Magnetite nanoparticles coated with ruthenium via SePh layer as a magnetically retrievable catalyst for the selective synthesis of primary amides in an aqueous medium

Article abstract of DOI:10.1039/c4dt01189a

The nanostructured magnetic oxide Fe₃O₄ has been coated with silica and then reacted with phenylselenyl chloride under a N ₂ atmosphere and RuCl₃·xH₂O successively in an aqueous medium to prepare Fe₃O₄@SiO ₂@SePh@Ru(OH)_x nanoparticles (NPs) for the first time. These magnetically retrievable NPs have been authenticated using TEM, SEM-EDX and powder-XRD and found to be an efficient catalyst for one pot conversion (organic solvent not required) of aldehydes, nitriles and benzyl amine to primary amides in water. For aldehydes and nitriles, the yields of primary amides are up to 93%. These NPs can be recycled more than 7 times for the conversion of benzonitrile to the corresponding amide. Gram-scale transformation carried out by using Fe₃O₄@SiO₂@SePh@Ru(OH) _x NPs as a catalyst gives ～86% yield.

Full text of DOI:10.1039/c4dt01189a

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Magnetite nanoparticles coated with ruthenium
via SePh layer as a magnetically retrievable catalyst
for the selective synthesis of primary amides in an
aqueous medium†
Cite this: Dalton Trans., 2014, 43,
12365
a
a
a
a
Hemant Joshi, Kamal Nayan Sharma, Alpesh K. Sharma, Om Prakash,
b
a
Arvind Kumar and Ajai Kumar Singh*
The nanostructured magnetic oxide Fe
nyl chloride under a N atmosphere and RuCl
Fe @SiO @SePh@Ru(OH) nanoparticles (NPs) for the first time. These magnetically retrievable NPs
3
O
4
has been coated with silica and then reacted with phenylsele-
2
3
·xH O successively in an aqueous medium to prepare
2
3
O
4
2
x
have been authenticated using TEM, SEM-EDX and powder-XRD and found to be an efficient catalyst for
one pot conversion (organic solvent not required) of aldehydes, nitriles and benzyl amine to primary
amides in water. For aldehydes and nitriles, the yields of primary amides are up to 93%. These NPs can be
recycled more than 7 times for the conversion of benzonitrile to the corresponding amide. Gram-scale
Received 23rd April 2014,
Accepted 28th May 2014
DOI: 10.1039/c4dt01189a
www.rsc.org/dalton
transformation carried out by using Fe
3
O
4
2 x
@SiO @SePh@Ru(OH) NPs as a catalyst gives ∼86% yield.
9
10
11
12
15
Pd NPs, supported silver NPs, Os–NHC complexes, gold,
Introduction
1
3
14
CeO2,
MnO ,
hydrotalcite-clay supported nickel NPs,
2
1
6
17
The amide functional group is important in organic molecules alumina, potassium fluoride doped Al
of biological interest, synthetic organic chemistry and pharma- manganese oxides, and ruthenium hydroxide coated on
ceuticals. For amide preparation, carboxylic acids or their alumina and ferrites. The catalytic conversion of aldehydes
derivatives (halides, anhydrides or esters) can be reacted to amides is another protocol in which Cu(II), indium, zinc,
2
O
3
,
silica-supported
1
8
1
19
2
0
21
1
,2
22
23
directly with amines. However, the direct methods use toxic scandium(III) triflate and supported Rh NPs have been
and corrosive materials which are sometimes expensive. Also, reported as efficient catalysts. For these two protocols there are
the by products are sometimes toxic. The reactions are often several disadvantages such as: the difficulty in separating
highly exothermic (difficult to control), complex, time consum- many of these catalysts from the products (resulting in loss of
ing and intolerant to sensitive functional groups. Therefore yield), low TON values, poor recyclability of the catalysts, the
the synthesis of amides is a problematic, particularly in requirement of an inert atmosphere for handling air-sensitive
8
pharmaceutical industry and research in this area is widely metal catalysts and harsh conditions (such as long reaction
3
acknowledged to be a priority. Metal-catalyzed transform- times e.g. 20–48 h, and reaction temperatures in the order of
ations have emerged in recent years as promising alternative 140 °C). Some functional groups do not withstand such harsh
routes for amide synthesis and many innovative protocols have conditions and the selectivity of the desired product decreases.
4
been developed and covered in a couple of reviews. They are The separation issues may be resolved and recyclability
generally based on substrates other than carboxylic acids and improved with the use of nanoparticles (NPs) with para/ferro-
5
6,7
their derivatives. The catalytic hydration of nitriles is one magetic properties, as they can be separated from the reaction
such promising protocol. The catalysts found to be efficient medium using an external magnet. Fe O magnetic NPs have
3
4
8
were palladium(II) containing γ-Keggin silicodecatungstate,
already emerged as robust, high surface area heterogeneous
2
4,25
catalyst supports.
The Fe O nanoparticles which are
3 4
coated with a thin layer of silica have further advantages such
2
6
a
as their stability and invariant catalytic activity. However,
they are rarely used in amide synthesis.
Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016,
1
9,25d
India. E-mail: aksingh@chemistry.iitd.ac.in, ajai57@hotmail.com;
Furthermore, to
the best our knowledge, the use of a Se layer in designing such
systems has not been reported before in the literature. There-
Fax: +91-01-26581102; Tel: +91-011-26591379
b
Analytical Sciences Division, Indian Institute of Petroleum, Dehradun 248005, India
†
Electronic supplementary information (ESI) available: NMR spectra, size distri-
fore it was thought worthwhile to layer Fe O NPs with Se and
bution graphs of the NPs, TEM–EDX spectra, and PXRD patterns. See DOI:
3 4
10.1039/c4dt01189a
Ru (which has been found to be an efficient catalytic centre in
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 12365–12372 | 12365

View Article Online
Paper
Dalton Transactions
amide synthesis). The utility and importance of such a cata- for 2 h. The color of the solution turned brown. The reaction
lytic system is evident from considerable current interest in mixture was cooled to room temperature and FeSO ·7H O
4
2
2
7
metal chalcogenide nanocrystals and their applications in (2.8 g) was added. It was followed by 0.1 M NaOH until a pH of
catalysis. For example Pd17Se15 NPs grafted on graphene oxide 10 was achieved. The resulting mixture was treated with ultra-
have been reported as an efficient catalyst for O-arylation reac- sound in a sealed flask at 40 °C for 30 min. After ageing for
2
7a
tions , along with PdP
2
NPs grafted on graphene oxide for 5 h, a black powder of Fe
Suzuki–Miyaura coupling. Thus a novel catalytic system (2 × 50 mL) and dried in vacuo.
Fe O @SiO @SePh@Ru(OH) ) has been designed by grafting
3
O
4
was obtained, washed with water
2
8
3
1
(
Synthesis of Fe O @SiO NPs. The mixture containing 1 g
3 4 2
3
4
2
x
x 3 4 3 4
Ru(OH) on selenated silica coated on Fe O and its catalytic of Fe O , 20 mL of water, 80 mL of ethanol, 3 mL of ammonia
application in the preparation of primary amides from alde- and 3 mL of tetraethylorthosilicate (TEOS) was refluxed for
hydes, nitriles and benzylamine in an aqueous medium have 10 h. The black precipitate of Fe O @SiO was collected using
3
4
2
been explored. The strong coordination of Se with Ru makes an external magnet. It was washed with water until the filtrate
the catalyst stable, nearly free from leaching (after two uses), was neutral and separated magnetically. The separated solid
and reusable for a greater number of cycles than the earlier was washed successively with ethanol and diethyl ether, and
2
5d
reported catalysts. In the present paper we report the results dried in vacuo to obtain Fe
of these investigations. The amide synthesis is complete in 7 h Synthesis of Fe @SiO
at a moderate temperature. For gram-scale preparation the (1 g) were sonicated in 5 mL toluene and 2 mmol of
3
O
4
@SiO
@SePh NPs. Fe
2
NPs.
3
1
3
O
4
2
3 4 2
O @SiO NPs
yield is promising.
PhSeCl was added to it under a nitrogen atmosphere. Nitrogen
to remove any generated HCl) was passed through the
reaction mixture for 12 h. The resulting brown colored
Fe @SiO @SePh NPs were collected using an external
magnet. They were washed with toluene and dried in vacuo.
(
3
O
4
2
Experimental
Physical measurement
2
5d
Synthesis of Fe O @SiO @SePh@Ru(OH) NPs.
The
@SePh NPs (2 g) were dispersed in water.
O (1 mmol) dissolved in water (60 mL) was added and
3
4
2
x
1
13
1
H and C{ H} NMR spectra were recorded using a Bruker
Spectrospin DPX 300 NMR spectrometer at 300.13, and
5.47 MHz respectively. The chemical shifts are reported in
ppm relative to the internal standard (tetramethylsilane) for
Fe
RuCl
3
O
4
@SiO
·xH
2
3
2
7
the mixture was stirred for 20 min. Aqueous sodium hydroxide
1 M) was added dropwise to the mixture until its pH reached
13. The resulting slurry was stirred further for 36 h at room
(
∼
1
13
1
the H and C{ H} NMR spectra. All of the reactions were
carried out in glassware dried in an oven. Powder X-ray diffrac-
tion (PXRD) studies were carried out using a Bruker D8
Advance diffractometer using Ni-filtered CuKα radiation, a
scan speed of 1 s and a scan step of 0.05°. Transmission elec-
tron microscopy (TEM) studies were carried out using a JEOL
JEM 200CX TEM instrument operated at 200 kV. The speci-
mens for these studies were prepared by dispersing the pow-
dered sample in ethanol by ultrasonic treatment. A few drops
of the resulting homogenized slurry were put on a porous
carbon film supported on a copper grid and dried in air. The
elemental composition of the NPs was studied with a Carl
ZEISS EVO5O scanning electron microscope (SEM) and the
associated EDX system Model QuanTax 200, which is based on
the SDD technology and provides an energy resolution of
temperature. The product was separated magnetically, washed
several times with water and methanol successively and dried
in vacuo for 2 h. The weight percentage of Ru in the catalyst was
found to be 5.48% which was obtained using ICP-AES analysis.
Hydration of nitriles
Nitrile (1.0 mmol) and Fe O @SiO @SePh@Ru(OH) (80 mg)
3
4
2
x
were placed in an oven-dried flask with a magnetic stirrer.
Water (4 mL) was added to the reaction mixture. The reaction
mixture was heated using an oil bath (kept at 120 °C), under
aerobic conditions (under reflux), and stirred until the
maximum conversion of nitrile to amide occurred. After com-
pletion of the reaction, the catalyst was removed from the reac-
tion mixture using an external magnet. The clear solution was
cooled slowly. Most of the time, analytically pure crystals of
the corresponding amide were obtained, which were separated
by decantation. In the case of solid nitrile the resulting
mixture was extracted with ethyl acetate (2 × 50 mL). The
organic layer was washed with water (2 × 50 mL) and dried
1
27 eV under Mn-Kα radiation. The sample was mounted on a
circular metallic sample holder with a sticky carbon tape. An
estimation of ruthenium in the nanoparticles was carried out
using an ICP-AES instrument (DRE, PS-3000UV, Leeman Labs,
Inc. USA).
over anhydrous Na
with a rotary evaporator and the resulting residue (amide) was
2 4
SO . The solvent of the extract was removed
Chemicals and reagents
FeCl ·6H O, urea, FeSO ·7H O, tetraethylorthosilicate (TEOS), purified using flash column chromatography on silica gel
3
2
4
2
RuCl
3
·xH
2
O, phenylselenyl chloride, obtained from Sigma- using an ethyl acetate–hexane (5 : 95) mixture as the eluent.
Synthesis of amides from aldehydes. Aldehyde (1.0 mmol),
toluene, acetone, ethyl acetate and ethanol) were dried and NH OH·HCl (1.2 eq.) and Fe O @SiO @SePh@Ru(OH)
x
Aldrich (USA) were used as received. The AR grade solvents
(
distilled before use according to standard procedures.
Synthesis of the magnetic NPs of Fe
2
3
4
2
2
9
(80 mg) were placed in an oven-dried flask with a magnetic
stirrer and water (4 mL) was added to the mixture. The reaction
3
0
3
O
4
.
3 2
FeCl ·6H O
(5.4 g) and urea (3.6 g) were stirred in water (200 mL) at 90 °C mixture was heated using an oil bath (kept at ∼120 °C), under
12366 | Dalton Trans., 2014, 43, 12365–12372
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
aerobic conditions (under reflux), and stirred until the
maximum conversion of aldehyde to the corresponding amide
occurred. Using the work up procedure described for the con-
version of nitriles, the amide was obtained.
Synthesis of amides from amines. Amine (1.0 mmol),
3 4 2 x
Fe O @SiO @SePh@Ru(OH) (100 mg) and water (4 mL) were
placed in an oven-dried flask with a magnetic stirrer. The reac-
tion mixture was heated using an oil bath (temperature
∼120 °C), under aerobic conditions, and stirred until the
maximum conversion of the amine to the corresponding
amide occurred. After completion of the reaction, the work up
procedure given above in the conversion of nitriles was fol-
lowed to obtain the amide.
Recyclability
3 4 2 x
Scheme 1 Synthesis of Fe O @SiO @SePh@Ru(OH) NPs.
To check the recyclability of Fe O @SiO @SePh@Ru(OH)
x
3
4
2
NPs, the catalyst was separated with an external magnet, after
completion of the reaction with benzonitrile. It was washed
patterns (Fig. 1, see the ESI Fig. S5a–c†), obtained confirm
these NPs as Fe @SiO @SePh@Ru(OH) , with nearly spheri-
cal morphology (size ∼6–15 nm; size distribution graphs of
3
O
4
2
x
with H O and ethanol successively, dried in vacuo and reused
2
with a new sample of benzonitrile.
Fe O and Fe O @SiO @SePh@Ru(OH) NPs are shown in the
3
4
3
4
2
x
ESI Fig. S1 and S2†). The nanoparticles have OH groups on the
surface and this has probably affected the quality of the TEM
images to some extent but they are as good as those reported
Hot filtration experiment
In an oven dried flask water (4 mL), Fe O @SiO @SePh@Ru-
3
4
2
x
(OH) NPs (80 mg) and benzonitrile (0.103 g, 1 mmol) were
2
5d
in an earlier work on a similar system.
refluxed, heated with an oil bath maintained at 120 °C, and
stirred. The reaction was stopped after 1.5 h and the catalyst
was separated using an external magnet. The reaction mixture
turned clear and was divided in two equal parts. One half of
the reaction mixture was transferred into another reaction
flask. In the remaining half the previously isolated NPs were
reintroduced as a catalyst. Thereafter, the reactions in both
vessels were allowed to proceed for another 5 h and conver-
Powder XRD of Fe O @SiO @SePh@Ru(OH) catalyst
3
4
2
x
The phase and purity of the different materials from Fe
3 4
O to
Fe O @SiO @SePh@Ru(OH) synthesized stepwise have been
3
4
2
x
studied using powder XRD. The patterns are shown in Fig. 1
and in the ESI Fig. S5.† The PXRD pattern of Fe exhibits
3 4
O
diffraction lines (hkl) at 220, 311, 400, 333 and 440. These
diffraction peaks in the pattern can be well indexed to the
1
sions were estimated with H NMR spectroscopy.
3 4
cubic phase of Fe O , as they are in good agreement with the
literature data (JCPDS 82-1533) (Fig. S5a in the ESI†). The
Results and discussion
silica coated nanoparticles (Fe O @SiO ) give a broader PXRD
3
4
2
pattern due to their non-crystalline nature, at 2θ = 20–29°
JCPDS 83-2470). It has peaks (hkl) at 220, 311, 400, 333, and
40, which correspond to the Fe core (Fig. S5b in the ESI†).
On immobilization of selenium onto Fe @SiO the
additional peaks due to Se (SePh) appear in PXRD pattern of
To design Fe O @SiO @SePh@Ru(OH) NPs, Fe O (size:
3
4
2
x
3 4
(
3
0
∼6–15 nm) prepared using a recently reported protocol was
4
3 4
O
coated with silica, and treated with phenylselenyl chloride
3
O
4
2
,
under a N2 atmosphere and RuCl ·xH O successively in an
3
2
aqueous medium (Scheme 1). Magnetic Fe
SePh@Ru(OH) NPs were separated using an external magnet,
washed with water, followed by Et O and dried in vacuo at
3 4 2
O @SiO @-
x
2
6
3 4 2 x
0 °C for 2 h. Neither Fe O @SiO @SePh@Ru(OH) nor its
precursor was found to be soluble in water or the organic
solvent. However, the OH groups are present on the surface
through which these NPs show excellent catalytic activity (see
the mechanism in Fig. 3). The weight percentage of Ru in
Fe O @SiO @SePh@Ru(OH) NPs was found to be 5.48%,
3
4
2
x
obtained using inductively coupled plasma-atomic emission
spectroscopic (ICP-AES) analysis, and the weight percentage of
Se in Fe O @SiO @SePh@Ru(OH) NPs was found to be
3
4
2
x
2
.55%, obtained using quantitative energy dispersive X-ray
spectroscopy. The TEM images (Fig. 2), SEM-EDX spectra (see
the ESI Fig. S3 and S4†) and powder X-ray diffraction (PXRD) Fig. 1 PXRD pattern of Fe O @SiO @SePh@Ru(OH) NPs.
3 4 2 x
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 12365–12372 | 12367

View Article Online
Paper
Dalton Transactions
3 4 2
Fe O @SiO @SePh (Fig. S5c in the ESI†), with peaks of
Fe O @SiO . The selenium peaks are narrow as SePh is in a
3
4
2
grafted form and is not nano-structured. Such an observation
3
1
is reported in case of phosphorus. Most of these peaks e.g. at
θ = 22, 32 and 42 (ESI Fig. S5c†) are consistent with earlier
reports on powdered/polycrystalline selenium. On layering
with Ru the dispersity of Se increases as it becomes part of the
metal’s coordination sphere. Thus peaks corresponding to Se
2
Scheme 2 Nano-Fe
3
O
4
@SiO
2
@SePh@Ru(OH)
x
catalyzed hydration.
3
2
Table 1 Optimization of the reaction conditions
have not been detected in the PXRD pattern of Fe
3 4 2
O @SiO @-
d
c
SePh@Ru(OH) (Fig. 1). Ruthenium is present as a complex
x
Time
(h)
Temp.
(°C)
Yield
(%)
Entry
Catalyst
entity (coordinated with SePh and OH). There is a strong
binding of Ru with selenium donor sites. These features prob-
1
2
3
Fe
Fe3O4@SiO
Fe @SiO
O
3 4
24
24
24
7
7
7
7
7
7
120
120
120
120
120
120
120
120
120
0
0
0
31
27
36
81
0
ably result in the high dispersity of Ru also on Fe
SePh. Therefore no Ru peaks were observed.
3
O
4
@SiO
No peaks
corresponding to any impurities were detected, indicating
good purity of Fe @SiO @SePh@Ru(OH) NPs.
2
@-
2
2
5d
3
O
RuCl
RuCl
4
2
@SePh
a
4
3
·xH
·xH
2
O
2
a
5
3
O + (PhSe)
2
(1 : 1)
O
4
2
x
6
7
8
Fe
Fe
Fe
Fe
3 4
O
3 4
O
3 4
O
3 4
O
@Ru(OH)
x
3
@SiO
@SiO
@SiO
2
2
2
@Ru(OH)
@SePh@Ru(OH)
@SePh@Ru(OH)
x
b
x
TEM and SEM-EDX of Fe
3 4 2 x
O @SiO @SePh@Ru(OH)
9
x
92
Transmission electron microscopy (TEM) images of Fe O @-
SiO @SePh@Ru(OH) NPs are shown in Fig. 2. The sizes of
2 x
these NPs are approximately ∼6–15 nm (Fig. S2 in the ESI†). is >99%. Oil bath temperature.
The SEM-EDX spectrum (Fig. S4 in the ESI†) supports the pres-
3
4
Reaction condition: catalyst (80 mg), substrate (1.0 mmol), H
2
O
a
b
c
(
4 mL). 5 mol% Ru. In dichloromethane. Selectivity of the reaction
d
ence of iron, oxygen, silicon, selenium, carbon and ruthenium
in Fe O @SiO @SePh@Ru(OH) NPs. Similarly the SEM-EDX
3
4
2
x
and benzylamine in water, under aerobic reaction conditions.
The experiments were performed to optimize the reaction con-
ditions for the hydration of benzonitrile as a substrate (Scheme 2),
in aqueous medium (see Table 1). The reactions were also con-
spectrum of Fe O @SiO @SePh given in the ESI (Fig. S3†) also
3
4
2
supports the presence of iron, oxygen, silicon, selenium, and
carbon in Fe O @SiO @SePh NPs. This indicates that the loss
3
4
2
of Se is insignificant during Ru layering.
ducted using nano-sized Fe
SiO @SePh. The hydration reaction with them did not proceed
at 120 °C even after 24 h (Table 1, entries 1–3). The reaction
using RuCl ·xH O as the catalyst was carried out at 120 °C and
3 4 3 4 2 3 4
O , Fe O @SiO and Fe O @-
Catalytic applications
2
The magnetic Fe
3 4 2 x
O @SiO @SePh@Ru(OH) NPs were explored
3
2
for the catalytic synthesis of amides from aldehydes, nitriles,
only gave a yield of ∼31% (Table 1, entry 4). The hydration
reaction in the presence of RuCl ·xH O and diphenyl disele-
3
2
nide (1 : 1 molar ratio) at 120 °C resulted in ∼27% yield of
amide (Table 1, entry 5). Most probably the insolubility of
diphenyl diselenide in water may be one of the reasons attribu-
ted to the poor yield of amide. On carrying out the reaction in
dichloromethane no conversion to amide was observed even
after 7 h (Table 1, entry 8). The hydration reaction using
Fe O @SiO @SePh@Ru(OH) NPs as the catalyst at a tempera-
3 4 2 x
ture of ∼80 °C for 7 h converted only ∼57% of the nitriles to
amides, while the reaction in the presence of these NPs at
1
20 °C for 3 h converted ∼62% of the nitriles to amides. The
continuation of the reaction further for 7 h at 120 °C led to a
2% conversion of benzonitrile to the corresponding amide
Table 1, entry 9). In Fe @SiO @SePh@Ru(OH) NPs
9
(
3
O
4
2
x
hydroxyl groups are present on the surface which contribute to
their excellent catalytic activity as demonstrated in the mecha-
nism shown in Fig. 3. The temperatures mentioned above are
of the oil bath. The effect of the magnetic bar on catalytic reac-
tion was found to be insignificant as a reaction of benzonitrile
with water under optimum conditions carried out with a
mechanical stirrer gave 90% conversion. It implies that with
high speed stirring the magnetite NPs are suspended in solu-
tion and the catalytic process occurs as expected (Scheme 2).
Fig. 2 TEM images (a) Fe
3
O
4
, (b) Fe
3 4 2 3 4 2
O @SiO , (c) Fe O @SiO @SePh,
(
d) Fe @SiO @SePh@Ru(OH)
3
O
4
2
x
NPs.
12368 | Dalton Trans., 2014, 43, 12365–12372
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
a
Table 2 One pot synthesis of amides from aldehydes
Entry
1
Substrate
Product
Yield%
88 (>99)
2
3
91 (>99)
90 (>99)
Fig. 3 The proposed mechanism for amide synthesis catalyzed with
Fe O @SiO @SePh@Ru(OH) NPs.
3 4 2 x
4
5
82 (>99)
91 (>99)
Using the optimized conditions, the scope of using
Fe O @SiO @SePh@Ru(OH) NPs as a catalyst was explored
3
4
2
x
for the one pot synthesis of primary amides from a variety of
aldehydes (Table 2) and nitriles (Table 3). The catalyst dis-
played high efficiency for the conversion of activated, unacti-
vated, and heterocyclic aldehydes in pure water. The
conversion rates were not greatly influenced by the substituent
on the aromatic ring of benzaldehyde. Interestingly, the reac-
tions of the ortho and meta-derivatives (Table 2, entries 4 and 8)
proceeded with similar rates, without a significant difference
in yields. Heterocyclic aldehydes (Table 2, entries 9 and 10),
which are extensively used as building-blocks in drug discov-
ery, undergo the hydration reaction with high yields, proving
the suitability of this protocol for the assembly of bio-mole-
cules. The one pot transformation of ferrocenecarboxaldehyde
into ferrocenecarboxamide (Table 2, entry 11) occurred with a
good yield (88%). The method commonly used for the prepa-
ration of ferrocenecarboxamide has a sequence of two-steps.
First ferrocenecarboxylic acid is reacted with thionyl chloride
6
92 (>99)
7
8
86 (>99)
85 (>99)
9
87 (>99)
86 (>99)
10
11
88 (>99)
(
odour unpleasant) and then treated with aqueous
3
3
ammonia. Thus the present protocol has advantages over
this method. There is only one step, a cheap starting material
is used, the reaction proceeds in water which is better for the
environment, and purification of the product is simple.
a
Reaction conditions: catalyst (80 mg), substrate (1.0 mmol),
OH·HCl (1.2 eq.), time (7 h), H O (4 mL), and temp. (120 °C). The
NH
2
2
selectivity of the reaction is given in the parentheses.
3 4 2 x
The efficiency of the Fe O @SiO @SePh@Ru(OH) NP cata-
lyst (Table 3) for the hydration of activated, unactivated,
heterocyclic and aliphatic nitriles in an aqueous medium is
also good. The rate of reaction does not alter much with the
substituents on the aromatic ring of benzonitrile as the conver-
The lifetime and level of reusability are important factors in
sion rates for the ortho and meta-derivatives (Table 3, entries 4 the practical applications of a heterogeneous catalyst. In this
and 8) are almost similar. On a gram-scale, the catalytic con- study, such properties of Fe O @SiO @SePh@Ru(OH) NPs
3
4
2
x
version of benzonitrile (1 g) to the corresponding amide was were tested for the hydration of benzonitrile. After completion
carried out (Scheme 3). The transformation proceeded effici- of the first reaction to afford the corresponding benzamide,
ently to give 1.04 g of benzamide (86% yield). There is only a the catalyst was recovered magnetically, washed with a metha-
small decrease in the percentage yield with respect to small- nol–ethanol mixture and dried at 50 °C. It was used again for
scale conversion.
further conversion of benzonitrile to the corresponding amide
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 12365–12372 | 12369

View Article Online
Paper
Dalton Transactions
a
a
Table 3 Hydration of nitriles
Table 4 Recycling experiments
Run
1
2
3
4
5
6
7
Yield%
92
92
92
91
91
90
90
a
Reaction conditions: catalyst (100 mg), substrate (1.0 mmol), time
O (4 mL), and temp. (120 °C). The selectivity of the reaction is
(
7 h), H
99%.
2
>
Entry
1
Substrate
Product
Yield%
92 (>99)
2
3
93 (>99)
91 (>99)
Scheme 4 Catalytic transformation of benzyl/2-thiophene amines.
under optimum conditions. There was no change in the
efficiency as shown by the percentage yield values (Table 4).
The catalyst can be reused more than 7 times with a very
minor change in efficiency (Table 4). The scope of using
Fe O @SiO @SePh@Ru(OH) NPs as a catalyst, was examined
4
5
6
84 (>99)
3
4
2
x
93 (>99) for the oxidation of amines to amides (Scheme 4). The reaction
was carried out using 1 mmol of benzylamine and 100 mg of
catalyst at 120 °C under ambient conditions for 7 h and for-
mation of the corresponding amide (I), by-product benzylidene-
90 (>99)
benzylamine (II) and benzaldehyde (III) were observed, with
poor conversion values. When the reaction time was increased
up to 15 h, (I) was obtained with 63% conversion.
7
8
87 (>99)
3 4 2 x
The magnetic nature of the Fe O @SiO @SePh@Ru(OH)
NPs means that they are able to be fully recovered with an
external magnet, without a significant change in efficiency.
After the separation of the catalyst, the clear liquid was cooled
slowly and in most of the cases analytically pure amide crystals
appeared, which could be separated by simple decantation.
Thus, the whole process was carried out in an aqueous
medium and no organic solvent used. The heterogeneity of the
86 (>99)
9
89 (>99)
87 (>99)
3 4 2 x
catalyst Fe O @SiO @SePh@Ru(OH) NPs for the hydration of
benzonitrile was examined using a hot filtration test. The reac-
tion was stopped at 37% conversion and after 1 min the reac-
tion mixture separated into a clear solution and a solid
1
0
(
catalyst) deposited on the magnetic bar. Half of the hot solu-
1
1
81 (>99)
tion was transferred into another reaction flask. The reaction
in the two portions continued at 120 °C for a further 5 h. The
conversion in the portion containing the magnetic catalyst pro-
gressed to 87%, while in the catalyst-free portion it reached
a
Reaction conditions: catalyst (80 mg), substrate (1.0 mmol), time
O (4 mL), and temp. (120 °C). The selectivity of the reaction is
(
7 h), H
2
4
2% from 37%, probably due to Ru leaching from the NPs.
given in the parentheses.
Thus the catalysis may be considered as largely heterogeneous.
Metal leaching was studied using ICP-AES analysis of the cata-
lyst before and after the two reaction cycles. The Ru in the cata-
lyst was found to be 5.48% before the reaction and 5.37% after
two cycles of the reaction. Thereafter no change in Ru content
of the catalyst was observed even after the seventh catalytic
cycle. These observations imply negligible Ru leaching after
two cycles of catalysis. This may be due to the strong binding
3
4
Scheme 3 Gram-scale transformation.
of Ru with Se. The outer rim of Ru on the surface of the NPs
12370 | Dalton Trans., 2014, 43, 12365–12372
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
is easily accessible for catalysis. It is desirable in a metal pro-
moted reaction for there to be no remnant of the metal in the
end product, which happens in the present case after the
Notes and references
1 See: (a) The Chemistry of Amides, ed. J. Zabicky, Wiley-Inter-
science, New York, 1970; (b) The Amide Linkage: Structural
Significance in Chemistry, Biochemistry and Materials Science,
ed. A. Greenberg, C. M. Breneman and J. F. Liebman, John
Wiley & Sons, New York, 2000; (c) Polyesters and Polyamides,
ed. B. L. Deopura, R. Alagirusami, M. Joshi and B. Gupta,
CRC Press, Boca Raton, 2008.
2 (a) J. S. Carey, D. Laffan, C. Thomson and M. T. Williams, Org.
Biomol. Chem., 2006, 4, 2337; (b) R. W. Dugger, J. A. Ragan and
D. H. B. Ripin, Org. Process Res. Dev., 2005, 9, 253.
3 D. J. C. Constable, P. J. Dunn, J. D. Hayler, G. R. Humphrey,
J. L. Leazer Jr., R. J. Linderman, K. Lorenz, J. Manley,
B. A. Pearlman, A. Wells, A. Zaks and T. Y. Zhang, Green
Chem., 2007, 9, 411.
4 (a) C. L. Allen and J. M. J. Williams, Chem. Soc. Rev., 2011,
40, 3405; (b) V. R. Pattabiraman and J. W. Bode, Nature,
2011, 480, 471.
5 K. Thalluri, K. C. Nadimpally, A. Paul and B. Mandal, RSC
Adv., 2012, 2, 6838.
6 (a) J. H. Kim, J. Britten and J. Chin, J. Am. Chem. Soc., 1993,
115, 3618; (b) R. Breslow, R. Fairweather and J. Keana,
J. Am. Chem. Soc., 1967, 89, 2135.
7 (a) A. Goto, K. Endo and S. Saito, Angew. Chem., Int. Ed.,
2008, 120, 3663; (b) V. Y. Kukushkin and A. J. L. Pombeiro,
Chem. Rev., 2002, 102, 1771.
second cycle. Thus Fe
suitable for pharmaceutical preparations also after two uses.
The leached Ru (also from RuCl ·xH O) appears to have
3 4 2 x
O @SiO @SePh@Ru(OH) NPs may be
3
2
poor catalytic activity in comparison to the one anchored on
magnetite NPs. Thus strong binding of Ru via Se (strong sigma
donor) results in a significant improvement in the catalytic
activity. Due to this reason, the catalytic performance (under
identical conditions) of Fe O @SiO @SePh@Ru(OH) (Table 1
3
4
2
x
entry 9) is better than that of the closely related NPs
of Fe @SiO @Ru(OH) (Table 1 entry 7). In a procedure
reported previously for a similar amide synthesis with
Fe @SiO @Ru(OH) NPs, there is a microwave effect. Thus
3
O
4
2
2
x
5d
3
O
4
2
x
their results are not directly comparable with ours. Further-
more, their recyclability is only 3 times. However, our catalyst
has a very promising efficiency without a microwave effect.
The possible mechanism for amide synthesis catalyzed with
Fe O @SiO @SePh@Ru(OH) NPs is shown in Fig. 3. This
3
4
2
x
catalytic amide synthesis probably occurs in four steps. The
first step is based on an aldoxime. In the second step a nitrile
is formed and coordinated to Ru. The intramolecular nucleo-
philic attack of the hydroxide species on the nitrile carbon
atom takes place to afford the ruthenium iminolate species in
the third step. The transformation into the original ruthenium
hydroxide species with the formation of the amide product
takes place in the last step.
8 T. Hirano, K. Uehara, K. Kamata and N. Mizuno, J. Am.
Chem. Soc., 2012, 134, 6425.
9
K. Shimizu, T. Kubo, A. Satsuma, T. Kamachi and
K. Yoshizawa, ACS Catal., 2012, 2, 2467.
Conclusions
1
0 (a) A. Y. Kim, H. S. Bae, S. Park, S. Park and K. H. Park,
Catal. Lett., 2011, 141, 685; (b) T. Mitsudome, Y. Mikami,
H. Mori, S. Arita, T. Mizugaki, K. Jitsukawa and K. Kaneda,
Chem. Commun., 2009, 3258.
3 4 2 x
Fe O @SiO @SePh@Ru(OH) NPs, which have been designed
for the first time, were used as a catalyst in the preparation of
primary amides from aldehydes (including ferrocenecarbox-
aldehyde), nitriles, and benzylamine in an aqueous medium 11 M. L. Buil, V. Cadierno, M. A. Esteruelas, J. Gimeno,
with high yield and selectivity. The catalyst is magnetically
separable which makes the work up of the reaction very easy.
J. Herrero, S. Izquierdo and E. Oñate, Organometallics,
2012, 31, 6861.
The catalyst is reusable for more than 7 reaction cycles for the 12 (a) R. S. Ramon, N. Marion and S. P. Nolan, Chem. – Eur. J.,
conversion of benzonitrile to the corresponding amide. It is
also efficient for gram-scale preparation of amides from benzo-
nitrile. There is virtually no leaching of Ru after the second
2009, 15, 8695; (b) R. S. Ramon, S. Gaillard, A. Poater,
L. Cavallo, A. M. Z. Slawin and S. P. Nolan, Chem. – Eur. J.,
2011, 17, 1238.
cycle which was confirmed by using ICP-AES analysis and car- 13 M. Tamura, H. Wakasugi, K. Shimizu and A. Satsuma,
rying out a hot filtration test.
Chem. – Eur. J., 2011, 17, 11428.
14 C. Battilocchio, J. M. Hawkins and S. V. Ley, Org. Lett.,
2
014, 16, 1060.
5 T. Subramanian and K. Pitchumani, Catal. Commun., 2012,
9, 109.
1
Acknowledgements
2
The authors thank the Council of Scientific and Industrial 16 C. P. Wilgus, S. Downing, E. Molitor, S. Bains, R. M. Pagni
Research (CSIR), New Delhi, India for the project no. 01(2421) and G. W. Kabalka, Tetrahedron Lett., 1995, 36, 3469.
0/EMR-II and the JRF/SRF to KNS and AS. The Department of 17 C. G. Rao, Synth. Commun., 1982, 12, 177.
Science and Technology (India) is acknowledged for the 18 K. T. Li, M. H. Shih, H. W. Huang and C. J. Hu, Synthesis,
research project (SR/S1/IC-40/2010), and the financial support 1988, 715.
for the use of the HR-TEM (NSIT) facility at IIT Delhi. HJ, OP 19 (a) K. Yamaguchi, M. Matsushita and N. Mizuno, Angew.
1
and AK thank the University Grants Commission (India) for
the JRF/SRF.
Chem., Int. Ed., 2004, 116, 1602; (b) M. Kotani, T. Koike,
K. Yamaguchi and N. Mizuno, Green Chem., 2006, 8, 735.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 12365–12372 | 12371

View Article Online
Paper
Dalton Transactions
2
0 (a) A. M. Asencio, M. Yus and D. J. Ramon, Tetrahedron, 27 (a) H. Joshi, K. N. Sharma, A. K. Sharma, O. Prakash and
2
012, 68, 3948; (b) N. C. Ganguly, S. Roy and P. Mondal,
A. K. Singh, Chem. Commun., 2013, 49, 7483;
(b) K. N. Sharma, H. Joshi, V. V. Singh, P. Singh and
A. K. Singh, Dalton Trans., 2013, 42, 3908; (c) K. N. Sharma,
H. Joshi, A. K. Sharma, O. Prakash and A. K. Singh, Organo-
metallics, 2013, 32, 2443.
Tetrahedron Lett., 2012, 53, 1413.
1 C. L. Allen, C. Burel and J. M. J. Williams, Tetrahedron Lett.,
2
2
2
2
2
010, 51, 2724.
2 B. K. Allam and K. N. Singh, Tetrahedron Lett., 2011, 52,
851.
5
28 H. Joshi, K. N. Sharma, A. K. Sharma and A. K. Singh,
Nanoscale, 2014, 6, 4588.
29 B. S. Furniss, A. J. Hannaford, P. W. G. Smith and
A. R. Tatchell, Vogel’s Textbook of Practical Organic Chem-
istry, ELBS, Longman Group U K Ltd., 5th edn, 1989.
3 H. Fujiwara, Y. Ogasawara, K. Yamaguchi and N. Mizuno,
Angew. Chem., Int. Ed., 2007, 46, 5202.
4 (a) A. Hu, G. T. Yee and W. Lin, J. Am. Chem. Soc.,
2
005, 127, 12486; (b) N. T. S. Phan, C. S. Gill,
J. V. Nguyen, Z. J. Zhang and C. W. Jones, Angew. 30 M. B. Gawande, A. Velhinho, I. D. Nogueira,
Chem., Int. Ed., 2006, 118, 2267; (c) R. Abu-Reziq,
H. Alper, D. Wang and M. L. Post, J. Am. Chem. Soc.,
C. A. A. Ghumman, O. M. N. D. Teodoro and P. S. Branco,
RSC Adv., 2012, 2, 6144.
2
006, 128, 5279; (d) C. O. Dalaigh, S. A. Corr, 31 M. A. Zolfigol, V. Khakyzadeh, A. R. Moosavi-Zare,
Y. Gunko and S. J. Connon, Angew. Chem., Int. Ed.,
A. Rostami, A. Zare, N. Iranpoor, M. H. Beyzavi and
R. Luque, Green Chem., 2013, 15, 2132.
2
007, 119, 4407; (e) A. H. Latham and M. E. Williams,
Acc. Chem. Res., 2008, 41, 411.
5 (a) V. Polshettiwar, M. N. Nadagouda and R. S. Varma,
Chem. Commun., 2008, 6318; (b) V. Polshettiwar,
32 (a) J. Lu, Y. Xie, F. Xu and L. Zhu, J. Mater. Chem., 2002, 12,
2755; (b) C. Dwivedi, C. P. Shah, K. Singh, M. Kumar and
P. N. Bajaj, J. Nanotechnol., 2011, 651971.
2
2
B. Baruwati and R. S. Varma, Chem. Commun., 2009, 1837; 33 (a) L. H. Ali, A. Cox and T. J. Kemp, J. Chem. Soc., Dalton
(
4
c) R. B. N. Baig and R. S. Varma, Chem. Commun., 2012,
8, 2582; (d) R. B. N. Baig and R. S. Varma, Chem.
Trans., 1973, 1468; (b) R. Zhang, Z. Wang, Y. Wu, H. Fu and
J. Yao, Org. Lett., 2008, 10, 3065.
Commun., 2012, 48, 6220.
34 (a) O. Prakash, K. N. Sharma, H. Joshi, P. L. Gupta and
A. K. Singh, Dalton Trans., 2013, 42, 8736; (b) F. Saleem,
G. K. Rao, A. Kumar, G. Mukherjee and A. K. Singh,
Organometallics, 2013, 32, 3595.
6 (a) Y. Deng, D. Qi, C. Deng, X. Zhang and D. Zhao, J. Am.
Chem. Soc., 2008, 130, 28; (b) A. Schatz, M. Hager and
O. Reiser, Adv. Funct. Mater., 2009, 19, 2109.
12372 | Dalton Trans., 2014, 43, 12365–12372
This journal is © The Royal Society of Chemistry 2014