Fabrication of Pd/CuFe2O4 hybrid nanowires: A heterogeneous catalyst for Heck couplings

Article abstract of DOI:10.1039/c7nj04361a

The development of environmentally benign transformations is indispensable in organic synthesis. Herein, a hybrid heterogeneous catalyst, palladium(0) on copper ferrite nanowires, has been synthesized, characterized, and for the first time, employed in the Jeffrey Heck reaction between iodoarenes and allylic alcohols, and good to excellent yields have been obtained. In addition, the catalyst was found to be suitable for the usual Heck coupling. The nanocatalyst was recovered and reused up-to multiple runs without any noticeable loss of its catalytic activity.

Full text of DOI:10.1039/c7nj04361a

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Fabrication of Pd/CuFe2O4 hybrid nanowires:
Heterogeneous catalyst for Heck couplings
Received 00th January 20xx,
Accepted 00th January 20xx
B. Lakshminarayana,a L. Mahendar,a P. Ghosal,b B. Sreedhar,c G. Satyanarayana,*a
and Ch. Subrahmanyam*a
DOI: 10.1039/x0xx00000x
www.rsc.org/
The development of environmentally benign transformations is indispensable in
organic synthesis. Herein, hybrid heterogeneous catalyst, palladium (0) on copper
ferrite nanowires has been synthesized, characterized and for the first time
employed in the Jeffrey Heck reaction between iodoarenes and allylic alcohols
with good to excellent yields. In addition, the catalyst was found to be suitable for
the usual Heck coupling. The nanocatalyst was recovered and reused upꢀto
multiple runs without any noticeable loss of catalytic activity.
Introduction:
The development of sustainable chemical processes part of heterogeneous catalysis and thus enables the
under environmentally benign conditions is synthesis of bioactive compounds through suitable
paramount interest in organic synthesis. In the organic transformations like CꢀC coupling, CꢀH
recent past, heterogeneous catalysis has gained activation.3ꢀ7 Therefore, it is essential to design
increasing interest, due to the advantageous of supported nanocatalysts for organic transformations
recovering and reusing the catalyst.1,2 In this for practical applications.7,8 In this regards, recent
context, supported nanocatalysts are an integral
efforts to develop tailorꢀmade metal oxides
supported nanocatalysts show some promise.9,10
Particularly, these metal oxide supported
heterogeneous nanocatalysts are preferred due to
their activity, better selectivity, and high stability
over conventional homogeneous counterparts, due
to ease of separation and recovery of catalysts from
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the reaction mixture.11ꢀ12 In particular, the active condensation and subsequent hydrogenation.35
metal can be immobilized on a high surface area Interestingly, Heck and Chalk independently but
materials, such as metal oxides,13 silica,14 simultaneously reported Pdꢀcatalyzed oneꢀpot
carbon,9,15 polymer16 and nanocomposites.17ꢀ19
synthesis of DHCs starting from allylic alcohols
and aryl halides.36,37 Subsequently, Jeffery
developed Pdꢀcatalyzed Heckꢀtype reaction that
either leads to the formation of βꢀaryl (or alkenyl)
carbonyls (DHCs) or to the selective formation of
βꢀaryl (or alkenyl) allylic alcohols.38ꢀ40 Recently, a
green approach for the carbonꢀcarbon bond forming
crossꢀcoupling reaction (e.g. Heck coupling)
renders a more practical and strategic advantage
over the standard protocol.41ꢀ44 The drawbacks of
unsupported Pdꢀcatalyst can be overcome by
utilizing supported Pdꢀcatalysts for CꢀC coupling
reactions.44
In this context, supported ferrite nanocatalysts are
an important class of magnetic materials with
proven applications in magnetoꢀthermal therapy,
microwave
absorbent
sensors
and
drug
delivery.20,21 The metal ferrite nanocatalysts can be
generated by partial substitution of other metal ions
in the Fe3O4 crystal lattice.22 The spinel ferrite
(MFe2O4) has the unique properties of wellꢀdefined
crystal structure and stability.23ꢀ25 Moreover,
MFe2O4 (M = Cu) nano ferrite was found to be the
best support when comapred to other nano ferrites
(M = Ni, Co and Zn).26,27
In this context, we report the synthesis and
characterization of Pd/CuFe2O4 hybrid nanowires.
Further, its application for the synthesis of
dihydrochalcones (JefferyꢀHeck type coupling),
cinnamic acid esters and stilbenes (Heck reaction)
have been explored.
Flavonoids got consideration as dietary constituents
of potential significance to wellbeing.28 Among a
few classes of flavonoids, dihydrochalcones
(DHCs) have a place with a noteworthy class of
bicyclic compounds, which are key antecedents for
flavonoid biosynthesis in plants. The two aromatic
rings in these compounds are connected by a threeꢀ
carbon bridge, particularly, propanone in
dihydrochalcones.29 DHCs are known to exhibit
multiple biological activities, such as antifungal,
antibacterial, anticancer properties and have gotten
Instruments used
Xꢀray powder diffraction was performed on a
PANalytical, X’pertPRO instrument with Cu Kαꢀ
radiation of wavelength 1.5406 Å. The augmented
voltage and current used for this instrument were
40 kV and 30 mA respectively. The step size used
for the scan is 0.017° per step in the 2θ angle range
of 20°ꢀ90°. The crystalline phases were indexed
based on JCPDSꢀICDD, PDF NO: 25ꢀ0283
(CuFe2O4) and 89ꢀ4897 (Pd). The chemical
impressive
consideration
as
nourishment
sweeteners.30ꢀ32 DHCs are also intermediates
towards flavenes and anthocyaninꢀtype dyes.33,34
Usually, DHCs synthesis can be accomplished via a
twoꢀstep
strategy
using
ClaisenꢀSchmidt
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composition of the catalysts was determined using CuFe2O4. The nanoꢀsized CuFe2O4 were
Xꢀray fluorescence (XRF) spectrometer. HRTEM synthesized by a solution combustion method by
was performed by depositing samples on a carbon using urea as the fuel. In a typical synthesis of
covered Cu grid on a 200 kV FEI model CuFe2O4. To
a
crystalline dish containing
TECNAIG2 SꢀTwin TEM instrument connected Cu(NO3)2.3H2O (1.208 g, 5 mmol), were added
with a moderate output CCD camera. The catalysts Fe(NO3)3.9H2O (4.04 g, 10 mmol) and urea (2.0 g,
were portrayed by Xꢀray photoelectron spectra 33.3 mmol) simultaneously, and dissolved with
(XPS) with omicron gear utilizing Al Kα radiation milliꢀQ water (5 mL). The resultant solution was
(1486.6 eV). The instrument was precalibrated with kept in a muffle furnace at 400 °C. Initially, the
a reference of C (1s) peak at 284.5 eV. Every solution boiled with froth and foam followed by
beginning material was synthesized and gotten ignition after complete dehydration and finally
from suppliers and used as received. Solvents were burned with flame yielding solid product within 2
sanitized by standard methodology. Experiments min. This solid material was further subjected to
1
were carried out under closed environment. H calcined at 400 °C, for 15 min.
NMR spectra were recorded at 400 MHz utilizing
Synthesis Pd/CuFe2O4nanowires:
BrukerAVANCE instrument at 278 K. Chemical
0.42 mmol of CuFe2O4 and 0.28 mmol of PdCl2
have been taken in a beaker and 25 ml of ethanol
was added and the solution was ultraꢀsonicated at
room temperature for 30 minutes. After sonication,
the solution was kept for stirring and 25 mL of
NaBH4 in water (0.5 M) was added dropwise to the
solution. The resultant solution was stirred
continuously for 2h at room temperature. After 2h
stirring, the solution was washed and centrifuged
with ethanol and water. Finally, the formed
material was centrifuged with acetone and dried
overnight under hot air oven at 60 °C. The resultant
material was grained and used for further analysis.
shift (δ) in ppm downfield from tetramethylsilane
with the dissolvable as the interior reference
(CDCl3: δ 7.26 ppm). Data is reported as follows:
chemical shift, multiplicity (s = singlet, d =
doublet, t = triplet, q = quartet, br = expansive, m =
multiplet), coupling constants (Hz), and integration.
13CNMR spectra were recorded on either a Bruker
AVANCE 100 MHz with complete proton
decoupling. Highꢀresolution mass spectra (HRꢀMS)
were recorded using QꢀTOF multimode source.
Experimental:
Combustion Synthesis of CuFe2O4:
Copper (II) nitrate trihydrate [Cu (NO3)2·3H2O]
(Merck), Iron (III) nitrate nonahydrate [Fe
(NO3)3·9H2O] (SigmaꢀAldrich), urea (H2NCONH2)
(Fisher Scientific) were utilized for the synthesis of
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Characterization of catalysts:
XPS:
The valence state of Pd/CuFe2O4 nanowires were
analyzed by XPS. Figure 2 showed the XPS core
level spectra for Pd 3d with characteristic, spinꢀ
orbit splitting of Pd 3d5/2 and Pd 3d3/2. Notably, an
approximately 0.1ꢀ0.3 eV chemical shift of the Cu
2p and Pd 3d coreꢀlevel was observed in the
standard Pd sample. In Figure 2, the peaks
corresponding to 3d5/2 and Pd 3d5/2 appeared at
337.3 and 340.9 eV, respectively. The Pd (3d5/2,
3d3/2) peaks at 339.6 and 335.7 eV were assigned to
Pd (0).45
XRD
For the examination of the crystalline phase of the
synthesized CuFe2O4 and Pd/CuFe2O4, powder Xꢀ
ray diffraction (XRD) measurements were carried
out. XRD patterns of exposed CuFe2O4 shown in
Figure 1 display characteristic peaks with dꢀspacing
of 2.516 A°, 2.315 A°, 1.768 A°,1.690 A°, 1.580
A° which relate to the (311), (222), (422), (312),
(511) and (440) planes, respectively. In a similar
way, the characteristic peaks at 2θ:30.57°, 35.78°,
36.67°, 40.15°(Pd), 46.63°(Pd), 57.36°,61.56°,
63.08°, 68.48°(Pd), 73.70°, 79.89°, 82.21°(Pd)
indicated the (220), (311), (222), (111), (200),
(511), (224), (400), (220), (533), (444),(311) planes
and confirms the deposition of Pd.
The typical spectrum of Cu 2p binding energy of
Pd/CuFe2O4 nanowire catalyst is shown in Figure
2. The peaks centered at about 933.4 and 953.1 eV
represents the Cu 2p3/2 and Cu 2p1/2 respectively. It
has been well established that the presence of
shakeꢀup peak (about 938ꢀ942 eV) and a higher Cu
2p3/2 binding energy (about 933.0ꢀ933.8 eV) are
two major XPS characteristics of CuO. While a
lower Cu 2p3/2 binding energy (about 932.2ꢀ933.1
eV) and the absence of the shakeꢀup peak are
characteristics of reduced copper species.46 In the
present case, the higher Cu 2p3/2 binding energy
(933.4 eV) and a shakeꢀup peak at 938ꢀ939 eV
indicated that the Cu2+ species existed in the
catalyst and the reduced copper species could not
be detected.
Figure 1: XRD pattern of as-synthesized CuFe2O4 and
Pd/CuFe2O4.
CuFe2O4
Pd/CuFe2O4
Reference:
Pd (0) - Jcpds No = 89-4897
CuFe2O4-CrystEngComm, 2012, 14, 5879-5885
The XPS spectrum of Fe 2p indicates three
dominant peaks corresponding to Fe 2p3/2 at 712.7
eV, Fe 2p1/2 at 724.5 eV and a satellite at 719.1 eV,
which is consistent with the presence of Fe3+.47
Moreover, the fitted Fe 2p3/2 peak shows an
20 30 40 50 60 70 80 90
2θ (Degree)
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additional peak at 710.2 eV, which is assigned to a XRF spectrometry which is shown in Figure 4. The
Fe3+ state in the CuꢀOꢀFe bond. The absence of Fe results indicated that the percentages of Pd, Cu and
2p3/2 peak at 709.3 eV suggests that no Fe2+ was Fe are 22.5%, 27.4% and 48% respectively.
present in sample.48
Figure 2: XPS pattern of as-synthesized Pd/CuFe2O4
Figure 3: HRTEM images of Pd/CuFe2O4 nanowires.
nanowires
HRTEM and XRF:
From the lowꢀmagnification TEM image (Figure
3), one can see a highꢀquality intertwining
nanowires with an average width of about 14 nm.
To determine the elemental composition of the
material, asꢀprepared Pd/CuFe2O4 was analyzed by
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Figure 4: The XRF spectrum of Pd/CuFe2O4
acetate (5 mL) and neutral NH4Cl solution (5 mL)
was added followed by extraction with ethyl
acetate (2 × 4 mL). The organic layers were dried
with Na2SO4 and concentrated in reduced vacuum.
Purification of the residue by silica gel column
chromatography
using
distilled
petroleum
ether/ethyl acetate as the eluent furnished the
cinnamates and stilbenes.
General Procedure 2 (For the synthesis of DHCs
7):
In an ovenꢀdried Schlenk tube, aryl vinyl alcohol 6
(0.5 mmol), iodoarenes 1 (0.5 mmol), Pd/CuFe2O4
nanowires catalyst (4 mol%), NaHCO3 (1 mmol)
and solvent (DMSO) (1.0 mL) were added. The
Catalytic Activity Test:
Reactions were monitored by TLC on silica gel
plate using a combination of petroleum ether and
ethyl acetate as eluents. Solvents were distilled
prior to use petroleum ether with a boiling range of
resulting reaction mixture was stirred at 120 °C for
24 h. The progress of the reaction was monitored
by TLC. After completion of the reaction, the
reaction mixture was allowed to cool to room
temperature, and then diluted with ethyl acetate (5
mL) and neutral NH4Cl solution (5 mL) was added
followed by extraction with ethyl acetate (2 × 4
mL). The organic layers were dried with Na2SO4
and concentrated in reduced vacuum. Purification
of the residue by silica gel column chromatography
using distilled petroleum ether/ethyl acetate as the
eluent furnished the DHCs 7.
40 °C to 60 °C was used. Acme’s silica gel (100ꢀ
200 mesh) was used for column chromatography
(approximately 20 g per one gram of crude
material).
General Procedure 1 (For the synthesis of
cinnamates 3 and stilbenes 5):
In an ovenꢀdried Schlenk tube, iodobenzene 1 (0.5
mmol), acrylates 2 or styrenes 4 (1 mmol),
Pd/CuFe2O4 nanowires catalyst (4 mol%), K2CO3
(1 mmol) and solvent (DMSO) (1.0 mL) were
added. The resulting reaction mixture was stirred at
C-C coupling reactions:
120 °C for 3 to 12 h. The progress of the reaction
For Heck coupling, preliminary examinations have
been carried out with substrates 4ꢀmethoxy
iodobenzene 1h and ethyl acrylate 2b in the
presence of the heterogeneous catalyst, and the
was monitored by TLC. After completion of the
reaction, the reaction mixture was allowed to cool
to room temperature, and then diluted with ethyl
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7
Pd/CuFe2O4
K2CO3
toluene
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
water
120
120
120
rt
ꢀ
77
68
ꢀ
results are summarized in Table 1. Thus, initially,
the reaction was conducted in the presence of base
K2CO3 (1 equiv) at 120 °C for 3 h. Gratifyingly, the
Heck product 3hb was obtained in nearly
quantitative yield (Table 1, entry 1).The reaction
with other polar solvents such as DMF, DMA, 1,4ꢀ
dioxane, THF, acetonitrile and water furnished the
product 3hb, in 85%, 65%, 76%, 69%, 50% and
10% yields, respectively (Table 1, entries 2 to 6,
15). Whereas, the reaction does not show progress
in less polar solvent toluene (Table 1, entry 7). The
reaction with different bases, such as Na2CO3 and
K3PO4, gave the Heck product 3hb, in 77% and
68% yields, respectively (Table 1, entries 8 and 9).
The reaction at ambient temperature totally retards
8
Pd/CuFe2O4 Na2CO3
9
Pd/CuFe2O4
Pd/CuFe2O4
Pd/CuFe2O4
ꢀ
K3PO4
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
10
11
12
13
14
15
60
59
ꢀ
120
120
120
120
Fe3O4
ꢀ
CuFe2O4
ꢀ
Pd/CuFe2O4
10
aReaction Conditions: aryl iodides (0.5 mmol), ethyl acrylate (1
mmol), Pd/CuFe2O4 (4 mol%), Base (1 mmol) and Solvent (1
mL) at 120 °C. bIsolated yields of product 3hb.
Further to optimize the load of Pdꢀnanocatalyst, the
reaction was performed with 2, 4, 8, and 10 mol%
of Pd/CuFe2O4 catalyst under standard conditions
and the results are shown in Figure 5, which
concludes that the 4 mol% was found to be an
optimal load to drive the reaction.
the reaction (Table 1, entry 10), but at 60 °C, gave
Figure 5: Optimization of the reaction about mol% of the
the product 3hb in 59% yield (Table 1, entry 11).
In absence of impregnated Pdꢀspecies, no progress
was noticed (i.e. with or without Fe3O4 or with
CuFe2O4; Table 1, entries 12 to 14). Thus reveals
the importance of Pdꢀspecies as an active catalyst.
catalyst.
Table 1: Optimization studies for the formation of cinnamic
acid ester 3hb.a
Entry
Catalyst
Base
(1
equiv)
Solvent
(1 mL)
Temp
(°C)
Yield
3hb(%)
b
1
2
3
4
Pd/CuFe2O4 K2CO3
DMSO
DMF
120
120
120
120
99
85
65
76
Pd/CuFe2O4
Pd/CuFe2O4
Pd/CuFe2O4
K2CO3
K2CO3
K2CO3
Further, we performed a comparative study
between simple, electron withdrawing groups
(EWG) and electron donating groups (EDG)
containing iodobenzene with methyl acrylate, under
DMA
1,4ꢀ
dioxane
THF
5
6
Pd/CuFe2O4
Pd/CuFe2O4
K2CO3
K2CO3
120
120
69
50
acetonitrile
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standard reaction conditions (K2CO3 as a base and completion and furnished the products 3ba-3bc, in
DMSO as a solvent at 120 °C for 3 h). In all these moderate yields.
cases, only with Pd/CuFe2O4, the Heck products Further to check the scope of the reaction, the Heck
were obtained in 95, 98 and 98% yields, reaction was performed between iodoarenes and
respectively. While no progress was observed with styrenes (Table 3). In this case, stilbenes were
unsupported CuFe2O4 (Scheme 1). Thus, reveals obtained, in fair to excellent yields. However,
the importance Pdꢀmetal to drive the reaction.
unlike the reaction with acrylates, longer times
were needed. This may be attributed to the less
reactive nature of the styrene double bond.
Scheme 1: Comparative studies with and without Pd-on
CuFe2O4.
In heterogeneous catalysis, to the best of our
knowledge, this report is first of its kind for the
synthesis of dihydrochalcones (DHCs), under
Jaffrey Heck reaction, catalyzed by Pd/CuFe2O4
nanowires. The Jaffrey Heck reaction was
performed by utilizing 3, 4ꢀdimethoxy phenyl vinyl
alcohol 6b and 4ꢀiodoanisole 1h as model
substrates, within the sight of the Pd/CuFe2O4
nanowires. No product was formed, without the
catalyst (Table 4, entry 1). Similarly, either with
CuFe2O4 or with Fe3O4 nanocatalysts, no progress
was detected (Table 4, entries 2 & 3). However,
streamlined conditions for the Heck coupling
(Table 1, entry 1), furnished the product 7bh only
38% yields (Table 4, entry 4). However, in the
presence of additive Et3BnNCl and DMSO solvent,
K2CO3 as a base, the yield of 7bh improved to 50%
(Table 4, entry 5). While the reaction with other
bases Na2CO3 and K3PO4 gave the product 7bh in
more or less same yield (Table 4, entries 6 & 7).
Gratifyingly, the reaction with a mild base
NaHCO3 turned out to the best and furnished the
product in 86% yield (Table 4, entry 8). On the
With these optimal reaction conditions in hand
(Table 1, entry 1), we extended the scope of the
reaction for different iodoarenes and acrylates. The
results are summarized in Table 2. Interestingly,
the reaction showed broad substrate scope with
regards to iodoarenes and acrylates, and furnished
the products in fair to near quantitative yields
(Table 2). Notably, the reaction was compatible
with wide variety of functional groups on the
aromatic ring of iodoarenes. For example, the
reaction was successful with electron donating
groups as well as with electron withdrawing
functional groups. It is worth mentioning that the
reaction of sterically demanding 2, 6ꢀdimethyl
iodobenzene 3b with different acrylates was also
successful, with reasonably long time for the
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other hand, the reaction with other solvents, such
as, toluene, DMF and DMA proved to be inferior
(Table 4, entries 9 to 11).
Table 2: Formation of various alkyl cinnamates 3aa-3jb from different iodoarenes 1a-j and alkyl acrylates 2a-c.a
aReaction Conditions: aryl iodides (0.5 mmol), acrylates (1mmol), Pd/CuFe2O4 (4 mol%), K2CO3 (1 mmol) and DMSO (1 mL) at
120 °C. bIsolated yields of product 3aa-3jb.
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Table 3: Formation of various stilbenes 5aa-5ja from different iodoarenes 1a-j and styrenes 4a-b.a
Journal Name
aReaction Conditions: aryl iodides (0.5 mmol), styrene (1 mmol), Pd/CuFe2O4 (4 mol%), K2CO3 (1 mmol) and DMSO (1 mL) at
120 °C. bIsolated yields of product 5aa-5ja.
b
Base (1 mmol), and DMSO (1 mL) at 120 °C. Isolated yields
Table 4: Optimization studies for the formation of DHCs 7bh.a
of product 7.
To further check the scope and utility of the
method, the above optimized conditions [i.e.
Entry
Catalyst
Base
Additive
Solvent
Yield
(%)
ꢀ
Pd/CuFe2O4 nanowires catalyst, Et3BnNCl
additive, NaHCO3 base and DMSO solvent, 120
1
2
ꢀ
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
K3PO4
ꢀ
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
CuFe2O4
ꢀ
ꢀ
°C, 24 h (Table 4, entry 8)] were explored with
3
Fe3O4
ꢀ
ꢀ
other allylic alcohols 6a-f and iodoarenes 1a-h, and
the results are depicted in Table 5. Interestingly, the
protocol was quite successful and furnished DHCs
7aa-fh, in fair to very good yields (Table 5). The
reaction was compatible with abroad range of
functional groups, particularly, on the aromatic ring
of iodoarenes 1. For example, the protocol was
amenable to OMe, F, Cl and CF3 substituents.
4
Pd/CuFe2O4
Pd/CuFe2O4
Pd/CuFe2O4
Pd/CuFe2O4
ꢀ
38
50
53
58
86
30
65
46
5
Et3BnNCl
Et3BnNCl
Et3BnNCl
6
7
8
Pd/CuFe2O4 NaHCO3 Et3BnNCl
9
Pd/CuFe2O4 NaHCO3 Et3BnNCl toluene
10
Pd/CuFe2O4 NaHCO3 Et3BnNCl
DMF
11
Pd/CuFe2O4 NaHCO3 Et3BnNCl
DMA
aReaction Conditions:aryl vinyl alcohols (0.5 mmol), aryl
iodides (1 mmol), Pd/CuFe2O4 (4 mol%), additive (0.5 mmol),
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Significantly, the reaction was also smooth with
strong electron withdrawing NO2 group (Table 5,
7ad, 7be & 7dd). Notably, the method was suitable
for the heteroꢀaromatic thiophene moiety as well
(Table 5, 7fh).
Table 5: Formation of DHCs 7aa-7fh from iodoarenes 1a-j and aryl vinyl alcohols 6a-f.a
aReaction Conditions:aryl vinyl alcohols (0.5 mmol), aryl iodides (1 mmol), Pd/CuFe2O4 (4 mol%), Et3BnNCl (0.5 mmol),
NaHCO3 (1 mmol), and DMSO (1 mL) at 120 °C. bIsolated yields of product 7aa-7fb.
On the other hand, the coupling of 2ꢀbromo phenyl due to bromo functionality at orthoꢀposition to the
vinyl alcohol 6g with iodoarenes 1b, 1e and 1h, allylic alcohol moiety, which could not permit the
gave simple Heck olefination products instead of double bond isomerization from allylic position to
ketones. These observations are as summarized in enol form, through reꢀcoordination to the Pdꢀ
Table 6. This can be attributed to the steric crowing
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catalyst. This observation is based on wellꢀ we noticed that it took 3 h to accomplish
established results from our studies (Table 6).40
quantitative yield upꢀto five reaction cycles.
Figure 6: Recyclability of Pd/CuFe2O4 nanowires catalyst in
Table 6: Formation Heck products 8gb-8gh from different
iodoarenes 1b-h and 2-bromophenyl vinyl alcohol 6g.a
Heck reaction.
aReaction Conditions: 2-bromo phenyl vinyl alcohol (0.5
mmol), aryl iodides (1 mmol),
Pd/CuFe2O4 (4 mol%),
Et3BnNCl (0.5 mmol), NaHCO3 (1 mmol), and DMSO (1 mL)
at 120 °C. bIsolated yields of product 8gb-8gh.
Heterogeneity of Pd/CuFe2O4 nanowires
catalyst:
The reusability of catalyst and the leaching of Pd
were studied by hot filtration method. The catalyst
was examined with XRF before and after the
recovery, which indicated that no leaching was
observed. This demonstrates the true heterogeneous
nature.
Conclusion:
In this work, we have developed a facile route for
the synthesis of dihydrochalcones (DHCs),
cinnamates, stilbenes by ligandꢀfree Heck and
Jaffrey Heck reactions using heterogeneous
Pd/CuFe2O4 catalyst. This synthesized Pd/CuFe2O4
nanowires catalyst was utilized the first time for
synthesis of dihydrochalcones (DHCs) with high
yields. Initially, we used Heck crossꢀcoupling
reaction as a model reaction to optimize the
reaction conditions for the synthesis of cinnamates
and stilbenes with good to excellent yields. Further,
the optimized catalyst was subjected to Jaffrey
Heck reaction which results fair to very good
yields. This study offers a promising green
approach and offers good to excellent yields of the
Recyclability:
We reused the recovered catalyst for the
subsequent runs. The catalyst was reused upꢀto five
continuous cycles with no obvious loss of
reactivity, utilizing 4 mol% of catalyst for the
reaction between 4ꢀmethoxy iodobenzene and ethyl
acrylate. The process of the recyclability of the
catalyst has also been studied (for details: see;
supporting information). From this investigation,
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products. Effectively, this green reaction approach
and true heterogeneous nature of the Pd/CuFe2O4
offer a promise for its usage in CꢀC bond forming a
reaction.
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Graphical Abstract:
Hybrid heterogeneous catalyst, palladium (0) on copper ferrite nanowires has been synthesized
and characterized. Significantly, this catalyst for the first time employed in the Jeffrey Heck
reaction between iodo-arenes and allylic alcohols. In addition, the catalyst was found to be
suitable to the usual Heck coupling. Interestingly, this nanocatalystwas recovered and reused up-
to multiple runs without any noticeable loss in its catalytic activity with good to excellent yields.