Synthesis of Iron Oxide Palladium Nanoparticles and Their Catalytic Applications for Direct Coupling of Acyl Chlorides with Alkynes

Article abstract of DOI:10.1002/cplu.201600321

A new, magnetic, silica-based, palladium nanocatalyst has been synthesized and employed for the first time in the direct coupling of acyl chlorides with terminal alkynes to prepare a variety of ynones. The synthesized nanocomposite is an excellent heterog

Full text of DOI:10.1002/cplu.201600321

Accepted Article
Title: Synthesis of Iron-oxide Palladium Nanoparticles and its catalytic applications
for direct coupling of acyl chlorides with alkynes
Authors: Rakesh K. Sharma K Sharma; Manavi Yadav; Rashmi Gaur; Radhika
Gupta; Alok Adholeya; Manoj Bhanudas Gawande
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Synthesis of Iron-oxide Palladium Nanoparticles and its catalytic
applications for direct coupling of acyl chlorides with alkynes
Rakesh K. Sharma,*[a] Manavi Yadav, [a] Rashmi Gaur, [a] Radhika Gupta, [a] Alok Adholeya [b] and Manoj
B. Gawande *[c]
Abstract: A new magnetic-silica based palladium nanocatalyst has
been synthesized and employed for the first time in the direct
coupling of acyl chlorides with terminal alkynes to prepare a variety
of ynones. The synthesized nanocomposite was found to be an
excellent heterogeneous catalyst for copper-free, phosphine-free, C-
C bond formation through Sonogashira reaction under aerobic
conditions at room temperature without the use of any additives and
inert conditions. The synthesized catalyst has been comprehensively
characterized by various techniques such as XRD, SEM, TEM, EDS,
XPS, ICP, FT-IR, VSM, AAS, etc. This nanocatalyst can be
magnetically recovered and reused up to multiple runs without any
noticeable loss in its catalytic activity.
and quinolines. [12]
Due to the widespread utility of ynones, considerable efforts
have been devoted towards developing protocols for their
synthesis using a plethora of transition metal derived catalysts.
Among all, the coupling reaction of acyl chlorides and terminal
alkynes catalyzed by palladium has received much attention of
late due to the versatile nature of this protocol, increased
functional group tolerance with improved yields and procedural
simplicity.[13] However, these methods require harsh conditions
such as high temperature, use of Grignard reagents, toxic
phosphine ligands, unwanted side reactions, reduced yields,
prolong reaction time, use of surfactants and toxic carbon
dioxide.[14]
In addition, the combination of Cu(I) with
triethylamine has been widely employed.[15] However, use of
Cu(I) catalyzed protocol involves high catalytic loading and
unwanted byproducts due to homocoupling of in-situ generated
Cu(I) acetylides. Besides suffering from various drawbacks,
most of the existing methodologies utilize homogeneous catalyst,
in spite of the fact that they are expensive, could not be
recovered and bring about unnecessary waste and hazard to the
environment.[16]
Taking these constraints into account, there is an urgent need
for the design and development of efficient heterogeneous
catalytic system with facile recovery from reaction media.
Heterogeneous catalysts not only provide easy separation but
also improve the catalytic activity and durability during the
catalytic cycles by immobilizing active metal species on solid
supports. Additionally, the choice of solid support plays an
imperative role in catalytic activity as it is responsible in holding
the active catalyst on its surface by strong co-ordination during
catalysis.[17] Recent examples of such heterogeneous catalysts
include ZnBr2@SiO2, Pd(II)-schiff base complex@MWCNTs,
and polystyrene supported Pd(0) complex for the acylation of
terminal alkynes with acyl chloride.[18] But these catalysts suffer
from cumbersome filtration techniques and have little
recyclability. From the sustainable perspective, high catalytic
activity, easy separation and high recyclability are desirable
Introduction
In current scenario, the society’s driving force is to search for
alternative methodologies for the formation of new bonds such
as C-C, C-O, C-N, C-S, for the synthesis of a vast array of
chemical compounds. Amongst all, the efficient and economical
formation of carbon-carbon (C-C) bond has been the most
promising reaction for the preparation of carbon scaffolds of high
importance from the organic synthetic viewpoint.[1]
In recent years, α, β-acetylenic carbonyl derivatives, best known
as ynones, have established considerable synthetic interest due
to their extensive utilization as key intermediates for the
synthesis of natural products, pharmaceuticals and as
precursors for functional materials with interesting properties.[2]
Due to their bifunctional electrophilicity and the tendency to
undergo sequential nucleophilic additions and cyclizations, they
have found broad application as three-carbon building blocks.
They have also been extensively utilized for the synthesis of
biologically active heterocyclic compounds including furans,[3]
furanones,[4]
isoxazoles,[5]
indolizidinones,[6]
pyrazoles,[7]
pyrroles,[8] pyrimidines,[9] pyridinones,[10] pyridopyrimidines,
[11]
attributes of
a solid-supported metal nanocatalyst. Among
[a]
Rakesh K. Sharma,* Manavi Yadav, Rashmi Gaur, Radhika Gupta
Department of Chemistry
University of Delhi
105, Block-B, First floor, GCNC, University of Delhi, Delhi-110007
E-mail: rksharmagreenchem@hotmail.com
Alok Adholeya
Biotechnology and Management of Bioresources Division
The Energy and Resources Institute
Darbari Seth Block, IHC Complex, Lodhi Road, New delhi-110003
Manoj B. Gawande*
Regional Centre of Advanced Technologies and materials,
Department of Physical Chemistry, Faculty of Science,
Palacký University, echtite 27, 783 71, Olomouc, Czech
Republic
various solid support materials, silica-coated magnetic
nanostructures are well-recognized as they offer practical
benefits over bulk supports, such as high surface area, high
complex loading, excellent stability, ease of work-up, handling
and separation of products, non-toxic characteristics, effortless
recovery and amenability for continuous processing.[19] Besides
this, the dense coating of silica not only prevents leaching of iron
from the core during the catalytic activity but also assists in
anchoring of other substrates. It also imparts excellent
properties to magnetic nanoparticles, thereby making it inert,
readily available, nontoxic and chemically stable.[20]
[b]
[c]
E-mail: manoj.gawande@upol.cz
In continuing our efforts to develop sustainable synthetic
pathways for organic transformations by using variety of
advanced materials,[21] herein, we report the synthesis of a novel,
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
highly active, palladium complex derived from
a modified
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(Figure 1b) confirmed the crystallinity of these nanoparticles and
was found to be consistent with XRD results. TEM image of
SMNP in Figure 1c depicts the dark core-shell structure of MNP
with almost uniform coating of silica of 4-5 nm thickness. High-
resolution transmission electron microscopy (HR-TEM) image of
the MNPs in Figure 1d depicts the average interplanar distance
of MNPs to be ∼0.20 nm, which corresponds to the (311) plane
of inverse spinel structured Fe3O4.
magnetic support, capable for ynones synthesis. This
nanocatalyst is of interest as it exhibits remarkable catalytic
performance due to its high stability, excellent activity and
effortless recovery than previously reported catalysts. Moreover,
this is the first report wherein fascinating properties of silica
coating and magnetic core are combined with catalytic
properties of palladium for the synthesis of ynones at room
temperature under copper-free and phosphine-free conditions.
Results and Discussion
Preparation and characterization of Pd-Sc@ASMNP
The synthesis of magnetic nanoparticles (MNPs) was performed
using co-precipitation technique.[22] In order to prevent
aggregation and provide stabilization to these MNPs, silica
coating was performed using sol-gel approach.[23] Further, to
provide scope for grafting of other substrates, the surface of
magnetic silica nanoparticles (SMNPs) was covalently coupled
with (3-Aminopropyl)triethoxysilane (APTES, NH2 linker). APTES
functionalized silica encapsulated magnetic nanoparticles
(ASMNPs) were then reacted with a ligand, salicyaldehyde (Sc),
and the resulting Sc@ASMNPs were metallated with palladium
chloride (PdCl2) to obtain the final catalyst (Pd-Sc@ASMNPs).
(Scheme 1)
Figure 1. TEM images of the nanoparticles obtained at different stages of
synthesis: (a) TEM image of MNPs, (b) SAED pattern of MNPs, (c) TEM
image of SMNPs, (d) HR-TEM image of MNPs, (e) TEM image of fresh Pd-
Sc@ASMNPs and (f) TEM image of recovered Pd-Sc@ASMNPs.
TEM image of final catalyst in Figure 1e elucidates the uniform
metal binding to the core-shell surface nanocomposites. Also,
the TEM image of recovered catalyst has been provided in
Figure 1f to confirm that shape and morphology remain
unaltered after the catalytic reaction.
Another technique that provides considerable amount of
information about the topography of the sample is the Scanning
electron microscopic (SEM) analysis. The transition from smooth
surface of MNP to spongy surface confirms the successful
coating of MNP by a silica shell. The FE-SEM images display
spherical morphology of the Pd-Sc@ASMNP catalyst with slight
aggregation and appears same as that of SMNP, thereby
suggesting that surface modification processes did not alter the
morphology of the nano-catalyst. In addition to this, the SEM
image of the recovered catalyst indicates that the shape and
morphology of the catalyst remain unaltered even after the
reaction. (See the supporting information)
Scheme 1. A schematic illustration of the formation of the Pd-Sc@ASMNP
core-shell nano-catalyst.
For the investigation of crystalline phase and purity of the
synthesized MNP and SMNP, powder X-Ray diffraction (XRD)
measurements were carried out. XRD measurement of bare
MNPs in Figure 2a exhibit six characteristic Bragg peaks
observed at 2θ: 30.366 o, 35.663 o, 43.024 o, 53.6 o, 57.299o, and
62.865 o which correspond to the (220), (311), (400), (422), (511)
and (440) crystallographic faces of magnetite. [25a] These results
were found to be consistent with the standard XRD data of the
Joint Committee on Powder Diffraction Standards (JCPDS) card
number (19-0629) and corresponds to inverse cubic spinel
For the investigation of particle size and morphology of the
synthesized nanocomposites, Transmission electron microscopy
(TEM) studies were conducted. Figure 1a depicts that MNPs are
relatively uniform and show slight agglomeration due to absence
of surfactants.[24] From the analysis of 50 colloidal aggregates of
MNPs, it was found that the average size of MNPs is
approximately between 8-10 nm (See the supporting
information). Further, the presence of an array of bright
diffraction rings in the selected area electron diffraction pattern
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Fe3O4 crystal.[25b] The mean crystallite size of the MNPs was
estimated by the Debye–Scherrer equation (Dhk 1/4k /β cos θ),
where D is the size of the axis parallel to the (hkl) plane, k is a
constant with a typical value of 0.89 for spherical particles, l is
the wave ength of radiation, β is the fu width at ha f maximum
(FWHM) in radians, and θ is the position of the diffraction peak
maximum. The average crystallite size was found to be ~9.8 nm
for the (311) reflection, which is in well accordance with TEM
results. In addition to the six diffraction peaks, the XRD
diffraction pattern of SMNPs showed a weak broad hump at
2θ=20–24o in Figure 2b, which is the characteristic of
amorphous silica.[25c] (for individual XRD peaks, see the
supporting information).
analyze
parent
nanocomposites
and
their
further
functionalization in the range of 4000-400 cm-1. The IR-
spectrum of MNPs depicts the Fe-O stretching absorption at
581cm-1 (Figure 4a), [27a] while after silica-coating the intensity
of this peak gets reduced a little (Figure 4b).[27b] Three new
sharp bands appear in spectrum of SMNPs in the region of
804, 955 and 1096 cm-1, corresponding to the Si-O-Si
symmetric, Si-O symmetric and Si-O-Si asymmetric stretching
modes respectively. The functionalization of APTES over
SMNPs was confirmed by peaks at 2935 cm-1 and 1637 cm-1,
which are characteristic peaks for CH2 and NH2 from amino-
propyl moiety of APTES (Figure 4c).
[27c]
The immobilization of
ligand onto ASMNPs was indicated by the presence of C=N
stretching vibration mode at 1652 cm-1 (Figure 4d) and its
further metallation with PdCl2 was observed by the shift of the
prominent peak 1652 cm-1 to 1644 cm-1 indicating strong metal-
ligand interaction (Figure 4e). [27d, 27e] (for detailed IR spectra,
see the supporting information).
Figure 2. XRD pattern of the (a) MNPs and (b) SMNPs.
Energy dispersive X-ray analysis was employed to determine
the composition of the synthesized nanocomposites. The EDS
spectra showed well-defined peaks of palladium, silica and iron
(See the supporting information), thereby confirming the
successful anchoring of palladium on the nanocomposites Pd-
Sc@ASMNPs. In order to quantify the amount of Pd in the final
catalyst, the nanocatalyst was subjected to ICP and the
corresponding metal loading was found to be 0.08588 mmol g-
1. Figure 3 displays the XPS spectrum of the Pd-Sc@ASMNPs.
The peaks of Pd 3d5/2 appeared at 337 eV and Pd 3d8/2
appeared at 342 eV, confirming Pd in +2 oxidation state.[26]
Figure 4. FT-IR spectra of (a) MNPs, (b) SMNPs, (c) ASMNPs, (d)
Sc@ASMNPs, and (e) Pd-Sc@ASMNPs.
The field-dependent magnetization measurements of
synthesized nanocomposites were conducted. The Figure 5
displays magnetization curves which display no hysteresis
indicating that the nanoparticles exhibit superparamagnetic
behavior at room temperature. Besides this, the
superparamagnetic behavior was also confirmed by the inset in
Figure 5 which shows negligible coercivity and remanence in
the absence of an external applied magnetic field. The
saturation magnetization value of MNPs was found to be 56
emu/g, which is lower than its bulk counterpart (90 emu/g),
indicating that particle size affects the magnetization value of
the particle under applied field. [28] In addition, functionalization
of MNPs resulted in further reduction of the magnetization
value which can be accredited to the contribution made by
non-magnetic silica shell and other functional groups present
at the surface of magnetic core. The magnetization value came
out to be 41 emu/g for SMNPs, 27 emu/g for ASMNPs and 19
emu/g for final nanocatalyst Pd-Sc@ASMNPs. In spite of
exhibiting lower magnetization value, the net magnetism of
final nanocatalyst was sufficiently high for its effective
separation from the reaction mixture via external magnet.
Figure 3. XPS spectra of Pd-Sc@ASMNPs.
Since, the presence of magnetic core inside Pd-Sc@ASMNP
prevents the analysis of organic functional group by NMR
spectroscopy, therefore, the FTIR technique was employed to
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heteroaryl acid chloride such as 2-thiophene carbonyl chloride
reacted smoothly with terminal alkynes to give the
corresponding ynones in excellent yields (Table 1, entries 6,
11). Under the same reaction conditions, cyclohexane carbonyl
chloride also afforded the desired coupling products in good
yields (Table 1, entries 7, 14).
Figure 5. Magnetization curves obtained by VSM at room
temperature for (a) MNPs, (b) SMNPs, (c) ASMNPs, (d) Pd-
Sc@ASMNPs and (e) inset: enlarged image near the coercive
field.
Figure 6. Effect of base and solvent on acylation of terminal
alkynes (Reaction conditions: Benzoyl chloride (1.0 mmol); Phenyl
acetylene (1.2 mmol); Pd-Sc@ASMNPs (20 mg); room
temperature; 2 h).
Catalytic activity of Pd-Sc@ASMPs for direct coupling of
acyl chlorides with terminal alkynes
In order to test the efficacy of the prepared nanocatalyst Pd-
Sc@ASMNPs and to determine the optimal reaction
conditions, benzoyl chloride and phenylacetylene were
selected as the prototype. As a starting point to optimize the
Sonogashira coupling reaction, the impact of different reaction
parameters such as solvents, base and catalyst amount was
evaluated under aerobic conditions. As can be seen from
Figure 6, among various base and solvent combinations,
highest yield was obtained when triethylamine was used as
base and 1:1 ratio of acetonitrile and water was used as
solvent. We also found that the higher reaction temperatures
did not favour the cross-coupling reaction. Consequently, all
the reactions were performed at room temperature. For the
determination of the optimal catalytic amount, we conducted a
blank test, where no significant yield was obtained. While the
reaction gave product when 10 mg of catalyst was employed,
but further enhancement in the yield of product was observed
when 20 mg of catalyst was taken. However, no further
increase in the yield was observed with 30 mg of catalyst.
Therefore, the best results were obtained with 20 mg of
catalyst (See the supporting information).
To examine the scope of this coupling reaction, various acid
chlorides (aliphatic, aromatic and heteroaromatic) were
coupled with terminal alkynes using the optimized methodology
(Table 1). It was observed that the reaction gave good yields in
2
hours demonstrating the effectiveness of the catalytic
system. To further expand the generality of this coupling
reaction, we investigated a variety of aroyl chlorides having
both activating and deactivating groups such as methyl,
methoxy, chloro, and nitro. It was observed that the reaction
was equally facile for both electron donating and electron
withdrawing substituents on the aroyl chlorides. However,
electron withdrawing substituents such as NO2, took longer to
form coupling products, although high conversions were still
obtained (Table 1, entries 5, 13). Besides, the nature and the
position of substitution in the aromatic ring did not have much
effect on the reaction (Table 1, entries 2, 3, 15, 16). Also,
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Table 1. Scope of catalytic activity of the Pd-Sc@ASMNPs in synthesis of ynonesa
Entry
1
Aroyl chloride
Acetylene
Product
Yield
(%)b
96
TONc
559
2
3
95
96
94
89
97
90
91
553
559
547
518
565
524
529
4
5d
6
7
8
9
90
92
524
536
10
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11
94
93
83
85
547
542
483
495
12
13d
14
15
16
95
95
553
553
aReaction conditions: Aroyl chloride (1.0 mmol); Acetylene (1.2 mmol); Catalyst (20 mg); Et3N (1.5 eq); 2 mL of acetonitrile and
water mixture (1:1); Room temperature; Time 2 h.
byields were determined by GC-MS.
cTON= Calculated using the 0.0017 mmol/g palladium (Obtained by ICP for 20 mg of Pd-Sc@ASMNPs). dreaction time 3 h.
Finally, in order to show the merit of this catalytic method, we
compared our obtained results with the previously reported work
(see the supporting information), and found that our catalyst
worked much more efficiently without additives. Hence, catalytic
efficiency of the present catalytic system is remarkable in terms
of mild reaction conditions, short reaction time and easy
recovery of the catalyst.
The reusability of the catalyst was also examined. After each
experiment, the catalyst was separated from the reaction
mixture by using external magnet, washed with ethyl acetate
and ethanol and dried under vacuum before its use in
subsequent reactions. After being recovered, the catalyst was
used up to six runs without noticeable deactivation (Figure 7).
SEM and TEM images of the recovered catalysts further
provided evidence of unaltered structure and morphology
(Figure 1f, and S2d), while EDS confirmed the presence of
palladium in the recovered catalyst (See the supporting
information).
set of experiments. In the first set, standard reaction was
performed and after the completion of the reaction, the catalyst
was separated using external magnet and the filtrate was
analysed under AAS, which showed negligible leaching. In the
second set, split test was conducted, where, a standard reaction
was carried out with catalyst for half an hour, which corresponds
to approximately 20-25% of the conversion by GC-MS. Then,
the nanocatalyst was removed from the reaction mixture using
magnet and the reaction was continued further. It was observed
that, no coupling product was detected up to 3 hours in the
reaction mixture under the same conditions, thereby indicating
truly heterogeneous nature of the magnetic nanocatalyst.
Hot-filtration Test
Estimation of the leaching rate and the heterogeneity nature of
the catalyst was determined by performing two corresponding
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Figure 7. Catalyst recycling test for six consecutive runs in the synthesis of
ynones.
Proposed catalytic mechanism
With regard to the mechanistic path for the present
transformation, the plausible mechanism would be the formation
of Pd(0) species (C) from the precursor (A) via intermediate (B)
and homocoupling of terminal alkynes. This is followed by the
oxidative addition of acid chloride to form intermediate (D).
Subsequent alkyne coordination results in the formation of acyl
palladium complex (F) via intermediate (E). In the final step, the
product is obtained in reductive elimination along with the
regeneration of the catalyst [18e,29] (Figure 8).
Figure 8. Proposed reaction mechanism.
Conclusions
In summary, the Pd-Sc@ASMNPs nanocatalyst was fabricated
successfully via a facile route. These nanocomposites endowed
large surface area, good durability, and excellent catalytic
activity towards the synthesis of ynones via Sonogashira cross-
coupling reaction with excellent yields and high turn-over
number. These methodologies provide a facile, efficient and
sustainable process for the C-C coupling and have wide
applicability towards a variety of acyl chlorides under mild
conditions. Moreover, the effortless recovery and reusability of
the catalyst for at least six runs without any marked loss of
activity makes it an efficient protocol to yield combinatorial
libraries of ynones. The reported outcomes open up the
possibility of using Pd-Sc@ASMNPs nanocatalyst for other
organic transformations and large scale industrial applications.
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Synthesis of the final catalyst Pd-Sc@ASMNPs
Experimental Section
For covalent grafting of the ligand on ASMNPs, 1 g of ASMNP was
refluxed with 2 mmol of salicyaldehyde (Sc) in acetone (100 mL) along
with molecular sieves for 3 h. The obtained product was washed with
ethanol and dried under vacuum. Finally, 0.5 g of grafted Sc@ASMNPs
was stirred with a solution of 0.1 mmol of PdCl2 in acetone for 3 h. The
resulting Pd-Sc@ASMNPs were separated magnetically and thoroughly
washed with deionized water and dried under vacuum.
General remarks
TEOS and APTES were obtained from Sigma-Aldrich and Fluka
respectively. Ferric sulphate and ferrous sulphate were purchased from
Sisco Research Laboratory. All the other reagents used were of
analytical grade and obtained from Spectrochem and Merck. Double
distilled water was used throughout the studies.
General procedure for Pd-Sc@ASMNPs nanocatalyst mediated
synthesis of ynones
Characterization
Powder X-ray diffraction (XRD) patterns were performed using a Bruker
D8 Advance diffractometer (Karlsruhe, bundesland, Germany) in the 2θ
range of 10-80o. FT-IR spectra were recorded on Perkin-Elmer Spectrum
2000 using KBr pallets. TEM images were acquired using FEI TECHNAI
G2 T20 transmission electron microscope operated at 200 kV with an
energy dispersive X-ray analyser. ImageJ software was used for image
processing and analysis. SEM images were obtained from Carl Zeiss
India scanning electron microscope. Digestions were performed on Anton
Paar multiwave 3000. The Pd content was determined using Inductively
coupled Plasma of PerkinElmer Optima 2100 DV and LABINDIA AA
7000 Atomic Absorption Spectrometer with acetylene flame. The XPS
spectrum was recorded on Omicron Make XPS system interface with EA
125 Energy Analyzer within monochromatic A uminium Kα X-Ray source
with energy of 1486.6 eV with energy resolution of 0.6 eV. The
magnetization values were obtained from vibrating sample
magnetometer (EV-9, Microsense, ADE). The derived products were
analyzed and confirmed on GC-MS (Agilent gas Chromatography, 6850
GC with a HP-5MS) and a quadrapole mass filter equipped 5975 mass
selective detector (MSD) using helium as carrier gas. BET study was
performed on Quantachrome Instruments Model: ASI‐CI‐11 Adsorbate
temperature 77 K, found that the surface area of final nano-catalyst Pd-
Sc@ASMNPs is 113 m2/g. NMR spectra were recorded on a 400 MHz
JEOL NMR spectrometer in deuterated chloroform (CDCl3).
For this purpose, 10 mL of round bottom flask was charged with benzoyl
chloride (1.0 mmol), 1:1 ratio of acetonitrile and water (2 mL) and
triethylamine (1.5 eq). To this, 1.2 mmol of terminal alkyne was added
along with the catalyst (20 mg) and the reaction was kept under room
temperature and aerobic conditions till its completion. The reaction was
monitored using thin layer chromatography and aliquots were analysed
on regular intervals using GC-MS. Finally, all the products were extracted
by ethyl acetate, dried over sodium sulphate, concentrated and were
confirmed by GC-MS (See SI).
Recycling procedure
After the reaction completion, the catalyst was separated using an
external magnet followed by washing with ethyl acetate and ethanol.
Then, the catalyst was used directly for next consecutive runs without
further purification.
Acknowledgements
One of the authors, Manavi Yadav thanks TERI, Gwal Pahari,
Gurgaon and USIC, University of Delhi, Delhi for providing
instrumental facilities. The authors acknowledge the assistance
provided by the Research Infrastructure NanoEnviCz, supported by
the Ministry of Education, Youth and Sports of the Czech Republic
under Project No. LM2015073, and support from the Ministry of
Education, Youth and Sports of the Czech Republic – project No.
LO1305.
Synthesis of Magnetic Nanoparticles (MNPs)
MNPs were synthesized using co-precipitation method where, both ferric
(6.0 g) and ferrous sulphate (4.2 g) were dissolved in water (250 mL)
under stirring at 60 oC resulting in a yellowish-orange solution. To this,
25% NH4OH (15 mL) was added with vigorous mechanical stirring
resulting in black precipitates. Then, the stirring was continued till half an
hour. The precipitated MNPs were separated using magnet and washed
several times with deionized water and ethanol.
Keywords: Pa adium based • Silica-coated magnetic
nanocatalysts • Sonogashira coupling • Synthesis of ynones •
Synthesis of silica-coated MNPs (SMNPs)
Silica coating of these MNPs was performed via sol-gel approach where,
a suspension of MNPs and 0.1 M HCl (2.2 mL) in ethanol and water (50
mL) was kept under sonication. To this, 5 mL of 25% NH4OH was added
followed by 1 mL TEOS addition and was kept for stirring at 60 oC for six
hours. The obtained materials were then separated magnetically and
washed with ethanol and dried under vacuum.
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Synthesis of APTES functionalized SMNPs (ASMNPs)
For the incorporation of amine groups onto surface of SMNPs, APTES
(0.5 mL) was added to disperse solution of 0.1 g of SMNPs in 100 mL of
ethanol and the resulting solution was stirred at 50 oC for 6 h. The
APTES functionalized SMNPs were separated with magnet and washed
several times with ethanol to remove the unreacted silylating agent.
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The Table of Contents
FULL PAPER
A new magnetic-silica based
palladium nanocatalyst synthesized
and applied for the first time in the
direct coupling of acyl chlorides with
terminal alkynes to prepare a variety
of ynones under copper-free,
phosphine-free, and aerobic
conditions at room temperature
without the use of any additives and
inert conditions.
Rakesh K. Sharma,*a Manavi Yadav,a
Rashmi Gaur,a Radhika Gupta,a Alok
Adholeya band Manoj B. Gawande*c
Page No. – Page No.
Silica-based Magnetite core-shell
Palladium Nano-catalyst in the
synthesis of ynones under copper-
free and phosphine-free conditions
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