Synthesis, characterization, and catalytic activity of metallo octamethylcalix (4) pyridino complexes encapsulated in MCM-41

Article abstract of DOI:10.1080/00397911.2012.745565

The synthesis and encapsulation of M⁺ⁿ-octamethylcalix(4) pyridino complexes using acetone and pyridine in H-MCM-41 have been achieved and presented. These hybrid catalysts are characterized by x-ray diffraction, infrared, thermal analysis, Brunauer-Emmett-Teller (BET) surface area, and scanning electron microscopy and tested for catalytic activity. They are active in the liquid-phase oxidation of p-xylene using H₂O₂ as oxidant and acetic acid as solvent in the temperature range of 30-100 °C. The variation of central transition-metal cation and the heterocyclic ring in the metallomacrocycle influence the catalytic activity.

Full text of DOI:10.1080/00397911.2012.745565

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Synthesis, Characterization,
and Catalytic Activity of Metallo
Octamethylcalix (4) Pyridino Complexes
Encapsulated in MCM-41
C. N. Rohitha a , S. J. Kulkarni a & N. Narender a
a Catalysis Group, Indian Institute of Chemical Technology ,
Hyderabad , India
Accepted author version posted online: 31 May 2013.Published
online: 25 Jul 2013.
To cite this article: C. N. Rohitha , S. J. Kulkarni & N. Narender (2013) Synthesis, Characterization,
and Catalytic Activity of Metallo Octamethylcalix (4) Pyridino Complexes Encapsulated in MCM-41,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 43:21, 2853-2866, DOI: 10.1080/00397911.2012.745565
To link to this article: http://dx.doi.org/10.1080/00397911.2012.745565
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Synthetic Communications1, 43: 2853–2866, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2012.745565
SYNTHESIS, CHARACTERIZATION, AND CATALYTIC
ACTIVITY OF METALLO OCTAMETHYLCALIX (4)
PYRIDINO COMPLEXES ENCAPSULATED IN MCM-41
C. N. Rohitha, S. J. Kulkarni, and N. Narender
Catalysis Group, Indian Institute of Chemical Technology, Hyderabad, India
GRAPHICAL ABSTRACT
Abstract The synthesis and encapsulation of Mþn-octamethylcalix(4)pyridino complexes
using acetone and pyridine in H-MCM-41 have been achieved and presented. These hybrid
catalysts are characterized by x-ray diffraction, infrared, thermal analysis, Brunauer–
Emmett–Teller (BET) surface area, and scanning electron microscopy and tested for cata-
lytic activity. They are active in the liquid-phase oxidation of p-xylene using H2O2 as oxi-
dant and acetic acid as solvent in the temperature range of 30–100 ꢀC. The variation of
central transition-metal cation and the heterocyclic ring in the metallomacrocycle influence
the catalytic activity.
[Supplementary materials are available for this article. Go to the publisher’s online
edition of Synthetic Communications1 for the following free supplemental resource(s):
Full experimental and spectral details.]
Keywords Encapsulation; MCM-41; metallomacrocycles; molecular sieves; oxidation
INTRODUCTION
The encapsulation of transition-metal complexes inside the pores of zeolites
has attracted attention because it provides a simple way of coupling the reactivity
of the metal complex with the robustness and stereochemistry of the host zeolite.[1]
Zeolite molecular sieves, owing to their varied intrinsic properties (e.g., acidity,
basicity, redox behavior, etc.), channel sizes, high surface areas, thermal and chemi-
cal stabilities, and shape selectivities, have been extensively used in oil refining,
petrochemical, fine chemical, catalysis, and gas purification industries.[2–4]
Encapsulation provides a convenient route for the heterogenization of the
homogeneous catalytic process.[5] These hybrid catalysts offer the advantage of
shape selectivity and site isolation, as provided by the zeolite matrix, while retaining
Received August 8, 2012.
Address correspondence to S. J. Kulkarni, Catalysis Group, Indian Institute of Chemical
Technology, Hyderabad 500607, India. E-mail: kulkarni_sjk@rediffmail.com
2853

2854
C. N. ROHITHA, S. J. KULKARNI, AND N. NARENDER
Scheme 1. Metallo octamethylcalix(4) pyridino complex.
the solution reactivity of the metal complex. The metal complex is trapped within the
molecular sieve and is not a surface-bound species.[6] Once assembled, these com-
plexes cannot be removed without destroying the lattice. There are several examples
in which the catalytic activity of the encapsulated complex is either increased or more
selective as compared to the same complex in solution.[7,8]
The metallomacrocycles encapsulated in the various molecular sieves are excel-
lent in the enzyme mimicking.[3,9–12] Many of them are expected to mimic the activity
of the biocatalysts such as chlorophyll, hemoglobin, or vitamin B12[13] as their central
moieties are the same. Using molecular sieves, we have synthesized these metalloma-
crocycles in one step with more than 70% yield.[14–19] Conventionally these macro-
cycles were synthesized using mineral acids such as sulfuric acid and then the
yields were 15 to 20% and separation, isolation, and purification of the products
became difficult.[20] Our method is ecofriendly, products are obtained good high
yield, and the catalysts can be reused. The mesoporous composite material
(MCM)-41 is an attractive support for metallomacrocycles because it provides a
large and tunable pore size, large internal surface area, and a regular array of porous
˚
channels. The large pore size of these molecular sieves (>20 A), facilitates the flow of
reactant and product molecules in and out of pore system.[21] Moreover MCM-41 is
oxidatively stable under the reaction conditions.
In this article, we report the synthesis and characterization of metallo octa-
methylcalix(4) pyridine complexes encapsulated in MCM-41 (herein after the encap-
sulated species is designated as Mþn-OMCPy-MCM-41) and their catalytic activity
in the liquid-phase oxidation of p-xylene using H2O2 oxidant in acetic acid. The
structure of metallomacrocyle is shown in Scheme 1. Chromium, manganese, iron,
and cobalt are selected as metal centers to the pyridine complex because of their
reported oxidation properties[22]
RESULTS AND DISCUSSION
Powder x-ray diffraction (XRD) patterns of uncalcined, calcined and metal
complex–encapsulated MCM-41 are depicted to study the crystallinity and to ensure
encapsulation. Powder XRD patterns of as-synthesized and calcined MCM-41
(Fig. S1 in the supporting information) reveal the typical four-peak pattern: a strong
peak at a low angle (d 100) around 2–3ꢀ and three weaker peaks at higher angles (110,
200, 210 reflection lines) around 4ꢀ, 4.7ꢀ, and 6ꢀ respectively. The XRD pattern of

MACROCYCLES IN MCM-41
2855
Figure 1. Powder XRD patterns of (a) H-MCM-41 and (b) Co-OMCPy-MCM-41.
Co–OMCPy-MCM-41 shows similar peaks as H-MCM-41, though slight changes in
the intensity of the peaks are seen (Fig. 1). These observations indicate that the hexag-
onal crystalline nature of MCM-41 is retained even after encapsulation of metalloma-
crocycle. This suggests that a high degree of long-range ordering of the structure is
preserved even after the inclusion of metallomacrocycle. A review of the literature shows
that the guest molecules are located exclusively inside the pores of MCM-4.[23,24] This
may be due to the presence of acid sites exclusively inside the pores.[25–27] These acid sites
are utilized as extra coordinating sites for metallomacrocycles.
Figure 2 shows the SEM images of metallomacrocycle supported and unsup-
ported MCM-41. The images are similar to each other, which explains that the
Figure 2. SEM images of (a) H-MCM 41 and (b) Co-OMCPy-MCM 41.

2856
C. N. ROHITHA, S. J. KULKARNI, AND N. NARENDER
Table 1. BET surface area of catalysts
No.
Catalyst
BET surface area (m2=g)
1
2
3
4
H-MCM-41
944
472
483
402
Co-OMCPy-MCM-41
Mn-OMCPy-MCM-41
Zn-OMCPy-MCM-41
encapsulated catalyst possesses the same morphology as the parent MCM-41. The
encapsulation of metallo octamethylcalix(4) pyridino complexes inside MCM-41 is
indicated by the absence of extraneous material in scanning electron microscopy
(SEM). SEM photographs indicate the presence of well-defined crystals without
any patches of metal complexes overlaid on their external surface.
The porous properties of the catalysts before and after encapsulation are mea-
sured by means of N2 adsorption studies at 77 K, and results are given in Table 1.
There is a drastic reduction of surface area of encapsulated catalysts as compared
to parent MCM 41. Because the molecular sieve framework is not affected by encap-
sulation as shown by XRD and SEM, the reduction of surface area is due to the
blocking of pores by metal complexes, and this provides direct evidence for the pres-
ence of a metal complex in the cavities.
Infrared (IR) spectra are used to explore the structure, nature of constituents,
their chemical linkage, surface properties and formation of intermediates. IR spectra
can also provide information on the integrity of the encapsulated complex and crys-
tallinity of the host MCM-41. Fourier transform (FT)–IR spectrum of uncalcined
and calcined MCM-41 (Fig. S2 in the supporting information) clearly show that
the bands due to the carbon long-chain template are removed after the thermal treat-
ment. The absence of bands around 3200–2850 cmꢁ1 indicates that the activation of
the support is effective for the formation of a free template structure where the sila-
nol groups are available for interacting with metallomacrocycles. The FT-IR spec-
trum of calcined H-MCM-41 shows specific bands around 460, 800, 960, and
1100 cmꢁ1, which are related to d (Si-O-Si), ns(Si-O-Si), n (Si-OH), and nas(Si-O-
Si), respectively and a broad band around 3450 cmꢁ1 for -OH group of surface
water.[28] Absorption bands at 1620–1650 cmꢁ1 are caused by the deformational
vibrations of the adsorbed water molecules.[29] Figure 3 shows comparison of IR
data of free Co-OMCPy complex, H-MCM 41, and Co-OMCPy–MCM 41. It is evi-
dent from the figure that Co-OMCPy-MCM 41 contains two more peaks (at 1431
and 1572 cmꢁ1) than H-MCM 41. These have surely come from the metal complex,
which has prominent peaks at 1420 and 1560 cmꢁ1as seen in Fig. 3(a). The small
peaks between 450 and 1250 in Fig. 3(a) are masked by the MCM 41 peaks in
Fig. 3(c). These results convincingly demonstrate the presence of a metallomacro-
cycle inside MCM-41. The IR spectra recorded before and after the encapsulation
show that no significant dealumination or expansion of cavities takes place, as the
molecular-sieve-structure-sensitive vibrations (e.g., the asymmetric stretch at
1100 cmꢁ1 and the symmetric stretch at 800 cmꢁ1) do not shift or broaden signifi-
cantly upon inclusion of metallomacrocycles. This result supports the observation
that the encapsulation process does not modify the MCM-41 framework. The bands
due to the encapsulated complex are weaker because of its low concentration and

MACROCYCLES IN MCM-41
2857
Figure 3. IR spectra of (a) free metal complex, (b) H-MCM-41, and (c) Co-OMCPy-MCM-41.
dilution effect of molecular sieve matrix and can only be observed in the regions
where MCM-41 matrix does not absorb, i.e., in the region of 1250–1600 cmꢁ1
.
Similar spectra are obtained for the other modified catalysts and are given in Fig. 4.
Mesoporous molecular sieves have high thermal stability and can retain their
structure even after calcination in air at 900 ꢀC for 12 h.[30,31] The thermal stability
of the encapsulated catalyst can be studied using thermal gravitational analysis
(TGA) and differential thermal analysis (DTA). It provides an idea about the
decomposition temperature of the metallomacrocycle encapsulated in MCM-41.
The TGA and DTA of as-synthesized and calcined MCM-41 are given in Fig. S3
in the supporting information. The calcined H-MCM 41 shows only one peak
around 100 ꢀC due to removal of adsorbed water. In case of Cr-OMCPy-MCM-41
(Fig. 5), there are two peaks in the DTA. The first peak in the temperature range
of 28–135 ꢀC corresponds to a weight loss of 1.38 wt% and is due to the removal
of physically adsorbed water in MCM 41. The second DTA peak is due to the
decomposition of encapsulated pyridino complex. The 13.08% weight loss

2858
C. N. ROHITHA, S. J. KULKARNI, AND N. NARENDER
Figure 4. IR spectra of (a) H-MCM-41, (b) Cr-OMCPy-MCM-41, (c) Mn-OMCPy-MCM-41, (d)
Fe-OMCPy-MCM-41, and (e) Co-OMCPy-MCM-41.
corresponds to the second DTA peak in the temperature range of 242–562 ꢀC. Simi-
lar DTA peaks are obtained for Mn and Co-OMCPy-MCM-41 (Figs. 6 and 7). Wei
et al. showed that the different thermal behavior of metallo macrocycles is associated
with change in metal centers. The thermal data of the free Co-OMCPy complex
(Figure 8) shows decomposition in four stages and is stable up to 340 ꢀC only. After
encapsulation in MCM-41 it is stable up to 420 ꢀC and has undergone single stage
decomposition. The greater difficulty in the decomposition of the metal complex
in Co-OMCPy-MCM 41 suggests that the complex is encapsulated inside the pores

MACROCYCLES IN MCM-41
2859
Figure 5. TGA-DTA of Cr-OMCPy-MCM-41.
and not adsorbed on the external surface. If it is adsorbed on surface it would have
decomposed around 340 ꢀC in four stages. Thus encapsulation produced an increase
of ꢂ80 ꢀC on the stabilization of the metal complex.[32]
CATALYTIC ACTIVITY STUDIES
The activity of the synthesized catalyst was checked by the liquid-phase oxidation
of p-xylene at room temperature in acetic acid using H2O2 oxidant (Scheme 2). H2O2
Figure 6. TGA-DTA of Mn-OMCPy-MCM-41.

2860
C. N. ROHITHA, S. J. KULKARNI, AND N. NARENDER
Figure 7. TGA-DTA of Co-OMCPy-MCM-41.
was chosen as a clean oxidant, because the use of inexpensive and environmentally
friendly reagents are important in modern catalysis. Moreover, H2O2 produces water
as by-product, thus showing its ‘‘green’’ nature. The effect of the reaction temperature
has been studied over Co-OMCPy-MCM 41 in the range of Rt–100 ꢀC and the results
are presented in Table 2. The greatest conversion and selectivity are obtained at room
temperature. The effect of the reaction time is studied in the range of 6–20 h, and results
Figure 8. TGA-DTA of free Co-OMCPy complex.

MACROCYCLES IN MCM-41
2861
Scheme 2. Oxidation of p-xylene.
are shown in Table 3. p-Xylene gives maximum conversion in 20 h. The effect of the
molar ratio of p-xylene=H2O2 in the liquid-phase oxidation of p-xylene is depicted in
Table 4 with reaction conditions. The best results are obtained with 1:4 molar ratio
(p-xylene–H2O2). The effect of variation of the catalyst amount of Co-OMCPy-
MCM-41 on oxidation is shown in Table 5. The oxidation of p-xylene is negligible in
the absence of catalysts, confirming that under the conditions of the experiments, the
oxidation is indeed catalytic in nature. Conversion increases linearly with increase in
catalyst amount and maximum conversion is obtained with 100 mg of catalyst.
The effect of the variation of the catalyst in the oxidation of the p-xylene is
given in Table 6 with reaction conditions. Molecular sieves alone without the metal
complexes are catalytically less active. Depending on the nature of the transition
metal, conversion of p-xylene varies and maximum is attained when cobalt is used.
Oxidation of p-xylene with free Co-OMCPy complex is less active compared to
encapsulated complex in MCM-41. This efficiency possibly arises from metal
Table 2. Effect of reaction temperature in the oxidation of p-xylenea
Selectivity (%)
Conversion
of p-xylene (%)
4-Methyl
benzaldehyde
4-Methyl
benzoic acid
Other
products
No.
Reaction temp. (ꢀC)
1
2
3
4
30 (RT)
60
80
98.4
97
53
55
37
72
21
27
42
16
26
18
21
12
98
95
100
aMolar ratio ¼ p-xylene=H2O2 ¼ 1:4, solvent ¼ AcOH, catalyst ¼ Co-OMCPy-MCM-41 ¼ 100mg, time ¼
20 h, 4-methylbenzyl alcohol, 1,4-benzenedicarboxaldehyde, etc.
Table 3. Effect of reaction time in the oxidation of p-xylenea
Selectivity (%)
Conversion of
p-xylene (%)
4-Methyl
benzaldehyde
4-Methyl
benzoic acid
No.
Reaction time (h)
Other products
1
2
3
20
12
6
98
64
53
53
55
56
21
11
26
26
34
18
aMolar ratio ¼ p-xylene=H2O2 ¼ 1:4, solvent ¼ AcOH, catalyst ¼ Co-OMCPy-MCM-41 ¼ 100 mg,
temp. ¼ Room temp, 4-methylbenzyl alcohol, 1,4-benzenedicarboxaldehyde, etc.

2862
C. N. ROHITHA, S. J. KULKARNI, AND N. NARENDER
Table 4. Effect of molar ratio of p-xylene=H2O2 in the oxidation of p-xylenea
Selectivity (%)
Molar ratio
No. p-xylene: H2O2 p-xylene (%) benzaldehyde benzoic acid Other products
Conversion of 4-Methyl
4-Methyl
1
2
3
4
5
6
1:1
1:2
1:3
1:4
1:5
1:8
11
38
38
27
31
53
42
46
22
36
25
21
26
34
40
37
44
26
32
20
70
98
100
100
aTime ¼ 20 h, temp. ¼ room temp., solvent ¼ AcOH, catalyst ¼ Co-OMCPy-
MCM-41 ¼ 100 mg, 4-methylbenzyl alcohol, 1,4-benzenedicarboxaldehyde, etc.
Table 5. Effect of variation of the catalyst amount in the oxidation of p-xylenea
Selectivity (%)
Catalyst
amount (mg)
Conversion of
p-xylene (%)
4-Methyl
benzaldehyde
4-Methyl
benzoic acid
No.
Other products
1
2
3
4
100
50
25
0
98
83
59
12
53
45
42
36
21
24
23
36
26
31
35
28
aMolar ratio ¼ p-xylene=H2O2 ¼ 1:4, catalyst ¼ Co-OMCPy-MCM-41, temp. ¼ room
temp., Time ¼ 20 h, 4-methylbenzyl alcohol, 1,4-benzenedicarboxaldehyde, etc.
complex coordination to molecular sieves, which renders them more resistant to
oxidative self destruction. The MCM-41 encapsulated complex does not undergo
any color change during the reaction and can be separated easily. In contrast the free
metal complex is completely destroyed and changed color from purple to black
during the reaction.
Table 6. Effect of variation of the catalyst in the oxidation of p-xylenea
Selectivity (%)
Conversion
of p-xylene (%)
4-Methyl
benzaldehyde
4-Methyl
benzoic acid
No.
Catalyst
H-MCM-41
Other products
1
2
3
4
5
6
7
8
31
43
98
41
82
68
17
44
32
67
53
46
55
49
32
37
15
28
21
23
12
14
14
25
53
5
Mn-OMCPy-MCM41
Co-OMCPy-MCM41
Cr-OMCPy-MCM41
Fe-OMCPy- MCM41
Zn-OMCPy-MCM41
Co-OMCPy Complex
Co- MCM-41
26
31
33
37
54
38
aMolar ratio ¼ p-xylene=H2O2 ¼ 1:4, solvent ¼ AcOH, temp. ¼ room temp., time ¼ 20 h, catalyst ¼ 100 mg,
4-methylbenzyl alcohol, 1,4-benzenedicarboxaldehyde, etc.

MACROCYCLES IN MCM-41
2863
Table 7. Reusability of catalysta
No.
Cycle
Selectivity of 4-methyl benzaldehyde (%)
1
2
3
First cycle
Second cycle
Third cycle
53
52
53
aMolar ratio ¼ p-xylene=H2O2 ¼ 1:4, time ¼ 20 h, 100 mg catalyst ¼ Co-OMCPy-
MCM-41, temp. ¼ room temp.
A wide range of solvents has been employed in this reaction including acetic
acid, acetonitrile, dichloromethane, methanol, ethyl acetate, and acetone. The best
results are obtained when acetic acid is used as a solvent compared to others.
These above presented results indicate that the optimized reaction conditions
to get the greatest conversion at the greatest selectivity for this oxidation reaction
is 1:4 molar ratio of p-xylene–H2O2 in acetic acid at room temperature for 20 h over
100 mg Co-OMCPy-MCM 41. The catalyst can easily be separated from the reaction
mixture by simple filtration and can be reused after thorough washing with acetone
and air drying. The recovered catalyst showed consistent activity even after the third
reuse (Table 7).
The metallo octamethylcalix(4)pyrrole complexes encapsulated in MCM-41
have not shown any significant activity in the liquid-phase oxidation of p-xylene.
On the other hand, with metallo calix(4)pyridino MCM-41, even at 30 ꢀC the yield
of 4-methylbenzaldehyde and the conversion of p-xylene are substantial. Our pre-
liminary studies show that the catalytic activity of metallomacrocycle encapsulated
in the molecular sieves varies with nature of macrocycle, nature of the cation,
oxidant, etc.
EXPERIMENTAL
The following chemicals were employed for the preparation of HMCM-41 and
for the oxidation of p-xylene: tetraethyl orthosilicate [(C2H5O)4Si, 99% Fluka], tetra-
ethylammonium hydroxide (TEAOH, 40% Fluka), aluminium isopropoxide (Fluka),
sodium hydroxide (NaOH, 98% Loba), cetyltrimethylammonium bromide (CTAB,
98% Lancaster), hydrogen peroxide (30%, Merck), and acetic acid (99.5%, Merck).
All the reagents in this study were used as received.
Synthesis of Co-OMCPy-MCM-41
HMCM-41 was synthesized in our laboratory using the reported pro-
cedure.[33,34] Equimolar ratio of pyridine and acetone were dissolved in 20 ml
dichloromethane. To this 0.5 g of calcined HMCM-41 was added followed by
1.8 mmol of (CH3COO)2Co ꢃ 4H2O and the reaction mixture was refluxed for 24 h.
The catalyst was filtered and purified by soxhlet extraction using various solvents
to remove unreacted species or species adsorbed on the surface and dried. The cat-
alysts were characterized by XRD, IR, thermal analysis, Brunauer–Emmett–Teller

2864
C. N. ROHITHA, S. J. KULKARNI, AND N. NARENDER
(BET) surface area, and SEM. IR and thermal data of pure cobalt octamethylcalix
(4) pyridinocomplex are also provided.
Physicochemical Characterization
All the samples are systematically characterized by various analytical methods.
The XRD pattern of the samples were obtained on a Regaku miniflux x-ray diffract-
ometer using Ni filtered CuKa (k ¼ 1.5406 Aꢀ) radiation at 2h ¼ 0–80ꢀ with a scan-
ning rate of 2ꢀ minꢁ1 and beam voltage and current of 30 kV and 15 mA,
respectively. The FT-IR spectra of the various samples were recorded on a Nicolet
740 FT-IR spectrometer at ambient conditions using KBr pellets. The DTA and
TG analysis of samples is recorded using TGA=SDTA Mettler Toledo 851e instru-
ment at a heating rate of 10 ꢀC=min ranging from 20 to 1000 ꢀC under nitrogen flow.
The BET surface area of the catalysts was measured out using AutoChem 2910
(Micromeritics) using N2 adsorption at ꢁ196 ꢀC by the single-point BET method tak-
ing 0.0162 nm2 as its cross-sectional area. The sample is preheated to remove moisture
in flow of pure He (99.99%) at 473 K for 2 h under evacuation up to 1 ꢄ 10ꢁ3 Torr.
The morphology of the catalysts is analyzed with SEM of Jeol-JSM-5410 instrument.
Shimadzu 14B gas chromatograph fitted with flame ionization detector and SE-30
column was used to analyze the reaction products of the catalytic activity studies.
General Procedure for Oxidation of p-Xylene
The liquid-phase oxidation of p-xylene was carried out over metallomacrocycle
encapsulated in MCM-41. In a typical reaction, 0.1 g of dried catalyst was added to
the stirred solution of p-xylene (2 mmol) in acetic acid (6 ml), followed by 8 mmol of
30% H2O2 (dropwise). Then reaction mixture was allowed to stir in the temperature
range of 30–100 ꢀC. The reaction was monitored by thin-layer chromatography
(TLC). After completion of the reaction, the catalyst was filtered and washed with
ethyl acetate. The combined filtrates were washed with saturated sodium bicarbonate
solution. The organic extract was dried over anhydrous sodium sulfate and solvent
was evaporated under reduced pressure. The products were quantified by gas chro-
matography, verified by GC-MS and purified by column chromatography over silica
gel (finer than 200 mesh). All the products are characterized by 1HNMR, 13C NMR,
and mass spectroscopy.
4-Methylbenzaldehyde
1H NMR (300 MHz, CDCl3): d 2.44 (s, 3H), 7.33 (d, J ¼ 3.9 Hz, 2H), 7.78 (d,
J ¼ 4.05 Hz, 2H), 9.97 (s, 1H). 13C NMR (75 MHz, CDCl3): d 21.9, 129.7, 129.9,
134.2, 145.6, 192.0. MS (EI) m=z: (relative intensity) 120 (Mþ., 90), 119 (100), 91 (90).
4-Methylbenzoic Acid
1H NMR (300 MHz, CDCl3): 2.44 (s, 3H), 7.28 (d, J ¼ 8.2 Hz, 2H), 8.01 (d,
J ¼ 8.2 Hz, 2H); 13C NMR (75 MHz, CDCl3): ¼21.8, 126.7, 129.3, 130.3, 144.7,
172.5.

MACROCYCLES IN MCM-41
2865
CONCLUSIONS
1. Using acetone and pyridine in the presence of HMCM-41 and Co(OAc)2 ꢃ 4H2O,
Co-OMCPy-MCM41 has been prepared. By changing transition metal acetate, a
series of Mþn–OMCPy-MCM 41 can be prepared. The molecular sieve–
encapsulated complexes do not undergo any color change during the reaction
and can be easily separated and reused.
2. Co-OMCPy-MCM-41 is active in the liquid-phase oxidation of p-xylene in acetic
acid using H2O2 as oxidant. It is a better catalyst than the corresponding octa-
methyl calix (4) pyrrole–MCM-41 catalyst. The major products are 4-methyl ben-
zaldehyde, 4-methyl benzoic acid, and 4-methyl benzyl alcohol. Further oxidation
to terephthalic acid does not occur to any significant extent.
3. The catalytic activity of metallomacrocycles encapsulated in MCM-41 depends
mainly on the nature of the cation and the heterocyclic ring. A large number of
enzyme-mimicking catalysts=biocatalysts can be developed by varying hetero-
cyclic ring and cations in metallomacrocycles. They are active in various reactions
at low temperatures (30–100 ꢀC).
SUPPORTING INFORMATION
XRD, IR, and TGA-DTA data of H-MCM-41 can be found via the
Supplementary Content section of this article’s Web page.
ACKNOWLEDGMENT
We are thankful to J. S. Yadav, director, IICT, for providing access to the
instrumentation facilities.
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