Tethering of nickel(II) Schiff-base complex onto mesoporous silica: An efficient heterogeneous catalyst for epoxidation of olefins

Article abstract of DOI:10.1016/j.poly.2011.04.040

A new hybrid catalyst has been prepared by tethering a nickel(II) Schiff-base complex via post-synthesis modification of mesoporous silica, MCM-41. The Schiff-base has been derived from salicylaldehyde and 3-aminopropyltriethoxysilane (3-APTES) which is c

Full text of DOI:10.1016/j.poly.2011.04.040

Polyhedron 30 (2011) 1857–1864
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Tethering of nickel(II) Schiff-base complex onto mesoporous silica: An efficient
heterogeneous catalyst for epoxidation of olefins
⇑
Susmita Bhunia, Subratanath Koner
Department of Chemistry, Jadavpur University, Jadavpur, Kolkata 700 032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new hybrid catalyst has been prepared by tethering a nickel(II) Schiff-base complex via post-synthesis
modification of mesoporous silica, MCM-41. The Schiff-base has been derived from salicylaldehyde and
Received 14 January 2011
Accepted 17 April 2011
Available online 3 May 2011
3-aminopropyltriethoxysilane (3-APTES) which is chemically anchored on MCM-41 via silicon alkoxide
route. The anchored Schiff-bases imposed a stable planar coordination geometry around the central
nickel ions. The catalyst has been characterized by elemental analysis, FT-IR, UV–Vis, small angle X-ray
diffraction (SAX) and transmission electron microscopy (TEM) studies. The SAX and TEM measurement
showed the mesoporosity of the catalyst. The activity of the catalyst has been assessed in the epoxidation
of olefins using tert-butyl-hydroperoxide (tert-BuOOH) as oxidant in heterogeneous condition. Immobi-
lized nickel catalyst was found to be catalytically more active and selective compared to the similar type
Keywords:
Mesoporous silica
Nickel(II)
Schiff-base complex
tert-BuOOH
Epoxidation
of nickel(II) complex as well as Ni(NO
reused several times without significant loss of activity.
3
)
2
Á6H
2
O in homogeneous media. The catalyst can be recycled and
Catalyst recycling
Ó 2011 Elsevier Ltd. All rights reserved.
1
. Introduction
Different approaches like encapsulation in zeolites [10–14], graft-
ing on polymers [15–17] and immobilization in polysiloxane mem-
branes [18] have been used to develop the efficient heterogeneous
catalyst. In recent years ordered mesoporous silica, for example,
MCM-41 has been receiving much attention as solid support
[19,20]. Properties like high surface area, large pore volume and
well-defined hexagonal arrays of channels and cavities [21,22] of
mesoporous silica made it suitable support for anchoring of metal
complexes. Nickel-based catalysts can be applied in a wide variety
of reactions [23,24]. Koola and Kochi [25], Burrows and coworkers
[26] and others [27,28] have developed mononuclear nickel com-
plexes as oxidation catalysts. Feringa and coworkers have studied
the effect of dinuclear Ni(II) complexes in the epoxidation of
unsubstituted alkenes [29]. Chatterjee and Mitra have also studied
the catalytic role of Schiff-base complex of nickel in the epoxida-
tion of olefins [30]. However reports on the supported nickel-based
efficient catalysts in epoxidation reaction are scarce. Generally
they show relatively poor catalytic activity [31–33].
In the course of our continuing investigation on different organ-
ic reactions using ordered mesoporous silica materials as heteroge-
neous catalytic support we have found that the hybrid material
demonstrates desirable catalytic efficacy [34,35]. Herein we report
the preparation and characterization of a heterogeneous nickel
Schiff-base catalyst which shows excellent catalytic efficacy to-
wards epoxidation of olefins using tert-BuOOH as oxidant. The
effect of different solvents on epoxidation reaction was also inves-
tigated. Catalytic efficacy of the anchored catalyst was compared
Epoxidation is one of the most important C@C bond functional-
ization methods, and epoxide group is an active intermediate for
laboratory syntheses as well as chemical industry [1–5]. Epoxides
can be converted into alcohols, polyethers and aldehydes which
show widespread applications in chemical and pharmaceutical
industry [6]. Olefin epoxidation catalyzed by transition metal com-
plexes has been a subject of great interest in the past few decades
[
7]. Metal catalyst serves as a relay for oxygen atom transfer from
the oxygen donor via the intermediacy of an oxo-metal species.
Several oxidants, such as oxygen, hydrogen peroxide, and tert-
butyl-hydroperoxide (tert-BuOOH) are used for the production of
epoxides from alkenes [8]. Hydrogen peroxide is environmentally
friendly oxidizing agent but due to its explosive nature tert-BuOOH
received increased attention for the development of atom efficient
catalytic methods [9]. The by-product, tert-BuOH, produced from
tert-BuOOH can be separated by distillation or recycled for other
industrial production.
Homogeneous catalysts suffer several disadvantages in compar-
ison to its heterogeneous analogs. In most of the cases the com-
pound decomposes or dimerizes or often autoxidation also takes
place during catalytic reaction in homogeneous process. Recycling
of catalysts is a task of great economic and environmental advan-
tages in chemical and pharmaceutical industry, especially when
expensive and/or toxic heavy metal compounds are employed.
⇑
Corresponding author. Tel.: +91 33 2414 6666x2778; fax: +91 33 2414 6414.
E-mail address: snkoner@chemistry.jdvu.ac.in (S. Koner).
with its corresponding neat complex as well as Ni(NO
under the similar reaction conditions.
3
)
2 2
Á6H O
0
277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.04.040

1
858
S. Bhunia, S. Koner / Polyhedron 30 (2011) 1857–1864
O
Si OH
O
O
O
EtO
CHO
HO
Si
O
-
3EtOH
a
Si OH
Si OH
+
EtO Si(CH
2
)
3
NH
2
+
O
O
EtO
Si
O
(CH ) NH
Si
2
3
2
3
-APTES
Si
O
Silica wall
of MCM-41
b
O
O
Si
O
H
Si
O
O
H
c
O
O
Si
Si CH ) N = C
(
2 3
O
Si
O
Si
(CH ) N = C
O
2
3
Si
O
O
Si
O
HO
2
+
Ni
O
O
Si
O
O
Si
O
Si(CH ) N = C
2 3
O
H
Si
O
Ni(II)-MCM-41
Scheme 1A. (a) Modification of MCM-41channel wall: APTES/chloroform; (b) condensation with salicylaldehyde in methanol; and (c) metal complex formation:
Ni(NO O/Methanol/Reflux.
Á6H
)
3 2
2
H
OHC
NH2
a
+
N=C
OH
OH
b
H
N=C
2
+
O
Ni
O
N=C
H
bis-(Salicylaldimine) nickel complex
Scheme 1B. (a) Condensation reaction between n-propylamine and salicylaldehyde in methanol and (b) metal complex formation: Ni(NO ) .6H O/Methanol/Reflux.
3 2 2

S. Bhunia, S. Koner / Polyhedron 30 (2011) 1857–1864
1859
Fig. 3. IR spectra of bis-(n-propylsalicylaldimine) nickel complex.
Fig. 1. Small-angle XRD pattern of (a) Si-MCM-41 and (b) Ni(II)-MCM-41.
Fig. 4. UV–Vis spectra of Ni(II)-MCM-41.
2 2 2 2 x
Fig. 2. IR spectra of (a) Si-MCM-41; (b) MCM-41-(SiCH CH CH NH ) ; and (c)
Ni(II)-MCM-41.
2
. Experimental
.1. Materials and physical measurements
All solvents used were of AR grade and they were distilled and
2
dried before use. Tetraethyl orthosilicate (TEOS, 98%), the cationic
surfactant cetyltrimethylammonium bromide (CTAB, 98%), 3-ami-
nopropyl-triethoxysilane (3-APTES), nickel nitrate hexahydrate,
salicylaldehyde, styrene, cyclooctene, trans-stilbene, 1-octene,
1
-hexene, tert-butyl-hydroperoxide (70% aqueous) were purchased
Fig. 5. UV–Vis spectra of bis-(n-propyl-salicylaldimine) nickel complex.
from Sigma–Aldrich/Fluka or Merck (India) and were used as
received. Elemental analyses (CHN) were performed using a Perkin
Elmer 2400 elemental analyzer. Fourier transform infrared (FTIR)
spectra of KBr pellets were measured on a Perkin Elmer RX1 FTIR
spectrometer. Electronic spectra were measured on a Shimadzu
CP-3101 UV–Vis spectrophotometer. The powder X-ray diffraction
(XRD) patterns of the samples were recorded on a Scintag
XDS-2000 diffractometer using Cu K radiation. The nickel content
of the sample was determined by Perkin Elmer Analyst-100 atomic
a
absorption spectrometer. Transmission electron microscopic (TEM)

1
860
S. Bhunia, S. Koner / Polyhedron 30 (2011) 1857–1864
images were recorded with a transmission electron microscope
Make: FEI, Model: STWIN) operating at an accelerating voltage
orthosilicate (TEOS) in basic solution with a molar composition
of the reactants 1.0 CTAB:7.5 TEOS:1.8 NaOH:500 H O. The gelati-
(
2
of 200 kV. The samples were ground and sonicated in isopropanol
and dispersed over carbon-coated copper grids. To study the pro-
gress of the reaction the products were collected at different time
intervals and identified and quantified by a Varian CP-3800 gas
chromatograph. Other instruments used in this study were the
same as reported earlier [36,37].
nous mixture was then hydrothermally treated at 110 °C for 60 h
in a Teflon lined autoclave. After cooling to room temperature
the resultant solid was recovered by filtration, washed with deion-
ized water and dried in air. The collected product was calcined at
823 K for 8 h to remove the occluded surfactants. This mesoporous
material is designated as Si-MCM-41.
Before functionalization, the support Si-MCM-41 was dehy-
drated at 150 °C for 3 h to remove the physisorbed water mole-
cules. Post synthesis organic modification of Si-MCM-41 was
performed by stirring 0.1 g of Si-MCM-41 with 0.004 mmol solu-
tion of 3-APTES in dry chloroform (10 ml) at room temperature
for 12 h under nitrogen atmosphere. The resulting white solid
2
.2. Preparation of catalyst
Mesoporous Si-MCM-41 was prepared according to the litera-
ture method [38] by hydrolyzing the structure directing agent
CTAB (cetyltrimethylammonium bromide) and tetraethyl
MCM-41-(SiCH
roform followed by dichloromethane and dried in air. The white
solid, MCM-41-(SiCH CH CH NH was refluxed with 50 mg
0.41 mmol) of salicylaldehyde in methanol at 60 °C for 8 h. The
2 2 2 2 x
CH CH NH ) was filtered, and washed with chlo-
2
2
2
2 x
)
(
resulting yellow colored solid was filtered, washed with methanol
followed by dichloromethane and dried in air. Finally Ni(II)-MCM-
4
1
1 was prepared by refluxing the above said yellowish solid with
0 mg (0.034 mmol) of Ni(NO O dissolved in 20 ml methanol
3
)
2
Á6H
2
at 60 °C for 12 h. The green solid thus obtained was filtered,
washed with methanol with soxhlet and dried in air. The prepared
catalyst is designated as Ni(II)-MCM-41 (Scheme 1A). Atomic
absorption spectrometric result showed nickel content of the cata-
lyst is ca. 0.04% (wt). The elemental analysis showed N:Ni and C:Ni
were 2.3 and 21.04, respectively, which indicates that the nickel(II)
2 2
ions have N O ligand environment as shown in Scheme 1A.
A complex, bis-(n-propyl-salicylaldimine)-nickel(II) with simi-
lar type of ligand (Scheme 1B) has also been synthesized according
to the previously reported one-pot synthetic route [39]. The cata-
lytic activity of this complex was compared with the catalyst
Ni(II)-MCM-41.
2.3. Catalytic reactions
The catalytic epoxidation of olefins were carried out in a two-
necked 50 ml flask equipped with a reflux condenser. In a typical
reaction, substrate, solvent, and catalysts were first mixed. The
mixture was then equilibrated to 70 °C in an oil bath. After addition
of oxidant, the reaction was stirred. The products of the epoxida-
tion reactions were collected at different time intervals and were
identified and quantified by gas chromatography. Blank experi-
ments were also performed in the absence of catalyst under the
same experimental conditions.
For the recycling experiments, the solid catalyst was first fil-
tered, washed with methanol (5 ml) for five times, and then with
acetonitrile (10 ml) to remove the occluded reactants and prod-
ucts. The recycled catalysts were then dried at room temperature
and re-used following the same experimental conditions as de-
scribed above.
To compare the catalytic efficacy of the heterogenized systems
with the corresponding homogeneous catalysts, we also carried
out the epoxidation reactions in acetonitrile solution of (i) bis-
(
n-propyl-salicylaldimine)-nickel(II) complex and (ii) Ni(NO
O. In all the cases the reaction conditions were the same. The
progress of the reactions was monitored by GC analysis.
3
)
2
Á
6H
2
3
. Results and discussion
3.1. Small angle X-ray powder diffraction study
Fig.
1 represents the small angle X-ray (SAX) powder
Fig. 6. Transmission electron micrograph (TEM) of Si-MCM-41(A) and Ni(II)-MCM-
4
1 (B).
diffraction patterns of the calcined Si-MCM-41 and the catalyst

S. Bhunia, S. Koner / Polyhedron 30 (2011) 1857–1864
1861
Table 1
Epoxidation of olefins using tert-BuOOH catalyzed by Ni(II)-MCM-41.
Alkenes
Time (h)
Temperature (°C)
Conversion (wt%)
100
% Yield of products
TOFb
Epoxides
61
Others
39a
2
0
70
1764
2
2
4
4
70
70
86
84
86
84
1194
704
2
2
4
4
70
70
71
58
71
58
1286
790
Reaction conditions: alkenes (500 mg); catalyst (20 mg); tert-BuOOH (1 ml); acetonitrile (8 ml); Temp. 70 °C. The products of the epoxidation reactions were collected at
different time intervals and were identified and quantified by Varian CP-3800 gas chromatograph equipped with an FID detector and a CP-Sil 8 CB capillary column.
a
Benzaldehyde.
b
Turnover frequency (TOF) = moles converted/mol of active site/time (h).
Table 2
Epoxidation of styrene using tert-BuOOH catalyzed by a variety of Ni-based heterogeneous catalysts.
Catalyst
Conversion (%)
% Yield of product
Epoxide
TONa
Ref.
Others
[
Ni/L]2+/montmorilloniteb
17
55
48
92
100
17
44
38
70
61
207
1000
981
883
35,294
[51]
[56]
[56]
[54]
NiO
NiO/SiO
11
10
22
39
2
[
Ni(Malonate)(H
2
O)
n
]
Ni(II)-MCM-41
This study
a
Turnover number (TON) = moles converted/mol of active site.
L = 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane.
b
Table 3
Epoxidation of styrene using tert-BuOOH catalyzed by a variety of catalysts having similar kind of ligand system.
Catalyst
Bis-(2-hydroxy-naphthylidine)-1,2-cyclohexanediaminato]-dioxo-Mn(III)
Mn(II) complex on mesoporous silica nanoparticle
bis-(2-hydroxy-naphthylidine)-1,2-cyclohexanediaminato]-dioxo-Co(III)
Co(II) complex on mesoporous silica nanoparticle
Cr(Sal-Ala)-MCM-41
Time (h)
% Yield of epoxide
Ref.
[
20
24
20
24
4
89.9
64
46.2
63
64.3
61.5
61
[57]
[60]
[57]
[60]
[61]
[61]
This study
[
Cr(Sal-Ala)-SBA-15
Ni(II)-MCM-41
4
20
Ni(II)-MCM-41. Si-MCM-41 shows three characteristic Bragg
reflections which can be indexed to (1 0 0), (1 1 0) and (2 0 0)
planes of a hexagonal lattice of mesoporous MCM-41 material
modification of Si-MCM-41 and subsequent formation of nickel(II)
complex onto the matrix are not inconsistent.
[
21,22]. The values of XRD unit cell parameter for Si-MCM-41
3.2. FT-IR and UV–vis spectroscopic study
and Ni(II)-MCM-41 were 4.05 and 3.79 nm, respectively. XRD pat-
tern remained the same after immobilization of the nickel(II)
Schiff-base complex in the mesoporous matrix. A small decrease
in d-spacing values in Ni(II)-MCM-41 in comparison to Si-MCM-
Infrared spectroscopy was used to characterize the surface
properties of silica-based samples. Several characteristic bands
for Si-MCM-41, MCM-41-(SiCH CH CH NH ) and Ni(II)-MCM-41
2 2 2 2 x
4
1 is attributable due to the complex formation of Ni(II) with the
are shown in Fig. 2. The bands appeared at 1070, 811 and
970 cm corresponds to the asymmetric and symmetric Si–O–Si
À1
Schiff-base ligand. Upon post synthetic grafting an overall decrease
in the intensity of the peaks was also observed. This result is attrib-
uted to the lowering of the local order, such as variations in the
wall thickness, or might be the result of the reduction of scattering
contrast between the channel wall of silicate framework and nickel
complex present in the pores. A similar type of behavior was
observed by Burkett et al. in phenyl modified mesoporous sieves
vibrations, and Si–OH vibrations, respectively. A broad band ap-
À1
peared in the range of 3600–3200 cm suggests that the presence
of silanol groups in MCM-41. Appearance of N–H and C–H vibra-
À1
À1
tion bands in the 3100–2800 cm and 1550–1250 cm region
upon grafting of APTES onto Si-MCM-41 confirm the attachment
of aminopropyl groups on the surface of the support. These bands
were absent in the case of Si-MCM-41. The characteristic band for
[
4
40,41] and by Lim and Stein for directly synthesized thiol-MCM-
1 [42]. Therefore, the changes of the diffraction lines upon organic
À1
azomethine group in Ni(II)-MCM-41 appears at 1630 cm which

1
862
S. Bhunia, S. Koner / Polyhedron 30 (2011) 1857–1864
À1
is shifted to a lower frequency by 13 cm in comparison to the
corresponding vibration bands for free azomethine group, suggest-
ing coordination of azomethine nitrogen with nickel(II).
maxima at 610 nm, whereas in bis-(n-propyl-salicylaldimine)-
nickel(II) complex a strong absorption band was appeared in the
range of 565–785 nm with a absorption maxima at 625 nm. These
bands can be ascribed due to several d ? d transition of similar
Fig. 3 represents the infrared spectroscopy of bis-(n-propylsali-
cylaldimine) nickel(II) complex. Presence of strong absorption
band at 1610 cm can be assigned to the vibration band of ˜C@N–
group. Shifting to the lower frequency of the azomethine group in
complex with compare to free Schiff-base ligand confirms the coor-
dination of the imine nitrogen to the metal center. The sharp band
6
2
energies which correspond to t2g
e
g
electronic configuration of
À1
Ni(II) centers. All samples exhibit several high intensity CT and
intra-ligand bands in the range of 200–485 nm [43]. The CT and
d ? d transition afforded evidences for complexation of Ni(II) ions
with the Schiff-base ligand.
À1
appeared at 2953 cm can be assigned to the presence of C–H
stretching frequency of methylene group.
3.3. Transmission electron microscopic study
Figs. 4 and 5 demonstrate the solid-state electronic spectra of
the catalyst Ni(II)-MCM-41 and bis-(n-propyl-salicylaldimine)-
nickel(II) complex, respectively. Ni(II)-MCM-41 shows a relatively
weak, broad band in the range of 570–720 nm having a absorption
Transmission electron micrographs of Si-MCM-41 and
Ni(II)-MCM-41 have been measured. Fig. 6A and B shows the
representative TEM micrographs of Si-MCM-41 and the catalyst
Table 4
Comparison of catalytic activity in epoxidation reactions of olefins catalyzed by Ni(II)-MCM-41, Ni(NO
3
)
2
Á6H
2
O and Ni(II) Schiff-base complex.
Catalyst
Alkenes
Reaction time (h)
Temp. (°C)
Conversion (wt%)
% Yield of products
TOFb
1764
Epoxides
61
Others
39a
Ni(II)-MCM-41
20
70
100
2
2
4
4
70
70
86
84
86
84
1194
704
2
2
4
4
70
70
71
58
71
58
1286
790
Ni(NO
3 2
) Á6H
2
O
20
70
60
7
53a
21
2
2
4
4
70
70
13
27
13
27
3.5
4.5
2
2
4
4
70
70
69
18
43
7
26
11
24
5
Ni(II) Schiff-base complex
20
70
87
47
40a
40
2
2
4
4
70
70
33
72
33
72
12
16
2
2
4
4
70
70
64
8
37
8
27
30
3
Reaction conditions: alkenes (500 mg); catalyst (20 mg of Ni(II)-MCM-41 or 2 mg of Ni(II) Schiff-base complex or 2 mg of Ni(NO
3
)
2
Á6H
2
O); tert-BuOOH (1 ml); acetonitrile
(
8 ml); Temp. 70 °C. The products of the epoxidation reactions were collected at different time intervals and were identified and quantified by Varian CP-3800 gas
chromatograph equipped with an FID detector and a CP-Sil 8 CB capillary column.
a
Benzaldehyde.
Turnover frequency (TOF) = TON/time (h).
b

S. Bhunia, S. Koner / Polyhedron 30 (2011) 1857–1864
1863
Ni(II)-MCM-41, respectively. Both Ni(II)-MCM-41 and Si-MCM-41
feature an open-ended lamellar type arrangement of hexagonal
porous tubules. When electron beam falls on MCM-41 type meso-
porous materials perpendicular to the pore axis, the pores are seen
to be arranged in patches composed of regular rows as has been
interpreted by Chenite et al. [44,45]. TEM micrograph of Si-MCM-
been studied under homogeneous reaction conditions. The results
of these catalytic reactions are given in Table 4. Comparison of
results of these catalytic reactions shows that the efficiency of
Ni(II)-MCM-41 catalyst is remarkably better than its corresponding
homogeneous analogs. Notably, concentration of active sites, i.e.
nickel(II) in Ni(II)-MCM-41 has also a significant effect on the
efficiency of the catalyst. Efficiency of the catalyst, Ni(II)-MCM-
41 enhanced as the percentage of nickel(II) centers is decreased
(see Supporting material; Table S1). In fact, it is well established
that heterogenization increases the activity of the homogeneous
catalysts due to site-isolation and cooperative effects between
the solid support and the metal complexes [58,59]. In case of
homogeneous catalysis, turns over frequencies (TOF) of the
epoxidation reaction are markedly low in comparison to the
heterogeneous process. Besides, homogeneous catalyst cannot be
recovered or reused after the reaction.
In the catalytic epoxidation of olefins the choice of solvent is an
important factor. Among acetonitrile, methanol, dichloromethane
and acetone, acetonitrile seems to be the best choice as reaction
medium due to higher catalytic activity (Table 5). The higher cata-
lytic activity in acetonitrile can be ascribed due to the optimum
polarity of the solvent that dissolves both olefin and tert-BuOOH.
Blank experiments were performed with styrene in the absence
of catalyst under the same experimental conditions in the presence
of oxidant. Negligible amount of styrene epoxide was obtained in
the absence of catalyst.
4
1 viewed along the pore axis reveals a hexagonal array having
channel dimension of ꢀ3.9 nm, which is consistent with the XRD
results. Ni(II)-MCM-41 also exhibits a similar type of array of
regular rows in TEM micrographs. Therefore, it can be concluded
that both Si-MCM-41 and Ni(II)-MCM-41 have a similar type of
external morphology. In our case, the morphology of the tubules
in Si-MCM-41 as well as Ni(II)-MCM-41 are rectilinear and they
are of 1200–1700 Å long. Comparison of TEM micrographs of
Si-MCM-41 and Ni(II)-MCM-41, it appears that the channels are
of similarly ordered, which is indicative of retention of mesoporous
nature of the Si-MCM-41 upon tethering of Ni(II)-Schiff-base
complex.
3.4. Epoxidation reaction
The mechanism involved in epoxidation reactions catalyzed by
nickel complexes in homogeneous and heterogeneous medium are
well established [46–49]. Epoxidation reactions catalyzed by metal
complex immobilized MCM-41 based catalysts are well known
[
50]. However, reports on the Ni-complex immobilized MCM-41
employed in epoxidation reaction are scarce in the literature.
Farzaneh and co-workers reported that Ni(II) complexes with
macrocyclic ligands of 1,8-dimethyl-1,3,6,8,10,13-hexa-azacycl-
otetradecane and 1,8-dibenzyl-1,3,6,8,10,13-hexa-azacyclote-
tradecane within montmorillonite and MCM-41 showed catalytic
activity in epoxidation reaction using tert-BuOOH as oxidant [51].
In the present study, Ni(II)-MCM-41 is found to be catalytically ac-
tive as well as selective in epoxidation reactions with various ole-
finic compounds using tert-BuOOH as oxidant. The results of the
catalytic epoxidation reactions are summarized in Table 1. Epoxi-
dation of cyclooctene goes smoothly, showing an excellent conver-
sion of 86% to form cyclooctene oxide with 100% selectivity.
Generally cyclooctene does not exhibit such a high conversion as
well as selectivity over Ni catalyst. Conversely, oxidation of cyclo-
octene catalyzed by metal complexes in homogeneous medium,
epoxide was not the sole product; cyclooctane-1,2-diol was also
generated as side product along with the desired epoxide [36,52].
Trujillano et al. employed Ni-saponite catalyst in the epoxidation
The overall catalytic activities of Ni(II)-MCM-41 in epoxidation
reactions were significant, which is reflected in the high turnover
numbers for all the olefins. To test if nickel is leaching out from
the catalyst during reaction, the liquid phase of the reaction mix-
ture is collected by filtration after completion of the reaction at
the reaction temperature (70 °C) and was subjected to atomic
absorption spectroscopic analysis. The analyses showed nickel
was absent in the filtrate. Besides, the filtrate mixture did not show
any catalytic activity towards epoxidation reaction. Therefore, it is
clear that nickel is not leaching out from the catalyst during reac-
tions. Both low and high concentration containing nickel(II)
(Ni = 0.68%; see Supporting material) catalysts were subjected to
leaching test. In both the cases leaching of metal during catalytic
reactions was not observed. These results confirm that the catalyst
is stable and can be reused several times without significant loss of
Table 5
of (Z)-cyclooctene with 70 wt% of H
oxidant than tert-BuOOH in this case, conversion remained within
0% even after 48 h [53]. We have succeeded to improve the con-
version of cyclooctene up to 90% with 100% selectivity using
Ni(Malonate)(H O) as catalyst in recent past [54]. Oxidation
2 2 2 2
O . Although H O was better
Solvent effects in epoxidation reactions of various olefins catalyzed by Ni(II)-MCM-41.
Alkenes
Time (h) % of conversion (% of yielda)
CH CN CH COCH MeOH
100 (61) 71 (32)
2
3
3
3
DCM
[
2
2
]
n
20
15 (10) 17 (9)
of styrene over various types of silicate or clay catalysts has been
receiving much attention [20,55]. Epoxidation of styrene catalyzed
by Ni(II)-MCM-41 showed 100% conversion with 61% yield. Epoxi-
dation of styrene with tert-BuOOH over transition metal immobi-
lized zeolite or molecular-sieves catalysts, the epoxide yield
seldom exceeded 40% in the previous studies [20,51,56] (Table
24
24
86 (86)
84 (84)
11 (11)
9 (9)
10 (10) 11 (7)
17 (17) 76 (66)
2). Epoxidation of styrene catalyzed by various metal complexes
having similar type of ligand system are given in Table 3. Catalyst
Ni(II)-MCM-41 demonstrates a comparable selectivity of styrene
epoxide. Notably, the yield of styrene epoxide improved up to
8
5–90% using certain copper/manganese based catalysts [37,57].
2
2
4
4
71 (71)
58 (58)
18 (18)
12 (12)
30 (30) 24 (24)
26 (24) 18 (9)
The heterogeneous epoxidation of trans-stilbene proceeded
smoothly with Ni(II)-MCM-41, showing an excellent conversion
of 84% with 100% selectivity. In the case of 1-hexene and 1-octene
the catalyst showed moderate conversion with 100% selectivity.
Catalytic efficacies of similar nickel(II) catalysts, viz. bis-(n-pro-
Reaction conditions: alkenes (500 mg); catalyst (20 mg); tert-BuOOH (1 ml); solvent
8 ml); Temp. 70 °C. The products of the epoxidation reactions were collected at
different time intervals and were identified and quantified by Varian CP-3800 gas
(
chromatograph equipped with an FID detector and a CP-Sil 8 CB capillary column.
a
pyl-salicylaldimine) nickel(II) complex and Ni(NO
3
)
2
Á6H
2
O have
Epoxide yield.

1
864
S. Bhunia, S. Koner / Polyhedron 30 (2011) 1857–1864
catalytic activity which reflects the advantages over their homoge-
neous counterparts.
[20] D.E. De Vos, M. Dams, B.F. Sels, P.A. Jacobs, Chem. Rev. 102 (2002) 3615.
[
21] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 (1992)
10.
7
[
22] J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowizc, C.T. Kresge, K.D. Schmitt, C.T.-
W. Chu, D.H. Olson, E.W. Shepard, S.B. McCullen, J.B. Higgins, J.L. Schlenker, J.
Am. Chem. Soc. 114 (1992) 10834.
4
. Conclusion
[
23] W. Nam, H.J. Kim, S.H. Kim, R.Y.N. Ho, J.S. Valentine, Inorg. Chem. 35 (1996)
1045.
24] F. Zaera, Catal. Today 81 (2003) 149.
25] J.D. Koola, J.K. Kochi, Inorg. Chem. 26 (1987) 908.
26] J.F. Kinneary, T.R. Wagler, C.J. Burrows, Tetrahedron Lett. 29 (1988) 877.
In summery, Ni(II)-Schiff-base complex has been successfully
[
[
[
tethered onto Si-MCM-41 upon post-synthesis modification of
mesoporous silica matrix. Epoxidation reaction of olefins using
tert-BuOOH as the oxidant, has been efficiently catalyzed by
Ni(II)-MCM-41 under heterogeneous condition. Yield of epoxides
is highly dependent on the solvent, and the best yields were
achieved in acetonitrile. Besides, catalyst can be recycled and re-
used without significant loss of catalytic activity.
[27] W. Nam, J.S. Valentine, J. Am. Chem. Soc. 115 (1993) 1772.
[28] B. Dangel, M. Clarke, J. Haleg, D. Sames, R. Rolt, J. Am. Chem. Soc. 119 (1997)
10865.
[
29] M.T. Rispens, O.J. Gelling, A.M. de Vries, A. Meetsma, F.V. Bolhuis, B.L. Feringa,
Tetrahedron 52 (1996) 3521.
[30] D. Chatterjee, A. Mitra, J. Mol. Catal. A: Chem. 144 (1999) 363.
[
[
[
31] K.J. Ciuffi, E.J. Nassar, L.A. Rocha, Z.N. da Rocha, S. Nakagaki, G. Mata, R.
Trujillano, M.A. Vicente, S.A. Korili, A. Gil, Appl. Catal. A 319 (2007) 153–
Acknowledgments
162.
32] G. Mata, R. Trujillano, M.A. Vicente, S.A. Korili, A. Gil, C. Belver, K.J. Ciuffi, E.J.
Nassar, G.P. Ricci, A. Cestari, S. Nakagaki, Micropor. Mesopor. Mater. 124
We acknowledge the Department of Science and Technology,
Government of India for funding a project (to S.K.) (SR/S1/IC-01/
009). We also acknowledge the Department of Science and Tech-
nology, Government of India for financial assistance to procure a
Gas Chromatograph in another project (to S.K.) (SR/S1/IC-23/
003). E.M. SINP is acknowledged for TEM measurement (on a
(
2009) 218.
33] A.R. Silva, C. Freire, B. de Castro, M.M.A. Freitas, J.L. Figueiredo, Micropor.
Mesopor. Mater. 46 (2001) 211.
34] S. Jana, S. Bhunia, S. Koner, Appl. Catal. A: Gen. 392 (2011) 225.
35] S. Bhunia, R. Sen, S. Koner, Inorg. Chim. Acta 363 (2010) 3993.
36] C. Adhikary, R. Bera, B. Dutta, S. Jana, G. Bocelli, A. Cantoni, S. Chaudhuri, S.
Koner, Polyhedron 27 (2008) 1556.
37] S. Jana, B. Dutta, R. Bera, S. Koner, Langmuir 23 (2007) 2492.
38] W.-H. Zhang, J.-L. Shi, L.-Z. Wang, D.-S. Yan, Chem. Mater. 12 (2000) 1408.
39] D. Britton, L.H. Pignolet, Acta Crystallogr, Sect. C 45 (1989) 819–821.
2
[
[
[
2
[
[
[
chargeable basis).
Appendix A. Supplementary data
[40] S.L. Burkett, S.D. Sims, S. Mann, Chem. Commun. (1996) 1367.
[
[
[
41] C.E. Fowler, S.L. Burkett, S. Mann, Chem. Commun. (1997) 1769–1770.
42] M.H. Lim, A. Stein, Chem. Mater. 11 (1999) 3285.
43] K.C. Gupta, A.K. Sutar, J. Macromol. Sci. Pure Appl. Chem., A 44 (2007) 1171.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2011.04.040.
[44] A. Chenite, Y. Le Page, A. Sayari, Chem. Mater. 7 (1995) 1015.
[
[
[
45] C.-F. Cheng, H. He, W. Zhou, J. Klinowski, J. Phys. Chem. 100 (1996) 390.
46] K.A. Jørgensen, Chem. Rev. 89 (1989) 431.
47] S.H. Jhung, J.-H. Lee, A.K. Cheetham, G. Férey, J.-S. Chang, J. Catal. 239 (2006)
References
9
7.
[
[
[
[
[
[
1] B.S. Lane, K. Burgess, Chem. Rev. 103 (2003) 2457.
[48] V. Mirkhani, M. Moghadam, S. Tangestaninejad, I. Mohammadpoor-Baltork, E.
Shams, N. Rasouli, Appl. Catal. A 334 (2008) 106.
[49] D.V. Deubel, G. Frenking, P. Gisdakis, W.A. Herrmann, N. Rösch, J. Sundermeyer,
Acc. Chem. Res. 37 (2004) 645.
[50] Q.-H. Xia, H.-Q. Ge, C.-P. Ye, Z.-M. Liu, K.-X. Su, Chem. Rev. 105 (2005) 1603.
[51] H. Sohrabi, M. Esmaeeli, F. Farzaneh, M. Ghandi, J. Incl. Phenom. Macrocycl.
Chem. 54 (2006) 23.
[52] R. Bera, C. Adhikary, S. Ianelli, S. Chaudhuri, S. Koner, Polyhedron 29 (2010)
2166–2170. and references therein.
[53] R. Trujillano, M.A. Vicente, V. Rives, S.A. Korili, A. Gil, K.J. Ciuffi, E.J. Nassar,
Micropor. Mesopor. Mater. 117 (2009) 309.
[54] R. Sen, S. Bhunia, D. Mal, S. Koner, Y. Miyashita, K.-I. Okamoto, Langmuir 25
(2009) 13667.
[55] E. Bouhlel, P. Laszlo, M. Levart, M.-T. Montaufier, G.P. Singh, Tetrahedron Lett.
34 (1993) 1123.
[56] V.R. Choudhary, R. Jha, P. Jana, Catal. Commun. 10 (2008) 205.
[57] X.-H. Lu, Q.-H. Xia, H.-J. Zhan, H.-X. Yuan, C.-P. Ye, K.-X. Su, G. Xu, J. Mol. Catal.
A 250 (2006) 62.
2] H.C. Kolb, M.S. VanNieuwenhze, K.B. Sharpless, Chem. Rev. 94 (1994) 2483.
3] R. Noyori, M. Aoki, K. Sato, Chem. Commun. (2003) 1977.
4] T. Katsuki, Chem. Soc. Rev. 33 (2004) 437.
5] T. Katsuki, K.B. Sharpless, J. Am. Chem. Soc. 102 (1980) 5974.
6] J.T. Lutz Jr., in: Kirk-Othmer, M. Grayson, D. Eckroth, G.J. Bushey, C.I. Eastman,
A. Klingsberg, L. Spiro (Eds.), Encyclopedia of Chemical Technology, 3rd ed.,
vol. 9, Wiley, New York, 1980, pp. 251–266.
7] L. Canali, D.C. Sherrington, Chem. Soc. Rev. 28 (1999) 85.
8] D.E. De Vos, B.F. Sels, P.A. Jacobs, Adv. Synth. Catal. 345 (2003) 457.
9] J.-M. Brégeault, Dalton Trans. (2003) 3289.
[
[
[
[
[
[
[
[
10] C. Bowers, P.K. Dutta, J. Catal. 122 (1990) 271.
11] M.R. Maurya, S.J.J. Titinchi, S. Chand, J. Mol. Catal. A: Chem. 214 (2004) 257.
12] M. Salavati-Niasari, Inorg. Chem. Commun. 8 (2005) 174.
13] M. Salavati-Niasari, J. Mol. Catal. A 229 (2005) 159.
14] S.M. Drechsel, R.C.K. Kaminski, S. Nakagaki, F. Wypych, J. Colloid Interface Sci.
2
77 (2004) 138.
15] F. Minutolo, D. Pini, A. Petri, P. Salvadori, Tetrahedron: Asymmetry 7 (1996)
293.
16] I.J. Drake, K.L. Fujdala, A.T. Bell, T.D. Tilley, J. Catal. 230 (2005) 14.
17] F. Minutolo, D. Pini, P. Salvadori, Tetrahedron Lett. 37 (1996) 3375.
18] I.F.J. Vankelecom, D. Tas, R.F. Parton, V. Van de Vyver, P.A. Jacobs, Angew.
Chem., Int. Ed. Engl. 35 (1996) 1346.
[
2
[58] T.J. Terry, G. Dubois, A. Murphy, T.D.P. Stack, Angew. Chem. 46 (2007) 945.
[59] M.W. McKittrick, C.W. Jones, J. Am. Chem. Soc. 126 (2004) 3052.
[60] D. Tang, W. Zhang, Y. Zhang, Z.-A. Qiao, Y. Liu, Q. Huo, J. Colloid Interface Sci.
356 (2011) 262.
[
[
[
[61] X. Wang, G. Wu, W. Wei, Y. Sun, Catal Lett. 136 (2010) 96.
[
19] S. Koner, K. Chaudhari, T.K. Das, S. Sivasanker, J. Mol. Catal. A 150 (1999) 295.