Copper-Schiff base alumoxane: A new and reusable mesoporous nano catalyst for Suzuki-Miyaura and Stille C-C cross-coupling reactions

Article abstract of DOI:10.1039/c6ra19725f

Herein for the first time, a mesoporous copper nano catalyst (SBA-Cu²⁺) were simply synthesized through immobilization of Cu²⁺ on surface of Schiff base alumoxane support. This nano catalyst was characterized by various techniques such as FT-IR, X-ray map, TG-DTA, BET, SEM, SEM-EDS, TEM, ICP-OES and XRD. The characterization results indicated that SBA-Cu²⁺ nanoflakes with 331.47 m² g^-1 specific surface area are thermally stable up to 306 °C. The SBA-Cu²⁺ nano catalysts showed significant activity for Suzuki-Miyaura and Stille cross-coupling reactions with good efficiency and reusability. In addition, the nanocatalyst could be recovered and reused several times without significant loss of its catalytic activity. Copper leaching from SBA-Cu²⁺ is very negligible for this coupling reaction.

Full text of DOI:10.1039/c6ra19725f

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: A. Ghorbani-
Choghamarani, M. Hajjami, A. A. Derakhshan and L. Rajabi, RSC Adv., 2016, DOI: 10.1039/C6RA19725F.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Please do not adjust margins
RSC Advances
Page 1 of 11
View Article Online
DOI: 10.1039/C6RA19725F
RSC Advanced
Paper
Received 00th January
20xx,
Copper-Schiff base alumoxane: a new and reusable mesoporous
nano catalyst for Suzuki–Miyaura and Stille C-C cross-coupling
reactions
Arash Ghorbani-Choghamarani,a* Ali Ashraf Derakhshan,a Maryam Hajjamia and Laleh Rajabib
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Herein for the first time, a mesoporous copper nano catalyst (SBA-Cu2+) were simply synthesized through immobilization of
Cu2+ on surface of Schiff base alumoxane support. This nano catalyst was characterized by various techniques such as FT-
IR, X-ray Map, TG-DTA, BET, SEM, SEM-EDS, TEM, ICP-OES and XRD. The characterization results indicated that SBA-Cu2+
nanoflakes with 331.47 m2 g-1 specific surface area are thermally stable up to 306 °C. The SBA-Cu2+ nano catalysts showed
significant activity for Suzuki-Miyaura and Stille cross-coupling reactions with good efficiency and reusability. In addition,
the nanocatalyst could be recovered and reused several times without significant loss of its catalytic activity. Copper
leaching from SBA-Cu2+ is very negligible for this coupling reaction.
efficient nano catalysts based on Cu is necessary. In this way,
the use of novel materials as a catalyst support is inevitable.
Immobilization of Cu species on solid supports in
1. Introduction
C–C bond construction is one of the most important chemical
transformations which can be used in the production of many
man-made products [1]. Over past decades, The Suzuki-
Miyaura and Stille cross-coupling reactions have been utilized
as powerful methodologies in C(sp2)–C(sp2) bond formation
[2]. In this field, the homogeneous palladium as the most
suitable and widely used catalyst has shown high yields, good
selectivity and convenient turnover numbers [3].
heterogeneous catalysts facilitates separation, minimizing
contamination and reusability of expensive catalysts. In order
to preparation of heterogeneous catalysts, various solid
supports including polymers, zeolites, silica, carbon nanotubes
and metal-organic frameworks (MOFs) have been utilized [11].
The nature of supports can influence the selectivity and
reactivity of the catalyst, therefore careful choice of supports
can be led to creation of new heterogeneous catalysts. As a
new suggestion, the carboxylate-alumoxane is a versatile
compound which can be introduce as a novel support for
heterogeneous catalysts. Carboxylate alumoxanes with general
formula [Al(O)x(OH)y(O2CR)z]n, 2x+y+z=3 are prepared from the
reaction of boehmite (γ-AlOOH) and carboxylic acids. The
surface of the alumoxanes is covered with covalently bound
carboxylate groups. The physical and chemical properties of
the alumoxane can be affected by the type of carboxylic acid,
and range from water soluble powders to hard solids that are
resistant to acids, bases and organic solvents [12, 13]. As a
precursor for alumoxane synthesis, Boehmite is a metastable
phase of Aluminium oxide with oxide-hydroxide bonds which
commonly used as supporting matrix [14, 15]. The advantages
of alumoxane as a catalyst support are included the low price
of boehmite and the availability of an almost infinite range of
carboxylic acids [16]. The only report on the catalytic used of
alumoxane were related to Zirconocene complex supported on
para-hydroxybenzoate-alumoxane (PHBA) as novel catalyst for
Despite the widespread applications as
a catalyst, the
homogeneous Pd complexes have the limiting aspects such as
toxicity and high price which led to limitation of them on
industrial scale applications [4]. As a viable alternative for Pd,
recently copper-based catalysts have attracted much attention
due to their biocompatibility and lower price as well as their
catalytic aptitude for cross-coupling reactions [5]. Despite
these advantages, only a few Suzuki or Stille reactions
involving copper catalyzed cross-coupling have been reported.
These copper based catalysts are including Cu/Schiff-
base@Fe3O4 [6], Cu nano colloid [7], 3D MOF {[Cu(4-
tba)2](solvent)}n [8], Cu@molecular sieve [9] and Pd-
Cu@Carbon [10]. Thus, to expand the copper catalyzed Suzuki
or Stille coupling reactions, the development of new and
This journal is © The Royal Society of Chemistry 20xx
RSC Adv., 2016, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 2 of 11
View Article Online
DOI: 10.1039/C6RA19725F
Paper
RSC Advances
olefin polymerization [17]. Nevertheless, there is no significant especially for C-C coupling reactions.
works about application of alumoxanes in the catalysis field
carboxylate bonds [12,18]. The Schiff base shows the C=N
vibrations in the
Currently there is no report about using the alumoxane
supports for Suzuki-Miyaura and Stille reactions.
In order to prepare new alumoxane catalysts, Schiff bases
ligands can play an important role in complexing of metal
cations on alumoxane surface. Therefore the using of
carboxylic Schiff-base molecules in the synthesis of alumoxane
can be led to formation of novel catalyst support. In this work
for the first time we report the successful synthesis of Copper-
Alumoxane nano catalyst through immobilization of Cu2+ on
Schiff-base alumoxane and using them as a new nanocatalyst
for the Suzuki-Miyaura and Stille coupling reaction (Fig. 1).
2. Results and discussion
2.1 Catalyst characterization
2.1.1. FT-IR analysis
In order to characterization of molecular structure of organic-
inorganic materials, FT-IR spectroscopy can be used as an
adequate technique. The FT-IR spectra of the Bo, SBA and SBA-
Cu2+ are provided in Fig. 2. In the Boehmite spectrum (Fig. 2a),
the stretching vibration of Al–OH has shown two strong peaks
at 3092 and 3316 cm−1. Also the hydrogen bands between Al–
OH groups have shown the two peaks (1071 and 1166 cm-1)
related to the symmetrical bending vibrations. As well as the
three peaks of 482, 615 and 741 cm-1 are related to the
vibrational modes of Al–O–Al [14]. The two absorption peaks
of 1385 and 1637 cm-1 are due to the stretching vibration of
the NO3- impurity and absorbed water in the boehmite
structure, respectively.
In the spectrum of SBA (Fig. 2b), there are several peaks in
1200-
1800 cm-1 region which are indicated formation of
carboxylate-alumoxane through the covalent bonding between
Bo and SB. The two absorption peaks in 1560 and 1492 cm-1
are related to the asymmetrical and symmetrical stretching
vibrations of bidentate carboxylate groups, respectively. As
well as the frequency of 1626 cm-1 is due to unidentate
frequency of 1663 cm-1 while phenolic C-O stretching
vibrations are observed at 1282 cm-1. Also the two frequencies
at 1600 and 1417 cm-1 are due to the vibrations of sp2 C=C in
the benzene rings [19]. In the spectrum of SBA-Cu2+ (Fig. 2c),
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 3 of 11
View Article Online
DOI: 10.1039/C6RA19725F
RSC Advances
decreasing in intensity of C=N peak (1663 cm-1) is referred to 2.1.3. X-ray diffraction
ARTICLE
chelation of Cu2+ by SBA ligands. It seems that chelation The X-ray diffraction patterns of Bo, SBA and SBA-Cu2+ are shown in
caused to reduce in bond vibrations. Also to increase in peak Fig. 4. The low angle XRD patterns (Fig. 4a) only for SBA-Cu2+
of 1560 cm-1 can be due to
revealed a single intense peak corresponding (100) plan. The other
peaks
Table 1. Surface properties of SBA-Cu2+ and boehmite
precursor
Specific surface
area [m2 g-1]
Specific pore
Pore diameter
[nm]
volume [cm3 g-1]
Sample
Vtot
(BET)
V
(BJH)
D
(BJH)
SBET
SBJH
Dav
Boehmite
SBA-Cu2+
2.28
2.48
0.0125 0.0125
22
1.21
1.64
331.47 397.13 0.8217 0.8404
9.91
Fig. 3. N2 adsorption–desorption isotherms and the corresponding
pore size distributions for boehmite nanoparticles (a and b) and
SBA-Cu2+ (c and d).
vibration of acetate ligand which connected to the Cu2+ [19]. It
seems that some of the Al-OH groups in boehmite
nanoparticles cannot be reacted with Schiff base SB. Because
the boehmite index peaks in SBA and SBA-Cu2+ spectra have
been existence. According to the literature [19], the stretching
frequencies of Cu-O and Cu-N emerge at 431–455 and 555–
470 cm−1 for Cu-Schiff base complex. But in the SBA-Cu2+,
these stretching peaks have covered with overlapping of Al-O-
Al stretching modes in the range of 400-800 cm-1.
2.1.2. Specific surface area analysis
The N2 adsorption-desorption isotherms, BET surface area and pore
volume of the Bo precursor and SBA-Cu2+ are shown in Fig. 3. It can
be seen from Fig. 3a and Fig. 3c, both of them show type-IV
isotherm (defined by IUPAC), which are characterized as
mesoporous materials. In Fig. 3 b and Fig. 3d, the pore size
distributions are shown micro and meso porosity in the Bo and SBA-
Cu2+ which there is reducing in pore size for SBA-Cu2+ versus Bo.
Table 1 is presented all data attained by Brunauer–Emmett–Teller
(BET) and Barrett–Joyner–Halenda (BJH) methods. The specific
surface area (SBET) for Bo precursor is 2.28 m2 g-1, with 22 nm
average pore diameter and a specific pore volume of 0.0125 cm3 g-
1. Despite of our expectation, Boehmite nano particles (Bo) have
shown the very low surface area, which can be due to sever
agglomeration among them. In return, SBA-Cu2+ with the specific
surface area (SBET) of 331.47 m2 g-1 and average pore diameter 9.91
nm has shown a specific pore volume of 0.8217 cm3 g-1. It seems
that alumoxane formation is caused to reduce in extent of
agglomeration and increasing of surface area. The Dav for boehmite
(Bo) and SBA-Cu2+ illustrated meso porosity while DBJH values
showed the micro porosity for them.
Fig. 4. The low angle (a) and wide angle (b) XRD patterns of Bo,
SBA and SBA-Cu2+
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 4 of 11
View Article Online
DOI: 10.1039/C6RA19725F
Paper
RSC Advances
corresponding to (110), (200) and (210) planes have shown low
intensities. Therefore, these results indicate a characteristic of
hexagonal order for SBA-Cu2+ while Bo and SBA have not shown
hexagonal order. It seems that Cu2+ induced the hexagonal ordering
to the SBA structure through Schiff base chelation.
The wide angle XRD pattern of Bo (Fig. 4b) indicates broad peaks at
2ϴ=14°, 28.1°, 38.5°, 45.7°, 49.2°, 51.2°, 55.2°, 61°, 64.3°, 67°, 68.3°,
Fig. 5. SEM images of (a) Bo, (b) SBA, (c) SBA-Cu2+ and (d)
schematically morphology of them
72° and 81° which can be attributed to the orthorhombic unit cell of
boehmite γ-AlOOH (JCPDS card 21-1307). The Low intensity and
broadening peaks shows that Bo nanoparticles had low crystallinity.
Just like Bo, the XRD pattern of SBA (Fig. 4b) revealed the same
diffraction lines but sharper and more intense than Bo. This may be
due to inadequate functionalization of Bo with Schiff-base
molecules because of some spherical hindrances. Also increasing in
sharpness and intensity of peaks represents its higher crystallinity.
In the other hand, the XRD spectrum of SBA-Cu2+ (Fig. 4b) illustrated
the same sharp diffraction peaks of SBA. The emersion of new
peaks at 2Ɵ = 33.5°, 35.5°, 37.2°, 57.2°, 62.5°, 77.3° and 91.1° are
related to the Cu+2 and CuO in the catalyst [20].
Fig. 6. TEM images of SBA-Cu2+ nano catalyst
2.1.4. SEM and TEM analysis
The SEM images of the parent Bo, SBA and SBA-Cu2+ are shown in sample the percentage of C, O and Al in Fig. 7(a) have been
Fig. 5. From Fig. 5(a), it can be seen that Bo sample was included recorded. In comparing with Bo, The SBA sample shows 3.8 %w for
nanoparticles with an average particle size in the range of 10–30 N element which confirms the presence of Shiff-base molecules
nm. Having surficial OH groups and tendency to hydrogen bonding (Fig. 7(b)). The EDS data for SBA-Cu2+ also confirms the presence of
among them caused to the agglomeration between Bo Cu2+ on the surface of SBA supports with the weight present about
nanoparticles.
7.79 %w (Fig. 7c).
Fig. 5(b) exhibited that the morphology of SBA is significantly The x-ray mapping of SBA-Cu2+ were recorded in order to
different from Bo. The SBA sample has the morphology of irregular evaluate the dispersion of Cu active sites in the catalyst. Fig. 8
nano flakes with about 20-30 nm thickness and 50-100 nm across. shows the elemental map images which confirmed the good
It can be seen from Fig. 5(c) the chelation of Cu2+ by SBA was led to dispersion of Cu on surface of catalyst. Also the dispersion of N in
roughen the surface of nano flakes. The magnified images and their the surface are indicated the presence of Sciff-base ligands in the
schematics illustrate significantly the morphology of SBA-Cu2+ catalyst.
catalyst (Fig. 5(d)). The TEM images confirmed the morphology of
SBA-Cu2+ and well distribution of Cu2+ at the surface of mesoporous
2.1.5. Thermal analysis (TG-DTA)
nano flakes (Fig. 6.). It can be seen that SBA-Cu2+ has to some Thermo gravimetric-differential thermal analysis (TG-DTA) reveals
extent cubic or hexagonal structures.
the thermal behavior of the SBA-Cu2+ nano catalyst. The TG curve in
The expected elements in the structure of Bo, SBA and SBA-Cu2+ can Fig. 9 indicates the three step weight loss that the first step (mass
be detected by SEM-EDS analysis presented in the Fig. 7. For Bo
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 5 of 11
RSC Advances
View Article Online
DOI: 10.1039/C6RA19725F
ARTICLE
Fig. 7. SEM-EDS data of (a) Bo, (b) SBA and (c) SBA-Cu2+
change: 1.49%) is related to the elimination of physisorbed water or
volatile solvent from the catalyst structure.
Fig.8 The x-ray map analysis for SBA-Cu2+ nano catalyst
Fig. 9. TG-DTA diagrams of SBA-Cu2+ nano catalyst
The second step weight loss (mass change: 10.1%) is mainly
initiated at 267 °C which DTA curve shows an exothermic peak at
306 °C. This step is referred to thermal decomposition of complex.
The third step weight loss (mass change: 12.69%) may be related to
the phase transfer of boehmite structure to the alumina phase
which can be accompanied by OH elimination. Because in SBA-Cu2+
there are some free Al-OH groups that could not reacted with Shiff-
base molecules. For this process, the DTA curve shows an
endothermic peak at 475 °C.
2.2. Evaluation of catalytic activity
The C-C coupling reactions of aryl halides (Suzuki-Miyaura and
Stille reactions) were used to evaluate catalytic performance
of SBA-Cu2+ catalyst.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 6 of 11
View Article Online
DOI: 10.1039/C6RA19725F
Paper
RSC Advances
In our primary experiments, Suzuki–Miyaura reaction between
iodobenzene and sodium tetraphenylborate (NaBPh4) was
selected as a model reaction to optimize the effects of base,
solvent, temperature and amount of SBA-Cu2+.
Table 2. Optimization of Suzuki coupling reaction over the SBA-
Cu2+ nano catalyst.
Reaction conditions: iodobenzene (1 mmol), NaPh4B (0.5 mmol), PEG
(2 mL), and 3 mmol base.
a Isolated yield
Unlike common boronic acid or esters, the prominent advantage of
NaBPh4 is that it can react with four equivalents of electrophilic
reagents. Therefore in aspect of economic and environmental
concerns, this is a green protocol in organic synthesis. Despite this
benefits, only a few works involving NaBPh4 for coupling reaction
have been reported. Thus, to expand the scope and reactivity of
sodium tetraphenyl borate, the development of new and efficient
catalytic protocols is necessary [23].
Catalyst Temp Time Yield
Entry Solvent Base
Table 2 presents the results of optimization conditions. Firstly,
4 to 11 mg of catalyst was used to catalyze the model reaction
at 80 °C in the presence of Na2CO3 and PEG as solvent. The
best result was obtained using 10 mg (0.379 ₓ 10-5 mol g-1) of
catalyst (Table 2, entry 8). While, there was no significant
improvement in the reaction yield by increasing the amount of
catalyst (Table 2, entry 9).
[mg]
[°C]
[min] [%]a
1
2
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
H2O
Et-OH
DMF
DMSO
PEG
PEG
PEG
PEG
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
NaHCO3
NaOAc
KH2PO4
NaOH
-
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
25
45
60
100
180
-
4
120 trace
3
5
60
60
60
30
30
30
30
30
30
30
30
30
30
30
30
30
180
180
30
20
15
38
58
70
85
94
95
81
35
25
-
4
6
5
7
In order to find out the best base for this coupling reaction, the
model reaction was evaluated in presence of NaHCO3, NaOAc,
KH2PO4, NaOH and K2CO3 (Table 2, entries 10-14). So the
results were confirmed that Na2CO3 is the best base among
them. No product has been obtained in using of NaOH or
K2CO3 as a base. It seems that the strength of these base
caused to the by-reactions. NaOH and K2CO3 are the strongest
base among other bases based on their Kb values. Knecht and
co-workers [21] have reported that the amount of free and
reactive OH- for KOH or NaOH is higher than Na2CO3 and
NaHCO3 bases, which caused to a strong combination with
6
8
7
9
8
10
11
10
10
10
10
10
10
10
10
10
10
10
10
10
9
10
11
12
13
14
15
16
17
18
19
20
21
22
K2CO3
-
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
78
88
15
trace
-
metal species leading to
a decrease in biphenyl yield.
Therefore, it seems that high level of free hydroxide in entries
13 and 14 have strong combination with Cu species or strong
reaction with NaBPh4 which caused to destroy the Suzuki
reaction.
17
45
96
The effects of various solvents on the model reaction were
studied by using Et-OH, DMSO, H2O and DMF instead of PEG
(Table 2, entries 15–18). The results show that the PEG was
Table 3. Suzuki–Miyaura coupling reaction with aryl halides and NaPh4B catalyzed by SBA-Cu2+
.
M.p. (°C)
Time
(min)
TOF
(h-1)
Entry
R
X
Yield [%]a
TON
Found
68-69
45-47
108-110
85-87
68-69
111-113
83-84
74-75
Reported
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
H
4-CH3
2-COOH
4-MeO
H
4-NO2
4-CN
4-Cl
4-CH3
I
I
I
I
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
30
80
90
95
40
160
180
120
110
170
600
360
480
40
94
91
89
92
90
92
91
89
91
88
55
64
28 b
86
80
68-70 [22]
44-46 [22]
248
240
235
242
237
242
240
235
240
232
145
168
37
496
180
156
153
355
91
111-113 [2]
88-90 [22]
68-70 [22]
112-114 [22]
85-86 [23]
80
77-79 [22]
117
131
82
14
28
4.6
325
268
45-47
44-46 [22]
4-OH
1-Br-naphthalene
H
161-163
Colorless oil
66-69
163-164 [23]
Colorless oil [24]
68-70 [22]
4-CN
4-iodopyridine
4-bromopyridine
83-84
66-68
66-68
85-86 [23]
69-70[25]
227
201
45
69-70[25]
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 7 of 11
RSC Advances
View Article Online
DOI: 10.1039/C6RA19725F
ARTICLE
Reaction conditions: aryl halides (1 mmol), NaPh4B (0.5 mmol), PEG (2 mL), Na2CO3 (3 mmol), SBA-Cu2+ catalyst (10 mg, 0.379 mol%) and 80 °C.
aIsolated yield
bContaining 20 mg nano catalyst and 95 °C reaction temperature
Table 4. Optimization of Stille coupling reaction over the SBA-
Cu2+ nano catalyst.
more effective than other solvents. Despite aprotic solvents
(DMSO and DMF), it seems that the protic solvents (PEG, Et-
OH and H2O) have better effect on the coupling reaction
catalyzed by SBA-Cu2+. It may be referred to the positive
interactions between protic solvent and polar functional
groups in SBA-Cu2+ which can be help to effective dispersion.
In the other side, the
Catalyst Temp Time Yield
Entry Solvent Base
[mg]
-
[°C]
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
25
45
60
100
[min] [%]a
PEG as a phase transfer catalyst can enhance the solubility of
the reagents (aryl halide, NaBPh4, base), as well as promote
basicity of Na2CO3. The alcoholic solvent as a protic solvent
have shown better yield than water because of its better
polarity to dissolve reagents.
In continuous, it found that the reaction yields were
impressionable to temperature factor. So, the effect of various
temperature were studied in rang of 25 to 100 °C (Table 2,
entries 19-22) and the best results were obtained at 80 °C
(Table 2, entry 8). After optimizing the conditions, a series of
aryl halides, which contain different substitution groups, such
as electron-donating and electron-withdrawing were used for
the synthesis of biphenyl derivatives in the presence of SBA-
Cu2+. Table 3 shows the summarized results of this study in the
optimized conditions (10 mg catalyst, Na2CO3 as base in PEG
solvent at 80 °C).
As expected, the Suzuki reaction for aryl iodides gave the best
yields in the shorter times (Table 3, entries 1-4). Aryl bromides
have shown high reactivity but relatively in longer reaction
times versus aryl iodides (Table 3, entries 5-11). And regularly,
the coupling of aryl chlorides were done in more difficult
conditions that led to the lower yields (Table 3, entries 12-13).
Overall, electronic effects have an effect on Suzuki reaction, so
that aryl halides with electron-donating groups gave little
higher yields than those with electron-withdrawing groups.
Ortho-substituted aryl halides with (Table 3, entry 3) gave
lower yields than those at para- substituted, which reveals that
steric hindrance has a negative effect on the Suzuki reaction.
1
2
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
H2O
Et-OH
DMF
DMSO
PEG
PEG
PEG
PEG
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
NaHCO3
NaOAc
KH2PO4
K2CO3
240
60
50
50
50
20
20
20
20
20
20
20
20
20
20
20
20
-
trace
14
32
54
70
81
93
94
71
55
43
18
76
89
32
22
4
3
5
4
6
5
7
6
8
7
9
8
10
11
10
10
10
10
10
10
10
10
10
10
10
10
9
10
11
12
13
14
15
16
17
18
19
20
21
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
240 trace
120
70
52
74
95
15
Reaction conditions: Iodobenzene (1 mmol), triphenyltin chloride
(0.5 mmol), PEG (2 mL), and 3 mmol base.
aIsolated yield
Table 5. Stille coupling reaction with aryl halides and triphenyltin chloride catalyzed by SBA-Cu2+.
M.p. (°C)
Time
(min)
TOF
(h-1)
Entry
R
X
Yield [%]a
TON
Found
68-69
45-47
108-110
85-87
68-69
111-113
83-84
74-75
Reported
1
2
3
4
5
6
7
8
9
10
11
12
13
H
4-CH3
2-COOH
4-MeO
H
4-NO2
4-CN
4-Cl
4-CH3
I
I
I
I
Br
Br
Br
Br
Br
Br
Br
Cl
20
120
125
100
25
93
90
89
86
92
90
91
85
89
87
59
67
88
68-70 [22]
44-46 [22]
245
237
235
227
243
237
240
224
235
229
155
177
222
735
118
113
136
583
190
180
112
141
114
22
111-113 [2]
88-90 [22]
68-70 [22]
75
80
112-114 [22]
85-86 [23]
120
100
120
420
240
30
77-79 [22]
45-47
44-46 [22]
4-OH
1-Br-naphthalene
H
161-163
Colorless oil
66-69
163-164 [23]
Colorless oil [24]
68-70 [22]
44
443
4-iodopyridine
66-68
69-70[25]
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 8 of 11
View Article Online
DOI: 10.1039/C6RA19725F
Paper
RSC Advances
14
4-bromopyridine
40
82
66-68
69-70[25]
206
310
Reaction conditions: aryl halides (1 mmol), triphenyltin chloride (0.5 mmol), PEG (2 mL), Na2CO3 (3 mmol), SBA-Cu2+ catalyst (10 mg, 0.379 mol%) and 80
°C.
aIsolated yield
Table 6. Comparison of SBA-Cu2+ nano catalyst for the Suzuki-Miyaura reaction with previously reported heterogeneous
catalysts.
Time
(min)
Temp
(°C)
Entry Substrate
Reagent
Catalyst type
Cu mol%
Yield (%)
Ref.
[6]
[7]
1
2
3
4
5
6
7
8
9
Ph-I
Ph-I
Ph-I
Ph-I
Ph-I
Ph-I
Ph-Br
Ph-I
Ph-Br
Ph-B(OH)2
Ph-B(OH)2
Ph-B(OH)2
Ph-B(OH)2
Ph-B(OH)2
Ph-B(OH)2
Ph4BNa
Fe3O4@SiO2-Isatin-Cu2+
Cu nano colloid
0.82
300
360
-
70
92
62
88
99
62
97.5
90
94
90
2
110
25
3D MOF {[Cu(4-tba)2](solvent)}n
Cu-Pd@4A molecular sieve
Cu@4A molecular sieve
Pd-Cu/Carbon
-
[8]
9
60
60
180
18
30
40
78
[9]
9
78
[9]
0.99
1
78
[10]
[11]
This work
Pd2+@Polystyrene
SBA-Cu2+
120
80
Ph4BNa
0.379
0.379
Ph4BNa
SBA-Cu2+
80
This work
Using the hetero aryl halides (Table 3, entries 14, 15) shows and bromides reacted in shorter times in compared to aryl
the lower yields in compare with ordinary aryl halides these chlorides.
can be due to withdrawing effect of heteroatom in aryl halide.
Also in Stille reaction, using the hetero aryl halides (Table 5,
In order to demonstrate applications of the SBA-Cu2+ as an entries 13, 14) indicates the moderate yields in compare with
active catalyst, it was evaluated in the C-C coupling through ordinary aryl halides these can be due to withdrawing effect of
Stille reaction. Therefore, the reaction of iodobenzene and heteroatom in aryl halide.
triphenyltin chloride were selected as a model reaction to
obtain optimized conditions. In this way Table 4 shows the
results of various conditions in model reaction. No product has
been achieved without SBA-Cu2+ catalyst (Table 4, entry 1).
Similar to the Suzuki-Miyaura reaction, the best amount of
nano catalyst were chosen 10 mg (0.379 ₓ 10-5 mol g-1) of the
SBA-Cu2+ (Table 4, entry 8). No significant improvement in
yield was detected through increasing the amount of the SBA-
Cu2+ (Table 4, entry 9). Using the various base in the model
reaction indicated that sodium carbonate was still the more
efficient base among them (Table 4, entries 10-13).
In continuous, evaluation of various solvents in model reaction
confirmed that the PEG is the best and effective solvent among
them (Table 4, entries 14-17). As previously mentioned, PEG as
a protic solvent have acted as phase transfer catalyst. Also
ethanol as a protic solvent have shown better yield than water
because of its better polarity to dissolve reagents. Finally, the
temperatures in ranging from 25 to 100 °C were chosen to
evaluate of the temperature effect in model reaction (Table 4,
entries 8, 18-21). It was found that the reaction catalyzed
effectively at 80 °C (Table 4, entry 8). As mentioned above, the
best results are obtained with 10 mg (0.379 mol%) of SBA-Cu2+
2.3. Copper content of nano catalyst
Inductively coupled plasma-optical emission spectrometry
(ICP-OES) have been used to evaluate the amount of loaded
Cu2+ on SBA-Cu2+. The results indicated the value of 37.9 ₓ 10-5
mol g-1 (2.41 %w Cu) in the nano catalyst sample. A hot
filtration test was also performed to confirm the
heterogeneous nature of the SBA-Cu2+. The nano catalyst was
separated by hot filtration after the first catalytic reaction.
Then the fresh reagents (Iodobenzene, NaPh4B, PEG and
Na2CO3) were added to the hot filtrated solution. The resulting
mixture was kept in reaction conditions (80°C) for another 60
in PEG solvent at 80°C and using Na2CO3 (Table 4, entry 8).
After optimization the reaction, various aryl halides with
triphenyltin chloride were employed in Stille reaction for the
synthesis of biphenyl derivatives. Table 5 summarized the
results of this study. These results reveal that various aryl
halides with electron-donating and electron-withdrawing
substituents were catalyzed equally facile by SBA-Cu2+ in
appropriate yields and lower times. As expected aryl iodides
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 9 of 11
View Article Online
DOI: 10.1039/C6RA19725F
RSC Advances
ARTICLE
analysis was performed with STA PT-1000 instrument in the
thermal range of 15-700 C with 11 mg of the samples (heating
rate of 10 °C min-1 under N2 atmosphere). Nitrogen sorption
and surface area measurement was carried on a Belsorp mini II
analyzer at 77 K.
min. The conversion was negligible after adequate time (8 h).
The negligible conversion in the amount of product indicated
that copper leaching from SBA-Cu2+ is very insignificant for
coupling reaction.
Prior to the analysis, degassing was done for all samples at 373
K in a vacuum line for 5 h. 1H NMR spectra were recorded on a
Bruker AVANCE DPX-400 (400 MHz for H). Chemical shifts are
given in ppm (δ) relative to internal TMS and coupling
constants Jare reported in Hz. The Cu content of the catalyst
was measured with an inductively coupled plasma atomic
emission spectrometer (ICP-OES simultaneous, Varian VISTA-
PRO Model). The ultrasonic bath (240 W-35 kHz, SONREX,
DT52 H, Bandelin, Germany) has been utilized for ultra-
sonication of solutions.
2.4. Reusability of catalyst
The reusability and recovery of the nano catalyst are very
important factors in aspect of commercial applications. Hence,
SBA-Cu2+ separated by centrifugation after completion of
reaction. Then the catalyst washed several times with water
and methanol and dried in oven. The recovered catalyst can be
reutilized for next reactions including the Suzuki-Miyaura and
Stille. The reusability studies indicated that SBA-Cu2+ can be
recovered and reused without noticeable decline in its
reactivity at least for seven runs. Fig. 10 shows that the
average isolated yields for Suzuki and Stille reaction in seven
runs are 91 and 90.14% respectively.
1
4.2. Catalyst preparation
4.2.1. Synthesis of Boehmite (Bo)
Boehmite nanoparticles (Bo) were prepared according to the
previously reported work [14]. Briefly, 50 mL NaOH solution
3.25 M and 30 mL aluminum nitrate [Al(NO3)3.9H2O] solution
1.77 M were prepared. The Al3+ solution was then slowly
precipitated with NaOH solution (2.94 mL min-1) by vigorous
stirring. Then obtained milky mixture was sonicated in the
ultrasonic bath for 3 h at the ambient temperature, filtered
and washed with distilled water. The gelatinous precipitate
was heated in the oven at 220 °C for 4 h.
2.5. Catalyst comparison
In order to show the activity of SBA-Cu2+, Table 6 presents the
comparison of our results on the Suzuki reaction with the
reported catalysts in the literature. There are limited number
of reports about copper catalyzed Suzuki reactions. This
comparison indicates that SBA-Cu2+ is comparable or may be
efficient than the other reported heterogeneous catalysts.
Moreover, SBA-Cu2+ is can be better than the other catalysts in
terms of price, stability and toxicity.
3. Conclusion
In summary, SBA-Cu2+ as a new mesoporous nano catalyst was
fabricated and characterized. The characterization results
confirmed the synthesized Schiff-base alumoxane support with
nano flakes morphology formed the stable framework for Cu2+
which can be thermally stable up to 306 °C. Also the copper
percentage in nano catalyst were indicated (2.41 w%; 37.9 ₓ
10-5 mol g-1). The SBA-Cu2+ showed significant catalytic activity
and high reusability for the Suzuki–Miyaura and Stille
reactions. This nanocatalyst is effective for reaction of various
aryl halides (including chlorides, bromides and iodides) with
NaBPh4 and Ph3SnCl. In addition, this nanocatalyst could be
recovered and reused at least for seven times without
significant loss of catalytic activity. Copper leaching from SBA-
Cu2+ is very negligible for this coupling reaction.
4.2.2. Synthesis of Schiff-base (SB)
Schiff base (SB) was prepared according to previous literature
[26]. In brief, 0.1 mol salicylaldehyde was added to a stirred
solution of 4-aminobenzoic acid (0.1 mol in 100 mL ethanol)
and the mixture was stirred for 30 min at ambient
temperature. The yellow precipitate of schiff-base was filtered
and recrystallized with methanol to obtain SB.
4.2.3. Synthesis of Schiff-Base Alumoxane (SBA) framework
2 g Boehmite (Bo) nanoparticles added to the stirred Schiff-
base solution (0.266 g SB in 50 mL DMF), then the obtained
mixture was refluxed for 17 h. After completion, the yellow
precipitate of Schiff-Base alumoxane was separated by
filtration and washed thoroughly by ethanol and methanol,
and dried at 70 °C.
4. Experimental
4.1. Reagents and materials
4.2.4. Synthesis of Cu2+-Schiff-Base Alumoxane (SBA-Cu2+)
At the Erlenmeyer flask, 0.25 g of SBA and 0.1 g Copper (II)
acetate were mixed into 50 mL ethanol. Then lid of the flask
was closed and stirred for 24 h at room temperature. After
completion, the blue-green mixture was filtered and washed
several time with ethanol to obtain SBA-Cu2+. The resulting
green catalyst (Fig. 1) was dried in oven at 60 °C.
Copper (II) acetate, aluminum nitrate [Al(NO3)3.9H2O] and
other chemical reagents were purchased from Merck, Sigma-
Aldrich, Fluka and Fisher chemical companies. All solvents and
reagents were of analytical grade and used for the reaction
without further purification. The powder XRD were recorded
on a Philips PW 3040 X-ray diffractometer with Cu Kα radiation
(λ=1.5406 Å) in a range of 0.5–100° (Bragg's angle). Scanning
electron micrographs (SEM) of the samples were recorded
using FE-SEM MIRA3 TESCAN (acceleration voltage 30 kV). This
microscope equipped with an energy dispersive X-ray detector
(EDS) which used for chemical composition analysis and
preparation of X-ray map of the nano catalyst. Transmission
electron micrographs (TEM) were collected by a JEOL-2100
microscope. Fourier-transform infrared (FTIR) spectra were
taken on Bruker alpha (German) with KBr pellets. TG-DTA
4.3. General procedure for Suzuki–Miyaura reaction
A mixture of aryl halides (1 mmol), NaPh4B (0.5mmol), Na2CO3
(3 mmol), SBA-Cu2+ nano catalyst (10 mg) and 2 mL solvent
(PEG) were added to a test tube equipped with a magnetic
stirrer bar. Until the completion of reaction, the mixture was
heated at 80 °C and monitored by TLC to evaluate progress of
reaction. After completion, the mixture was cooled down and
catalyst was filtered off. Then separated catalyst washed
several times via acetone and dried in oven. In a separating
funnel, diethyl ether (4mL, 4 times) was utilized to extraction
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
Please do not adjust margins

Please do not adjust margins
RSC Advances
Page 10 of 11
View Article Online
DOI: 10.1039/C6RA19725F
Paper
RSC Advances
5
6
(a) V. Calo, A. Nacci, A. Monopoli, E. Ieva and N. Cioffi,
Org. Lett., 2005, , 617-620;(b) Y. Liu, D. Li and C. M. Park,
of organic phase from PEG filtrate by aid of adding water. At
the end, the diethyl ether was evaporated in order to obtain
corresponding biaryl product. The melting point of the final
products were measured at the end. The biaryl products were
characterized by H NMR spectra. The selected H NMR data
for compounds 1 and 6 are in good agreement with those
previously reported.
7
Angew. Che. Int. Ed., 2011, 50, 7333-7336;(c) N. Gigant
and I. Gillaizeau, Org. Lett., 2012, 14, 3304-3307.
S. S. Miri, M. Khoobi, F. Ashouri, F. Jafarpour, P. R.
Ranjbar and A. Shafiee, Turk. J. Chem., 2015, 39, 1232-
1246.
M. B. Thathagar, J. Beckers and G. Rothenberg, J. Am.
Chem. Soc., 2002, 124, 11858-11859.
B. Wang, P. Yang, Z. W. Ge and C. P. Li, Inorg. Chem.
Commun., 2015, 61, 13-15.
1
1
7
8
9
1,1'-Biphenyl: 1H NMR (400 MHz, CDCl3): δH (ppm)= 7.62-7.64 (m,
4H), 7.40-7.50 (m, 4H), 7.36-7.40 (tt, J=7.6, 1.2 Hz, 2H).
4-Nitro-1,1'-biphenyl: 1H NMR (400 MHz, CDCl3): δH (ppm)= 8.31-
8.34 (dt, J= 8.8, 2.4 Hz, 2H), 7.75-7.78 (dt, J= 8.8, 2.4 Hz, 2H), 7.64-
7.67 (m, 2H), 7.50-7.55 (m, 2H), 7.45-7.49 (tt, J= 7.6, 2.4 Hz, 1H).
A. Fodor, Z. Hell and L. Pirault-Roy, Appl. Catal. A-Gen.,
2014, 484, 39-50.
10 S. J. Kim, S. D. Oh, S. Lee and S. H. Choi, J. Ind. Eng. Chem.,
2008, 14, 49-456.
11
(a) B. Karimi and P. Fadavi Akhavan, Chem. Commun.,
2011, 47 7686;(b) S. Rostamnia and H. Xin, Appl.
4.4. General procedure for Stille reaction
,
A mixture of aryl halides (1 mmol), Ph3SnCl (0.5 mmol), Na2CO3
(3 mmol), SBA-Cu2+ nano catalyst (10 mg) and 2 mL solvent
(PEG) were added to a test tube equipped with a magnetic
stirrer bar. Until the completion of reaction, the mixture was
heated at 80 °C and monitored by TLC to evaluate progress of
reaction. After completion, the mixture was cooled down and
catalyst was filtered off. Then separated catalyst washed
several times via acetone and dried in oven. In a separating
funnel, diethyl ether (4mL, 4 times) was utilized to extraction
of organic phase from PEG filtrate by aid of adding water. At
the end, the diethyl ether was evaporated in order to obtain
corresponding biaryl product. The melting point of the final
products were measured at the end. The biaryl products were
Organomet. Chem., 2013, 27, 348;(c) R. Zhang, W. Ding,
B. Tu and D. Zhao, Chem. Mater., 2007, 19, 4379;(d) S.
Mandal, D. Roy, R.V. Chaudhari and M. Sastry, Chem.
Mater., 2004, 16, 3714;(e) C. D. Wu, A. Hu, L. Zhang and
W. B. Lin, J. Am. Chem. Soc., 2005, 127, 8940;(f) X. Pan, Z.
Fan, W. Chen, Y. Ding, H. Luo and X. Bao, Nat. Mater.,
2007,
A. Solhy, V. Martinez, Y. Kihn, O. Ersen, K. Philippot, B.
Chaudret and P. Serp, Angew. Chem. Int. Ed., 2009, 48
6, 507;(g) E. Castillejos, P.J. Debouttiere, L. Roiban,
,
2529;(h) L. Bai and J. X. Wang, Adv. Synth. Catal., 2008,
350, 315.
12 A. A. Derakhshan, L. Rajabi and H. Karimnezhad, Powder.
Technol., 2012, 225, 156–166.
13 (a) F. Surivet, T. M. Lam, J. P. Pascualt and C. Mai,
1
1
characterized by H NMR spectra. The selected H NMR data
for compounds 2 and 7 are in good agreement with those
previously reported.
Macromolecules., 1992, 25
Whitesides, J. P. Mathias and C.T. Seto, Science., 1991,
254, 1312–1319.
,
5742–5751;(b) G. M.
4-Methyl-1,1'-biphenyl: 1H NMR (400 MHz, CDCl3): δH (ppm)=
14 L. Rajabi and A. A. Derakhshan, Sci. Adv. Mater., 2010,
163–172.
15 J. Liu, X. Liao and B. Shi, Res. Chem. Intermed., 2014, 40
249-258.
16 A. A. Derakhshan and L. Rajabi, Powder. Technol., 2012,
226, 117–129.
17 S. J. Obrey and A. R. Barron, Macromolecules., 2002, 35
2,
7.63-7.65 (m, 2H), 7.55-7.57 (m, 2H), 7.46-7.52 (m, 2H), 7.36-
7.40 (tt, J= 7.2, 1.2 Hz, 1H), 7.30-7.32 (d, J= 8 Hz, 2H), 2.46 (s,
3H).
[1,1'-Biphenyl]-4-carbonitrile: 1H NMR (400 MHz, CDCl3): δH
(ppm)= 7.74-7.77 (m, 2H), 7.69-7.72 (m, 2H), 7.60-7.63 (m, 2H),
7.49-7.53 (m, 2H), 7.43-7.47 (m, 1H).
,
,
1499–1503.
18 C. C. Landry, N. Pappe, M. R. Mason, A. W. Apblett, A. N.
Tyler, A. N. Maclnnes and A. R.Barron, J. Mater. Chem.,
1995, 5, 331-341.
19 S. A. Abdel-Latif, H. B. Hassib and Y. M. Issa, Spectrochim.
Acta. A., 2007, 67, 950–957.
20 B. Wang, X. L. Wu, C. Y. Shu, Y. G. Guo and C. R. Wang, J.
Mat. Chem., 2010, 20, 10661-10664.
Acknowledgements
Authors thank Ilam University and Iran National Science
Foundation (INSF) for financial support of this research project.
References
21 D. B. Briggs, R. T. Pekarek and M. R. Knecht, J. Phys.
Chem. C, 2014, 118, 18543.
1
(a) A. M .Trzeciak and J. Ziolkowski, J. Coord. Chem. Rev.,
2005, 249, 2308-2322;(b) V. Farina, Adv. Synth. Catal.,
2004, 346, 1553-1582;(c) B. M. Choudary, S. Madhi, N. S.
Chowdari, M. L. Kantam and B. Sreedhar, J. Am. Chem.
22 Y. Y. Peng, J. Liu, X. Lei and Z. Yin, Green Chem., 2010, 12
1072.
23 L. Bai and J. X. Wang, Adv. Synth. Catal., 2008, 350, 315.
,
Soc., 2002, 124,
Leumann, J. Org. Lett., 2001,
14127-14136;(d) A. Haberli and C.
, 489-492.
24 E. H. Binns and K. H. Squire, Trans. Faraday Soc., 1962,
58, 762-770.
3
2
(a) M. Tobisu, T. Xu, T. Shimasaki and N. Chatani, J. Am.
Chem. Soc., 2011, 133, 19505;(b) J. H. Li, Y. Liang and Y. Y.
Xie, Tetrahedron., 2005, 61, 7289;(c) A. Ghorbani-
25 B. J. Haworth, I. M. Heibron and D. H. Hey, J. Chem. SOC.,
1940, 349.
26 Y. Leng, J. Liu, C. Zhang and P. Jiang, Catal. Sci. Technol.,
Choghamarani and M. Norouzi, Appl. Organometal.
Chem., 2016, 30, 140–147.
2014, 4, 997-1004.
3
4
(a) B. C. Makhubela, A. Jardine and G. S. Smith, Appl.
Catal. A-Gen., 2011, 393, 231-241;(b) N. Iranpoor, H.
Firouzabadi, S. Motevalli and M. Talebi, J. Organomet.
Chem., 2012, 708, 118-124.
J. Mao, J. Guo, F. Fang and S. J. Ji, Tetrahedron., 2008, 64
3905-3911.
,
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 11 of 11
RSC Advances
View Article Online
DOI: 10.1039/C6RA19725F
Graphical Abstract
Copper-Schiff base alumoxane: a new and reusable nanocatalyst for Suzuki–
Miyaura and Stille C-C cross-coupling reactions
Arash Ghorbani-Choghamarani,* Maryam Hajjami, Ali Ashraf Derakhshan and Laleh Rajabi
For the first time, Cu(II) supported on Schiff-base alumoxane framework was used as
an effective and recyclable nanocatalyst in Suzuki-Miyaura and Stille cross coupling
reactions.