Polymer anchored ruthenium complex: A highly active and recyclable catalyst for one-pot azide-alkyne cycloaddition and transfer-hydrogenation of ketones under mild conditions

Article abstract of DOI:10.1016/j.jorganchem.2014.11.007

A new polymer supported Ru(III) complex has been synthesized and characterized. The catalytic performance of the complex has been tested for the first time azide-alkyne cycloaddition reaction in water and transfer-hydrogenation reaction of ketones in open air. 1,4-disubstituted-1,2,3-triazoles were obtained in excellent yields from azides and terminal alkynes in aqueous medium in the presence of the above catalyst. Aromatic ketones have been converted to their corresponding alcohols using the polymer supported Ru(III) catalyst. The effects of solvents, reaction time, catalyst amount for the azide-alkyne cycloaddition reaction and transfer-hydrogenation reaction were studied. This catalyst showed excellent catalytic activity and recyclability. The polymer supported Ru(III) catalyst could be easily recovered by filtration and reused more than five times without appreciable loss of its initial activity. There was no evidence of leached Ru from the catalyst during the course of reaction has been observed, suggesting true heterogeneity in the catalytic process.

Full text of DOI:10.1016/j.jorganchem.2014.11.007

Journal of Organometallic Chemistry 776 (2015) 170e179
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Polymer anchored ruthenium complex: A highly active and recyclable
catalyst for one-pot azideealkyne cycloaddition and
transfer-hydrogenation of ketones under mild conditions
Rostam Ali Molla a, Anupam Singha Roy a, Kajari Ghosh a, Noor Salam a, Md Asif Iqubal b,
,
, *
K. Tuhina c **, Sk Manirul Islam a
a Department of Chemistry, University of Kalyani, Kalyani, Nadia 741235, W.B., India
b Department of Chemistry, IIT Roorkee, Roorkee 247667, Uttarakhand, India
c Department of Chemistry, B.S. College, Canning, S-24 PGS, 743329 W.B., India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new polymer supported Ru(III) complex has been synthesized and characterized. The catalytic per-
formance of the complex has been tested for the first time azideealkyne cycloaddition reaction in water
and transfer-hydrogenation reaction of ketones in open air. 1,4-disubstituted-1,2,3-triazoles were ob-
tained in excellent yields from azides and terminal alkynes in aqueous medium in the presence of the
above catalyst. Aromatic ketones have been converted to their corresponding alcohols using the polymer
supported Ru(III) catalyst. The effects of solvents, reaction time, catalyst amount for the azideealkyne
cycloaddition reaction and transfer-hydrogenation reaction were studied. This catalyst showed excellent
catalytic activity and recyclability. The polymer supported Ru(III) catalyst could be easily recovered by
filtration and reused more than five times without appreciable loss of its initial activity. There was no
evidence of leached Ru from the catalyst during the course of reaction has been observed, suggesting true
heterogeneity in the catalytic process.
Received 23 September 2014
Received in revised form
1 November 2014
Accepted 6 November 2014
Available online 20 November 2014
Keywords:
Supported catalyst
Ruthenium
Azideealkyne cycloaddition
1,2,3-Triazoles
Water
Transfer-hydrogenation
© 2014 Elsevier B.V. All rights reserved.
Introduction
To get rid from these serious issues various solid-supported
copper catalysts were also reported. The supports employed to
The copper-catalyzed azideealkyne cycloaddition (CuAAC)
yielding 1,2,3-triazoles is a powerful one pot click reaction [1].
1,2,3-triazoles are five-membered nitrogen heterocyclic com-
pounds that are widely used in various research fields including
synthetic organic, medicinal, materials, and biological chemistry
[2e5]. Most azideealkyne cycloaddition (AAC) have been carried by
homogeneous copper catalysts [6e10]. Homogeneous catalysts
have some disadvantages, such as they may easily be destroyed
during the course of the reaction and they cannot be easily recov-
ered after the reaction for reuse and the use of copper salt is
restricted as it often leads to the formation of undesired homo-
coupled product of alkyne [11e13].
date are activated carbon, inorganic materials, such as zeolites,
amine-bound silica, superparamagnetic mesoporous silica,
AlO(OH), metal oxide, hydrotalcite, an ionic liquid, a ligand-bound
organic polymer, and polysaccharide [14e23]. Most of these re-
ported CuAAC studies are on two component reaction systems
using organic azides which are synthesized in advance. These
organic azides are potential hazards especially in the isolation or
the purification process and thus can be problematic. To overcome
these drawbacks some copper catalysts were reported where
organic azides were synthesised in situ to avoid the handling of
such hazardous materials [24e27]. But these methodologies suffer
from several drawbacks like use of long reaction time and elevated
temperature.
It is thus desirable to develop an efficient one-pot methodology
to avoid all these difficulties. More recently, it has been disclosed
that (pentamethylcyclopentadienyl) ruthenium chloride com-
plexes can effectively catalyze the facile cycloaddition of a wide
range of azides and terminal alkynes (RuAAC) to afford regiose-
lectively the complementary 1, 5-disubstituted 1,2,3-triazoles
* Corresponding author. Tel.: þ91 33 2582 8750; fax: þ91 33 2582 8282.
** Corresponding author.
E-mail addresses: tuhina31@yahoo.com (K. Tuhina), manir65@rediffmail.com
(S.M. Islam).
http://dx.doi.org/10.1016/j.jorganchem.2014.11.007
0022-328X/© 2014 Elsevier B.V. All rights reserved.

R.A. Molla et al. / Journal of Organometallic Chemistry 776 (2015) 170e179
171
[28,29]. But Pei et al. reported that ruthenium complexes lacking
polystyrene (5.5 mmol Cl/g of resin) was treated with 0.979 g of b-
cyclopentadienyl ligands, can catalyze the cycloaddition of terminal
acetylenes and azides to give selectively 1, 4-substituted triazole
regioisomers rather than 1, 5-disubstituted 1,2,3-triazoles [30,31].
In our present work, we have synthesized a polymer anchored
ruthenium(III) complex and utilized it to catalyze the azideealkyne
cycloaddition reaction. During the course of our effort to develop
ruthenium mediated cycloaddition of azides and alkynes, we have
found that polymer anchored ruthenium(III) complex not only
catalyze the three component cycloaddition of terminal acetylenes,
sodium azide and alkyl halides to give selectively 1,4-substituted
triazole regioisomers but also catalyze the transfer-hydrogenation
reaction under mild conditions.
alanine in DMF to produce the corresponding polymer supported
ligand (PS-L). Then, the polymer was washed thoroughly with DMF
to remove excess
b-alanine. Finally, it was washed with double
distilled water, dried and stored at room temperature for
further use.
In the second step, the polymer supported b-alanine ligand (1 g)
in DMF (20 mL) was treated with 5 mL 1% (w/v) DMF solution of
RuCl3.3H2O over a period of nearly 30 min under constant stirring.
The reaction mixture was refluxed for 24 h. The deep grey coloured
ruthenium complex thus formed was filtered and washed thor-
oughly with ethanol and dried in room temperature under vacuum.
Amongst the many catalytic applications of Ru(III) in organic
synthesis transfer-hydrogenation has become very popular in the
last decade. It is indeed a very powerful tool for the reduction of
ketones to their corresponding alcohols. The catalytic transfer-
hydrogenation of ketones represents a viable method, not only in
the laboratory but also on a commercial scale, because of its ease of
handling, lower cost and safety compared with the typically used
expensive, hazardous and dangerous reagents such as borane
reagents, high-pressure hydrogen gas [32e37]. Among the different
metal catalyzed transfer-hydrogenation reactions, ruthenium-
based catalytic systems are found to be effective in the transfer-
hydrogenation of ketones [38].
General procedure for the formation of triazoles
Polymer supported metal catalyst (25 mg, 21 ꢁ 10ꢀ3 mmol) in
water (5 mL) was taken in a 50 mL round bottom flask. Then
phenylacetylene (1 mmol), sodium azide (1.2 mmol) and benzyl
bromide (1 mmol) were added and stirred at room temperature for
180 min. After the completion of the reaction, the catalyst was
filtered off and washed with water followed by acetone and dried in
oven. The filtrate was extracted with ethyl acetate (3 ꢁ 20 ml) and
the combined organic layers were dried with anhydrous Na2SO4 by
vacuum. All the prepared compounds were confirmed by 1H and
13C NMR.
Herein we report the synthesis and characterization of a poly-
mer supported ruthenium catalyst and illustrate its application for
the synthesis of 1,4-disubstituted triazoles via three-component
coupling of alkynes, azides and alkyl halides in water medium
and transfer-hydrogenation reaction of various ketones in open air.
General procedure for the catalytic transfer hydrogenation reaction
The substrate (ketone) (2.4 mmol), ruthenium catalyst
(2.5 mmol), and propan-2-ol (5 mL) were introduced into a two
necked round-bottomed flask fitted with a condenser and heated at
80 ꢂC for 15e20 min in an open air atmosphere. Then, a solution of
KOH (0.05 mmol) in 2-propanol (5 mL) was introduced to initiate
the reaction and it was heated at 80 ꢂC. The progress of the reaction
was monitored by GC analysis of the samples.
Experimental section
Materials
Analytical grade reagents and freshly distilled solvents were
used throughout the experiments. All reagents and substrates were
purchased from Merck. Liquid substrates were predistilled and
dried by molecular sieve and solid substrates were recrystallized
before use. Distillation, purification of the solvents and substrate
were done by standard procedures. 5.5% crosslinked chloromethy-
lated polystyrene and ruthenium trichloride were purchased from
Sigma Aldrich and used as without further purification.
Results and discussion
Characterization of the polymer supported catalyst
Due to insolubilities of the polymer supported ruthenium
catalyst in all common organic solvents, its structural investigation
was limited to its physicochemical properties, chemical analysis,
SEM, TGA, IR and UVevis spectroscopic data. Table 1 provides the
data of elemental analysis of polymer supported ligand and the
polymer supported ruthenium catalyst. Ruthenium content in the
catalyst determined by AAS suggests 8.50 wt% Ru in the catalyst.
Various frameworks bonding present in the polymer supported
metal catalyst were obtained from the FT-IR spectrum (Fig. 1). The
sharp CeCl peak due to eCH2Cl group in polymer (Fig. S1, sup-
porting information) at 1264 cmꢀ1 had disappeared in the polymer
anchored ligand. A new strong band appeared at 3426 cmꢀ1
showed the presence of a secondary (eNHe) amine group in the
ligand. The (C]O), nasym (COO) and nsym (COO) stretching vibrations
are observed at 1733, 1667 and 1513 cmꢀ1 for polymer anchored
bidente ligand [39] bound to the central metal ion through the
carboxylic OH and the secondary amino group; (eNHe). The bands
at 1667 and 1513 cmꢀ1, due to nasym (COO) and nsym (COO) of the
amino acids, appear at 1663 and 1510 cmꢀ1 in the complex. The
shifting of these two bands suggests the involvement of the car-
boxylic group of the polymer supported ligand in the complex
formation [40,41]. The participation of OH group in bonding was
confirmed from the shift in the position of the CeO stretching vi-
bration of the free ligand (1424 cmꢀ1) in the spectra of the complex.
The decrease in the intensity of NeH stretching frequency of the
Physical measurements
The FT-IR spectra of the samples were recorded from 400 to
4000 cmꢀ1 on a Perkins Elmer FT-IR 783 spectrophotometer using
KBr pellets. UVevis spectra were taken using a Shimadzu UV-
2401PC doubled beam spectrophotometer having an integrating
sphere attachment for solid samples. Thermogravimetric analysis
(TGA) was carried out using a Mettler Toledo TGA/DTA 851e. Sur-
face morphology of the samples was measured using a scanning
electron microscope (SEM) (ZEISS EVO40, England) equipped with
EDX facility. Ruthenium content in the catalyst was determined
using a Varian AA240 atomic absorption spectrophotometer (AAS).
NMR spectra were recorded on a Varian Mercury plus NMR spec-
trometer (1H NMR at 300 and 500 MHz and 13C NMR at 75 MHz and
125 MHz) in pure deuterated solvents.
Synthesis of the metal complex
The synthesis of the immobilized polymer supported ruth-
enium(III) catalyst is illustrated in Scheme 1. It was readily prepared
through a two-step procedure. First, 0.2 g of chloromethylated

172
R.A. Molla et al. / Journal of Organometallic Chemistry 776 (2015) 170e179
O
RuCl3/DMF
DMF
C
CH2
CH2
NH
CH2
CH2
NH2
+
OH
Ru
2 Cl
100 0C 48 h
/
Reflux / 24 h
OH
N
H
CH2Cl
OH
O
Cl
C
C
O
OH2
O
PS-L
PS-L-Ru
Scheme 1. Synthesis of the polymer supported Ru(III) catalyst.
Table 1
also inform that the attachment of metal on the surface of the
polymer matrix.
Chemical composition of polymer anchored ligand and polymer supported catalyst.
The electronic spectrum (Fig. 4) of the polymer supported
ruthenium catalyst has been recorded in the diffuse reflectance
spectrum mode as MgCO3/BaSO4 disc. The polymer supported
ruthenium(III) complex is in the þ3 oxidation state. The electronic
spectra of ligand and the complex showed three to four bands in
the region 680e217 nm. The bands around 619e506 nm range have
been assigned to the spin allowed ded transition. The absorption
Compound
C%
H%
Cl %
N%
Metal%
PS-L
PS-L-Ru
71.34
58.66
6.80
5.36
8.45
5.90
4.10
2.95
e
8.50
secondary amine group in the complex indicates that the ‘N’ of
amino group may be coordinated to the metal [42]. Weak bands in
the far IR region at ~300e310 cmꢀ1 and ~440e460 cmꢀ1 have been
around 260e275 nm may be attributed to
pep* transition in
phenyl moiety. The other high intensity bands around 379e494 nm
have been assigned to charge transfer transitions (LMCT) [45].
Thermal stability of the complexes was investigated using TGA
at a heating rate of 10 ꢂC/min in air over a temperature range of
30e600 ꢂC. TGAeDTA curves of the polymer supported ligand and
supported ruthenium catalyst are shown in Fig. 5. The ligand and
ruthenium complexe were stable up to 350e370 ꢂC and above this
temperature they decomposed. Thermogravimetric study suggests
that the polymer supported ruthenium complexe degrade at
considerably higher temperature.
assigned to
n
and
n
vibrations [43,44]. Thus, making
RueCl
RueN/O
precise assignments to distinguish RueO from RueN bands in the
far IR region is rather difficult.
The scanning electron micrographs (Fig. 2) of the polymer
supported ligand and ruthenium catalyst clearly show the
morphological change which occurred on the surface of poly-
styrene after loading of metal on it. Energy dispersive spectros-
copy analysis of X-rays (EDAX) data for the polymer anchored
ligand and ruthenium catalyst are given in (Fig. 3). The EDAX data
Fig. 1. FT-IR Spectra of polymer anchored ligand (a) PS-L and (b) PS-L-Ru complex.

R.A. Molla et al. / Journal of Organometallic Chemistry 776 (2015) 170e179
173
Fig. 2. FE-SEM of polymer anchored ligand (PS-L) (A) and PS-L-Ru complex (B).
Catalytic activities
amount of 1,2,3-triazole was obtained in the absence of polymer
supported catalyst. To optimize the reaction conditions various
solvents were screened. The influence of solvents on the yield are
summarised in Table 2. From Table 2, it was found that water was
the most effective solvent, while the use of other solvents such as
toluene, ethanol, CH3CN, CH2Cl2, dioxane resulted in lower yields.
The reaction was carried out for different time also (Fig. 6),
ranging from 60 min to 180 min and it was found that at
180 min the yield of the reaction was 100% at room temperature.
The influence of amount of catalyst on the yield was also
investigated (Fig. 7). An increase in the catalyst amount from 10 mg
to 25 mg resulted in an increase in the yield up to 100%. Further
increase in catalyst amount had no profound effect on the yield of
the desired product.
Azideealkyne cycloaddition reaction
Three component coupling reaction of alkyne, azide and alkyl
halide represents a powerful method for the 1,2,3-triazole forma-
tion. Construction of 1,2,3-triazole compounds via the polymer
supported ruthenium catalyzed azideealkyne cycloaddition reac-
tion is an interesting area in organic synthesis. We started our
investigation for azideealkyne cycloaddition reaction (Scheme 2)
of phenylacetylene and benzyl bromide with sodium azide as
model reaction. The performance of ruthenium-catalyzed azide-
ealkyne cycloaddition reaction is known to be governed by the
number of factors such as the solvent, reaction time and catalyst
amount etc. The influences of catalyst amount, solvent and reaction
time were tested for cycloaddition reaction and found that trace
With these optimized reaction conditions, a wide range of
diversely substituted phenylacetylenes were reacted with various
substituted and non-substituted benzyl halides and sodium azide
to produce the corresponding 1,4-disubstituted-1,2,3-triazoles. The
results are summarized in Table 3.
The substitution of electron withdrawing and electron donating
groups on the phenyl ring of phenylacetylenes did not have any
appreciable influence on the outcome of the reaction (Table 3,
entries 4 and 11). The reaction went uniformly for all o-, m-, and
Fig. 4. DRS-UVevisible absorption spectra of the polymer supported ligand and
Fig. 3. EDAX spectra of polymer supported ligand (PS-L) (A) and PS-L-Ru complex (B).
ruthenium catalyst.

174
R.A. Molla et al. / Journal of Organometallic Chemistry 776 (2015) 170e179
Fig. 5. Thermogravimetric weight loss plots for the polymer supported ligand (PS-L) and PS-L-Ru complex.
Scheme 2. Azideealkyne cycloaddition reaction.
Table 2
p-substituted phenylacetylenes (Table 3, entries 4, 3, and 2). The
1,4-diethynylbenzene produced the corresponding bis-triazole
derivatives (Table 3, entry 5). The hetero-aryl substituted acety-
lene 3- ethynylthiophene underwent a clean reaction to produce
1-benzyl-4(thiophen-3-yl)-1,2,3-triazole (Table 3, entry 6). Alkyl
acetylene such as propargyl alcohol also participated in this reac-
tion to provide the corresponding product (Table 3, entry 7). No
rigorous extraction of product by solvent and work-up were
necessary. A simple washing of the reaction residue by ethanol
followed by evaporation of the solvent furnished the pure product.
Chromatographic separation was not a necessary requirement.
Thus this procedure avoids use of a hazardous organic solvent in
the whole process.
Effect of solvents on 1,4-disubstituted 1,2,3- triazoles synthesis catalyzed by polymer
supported Ru(III) catalyst.
Entry
Solvent
Isolated yield (%)
1
2
3
4
5
6
7
Toluene
Ethanol
CH3CN
CH2Cl2
Dioxane
DMSO
H2O
40
76
58
52
37
82
100
Reaction condition: phenylacetylene (1 mmol), benzyl bromide (1 mmol) and so-
dium azide (1.2 mmol), catalyst (25 mg, 21 ꢁ 10ꢀ3 mmol) in 5 mL water, time
180 min at room temperature (40 ꢂC).
Fig. 6. Effect of reaction time on azideealkyne cycloaddition reaction.
Fig. 7. Effect of catalyst amount on azideealkyne cycloaddition reaction.

R.A. Molla et al. / Journal of Organometallic Chemistry 776 (2015) 170e179
175
Table 3
Polymer supported ruthenium(III) catalyzed azidesealkyes cycloaddition reactions.
Entry
Halides
Alkynes
Triazoles
Isolated
Yield (%)
N
N
1
100
Br
N
Ph
N
N
2
93
N
Ph
Br
Br
Br
Br
N
N
3
89
N
Ph
F
F
N
N
4
5
94
89
NO2
Br
N
Ph
N
NO2
Br
N
N
Ph
Ph
N
N
N
N
N
6
7
83
83
89
Br
Br
Br
N
Ph
S
S
N
N
OH
N
OH
Ph
N
N
N
8
9
Ph
CF3
CF3
N
N
90
Br
N
Ph
Br
Br
(continued on next page)

176
R.A. Molla et al. / Journal of Organometallic Chemistry 776 (2015) 170e179
Table 3 (continued)
Br
N
10
76
85
N
N
Ph
Br
N
N
11
N
N
N
Ph
Ph
OMe
OMe
87
Br
N
12
N
N
Reaction conditions: alkynes (1 mmol), benzyl halides (1 mmol) and sodium azide (1.2 mmol), time
(180 min), catalyst (25 mg, 21 ꢁ 10-3 mmol) in 5 mL water, at room temperature (40 ꢂC) and all the
prepared compounds were confirmed by 1H NMR, 13C NMR.
In order to optimize the reaction conditions such as base and
reaction temperature, the transfer hydrogenation reaction of cyclo-
hexanone to cyclohexanol was chosen as model reaction in the
presence of polymer supported ruthenium catalyst in i-PrOH
(Table 4). The reaction rates were found to be strongly dependent on
the base employed and variety of bases were screened. A remarkable
increase in the product formation was observed in presence of strong
inorganic bases like NaOH or KOH. When weak inorganic bases such
as NaHCO3, Na2CO3 and CH3COONa or organic bases such as trie-
thylamine, pyridine were employed, the conversion of the product
was drastically reduced. Temperature was found to have a strong
influence on the performance of the catalyst and a decrease in the
conversion was observed at lower temperature. The formation of
cyclohexanol proceeded slowly at 40 ꢂC. The results obtained from
the optimization of reaction conditions indicate that relatively high
conversion can be achieved in the transfer hydrogenation of cyclo-
hexanone to cyclohexanol with polymer supported catalyst using i-
PrOH/KOH at 80 ꢂC. Next, to optimize the effect of catalyst amount,
Scheme 3. Ruthenium catalyzed transfer-hydrogenation of ketones.
Transfer-hydrogenation reaction
Transfer hydrogenation reaction, in which hydrogen is trans-
fered from one organic molecule to another, is of great importance
and has become an efficient method in organic synthesis. The use of
ruthenium complex, as an effective catalyst for transfer hydroge-
nation reaction, encouraged us to carry out this type of reaction
using polymer supported ruthenium catalyst (Scheme 3).
Table 4
Effect of base and temperature on the transfer hydrogenation of cyclohexanone.
Entry
Base
Temperature (ꢂC)
Yield (%)a
Table 5
1
2
3
4
5
6
7
8
e
80
30
80
90
80
80
60
80
90
80
80
40
80
90
80
0
<10
84
84
22
20
60
98
98
<10
12
50
95
95
Effect of catalyst amount and reaction time on the transfer hydrogenation of
cyclohexanone.
NaOH
NaOH
NaOH
NaHCO3
Na2CO3
KOH
KOH
KOH
Et3N
CH3COONa
i-PrOK
i-PrOK
i-PrOK
Pyridine
Entry
Catalyst (
m
mol)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
9
e
90
90
90
90
90
90
70
80
100
0
45
60
81
98
98
85
90
98
1.0
1.5
2.0
2.5
3.0
2.5
2.5
2.5
9
10
11
12
13
14
15
<10
Reaction conditions: cyclohexanone (2.4 mmol), 0.05 mmol KOH in i-PrOH (5 mL) at
80 ꢂC in air.
Reaction conditions: cyclohexanone (2.4 mmol), catalyst (2.5
m
mol), base
(0.05 mmol) in i-PrOH (5 mL) in air.
Bold values represent optimized condition.
a
a
Yield was determined by GC analysis, internal standard (m-xylene, 30
m
L,
Yield was determined by GC analysis, internal standard (m-xylene, 30 mL,
0.24 mmol).
0.24 mmol).

R.A. Molla et al. / Journal of Organometallic Chemistry 776 (2015) 170e179
Table 6 (continued )
177
Table 6
Transfer hydrogenation of various ketones catalyzed by polymer supported Ru(III)
catalyst.
Entry
13
Ketone
Isolated yield (%)a
85
TON
Isolated yield (%)a
97.5
TON
936
816
Entry
1
Ketone
O
C
O
MeO
14
15
86
84
826
804
O
C
2
3
97
87
931
835
O
O
C
O
Et
Reaction conditions: ketone (2.4 mmol), KOH (0.05 mmol) in i-PrOH (5 mL), catalyst
(2.5
mol) at 80 ꢂC in air for 90 min.
Yield was determined by GC analysis, internal standard (m-xylene, 30
0.24 mmol).
m
a
m
L,
4
5
98
94
941
902
O
different amount of catalyst was tested in the transfer hydrogenation
reaction of cyclohexanone in i-PrOH/KOH and the results are sum-
marized in Table 5. It was found that 2.5 mmol of ruthenium catalyst
O
was the most effective catalytic system. This transfer-hydrogenation
reaction was also found to be highly sensitive to the reaction time.
From the results (Table 5, entries 6e9), it can be shown that the
formation of cyclohexanol initially increased with the progress of the
reaction, reached a maximum and then remained unchanged.
Reasonably good conversion (98%) for the formation of cyclohexanol
was observed at the optimum reaction time of 90 min. Longer re-
action time of 90 mine120 min doesn't produce a considerable
improvement in the conversion of cyclohexanone to cyclohexanol.
From the above discussion, it is shown that the best yield was ob-
tained by using the base KOH in i-PrOH solvent at 80 ꢂC for 90 min
under open air with the polymer supported ruthenium(III) catalyst
6
88
849
O
(2.5 mmol).
7
99
95
90
91
89
950
912
864
874
854
O
O
Under the optimized conditions, the transfer hydrogenation
reaction of a range of ketones was investigated to know about the
scope of our method. The transfer hydrogenation reaction of several
aromatic and aliphatic ketones was carried out with the ruthenium
catalyst using i-PrOH and KOH at 80 ꢂC and the results are sum-
marized in Table 6. The products were identified by GC after doing
the required workup. The polymer supported ruthenium complex
catalyzed the transfer hydrogenation of ketones to their corre-
sponding alcohols with good to excellent yields in all the cases.
Excellent yields are obtained for both aliphatic and aromatic ke-
tones. The complex efficiently catalyzed the reduction of aliphatic
ketones such as methyl ethyl ketone, methyl propyl ketone and
diethyl ketone (Table 6, entries 7e9) to their corresponding alco-
hols. Moreover, this catalyst efficiently catalyzed the reduction of
benzophenone, 2-adamantanone, cyclopentanone and cyclo-
heptanone to their corresponding alcohols (Table 6, entries 1e3 and
5). The complex also showed good activity for eight membered
cyclic ketone cyclooctanone with 88% isolated yield (Table 6, entry
6). The isolated yield of alcohol in case of acetophenone is 89%. The
presence of electron withdrawing (Cl) and electron donating
(ꢀOCH3) substituents on the substrates plays a significant role in
the conversion of ketones to alcohols. 4-chloro acetophenone and
4-methoxy acetophenone were converted to their corresponding
alcohols with 93% and 85%, respectively (Table 6, entries 12 and 13).
Electron-withdrawing substituent (Cl) on the aryl ring gave higher
8
9
O
10
11
O
(
)
4
O
C
12
93
893
O
C
Cl

178
R.A. Molla et al. / Journal of Organometallic Chemistry 776 (2015) 170e179
conversions compared to that of acetophenone whereas electron-
donating substituents (ꢀOCH3) on the ring gave lower conver-
sions than that of acetophenone.
No catalysts deterioration was observed, confirming the high
stability of the heterogeneous catalyst under the reaction
conditions.
Heterogeneity test
Conclusion
An important point concerning the use of heterogeneous cata-
lyst is its lifetime, particularly for industrial and pharmaceutical
applications. Heterogeneity of the catalyst was examined by the
“hot filtration test” for the transfer hydrogenation reaction.
In conclusion, we have reported the preparation and charac-
terisation of polystyrene supported Ru(III) complex and its suc-
cessful applications for the azideealkyne cycloaddition reaction in
aqueous medium at room temperature and transfer hydrogenation
reaction in open air. The Ru(III) catalyzed one-pot azideealkyne
cycloaddition reaction is a efficient method for rapid and green
synthesis of 1,2,3 triazoles with excellent yield via multi-
component coupling in aqueous medium at room temperature.
To the best of our knowledge, we are not aware of synthesis of 1,4-
disubstituted 1,2,3-triazoles in water using polymer supported
ruthenium catalyst and thus we believe that this protocol will find
an useful application in green organic synthesis. This polymer
supported Ru(III) catalyst is found to be an efficient catalyst in
transfer hydrogenation of both aliphatic as well as aromatic ketones
in the presence of isopropanol/KOH. This catalyst was effective for
transfer hydrogenation of ketones to their alcohols. The present
system is highly air and moisture stable and the catalyst can be
synthesized readily from inexpensive and commercially available
starting materials. Moreover, the catalyst can be reused for six
consecutive cycles with consistent catalytic activity. Further work is
in progress to broaden the scope of this catalytic system for other
organic transformation.
Hot-filtration test
Hot-filtration test was performed in the transfer hydrogenation
reaction to investigate whether the reaction proceeded in a het-
erogeneous or a homogeneous fashion. After continuing the re-
action for 1 h, the catalyst was removed by filtration and the
determined conversion was 76%. The resulting filtrate was sub-
jected to heating for further 2 h it has been found that after sep-
aration of the catalyst no conversion takes place in the filtrate part.
This confirms that the reaction did not proceed upon the removal
of the solid catalyst. Further, no evidence for leaching of ruthe-
nium or decomposition of the complex catalyst was observed
during the catalytic reaction and no metal could be detected by
atomic absorption spectroscopic measurement of the filtrate after
removal of catalyst. These studies clearly demonstrated that metal
was intact to a considerable extent with the heterogeneous sup-
port, and there is no significant amount of leaching occurred
during reaction.
Catalyst reusability
Acknowledgments
Recovery and reuse of catalyst are important issues in het-
erogeneous catalysis. Easy catalyst separation and recycling in
successive batch operations can greatly increase the efficiency of
the reaction. We studied the reusability of the present hetero-
geneous ruthenium catalyst in the azideealkyne cycloaddition
reaction, taking the reaction of benzyl bromide and phenyl-
acetylene (Fig. 8). After completion of the reaction, the catalyst
was recovered by simple filtration and washed with ethyl acetate
followed by acetone then dried in reduced pressure. The recov-
ered catalyst was employed in the next run with further addition
of substrates in appropriate amount under optimum reaction
conditions. Reusability test was also performed for transfer hy-
drogenation of cyclohexanone and the results are given in Fig. 8.
The catalysts show almost same activity up to six reaction cycles.
SMI acknowledges DST (ref no: SB/S1/PC-107/2012) and CSIR
(02(0041)/11/EMR-II, dated: 19-12-2011) for financial support.
RAM acknowledges UGC, New Delhi, India for his Maulana Azad
National Fellowship (F1-17.1/2012-13/MANF-2012-13-MUS-WES-
9628/SA-III). ASR acknowledges CSIR, New Delhi, India for his se-
nior research fellowship. NS acknowledges UGC, New Delhi, India
for his senior research fellowship.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2014.11.007.
References
[1] S. Kale, S. Kahandal, S. Disale, R. Jayaram, Curr. Chem. Lett. 1 (2012) 69.
[2] (a) S. Wacharasindhu, S. Bardhan, Z.K. Wan, K. Tabei, T.S. Mansour, J. Am.
Chem. Soc. 131 (2009) 4174;
(b) Y.X. Liu, W.M. Yan, Y.F. Chen, J.L. Petersen, X.D. Shi, Org. Lett. 10 (2008)
5389;
(c) A.R. Katritzky, S. Bobrov, K. Kostyantyn, Y. Ji, P.J. Steel, J. Org. Chem. 68
(2003) 5713.
[3] (a) R. Manetsch, A. Krasiski, Z. Radi, J. Raushel, P. Taylor, K.B. Sharpless,
H.C. Kolb, J. Am. Chem. Soc. 126 (2004) 12809;
(b) M. Whiting, J. Muldoon, Y.C. Lin, S.M. Silverman, W. Lindstrom, A.J. Olson,
H.C. Kolb, M.G. Finn, K.B. Sharpless, J.H. Elder, V.V. Fokin, Angew. Chem. Int. Ed.
45 (2006) 1435;
(c) J. Wang, G. Sui, V.P. Mocharla, R.J. Lin, M.E. Phelps, H.C. Kolb, H.R. Tseng,
Angew. Chem. Int. Ed. 45 (2006) 5276.
[4] (a) H. Nandivada, X.W. Jiang, J. Lahann, Adv. Mater. 19 (2007) 2197;
(b) C.F. Ye, G.L. Gard, R.W. Winter, R.G. Syvret, B. Twamley, J.M. Shreeve, Org.
Lett. 9 (2007) 3841;
(c) P. Wu, A.K. Feldman, A.K. Nugent, C.J. Hawker, A. Scheel, B. Voit, J. Pyun,
ꢀ
J.M.J. Frechet, K.B. Sharpless, V.V. Fokin, Angew. Chem. Int. Ed. 43 (2004) 3928.
[5] (a) D.R. Buckle, C.J.M. Rockell, J. Chem. Soc. Perkin Trans. 1 (1982) 627;
(b) M.J. Genin, D.A. Allwine, D.J. Anderson, M.R. Barbachyn, D.E. Emmert,
S.A. Garmon, D.R. Graber, K.C. Grega, J.B. Hester, D.K. Hutchinson, J. Morris,
R.J. Reischer, C.W. Ford, G.E. Zurenko, J.C. Hamel, R.D. Schaadt, D. Stapert,
B.H. Yagi, J. Med. Chem. 43 (2000) 953.
Fig. 8. Catalyst reusability test of the polymer supported Ru catalyst.

R.A. Molla et al. / Journal of Organometallic Chemistry 776 (2015) 170e179
[24] C. Zhang, B. Huang, Y. Chenb, D.M. Cui, New. J. Chem. 37 (2013) 2606.
179
[6] S.Q. Bai, L. Jiang, J.L. Zuoc, T.S. Andy Hor, Dalton Trans. 42 (2013) 11319.
ꢀ
[7] Z. Gonda, Z. Novak, Dalton Trans. 39 (2010) 726.
[8] D. Wang, M. Zhao, X. Liu, Y. Chen, N. Lia, B. Chen, Biomol. Chem. 10 (2012)
229.
[9] P. Ji, J.H. Atherton, M.I. Page, Org. Biomol. Chem. 10 (2012) 7965.
[10] F. Wang, H. Fu, Y. Jiang, Y. Zhaoa, Green. Chem. 10 (2008) 452e456.
[11] K.R. Gruenwald, A.M. Kirillov, M. Haukka, J. Sanchiz, A.J.L. Pombeiro, Dalton
Trans. (2009) 2109.
[25] P. Abdulkin, Y. Moglie, B.R. Knappett, D.A. Jefferson, M. Yus, F. Alonso,
A.E.H. Wheatley, Nanoscale 5 (2013) 342.
[26] L. Jiang, Z. Wang, S.Q. Bai, T.S. Andy Hor, Dalton Trans. 42 (2013) 9437.
[27] F. Nador, M.A. Volpe, F. Alonso, A. Feldhoff, A. Kirschning, G. Radivoy, Appl.
Catal. A: Gen. 455 (2013) 39.
[28] (a) L. Zhang, X. Chen, P. Xue, H.H.Y. Sun, I.D. Williams, K.B. Sharpless,
V.V. Fokin, G. Jia, J. Am. Chem. Soc. 127 (2005) 15998;
[12] M. Singla, M. Gupta, P. Mathur, M.S. Hundal, Trans. Met. Chem. 33 (2008) 175.
[13] (a) V. Aucagne, D.A. Leigh, Org. Lett. 8 (2006) 4505;
(b) P. Siemsen, R.C. Livingston, F. Diederich, Angew. Chem. Int. Ed. 39 (2000)
2632.
[14] (a) B.H. Lipshuz, B.R. Taft, Angew. Chem. 118 (2006) 8415;
(b) P. Cintas, K. Martina, B. Robaldo, D. Garella, L. Boffa, G. Cravotto, Collect.
Czech. Chem. Commun. 72 (2007) 1014;
(b) B.C. Boren, S. Narayan, L.K. Rasmussen, L. Zhang, H. Zhao, Z. Lin, G. Jia,
V.V. Fokin, J. Am. Chem. Soc. 130 (2008) 8923;
(c) B.C. Boren, V.V. Fokin, Org. Lett. 9 (2007) 5337;
(d) S. Oppilliart, G. Mousseau, L. Zhang, G. Jia, P. Thuery, B. Rousseau,
J.C. Cintrat, Tetrahedron 63 (2007) 8094.
[29] (a) D.R. Hou, T.C. Kuan, Y.K. Li, R. Lee, K.W. Huang, Tetrahedron Lett. 66 (2010)
9415;
(c) H. Sharghi, R. Khalifeh, M.M. Doroodmand, Adv. Synth. Catal. 351 (2009)
207;
(d) H. Kang, H.J. Lee, J.C. Park, H. Song, K.H. Park, Top. Catal. 53 (2010) 523;
(e) F. Alonso, Y. Noglie, G. Radivoy, M. Yus, Org. Biomol. Chem. 9 (2011) 6385.
[15] (a) S. Chassaing, M. Kumarraja, A.S.S. Sido, P. Pale, J. Sommer, Org. Lett. 9
(2007) 883;
(b) A.H. Yap, S.M. Weinreb, Tetrahedron Lett. 47 (2006) 3035;
(c) M.M. Majireck, S.M. Weinreb, J. Org. Chem. 71 (2006) 8680;
(d) J.R. Johansson, P. Lincoln, B. Norden, N. Kann, J. Org. Chem. 76 (2011) 2355;
(e) Y. Lo, T.H. Wang, C.Y. Lee, Y.H. Feng, Organometallics 31 (2012)
6887e6899.
[30] P.N. Liu, H.X. Siyang, L. Zhang, S.K.S. Tse, G. Jia, J. Org. Chem. 77 (2012) 5844.
[31] P.N. Liu, J. Li, F.H. Su, K.D. Ju, L. Zhang, C. Shi, H.H.Y. Sung, I.D. Williams,
V.V. Fokin, Z. Lin, G. Jia, Organometallics 31 (2012) 4904.
[32] S. Gladiali, E. Alberico, Chem. Soc. Rev. 35 (2006) 226.
[33] A.J. Blacker, in: J.G. de Vries, C.J. Elsevier (Eds.), Handbook of Homogeneous
Hydrogenation, Wiley-VCH, Weinheim, 2007, p. 1215.
[34] T. Ikariya, A.J. Blacker, Acc. Chem. Res. 40 (2007) 1300.
[35] C. Wang, X.F. Wu, J.L. Xiao, Chem. Asian J. 3 (2008) 1750.
[36] J.S.M. Samec, J.E. Bckvall, P. Andersson, P. Brandt, Chem. Soc. Rev. 35 (2006) 237.
[37] S. Gladiali, E. Alberico, in: M. Beller, C. Bolm (Eds.), Transition Metals for
Organic Synthesis, second ed., Wiley-VCH, Weinheim, 2004, pp. 145e166.
[38] (a) E.P. Kelson, P.P. Phengsy, J. Chem. Soc. Dalton Trans. (2000) 4023;
(b) R.N. Prabhu, R. Ramesh, J. Organomet. Chem. 718 (2012) 43;
(c) H. Dyer, A. Picot, L. Vendier, A. Auffrant, P. Le Floch, S. Sabo-Etienne, Or-
ganometallics 30 (2011) 1478;
(b) A. Alix, S. Chassaing, P. Pale, J. Sommer, Tetrahedron 64 (2008) 8922;
(c) S. Chassaing, A.S.S. Sido, A. Alix, M. Kumarraja, P. Pale, J. Sommer, Chem.
Eur. J. 14 (2008) 6713;
(d) S. Chassaing, A. Alix, T. Boningari, K.S.S. Sido, M. Keller, P. Kuhn, B. Louis,
J. Sommer, P. Pale, Synthesis (2010) 1557;
ꢀ
ꢀ
(e) V. Beneteau, A. Olmos, T. Boningari, J. Sommer, P. Pale, Tetrahedron Lett. 51
(2010) 3673.
[16] (a) T. Miao, L. Wang, Synthesis (2008) 363;
(b) T. Shamin, S. Paul, Catal. Lett. 136 (2010) 260;
(c) P. Veerakumar, M. Velayudham, K.-L. Lu, S. Rajagopal, Catal. Sci. Technol. 1
(2011) 1512e1525.
[17] B.S. Lee, M. Yi, S.Y. Chu, J.Y. Lee, R. Kwon, K.R. Lee, D. Kang, W.S. Kim, H.B. Lim,
J. Lee, H.J. Youn, D.Y. Chi, N.H. Hur, Chem. Commun. 46 (2010) 3935.
[18] I.S. Park, M.S. Kwon, Y. Kim, J.S. Lee, J. Park, Org. Lett. 10 (2008) 497.
[19] (a) T. Katayama, K. Kamata, K. Yamaguchi, N. Mizuno, ChemSusChem 2 (2009) 59;
(b) K. Yamaguchi, T. Oishi, T. Katayama, N. Mizuno, Chem. Eur. J. 15 (2009) 10464.
[20] K. Namitharan, M. Kumarraja, K. Pitchumani, Chem. Eur. J. 15 (2009) 2755.
[21] H. Hagiwara, H. Sasaki, T. Hoshi, T. Suzuki, Synlett (2009) 643.
[22] (a) M. Lammens, J. Skey, S. Wallyn, R. O'Reilly, F.D. Prez, Chem. Commun. 46
(2010) 8719;
(d) I. Nieto, M.S. Livings, J.B. Sacci, L.E. Reuther, M. Zeller, E.T. Papish, Organ-
ometallics 30 (2011) 6339;
́
(e) H. Matsunaga, T. Ishizuka, T. Kunieda, Tetrahedron Lett. 46 (2005) 3645.
[39] G.G. Mohamed, M.M. Omar, A.H.H. Hindy, Spectrochim. Acta. A 62 (2005)
1140.
[40] G.K. Sandhu, S.P. Verma, Polyhedron 6 (1987) 587.
[41] N. Rao, P.V. Rao, V. Raju, M.C. Ganorkar, Indian J. Chem. 24A (1985) 877.
[42] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, Wiley, New York, 1997.
(b) Z. Zhang, C. Dong, C. Yang, D. Hu, J. Long, L. Wang, H. Li, Y. Chen, D. Kong,
Adv. Synth. Catal. 352 (2010) 1600;
(c) Y.M.A. Yamada, S.M. Sarkar, Y. Uozumi, J. Am. Chem. Soc. 134 (2012) 9285;
(d) T. Suzuka, Y. Kawahara, K. Ooshiro, T. Nagamine, K. Ogihara, M. Higa,
Heterocycles 85 (2012) 615.
[43] P. Neubold, B.P.C. Della Vedova, K. Wieghardt, B.N.J. Weris, Inorg. Chem. 29
(1990) 3355 and references therein.
[23] A. Kumar, S. Aerry, A. Saxena, A. De, S. Mozumdar, Green. Chem. 14 (2012)
1298.
[44] J.A. Broomhead, L.A.P. Kane-Maguire, J. Chem. Soc. A (1967) 546.
[45] G. Venkatachalam, R. Ramesh, Inorg. Chem. Commun. 8 (2005) 1009.