis of the support. The broad bands at 3300−3500 cm
are due to primary and secondary amines in the structures of
AuNPs-ATP, AuNPs-ATP-CC , G , AuNPs-ATP-CC , and G
2
1
1
2
(
Figure S1 in the Supporting Information).
The weight loss of the dendrimer between 25 and 600 °C as a
Figure 3. FE-SEM image of [Ru-H@AuNPs-TD].
function of temperature was determined using TGA, which is an
irreversible process because of the thermal decomposition. The
TGA plots of AuNPs-ATP, AuNPs-ATP-CC , G , AuNPs-ATP-
The energy dispersive X-ray (EDX) results for AuNPs-TD and
[Ru-H@AuNPs-TD], shown in Figure 4, clearly showed the
presence of Ru in [Ru-H@AuNPs-TD].
The XPS spectra of the Ru 3d region are shown in Figure 5.
The Ru 3d3/2 peak could not be clearly observed, because the C
1s peak of the organic moieties overlaps with the Ru 3d3/2 peak.
The binding energy of the Ru 3d5/2 peak is 281.4 eV, which
clearly showed the presence of Ru species in [Ru-H@AuNPs-
TD].
1
1
CC and G depict a two-step thermal decomposition (Figure S2
2
2
in the Supporting Information). The first weight loss step
corresponds to the removal of physically adsorbed water, and the
main weight loss in the second step is due to the removal of
organic moieties on the surface. The observed total weight loss is
14%. A summary of the elemental analysis and TGA data is
included in Table 1.
The elemental mapping for Ru and Au together with an SEM
image is shown in Figure 6. The resulting images clearly showed
the distribution of Au and Ru elements in the texture of the [Ru-
H@AuNPs-TD].
Table 1. TGA and Elemental Analysis Results for Syntheses of
Gold Nanoparticle Cored Triazine Dendrimers
elemental analysis (%)
sample
TGA organic wt (%)
C
H
N
S
Further characterization of [Ru-H@AuNPs-TD] was per-
formed by transmission electron microscopy (TEM). The TEM
images of [Ru-H@AuNPs-TD] showed well-defined spherical
Au nanoparticles dispersed in a dendrimer matrix (Figure 7). The
average sizes of the Au nanoparticles are in the range of 15−22
nm (Figure 8). The larger particle sizes of the Au nanoparticles
prepared by this method in comparison to those in dendron
synthesis followed by AuNP coordination can be attributed to
the fragility of the Au−S bonds. This leads to Oswald ripening,
and a large dispersity of particle sizes from 5 to 60 nm was
obtained. The ruthenium content of [Ru-H@AuNPs-TD],
measured by ICP, showed a value of about 0.293 mmol/g.
From the TEM size distributions, one can obtain the average
core diameter (D) of the nanoparticles. The average number of
gold atoms in a cluster can then be calculated using eq 1, in which
AuNPs-ATP
AuNPs-ATP-CC1
G1
5
7
5.36
8.44
0.66
0.99
1.28
1.65
2.43
0.25
0.62
1.19
1.79
2.38
2.28
2.22
2.25
2.24
3.18
10
13
14
10.13
14.51
17.66
AuNPs-ATP-CC2
G2
An increase in the amount of carbon, hydrogen, and nitrogen
in each step and sulfur in the last step confirmed the successful
synthesis of the dendrimer. After preparation and character-
ization of AuNPs-TD, the ruthenium hydride catalyst was
immobilized on it to produce [Ru-H@AuNPs-TD] (Scheme 2).
The FT-IR spectrum of the complex [RuHCl(CO)(PPh ) ]
3
3
−1
showed characteristic bands at 2013 cm (Ru−H) and 1922
−3
36−39
−1
d is the density of gold (59 atoms nm ).
cm (CO) (Figure S3 in the Supporting Information).
According to Figure S4 in the Supporting Information, the FT-IR
spectrum of AuNPs-TD showed no aforementioned band in this
⎛
π ⎞
D3
NAu = d⎝
⎜ ⎟
⎠
(1)
region. The appearance of bands at 2052 and 1947 cm− in the
FT-IR spectrum of [Ru-H@AuNPs-TD] indicates that the
ruthenium complex has been successfully supported on the
dendrimer.
1
6
In this work, the average core diameter (D) is about 33 nm.
Therefore, the value of NAu is 1.11 × 10 atoms in a hypothetical
6
cluster.
D
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Article
Figure 6. SEM image and elemental mapping of Au and Ru.
Figure 4. SEM-EDX spectra of (a) AuNPs-TD and (b) [Ru-H@AuNPs-
TD].
Figure 5. XPS spectra of the Ru 3d region showing the peaks
corresponding to Ru 3d5/2 (orange line) and C 1s (pink line) in [Ru-H@
AuNPs-TD]. The black line is the average of these two peaks.
The ruthenium and gold contents of [Ru-H@AuNPs-TD],
measured by ICP, showed values of about 0.293 mmol of Ru/g
20
20
(1.76 × 10 atoms/g) and 0.84 mmol of Au/g (5.05 × 10
Figure 7. TEM images of the [Ru-H@AuNPs-TD] at different scales.
atoms/g). By consideration of the results of ICP analysis for Au
and NAu in a hypothetical cluster, the number of Au particles is
E
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Article
Table 2. Optimization of the Conditions in the Suzuki−
Miyaura Cross-Coupling of 4-Iodoanisole with
Phenylboronic Acid Catalyzed by [Ru-H@AuNPs-TD]
a
amt of catalyst
yield
b
entry
1
(mmol)
base
solvent
T (°C)
80
(%)
0
K CO3
2
toluene/H O
0
2
(
2/1)
2
3
4
5
0.005
0.008
0.011
0.014
K CO3
toluene/H O
80
80
80
80
36
57
85
87
2
2
(
2/1)
K CO3
2
toluene/H O
2
(
2/1)
K CO3
2
toluene/H O
2
(
2/1)
K CO3
2
toluene/H O
2
(
2/1)
6
7
8
0.011
0.011
0.011
K CO3
DMF
80
80
80
34
28
31
2
Figure 8. Histogram of Au particle size distribution.
K CO3
2
H O
2
K CO3
DMF/H O
2
14
2
about 4.55 × 10 . Therefore, the number of Ru atoms per Au
(
2/1)
5
nanoparticle is 3.9 × 10 .
9
0.011
0.011
0.011
K CO3
2
EtOH
80
80
80
35
53
68
Catalytic Experiments. Suzuki−Miyaura Cross-Coupling
Reactions of Aryl Halides with Arylboronic Acids. First, the
reaction conditions such as amount of catalyst, kinds of solvent
and base, and temperature were optimized in the Suzuki−
Miyaura cross-coupling reaction of 4-iodoanisole with phenyl-
boronic acid in the presence of [Ru-H@AuNPs-TD]. The results
are summarized in Table 2. In the optimization of the amount of
1
1
0
1
K CO3
2
toluene
K CO3
2
toluene/H O
(1/1)
2
12
13
14
0.011
0.011
0.011
0.011
0.011
0.011
K CO3
toluene/H O
room
temp
21
54
88
67
46
28
2
2
(
2/1)
K CO3
2
toluene/H O
50
100
80
80
80
2
(
2/1)
K CO3
2
toluene/H O
(2/1)
2
[
Ru-H@AuNPs-TD] catalyst, the highest yield was obtained in
the presence of 0.011 mmol of [Ru-H@AuNPs-TD] on the basis
of the Ru content. Smaller amounts of [Ru-H@AuNPs-TD] gave
lower yields, while when the amount was increased to 0.014
mmol, no significant increase was observed in the yield (entries
15
Na CO3 toluene/H O
2
2
(
2/1)
1
1
6
7
NaOH
toluene/H O
2
(
2/1)
Et N
3
toluene/H O
2
2
−5). It is noteworthy that in the absence of [Ru-H@AuNPs-
(
2/1)
TD] no product was detected in the reaction mixture (entry 1).
a
Reactions were performed using 4-iodoanisole (1 mmol), phenyl-
boronic acid (1.1 mmol), [Ru-H@AuNPs-TD], solvent (3 mL), and
base (1.5 mmol) under an Ar atmosphere for 3.5 h. Isolated yield.
Among the solvents used, aqueous toluene (toluene/H O 2/1 v/
2
b
v) was chosen as the reaction medium (entries 4 and 6−11). It
seems that the water attacks phenylboronic acid to form Ph−
B(OH) and facilitates the elimination of B(OH) .
3
3
In addition, the model reaction was carried out at different
temperatures; on the basis of the obtained results, the optimum
reaction temperature was found to be 80 °C (Table 2, entries 4
and 12−14). Then, the same reaction was carried out in the
presence of different organic and inorganic bases; K CO was
studies, under the same reaction conditions, the aryl iodides were
found to be more reactive than other aryl halides. Using the same
amount of [Ru-H@AuNPs-TD] catalyst, the aryl chlorides
needed higher temperature and longer reaction times. To the
best of our knowledge, this is the first report on the application of
a ruthenium hydride catalyst in the Suzuki−Miyaura C−C
coupling reaction.
Under the same reaction conditions described for heteroge-
neous [Ru-H@AuNPs-TD] catalyst, some of the reactions were
repeated in the presence of homogeneous [RuHCl(CO)-
2
3
found to be the most effective base (entries 4 and 15−17).
Therefore, it was concluded that the optimum reaction
conditions involved 4-iodoanisole (1 mmol), phenylboronic
acid (1.1 mmol), K CO (1.5 mmol), and the [Ru-H@AuNPs-
2
3
TD] catalyst (0.011 mmol, based on the Ru content) in toluene/
H O (2/1) at 80 °C under an Ar atmosphere.
2
In order to show the role of the ruthenium species, G2
(PPh ) ] catalyst (Table 3, entries 1, 5, and 9). The results
3 3
(
AuNPs-TD) was used as a catalyst in the model reaction. The
showed that the heterogeneous [Ru-H@AuNPs-TD] catalyst is
more efficient than the homogeneous catalyst. This can be
related to the dispersion on a nanomatrix in which the
catalytically active species are isolated.
Synthesis of Diaryl Ketones by the Reaction of Arylboronic
Acids with Aryl Aldehydes Catalyzed by [Ru-H@AuNPs-TD].
The catalytic activity of this [Ru-H@AuNPs-TD] catalyst was
further studied in the synthesis of diaryl ketones by the reaction
of arylboronic acids with aryl aldehydes (Ald). Initially, the
reaction of phenylboronic acid (PBA) with 4-nitrobenzaldehyde
was chosen as a model reaction to optimize the experimental
conditions such as ratio of phenylboronic acid to aldehyde,
results showed that the amount of biphenyl derivative was as
same as that in a blank experiment in the absence of [Ru-H@
AuNPs-TD] catalyst. This showed that the catalytically active
species is Ru and the Au nanoparticles play a supporting role.
The generality of this method was investigated in the Suzuki−
Miyaura cross-coupling of different aryl halides with arylboronic
acids (phenyl and 4-methoxyphenylboronic acids) in the
presence of [Ru-H@AuNPs-TD] under the optimized reaction
conditions. The results, which are summarized in Table 3,
showed that in this catalytic system the biphenyl derivatives were
produced in good to moderate yields. On the basis of these
F
DOI: 10.1021/acs.organomet.6b00163
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 3. Suzuki−Miyaura Cross-Coupling of Aryl Halides
presence of 0.023 mmol of [Ru-H@AuNPs-TD] (entries 5 and
7−10). Note that, in the absence of [Ru-H@AuNPs-TD], no
appreciable amount of product was obtained (entry 10).
with Arylboronic Acid Catalyzed by the [Ru-H@AuNPs-TD]
a
Recyclable Nanocatalyst
Different solvents such as toluene THF, DMF, DMSO,
methanol (with trace amounts of water), and water were used as
reaction media. As can be seen, the highest yield was obtained in
toluene (Table 4, entries 5 and 11−15). Finally, when different
bases such as K CO , NaOH, KOH, and NEt were used in the
entry
R′
R″
X
time (h)
yield (%) ,
bc
1
2
3
4
5
6
7
8
9
MeO
H
H
H
I
3.5
3
85 (68)
84
2
3
3
I
model reaction, K CO was selected as base.
2
3
MeO
H
4-MeO
4-MeO
H
I
4.5
5
80
Therefore, the optimized reaction conditions are phenyl-
boronic acid (1 mmol), aryl aldehyde (2 mmol), [Ru-H@
AuNPs-TD] (0.023 mmol, based on the Ru content), toluene (3
mL), K CO (2 mmol), and H O (1 mmol) at 110 °C under an
I
81
H
Br
Br
Br
Br
Cl
Cl
7
78 (31)
75
H
4-MeO
H
8.5
9.5
10
2
3
2
Me
MeO
H
71
argon atmosphere for 8 h (the role of water is in the hydrolysis of
H
75
d
ruthenium alkoxide, which is an intermediate in the catalytic
H
16
67 (16)
65
14
d
cycle).
10
H
4-MeO
20
a
In order to explore the scope and generality of the reaction,
arylboronic acids were reacted with different aromatic aldehydes
under the optimized conditions. The results are shown in Table
5. The reactions of arylboronic acids with aliphatic aldehydes
were sluggish in giving the corresponding ketones, but aromatic
Reactions (unless specified otherwise) were performed using aryl
halide (1 mmol), phenylboronic acid (1.1 mmol), K CO (1.5 mmol),
2
3
[
Ru-H@AuNPs-TD] (0.011 mmol, based on the Ru content), and
b
toluene/H O (3 mL) at 80 °C under an Ar atmosphere. Isolated
yield. The yields in parentheses refer to the homogeneous
2
c
[
RuHCl(CO)(PPh ) ] catalyst using the same amount of [Ru-H@
3 3
d
AuNPs-TD] catalyst. The reaction was performed under reflux
Table 5. Cross-Coupling Reaction of Aromatic Aldehydes
conditions.
a
with Phenylboronic Acid Catalyzed by [Ru-H@AuNPs-TD]
amount of [Ru-H@AuNPs-TD] catalyst, and kind of solvent and
base. The results are summarized in Table 4.
First, the PBA/Ald ratio was optimized and the best results
were detected with a 1/2 PBA/Ald ratio (Table 4, entries 1−6).
Then, the amount of [Ru-H@AuNPs-TD] was also optimized in
the model reaction and a higher yield was produced in the
Table 4. Optimization of the Conditions in the Cross-
Coupling Reaction of 4-Nitrobenzaldehyde with
Phenylboronic Acid Catalyzed by [Ru-H@AuNPs-TD]
a
amt of catalyst
(mmol)
yield
b
entry PBA/Ald
solvent
base
(%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1/1
1.5/1
2/1
1/1.5
1/2
1/2.5
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
0.023
0.023
0.023
0.023
0.023
0.023
0.014
0.008
0.038
0
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
THF
K CO3
61
54
42
74
85
88
58
24
90
0
2
K CO3
2
K CO3
2
K CO3
2
K CO3
2
K CO3
2
K CO3
2
K CO3
2
K CO3
2
0
1
2
3
4
5
6
7
8
K CO3
2
0.023
0.023
0.023
0.023
0.023
0.023
0.023
0.023
K CO3
2
66
45
38
34
26
51
42
36
DMF
K CO3
2
DMSO
methanol
K CO3
2
K CO3
2
H O
2
K CO3
2
toluene
toluene
toluene
NaOH
KOH
NEt3
a
Reaction conditions: phenylboronic acid (1 mmol), aldehyde (2
mmol), [Ru-H@AuNPs-TD] (0.023 mmol, based on the Ru content),
a
Reaction conditions: phenylboronic acid, 4-nitrobenzaldehyde, [Ru-
H@AuNPs-TD], base (2 mmol), H O (1 mmol), and solvent (3 mL)
at 110 °C under an argon atmosphere for 8 h. Isolated yield.
K CO (2 mmol), and H O (1 mmol) at 110 °C under an argon
atmosphere for 8 h. Isolated yield.
2
2
3
2
b
b
G
DOI: 10.1021/acs.organomet.6b00163
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
aldehydes gave good yields. Nitro-substituted aryl aldehydes
reacted with arylboronic acids more easily, and the correspond-
ing biaryl ketones were produced in high yields; under the same
reaction conditions, phenylboronic acids bearing a methoxy
group gave higher yields.
The possibility of the presence of an induction period in both
reactions was investigated. The reaction profiles (Figure 9)
showed no obvious induction period in the synthesis of diaryl
ketones (Figure 9A) and in the Suzuki−Miyaura cross-coupling
reaction (Figure 9B).
Table 6. Results of the [Ru-H@AuNPs-TD] Catalyst
Recovery
a
Suzuki−Miyaura reaction
diaryl ketone synthesis
b
b
run
yield (%)
Ru leached (%)
yield (%)
Ru leached (%)
1
2
3
4
85
78
72
68
4
2
1
0
85
74
68
62
6
4
1
0
a
Conditions for the Suzuki−Miyaura reaction: 4-iodoanisole (1
mmol), phenylboronic acid (1.1 mmol), K CO (1.5 mmol), [Ru-
2
3
H@AuNPs-TD] (0.011 mmol, based on the Ru content), and
toluene/H O (3 mL) at 80 °C under an Ar atmosphere. Conditions
2
for the diaryl ketone synthesis: phenylboronic acid (1 mmol), 4-
nitrobenzaldehyde (2 mmol), [Ru-H@AuNPs-TD] (0.023 mmol,
based on the Ru content), K CO (2 mmol), and H O (1 mmol) at
2
3
2
b
1
10 °C under an Ar atmosphere for 8 h. Isolated yield.
Miyaura reaction and 0.251 mmol/g (about 11% of the initial Ru
is leached) in the synthesis of diaryl ketones. The decrease in the
yield during the consecutive cycles can be attributed to the
leaching of ruthenium hydride catalyst during each cycle.
In both reactions, the hot-filtration test was also performed. In
the synthesis of diaryl ketone, [Ru-H@AuNPs-TD] was filtered
off in the model reaction after 3 h (33% conversion), and the
filtrate was then stirred at 110 °C. The results showed that the
reaction progress was only 4%. For the Suzuki−Miyaura cross-
coupling reaction, [Ru-H@AuNPs-TD] was filtered off after 90
min (31% conversion) and the filtrate was then stirred at 80 °C.
In this case, the reaction progress was only 3%.
The nature of the recovered [Ru-H@AuNPs-TD] catalyst was
studied by FT-IR spectroscopy. The presence of bands at 2052
and 1946 cm− in the FT-IR spectrum of the recovered [Ru-H@
AuNPs-TD] catalyst (Figure S5 in the Supporting Information)
confirmed that the ruthenium complex retained its initial
structure during the catalytic experiments.
1
CONCLUSION
■
In summary, we introduced a new heterogeneous catalytic
system based on a ruthenium hydride complex immobilized on
gold nanoparticles functionalized with triazine dendrimers and
investigated its catalytic activity in Suzuki−Miyaura cross-
coupling reactions of phenylboronic acids and aryl halides and
syntheses of diaryl ketones by the reaction of arylboronic acids
and aromatic aldehydes. Under the optimized reaction
conditions, all reactions afforded the related biphenyl derivatives
and diaryl ketones in good to excellent yields. Moreover, this
catalyst, [Ru-H@AuNPs-TD], can be well-dispersed in the
reaction medium, conveniently separated from the reaction
mixture, and reused several times without significant loss of its
activity.
Figure 9. Reaction profile for (A) synthesis of diaryl ketones by the
reaction of phenylboronic acid (1 mmol), 4-nitrobenzaldehyde (2
mmol), [Ru-H@AuNPs-TD] (0.023 mmol, based on the Ru content),
K CO3 (2 mmol), and H O (1 mmol) at 110 °C under an Ar
2
2
atmosphere and (B) Suzuki−Miyaura cross-coupling reaction of 4-
iodoanisole (1 mmol), phenylboronic acid (1.1 mmol), K CO (1.5
2
3
mmol), [Ru-H@AuNPs-TD] (0.011 mmol, based on the Ru content),
and toluene/H O (3 mL) at 80 °C under an Ar atmosphere.
2
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00163.
■
*
S
Catalyst Reusability. The reusability of [Ru-H@AuNPs-
TD] was studied as described in the Experimental Section. The
results showed that [Ru-H@AuNPs-TD] could be reused several
times with a slight loss in its activity (Table 6). The amount of
[
Ru-H@AuNPs-TD] catalyst leached was measured by ICP. The
results showed that the amount of ruthenium in the recovered
Ru-H@AuNPs-TD] catalyst after the fourth run was 0.263
mmol/g (about 9% of the initial Ru is leached) in the Suzuki−
FT-IR spectra of [AuNPs-TD], [RuHCl(CO)(PPh ) ],
3 3
AuNPs-TD, [Ru-H@AuNPs-TD], and recovered catalyst
and a thermogravimetric analysis curve of the catalyst
(PDF)
[
H
DOI: 10.1021/acs.organomet.6b00163
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
26) Wang, M.; Yuan, X.; Li, H.; Ren, L.; Sun, Z.; Hou, Y.; Chu, W.
AUTHOR INFORMATION
■
*
*
Catal. Commun. 2015, 58, 154−157.
(
2011, 133, 19505−19511.
(28) Dumbre, D.; Yadav, P.; Bhargava, S.; Choudhary, V. J. Catal. 2013,
Corresponding Authors
E-mail for M.M.: moghadamm@sci.ui.ac.ir.
E-mail for S.T.: stanges@sci.ui.ac.ir.
27) Tobisu, M.; Xu, T.; Shimasaki, T.; Chatani, N. J. Am. Chem. Soc.
3
01, 134−140.
29) Gonzalez-Arellano, C.; Corma, A.; Iglesias, M.; San
Catal. 2006, 238, 497−501.
30) Na, Y.; Park, S.; Han, S. B.; Han, H.; Ko, S.; Chang, S. J. Am. Chem.
Soc. 2004, 126, 250−258.
31) Salam, N.; Kundu, S. K.; Roy, A. S.; Mondal, P.; Ghosh, K.;
Bhaumik, A.; Islam, S. Dalton Trans. 2014, 43, 7057−7068.
32) Hoshi, T.; Nakazawa, T.; Saitoh, I.; Mori, A.; Suzuki, T.; Sakai, J-i.;
Notes
(
́
́
chez, F. J.
The authors declare no competing financial interest.
(
ACKNOWLEDGMENTS
■
(
This paper is dedicated to Professor Nasser Iranpoor on the
occasion of his 62th birthday and his honorable retirement. The
authors are grateful to the Research Council of the University of
Isfahan for financial support of this work.
(
Hagiwara, H. Org. Lett. 2008, 10, 2063−2066.
(
33) Planas, J. G.; Gladysz, J. Inorg. Chem. 2002, 41, 6947−6949.
(34) Chen, J.; Wang, M.; Liu, B.; Fan, Z.; Cui, K.; Kuang, Y. J. Phys.
Chem. B 2006, 110, 11775−11779.
35) Shakeri-Zadeh, A.; Eshghi, H.; Mansoori, G. A.; Hashemian, A. R.
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DOI: 10.1021/acs.organomet.6b00163
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