Mn(II) and VO(IV) Schiff base complexes encapsulated in nanocavities of zeolite-Y: catalytic activity toward oxidation of alkenes and reduction of aldehydes

Article abstract of DOI:10.1007/s13738-016-0915-x

Oxovanadium(IV) and manganese(II) complexes of two Schiff base ligands, bis(2,4-dihydroxyacetophenone)-1,2-propandiimine (H₂L₁) and bis(2,4-dihydroxyacetophenone)-ethylenediimine (H₂L₂) were synthesized and characterized. The encapsulation of these complexes in the nanocavities of zeolite-Y was achieved by a flexible ligand method. The prepared heterogeneous catalysts have been characterized by FTIR, NMR and atomic absorption spectroscopy, X-ray diffraction patterns, scanning electron microscopy and BET. The catalytic activities of the encapsulated complexes were studied in the oxidation of alkenes with H₂O₂ and the reduction of aldehydes with NaBH₄. In most cases, the manganese (II) complexes (MnL₁-Y, MnL₂-Y) showed better activity than the oxovanadium (IV) complexes (VOL₁-Y, VOL₂-Y) in both oxidation of alkenes and reduction of aldehydes. The catalytic activity of the recovered catalysts was compared with the fresh ones.

Full text of DOI:10.1007/s13738-016-0915-x

J IRAN CHEM SOC
DOI 10.1007/s13738-016-0915-x
ORIGINAL PAPER
Mn(II) and VO(IV) Schiff base complexes encapsulated
in nanocavities of zeolite‑Y: catalytic activity toward oxidation
of alkenes and reduction of aldehydes
Saeed Rayati1 · Saeedeh Shokoohi1 · Elaheh Bohloulbandi1
Received: 3 January 2016 / Accepted: 13 June 2016
© Iranian Chemical Society 2016
Abstract Oxovanadium(IV) and manganese(II) com-
plexes of two Schiff base ligands, bis(2,4-dihydroxyace-
tophenone)-1,2-propandiimine (H2L1) and bis(2,4-
dihydroxyacetophenone)-ethylenediimine (H2L2) were
synthesized and characterized. The encapsulation of these
complexes in the nanocavities of zeolite-Y was achieved by
a flexible ligand method. The prepared heterogeneous cata-
lysts have been characterized by FTIR, NMR and atomic
absorption spectroscopy, X-ray diffraction patterns, scan-
ning electron microscopy and BET. The catalytic activities
of the encapsulated complexes were studied in the oxida-
tion of alkenes with H2O2 and the reduction of aldehydes
with NaBH4. In most cases, the manganese (II) complexes
(MnL1-Y, MnL2-Y) showed better activity than the oxova-
nadium (IV) complexes (VOL1-Y, VOL2-Y) in both oxida-
tion of alkenes and reduction of aldehydes. The catalytic
activity of the recovered catalysts was compared with the
fresh ones.
base ligands are well known to mimic the catalytic cycle
of cytochrome P-450 and have attracted research interest
in recent years [3, 4]. Encapsulated metallomacrocycles
in the nanopores of zeolite-Y combine the advantages of
homo- and heterocatalytic systems. These nanocomposite
materials have been extensively used as biomimetic hetero-
geneous catalysts for oxidation reactions with a variety of
oxidants [5–8] and reduction reactions with sodium boro-
hydride [9–13].
We have developed many catalytic systems using tran-
sition metal complexes of Schiff base ligands for various
oxidative chemical transformations [5, 14–16]. In com-
parison with the application of transition metal Schiff
base complexes as oxidative catalysts, their ability to
reduction reactions has received considerably less atten-
tion in organic synthesis [12, 13]. As an ongoing effort to
emphasize the role of transition metal complexes of Schiff
base ligands as reduction-promoting catalysts, herein, we
report an efficient reduction of different aldehydes using
NaBH4 and also heterogeneous oxidation of different alk-
enes with H2O2 in the presence of a oxovanadium(IV) and
manganese(II) Schiff base complexes encapsulated in the
nanocavities of zeolite-Y.
Keywords Zeolite · Heterogeneous catalyst · Schiff base ·
Nanocavity · Oxidation · Reduction
Introduction
Zeolites are attractive materials for encapsulation of tran-
sition metal complexes, organic dyes, polymers and orga-
nometallic compounds within their voids [1, 2]. The zeo-
lite-encapsulated transition metal complexes of Schiff
Experimental
Materials
(2,4-Dihydroxyacetophenone),1,2-diaminopropane, ethyl-
enediamine, zeolite-Y (Na52[(AlO2)52(SiO2)140]), hydrogen
peroxide (30 %) and sodium borohydride were obtained
from Merck. Other materials were of commercial reagent
grade and were purchased from Sigma-Aldrich or FLUKA
companies and treated when necessary.
* Saeed Rayati
rayati@kntu.ac.ir; srayati@yahoo.com
1
Department of Chemistry, K. N. Toosi University
of Technology, P.O. Box 16315-1618, Tehran 15418, Iran
1 3

J IRAN CHEM SOC
Physicochemical characterization techniques
was dissolved in 20 mL of ethanol. Ethanolic solutions
of 1 mmol vanadyl acetylacetonate or manganese acetate
were added to above solution, and the reaction mixture was
refluxed for 2 h. The colored solution was concentrated
to yield colored powders. The products were washed with
warm ethanol.
M–Y was prepared by ion-exchange method: Typically,
3 g of one type of the above-mentioned metal ion was first
dissolved in 100 mL deionized water. Then, 1.25 g Na–Y
was added to the solution and further stirred for 24 h at
90 °C. The solid was filtered and washed with deionized
water and dried at room temperature.
Encapsulation of metal complex was performed with the
flexible ligand method. M–Y (0.7 g) and 1.25 g of ligand
were mixed in 50 mL of methanol, and the reaction mixture
was refluxed for 17 h in an oil bath with stirring. The result-
ing material was separated by filtration and then extracted
with methanol using Soxhlet extractor for 72 h to remove
unreacted ligand from the cavities of the zeolite as well as
those located on the surface of the zeolite along with neat
complexes, if any. The unreacted metal ions present in
the zeolite were removed by stirring with aqueous 0.01 M
NaCl solution. The resulting solid was filtered and washed
with distilled water until free from chloride ions. Finally, it
was dried at 120 °C in an air oven for several hours.
NMR spectrum was recorded in CDCl3 with a Bruker FT-
NMR 500 (500 MHz) spectrometer. Fourier transform infrared
spectra (FTIR) were collected in anABB Bomem FTLA 2000-
100 spectrophotometer with KBr disk in the 400–4000 cm−1
range. Ultraviolet–visible (UV–Vis) spectra were carried on
the 200–700 nm range with a Lambda 25 PerkinElmer Spec-
trophotometer. For powder X-ray diffraction (XRD) analysis,
self-oriented films were placed on neutral glass sample hold-
ers. The patterns were obtained in the reflection mode on a
STOE STADIP diffractometer using monochromatized Cu
Kα radiation as incident beam. Data were collected over the
2θ range of 10°–80°. Nitrogen sorption experiments were
recorded using a Belsorp-BEL, Inc. analyzer at 77 K. The sur-
face areas were calculated by Brunauer–Emmett–Teller (BET)
method, and the pore size distributions were calculated from
the adsorption branch of the isotherms using BJH method. The
scanning electron microscopy (SEM) images were obtained
using a VEGA3 TESCAN scanning electron microscope. The
conversions of the products were accomplished by GC-FID on
a Shimadzu GC-14B instrument equipped with a flame ioni-
zation detector and a SAB-5 capillary column (phenyl methyl
siloxane 30 m × 320 mm × 0.25 mm). After completely
destroying the zeolitic framework, vanadium and manganese
percentages were analyzed by atomic absorption spectropho-
tometry (AAS) with flame atomization (Varian AA240).
Catalytic measurements
Preparation of the ligands
General procedure for catalytic oxidation of alkenes
with hydrogen peroxide
To an ethanolic solution (30 mL) of 1,2-diaminopropane
(0.074 g, 1 mmol for H2L1) or ethylenediamine (0.059 g,
1 mmol for H2L2), 2,4-dihydroxyacetophenone (0.304 g,
2 mmol) was added. The solution was stirred and heated
to reflux for 1 h. Then, obtained precipitate was filtered off
and washed with warm ethanol.
In a typical procedure, to a mixture of alkene (0.32 mmol)
and catalyst (0.0008 mmol) in CH3CN (1 mL), was added
1 mL of H2O2. The reaction mixture was refluxed for 4 h.
The progress of the reaction was monitored by GLC.
Analysis calculated for bis(2,4-dihydroxyacetophenone)-
1,2-propandiimine (H2L1) C19H22N2O4 (342.16), selected
FTIR data, υ (cm−1): 3422 (O–H), 2856–2982 (C–H), 1623
(C=N), 1537 (C=C), 1052 (C–O). 1H NMR (δ): 1.26–1.28 (d,
3H, NCH2CH(CH3)N), 2.2–2.3 (d, 6H, (CH3) C=N), 3.5–3.7
(m, 1H, NCH2CH(CH3)N), 4.18–4.19 (m, 2H, NCH2CH(CH3)
N), 6.03–7.40 (m, 6H, ArH), 16.52–16.67 (s, 4H, OH). UV–
Vis (CHCl3): 279 nm (π → π*), 306 nm (n → π*).
General procedure for catalytic reduction of aldehydes
with sodium borohydride
To a mixture of aldehyde (0.1 mmol) and catalyst
(0.003 mmol) in methanol (1 mL), 1.8 mg NaBH4
(0.05 mmol) was added. The reaction mixture was stirred
magnetically at room temperature for 2 min, and the pro-
gress of the reaction was monitored by GC.
Analysis calculated for bis(2,4-dihydroxyacetophenone)-
ethylenediimine (H2L2): C18H20N2O4 (328.18), selected
FTIR data, υ (cm−1): 3367 (O–H), 2856–2933 (C–H), 1633
(C=N), 1589 (C=C), 1084 (C–O). 1H NMR (δ): 2.2–2.3 (s,
6H, (CH3) C=N), 3.81 (s, 4H, N(CH2)2N), 6.02–7.44 (m,
6H, ArH), 16.53 (s, 4H, OH). UV–Vis (CHCl3): 281 nm
(π → π*), 314 nm (n → π*).
Results and discussion
Characterization of the catalysts
The metal-exchanged M–Y zeolite (M = Mn(II) and
VO(IV)) was prepared by exchanging Na+ of the zeolite
with the desired metal ion. In order to insert the Schiff base
The procedures for the preparation of metal (M = Mn
and VO) complexes are as follows: 1 mmol H2L1 or H2L2
1 3

J IRAN CHEM SOC
ligands in the cavity of the zeolite, an excess amount of the
ligands refluxed with M–Y zeolite in an oil bath with stir-
ring. The percentages of metal content of various catalysts
estimated by atomic absorption spectrometer are presented
in Table 1.
The FTIR spectral data can give information regard-
ing the crystallinity of the zeolite and the encapsulation of
complexes. Comparison of the spectra of neat complexes
with Schiff base ligands provides evidence for the coor-
dinating mode of ligand in the complexes (Table 2). The
sharp and strong band is observed at 1623 and 1633 cm−1
due to ν(C=N) of azomethine group of the H2L1 and H2L2
ligands, respectively. This band is appeared at ~1614–
1627 cm−1 in the spectra of neat complexes and at ~1627–
1644 cm−1 in the spectra of encapsulated complexes that
suggests the coordination of azomethine nitrogen to the
metal center [17]. The phenolic –OH vibration of the Schiff
Table 1 Metal content of the catalysts
No.
Catalyst
Metal content (wt%)
1
2
3
4
MnL1-Y
MnL2-Y
VOL1-Y
VOL2-Y
4.19
3.14
2.5
2.6
Table 2 IR spectral data of ligands and zeolite-encapsulated metal
complexes
base ligands H2L1 (3422 cm−1) and H2L2 (3354 cm−1
)
disappeared in that of the neat complexes, indicating the
involvement of this group in coordination with the metal
ion, via de-protonation.
Samples
Wave number (cm−1
)
ν(Al–O–Si)
ν(Al–O–Si)
ν(C=C)
ν(C=N)
ν(O–H)
The FTIR studies of Na–Y- and zeolite-encapsulated
metal complexes show that the peak intensities are weak
due to low concentration of the complexes in zeolite. In
the IR spectra of the modified zeolites, a broad band in
the range of 3200–3600 cm−1 is attributed to the adsorb-
ing tendency of surface hydroxyl groups, and the bands at
450–1200 cm−1 are because of lattice (Si/Al)O4 vibrations
[18]. The asymmetric stretching and symmetric stretch-
ing of the Al–O–Si framework of the zeolite are presented
in Table 2. No shift or broadening of zeolite vibrations
is observed upon insertion of the complexes, which pro-
vides further evidence that the zeolite framework remains
unchanged.
H2L1
–
–
1537
1589
1492
1502
1540
1532
–
1623
1633
1614
1627
1614
1610
–
3422
3354
3474
3424
3415
3389
3219
3402
3424
3438
3498
3506
H2L2
–
–
MnL1
–
–
MnL2
–
–
VOL1
–
–
VOL2
–
–
Mn-Y
VO-Y
MnL1-Y
MnL2-Y
VOL1-Y
VOL2-Y
689
691
796
793
793
795
1007
1003
1010
1052
996
1057
–
–
1548
1555
1541
1590
1627
1644
1634
1632
Fig. 1 XRD patterns of (a)
Mn-Y and (b) MnL1-Y
1 3

J IRAN CHEM SOC
The powder X-ray diffraction patterns of the Mn-
exchanged zeolites and the encapsulated Mn–Schiff base
complex in zeolite are shown in Fig. 1.
The XRD pattern of Mn–Y-entrapped complex is sim-
ilar to that of neat Mn–Y. Except the zeolite with encap-
sulated Mn—Schiff base has slightly weaker intensity.
These observations indicate that the framework and crys-
tallinity of the zeolite do not suffer any significant struc-
tural changes during encapsulation of the metal complex
and that the complex was well distributed in the cages.
The relative peak intensities of the 220 and 311 reflections
appearing at 2θ = 10° and 12° have been thought to be cor-
related with the locations of cations [19, 20]. In zeolite-Y,
the peak intensity is in the order: I220 > I311 [21], while in
Mn-exchanged and Mn-entrapped complex, the order of
peak intensity became I311 > I220 (Fig. 1). The difference
indicates that the ion Mn2+ exchanged which substitutes at
the location of Na+.
After careful comparison of XRD patterns of Mn–Y and
MnL1-Y, new diffraction peak was observed with 2θ values
of 17.43° in MnL1-Y but not observed in Mn–Y. This new
peak suggests the allocation and formation of metal com-
plex in the cavity of zeolite.
To study the textural characteristics of the encapsulated
VOL2 complex in comparison with the VO–Y zeolite,
nitrogen adsorption–desorption isotherms were recorded
(Fig. 2).
The VO–Y and VOL2-Y present type I isotherms accord-
ing to the IUPAC classification [22], showing a high uptake
of nitrogen at very low relative pressures, which is charac-
teristic of microporous nature of the materials.
Table 3 summarizes the BET surface area (SBET), the
total pore volume and the average pore size of the cata-
lyst support. The surface area of VO–Y was observed to
be 106.11 m2g−1. However, in the case of VOL2-Y, the
surface area was drastically reduced to 72.88 m2g−1. The
average pore size of VO–Y was 24.93 nm, and it reduced to
23.30 nm on VOL2-Y, possibly due to the presence of metal
complex in the pores of zeolite [23]. The decrease in the
surface area and pore volume clearly suggests that the metal
complex was encapsulated in the zeolite nanocavities.
Typical scanning electron micrographs obtained for the
parent Na–Y, MnL1-Y and VOL1-Y are shown in Fig. 3a–c.
The Na–Y has a cubic angular shape. The SEM analysis of
the MnL1-Y and VOL1-Y shows that the crystalline nature
of Na–Y remains almost the same even after complexation
occurs in the cavities of zeolite.
Fig. 2 N2 adsorption–desorption isotherms corresponding to VO-Y
and VOL2-Y
Table 3 Textural properties of VO-Y and its complex-encapsulated
analogue
Sample
SBET (m2g−1
)
Average pore size
(nm)
Pore volume
(cm3g−1
)
NMR, FTIR and the above-mentioned spectral stud-
ies confirm the possible proposed structure of the com-
plexes in the free and encapsulated systems, as given in
Scheme 1.
VO-Y
106.11
72.88
24.93
23.30
0.17
VOL2-Y
0.096
Fig. 3 SEM images of a Na–Y,
b MnL1-Y and c VOL1-Y
1 3

J IRAN CHEM SOC
Scheme 1 Proposed framework
structure of zeolite with encap-
sulated metal Schiff base com-
plexes of Mn(II) and VO(IV)
Table 4 Catalytic activity in epoxidation of cyclooctene over MnL1-
Y under different reaction conditions
Entry Reaction parameters
Conditions
Conversion %a
1
Solvent (dielectric con-
stants)
CH3CN (37.5) 70
CH3OH (32.7)
3
2
C2H5OH (26.6)
CH2Cl2 (8.9)
0
CHCl3 (4.9)
0
2
3
Amount of catalyst (mg)
Amount of H2O2 (mL)
None
1.2
2.4
None
1
0
70
56
0
70
70
2
Fig. 4 Screening of the different ImH/catalyst molar ratios on the on
the epoxidation of cyclooctene with H2O2. See the footnote of Table 4
a
Reaction conditions: cyclooctene (0.32 mmol), solvent (1 mL),
ImH (0.032 mmol); the reactions were run for 4 h under reflux
Catalytic activity studies
Heterogeneous catalytic epoxidation of olefins
Epoxidation of olefins has been investigated using the
encapsulated catalysts in the presence of H2O2 as a green
oxidant. To screen the performances of the encapsulated
catalysts, MnL1-Y was chosen as the representative cata-
lyst to study the influence of various reaction parameters to
acquire maximum oxidation.
The solvent plays an important and crucial role in cata-
lytic performance. To investigate the effect of solvent on
the oxidation of cyclooctene over the MnL1-Y as catalyst,
chloroform, acetonitrile, dichloromethane, methanol and
ethanol were used as solvents and the highest conversion
was obtained in acetonitrile (Table 4, entry 1). The solvent
was changed from polar solvent (acetonitrile) to low polar
solvent (chloroform) keeping other reaction conditions
Fig. 5 Screening of the epoxidation of cyclooctene by homogeneous
and heterogeneous catalysts with H2O2. See the footnote of Table 4
constant. Cyclooctene conversion was found to be 70 %
in acetonitrile, which decreased markedly in the CHCl3 to
0 % after 4 h. This could be explained by the polarity of
1 3

J IRAN CHEM SOC
Table 5 Epoxidation of olefins using H2O2 catalyzed by MLx-Y (M = Mn and VO, x = 1 and 2).a
Entry
Alkenes
Product
Catalyst
Conversion Selectivity
TONc
b
%
%
1
MnL1Y
MnL2Y
VoL1Y
VoL2Y
MnL1Y
MnL2Y
VoL1Y
VoL2Y
MnL1Y
MnL2Y
VoL1Y
VoL2Y
MnL1Y
MnL2Y
VoL1Y
VoL2Y
MnL1Y
MnL2Y
VoL1Y
VoL2Y
MnL1Y
MnL2Y
VoL1Y
VoL2Y
MnL1Y
MnL2Y
VoL1Y
VoL2Y
31
41
6
100
100
80
81
78
124
164
30
13
33
23
23
17
100
81
24
31
92
77
41
41
68
63
43
57
70
63
19
26
4
64
2
3
4
5
6
7
168
144
92
64
100
100
100
81
72
63
100
78
80
68
400
400
132
196
368
392
204
196
272
252
172
228
280
252
76
84
100
100
100
100
100
100
100
100
100
100
100
100
104
16
16
4
8
4
1
2
a
b
c
(0.32 mmol) alkene, (1 mL) H2O2, (1 mL) CH3CN, (4 h) time, under reflux
Conversions and selectivities were determined by GC based on the starting alkene
TON: (total turnover number) the ratio of the number of moles of product to the number of moles of catalyst
the used solvent [24]. The higher conversions in acetoni-
trile (70 % with H2O2) relative to the others possibly may
be due to the higher boiling point of acetonitrile.
To test the influence of the amount of the catalyst on
the catalytic reactivity of cyclooctene epoxidation, vari-
ous amounts of catalyst were used and compared. In the
absence of the catalyst (Table 4, entry 1), the reactions
did not proceed under reflux. The highest conversion of
cyclooctene was obtained with 1.2 mg of catalyst and fur-
ther increase in the amount of catalyst to 2.4 mg, the %
cyclooctene conversion decreased to 56 %. This is may
be due to faster decomposition of H2O2 in the presence of
excess of the catalyst [25].
Different oxidant (H2O2) concentrations have been stud-
ied in the oxidation of cyclooctene (Table 4, entry 3). In
the absence of oxidant, no activity is observed and the oxi-
dation of cyclooctene required 1 mL of H2O2 for comple-
tion. Further addition of H2O2 to the reaction mixture led to
similar results.
Fig. 6 Results obtained in the epoxidation of cyclooctene with H2O2
by MnL1-Y with a catalyst reused several times. Reaction conditions:
cyclooctene (0.32 mmol), solvent (1 mL), H2O2 (1 mL); the reactions
were run for 4 h under reflux
1 3

J IRAN CHEM SOC
The reactivity of manganese catalysts in the oxida-
tion reactions can be improved by the addition of differ-
ent nitrogenous bases as co-catalyst [26–28]. For a better
understanding of the role of the imidazole in this catalytic
system, the effect of different molar ratios of the ImH/cata-
lyst on the epoxidation of cyclooctene was investigated.
In the absence of imidazole, the reaction proceeds only in
19 % yield, whereas the addition of imidazole increased the
reaction conversion (Fig. 4).
An increase in the ImH/catalyst molar ratio up to 40
remarkably improved the reaction rate. Beyond this ratio, a
significant decrease in catalytic efficiency is observed, which
may be attributed to the formation of an inactive species [29].
In order to demonstrate the effect of encapsulation of the
catalysts in the nanocavities of the zeolite-Y, on the cata-
lytic activity of manganese (III) Schiff base complexes in
the oxidation reactions, the epoxidation of cyclooctene
with H2O2 was carried out in the presence of neat MnL1
and MnL1-Y in a comparative manner (Fig. 5).
In order to verify the catalytic scope of this catalytic
system, under optimized conditions, it has also been
applied for epoxidation of a wide variety of alkenes
(Table 5). It was obvious that this catalyst (MnL1-Y) could
efficiently convert 4-methoxystyrene, α-methylstyrene,
cyclooctene and cyclohexene to their corresponding epox-
ides. However, catalytic epoxidation of styrene and 4-chlo-
rostyrene was found less efficient. The terminal linear
alkene (1-octene) was null reaction. Because of the low
π-electron density of linear terminal alkene, they are less
reactive toward electrophiles than internal alkenes [30].
Much reactivity observed in the case of MnL1-Y in com-
parison with MnL2-Y seems to be due to its higher con-
centration of the manganese catalyst in the nanocavities of
the zeolite-Y (Table 1).
The effect of transition metal complexes encapsulated in
zeolite, MLx–Y (M = Mn(II) and VO(IV), x = 1 and 2),
was studied on the epoxidation of variety of alkenes with
hydrogen peroxide, and the results are shown in Table 5. It
is clear from results that manganese complexes encapsu-
lated in zeolite are more active than vanadium complexes.
The reusability of a heterogeneous catalyst is of
great importance in catalyst design. The homogeneous
MnL1 is readily degraded and cannot be recovered even
once; in contrast, the supported manganese Schiff base
The encapsulated catalyst was more active than the cor-
responding neat complex, and the turnover number (TON)
increases dramatically in the Mn–Schiff base complex into
the zeolite-Y. Also oxidation of cyclooctene in the presence
of neat VOL1 led to the formation of 30 % cyclooctene
oxide as the sole product.
Fig. 7 Reduction of aldehydes
with NaBH4 in the presence
of MnL1-Y in methanol at
room temperature; Reaction
conditions: the molar ratios for
catalyst/substrate/NaBH4 are
1:30:15
1 3

J IRAN CHEM SOC
catalyst can be filtered and reused several times without
significant loss of its activity. The reusability of MnL1-
Y catalyst was tested over three consecutive runs, and
the consequent results are illustrated in Fig. 5. The used
catalyst was recovered and rinsed with copious amount
of methanol after each catalytic run. The washed cat-
alyst was dried at 110 °C for 24 h before reuse. The
catalytic activity after the first cycle of MnL1-Y has
an obvious decrease compared with the fresh catalyst
(Fig. 6).
Conclusion
It can be concluded that MLx (M = Mn(II) and VO(IV),
x = 1 and 2) complexes can be encapsulated in Na–Y zeo-
lite supercages without structural modification or loss of
crystallinity of the zeolite framework. The physicochemi-
cal studies confirmed the encapsulation of metal complexes
in the supercages of zeolite-Y. Catalytic activity of the pre-
pared catalysts in both oxidation of alkenes with H2O2 and
reduction of aldehydes with NaBH4 was investigated. In the
both catalytic reactions, manganese complexes show higher
catalytic activity than the vanadium ones.
This decrease in activity is also accompanied with an
apparent decrease in the amount of manganese content.
Acknowledgments This work has been supported by the Iran
National Science Foundation (INSF) (Grant No. 88001216).
Heterogeneous catalytic reduction of aldehydes
The high catalytic activity of MnL1-Y in the oxidation of
alkenes prompted us to explore its catalytic activity in the
reduction of aromatic aldehydes to their corresponding
alcohols with sodium borohydride at room temperature
(Fig. 7).
Results in Fig. 7 showed that in the presence of this
catalyst, high-to-excellent conversions (56–100 %) were
obtained for most of the aldehydes. While the reduction
of 4-chlorobenzaldehyde in the presence of MnL1-Y led
to 93 % reduction of the aldehyde (reaction 1 in Fig. 7),
running the reaction in the absence of the catalyst gave the
product with a yield of 25 %.
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