Maghemite-Copper Nanocomposites: Applications for Ligand-Free Cross-Coupling (C-O, C-S, and C-N) Reactions

Article abstract of DOI:10.1002/cctc.201500546

A magnetically retrievable, efficient, and benign maghemite-Cu nanocatalyst was synthesized from inexpensive precursors and applied for C-O, C-N, and C-S bond-formation reactions. The obtained maghemite-Cu nanocatalyst was characterized by various techniques such as XRD, X-ray photoelectron spectroscopy, field-emission gun SEM with energy-dispersive spectroscopy, atomic absorption spectroscopy, TEM, high-angle annular dark-field scanning transmission electron microscopy, FTIR spectroscopy, and M?ssbauer spectroscopy. Excellent catalytic activity, ease of recovery, and reusability without a significant loss of yield make the present protocol highly sustainable to deal with industrial and environmental concerns. Magnetic attraction: A magnetically retrievable, efficient, and benign maghemite-Cu nanocatalyst is synthesized from inexpensive precursors and applied for C-O, C-N, and C-S bond-formation reactions. Excellent catalytic activity, ease of recovery, and reusability without significant loss of yield make the present protocol highly sustainable to deal with industrial and environmental concerns.

Full text of DOI:10.1002/cctc.201500546

DOI: 10.1002/cctc.201500546
Full Papers
Maghemite-Copper Nanocomposites: Applications for
Ligand-Free Cross-Coupling (CÀO, CÀS, and CÀN)
Reactions
Rakesh K. Sharma,*[a] Rashmi Gaur,[a] Manavi Yadav,[a] Anuj K. Rathi,[b] Jiri Pechousek,[b]
Martin Petr,[b] Radek Zboril,[b] and Manoj B. Gawande*[b]
A magnetically retrievable, efficient, and benign maghemite-Cu
nanocatalyst was synthesized from inexpensive precursors and
applied for CÀO, CÀN, and CÀS bond-formation reactions. The
obtained maghemite-Cu nanocatalyst was characterized by
various techniques such as XRD, X-ray photoelectron spectros-
copy, field-emission gun SEM with energy-dispersive spectros-
copy, atomic absorption spectroscopy, TEM, high-angle annular
dark-field scanning transmission electron microscopy, FTIR
spectroscopy, and Mçssbauer spectroscopy. Excellent catalytic
activity, ease of recovery, and reusability without a significant
loss of yield make the present protocol highly sustainable to
deal with industrial and environmental concerns.
Introduction
Since the era of the Wohler synthesis of urea, the demand for
effective, competent, and sustainable practices to perform vari-
ous organic transformations has been a major challenge in the
world of chemical research.[1] However, during the past few
years, the integration of sustainable chemistry with precise
nanotechnology has contributed significantly to the resolution
of this problem by the introduction of supported heterogene-
ous nanocatalysts.[2] This is because of the advantages provid-
ed by heterogeneous nanocatalysts, which include a high sur-
face area, high metal loading, excellent stability, and the facile
separation and recyclability of the catalyst.[3] Thus, nowadays
these supported nanocomposites are an integral major feature
of catalysis science and technology, and most organic industri-
al chemistry relies on them.[4] Consequently, there is a critical
need for a superior and advanced heterogeneous nanocatalytic
systems to perform various organic transformations. In this
context, supported nanomaterials have been employed in sev-
eral types of solid nanosupports, which include silica, alumina,
iron oxide, polymers, and carbon.[5,6] Of these, “iron oxides”
have garnered much attention because of their unique charac-
teristics, which include their nontoxic nature, chemical stability,
and economical viability as they can be prepared easily from
low-cost precursors.[7]
The most significant and unique characteristic is that they
are magnetically separable, which offers a good alternative to
filtration and centrifugation methods. These outstanding fea-
tures impart radical and remarkable transformations in organic
synthesis and drive researchers towards the design and devel-
opment of new heterogeneous nanocatalysts.[8–13] Recently,
considerable attempts have been made towards selective CÀ
heteroatom (CÀO, CÀN, and CÀS) bond formation.[14] These re-
actions are powerful tools for the formation of a variety of sub-
strates that are of biological, pharmaceutical, industrial, and
material interests.[15] The cross-coupling reactions of different
nucleophiles with aryl halides have been achieved by the Ull-
mann,[16] Buchwald,[17] Hartwig,[18] Evans,[19] and Chan meth-
ods.[20] Among these, the classical Ullmann condensation reac-
tion is efficient as it involves Cu as a catalyst, which often pro-
vides a high catalytic activity similar to expensive and toxic
noble metals, such as Pd.[21] Furthermore, the Ullmann reaction
employs easily available aryl halide as the aryl donor in com-
parison to boronic acid and organotrifluoroborates, which are
used in other reactions.[19–22] However, their practical utility is
hindered because of the involvement of harsh reaction condi-
tions such as high temperatures, the use of expensive and
complex ligands, the employment of single-use catalysts, and
the low yields. Additionally, most of these catalyst are homoge-
neous and, therefore, not only cause the problem of catalyst
separation and recycling but also lead to large amounts of
waste on scale up.[23]
[a] Prof. R. K. Sharma, R. Gaur, M. Yadav
Green Chemistry Network Center
Department of Chemistry
University of Delhi
Delhi, 110007 (India)
E-mail: rksharmagreenchem@hotmail.com
[b] Dr. A. K. Rathi, Dr. J. Pechousek, M. Petr, Prof. R. Zboril, Dr. M. B. Gawande
Regional Centre of Advanced Technologies and Materials
Faculty of Science
In the early 20th century, the discovery of heterogeneous cat-
alysts, which include Pd,[24] Cu,[25] and Ni[26] were reported as ef-
fective and reusable catalysts under much milder reaction con-
ditions. Unfortunately, these existing heterogeneous catalysts
proceed with the use of expensive ligands and tedious isola-
tion procedures, such as centrifugation or filtration, for the re-
Department of Physical Chemistry
Palacky University
ˇ
˚
Slechtitelu 11, 783 71, Olomouc (Czech Republic)
E-mail: manoj.gawande@upol.cz
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201500546.
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covery of the expensive metal catalyst. Consequently, one of
the major challenges in chemical synthesis is to establish
a promising method for CÀheteroatom bond formation that
circumvents these problems. Thus, in pursuit of our research
interests in the design and synthesis of nanocatalysts based on
iron oxides for various benign organic transformations,[27,28]
herein we describe the fabrication, characterization, and appli-
cations of a maghemite-supported Cu nanocatalyst for three
different types of coupling reactions, OÀaryl, NÀaryl, and SÀ
aryl (Scheme 1).
Figure 1. XRD patterns of maghemite and the maghemite-Cu nanocatalyst.
which is in agreement with the result obtained from TEM (20–
40 nm). The peaks observed in the XRD pattern at 2q=220,
311, 400, 422, 511, and 440 are attributed to maghemite. Al-
though magnetite (Fe3O4) and maghemite (g-Fe2O3) have the
same spinel arrangement and their XRD peak locations are
quite close to each other, further characterization by Mçssba-
uer spectroscopy, which clearly showed that the sample does
not contain magnetite and corresponds to maghemite. As
a result of their low concentration, signals for Cu nanoparticles
(NPs) were not observed in the XRD pattern of g-Fe2O3-Cu
(Figure 1).
Scheme 1. Maghemite-Cu-catalyzed cross-coupling (CÀO, CÀS, and CÀN) re-
actions.
The nature of the Cu on the surface of maghemite was con-
firmed by XPS. The spectrum shows the presence of Cu0 and
CuO from the doublet peaks at a binding energy (BE) of
932.49 and 952.29 eV (assigned to Cu2p1) and BE=933.67 and
953.46 eV (assigned to Cu2p3), which match perfectly with the
positions of Cu0 and CuO, respectively (Figure 2).[30]
Notably, this catalytic system is a simple yet effective ap-
proach as it avoids several multistep postsynthetic functionali-
zation processes and the use of toxic and complex ligands,
which thus renders the present protocol straightforward, supe-
rior, and cost effective.
Results and Discussion
Characterization techniques
The maghemite-Cu nanocatalyst was prepared by a simple wet
impregnation
technique
followed
by
dehydration[29]
(Scheme 2) and characterized by XRD, atomic absorption spec-
Scheme 2. Synthesis of the maghemite-Cu nanocatalyst.
Figure 2. XPS spectrum of the maghemite-Cu nanocatalyst (Cu2p spectrum).
troscopy (AAS), TEM, field-emission gun scanning electron mi-
croscopy with energy-dispersive spectroscopy (FEG-SEM-EDS),
X-ray photoelectron spectroscopy (XPS), Mçssbauer spectros-
copy, and high-angle annular dark-field scanning transmission
electron microscopy (HAADF-STEM).
To exclude the presence of the Cu+ valence state, the Auger
Cu LMM spectrum was acquired (Figure S2), and no evidence
of Cu+ ions was found.
The Cu content in catalyst was found to be 4.7 mol% by
AAS (Figure S1). TEM analysis of the maghemite-Cu material re-
vealed that the overall diameter of the as-synthesized NPs was
in the range 20–40 nm (Figure 3). EDS and HAADF-STEM
images of the maghemite-Cu nanocatalyst are shown in (Fig-
The powder XRD profiles of maghemite and maghemite-Cu
are depicted in Figure 1; the crystallite size of the catalyst was
determined by the Debye–Scherrer equation to be 28.7 nm,
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Figure 3. TEM images of the maghemite-Cu nanocatalyst.
ure 4a–f). The EDS profile indicates the presence of Fe and Cu
species in the catalysts clearly (Figure 4 f). Element mapping of
maghemite-Cu revealed that the Cu NPs are dispersed uni-
formly on the surface of maghemite. The element mapping of
C is not revealed because a huge amount of C exists in the
support film of the TEM grid. Cu NPs are distributed on the
surface of maghemite (Scheme 2), which is confirmed by
HAADF-STEM images (Figure 4b). The phase identification,
chemical nature, and magnetic properties were analyzed by
Mçssbauer spectroscopy. The 57Fe Mçssbauer spectra of the
studied material were measured (Figure 5) by employing
a MS2007 Mçssbauer spectrometer[31,32] that was operated at
a constant acceleration mode and equipped with a 57Co (Rh)
source. At room temperature, the Mçssbauer spectrum of the
sample shows one slightly asymmetrical sextet component
(Figure 5), for which the values of the hyperfine parameters
(Table S1) approach those reported for a gamma-phase (g-
Fe2O3) iron(III) oxide.[33,34] The distribution of the hyperfine
magnetic field (Bhf) was applied to fit the spectrum correctly
because of the non-Lorentzian profile of the Mçssbauer reso-
nant lines. This feature is typical for g-Fe2O3 nanoparticles and
implies an evolution of the collective magnetic excitations as
the nanoparticle superspin rotates around the particularly easy
axis of magnetization established by the magnetic anisotropy
of the particle.[35]
Figure 5. 57Fe Mçssbauer spectra of the maghemite-Cu nanocatalyst record-
ed a) at room temperature without an external magnetic field, b) at 5 K with
a magnetic field of 5 T. Inset in a shows the distribution of the hyperfine
magnetic field used to evaluate the room-temperature spectrum.
Furthermore, g-Fe2O3 NPs are in a magnetically blocked state
because no doublet (superparamagnetic) component is ob-
served in the spectrum and they have an average blocking
temperature higher than 300 K with respect to the timeframe
of the Mçssbauer technique (~10À8 s), which indicates that the
NPs in the system are bigger than 15 nm.[34] At a lower temper-
ature (5 K) and with the application of an external magnetic
field (low-temperature irradiation facility, LTIF; 5 T), the Mçss-
bauer spectrum of the sample is split into two sextets
(Figure 5). The first sextet that has a lower isomer shift (d) and
higher hyperfine magnetic field (Beff) represents Fe ions in the
T sites of the g-Fe2O3 spinel crys-
tal structure and the other
sextet that has a higher d and
lower Beff represents g-Fe2O3
O
sites. The hyperfine parameters
of the sextets are given in
Table S1. The isomer shifts of
both sextets fall in the range re-
ported for a high-spin (S=5/2)
Fe3+ state, and no other spectral
components are observed. The
synthesized
maghemite-Cu
nanocatalyst has a single-phase
character without any admix-
tures of iron oxide, and the
spectral ratio of T/O is close to
1:1.94, which reflects the non-
stoichiometric nature of maghe-
mite, probably because of the
occurrence of vacancies at the T
sites.[34] Under these conditions
Figure 4. HAADF-STEM images of the maghemite-Cu nanocatalyst; a) HAADF image that shows Cu at 30 nm;
b) HAADF image that shows Cu; c) HAADF image that shows Fe; d) HAADF image that shows O; e) HAADF image
that shows Cu, Fe, and O together in maghemite-Cu at 30 nm; f) EDS spectrum that indicates the presence of Cu.
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(5 K, 5 T) the two sextets are better resolved by comparing the
low-temperature spectrum with that without an external mag-
netic field as Bext adds to the Bhf value of the T and O sextets.[34]
Moreover, the second and fifth lines of both subspectra are
almost suppressed, which indicates that the atomic magnetic
moments that belong to the T and O sites almost perfectly
align to and against the direction of Bext, respectively. This im-
plies that the spin-canting phenomenon is not evolved.[34] The
analysis also revealed that the NPs in the assembly are larger
than ~10 nm as the second and fifth lines in the LTIF Mçssba-
uer spectrum (of both subspectra) are almost suppressed.
Here, the spin-canting phenomenon appears only slightly for
smaller particles in the assembly because of the particle size
distribution, which is in accordance with the utilized the hyper-
fine field distribution. The nonzero values of the quadrupole
splitting parameter (DEQ) reflect the interaction of maghemite
nanoparticles with Cu on their surface; the adsorption of Cu
probably alters the surrounding or the surface NP atoms,
which causes the electronic charge to deviate from spherical
symmetry.[36]
was elevated to 50 mg. However, there was no increase in the
yield if catalyst was added beyond this amount (Table 1, en-
tries 3, 7, and 8). The effect of temperature was also investigat-
ed. At a high temperature of 1308C, an excellent yield was ob-
tained, but no further enhancement in conversion was ob-
served at 1508C (Table 1, entries 8–10).
After the optimization of the reaction parameters, the cata-
lytic activity of the maghemite-Cu nanocatalyst was examined
for the CÀO (O-arylation) cross-coupling reaction with various
derivatives of phenols and substituted aryl iodides (Table 2).
Notably, the presence of an electron-donating group, such as
Me, OMe, and tBu, on the phenol groups at the para positions
provided good to excellent yields (Table 2, entries 2–8); where-
as comparatively lower yields were obtained because of the
steric effect at the ortho/meta position of phenols (Table 2, en-
tries 9–11). Interestingly, naphthalene homologues of phenol,
such as 2-naphthol, gave excellent yields of the corresponding
products (Table 2, entry 12). The versatility of the maghemite-
Cu nanocatalyst was also explored for the S- and N-arylation of
substituted thiophenol, aniline, imidazole, thiophenols, indole,
and pyrazole with aryl iodide (Table 3). We observed that
phenyl iodide with an electron-withdrawing group (NO2) at the
para position gave excellent yields (Table 3, entries 1–6),
whereas an electron-donating group (Me) at the para position
gave low to moderate yields (Table 3, entries 7–9). Further-
more, the N-arylation of aniline, indole, pyrrole, and imidazole
with iodobenzene gave good yields of the corresponding cou-
pled products (Table 3, entries 10–14).
Herein, the catalytic efficiency of the maghemite-Cu nanoca-
talyst was investigated using 4-hydroxytoluene (1a) and iodo-
benzene (2a) as model substrates (Table 1). The effect of vari-
Table 1. Optimization of reaction.[a]
The recovery and reusability of a catalyst are the two impor-
tant factors that need to be evaluated, thus the recyclability of
the maghemite-Cu nanocatalyst was examined in the reaction
of 4-hydroxyphenol and phenyl iodide under identical opti-
mized experimental conditions. In each cycle, the catalyst was
separated magnetically, washed with ethanol, and dried at
608C under vacuum to remove residual solvents. The yields
were 94, 93, 93, 92, 90, and 88% from the first to the sixth
cycle, respectively. The FTIR spectra of the fresh and recycled
catalysts (after the sixth run) were very similar (Figure S3). This
means that the efficiency of the catalyst is unaltered during
the reaction, hence the maghemite-Cu nanocatalyst is
a benign catalyst in terms of recovery and recyclability. We
also performed a leaching study of Cu metal by AAS, and the
results revealed that the concentration of Cu in the filtrate was
negligible (<0.1 ppm). Additionally, UV/Vis spectroscopic stud-
ies showed no absorption peak of Cu metal in the supernatant
of the reaction mixture (data not shown).The reason behind
the decrease in yield could be explained in terms of the con-
glomeration and aggregation of the Cu nanocatalyst into large
particles. This result showed that there was barely any change
in the amount of Cu compared with that of the fresh catalyst.
A proposed mechanism is illustrated in Figure 6. The reaction
is assumed to occur through oxidative addition followed by re-
ductive elimination. Initially, the nucleophile adds to the ma-
ghemite-Cu nanocatalyst to form complex I, which reacts oxi-
datively with ArÀX to form complex II, and this intermediate fi-
nally bestows the desired product III by reductive elimination
in the presence of base.[37]
Entry Base
Solvent [mL] Catalyst [mg] T [8C] t [h] Yield [%]
1
Na2CO3 DMF
K2CO3 DMF
80
130
130
130
130
130
130
130
130
90
24
24
24
24
24
48
24
24
24
24
31
58
2
3
4
5
6
7
8
9
10
80
Cs2CO3 DMF
Cs2CO3 Toluene
Cs2CO3 DMSO
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
Cs2CO3 DMF
80
94
80
63
80
84
no catalyst
trace
80
94
67
94
40
50
50
50
150
[a] Reaction conditions: 4-hydroxytoluene (1 mmol), iodobenzene
(1 mmol), base (2 equiv.), solvent (3 mL), maghemite-Cu (40–80 mg; 2.9–
5.9 mol%), 1308C, 24 h, N2 atmosphere.
ous important parameters such as the amount of catalyst, tem-
perature, solvent, and base were investigated to obtain an op-
timum reaction profile for the cross-coupling reaction. Notably,
cesium carbonate was the best base with maghemite-Cu com-
pared to potassium carbonate and sodium carbonate in DMF
at 1308C under N2 and gave the desired product selectively in
94% yield (Table 1, entries 1–3 and 8). The coupling reaction
also worked well in other organic solvents, which included
DMSO and toluene, but DMF appeared to be the best (Table 1,
entries 3–5). Control experiments confirmed that no conversion
occurred without catalyst even after 48 h of reaction (Table 1,
entry 6). The highest yield was attained if the catalyst loading
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a simple impregnation procedure without the use of
cumbersome linkers or ligands. Furthermore, the
cross-coupling reactions proceeded successfully and
were convincingly superior in terms of yield. This
may be attributed to the nanometer size of the ma-
ghemite solid support material, which allowed the
immobilization of a high amount of complex and
enhanced the dispersion of the catalytically active
sites in the reaction medium and thus improved
their accessibility to the substrate. In addition, a hot
filtration test was performed, which suggested that
the nanocatalyst catalyzes the cross-coupling reac-
tion in a truly heterogeneous manner. Thus, the sali-
ent features of the catalyst lie in its simplicity, eco-
nomic feasibility, liberty from complex ligands, and
excellent yields without the need for traditional fil-
tration, which makes it an attractive and sustainable
option.
Table 2. Maghemite-Cu catalyzed CÀO cross-coupling (O-arylation) of substituted
phenols with derivatives of iodobenzene.[a]
Entry
1
Aryl iodide
Phenol
Product
Yield[b] [%]
87
2
3
4
5
6
7
8
94
99
98
99
99
98
99
Experimental Section
Powder XRD patterns of iron oxide samples were re-
corded at RT by using an X’Pert PRO MPD diffractome-
ter (PANalytical) in Bragg–Brentano geometry with iron-
filtered CoKa radiation (40 kV, 30 mA, l=0.1789 nm)
and equipped with an X’Celerator detector, programma-
ble divergence, and diffracted beam antiscatter-slits.
The angular range of measurement was set as 2q=10–
1058 with a step size of 0.0178. The crystalline phases in
the experimental XRD patterns were identified by using
the X’Pert High Score Plus software that includes a PDF-
4+ and ICSD databases. (Sample preparation: grinding
if needed and compression in the sample holder with
a flat glass. The sample area in the sample holder is
ꢀ2 cm2). TEM images were obtained by using a Hitachi
H8100 microscope with a ThermoNoran light elements
EDS detector and
a charge-coupled device (CCD)
9
88
camera for image acquisition. The maghemite-Cu fine
powder was placed on a carbon stub, and the images
were recorded at 5–15 kV by using a large-field detector
(LFD) under low vacuum. Elemental analysis was per-
formed by using a light elements EDS detector from
Oxford. The maghemite-Cu powder was spread on
a double-sided carbon tape and analyzed using an ac-
celeration voltage of 25 kV. Microscopic images were
obtained by using a HRTEM TITAN 60–300 with X-FEG-
type emission gun that was operated at 80 kV. The
point resolution is better than 0.08 nm in TEM mode. El-
emental mapping was obtained by STEM-EDS with an
acquisition time of 20 min. Sample preparation: The
powder samples were dispersed in ethanol and ultraso-
nicated for 5 min. One drop of this solution was placed
on a copper grid with a holey carbon film. The sample
was dried at RT. For surface investigation, a PHI 5000
10
11
12
36
13
93
[a] Reaction conditions: phenol (1 mmol), aryl iodide (1 mmol), Cs2CO3 (2 equiv.), DMF
(3 mL), maghemite-Cu (50 mg), 1308C, 24 h, N2 atmosphere. [b] GC–MS yield.
VersaProbe II XPS system (Physical Electronics) with monochromat-
ic AlKa source (15 kV, 50 W) and photon energy of 1486.7 eV was
employed. Dual-beam charge compensation was used for all meas-
urements. All the spectra were measured under a vacuum of 1.6”
10À7 Pa at RT (228C). The survey spectra was measured with a pass
energy of 187.850 eV and an electronvolt step of 0.8 eV, whereas
a pass energy of 23.500 eV and electronvolt step of 0.2 eV were
Conclusions
We have prepared a viable, versatile, ligand-free, and magneti-
cally separable heterogeneous maghemite-Cu nanocatalyst for
different types of CÀO, CÀN, and CÀS cross-coupling reactions.
This catalyst was prepared from inexpensive precursors using
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used for the high-resolution spectra. Dual-beam charge
compensation was set up for all measurements. The
spectra were evaluated by using the MultiPak (Ulvac -
PHI, Inc.) software. All BE values were referenced to the
C1s carbon peak at BE=284.80 eV.
Table 3. Maghemite-Cu catalyzed CÀS and CÀN cross-coupling (N- and S-arylation) of
thiophenol, aniline, indole, imidazole, and pyrrole with substituted iodobenzenes.[a]
Catalyst preparation
Entry
1
Aryl halide
PhenylÀNuÀH
Product
Yield[b] [%]
98
Preparation of maghemite (g-Fe2O3)
Typically, FeSO4·7H2O (6.06 g, 21.79 mmol) and
FeCl3·6H2O (11.75 g, 45.08 mmol) were dissolved in de-
ionized water (100 mL, previously degassed with N2)
under a N2 atmosphere. The resulting mixture was
stirred for 15 min and heated at 608C under vigorous
stirring. When the temperature reached 608C, aqueous
NH4OH (25 mL, 25–28% w/w) was added dropwise,
a black precipitate formed immediately, and heating
was continued for 2 h under a N2 atmosphere. After vig-
orous stirring for 2 h, the precipitate was separated
magnetically and washed thoroughly with water until
the supernatant liquor reached neutrality. The obtained
material was dried in an oven at 1008C for 12 h, and
75% yield of maghemite was obtained.
2
3
99
98
4
5
6
7
8
98
97
99
50
67
Preparation of maghemite-Cu nanocatalyst
Maghemite (2 g) and CuCl2 (for 5 wt% of Cu on maghe-
mite) were stirred at RT in aqueous solution (50 mL) for
1 h. After impregnation, the suspension was adjusted to
pH 12–13 by adding sodium hydroxide (1.0m) and fur-
ther stirred for 20 h. The solid was collected and
washed with distilled water (5”20 mL). The resulting
maghemite-Cu NPs were sonicated for 10 min, washed
with distilled water and subsequently with ethanol, and
dried under vacuum at 608C for 24 h. The Cu content
was found to be 4.7% using AAS.
9
77
99
98
Experimental procedure for the cross-coupling (CÀ
O, CÀN, CÀS) reactions catalyzed by the maghe-
mite-Cu nanocatalyst
10
11
In an oven-dried 10 mL round-bottomed flask, aryl
iodide (1 mmol), phenol/imidazole/aniline/thiophenol/
pyrrole (1 mmol), and Cs2CO3 (2 equiv.) were stirred in
DMF (3 mL), and the catalyst (50 mg) was added under
N2. The resulting mixture was stirred at 1308C in an oil
bath for 24 h. The progress of reaction was monitored
by TLC and GC–MS. After the completion of the reac-
tion, the catalyst was recovered with an external
magnet and then washed with ethanol and water. The
obtained catalyst was dried under vacuum at 608C and
reused in the next run. The reaction mixture was diluted
with water and extracted by ethyl acetate (3”30 mL).
The combined organic layers were dried over anhydrous
Na2SO4 and analyzed by GC–MS.
12
13
14
99
82
99
Acknowledgements
[a] Reaction conditions: nucleophile (1 mmol), aryl iodide (1 mmol), Cs2CO3 (2 equiv.),
DMF (3 mL), maghemite-Cu (50 mg), 1308C, 24 h, N2 atmosphere. [b] GC–MS yield.
R.G. expresses her gratitude to the University Grand
Commission, Delhi, India for the award of junior re-
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2767; f) B. Liu, W. Zhang, F. Yang, H. Feng, X. Yang, J. Phys. Chem. C
2011, 115, 15875–15884.
[7] a) S. Shylesh, V. Schünemann, W. R. Thiel, Angew. Chem. Int. Ed. 2010,
49, 3428–3459; Angew. Chem. 2010, 122, 3504–3537; b) V. Polshettiwar,
R. Luque, A. Fihri, H. Zhu, M. Bouhrara, J. M. Basset, Chem. Rev. 2011,
111, 3036–3075; c) R. N. Baig, R. S. Varma, Chem. Commun. 2013, 49,
752–770; d) D. Zhang, C. Zhou, Z. Sun, L.-Z. Wu, C.-H. Tung, T. Zhang,
Nanoscale 2012, 4, 6244–6255; e) H. Song, Acc. Chem. Res. 2015, 48,
491–499.
[8] S. R. Kale, S. S. Kahandal, M. B. Gawande, R. V. Jayaram, RSC Adv. 2013, 3,
8184–8192.
[9] M. B. Gawande, P. S. Branco, R. S. Varma, Chem. Soc. Rev. 2013, 42,
3371–3393.
[10] R. B. N. Baig, R. S. Varma, Chem. Commun. 2012, 48, 2582–2584.
[11] B. R. Vaddula, A. Saha, J. Leazer, R. S. Varma, Green Chem. 2012, 14,
2133–2136.
[12] A. Rezaeifard, M. Jafarpour, P. Farshid, A. Naeimi, Eur. J. Inorg. Chem.
2012, 5515–5524.
[13] P.-H. Li, B.-L. Li, Z.-M. An, L.-P. Mo, Z.-S. Cui, Z.-H. Zhang, Adv. Synth.
Catal. 2013, 355, 2952–2959.
[14] a) B. C. Ranu, R. Dey, T. Chatterjee, S. Ahammed, ChemSusChem 2012, 5,
22–44; b) S. V. Ley, A. W. Thomas, Angew. Chem. Int. Ed. 2003, 42, 5400–
5449; Angew. Chem. 2003, 115, 5558–5607; c) P. F. Larsson, A. Correa, M.
Carril, P. O. Norrby, C. Bolm, Angew. Chem. Int. Ed. 2009, 48, 5691–5693;
Angew. Chem. 2009, 121, 5801–5803.
[15] a) G. Evano, N. Blanchard, M. Toumi, Chem. Rev. 2008, 108, 3054–3131;
b) G. Evano, C. Theunissen, A. Pradal, Nat. Prod. Rep. 2013, 30, 1467–
1489; c) F. Hervµs, G. Morreale de Escobar, F. Escobar del Rey, Endocrinol-
Figure 6. Proposed reaction mechanism.
search fellowship. Also, thanks are given to USIC-CLF, University
of Delhi. The authors acknowledge support from the Ministry of
Education, Youth and Sports of the Czech Republic (LO1305) and
by the Operational Program Education for Competitiveness - Eu-
ropean Social Fund (project CZ.1.07/2.3.00/30.0041 and CZ.1.07/
2.4.00/31.0189) of the Ministry of Education, Youth and Sports of
the Czech Republic. M.P. gratefully acknowledges the financial
ˇ
ˇ
ˇ
ˇ
ˇ
ogy 1976, 98, 77–83; d) M. Kozˇísek, J. Bray, P. Rezµcovµ, K. Saskovµ, J.
Brynda, J. Pokornµ, J. Konvalinka, J. Mol. Biol. 2007, 374, 1005–1016.
[16] a) J. Hassan, M. Sevignon, C. Gozzi, E. Schulz, M. Lemaire, Chem. Rev.
2002, 102, 1359–1470; b) S. V. Ley, A. W. Thomas, Angew. Chem. Int. Ed.
2003, 42, 5400–5449; Angew. Chem. 2003, 115, 5558–5607; c) M. E.
Jung, D. Jachiet, J. C. Rohtoff, Tetrahedron Lett. 1989, 30, 4211–4214;
d) R. K. Gujadhur, C. G. Bates, D. Venkataraman, Org. Lett. 2001, 3, 4315–
4317; e) C. Palomo, M. Oiarbide, R. Lopez, E. Gomez-Bengoa, Chem.
Commun. 1998, 2091–2092.
´
support from the internal student grant IGA of Palacky University
in Olomouc, Czech Republic, (IGA-PrF-2015-017).
[17] a) R. A. Widenhoefer, H. A. Zhong, S. L. J. Buchwald, J. Am. Chem. Soc.
1997, 119, 6787–6795; b) J. P. Wolfe, J. F. Marcoux, S. L. Buchwald, Acc.
Chem. Res. 1998, 31, 805–818; c) D. Zim, S. L. Buchwald, Org. Lett. 2003,
5, 2413–2415; d) M. C. Harris, X. Huang, S. L. Buchwald, Org. Lett. 2002,
4, 2885–2888; e) J. P. Wolfe, H. Tomori, J. P. Sadighi, J. Yin, S. L. Buch-
wald, Org. Chem. 2000, 65, 1158–1174; f) S. I. Kuwabe, K. E. Torraca, S. L.
Buchwald, J. Am. Chem. Soc. 2001, 123, 12202–12206.
[18] a) J. F. Hartwig, Acc. Chem. Res. 1998, 31, 852; b) J. F. Hartwig, Angew.
Chem. Int. Ed. 1998, 37, 2046–2067; Angew. Chem. 1998, 110, 2154–
2177; c) G. Mann, C. Incarvito, A. L. Rheingold, J. F. Hartwig, J. Am. Chem.
Soc. 1999, 121, 3224–3225.
[19] a) D. A. Evans, J. L. Katz, T. R. West, Tetrahedron Lett. 1998, 39, 2937–
2940; b) C. Decicco, P. S. Song, D. A. Evans, Org. Lett. 2001, 3, 1029–
1032.
[20] D. M. T. Chan, K. L. Monaco, R. Wang, M. P. Winters, Tetrahedron Lett.
1998, 39, 2933–2936.
[21] a) A. Aranyos, D. W. Old, A. Kiyomori, J. P. Wolfe, J. P. Sadighi, S. L. Buch-
wald, J. Am. Chem. Soc. 1999, 121, 4369–4378; b) D. Ma, Q. Cai, H.
Zhang, Org. Lett. 2003, 5, 2453–2455.
[22] a) G. A. Molander, L. Jean-GØrard, J. Org. Chem. 2009, 74, 1297–1303;
b) G. A. Molander, T. Ito, Org. Lett. 2001, 3, 393–396; c) S. Sueki, Y. Kuni-
nobu, Org. Lett. 2013, 15, 1544–1547.
[23] a) H. Z. Yu, Y. Y. Jiang, Y. Fu, L. Liu, J. Am. Chem. Soc. 2010, 132, 18078–
18091; b) D. Ma, Q. Cai, Org. Lett. 2003, 5, 3799–3802; c) C. T. Yang, Y.
Fu, Y. B. Huang, J. Yi, Q. X. Guo, L. Liu, Angew. Chem. Int. Ed. 2009, 48,
7398–7401; Angew. Chem. 2009, 121, 7534–7537; d) F. Y. Kwong, S. L.
Buchwald, Org. Lett. 2003, 5, 793–796; e) F. Y. Kwong, A. Klapars, S. L.
Buchwald, Org. Lett. 2002, 4, 581–584.
[24] a) M. Hosseini-Sarvari, Z. Razmi, RSC Adv. 2014, 4, 44105–44116; b) H.
Joshi, K. N. Sharma, A. K. Sharma, A. K. Singh, Nanoscale 2014, 6, 4588–
4597; c) Z. Jiang, J. She, X. Lin, Adv. Synth. Catal. 2009, 351, 2558–2562.
[25] a) P. Zhang, J. Yuan, H. Li, X. Liu, X. Xu, M. Antonietti, Y. Wang, RSC Adv.
2013, 3, 1890–1895; b) K. Swapna, S. N. Murthy, M. T. Jyothi, Y. V. D. Na-
geswar, Org. Biomol. Chem. 2011, 9, 5978–5988; c) N. Salam, S. K.
Keywords: copper · cross-coupling · heterogeneous catalysis ·
magnetism · sustainable chemistry
[1] a) R. S. Varma, Green Chem. 2014, 16, 2027–2041; b) Z. Guo, B. Liu, Q.
Zhang, W. Deng, Y. Wang, Y. Yang, Chem. Soc. Rev. 2014, 43, 3480–
3524; c) R. Hudson, Y. Feng, R. S. Varma, A. Moores, Green Chem. 2014,
16, 4493–4505.
[2] a) M. B. Gawande, R. Luque, R. Zboril, ChemCatChem 2014, 6, 3312–
3313; b) D. Wang, D. Astruc, Chem. Rev. 2014, 114, 6949–6985; c) R. K.
Sharma, Y. Monga, A. Puri, G. Gaba, Green Chem. 2013, 15, 2800–2809;
d) K. V. Ranganath, J. Kloesges, A. H. Schäfer, F. Glorius, Angew. Chem.
Int. Ed. 2010, 49, 7786–7789; Angew. Chem. 2010, 122, 7952–7956.
[3] a) I. I. Slowing, B. G. Trewyn, S. Giri, V. S. Y. Lin, Adv. Funct. Mater. 2007,
17, 1225–1236; b) I. I. Slowing, J. L. Vivero-Escoto, B. G. Trewyn, V. S. Y.
Lin, J. Mater. Chem. 2010, 20, 7924–7937; c) M. Pagliaro, R. Ciriminna, G.
Palmisano, J. Mater. Chem. 2009, 19, 3116–3126; d) J. M. Rosenholm, C.
Sahlgren, M. Linden, Nanoscale 2010, 2, 1870–1883.
[4] a) S. Chaturvedi, P. N. Dave, N. K. Shah, J. Saudi Chem. Soc. 2012, 16,
307–325; b) K. H. Park, K. Jang, S. U. Son, D. A. Sweigart, J. Am. Chem.
Soc. 2006, 128, 8740–8741.
[5] a) R. K. Sharma, A. Pandey, S. Gulati, A. Adholeya, Chem. Eng. J. 2012,
210, 490–499; b) R. K. Sharma, A. Pandey, S. Gulati, A. Adholeya, J.
Hazard. Mater. 2012, 209, 285–292; c) R. K. Sharma, Y. Monga, Appl.
Catal. A 2013, 454, 1–10.
[6] a) J. E. Mondloch, Q. Wang, A. I. Frenkel, R. G. Finke, J. Am. Chem. Soc.
2010, 132, 9701–9714; b) S. Miao, C. Zhang, Z. Liu, B. Han, Y. Xie, S.
Ding, Z. Yang, J. Phys. Chem. C 2008, 112, 774–780; c) S. Ko, J. Jang,
Angew. Chem. Int. Ed. 2006, 45, 7564–7567; Angew. Chem. 2006, 118,
7726–7729; d) S. C. Tsang, V. Caps, I. Paraskevas, D. Chadwick, D.
Thompsett, Angew. Chem. Int. Ed. 2004, 43, 5645–5649; Angew. Chem.
2004, 116, 5763–5767; e) M. Zhu, G. Diao, Nanoscale 2011, 3, 2748–
ChemCatChem 2015, 7, 3495 – 3502
www.chemcatchem.org
3501
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
Kundu, A. S. Roy, P. Mondal, S. Roy, A. Bhaumik, S. M. Islam, Catal. Sci.
Technol. 2013, 3, 3303–3316; d) J. Mondal, A. Modak, A. Dutta, A. Bhau-
mik, Dalton Trans. 2011, 40, 5228–5235; e) H. J. Xu, Y. F. Liang, X. F.
Zhou, Y. S. Feng, Org. Biomol. Chem. 2012, 10, 2562–2568; f) D. Saberi,
M. Sheykhan, K. Niknam, A. Heydari, Catal. Sci. Technol. 2013, 3, 2025–
2031; g) M. Wang, B. Yuan, T. Ma, H. Jiang, Y. Li, RSC Adv. 2012, 2, 5528–
5530; h) S. L. Buchwald, C. Bolm, Angew. Chem. Int. Ed. 2009, 48, 5586–
5587; Angew. Chem. 2009, 121, 5694–5695.
Kadam, D. K. Murade, S. B. Bhorkade, M. B. Gawande, ACS Sustainable
Chem. Eng. 2014, 2, 1699–1706.
ˇ
ˇ
ˇ
[31] J. Pechousek, D. Jancík, J. Frydrych, J. Navarík, P. Novµk, AIP Conf. Proc.
2012, 1489, 186–193.
ˇ
ˇ
[32] J. Pechousek, R. Prochazka, D. Jancík, J. Frydrych, M. Mashlan, J. Phys.
Conf. Ser. 2010, 217, 012006.
ˇ
ˇ
ˇ
ˇ
ˇ
[33] J. Tucek, P. Tucek, J. Cuda, J. Filip, J. Pechousek, L. Machala, R. Zboril,
AIP Conf. Proc. 2012, 1489, 56–74.
ˇ
[26] a) B. H. Lipshutz, D. M. Nihan, E. Vinogradova, B. R. Taft, Z. V. Boskovic,
Org. Lett. 2008, 10, 4279–4282; b) A. K. Gupta, G. Tirumaleswara Rao,
K. N. Singh, Tetrahedron Lett. 2012, 53, 2218–2221.
[27] a) M. B. Gawande, S. N. Shelke, R. Zboril, R. S. Varma, Acc. Chem. Res.
2014, 47, 1338–1348; b) M. B. Gawande, A. K. Rathi, I. D. Nogueira, R. S.
[34] J. Tucek, R. Zboril, D. Petridis, J. Nanosci. Nanotechnol. 2006, 6, 926–
947.
ˇ
ˇ
ˇ
[35] J. Tucek, L. Machala, J. Frydrych, J. Pechousek, R. Zboril in Mçssbauer
Spectroscopy: Applications in Chemistry, Biology, and Nanotechnology
(Eds.: V. K. Sharma, G. Klingelhofer, T. Nishida), Wiley, 2013, pp. 351–
392.
ˇ
Varma, P. S. Branco, Green Chem. 2013, 15, 1895–1899; c) A. Panµcek, R.
Prucek, J. Hrbac, T. Nevecna, J. Steffkova, R. Zboril, L. Kvitek, Chem.
Mater. 2014, 26, 1332–1339.
[36] N. N. Greenwood, T. C. Gibb, Mçssbauer Spectroscopy, Chapman&Hall
Ltd., London, 1971.
[28] M. B. Gawande, A. K. Rathi, P. S. Branco, I. D. Nogueira, A. Velhinho, J. J.
Shrikhande, U. U. Indulkar, R. V. Jayaram, C. A. A. Ghumman, N. Bundale-
ski, O. M. N. D. Teodoro, Chem. Eur. J. 2012, 18, 12628–12632.
[29] M. B. Gawande, V. D. B. Bonifacio, R. S. Varma, I. D. Nogueira, N. Bundale-
ski, C. A. A. Ghumman, O. M. N. D. Teodoro, P. S. Branco, Green Chem.
2013, 15, 1226–1231.
[37] a) L. Rout, S. Jammi, T. Punniyamurthy, Org. Lett. 2007, 9, 3397–3399;
b) B. Sreedhar, R. Arundhathi, P. L. Reddy, M. L. Kantam, J. Org. Chem.
2009, 74, 7951–7954.
Received: May 16, 2015
Revised: July 13, 2015
[30] a) M. C. Biesinger, L. W. M. Lau, A. R. Gerson, R. S. C. Smart, Appl. Surf.
Sci. 2010, 257, 887–898; b) S. N. Shelke, S. R. Bankar, G. R. Mhaske, S. S.
Published online on September 17, 2015
ChemCatChem 2015, 7, 3495 – 3502
www.chemcatchem.org
3502
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim