Transition metal nanoparticles stabilized by ammonium salts of hyperbranched polystyrene: effect of metals on catalysis of the biphasic hydrogenation of alkenes and arenes

Article abstract of DOI:10.1016/j.tet.2015.04.081

Abstract Hyperbranched polystyrene bearing ammonium salts (HPS-NR₃⁺Cl^-) behaves as an excellent stabilizer of ruthenium, rhodium, iridium, palladium, and platinum nanoparticles from 1 to 3 nm in size uniformly dispersed in the polymer matrix. The catalytic performance of the resulting metal-polymer composites, M@HPS-NR₃⁺Cl^-, is dependent on the metal. This dependence was investigated by assessing the hydrogenation of alkenes and arenes. The utility of M@HPS-NR₃⁺Cl^- as reusable catalysts in aqueous/organic biphasic systems was demonstrated by examining the catalysis of the hydrogenation of aromatic compounds containing various functional groups by Ru@HPS-NR₃⁺Cl^-.

Full text of DOI:10.1016/j.tet.2015.04.081

Tetrahedron xxx (2015) 1e10
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Transition metal nanoparticles stabilized by ammonium salts
of hyperbranched polystyrene: effect of metals on catalysis
of the biphasic hydrogenation of alkenes and arenes
,c,
Lei Gao a, Keisuke Kojima b, Hideo Nagashima a
*
a Institute for Materials Chemistry and Engineering, Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
b Chemical Research Laboratories, Nissan Chemical Industry, Ltd., Funabashi, Chiba 274-8507, Japan
c CREST, Japan Science and Technology Agency (JST), Kasuga, Fukuoka 816-8580, Japan
a r t i c l e i n f o
a b s t r a c t
Hyperbranched polystyrene bearing ammonium salts (HPS-NRþ3 Clꢀ) behaves as an excellent stabilizer of
ruthenium, rhodium, iridium, palladium, and platinum nanoparticles from 1 to 3 nm in size uniformly
dispersed in the polymer matrix. The catalytic performance of the resulting metal-polymer composites,
M@HPS-NRþ3 Clꢀ, is dependent on the metal. This dependence was investigated by assessing the hy-
drogenation of alkenes and arenes. The utility of M@HPS-NRþ3 Clꢀ as reusable catalysts in aqueous/organic
biphasic systems was demonstrated by examining the catalysis of the hydrogenation of aromatic com-
pounds containing various functional groups by Ru@HPS-NRþ3 Clꢀ.
Article history:
Received 12 March 2015
Received in revised form 18 April 2015
Accepted 23 April 2015
Available online xxx
Keywords:
Nanoparticle
Hydrogenation
Hyperbranched polymer
Catalysis
Ó 2015 Elsevier Ltd. All rights reserved.
Biphasic
1. Introduction
reported the synthesis of NPs of late transition metals, including
ruthenium, rhodium, iridium, palladium, and platinum, stabilized
Due to increasing interest in environmentally benign chemical
processes, high catalytic activity and catalyst recycling without
leaching of metallic species into products are currently important
issues.1 The immobilization of metal compounds on solid supports,
such that the catalyst may be separated from the product by fil-
tration, is one potential solution that has been investigated on both
laboratory and industrial scales.1,2 In addition, biphasic catalyst
systems in which the catalyst is recovered from the product by
simple phase separation is another possibility.1,3 The immobiliza-
tion of organometallic species in solution has been widely in-
vestigated, and the immobilization of metal colloids in the aqueous
phase4 has also received considerable attention, especially with
regard to the use of transition metal nanoparticles (NPs).5
Small metal NPs are not inherently stable and will rapidly ag-
gregate to form larger particles. However, they can be stabilized by
the addition of appropriate compounds such as organic surfactants,
heteroatom ligands, ionic liquids, and polymers.4,5 A typical exam-
ple are tetraalkylammonium salts, which have been studied since
the early days of NP chemistry.6 In a series of papers, Roucoux et al.
by tetraalkylammonium salts, and assessed the catalysis of these
materials.7 Metal NPs dispersed in polyvinylpyrrolidone (PVP) has
also been studied in detail.8 However, in such cases, the metal NPs
stabilized by these conventional supports havebeenprepared in situ
in water or alcohols and immediately used as catalysts, due to their
continued instability.7,8 In fact, there are few examples of the iso-
lation of these NPs in the solid state.9 Although applications of metal
NP catalysts in the aqueous phase to biphasic catalysis have been
examined, catalyst recycling has been reported infrequently, even in
studies employing high substrate/catalyst (S/C) ratios.7 Since NPs
supported by organoammonium salts or PVP cannot be dispersed in
organic solvents, biphasic catalysis, in which the catalyst is in an
organic phase and the substrate is in an aqueous phase, has rarely
been investigated. In this context, the development of new supports
for metal NPs has become a key issue with regard to the de-
velopment of newcatalytic systems, and improvements in supports,
such as by the modification of PVP, have been actively pursued.10
The catalytic hydrogenation of alkenes, arenes, and ketones is
often used to assess the catalytic properties of NPs supported by
organic or polymeric stabilizers.4e10 Although metal NPs generally
show good catalytic activity for alkene hydrogenation, it is more
difficult to achieve arene hydrogenation with high activity and
* Corresponding author. Tel./fax: þ81 92 583 7819; e-mail address: nagasima@
cm.kyushu-u.ac.jp (H. Nagashima).
http://dx.doi.org/10.1016/j.tet.2015.04.081
0040-4020/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Gao, L.; et al., Tetrahedron (2015), http://dx.doi.org/10.1016/j.tet.2015.04.081

2
L. Gao et al. / Tetrahedron xxx (2015) 1e10
selectivity.11 As a result, arene hydrogenation is often performed at
high temperatures under high H2 pressures. It is therefore desirable
to identify highly reactive metal NP catalysts that will improve the
reaction conditions. From the environmental point of view, the cat-
alyst should be separated from the product with ease and it is also
beneficial if the recovered catalyst is reusable. As well, with regard to
organic synthesis, reactions should proceed with high selectivity
undermildconditions. Ofparticularimportanceisthehydrogenation
of aromatic compounds containing reducible functional groups.12
The selective hydrogenation of aromatic compounds containing
glycidyl ether moieties while keeping the epoxido group intact is
a typical goal,13a because epoxides are sensitive towards acids and
bases and sometimes are reactive towards H2 in the presence of
metal catalysts.13a However, dispersible metal NPs stabilized by
conventional supports are often unstable in solution, resulting in
aggregation of the metals. This is the reason why these catalysts
typically exhibit high catalytic activity only at the initial stage of the
reaction and are difficult to recycle without any decline in effi-
ciency.14 To the best of our knowledge, there have been few reports
of the hydrogenation of aromatic molecules including reducible
functional groups, and no studies of the selective hydrogenation of
substrates including epoxido groups.
Recently, we reported that the ammonium salts of hyper-
branched polystyrene (HPS-NRþ3 Clꢀ) act as a novel stabilizer for
metal NPs.15 Hyperbranched polymers are dendritic macromole-
cules having highly branched polymer chains and a spherical
shape.16 It is noteworthy that many functional groups are present
preferentially on the surfaces of such polymers. The ammonium
salts of hyperbranched polystyrene (HPS-NRþ3 Clꢀ) are readily pre-
pared in three steps starting from a monomer, and are now pro-
duced on industrial scales.15a The excellent properties of HPS-
NRþ3 Clꢀ as metal NP supports have been studied by our own re-
search group, and M@HPS-NR3þClꢀ containing gold, palladium, and
platinum NPs 1e3 nm in size have been successfully prepared
(Fig. 1). The resulting M@HPS-NRþ3 Clꢀ (M¼Au, Pt, or Pd) are dis-
persible in a variety of solvents by judicious choice of the R group,
and exhibit good catalytic activity for the biphasic hydrogenation of
alkenes15a and the aerobic oxidation of alcohols with O2.15b The
recycling of these catalysts through simple phase separation is also
readily achieved. These results prompted us to assess M@HPS-
NRþ3 Clꢀ with regard to arene hydrogenation. In this paper, we de-
scribe the preparation and catalysis of ruthenium, rhodium, and
iridium NPs supported by HPS-NRþ3 Clꢀ. The catalytic properties of
these newly prepared M@HPS-NRþ3 Clꢀ are first compared with
those of the previously reported Pd and Pt@HPS-NRþ3 Clꢀ catalysts
based on the hydrogenation of several alkenes and toluene. Al-
though Ru@HPS-NRþ3 Clꢀ was not an efficient catalyst for the hy-
drogenation of alkenes compared with the rhodium, palladium,
and platinum homologues, it was applicable to the hydrogenation
of aromatic compounds bearing reducible functional groups. Two
types of water/organic biphasic hydrogenation, in which the cata-
lyst was in either the organic or the aqueous phase, were achieved,
and the catalyst phase was reusable without any decline of catalyst
efficiency. Furthermore, no metal leaching was observed.
2. Results and discussion
2.1. Preparation of ruthenium, rhodium, and iridium NPs
stabilized by HPS-NRD3 ClL
As reported previously, Pd and Pt NPs supported by the ammo-
nium salts of hyperbranched polystyrene (HPS-NRþ3 Clꢀ, R¼n-butyl
(nBu) or n-octyl (nOct)) were prepared by the thermal de-
composition of Pd2(dba)3$CHCl3 or Pt(dba)2 in the presence of HPS-
NRþ3 Clꢀ. As such, four of these material were prepared according to
methods reported previously: Pt@HPS-NnBuþ3 Clꢀ (Pt-1), Pd@HPS-
NnBuþ3 Clꢀ (Pd-1), Pt@HPS-NnOctþ3 Clꢀ (Pt-2), and Pd@HPS-
NnOct3þClꢀ (Pd-2).15a,15c The ruthenium (Ru), rhodium (Rh), and
iridium (Ir) NPs stabilized by the HPS-NRþ3 Clꢀ were synthesized by
the NaBH4 reduction of MCl3$3H2O (M¼Ru, Rh, or Ir) in the presence
of HPS-NRþ3 Clꢀ (Scheme 1). The preparation of Ru-1, Rh-1, and Ir-1
NPs stabilized by HPS-NnBu3þClꢀ was carried out in water, whereas
aqueous THF was used for the synthesis of Ru-2, Rh-2, and Ir-2 NPs
supported by HPS-NnOct3þClꢀ. Since HPS-NRþ3 Clꢀ contains both
hydrophobic portions, due to the polystyrene backbone, and hy-
drophilic regions, due to the charge on the ammonium groups, the
dispersibility of M@HPS-NRþ3 Clꢀ was tunable by employing the
appropriate R group. As an example, M@HPS-NnBuþ3 Clꢀ was readily
dispersed in water but not in toluene or EtOAc. In contrast, M@HPS-
NnOctþ3 Clꢀ could be dispersed in common organic solvents but not
in water. Alcohols were good solvents for both of these materials.
Scheme 1 shows the preparative procedures and transmission
electron microscopy (TEM) images of representative samples of Ru-
1, Rh-1, Ir-1, Pd-1, and Pt-1. The average NP sizes and size distri-
butions in these materials are summarized in Table 1. In all cases,
the NPs were uniform and had average particle sizes in the range of
1e3 nm. The metal content of each M@HPS-NRþ3 Clꢀ was 9e13 wt %,
as determined by inductively coupled plasma-mass spectrometry
(ICP-MS) analysis (Table 1). It is known that metal NPs stabilized by
organic ammonium salts or PVP are only stable in the solution state,
such that removal of the solvent causes precipitation of the bulk
metals.7e9 In sharp contrast, M@HPS-NRþ3 Clꢀ could be stored for
over a month either in solution or in the solid state under aerobic
conditions. No precipitate was observed from the stock solution
over this time span. As well, there were no evident differences in
the dispersibility of the solid sample before and after storage, and
neither the particle size of the M@HPS-NRþ3 Clꢀ nor the catalytic
activity was changed. The former was evidenced by TEM images of
Ru-1 after storage for one month in an aqueous solution or in the
solid state, as shown in the Supplementary data, whereas the latter
was proved by toluene hydrogenation under standard conditions
(S/C¼333, PH2¼30 atm, 30 ꢁC, 1 h). The >99% yield obtained from
this trial was comparable to that shown in Table 5, entry 17.
2.2. Catalytic hydrogenation of alkenes by M@HPS-NRD3 ClL
The catalytic properties of the M@HPS-NRþ3 Clꢀ materials were
investigated by studying the hydrogenation of mono-, di-, tri-, and
Fig. 1. Molecular images of HPS-NRþ3 Clꢀ and M@HPS-NR3þClꢀ
.
Please cite this article in press as: Gao, L.; et al., Tetrahedron (2015), http://dx.doi.org/10.1016/j.tet.2015.04.081

L. Gao et al. / Tetrahedron xxx (2015) 1e10
3
Scheme 1. Preparation of Ru, Rh, Ir, Pd, and Pt nanoparticles stabilized by HPS-NRþ3 Clꢀ and TEM images of Ru-1, Rh-1, Ir-1, Pd-1, and Pt-1. Images of Ru-2, Rh-2, Ir-2, Pd-2, and Pt-2
are presented in the Supplementary data.
Table 1
Table 3
Metal content and nanoparticle size of M@HPS-NRþ3 Clꢀ
Hydrogenation of 2,3-dimethyl-2-butene over M@HPS-NRþ3 Clꢀ in EtOH at 30 ꢁC (S/
C¼500)a
Entry
Metal NPs
Metal
Particle
contenta (wt %)
sizeb (nm)
Entry
Reaction
Cat
P(H2)
10
Time (h)
1
Conv.b (%)
73
1
2
3
4
5
6
7
8
9
Ru-1
Ru-2
Rh-1
Rh-2
Ir-1
12
12
12
13
9
1.7ꢂ0.3
1.2ꢂ0.2
1.9ꢂ0.4
1.7ꢂ0.3
1.9ꢂ0.4
1.7ꢂ0.3
2.1ꢂ0.4
2.3ꢂ0.4
1.9ꢂ0.3
1.7ꢂ0.4
1
Ru-1
2
3
4
5
6
7
8
9
Ru-2
Rh-1
Rh-2
Ir-1
10
10
10
10
10
10
10
10
1
3
1
3
3
3
3
3
3
3
3
>99
97
>99
0
0
66
Ir-2
9
Ir-2
Pd-1
Pd-2
Pt-1
Pt-2
9
Pd-1
Pd-2
Pt-1
Pt-2
11
11
11
82
>99
>99
>99
10
10
11
a
10
Determined by ICP-MS.
Measured by TEM.
b
a
The reaction was carried out with the catalyst (0.2 mol %) in EtOH (2 mL) at 30 ꢁ
under hydrogen pressure as indicated in the table.
C
b
Determined by 1H NMR using mesitylene as an internal standard.
Table 2
Table 4
Hydrogenation of cyclohexene over M@HPS-NRþ3 Clꢀ in EtOH at 30 ꢁC (S/C¼500)a
Selected examples of the mono- and biphasic hydrogenation of cyclohexene to as-
certain the highest TOF (hꢀ1) values for Rh-1, Pd-1, and Pt-1a
Entry
Reaction
Cat
P(H2)
Time (h)
Conv.b (%)
Entry
Cat
Solvent
S/C
5000
10,000
5000
10,000
5000
10,000
5000
Convb (%)
TOF (hꢀ1
)
1
Ru-1
Ru-2
10
3
>99
1
2
3
4
5
6
7
8
9
Rh-1
Rh-1
Pd-1
Pd-1
Pt-1
Pt-1
Rh-1
Pd-1
Pt-1
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOAc/H2O
EtOAc/H2O
EtOAc/H2O
>99
87
>99
83
>99
52
76
5000
8700
5000
8300
5000
5200
3800
3750
1600
2
3
4
5
6
7
8
9
10
10
1
1
3
1
1
3
3
1
1
1
1
15
>99
>99
>99
21
Rh-1
Rh-2
Ir-1
1
10
10
1
1
1
Ir-2
13
Pd-1
Pd-2
Pt-1
Pt-2
>99
>99
>99
>99
5000
5000
75
32
10
11
a
1
The reaction was carried out with the catalyst (0.01e0.02 mol %) in EtOH (2 mL)
or a mixture of EtOAc (2 mL) and H2O (2 mL) for 1 h at 30 ꢁC under a hydrogen
atmosphere (1 atm).
a
The reaction was carried out with the catalyst (0.2 mol %) in EtOH (2 mL) for 1 h
at 30 ꢁC under hydrogen pressure as indicated in the table.
b
b
Determined by GC with n-decane as an internal standard.
Determined by GC with n-decane as an internal standard.
Please cite this article in press as: Gao, L.; et al., Tetrahedron (2015), http://dx.doi.org/10.1016/j.tet.2015.04.081

4
L. Gao et al. / Tetrahedron xxx (2015) 1e10
hydrogenation of cyclohexene could be performed at 30 ꢁC under
1 atm of H2 in 1 h. All of the reactions went to completion at an S/C
ratio of 5000. In trials for, which S/C was set at 10,000, the con-
versions varied from 50 to 90%, from, which the turnover frequency
(TOF) values for Rh-1, Pd-1, and Pt-1 can be estimated to be 5000 to
9000 hꢀ1 under these conditions. The TOF values of these nano-
particle catalysts were comparable or higher than those reported in
the literature.20 As an example, Hensen and co-workers have re-
cently reported the hydrogenation of 1-octene with Rh NPs stabi-
Table 5
Mono- and biphasic hydrogenation of toluene with M@HPS-NRþ3 Clꢀ
Entry
Catalyst
Solvent
H2 (atm)
conv.d(%)
TOF (hꢀ1
)
lized by PVP, in which the TOF at 70 ꢁC was 10,000 hꢀ1 20a
.
1
2
3
4
5
6
7
8
Rh-1
EtOHa
30
30
30
30
30
30
30
30
30
30
30
30
30
1
10
50
Trace
Trace
<1
0
0
0
0
Trace
Trace
Trace
35
8
30
95
>99
27
>99
48
6
50
167
d
The advantage of the M@HPS-NnBuþ3 Clꢀ series is its unique
dispersibility in solvents, such that it is dispersible in water but not
soluble in EtOAc. Biphasic hydrogenation, in which the cyclohexene
was in the organic phase and the catalyst was in the aqueous phase,
was therefore examined using Rh-1, Pd-1, or Pt-1 as the catalyst
(Table 4, entries 7e9). Although the catalytic activity was some-
what lower than that observed during the single phase experiment
in EtOH, the reaction proceeded smoothly and TOF values reached
1600, 3750, and 3800 hꢀ1 in the trials using Pt-1, Pd-1, and Rh-1,
respectively. This suggests the possibility of recycling the catalyst
by phase separation, and results of such tests are described further
on.
H2Ob
Rh-2
Ir-1
EtOHa
EtOHa
d
H2Ob
d
Ir-2
Pd-1
EtOHa
d
EtOHa
d
H2Ob
d
9
Pd-2
Pt-1
EtOHa
d
10
11
12
13
14
15
16
17
18e
19
20
21
22
23
EtOHa
d
H2Ob
d
Pt-2
Ru-1
EtOHa
d
EtOHa
175
27
H2Ob
H2Ob
5
100
316
>333
900
>333
160
20
H2Ob
10
30
30
30
30
30
30
30
H2Ob
2.3. Catalytic hydrogenation of toluene by M@HPS-NRD3 ClL
H2Ob
EtOAc/H2Oc
n-Hexane/H2Oc
CH2Cl2/H2Oc
Et2O/H2Oc
EtOHa
Similar experiments for the hydrogenation of toluene generated
different results from those obtained during the hydrogenation of
alkenes. The reactions shown in Table 5 were performed at 30 ꢁC for
1 h. When EtOH was used as the solvent, the iridium, palladium and
platinum catalysts did not show any reactivity even under 30 atm of
H2. In sharp contrast, the rhodium catalysts showed some activity
and the ruthenium catalysts, under 30 atm of H2, gave the highest
activity among the various trials. In experiments with S/C¼2000,
a TON value of 1540 was achieved (representing a 77% toluene
conversion) after 5 h when Ru-1 was used as the catalyst, whereas
the reaction went to completion (TON >2000) when employing
Ru-2. The trials investigating biphasic catalysis (S/C¼333 at 30 ꢁC
for 1 h) were carried out using M@HPS-NRþ3 Clꢀ with the catalyst
immobilized in the aqueous phase. In the absence of an organic
solvent, no reaction took place when using Ir-1, Pd-1, or Pt-1, al-
though Ru-1 exhibited good catalytic performance under from 1 to
30 atm of H2. The reaction thus took place even under 1 atm of H2,
although the conversion of toluene was less than 10%
(TOF¼27 hꢀ1). The effect of hydrogen pressure was significant in
the hydrogenation reactions catalyzed by Ru-1, and the TOF value
could be increased by raising the hydrogen pressure, such that the
reaction was complete within 1 h under 30 atm of H2. When the S/C
was set at 3333, the conversion after 1 h was 27%, corresponding to
a TOF of 900 hꢀ1, a value that is higher than previous values re-
ported in the literature.21 The addition of organic solvents to this
aqueous catalyst system led to biphasic hydrogenation, and good
TOF values were obtained when either EtOAc or Et2O was used as
the organic phase.
It was curious that the rhodium catalysts did not show good
catalytic performance for the hydrogenation of toluene, since
rhodium NPs have been shown to efficiently catalyze the hydro-
genation of arenes.22,23 The lower conversion observed in the case
of toluene was ascribed to the facile decomposition of the catalyst
under the reaction conditions. When Rh-1 was used as the catalyst,
TEM images after the hydrogenation showed the presence of large
particles in either EtOH or H2O. In contrast, no catalyst deactivation
or aggregation of Rh NPs was observed following alkene hydroge-
nation with Rh-1 under 1 atm of H2. These catalysts were also
found to be recyclable, as described further on. Consequently, it is
likely that the application of high H2 pressures induced the rapid
aggregation of the Rh NPs.
92
52
306
260
Ru-2
a
The reaction was carried out in EtOH in the presence of the catalyst
(0.2e0.3 mol %) at 30 ꢁC for 1 h.
b
The reaction was performed in water with 0.3 mol % catalyst.
A 1/1 mixture of water and organic solvent was used for the biphasic system
c
with 0.3 mol % catalyst.
d
Determined by GC analysis with n-decane as an internal standard.
0.03 mol % Ru-1 was used (S/C¼3333).
e
tetrasubstituted alkenes at 30 ꢁC under 1 atm of H2.17 The reactions
were carried out in EtOH, which gave a homogeneous solution of
the catalyst and the substrate. The substrate/catalyst ratio (S/C) was
set at 500. The hydrogenations of 1-octene and cyclohexene were
examined, and the results of cyclohexene hydrogenation are sum-
marized in Table 2. The high catalytic activities of the rhodium (Rh-
1, Rh-2), palladium (Pd-1, Pd-2), and platinum catalysts (Pt-1, Pt-2)
were clearly demonstrated, and each reaction was complete within
1 h (entries 4e5, 8e11). The ruthenium catalyst did not exhibit
catalytic activity under 1 atm of H2, although the reaction did
proceed under 10 atm of H2 (entries 1e3). In contrast, the catalytic
activity of the iridium compounds was significantly lower. It should
be noted that there was no substantial difference in catalytic ac-
tivity between the two supports, HPS-NnBuþ3 Clꢀ and HPS-
NnOctþ3 Clꢀ, as long as EtOH was used as the solvent. Similar results
were obtained for the hydrogenation of 1-octene and 1-
methylcyclohexene, as described in the Supplementary data.
It is well known that the efficient hydrogenation of tetrasub-
stituted alkenes is challenging when using conventional cata-
lysts.2,17,18 Table 3 shows the results of the hydrogenation of 2,3-
dimethyl-2-butene, in which a higher H2 pressure (10 atm) is seen
to be necessary to complete the hydrogenation reaction within the
span of a few hours. It is of interest that the activity of the ruthenium
catalysts was comparable to that of the rhodium and platinum
catalysts under 10 atm of H2.19 The palladium catalysts showed
somewhat lower activity under the same conditions and, again, the
iridium catalysts were not effective even under 10 atm of H2.
Trials using lower catalyst loadings showed that the initial cat-
alytic activity was dependent on the metal employed, as evident
from Table 4. Using Rh-1, Pd-1, or Pt-1 as the catalyst, the
Please cite this article in press as: Gao, L.; et al., Tetrahedron (2015), http://dx.doi.org/10.1016/j.tet.2015.04.081

L. Gao et al. / Tetrahedron xxx (2015) 1e10
5
2.4. Catalytic hydrogenation of arenes with functional groups
Table 6
Hydrogenation of various arenes catalyzed by Ru-1a
The utility of Ru-1 was demonstrated by the hydrogenation of
substituted arenes in water, as shown in Table 6 [S/C¼333 under H2
(30 atm)]. Toluene, phenol, and anisole underwent hydrogenation
smoothly at 30 ꢁC under 30 atm of H2. After 1 h, the corresponding
products methylcyclohexane, cyclohexanol, and methyl cyclohexyl
ether, respectively, were obtained in quantitative yields (entries
1e3). Hydrogenation of phenol resulted in the exclusive formation
of cyclohexanol, although the generation of cyclohexanone has
been reported in certain cases.13a Compared with these substrates,
the hydrogenation of acetophenone under the same conditions was
slower, since the reduction of the ketone was competing with arene
hydrogenation (entry 4). The hydrogenations of benzonitrile, ni-
trobenzene, and bromobenzene did not take place under these
conditions. At 80 ꢁC, aniline was formed (79% over 5 h) from ni-
trobenzene, whereas in the case of bromobenzene dehalogenation
was accompanied by arene hydrogenation to form cyclohexane. The
substituent on the arene ring has been reported to have an effect on
the rate of hydrogenation, such that electron-withdrawing sub-
stituents retard the reaction.14 The reaction of acetophenone (entry
4) was not a suitable test of the substituent effect because the
carbonyl reduction predominantly occurred over the arene hydro-
genation. In contrast, the shorter reaction times in entries 1e3
compared to those in entries 8 and 9 are in agreement with this
effect. However, as shown by the comparison of entries 8 and 9 with
entries 10e13, the reaction rate is about the same or even lower
when the carbonyl group of an ester or an amide is not directly
bonded to the benzene ring. These results may be ascribed to the
coordination of the ester and amide carbonyl to the catalyst surface,
thereby acting as a catalyst poison. In other words, the results
shown in entries 5e9 could be explained by both the electron-
withdrawing properties of the cyano-, nitro-, and bromo groups
and catalyst poisoning by the lone pair contained in these func-
tional groups. A chiral alcohol, (R)-1-phenylethanol, was subjected
to hydrogenation at 30 ꢁC to give (R)-1-cyclohexylethanol in high
yield without racemization (entry 14; the details are given in
Supplementary data).
Entry
1
Substrate
Temp (ꢁC)
30
Time (h)
1
yieldb (%)
>99
2
30
1
>99
3
4
30
30
1
1
>99
74c
5
6
7
8
30
30
30
30
1
1
0
0
1
0
12
95
9
30
30
18
12
92
96
Disubstituted arenes, ortho-, meta-, and para-xylene, were hy-
drogenated to give the corresponding dimethylcyclohexanes in 93,
82, and 89% yields within 1 h. In all cases, the cis isomers were the
major products; the cis/trans ratios were 92/8, 89/11, and 75/25,
respectively, which is consistent with the results of reactions cat-
alyzed by other dispersed metal NP systems.7b
10
As described above, the arene hydrogenation would compete
with reduction of the oxo group during the reaction of acetophe-
none (Table 6, entry 4). Prolonging the reaction time to 12 h
resulted in complete hydrogenation of both the arene ring and the
oxo group to give 1-cyclohexylethanol in 94% yield (conversion of
acetophenone >99%). In contrast, effective suppression of arene
hydrogenation was achieved by the addition of pyridine (0.5 equiv
relative to acetophenone) to give 1-phenylethanol as shown in
Scheme 2. Similar complete and selective hydrogenations were also
observed upon using 4-phenyl-2-butanone as the substrate. The
effect of pyridine on the selective reduction of ketones is similar to
that observed for the heterogeneous platinum catalysts.24 In sharp
contrast, the hydrogenation of benzaldehyde and 3-phenylpropanal
afforded benzyl alcohol and 3-phenyl-1-propanol in 89% (30 ꢁC,
12 h) and 52% (50 ꢁC, 36 h) yields, respectively. In such cases, only
reduction of the aldehyde groups to the corresponding primary
alcohols was observed without further hydrogenation of the aro-
matic ring, even in the absence of pyridine.
11
30
24
93
12
13
50
50
36
12
90
95
14
30
12
92d
a
All reactions were carried out with the substrate (1 mmol) and Ru-1
(Ru¼0.3 mol %, S/C¼333) in H2O (1 mL).
b
For entries 1e7, GC yields with n-decane as an internal standard; for entries
8e14, isolated yields.
A special feature of M@HPS-NRþ3 Clꢀ is the potential preparation
of both water-dispersible and organo-dispersible catalysts, as de-
scribed above. The organo-dispersible Ru-2 catalyst is applicable to
the biphasic hydrogenation of water-soluble substrates. In a typical
c
The ratio of 1-cyclohexylethanone to 1-phenylethanol was 39/61 as determined
by 1H NMR.
d
Both the starting material and the product were >99% ee by chiral GC analysis.
Please cite this article in press as: Gao, L.; et al., Tetrahedron (2015), http://dx.doi.org/10.1016/j.tet.2015.04.081

6
L. Gao et al. / Tetrahedron xxx (2015) 1e10
Table 7
Hydrogenation of various arenes containing epoxido-groups catalyzed by Ru-1a
Entry Substrate
Product
Time (h) Yieldb
(%)
1
6
24
24
90
96
2
3
93
4c
The precursor of entry 4 The product of entry 4 24
83d
a
All reactions were carried out with the substrate (1 mmol) and Ru-1
(Ru¼0.3 mmol%, S/C¼333) in H2O (1 mL) at 30 ꢁC under H2 (30 atm).
b
Isolated yield.
c
Substrate¼0.5 mmol, S/C¼56, in a 1/1 mixture of EtOAc/H2O (6 mL).
d
Isolated yield after column chromatography. The ratio of cis to trans isomers was
87/13 as determined by 1H NMR.
Scheme 2. Selectivity during the hydrogenation of arenes containing carbonyl groups
as catalyzed by Ru-1 in the absence or presence of pyridine.
example, the hydrogenation of 1-(2-(2-(2-methoxyethoxy)ethoxy)
ethoxy) benzene was performed in benzotrifluoride (BTF) (S/
C¼100) at 30 ꢁC under H2 (30 atm) for 24 h (Scheme 3). The product
was readily separated by extraction of the reaction mixture with
water, while the catalyst remained in the BTF layer. The desired
product was obtained from the combined aqueous layers in over
90% yield.
of epoxido-containing arenes took place.13b,13c To ensure the suc-
cessful hydrogenation of aryl and heteroaryl glycidyl ethers while
keeping the epoxido group intact it was therefore necessary to use
Rh@CNF, which is more expensive than Ru@CNF.13a
2.6. Recycling of the catalyst
The final goal of this study was to demonstrate biphasic hydro-
genation and catalyst recycling. Table 8 summarizes four experi-
mental trials regarding catalyst recycling: (A) the hydrogenation of
cyclohexene by Rh-1, (B) the hydrogenation of toluene by Ru-1, (C)
the hydrogenation of glycidyl phenyl ether by Ru-1, and (D) the
hydrogenation of 1-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy) ben-
zene by Ru-2. Experiment A was performed at 30 ꢁC under 1 atm of
H2 and an S/C of 2000 was found to be suitable for one cycle of the
reaction, which was complete in 1 h. The aqueous phase containing
Rh-1 was recycled five times without any decline in the catalyst’s
efficiency and the total TON reached a value of 10,000.26 In two
additional experiments using Ru-1, the S/C was set to 1000 (ex-
periment B) and 333 (experiment C), and the reactions were carried
out at 30 ꢁC under 30 atm of H2. Here the catalyst phase could be
recycled over five trials while maintaining the catalytic activity.
Experiment D was different from the above three trials, such that
the Ru-2 was immobilized in the organic phase (BTF). Although
a longer reaction time was required to complete the reaction, even
with a relatively large catalyst loading (S/C¼100), the catalyst phase
was reusable three times. In all cases, the recovered M@HPS-
NRþ3 Clꢀ was subjected to TEM analysis. The particle size of the Rh-1
was observed to be unchanged over the five recycling trials in ex-
periment A. In contrast, a slight increase in the particle size was
found during the three experiments using the ruthenium catalysts.
For example, the Ru-1 particle size was changed from 1.4ꢂ0.3 nm to
1.6ꢂ0.3 nm in experiment B (Fig. 2). We also assessed the leaching
of metallic species into the product in these catalyst recycling ex-
periments. In all cases, the residual amount of metal in the phase
Scheme 3. Hydrogenation of a water-soluble substrate, 1-(2-(2-(2-methoxyethoxy)
ethoxy)ethoxy) benzene, catalyzed by Ru-2.
2.5. Catalytic hydrogenation of arene ring with the epoxido-
group remaining intact
It is known that the ring-opening reaction of epoxido groups is
significantly promoted by H2 activated by transition metal cata-
lysts.13a However, it was found during trials with Ru-1 that the
benzene rings of several aromatic compounds containing epoxido
groups were successfully hydrogenated while the epoxido groups
remained intact, as summarized in Table 7. In entries 1 and 2, the
hydrogenations of both phenyl and benzyl glycidyl ethers pro-
ceeded smoothly to give the corresponding cyclohexyl compounds.
No by-products were observed in either case. The selective hydro-
genation of a furan derivative (entry 3) gave a tetrahydrofurfuryl
glycidyl ether. The product shown in entry 4 represents an impor-
tant type of compound used as a cross-linking reagent in the pro-
duction of epoxy resins.25 Similar to the hydrogenation of para-
xylene, the product was also a mixture of cis and trans isomers, at
a ratio of 87/13. We have previously reported ruthenium NPs sup-
ported by carbon nanofibers (CNFs), which was useful as a reusable
catalyst for arene hydrogenation. Although their catalytic efficiency
was high (TON >5000), these Ru@CNFs only catalyzed the reaction
at high temperatures (100 ꢁC) at, which the ring-opening reaction
Please cite this article in press as: Gao, L.; et al., Tetrahedron (2015), http://dx.doi.org/10.1016/j.tet.2015.04.081

L. Gao et al. / Tetrahedron xxx (2015) 1e10
7
Table 8
containing the product was measured by ICP-MS and it was found
that the amount of metal was below the detection limit of the
method (<0.28 ppm).
Catalyst recycling of M@HPS-NRþ3 Clꢀ following biphasic hydrogenation of alkenes
and aromatic compounds
(A) Hydrogenation of cyclohexene to cyclohexane catalyzed by Rh-1a
3. Conclusion
Run
1st
2nd
3rd
4th
5th
Convb (%)
>99
>99
>99
>99
>99
Rhodium, ruthenium, and iridium NPs with sizes of 1e3 nm
were effectively stabilized by the ammonium salts of hyper-
branched polystyrene (HPS-NRþ3 Clꢀ). The resulting M@HPS-NR3þClꢀ
were sufficiently stable so as to allow their storage either in solu-
tion or in the solid state for over a month. The dispersibility of these
materials could be tuned by careful selection of the R group;
M@HPS-NnBuþ3 Clꢀ was dispersible in water but not in toluene and
EtOAc, whereas M@HPS-NnOctþ3 Clꢀ could be dispersed in common
organic solvents but not in water. Rh-1 and Rh-2, as well as their
palladium and platinum analogues, showed high catalytic activity
towards mono-, di-, tri-, and tetrasubstituted alkenes under mild
conditions. In contrast, the ruthenium derivatives, Ru-1 and Ru-2,
exhibited good catalytic performance for arene hydrogenation. The
hydrogenation of aromatic compounds having various functional
groups was achieved by Ru-1 immobilized in an aqueous phase.
Successful hydrogenation of the aromatic or heteroaromatic ring in
several aryl or heteroaryl glycidyl ethers suggested that the present
biphasic hydrogenation is tolerant of functional groups normally
sensitive towards acids and bases. Water/organic biphasic hydro-
genations were achieved using Ru-1 dispersed in the aqueous
phase, and were applicable to the hydrogenation of organo-soluble
substrates. In contrast, the immobilization of Ru-2 in BTF led to the
successful hydrogenation of a water-soluble substrate. Catalyst
recycling trials with phenyl glycidyl ether proceeded smoothly
under mild conditions in which the ring-opening reaction of
epoxido groups was not observed. The excellent durability of
M@HPS-NRþ3 Clꢀ in catalyst recycling experiments was demon-
strated by TEM analysis of the particle size before and after the
reactions, with almost no change after several recycling trials. It is
important to note that, in all of the catalyst recycling experiments,
the catalyst was recyclable without any decline in the catalyst ef-
ficiency, and with no leaching of the metal observed in the product.
These results clearly demonstrate the utility of HPS-NRþ3 Clꢀ as
a support for second and third row late transition metals, and the
promising potential applications of M@HPS-NRþ3 Clꢀ to other cata-
lytic reactions mediated by metal NPs. Finally, we wish to empha-
size that homogeneous catalysis has been developed using soluble
organometallic complexes as the catalyst. The next generation of
homogeneous catalysts should be expanded to include dispersible
nanometal particles, which are anticipated to exhibit high catalytic
activity as well as possible recycling without metal leaching. The
results presented in this paper are considered a step towards the
eventual application of such materials.
(B) Hydrogenation of toluene to methylcyclohexane catalyzed by Ru-1c
Run
1st
2nd
3rd
4th
5th
Convd (%)
>99
>99
>99
>99
>99
(C) Hydrogenation of glycidyl phenyl ether to cyclohexyl glycidyl ether catalyzed
by Ru-1e
Run
1st
2nd
3rd
4th
5th
Convf (%)
>99
90
>99
91
>99
91
>99
90
>99
Yieldg (%)
90
(D) Hydrogenation of 1-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy) benzene to (2-(2-
(2-methoxyethoxy)ethoxy)ethoxy) cyclohexane catalyzed by Ru-2h
Run
1st
2nd
3rd
Convi (%)
>99
92
>99
90
>99
92
Yieldj(%)
a
Each experiment was carried out with S/C¼2000 in a biphasic system composed
of EtOAc and H2O (1:1) under H2 (1 atm) at 30 ꢁC for 1 h.
b
Determined by GC analysis with n-decane as an internal standard.
Each experiment was carried out with S/C¼1000 in a biphasic system composed
c
of EtOAc and H2O (1:1) under H2 (30 atm) at 30 ꢁC for 4 h.
d
Determined by GC analysis with n-decane as an internal standard.
Each experiment was carried out with S/C¼333 in a biphasic system composed
e
of EtOAc and H2O (1:1) under H2 (30 atm) at 30 ꢁC for 6 h.
f
Determined by 1H NMR.
Isolated yield.
Each experiment was carried out with S/C¼100 in BTF under H2 (30 atm) at
g
h
30 ꢁC for 24 h.
i
Determined by 1H NMR.
Isolated yield.
j
4. Experimental section
4.1. General methods
All reagents were used as-received and were obtained from
commercial suppliers, with the exceptions of N,N-dimethyl-3-
phenylpropionamide27 and 1-(2-(2-(2-methoxyethoxy)ethoxy)eth-
oxy) benzene,28 both of which were synthesized according to re-
ported methods. The butyl and octyl derivatives of HPS-NR3Cl and
their palladium and platinum composites were prepared according
to a method reported previously.15 The two aldehydes, benzaldehyde
and 3-phenylpropanal, were distilled under reduced pressure before
use, while the other substrates were used as-received. 1H and 13C
NMR spectra were acquired on ECA-400 (396 MHz) or ECA-600
(600 MHz) spectrometers in CDCl3. Transmission electron micros-
copy (TEM, JEOL JEM-2100F, V¼200 kV), high resolution mass
Fig. 2. TEM images and particle size distributions of Ru-1: A) before and B) after five
repeated cycles of toluene hydrogenation (experiment B). Similar TEM images before
and after catalyst recycling trials for the other three reactions (experiments A, C, and D)
are provided in the Supplementary data.
Please cite this article in press as: Gao, L.; et al., Tetrahedron (2015), http://dx.doi.org/10.1016/j.tet.2015.04.081

8
L. Gao et al. / Tetrahedron xxx (2015) 1e10
spectrometry (HRMS) and inductively coupled plasma mass spec-
trometry (ICP-MS, Shimadzu ICPM-8500) analyses were performed
at the Analytical Center in the Institute for Materials Chemistry and
Engineering, Kyushu University. Neither organic by-products nor
metal residues were observed during analysis by NMR or ICP-MS in
all the cases described below, indicating no further purification was
required. To avoid possible contamination by impurities from the
solventorthereagents, isolatedyieldsweredetermined afterpassing
productsthrough a short chromatographic column, unless otherwise
noted. Spectral data for new products are presented below, while
data for other products are described in the Supplementary data, and
were found to be consistent with those reported in the literature.
under a hydrogen atmosphere (1 atm). Alternatively, the reaction
was performed in an autoclave fitted with an inner glass tube under
10 atm of H2. The mixture was subsequently diluted with diethyl
ether and passed through a short column of Celite to remove the
metal nanoparticles. The conversion of the alkene was determined
by GC analysis using n-decane as an internal standard, except when
employing 2,3-dimethyl-2-butene as the substrate, for, which the
conversion was determined by 1H NMR using mesitylene as an
internal standard. In the experiments shown in Table 4, hydroge-
nation was performed with lower catalyst loadings. Cyclohexene (2
or 4 mmol for S/C¼5000 or 10,000, respectively) was treated with
M@HPS-NnBuþ3 Clꢀ (M¼0.4
mmol) in 2 mL of EtOH or a mixture of
EtOAc (2 mL) and H2O (2 mL) at 30 ꢁC under hydrogen (1 atm). After
a work-up similar to that described above, the conversion of the
alkene was determined by GC analysis using n-decane as an in-
ternal standard.
4.2. Preparation of M@HPS-NRD3 ClL (M[Ru, Rh, and Ir)
4.2.1. Preparation of water-dispersible Ru@HPS-NnBuþ3 Clꢀ (Ru-1,
Rh-1,and Ir-1). To an aqueous solution of HPS-NnBuþ3 Clꢀ (600 mg
in 20 mL of H2O) was added a solution of RuCl3$3H2O (155 mg,
0.59 mmol, in 10 mL of H2O) with stirring to obtain a dark brown
mixture. The resulting solution was cooled to 0 ꢁC and stirred for
30 min. A freshly prepared aqueous solution of NaBH4 (223 mg,
10 equiv relative to Ru, in 10 mL of H2O) was rapidly added to the
reaction mixture with vigorous stirring. Immediately the solution
turned black, indicating the formation of Ru nanoparticles. The
reaction mixture was stirred for 1 h at 0 ꢁC and subsequently
subjected to dialysis using a membrane tube with a cutoff molec-
ular weight of 30 kDa. After removal of water by freeze-drying, Ru-
1 was obtained as a black solid (580 mg).
4.2.3.2. Hydrogenation of toluene. In a stainless autoclave fitted
with an inner glass tube, toluene (184.2 mg, 2.0 mmol) was treated
with H2 (30 atm) in the presence of M@HPS-NRþ3 Clꢀ
(M¼0.004 mmol, S/C¼500, in 2 mL of EtOH) with stirring at 30 ꢁC
for 1 h. The mixture was diluted with diethyl ether and passed
through a short column of Celite to remove the metal nanoparticles.
The conversion was determined by GC analysis using n-decane as
an internal standard. In the trial for, which the S/C was set at 2000,
toluene (368.4 mg, 4.0 mmol) was treated with H2 (30 atm) in the
presence of Ru-1 or Ru-2 (0.002 mmol in 2 mL of EtOH) with
stirring at 30 ꢁC for 5 h.
The reaction in H2O was carried out as follows. Toluene (92.
1 mg, 1.00 mmol) was treated with H2 (30 atm) in the presence of
Ru-1 (0.003 mmol, S/C¼333, in 1 mL of H2O) with stirring at 30 ꢁC
for 1 h. The mixture was extracted with EtOAc (3 mLꢃ5), and the
conversion was determined by GC analysis using n-decane as an
internal standard. These reactions were also performed on larger
scales [toluene¼24 mmol (S/C¼1400) and 60 mmol (S/C¼4000)], as
described in the Supplementary data.
In a similar fashion, Rh-1 was obtained as a black solid (565 mg)
from HPS-NnBuþ3 Clꢀ (600 mg in 20 mL of H2O) and RhCl3$3H2O
(153 mg, 0.58 mmol, in 10 mL of H2O) by treatment with NaBH4
(219 mg, 10 equiv to Rh, in 10 mL of H2O).
Preparation of Ir-1 (black solid, 552 mg) was performed using
HPS-NnBuþ3 Clꢀ (600 mg in 20 mL H2O), IrCl3$3H2O (118 mg,
0.33 mmol, in 10 mL of H2O), and NaBH4 (125 mg, 10 equiv to Ir, in
10 mL of H2O).
4.2.4. Hydrogenation of substituted benzenes. In a typical example,
a substituted benzene (1.0 mmol), as shown in Table 6, was treated
with H2 (30 atm) with stirring at 30 or 50 ꢁC in the presence of Ru-1
(Ru¼0.003 mmol, S/C¼333, in 1 mL of H2O) in an autoclave with an
inner glass tube. The product was extracted with EtOAc (3 mLꢃ5)
and the combined extracts were dried over Na2SO4 and concen-
trated under reduced pressure. The crude product was purified
using a short silica gel column. The hydrogenation of anisole on
a large scale [toluene¼24 mmol (S/C¼1400)] is described in the
Supplementary data.
4.2.2. Preparation of organo-dispersible M@HPS-NnOctþ3 Clꢀ (Ru-2,
Rh-2,and Ir-2). A THF/H2O mixture (4/1 v/v) was used in the fol-
lowing synthesis procedures. To a solution of HPS-NnOctþ3 Clꢀ
(600 mg in 20 mL of the aqueous THF) was added a solution of
RuCl3$3H2O (155 mg, 0.59 mmol in 80 mL of the aqueous THF) with
stirring, after, which the mixture was cooled to 0 ꢁC and stirred for
30 min. A solution of NaBH4 (223 mg, 10 equiv relative to Ru, in
10 mL H2O) was rapidly added to the vigorously stirred reaction
mixture. The solution immediately turned black, indicating the
formation of Ru nanoparticles. The reaction mixture was stirred at
0 ꢁC for 1 h, following, which the THF was removed by evaporation
and the aqueous layer was extracted with CHCl3 (20 mLꢃ5). After
the combined extracts were dried over anhydrous Na2SO4, the
solvent was removed by evaporation. On vacuum drying, Ru-2 was
obtained as a black solid (650 mg).
In a similar manner, Rh-2 was obtained as a black solid (646 mg)
from HPS-NnOctþ3 Clꢀ (600 mg in 20 mL of the aqueous THF) and
RhCl3$3H2O (153 mg, 0.58 mmol in 10 mL of the aqueous THF) by
treatment with NaBH4 (219 mg, 10 equiv to Rh, in 10 mL of H2O).
Preparation of Ir-2 (black solid, 636 mg) was performed using
HPS-NnOctþ3 Clꢀ (600 mg in 20 mL of the aqueous THF), IrCl3$3H2O
(118 mg, 0.33 mmol in 80 mL of the aqueous THF), and NaBH4
(125 mg, 10 equiv to Ir, in 10 mL of H2O).
4.2.5. Hydrogenation of arenes containing carbonyl group-
s. Hydrogenation reactions of aromatic compounds containing
carbonyl groups in the absence of pyridine were carried out in
a similar manner to those described in Section 4.2.4. A typical
procedure in the presence of pyridine was as follows: acetophe-
none (120.1 mg, 1.0 mmol) was treated with Ru-1 (0.003 mmol, S/
C¼333, dissolved in 1 mL of H2O) in the presence of pyridine
(40.0 mg, 0.5 mmol). The mixture was stirred at 30 ꢁC under 30 atm
of H2 for 12 h, following, which the pyridine was neutralized by
adding a dilute aqueous HCl solution. The aqueous layer was
extracted with EtOAc (3 mLꢃ5) and the solution was dried over
Na2SO4. Removal of the solvents under reduced pressure gave the
product. In the case of 4-phenyl-2-butanone, the reaction was
carried out at 50 ꢁC for 24 h. Hydrogenation of aromatic aldehydes
was performed in the absence of pyridine.
4.2.3. Comparison of the catalytic performance of M@HPS-NRþ3 Clꢀ
4.2.3.1. Hydrogenation of alkenes. The alkenes shown in
Tables 2 and 3 (2.0 mmol) were treated with M@HPS-NRþ3 Clꢀ
(M¼0.004 mmol, S/C¼500, in 2 mL of EtOH) with stirring at 30 ꢁC
4.2.6. Hydrogenation of arenes containing epoxido-groups. In a typ-
ical procedure, phenyl glycidyl ether (150.2 mg, 1.0 mmol) was
Please cite this article in press as: Gao, L.; et al., Tetrahedron (2015), http://dx.doi.org/10.1016/j.tet.2015.04.081

L. Gao et al. / Tetrahedron xxx (2015) 1e10
9
treated with Ru-1 (Ru¼0.003 mmol, S/C¼333, in 1 mL of H2O) with
stirring under 30 atm of H2 in an autoclave with an inner glass tube
for 6 h. The aqueous layer was subsequently extracted with EtOAc
(3 mLꢃ5) and the solution was dried over Na2SO4. After removal of
the solvent, the crude product was passed through a short silica gel
column to give the desired product.
Research from Ministry of Education, Culture, Sports, Science and
Technology, Japan (No. 26620089).
Supplementary data
Supplementary data (These data include the TEM images of
M@HPS-NRþ3 Clꢀ, results of alkenes hydrogenation, the large scale
experiments for arene hydrogenation, TEM images before and after
catalyst recycling, details for metal leaching by ICP-MS, and the
actual data of chiral GC, 1H, 13C NMR, FTIR spectra.) related to this
article can be found at http://dx.doi.org/10.1016/j.tet.2015.04.081.
1,4-Bis(glycidyloxy)cyclohexane: Colorless oil, a mixture of cis-
and trans-. 1H NMR
d 1.27e1.37 (m, 1H, trans-), 1.50e1.64 (m, 1H,
cis-), 1.71e1.84 (m, 1H, cis-), 1.96e2.04 (m, 1H, trans-), 2.58e2.63
(m, 1H, cis- and trans-), 3.09e3.15 (m, 1H, cis-), 3.31e3.37 (m, 1H,
trans-), 3.39e3.45 (m, 2H, cis- and trans-), 3.63e3.73 (m, 1H, cis-
and trans-); 13C NMR
d 27.3, 27.6, 29.0, 29.2, 44.65, 44.70, 51.25,
51.30, 68.58, 68.62, 69.2, 75.5. HRMS (FABþ for MeHþ) C12H21O4:
229.1443 (calcd 229.1440).
References and notes
1. (a) Sheldon, R. A. Chem. Soc. Rev. 2012, 41, 1437e1451; (b) Catalyst Separation,
Recovery and Recycling: Chemistry and Process Design; Cole-Hamilton, D. J.,
Tooze, R. P., Eds.; Springer: Dordrecht, Netherlands, 2006; (c) Recoverable Cat-
alysts and Reagents-perspective and Prospective; Gladysz, J. A., Ed.Chem. Rev.;
2002; 102, pp 3215e3892; (d) Facilitated Synthesis; Bergbreiter, D. E., Kobayashi,
S., Eds.Chem. Rev.; 2009; 109, pp 257e838; (e) Uozumi, Y.; Yamada, Y. M. A.
Chem. Rec. 2009, 9, 51e65.
4.2.7. The catalyst recycling experiments. A solution of cyclohexene
(164.2 mg, 2.0 mmol) dissolved in EtOAc (2 mL) was treated with an
aqueous solution of Rh-1 (Rh¼0.001 mmol, S/C¼2000, in 2 mL of
H2O) with stirring at 30 ꢁC under a hydrogen atmosphere (1 atm).
The organic layer was separated using a separatory funnel and the
extent of conversion was determined by GC analysis with n-decane
as an internal standard. The aqueous phase was subsequently ap-
plied to another hydrogenation.
Similarly, the hydrogenation of toluene (368.4 mg, 4.0 mmol,
dissolved in 2 mL of EtOAc) was performed in an autoclave in the
presence of Ru-1 (Ru¼0.004 mmol, S/C¼1000, in 2 mL of H2O) with
stirring at 30 ꢁC under H2 (30 atm) for 4 h. The aqueous phase was
then applied to another run of the hydrogenation.
2. Representative references for heterogeneous catalysis, see: (a) Augustine, R. L.
Heterogeneous Catalysis for the Synthetic Chemist; Marcel Dekker: New York, NY,
1996; (b) Smith, G. V.; Notheisz, F. Heterogeneous Catalysis in Organic Chemistry;
Academic: California, 1999; (c) Nishimura, S. Handbook of Heterogeneous Cat-
alytic Hydrogenation for Organic Synthesis; Wiley: New York, NY, 2001.
3. Representative reference for multiphase catalysis, see: (a) Multiphase Homo-
ꢀ
geneous Catalysis; Cornils, B., Herrmann, W. A., Horvath, I. T., Leitner, W.,
Mecking, S., Olivier-Bourbigou, H., Vogt, D., Eds.; Wiley-VCH: Weinheim, Ger-
many, 2005; (b) Regulated Systems for Multiphase Catalysis; Leitner, W.,
€
Holscher, M., Eds.; Springer: Berlin, Germany, 2008.
4. Roucoux, A.; Schluz, J.; Patin, H. Chem. Rev. 2002, 102, 3757e3778.
Similar catalyst recycling experiments were performed using
glycidyl phenyl ether (150.2 mg, 1.0 mmol dissolved in 1 mL of
EtOAc) as the substrate in the presence of Ru-1 (Ru¼0.003 mmol, S/
C¼333, in 1 mL of H2O) for 6 h with stirring at 30 ꢁC under H2
(30 atm). The organic layer was separated using a separatory funnel
and the aqueous layer was extracted with EtOAc several times. The
combined extracts were dried over Na2SO4 followed by evaporation
of the EtOAc under a reduced pressure to obtain the product.
In all the trials described above, five replicate reactions were
performed. TEM images before and after the fifth catalytic cycle
showed almost no change in the particle size. No hydrolysis of the
EtOAc was observed.
5. Typical reviews about transition metal nanoparticles in catalysis: see: (a)
Bonnemann, H.; Richards, R. M. Eur. J. Inorg. Chem. 2001, 10, 2455e2480; (b)
€
Astruc, D.; Lu, F.; Aranzaes, J. R. Angew. Chem., Int. Ed. 2005, 44, 7852e7872; (c)
Ott, L. S.; Finke, R. G. Coord. Chem. Rev. 2007, 251, 1075e1100; (d) Yan, N.; Xiao,
C.; Kou, Y. Coord. Chem. Rev. 2010, 254, 1179e1218.
€
€
6. (a) Bonnemann, H.; Brijoux, W.; Brinkmann, R.; Fretzen, R.; Joussen, T.; Koppler,
R.; Korall, B.; Neiteler, P.; Richter, J. J. Mol. Catal. 1994, 86, 129e177; (b)
€
Bonnemann, H.; Braun, G.; Brijoux, W.; Brinkmann, R.; Schulze Tilling, A.;
Seevogel, K.; Siepen, K. J. Organomet. Chem. 1996, 520, 143e162.
7. (a) Schulz, J.; Roucoux, A.; Patin, H. Chem. Commun. 1999, 535e536; (b) Schulz,
ꢀ
J.; Roucoux, A.; Patin, H. Chem.dEur. J. 2000, 6, 618e624; (c) Mevellec, V.;
Roucoux, A.; Ramirez, E.; Philippot, K.; Chaudret, B. Adv. Synth. Catal. 2004, 346,
72e76; (d) Nowicki, A.; Le Boulaire, V.; Roucoux, A. Adv. Synth. Catal. 2007, 349,
ꢀ
2326e2330; (e) Denicourt-Nowicki, A.; Romagne, M.-L.; Roucoux, A. Catal.
Commun. 2008, 10, 68e70; (f) Hubert, C.; Denicourt-Nowicki, A.; Guegan, J.-P.;
ꢀ
Roucoux, A. Dalton Trans. 2009, 7356e7358 Guyonnet Bile, E.; Denicourt-
Nowicki, A.; Sassine, R.; Beaunier, P.; Launay, F.; Roucoux, A. ChemSusChem
4.2.8. Hydrogenation of 1-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)
benzene and the catalyst recycling. A solution of 1-(2-(2-(2-
methoxyethoxy)ethoxy)ethoxy) benzene (123.2 mg, 0.5 mmol)
and Ru-2 (Ru¼0.005 mmol, S/C¼100) dissolved in 2 mL of benzo-
trifluoride (BTF) was treated with H2 (30 atm) while stirring in an
autoclave with an inner glass tube. After 24 h, the resulting mixture
was extracted with H2O several times. The BTF layer containing the
Ru NPs was dried over Na2SO4 and subjected to another run of the
catalytic cycle. The aqueous solution obtained was repeatedly
extracted with CHCl3 and the combined extracts were dried over
Na2SO4. Removal of the solvent gave the product. The catalyst
recycling experiments were repeated three times and TEM images
before and after the third catalytic cycle indicated only slight
changes in the particle size.
2010, 3, 1276e1279; (g) Guyonnet Bile, E.; Sassine, R.; Denicourt-Nowicki, A.;
ꢀ
Launay, F.; Roucoux, A. Dalton Trans. 2011, 40, 6524e6531; (h) Pelisson, C.-H.;
Hubert, C.; Denicourt-Nowicki, A.; Roucoux, A. Top. Catal. 2013, 56, 1220e1227
and references cited therein.
8. Toshima, N.; Yonezawa, T. New J. Chem. 1998, 22, 1179e1201 see also the ref-
erences cited therein.
ꢁ
9. Pellegatta, J.-L.; Blandy, C.; Colliere, V.; Choukroun, R.; Chaudret, B.; Cheng, P.;
Philippot, K. J. Mol. Catal. A: Chem. 2002, 178, 55e61.
10. (a) Yan, N.; Zhang, J.-g.; Tong, Y.; Yao, S.; Xiao, C.; Li, Z.; Kou, Y. Chem. Commun.
2009, 4423e4425; (b) Yan, N.; Yuan, Y. A.; Dyson, P. J. Chem. Commun. 2011,
2529e2531.
11. (a) Widegren, J. A.; Finke, R. G. J. Mol. Catal. A: Chem. 2003, 191, 187e207; (b)
Denicourt-Nowicki, A.; Roucoux, A. Curr. Org. Chem. 2010, 14, 1266e1283; (c)
Gual, A.; Godard, C.; Castillon, S.; Claver, C. Dalton Trans. 2010, 39, 11499e11512;
(d) Scholten, J. D. Curr. Org. Chem. 2013, 17, 348e363.
12. (a) Fache, F.; Lehuede, S.; Lemaire, M. Tetrahedron Lett. 1995, 36, 885e888; (b)
Sajiki, H.; Hattori, K.; Hirota, K. Chem.dEur. J. 2000, 6, 2200e2204; (c) Hara, Y.;
Inagaki, H. Chem. Lett. 2002, 1116e1117.
13. (a) Motoyama, Y.; Takasaki, M.; Yoon, S. H.; Mochida, I.; Nagashima, H. Org. Lett.
2009, 11, 5042e5045; (b) Motoyama, Y.; Takasaki, M.; Higashi, K.; Yoon, S. H.;
Mochida, I.; Nagashima, H. Chem. Lett. 2006, 35, 876e877; (c) Takasaki, M.;
Motoyama, Y.; Higashi, K.; Yoon, S. H.; Mochida, I.; Nagashima, H. Chem.dAsian.
J. 2007, 2, 1524e1533.
(2-(2-(2-Methoxyethoxy)ethoxy)ethoxy)cyclohexane: Colorless
oil. 1H NMR
d
1.14e1.33 (m, 5H), 1.49e1.58 (m, 1H), 1.68e1.80 (m,
2H), 1.87e1.97 (m, 2H), 3.22e3.30 (m, 1H), 3.38 (s, 3H), 3.53e3.58
(m, 2H), 3.59e3.71 (m, 10H). 13C NMR
d 24.4, 26.0, 32.4, 59.2, 67.3,
70.7, 70.77, 70.79, 71.1, 72.1, 78.2. HRMS (FABþ for MeHþ) C13H27O4:
14. (a) Lu, F.; Liu, J.; Xu, J. Adv. Synth. Catal. 2006, 348, 857e861; (b) Lu, F.; Liu, J.; Xu,
J. J. Mol. Catal. A: Chem. 2007, 271, 6e13.
247.1908, (calcd 247.1909).
15. (a) Kojima, K.; Chikama, K.; Ishikawa, M.; Tanaka, A.; Nishikata, T.; Tsutsumi, H.;
Igawa, K.; Nagashima, H. Chem. Commun. 2012, 10666e10668; (b) Gao, L.;
Nishikata, T.; Kojima, K.; Chikama, K.; Nagashima, H. Chem.dAsian J. 2013, 8,
3152e3163; (c) Nishikata, T.; Tsutsumi, H.; Gao, L.; Kojima, K.; Chikama, K.;
Nagashima, H. Adv. Synth. Catal. 2014, 356, 951e960; (d) Chaiyanurakkul, A.;
Gao, L.; Nishikata, T.; Kojima, K.; Nagashima, H. Chem. Lett. 2014, 43,
1233e1235.
Acknowledgements
This work was supported by the CREST Program of Japan Science
and Technology Agency (JST) Japan and Grant in Aid for Scientific
Please cite this article in press as: Gao, L.; et al., Tetrahedron (2015), http://dx.doi.org/10.1016/j.tet.2015.04.081

10
L. Gao et al. / Tetrahedron xxx (2015) 1e10
16. For reviews of hyperbranched polymers, see: (a) Ifran, M.; Seiler, M. Ind. Eng.
Chem. Res. 2010, 49, 1169e1196; (b) Wilms, D.; Stiriba, S.-E.; Frey, H. Acc. Chem.
Res. 2010, 43, 129e141; (c) Zhou, Y.; Huang, W.; Liu, J.; Zhu, X.; Yan, D. Adv.
Mater. 2010, 22, 4567e4590; (d) Seiler, M. Fluid Phase Equilib. 2006, 241,
155e174; (e) Voit, B. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 2679e2699; (f)
Gao, C.; Yan, D. Prog. Polym. Sci. 2004, 29, 183e275; (g) Yates, C. R.; Hayes, W.
Eur. Polym. J. 2004, 40, 1257e1281; (h) Jikei, M.; Kakimoto, M.-A. Prog. Polym. Sci.
2001, 26, 1233e1285; (i) Voit, B. J. Polym. Sci. Part A: Polym. Chem. 2000, 38,
2505e2525; (j) Kim, Y. H. J. Polym. Sci. Part A: Polym. Chem. 1998, 36, 1685e1698.
17. In general, the rate was decreased in the order, R-CH¼CH2>R-CH¼CH-
R>RCH¼CR2>R2C¼CR2; (a) Kraus, M. In Handbook of Heterogeneous Catalysis;
Ertl, G., Knozinger, H., Wietkamp, J., Eds.; Wiley-VCH: Weinheim, Germany,
1997; Vol. 3, Chapter 5.3.1; (b) Deem, M. W.; Newsam, J. M. J. Am. Chem. Soc.
1992, 114, 7189e7198.
hydrogenation of toluene by ruthenium NPs stabilized with certain organic
surfactants under almost the same conditions as shown in Table 6. They defined
the TOF as the number of moles of H2 consumed per mole of ruthenium in-
troduced per hour, and reported the TOF for toluene hydrogenation to be
600 hꢀ1. Our TOF of 900 hꢀ1 corresponds to 2700 hꢀ1 according to the defi-
nition of Roucoux. See Ref. 7d.
22. For a recent review on rhodium nanoparticles for hydrogenation Guerrero, M. ;
T.; Than Chau, N.; Noel, S.; Denicourt-Nowicki, A.; Hapiot, F.; Roucoux, A.;
Monflier, E.; Philippot, K. Curr. Org. Chem. 2013, 17, 364e399.
23. It is known that platinum catalysts also promote arene hydrogenation.2 In fact,
we observed that Pt-1 shows catalytic activity for the hydrogenation of arenes
in water, but only at higher temperatures.15d
24. Fujiwara, Y.; Iwasaki, Y.; Maegawa, T.; Monguchi, Y.; Sajiki, H. ChemCatChem
2011, 3, 1624e1628.
18. (a) Crabtree, R. H. Acc. Chem. Res. 1979, 12, 331e337; (b) Cui, X.; Burgess, K.
25. Remeikyte, A.; Ostrauskaite, J.; Grazuleviciene, V. J. Appl. Polym. Sci. 2013, 129,
Chem. Rev. 2005, 105, 3272e3296.
1290e1298.
19. The effects of hydrogen pressure on the reactions catalyzed by Ru-1 and Ru-2
was observed during the hydrogenation of 1-octene, which was carried out at
30 ꢁC for 1 h. The resulting 1-octene conversions were trace, 12, and >99% at H2
pressures of 1, 10, and 20 atm, respectively. The pressure effect during the
hydrogenation of toluene is summarized in Table 5. The reaction profiles for the
hydrogenations of toluene and anisole in water showed no induction period as
shown in the Supplementary data.
26. As noted in Table 4, the highest TOF obtained for Rh-1 during cyclohexane
hydrogenation was 8700 after 1 h. Similar TOF values have been reported using
rhodium NPs stabilized by PVP or other water soluble polymers, although the
reaction conditions were somewhat more harsh.20 We performed the catalyst
recycling five times, using S/C¼2000 for each cycle, obtaining a total TON value
of 10,000 during the recycling trials.
27. Hobbs, C. F.; Weingarten, H. J. Org. Chem. 1968, 33, 2385e2388.
28. Kimura, M.; Kajita, K.; Onoda, N.; Morosawa, S. J. Org. Chem. 1990, 55,
4887e4892.
20. (a) Quek, X.-Y.; Gua, Y.; Hensen, E. J. M. Catal. Today 2012, 183, 72e78; (b) Mao,
H.; Liao, X.; Shi, B. Catal. Commun. 2011, 16, 210e214.
21. We defined the TOF as the number of moles of toluene consumed per mole of
ruthenium introduced per hour. Roucoux et al. recently reported the
Please cite this article in press as: Gao, L.; et al., Tetrahedron (2015), http://dx.doi.org/10.1016/j.tet.2015.04.081