Polymer-anchored Ru(II) complex as an efficient catalyst for the synthesis of primary amides from nitriles and of secondary amides from alcohols and amines

Article abstract of DOI:10.1002/aoc.3233

A polymer-anchored ruthenium(II) catalyst was synthesized and characterized. Its catalytic activity was evaluated for the preparation of primary amides from aqueous hydration of nitriles in neutral condition. A range of nitriles were successfully converted to their corresponding amides in good to excellent yields. The catalyst was also effective in the preparation of secondary amides from the coupling of alcohols and amines. The catalyst can be facilely recovered and reused six times without a significant decrease in its activity.

Full text of DOI:10.1002/aoc.3233

Full Paper
Received: 18 July 2014
Revised: 22 August 2014
Accepted: 17 September 2014
Published online in Wiley Online Library: 21 October 2014
(wileyonlinelibrary.com) DOI 10.1002/aoc.3233
Polymer-anchored Ru(II) complex as an efficient
catalyst for the synthesis of primary amides
from nitriles and of secondary amides from
alcohols and amines
Sk Manirul Islam*, Kajari Ghosh, Anupam Singha Roy† and Rostam Ali Molla†
A polymer-anchored ruthenium(II) catalyst was synthesized and characterized. Its catalytic activity was evaluated for the prepara-
tion of primary amides from aqueous hydration of nitriles in neutral condition. A range of nitriles were successfully converted to
their corresponding amides in good to excellent yields. The catalyst was also effective in the preparation of secondary amides
from the coupling of alcohols and amines. The catalyst can be facilely recovered and reused six times without a significant de-
crease in its activity. Copyright © 2014 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web-site.
Keywords: polymer anchor; ruthenium(II) complex; nitriles; amides
complexes suffer from various drawbacks, especially the difficulty in
separation of product and catalyst from the reaction mixture, the
Introduction
The amide bond plays a key role in organic and biological chemistry.
Amides have been widely used as raw materials for engineering
plastics, intensifiers of perfume, antiblock reagents, colour pigments
for inks, detergents, lubricants and intermediates in peptide and
protein synthesis.[1–7] The classical method for amide synthesis is
the acylation of amines with carboxylic acid derivatives (acid chlo-
rides, anhydrides, active esters, etc.).[8,9] Several alternative strategies
such as the Staudinger reaction,[10–12] the Schmidt reaction,[13,14] the
Beckmann rearrangement,[15,16] direct amide formation from
unactivated carboxylic acids with amines[17,18] and the oxidative
amidation of aldehydes[19–26] have been developed. Many of these
methods have innate drawbacks of producing a stoichiometric
amount of waste product and of using highly hazardous reagents.
Two methods via the hydration of nitriles[27,28] and direct amidation
of alcohols with amines[1,29,30] can be potentially elegant alternative
pathways since they use cheap, abundant and stable starting
materials.
The catalytic hydration of nitriles is an ideal atom-economic
reaction and is one of the most important technologies for the
large-scale synthesis of amides.[31–33] Traditional methods of
hydrating nitriles to amides involve the use of strong bases or acids
under harsh conditions, often inducing undesired hydrolysis to
carboxylic acids. During neutralization, salt formation can lead to
contamination, separation and pollution problems. Moreover, poor
tolerance for sensitive functional groups is often observed under
such conditions.[34–38] Therefore, the development of efficient pro-
cedures for the synthesis of amides that circumvent the extrava-
gant use of stoichiometric reagents and/or acidic and basic media
is highly desirable. Metalloenzymes,[39] heterogeneous transition
metal catalysts[40] and a variety of homogeneous catalysts have
been employed in the large-scale industrial production of amides
from nitriles.[41,35,42–48] The methods involving homogeneous metal
use of inert atmosphere for handling air-sensitive metal catalysts,
relatively short catalyst lifetime, a low tolerance for harsh conditions
(high pressure and temperature) and the cost of the catalyst
itself.[31,49,50] In contrast, heterogeneous catalysis is a valid alterna-
tive with the important advantage that the catalyst can be easily
separated.[51,52]
Water, with its unique properties, has seen increased use as a
solvent in stoichiometric and catalytic reactions. Recently several
homogeneous and heterogeneous nitrile hydration reactions have
been reported.[51,53,54]
The direct catalytic conversion of alcohols and amines into
amides that evolve dihydrogen as the sole by-product is a particu-
larly desirable reaction due to its high atom efficiency and widely
available starting materials.[29,31] These reactions produce less
waste than traditional amide syntheses that often produce toxic
chemical waste with tedious procedures. Recently, several groups
have reported catalytic amide formation from alcohols, using
homogeneous transition metal catalysts to oxidize the alcohol to
aldehyde in situ and then further oxidize the hemiaminal to the
desired amide via the loss of 2 equiv. of H2.[55,56,9] One such
metal-catalysed approach that has seen significant research in
recent years is the oxidation of alcohols to amides using ruthenium
catalysts.[2] In contrast, heterogeneous catalysts have received
more and more attention because of the advantages of high cata-
lytic efficiency.[57–66] However, little progress has been made in
*
Correspondence to: S. M. Islam, Department of Chemistry, University of Kalyani,
Kalyani, Nadia, 741235, WB, India. E-mail: manir65@rediffmail.com
†
These authors contributed equally to this study.
Department of Chemistry, University of Kalyani, Kalyani, Nadia, 741235, WB, India
Appl. Organometal. Chem. 2014, 28, 900–907
Copyright © 2014 John Wiley & Sons, Ltd.

Heterogeneous Ru(II) complex as a catalyst for synthesis of amides
the direct amidation from alcohols and amines using supported
heterogeneous catalysts. The field still needs further improve-
ment in terms of catalytic efficiency, and the scope of the
substrates for direct amidation also needs further improvement.
Since then this area has been the subject of considerable
research activity.[67–69]
Herein we report the synthesis and characterization of a newly
synthesized polymer-anchored ruthenium(II) complex and its
catalytic applications to the preparation of primary amides from
hydration of nitriles in aqueous medium and of secondary
amides from alcohols and amines.
Synthesis of Catalyst
The outline for the preparation of the polymer-anchored ruthenium
(II) complex is shown in Scheme 1.
Preparation of polymer-anchored ligand
Chloromethylated polystyrene (PS-CH2Cl) was converted into
PS-CHO according to the literature.[71] Triethylenetetramine
(teta) was reacted with PS-CHO (in 1:2 molar ratio) in methanol
solvent under refluxing condition for 24 h to prepare a yellow
Schiff base compound. The mixture was cooled to room temper-
ature and then filtered. The residue was washed with ethanol
and dried under vacuum.
Preparation of polymer-anchored ruthenium catalyst
Experimental
RuCl3ꢀ3H2O (1.9mmol) was dissolved in excess DMSO under
refluxing condition resulting in the formation of [Ru(DMSO)4Cl2]
complex.[72] The anchored ligand (1.0g) was then added to this
solution with stirring under reflux condition and the mixture was
refluxed for 24h, forming the brown catalyst. It was filtered and
washed with ethanol.
Materials and Instrumentation
Analytical-grade reagents and freshly distilled solvents were used
throughout the experiments. Chloromethylated poly(styrene divinyl
benzene) was supplied by Sigma-Aldrich, USA. Other reagents were
obtained from Merck Co. The chemical analysis was done by usual
procedures. The purities of solvents and substrates were checked
by gas chromatography. Ruthenium chloride was purchased from
Arora Matthey, India, and used as received. Liquid substrates were
predistilled and dried with appropriate molecular sieves. Distillation
and purification of solvents and substrates were done by standard
procedures.[70]
General Procedure for Hydration of Nitrile to Amide
Under air, 1 mmol of nitrile, 3 ml of water and 2 × 10ꢁ2 mmol of
[PS-teta-Ru] were added to a Teflon-sealed, screw-cap, round-
bottomed flask and stirred at 90 °C for 7 h. GC yields were obtained
by taking a small aliquot (ca 50 μl from the hot solution and
extracting with CH2Cl2 (3 × 2 ml)). The catalyst can be easily separated
by filtration. Isolated yields were obtained by either decanting the
aqueous layer from the product crystals or by evaporation of the
solvent followed by column chromatography over silica gel (ethyl
acetate as eluent).
A PerkinElmer 2400 C elemental analyser was used to collect
micro-analytical data (C, H and N). FT-IR spectra of the samples
were recorded with a PerkinElmer FT-IR 783 spectrophotometer
using KBr pellets. A Mettler Toledo TGA/SDTA 851 instrument
was used for thermogravimetric analysis (TGA). The morphology
of the functionalized polystyrene and complex was analysed
using a scanning electron microscopy (SEM) instrument (Zeiss
EVO40, UK) equipped with energy-dispersive X-ray analysis
(EDAX) facility. The metal content in the catalyst was determined
using atomic absorption spectrophotometry (AAS; Varian AA240).
All spectra were recorded at 300 and 400 MHz for 1H NMR and 75
and 100MHz for 13C NMR. The characterizations of the products
General procedure for Formation of Amides from Alcohols and
Amines
To an oven-dried, nitrogen-purged, round-bottomed flask
containing alcohol (3 mmol), amine (3.33 mmol), 3-methyl-
2-butanone (0.8ml, 7.5mmol), Cs2CO3 (97.7 mg, 0.30 mmol) and
tBuOH (3 ml), 2 × 10ꢁ2 mmol of [PS-teta-Ru] was added, and
the reaction was heated at reflux for 18 h. On completion, the
reaction was allowed to cool to room temperature before
the solvent was removed in vacuo. The catalyst can be easily
separated by filtration. The crude product was purified by
column chromatography (Et2O–petroleum ether as eluent)
before recrystallization (from dichloromethane–hexane), to afford
the corresponding amide in good yield.
1
were carried out using H NMR and 13C NMR spectroscopy using
Bruker DPX-300 and DPX-400 with samples in CDCl3 with
tetramethylsilane and DMSO-d6 as internal standards.
Results and Discussion
Catalyst Characterization
The polymer-anchored ligand and catalyst were well characterized.
Due to the insolubility of the polymer-anchored metal complex in
all common organic solvents, its structural investigation is limited
to physicochemical properties, chemical analysis, SEM, TGA and
FT-IR, electron paramagnetic resonance (EPR) and UV–visible
spectral data. Table 1 provides the results of elemental analysis of
polymer-anchored ligand and polymer-anchored ruthenium cata-
lyst. The metal content of the polymer-anchored catalyst was
estimated using AAS, suggesting 6.62wt% Ru in the catalyst.
Scheme 1. Preparation of polymer-anchored ruthenium(II) catalyst.
Appl. Organometal. Chem. 2014, 28, 900–907
Copyright © 2014 John Wiley & Sons, Ltd.
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S. M. Islam et al.
Table 1. Chemical composition of polymer-anchored ligand and poly-
mer-anchored catalyst
The attachment of metal onto the support is confirmed from a
comparison of the FT-IR spectra (Fig. 1) of the polymer before
and after loading with metal, in the mid-IR (400–4000 cmꢁ1
)
Compound Colour
C (%)
H (%) Cl (%) N (%) Metal (%)
region. The IR spectrum of pure PS-CH2Cl has an absorption
band at 1261 cmꢁ1 due to the C–Cl group, which is weak in the
spectra of ligand and catalyst. FT-IR spectra show a stretching
vibration of –CH2 at 2924 cmꢁ1 for the polymer-bound ligand and
its complex. The stretching vibration of C¼N bond appears at
1642 cmꢁ1 for the polymer-bound ligand which is lowered to
1607 cmꢁ1 in the spectrum of the metal complex, indicating the co-
ordination of azomethine nitrogen to the metal.[73] A strong broad
band around 3429 cmꢁ1 in the spectrum of the polymeric support
is observed due to NH (secondary amine) vibration which is lowered
to 3400 cmꢁ1 in the spectrum of the metal complex. For the far-IR
data, the bands are due to the Ru–N stretching vibrations at around
470 cmꢁ1, which establish the formation of the metal complex
through Ru–N bonding. The peak of Ru–Cl for the metal complex
is observed at around 325 cmꢁ1 according to the literature.[74]
The electronic spectrum (Fig. 2) of the polymer-anchored metal
complex was recorded in diffuse reflectance spectrum mode as
MgCO3/BaSO4 discs. The polymer-anchored ruthenium(II) complex
is in the +2 oxidation state. The electronic spectrum of the ruthenium
complex shows four bands in the region 220–710 nm. The bands in
the 580–700 nm range have been assigned to the spin-allowed
d–d transition. The other bands around 304–480 nm have been
assigned to charge transfer transitions arising from the excitation of
electrons from the metal t2g level to the unfilled molecular orbitals
derived from the π* level of the ligand. The bands below 300 nm
are characterized by intra-ligand charge transfer.[75]
PS-teta
Yellow
Brown
75.69
67.16
7.42
6.58
6.55
8.14
10.34
9.17
—
PS-teta-Ru
6.62
Figure 1. FT-IR spectra of (a) polymer-anchored ligand and (b) polymer-
anchored ruthenium(II) catalyst.
Field-emission SEM micrographs of single beads of polymer-
anchored ligand (PS-teta) and its complex (PS-teta-Ru) were
recorded and it is observed that morphological changes occur on
the polystyrene beads at various stages of the synthesis. The SEM
images of polymer-anchored ligand and the immobilized ruthe-
nium(II) complex on functionalized polymer are shown in Fig. 3.
The pure PS-CH2Cl bead has a smooth surface while polymer-
anchored ligand and complex show slight roughening of the top
layer of polymer beads. This roughening is greater in the complex.
Also the presence of ruthenium metal can be further proved using
EDAX (Fig. 4) which suggests the formation of metal complex with
the polymer-anchored ligand.
The thermal stability of the complex was investigated using
TGA-DTA at a heating rate of 10 °Cminꢁ1 in air over a temperature
range of 30–600 °C. The TGA curve of the polymer-anchored Ru(II)
complex is shown in Fig. S1 (supporting information). The polymer-
anchored ruthenium(II) complex decomposes at 360–400 °C. So from
Figure 2. Diffuse reflectance UV–visible absorption spectra of polymer-
anchored Ru(II) complex and ligand.
Figure 3. Field-emission SEM images of (A) polymer-anchored ligand (PS-teta) and (B) PS-teta-Ru.
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Copyright © 2014 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 900–907

Heterogeneous Ru(II) complex as a catalyst for synthesis of amides
Scheme 2. Hydration of nitriles to amides.
Scheme 3. Hydration of benzonitrile under optimized conditions.
the thermal stability, it is concluded that the polymer-anchored
metal complex degrades at considerably higher temperature.
The X-band EPR spectra of the Ru complex in fresh and used
catalysts were recorded in the solid state at room temperature
(Fig. 5). The EPR spectra of both fresh and used catalyst are quite
similar and also match with the EPR spectra of previously reported
Ru(II) complexes.[76] Hence, we can predict that Ru remains in the
+2 oxidation state before and after the reaction.
Catalytic Activities of PS-teta-Ru
Catalytic activity of PS-teta-Ru for preparation of primary amides
The catalytic activity of the polymer-anchored ruthenium(II) complex
was verified for the hydration of nitriles in aqueous medium to pro-
duce the respective primary amides (Scheme 2). Aqueous hydration
of benzonitrile to benzamide in air was taken as the model reaction
(Scheme 3). The temperature of the reaction was varied. No reaction
occurs at room temperature. Very little conversion is observed at
50 °C. The temperature is gradually raised to 75 °C, and finally 92%
product yield is obtained at 90 °C. The reaction temperature is further
raised but no major change in conversion is noticed (Fig. 6).
With the optimized reaction conditions determined, the scope of
the reaction was explored using the hydration of a range of nitriles
to the corresponding amides in air. The results are summarized in
Table 2. All nitriles are efficiently converted to amides with 90–99%
conversion in 7 h and at 90 °C. After completion, the reactions were
cooled to 0 °C and, in most cases, the product amides crystallize
out as white needles and are easily isolated. The identity of the iso-
lated amides was confirmed using GC and NMR spectroscopy.
The substituted benzonitriles bearing electron-withdrawing
groups (Table 2, entries 2–10) exhibit slightly more efficient
Figure 4. EDX spectra of (A) polymer-anchored ligand and (B) polymer-
anchored Ru(II) complex.
Figure 5. X-band EPR spectra of Ru(II) for (a) fresh catalyst and (b)
used catalyst.
Figure 6. Variation of yield of amide with temperature.
Appl. Organometal. Chem. 2014, 28, 900–907
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S. M. Islam et al.
Table 2. Hydration of various nitriles catalysed by PS-teta-Ru
trifluoromethyl (entry 10), methoxy (entries 11 and 12), thiomethyl
(entry 13), methyl (entries 14–16), pyridyl (entries 17–19), furyl
(entry 20), thiophenyl (entries 21 and 22), indoyl (entry 23) and
naphthyl (entry 24) functional groups, which establishes a wide
synthetic scope.
Entry
R
Amide yield (%)
1
C6H5
(4-Cl)C6H4
92
97
95
94
95
99
97
98
96
96
94
90
91
93
90
92
97
98
96
94
95
94
98
92
2
Catalytic activity of PS-teta-Ru for the preparation of secondary amides
3
(3-Cl)C6H4
The successful yields of primary amides from the aqueous hydra-
tion of nitriles inspired us to shift our focus to the preparation
of secondary amides. We chose to examine the coupling of
3-phenylpropan-1-ol with benzylamine as a model reaction
(Scheme 4). In an initial attempt using acetone as the hydrogen
acceptor with tBuOH as solvent and K2CO3 as base, the desired
amide is formed with 70% conversion.
The effect of various reaction parameters, namely base, hydro-
gen acceptor and solvent, were studied for optimization of reaction
conditions. The choice of base was taken as a starting point for the
optimization. Replacement of K2CO3 with KHCO3, KOH or KOtBu
leads to lower conversions, as does the use of Na2CO3. However,
the use of Cs2CO3 leads to 74% of the desired amide and this base
was selected for further optimization reactions. In the absence of
base, no conversion to the amide is observed. Similarly, the use of
Et3N as base also leads to no conversion (Table 3).
4
(2-Cl)C6H4
5
(4-Br)C6H4
(4-F)C6H4
6
7
(3-F)C6H4
8
(4-NO2)C6H4
(2-NO2)C6H4
(4-CF3)C6H4
(4-MeO)C6H4
(2,3-MeO)C6H4
(4-MeS)C6H4
(4-Me)C6H4
(2-Me)C6H4
(3-Me)C6H4
3-Pyridyl
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
4-Pyridyl
2-Pyridyl
2-Furyl
2-Thiophenyl
(3-Me)-2-thiophenyl
3-Indolyl
Table 3. Choice of base for coupling of alcohol and amine
Entry
Base
Yield of amide (%)
2-Naphthyl
Conditions: nitrile (1 mmol), [PS-teta-Ru] (2 × 10ꢁ2 mmol), H2O (3 ml),
90 °C, 7 h, in air. The products were isolated either by decantation or
1
2
3
4
5
6
7
8
None
0
70
63
62
60
58
74
0
K2CO3
KHCO3
KOH
by column chromatography. They were identified by 1H NMR and 13
NMR analyses.
C
KOtBu
Na2CO3
Cs2CO3
Et3N
conversions to amides than those with electron-donating groups
(entries 11–16). Presumably, the presence of an electron-
withdrawing group makes the nitrile carbon more susceptible to
nucleophilic attack by an activated water molecule. This is in
agreement with results for other catalyst systems[53] although
there have been exceptions reported.[77] As previously
reported,[78,79] ortho-substituted benzonitriles exhibit lower con-
version relative to meta- and para-substituted benzonitriles (en-
tries 2–4, 6–9, 14–16), which is attributed to steric hindrance of
the ortho-substituted benzonitriles. The conversion proceeds
smoothly even in the presence of heteroatoms such as N, O and
S in the substrates (entries 17–23) and a range of heterocyclic
aromatic amides are obtained in excellent isolated yields. Even
indole-3-carbonitrile (entry 23) and 2-naphthonitrile (entry 24)
are converted to indole-3-carboxamide (98%) and 2-naphthamide
(92%), respectively, in admirable yields. It is interesting to note
that in all these reactions no other by-products such as carboxylic
acids are present. Thus, the catalytic conditions described here are
compatible with halide (entries 2–7), nitro (entries 8 and 9),
Conditions: 3-phenyl-1-propanol (1.0mmol), benzylamine
(1.1 mmol), acetone (7.5 mmol) [PS-teta-Ru] (2 × 10ꢁ2 mmol),
solvent (1 ml), reflux, 18 h.
Table 4. Optimization of hydrogen acceptor (ketone) and solvent
Entry
Ketone
Solvent
Yield of amide (%)
1
2
3
4
5
6
7
8
9
10
Acetone
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
tBuOH
DME
74
76
71
90
75
90
88
80
83
30
2-Butanone
Pinacolone
3-Methyl-2-butanone
Cyclohexanone
Acetophenone
3-Methyl-2-butanone
3-Methyl-2-butanone
3-Methyl-2-butanone
3-Methyl-2-butanone
2-MeTHF
Dioxane
Toluene
Conditions: 3-phenyl-1-propanol (1.0 mmol), benzylamine (1.1 mmol),
Cs2CO3 (0.30 mmol), [PS-teta-Ru] (2 × 10ꢁ2 mmol), solvent (1 ml),
reflux, 18 h.
Scheme 4. Model reaction for the formation of secondary amides.
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Heterogeneous Ru(II) complex as a catalyst for synthesis of amides
Table 5. Reaction of various alcohols with amines catalysed by PS-teta-Ru
Entry
R2
R3
Yield (%)
1
C6H5CH2CH2
C6H5CH2CH2
C6H5CH2
C6H5
C6H5CH2
C6H5
90
87
87
86
79
87
86
83
94
88
92
93
92
96
62
96
94
96
66
56
2
3
4
C6H5
C6H5
5
C6H5CH2CH2
C6H5CH2CH2
CH3CH2CH(CH3)
C6H5CH(CH3)CH2
C6H5CH(C6H5)CH2
C6H5(CH2)3CH2
CH3(CH2)3CH2
CH3(CH2)6CH2
CH2¼CH(CH2)2CH2
(MeO)CH2
(4-Cl)C6H4
(4-MeO)C6H4
C6H5
6
7
8
C6H5
9
C6H5
10
11
12
13
14
15
16
17
18
19
20
C6H5
C6H5
C6H5
C6H5
C6H5
(3-Indoyl)CH2
2-Furyl
C6H5
CH3(CH2)3
C6H5
(4-MeO)C6H4CH2CH2
(4-MeO)C6H4
(4-F)C6H4
C6H5
C6H5
C6H5CH2CH2
Morpholine
Conditions: alcohol (3 mmol), amine (3.33 mmol), 3-methyl-2-butanone (0.8 ml, 7.5 mmol), Cs2CO3 (97.7 mg, 0.30 mmol), tBuOH (3 ml),
[PS-teta-Ru] (2 × 10ꢁ2 mmol), reflux, 18 h. The products were isolated by column chromatography and determined by 1H
NMR and 13C NMR analyses.
The choice of hydrogen acceptor was then examined. Firstly
simple alkenes and then dodec-1-ene, styrene and cyclohexene
were selected as hydrogen acceptors for this reaction, but they
do not give good results. Even use of hex-1-yne does not prove
satisfactory. In a next attempt a series of ketones were tested as
hydrogen acceptor in this reaction. Acetone gives quite a satisfac-
tory yield of amide as a product. Replacement of acetone with
alternative ketones is found to be successful, as evident from
Table 4. 2-Butanone (entry 2) and cyclohexanone (entry 5) give very
similar results, while pinacolone (entry 3) gives a reduced
conversion, presumably for steric reasons. The use of 3-
methylbutan-2-one (entry 4) or acetophenone (entry 6) gives im-
proved results in amide yield. The use of nonhydroxylic polar sol-
vents affords comparable results (entries 7–9), although the use of
toluene (entry 10) leads to less amide formation.
Test for Heterogeneity
The leaching of ruthenium from polymer-anchored ruthenium(II)
complex is confirmed from analysis of the used catalyst (FT-IR) as
well as the product mixtures (AAS and UV–visible). Analysis of the
used catalyst does not show appreciable loss in the ruthenium con-
tent as compared to the fresh catalyst. The FT-IR spectrum of the
recycled catalyst is quite similar to that of fresh sample indicating
the heterogeneous nature of this complex. Analysis of the product
Now the optimized reaction parameters are as follows: Cs2CO3 as
base, iPrCOMe as hydrogen acceptor and tBuOH as solvent. With
this catalytic system chosen, the reaction was applied to the synthe-
sis of a range of amides (Table 5) with good isolated yields. It is very
interesting to note that the introduction of a methoxy group into
the molecule (entries 6, 14, 17 and 18) gives excellent amide yields
(87–96%) with almost no by-product.
Secondary amines are poor substrates in this reaction, showing
lower product formation. The use of an indole-containing substrate
(entry 15) gives a lower yield than anticipated (62%).
In the case of the coupling of 3-phenyl-1-propanol and
morpholine (entry 20), moderate yield (56%) of the tertiary amide
product is obtained. Thus a more efficient catalytic system for the
preparation of tertiary amides is under study.
Figure 7. Recycling efficiency of PS-teta-Ru complex.
Appl. Organometal. Chem. 2014, 28, 900–907
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S. M. Islam et al.
mixtures shows that if any ruthenium is present it is below the de-
tection limit. UV–visible spectroscopy was also used to determine
the stability of this catalyst. The UV–visible spectra of the reaction
solution, at the first run, does not show any absorption peaks
characteristic of ruthenium metal, which indicates that the leaching
of metal does not take place during the course of the reaction. The
metal content of the recycled catalyst was determined with
the help of AAS and it is found that the ruthenium content of the
recycled catalyst remains almost unaltered. These observations
strongly suggest that the present catalyst is truly heterogeneous
in nature.
Heterogeneity testing was carried out for the hydration of
benzonitrile as an example. For the rigorous proof of heterogeneity,
a test was carried out by filtering catalyst from the reaction mixture at
90° for 4 h and the filtrate was allowed to react up to the completion
of the reaction (7 h). The reaction mixture at 4 h and the filtrate were
analysed using GC. No change in the yield of amide is found which
indicates that the present catalyst is heterogeneous in nature.
References
[1] K. Yamaguchi, H. Kobayashi, Y. Wang, T. Oishi, Y. Ogasawara, N. Mizuno,
Catal. Sci. Technol. 2013, 3, 318.
[2] C. Chen, S. Hyeok Hong, Org. Biomol. Chem. 2011, 9, 20.
[3] C. E. Mabermann, in Encyclopedia of Chemical Technology, Vol. 1 (Ed.: J. I.
Kroschwitz), John Wiley, New York, 1991, p. 251.
[4] D. Lipp, in Encyclopedia of Chemical Technology, Vol. 1 (Ed.: J. I.
Kroschwitz), John Wiley, New York, 1991, p. 266.
[5] R. Opsahl, in Encyclopedia of Chemical Technology, Vol. 2 (Ed.: J. I.
Kroschwitz), John Wiley, New York, 1991, p. 346.
[6] A. Greenberg, C. M. Breneman, J. F. Liebman (Eds), The Amide Linkage:
Structural Significance in Chemistry, Biochemistry and Material Science,
Wiley, New York, 2000.
[7] J. S. Carey, D. Laffan, C. Thomson, M. T. Williams, Org. Biomol. Chem.
2006, 4, 2337.
[8] E. Valeur, M. Bradley, Chem. Soc. Rev. 2009, 38, 606.
[9] S. Gaspa, A. Porcheddu, L. De Luca, Org. Biomol. Chem. 2013, 11, 3803.
[10] E. Saxo, C. Z. Bertozzi, Science 2000, 287, 2007.
[11] F. Damkaci, P. De Shong, J. Am. Chem. Soc. 2003, 125, 4408.
[12] Y. G. Gololobov, L. F. Kasukhin, Tetrahedron 1992, 48, 1353.
[13] T. Ribelin, C. E. Katz, D. G. English, S. Smith, A. K. Manukyan, V. W. Day,
B.Neuenswander, J. L. Poutsma, J. Aube,Angew. Chem. Int. Ed. 2008, 47, 6233.
[14] S. Lang, J. A. Murphy, Chem. Soc. Rev. 2006, 35, 146.
[15] N. A. Owston, A. J. Parker, J. M. J. Williams, Org. Lett. 2007, 9, 3599.
[16] M. Hashimoto, Y. Obora, S. Sakaguchi, Y. Ishii, J. Org. Chem. 2008, 73, 2894.
[17] L. Perreux, A. Loupy, F. Volatron, Tetrahedron 2002, 58, 2155.
[18] C. L. Allen, A. R. Chhatwal, J. M. J. Williams, Chem. Commun. 2012, 48, 666.
[19] J. W. W. Chang, T. M. U. Ton, S. Tania, P. C. Taylor, P. W. H. Chan, Chem.
Commun. 2010, 46, 922.
Recycling of Catalyst
The catalyst remains insoluble under the reaction conditions used
here and hence can be easily separated by simple filtration
followed by washing. The catalyst was washed with dichlorometh-
ane and dried at 100°C. Hydration of benzonitrile was carried out
with the recycled catalyst under the optimized reaction conditions.
The catalyst was recycled in order to test its activity as well as its
stability. The obtained results are presented in Fig. 7. As can be
seen, the recycled catalyst does not show any appreciable change
in activity which indicates that the catalyst is stable and can be
regenerated for repeated use. Similarly, recycling of the catalyst
was tested for the reaction between 3-phenylpropan-1-ol and
benzylamine. No appreciable change in conversion indicates that
the catalyst can be reused.
[20] T. M. U. Ton, C. Tejo, S. Tania, J. W. W. Chang, P. W. H. Chan, J. Org. Chem.
2011, 76, 4894.
[21] S. C. Ghosh, J. S. Y. Ngiam, C. L. L. Chai, A. M. Seayad, T. T. Dang, A. Chen,
Adv. Synth. Catal. 2012, 354, 1407, and references therein.
[22] S. C. Ghosh, J. S. Y. Ngiam, A. M. Seayad, D. T. Tuan, C. L. L. Chai, A. Chen,
J. Org. Chem. 2012, 77, 8007.
[23] K. S. Goh, C. H. Tan, RSC Adv. 2012, 2, 5536.
[24] X. Liu, K. F. Jensen, Green Chem. 2012, 14, 1471.
[25] G. L. Li, K. K. Y. Kung, M. K. Wong, Chem. Commun. 2012, 48, 4112.
[26] M. Zhu, K. I. Fujita, R. Yamaguchi, J. Org. Chem. 2012, 77, 9102.
[27] R. García-Álvarez, P. Crochet, V. Cadierno, Green Chem. 2013, 15, 46.
[28] T. Mitsudome, Y. Mikami, H. Mori, S. Arita, T. Mizugaki, K. Jitsukawaa,
K. Kaneda, Chem. Commun. 2009, 3258.
[29] G. E. Dobereiner, R. H. Crabtree, Chem. Rev. 2010, 110, 681.
[30] C. Gunanathan, T. Ben-David, D. Milstein, Science 2010, 317, 790.
[31] T. Oshiki, H. Yamashita, K. Sawada, M. Utsunomiya, K. Takahashi,
K. Takai, Organometallics 2005, 24, 6287.
[32] V. Polshettiwar, R. S. Varma, Chem. Eur. J. 2009, 15, 1582.
[33] P. K. Mascharak, Coord. Chem. Rev. 2002, 225, 201.
[34] T. J. Ahmed, S. M. M. Knapp, D. R. Tyler, Coord. Chem. Rev. 2010, 255, 949.
[35] V. Y. Kukushkin, A. J. L. Pombeiro, Inorg. Chim. Acta 2005, 358, 1.
[36] V. Y. Kukushkin, A. J. L. Pombeiro, Chem. Rev. 2002, 102, 1771.
[37] J. L. Eglin, Comments Inorg. Chem. 2002, 23, 23.
[38] A. W. Parkins, Platinum Met. Rev. 1996, 40, 169.
[39] B. Schultz, K. Drauz, H. Waldmann, Enzyme Catalysis in Organic Synthesis,
Wiley-VCH, Weinheim, 2002, pp. 699.
[40] K. Weissermel, H. J. Arpe, Industrial Organic Chemistry, 4th edn, Wiley-
VCH, Weinheim, 2003, pp. 310.
Conclusions
We have developed and characterized an efficient polymer-
anchored ruthenium(II) complex catalyst. This catalyst is efficient for
the hydration of nitriles with various functional groups. The primary
amides from these nitriles are prepared via an ideal green process,
i.e. water as the green solvent and in air. This catalyst also shows
excellent catalytic activity in the preparation of secondary amides
from alcohols and amines. The advantages of the catalytic system
discussed here include easy catalyst preparation and simple reaction
setup. The catalyst is stable under the reaction conditions used. This
heterogeneous catalyst shows no significant loss of activity in
recycling experiments. The active sites do not leach out from the
support and thus the catalyst can be reused without appreciable loss
of activity, indicating that the anchoring procedure is effective. The
reusability of this catalyst is high and it can be reused six times with-
out significant decrease in its initial activity. We expect that the pres-
ent catalytic system will have a bright future in industrial applications.
[41] K. Tani, Y.Kataoka, A. Togni,H.Grutzmacher,Catalytic Heterofunctionalization,
Wiley-VCH, New York, 2001, pp. 171.
[42] M. N. Kopylovich, V. Y. Kukushkin, M. Hauka, J. J. R. Frausto da Silva,
A. J. L. Pombeiro, Inorg. Chem. 2002, 41, 4798.
[43] W. K. Fung, X. Huang, M. L. Man, S. M. Ng, M. Y. Hung, Z. Lin, C. P. Lau,
J. Am. Chem. Soc. 2003, 125, 11539.
[44] X. Jiang, A. J. Minnaard, B. L. Feringa, J. G. de Vries, J. Org. Chem. 2004, 69, 2327.
[45] K. L. Breno, M. D. Pluth, D. R. Tyler, Organometallics 2003, 22, 1203.
[46] K. L. Breno, M. D. Pluth, C. W. Landorf, D. R. Tyler, Organometallics 2004,23, 1738.
[47] S. I. Murahashi, T. Naota, Bull. Chem. Soc. Jpn. 1996, 69, 1805.
[48] T. Ghaffar, A. W. Parkins, J. Mol. Catal. A 2000, 160, 249.
[49] A. Goto, K. Endo, S. Saito, Angew. Chem. 2008, 120, 3663.
[50] C. Battilocchio, J. M. Hawkins, S. V. Ley, Org. Lett. 2014, 16, 1060.
[51] T. Subramanian, K. Pitchumani, Catal. Commun. 2012, 29, 109.
[52] Y.-M. Liu, L. He, M.-M. Wang, Y. Cao, H.-Y. He, K.-N. Fan, ChemSusChem
2012, 5, 1392.
Acknowledgements
SMI acknowledges the Department of Science and Technology
(DST) and Council of Scientific and Industrial Research (CSIR), New
Delhi, India, for funding. RAM acknowledges UGC, New Delhi, for
his Maulana Azad National Fellowship (F1-17.1/2012-13/MANF-
2012-13-MUS-WES-9628/SA-III). ASR acknowledges CSIR, New Delhi,
for providing his senior research fellowship.
[53] W.-C. Lee, B. J. Frost, Green Chem. 2012, 14, 62.
wileyonlinelibrary.com/journal/aoc
Copyright © 2014 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 900–907

Heterogeneous Ru(II) complex as a catalyst for synthesis of amides
[54] R. B. Nasir Baig, M. N. Nadagouda, R. S. Varma, Green Chem. 2014, 16, 2122.
[55] A. J. A. Watson, A. C. Maxwell, J. M. J. Williams, Org. Lett. 2009, 11, 2667.
[56] S. Muthaiah, S. C. Ghosh, J. E. Jee, C. Chen, J. Zhang, S. H. Hong, J. Org.
Chem. 2010, 75, 3002.
[70] A. I. Vogel, Textbook of Practical Organic Chemistry (Quantitative
Analysis), 5th edn, Longman, London, 1998.
[71] J. M. Frechet, C. Schuerch, J. Am. Chem. Soc. 1971, 93, 492.
[72] E. Alessio, Chem. Rev. 2004, 104, 4203.
[57] D. Astruc, F. Lu, J. R. Aranzaes, Angew. Chem. 2005, 117, 8062.
[58] J. M. Campelo, D. Luna, R. Luque, J. M. Marinas, A. A. Romero,
ChemSusChem 2009, 2, 18.
[73] M. R. Mauryaa, S. J. J. Titinchi, S. Chand, I. M. Mishra, J. Mol. Catal. A 2002, 180, 201.
[74] A. Garza-Ortiz, P. U. Maheswari, M. Siegler, A. L. Spek, J. Reedijk, Inorg.
Chem. 2008, 47, 6964.
[59] J. Lu, P. H. Toy, Chem. Rev. 2009, 109, 815.
[75] P. Anitha, R. Manikandan, A. Endo, T. Hashimoto, P. Viswanathamurthi,
[60] R. J. White, R. Luque, V. L. Budarin, J. H. Clark, D. J. Macquarrie, Chem.
Soc. Rev. 2009, 38, 481.
[61] A. S. K. Hashmi, G. J. Hutchings, Angew. Chem. 2006, 118, 8064.
[62] T. V. W. Janssens, B. S. Clausen, B. Hvolbaek, H. Falsig, C. H. Christensen,
T. Bligaard, J. K. Norskov, Top. Catal. 2007, 44, 15.
Spectrochim. Acta A 2012, 99, 174.
[76] E. Sondaz, A. Gourdon, J. P. Launay, J. Bonvoisin, Inorg. Chim. Acta 2001, 316, 79.
[77] K. Yamaguchi, M. Matsushita, N. Mizuno, Angew. Chem. Int. Ed. 2004, 43, 1576.
[78] M. Muranaka, I. Hyodo, W. Okumura, T. Oshiki, Catal. Today 2011, 164, 552.
[79] R. Ramon, N. Marion, S. P. Nolan, Chem. Eur. J. 2009, 15, 8695.
[63] B. K. Min, C. M. Friend, Chem. Rev. 2007, 107, 2709.
[64] A. Corma, H. Garcia, Chem. Soc. Rev. 2008, 37, 2096.
[65] G. J. Hutchings, Chem. Commun. 2008, 1148.
[66] A. Corma, A. Leyva-Perez, M. J. Sabater, Chem. Rev. 2011, 111, 1657.
[67] N. D. Schley, G. E. Dobereiner, R. H. Crabtree, Organometallics 2011, 30, 4174.
[68] B. Gnanaprakasam, D. J. Milstein, J. Am. Chem. Soc. 2011, 133, 1682.
[69] H. Zeng, Z. Guan, J. Am. Chem. Soc. 2011, 133, 1159.
Supporting Information
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