Oxidation of benzyl alcohol and styrene using H2O2 catalyzed by tetraazamacrocycle complexes of Cu(II) and Ni(II) encapsulated in zeolite-Y

Article abstract of DOI:10.1016/j.apcata.2010.03.027

Encapsulation of 7,16-diacetyl[M{Me₄(Bzo)₂[14]tetraeneN₄}], {M = Cu(II) and Ni(II)} tetraazamacrocycle complexes in the cavity of Zeolite-Y by the template synthesis method has been described. These complexes have been cha

Full text of DOI:10.1016/j.apcata.2010.03.027

Applied Catalysis A: General 381 (2010) 8–17
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Oxidation of benzyl alcohol and styrene using H2O2 catalyzed by
tetraazamacrocycle complexes of Cu(II) and Ni(II) encapsulated
in zeolite-Y
Vipin Kumar Bansala, Pompozhi Protasis Thankachana,∗, Rajendra Prasadb
a Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, Uttrakhand, India
b School of Chemical Sciences, Faculty of Science and Technology, The University of the South Pacific, Suva, Fiji
a r t i c l e i n f o
a b s t r a c t
Article history:
Encapsulation of 7,16-diacetyl[M{Me4(Bzo)2[14]tetraeneN4}], {M = Cu(II) and Ni(II)} tetraazamacrocy-
cle complexes in the cavity of Zeolite-Y by the template synthesis method has been described. These
complexes have been characterized using various physico-chemical techniques viz., spectroscopic (elec-
tronic and IR) studies, thermal analysis, metal analysis, field emission scanning electron micrographs
and X-ray powder diffraction patterns. These encapsulated tetraazamacrocycle complexes have been
used as a heterogeneous catalyst for the oxidation of styrene and for the solvent free oxidation of ben-
zyl alcohol using hydrogen peroxide as oxidant. The solvent free catalyzed oxidation of benzyl alcohol
catalyzed by 7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY gives benzaldehyde as the major prod-
uct, while that of styrene gives benzaldehyde and styrene oxide as major oxidation products when
7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY is used as catalyst.
Received 1 December 2009
Received in revised form 10 March 2010
Accepted 11 March 2010
Available online 17 March 2010
Keywords:
Zeolite encapsulation
Oxidation
Benzyl alcohol
Styrene
Heterogeneous catalysis
Tetraazamacrocycle
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
(TS). In ZS method, transition metal complexes, which are sta-
ble under the condition of zeolite synthesis such as high pH
Transition metal complexes show good catalytic activity and
selectivity and therefore are widely used as homogeneous as well
as heterogeneous catalysts in various chemical reactions [1–7].
The requirement of cheap and environment-friendly catalysts has
biased research activity in favour of heterogeneous catalysts, due
to their advantages over homogeneous catalysts such as easy sep-
aration from reaction mixture, selectivity and recyclability. For the
heterogenization of a homogeneous catalyst various methods are
used such as polymer anchoring [8,9], polymerization of homo-
geneous catalyst itself [10,11], immobilization of metal complex
on a solid support like alumina, silica or zeolites [12–17] and
covalently anchoring to multi-wall carbon nanotubes (MWNTs)
[18]. Among these methods of heterogenization, encapsulation
of metal complexes inside the supercages of zeolite has been
found to be convenient and advantageous due to the selectivity,
reusability and thermal and chemical stability. Generally speak-
ing three approaches have been used for the preparation of zeolite
encapsulated metal complexes. These are zeolite synthesis method
(ZS), flexible ligand method (FL) and template synthesis method
and high temperature, are added to the synthesis mixture. The
resulting zeolite encapsulates the metal complexes in its cavity.
In FL method if the size of ligand is smaller than the diame-
ter of zeolite channels, the ligand is diffused freely through the
zeolite channels. The ligand reacts easily with the desired metal
ions which have been previously exchanged in the supercages
of zeolite and makes a stable metal complex. When the ligand
size is larger than the diameter of zeolite channels, then tem-
plate synthesis (TS) method is used. In this method, the molecules
of the ligand species are diffused freely into the zeolite cavity
where they assemble around the resident metal ions (fixed by ion
exchange) in the zeolite cavity. The size of the synthesized metal
complex will be too large to escape out from the supercages of zeo-
lite. These encapsulated metal complexes in the cavity of zeolite
have been called by several research groups as “zeolite encapsu-
lated metal complex (ZEMC)”or “ship-in-a-bottle” [19,20]. ZEMC
catalysts behave functionally in a similar way to many enzyme
catalysts and are often referred to as “zeozymes” [21,22]. Tetraaza-
macrocycle complexes of various metals were easily encapsulated
in zeolite cavities and successfully used as heterogeneous cata-
lyst in various oxidation reactions such as oxidation of phenol,
styrene, benzyl alcohol, cyclohexene, cyclohexane and ethylben-
zene [5,6,23–25].
∗
Corresponding author. Tel.: +91 1332 285331; fax: +91 1332 273560.
E-mail address: ppthnfcy@iitr.ernet.in (P.P. Thankachan).
0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.03.027

V.K. Bansal et al. / Applied Catalysis A: General 381 (2010) 8–17
9
Oxidation of benzyl alcohol to benzaldehyde is an industri-
ally important reaction. Chlorine free benzaldehyde is a versatile
chemical intermediate widely used in the manufacture of phar-
maceuticals, perfume and flavoring chemicals. The oxidation of
styrene gives a variety of products such as carbonyl compounds,
epoxides, diols and products of oxidative cleavage of C–C bond. Sev-
eral research groups have developed different catalytic methods
for oxidation of benzyl alcohol benzaldehyde and styrene. ZEMC
catalysts are successfully employed for this purpose [26–32].
In this research, we have synthesized and characterized 7,16-
diacetyl[M{Me4(Bzo)2[14]tetraeneN4}], {M = Cu(II) and Ni(II)}
tetraazamacrocycle complexes and encapsulated these complexes
in the supercages of zeolite-Y by the template synthesis method.
These complexes have been characterized by using various
physico-chemical techniques viz. UV–vis, FT-IR, XRD, TG/DTA, AAS
and FE-SEM. Catalytic activity of these encapsulated complexes
towards oxidation of benzyl alcohol and styrene was investigated.
ties of the reaction products were confirmed with a GC–MS model
Perkin-Elmer Clarus 500. Catalyzed reactions were analyzed using
a Hewlett Packard gas chromatograph model 5890 A, fitted with FID
detector and a (30 m × 0.53 mm × 2.65 ␮m) HP-1capillary column.
2.3. Preparations
2.3.1. Preparation of complex
7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]
The complex [Cu{Me4(Bzo)2[14]tetraeneN4}] (0.5 g, 1.23 mmol)
and acetyl chloride (0.3 ml, 4.2 mmol) were dissolved in 100 ml
anhydrous benzene, followed by drop by drop addition of triethy-
lamine (1.5 ml, 10.8 mmol), keeping the temperature at 0 ◦C. The
reaction mixture was protected from moisture and stirred for 2 h
at 0–5 ◦C. The reaction mixture was allowed to stand at room tem-
perature for 6 h and then filtered. The filtrate was evaporated to
dryness under reduced pressure. The product was washed with
hot water till the washings became colourless. The compound was
dried at 75 ◦C in a vacuum oven. The dry residue was extracted
in chloroform. The compound was purified by passage through
a 15 cm × 2.5 cm alumina column eluting with chloroform. Three
colored bands of two acylated products along with the parent com-
pound were observed. The first and second bands were minor and
were discarded. The third yellowish green band, eluted with chlo-
roform, was collected. The bulk of the solvent was removed at
reduced pressure. Fine dark violet crystals were obtained. Yield
0.34 g (56.4%) m.p. > 300 ◦C. Analyzes found C, 63.60; H, 5.23; N,
11.50%. C26H26N4O2Cu calcd.: C, 63.72; H, 5.35; N, 11.43%. UV–vis
(in CHCl3 ꢀmax, nm/εmax, L mol−1 cm−1); 636 (2029), 412sh (20854),
380 (58593), 314 (21700), 285 (31454) and 252 (44770) IR (KBr
pellet, ꢁ, cm−1): ꢁ (C O) 1662 cm−l, ꢁ(N C–C) 1531 cm−l, ꢁ(C C)
1448 cm−l and ꢁ( C–H) 1386 cm−l. FAB mass (m/z) [M + 1]+ 491,
490.06 (calcd. molecular weight).
2. Experimental
2.1. Materials and methods
All common chemicals and solvents were of analytical grade
and were purchased from Rankem (India). Benzyl alcohol, o-
phenylenediammine and 30% H2O2 were purchased from Rankem
(India). Nickel acetate, copper acetate, acetylacetone, triethy-
lamine and acetylchloride were obtained from Loba Chemie (India).
Styrene was obtained from Acros Organics (USA). Zeolite-Y (Si/Al
∼2.53) obtained from Sud Chemie (India), was dried at 400 ◦C for
6 h before being used as host material for encapsulating complexes.
The benzene used for the synthesis of acylated tetraazamacrocycle
complexes was dried over sodium wire and distilled. Tetraaza-
macrocycle complexes [M(Me4(Bzo)2[14]tetraeneN4)] {M = Cu(II)
and Ni(II)} were prepared following the procedure described in the
literature [33,34].
2.3.2. Preparation of complex
7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]
Forthe synthesis of7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]
the procedure adopted was similar to that described above
except that the complex [Ni{Me4(Bzo)2[14]tetraeneN4}] (0.49 g,
1.23 mmol) was used. Yield 0.41 g (68.7%) m.p. > 300 ◦C. Ana-
lyzes found C, 64.22; H, 5.41; N, 11.61%. C26H26N4O2Ni calcd.: C,
64.36; H, 5.40; N, 11.55%. UV–vis (in chloroform ꢀmax, nm/εmax,
L mol−1 cm−1); 585 (5728), 416sh (13205), 392 (36404), 335
2.2. Instrumentation and analysis
IR spectra of neat macrocycle complexes and zeolite encapsu-
lated metal macrocycle complexes were recorded on a Thermo
Nicolet–NEXUS Aligent 1100 FT-IR spectrometer in KBr. Elec-
tronic spectra of neat macrocycle complexes were recorded on a
Shimadzu 1601 UV–vis spectrophotometer in chloroform, while
electronic spectra of zeolite encapsulated metal macrocycle com-
plexes were recorded in nujol by layering the mull of the sample
inside one of cuvettes while keeping the other one layered with
nujol as reference. The FAB mass spectra of neat acylated macro-
cycle complexes were recorded on a Jeol SX-102/DA-6000 mass
spectrometer in 3-nitrobenzyl alcohol matrix using xenon as FAB
gas. 1H NMR was recorded on a Bruker DRX-500 spectrometer
in chloroform-d. Elemental analyzes of neat tetraazamacrocycle
complexes were carried out on an Elementar Vario EL-III ana-
lyzer. XRD patterns were recorded using a Bruker AXS D8 Advance
X-ray powder diffractometer with a Cu K␣ target. TG/DTA of zeo-
lite encapsulated macrocycle complexes were recorded using a TG
Stanton Redcroft STA 780. Copper and nickel metals were analyzed
using a Perkin–Elmer A Analyst 800 atomic absorption spectrome-
ter after completely destroying the zeolite framework with hot and
concentrated nitric acid and diluting with double distilled water to
a specific volume. Field emission scanning electron micrographs
of zeolite encapsulated tetraazamacrocycle metal complexes were
recorded using a Quanta 200 FE-SEM instrument. The zeolite encap-
sulated tetraazamacrocycle metal complexes were coated with a
thin film of gold before recording the FE-SEM to protect surface
material from thermal damage by the electron beam. The identi-
(7089), 267 (29947), IR (KBr pellet, ꢁ, cm−1): ꢁ(C O) 1646 cm−l
ꢁ(N C–C) 1535 cm−l, ꢁ(C C) 1434 cm−l and ꢁ( C–H) 1380 cm−l
,
.
FAB mass (m/z) [M + 1]+ 486, 485.21 (calcd. molecular weight),
1H NMR (in CDCl3): ı 2.04 (s 12H, CH3), 6.65–6.67 (m 8H, arom.),
2.53 ppm (s 6H, –COCH3).
2.3.3. Preparation of M(II)-NaY {M = Cu(II) and Ni(II)}
A 4.0 g amount of NaY zeolite was taken in 300 ml of distilled
water and to this cupric acetate (3.99 g, 20 mmol) was added for
the preparation of Cu(II)-NaY/nickel acetate (4.98 g, 20 mmol) for
Ni(II)-NaY was added. The reaction mixture was heated on an oil
bath at 90 ◦C for 24 h with constant stirring. The reaction mixture
was filtered off and washed with hot distilled water until the filtrate
was from metal ion free (confirmed by AAS of filtrate). The solid
residue was dried in an oven at 120 ◦C for 24 h. The ion exchange
degree of the zeolite was determined with an atomic absorption
spectrophotometer.
2.3.4. Preparation of [M(C6H8N2)2]2+-NaY {M = Cu(II) and Ni(II)}
For the preparation of [M(C6H8N2)2]2+-NaY {M = Cu(II)
and Ni(II)}, Cu(II)-NaY (2.0 g)/Ni(II)-NaY (2.0 g) and o-
phenylenediammine (0.38 g, 3.5 mmol) were mixed in 150 ml
methanol in a round bottom flask. The reaction mixture was

10
V.K. Bansal et al. / Applied Catalysis A: General 381 (2010) 8–17
refluxed on an oil bath for 20 h with constant stirring. The solid,
consisting of zeolite encapsulated [Cu(C6H8N2)2]2+ denoted as
[Cu(C6H8N2)2]2+-NaY and zeolite encapsulated [Ni(C6H8N2)2]2+
denoted as [Ni(C6H8N2)2]2+-NaY, was filtered. The solid was
washed with methanol till the washings became colourless and
then dried at 80 ◦C in vacuum oven for 24 h.
3. Results and discussion
3.1. Characterization of catalysts
The complexes 7,16-diacetyl[M{Me4(Bzo)2[14]tetraeneN4}]
{M = Cu(II) and Ni(II)} were synthesized by the acylation of
[M{Me4(Bzo)2[14]tetraeneN4}] {M = Cu(II) and Ni(II)} and char-
acterized by various physico-chemical techniques. Encapsulation
of these tetraazamacrocycle complexes in the nanocavity of zeo-
lite was carried out by template synthesis method, in which
tetraazamacrocycle complexes were synthesized in the nanocavity
of zeolite-Y. Encapsulation was carried out in three steps. In the first
step, the desired metals nickel(II) and copper(II) were exchanged
with the Na+ ion of zeolite-Y. In the second step, the molecules that
constitute the ligand species that make the complex in the nanocav-
ity of zeolite with previously exchanged Ni(II) and Cu(II) metal were
diffused in zeolite pores. The size of the synthesized metal complex
will be too large to escape out from the supercages of zeolite. This
process is called “ship-in-a-bottle”. The uncomplexed metal ions in
the nanocavity of zeolite as well as its surface if any were removed
by exchanging the metal ion with 0.1 M NaCl aqueous solution. The
complex synthesized at the surface of zeolite was removed by soxh-
let extraction with dichloromethane followed by acetonitrile, so
that the metal content found after analysis would be due to the
presence of encapsulated metal macrocycle complex in the cav-
ity of zeolite alone. Zeolite encapsulated complexes thus obtained
were dried in a vacuum oven at 120 ◦C for 48 h to remove moisture.
After that, acylation at the 7,16 positions of the tetraazamacrocycle
complexes were carried out in the cavity of zeolite (Scheme 1). The
percentage of metal ion after encapsulation in zeolite was deter-
mined by AAS. The percentage of metal content, molecular formula
and colour is shown in Table 1.
2.3.5. Preparation of [M(Me4(Bzo)2[14]tetraeneN4)]-NaY
{M = Cu(II) and Ni(II)}
Zeolite
encapsulated
complexes
[M(C6H8N2)2]2+-NaY
{M = Cu(II) and Ni(II)}, 2.0 g each and acetylacetone (0.4 ml,
3.8 mmol) were taken in 150 ml of methanol in a round bottom
flask. The reaction mixture was refluxed in an oil bath with
constant stirring for 24 h. Thus obtained mixture was filtered,
washed with dichloromethane and dried for 20 h at 80 ◦C. The
catalyst thus obtained was subjected to soxhlet extraction with
dichloromethane, followed by acetonitrile for 12 h to remove
excess unreacted products and neat complex adsorbed on the
surface of zeolite-Y .The uncomplexed copper and nickel metal
ions present in the cavity and on the surface of zeolite were
removed by stirring the compounds with aqueous 0.1 M NaCl
solution for 12 h. The resulting solid was filtered and washed with
distilled water until free from chloride ions (confirmed by adding
AgNO3 solution to the filtrate). The solid thus obtained was dried
in a vacuum oven at 120 ◦C for 48 h to constant weight.
2.3.6. Preparation of
7,16-diacetyl[M{Me4(Bzo)2[14]tetraeneN4}]-NaY {M = Cu(II) and
Ni(II)}
Zeolite
encapsulated
[M(Me4(Bzo)2[14]tetraeneN4)]-NaY
{M = Cu(II) and Ni(II)} (2 g) was placed in 100 ml of anhydrous
benzene in a round bottom flask. Triethylamine (3.9 ml, 28 mmol)
was added to it. The reaction mixture was refluxed in an oil bath
with constant stirring for 2 h. The reaction mixture was cooled to
room temperature and acetylchloride (2 ml, 28 mmol) was added,
and the reaction mixture was again refluxed for 4 h with constant
stirring, protected from moisture. The products were filtered and
washed with methanol and finally washed with hot water. The
compound was dried in an oven at 90 ◦C for 24 h.
3.2. Electronic spectral studies
The electronic spectrum of neat macrocycle complex 7,16-
diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}] exhibits six bands at
636, 412, 380, 314, 285 and 252 nm (Table 2), while the 7,16-
diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}] exhibits five bands at 585,
416sh, 392, 335 and 267 nm; these are in agreement with the liter-
ature values [35]. The absorption band observed above 435 nm are
due to ␲ → ␲* transitions within a ligand. The transitions observed
at 585 nm in 7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}] and
636 nm in 7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4} are
attributed to d–d transitions due to Ni(II) and Cu(II). The
spectral behavior of these complexes is consistent with that
of square planar coordination of Ni(II) and Cu(II) [36]. The large
molar absorbance of d–d transitions could be the result of
intensity stealing from strong UV absorption bands [37]. All the
encapsulated complexes exhibit the almost identical spectral
patterns to those of their neat macrocycle complexes. Zeolite
encapsulated 7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}] com-
plexes exhibit spectral bands at 590, 397 and 265 nm while
7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}] complexes exhibit
spectral bands at 642, 383, 286 and 242 nm (Fig. 1, Table 2).
Precursors of these acylated complexes also show similar behavior
[5,38]. The presence of these spectral bands in the electronic
spectra of encapsulated complexes confirmed the existance of
complexes in the cavity of zeolite-Y.
2.4. Catalytic activity
2.4.1. Oxidation of benzyl alcohol
Solvent free catalytic oxidation of benzyl alcohol was carried
out in a 50 ml round bottom flask fitted with a water circulated
condenser using zeolite encapsulated Cu(II) tetraazamacrocycle
complexes as catalyst. In a typical reaction, benzyl alcohol (3.24 g,
30 mmol) and 30% H2O2 (5.10 g, 45 mmol) were mixed and the reac-
tion mixture was heated in an oil bath with continuous stirring at
75 ◦C. An appropriate amount of catalyst (30 mg) was added to the
hot mixture and the reaction was continued. The progress of the
reaction was determined by analyzing the reaction mixture using
a gas chromatograph by withdrawing small aliquots of the reac-
tion mixture at specific interval of time. The identity of reaction
products was confirmed by GC–MS.
2.4.2. Oxidation of styrene
The catalytic oxidation of styrene was carried out using zeo-
lite encapsulated Ni(II) tetraazamacrocycle complexes as catalyst.
Styrene (1.56 g, 15 mmol), H2O2 (3.52 g, 30 mmol) and catalyst
(35 mg) were taken in 10 ml of acetonitrile and the reaction was car-
ried out at 70 ◦C in an oil bath with continuous stirring. The progress
of reaction was determined as described above. The identity of the
oxidation products was confirmed by GC–MS.
3.3. FT-IR spectral studies
A partial list of IR spectral data of neat as well as zeolite
encapsulated tetraazamacrocycle complexes has been given in
Table 2. The intensity of IR bands in all zeolite encapsulated
complexes is weak in comparison to those of the neat com-

V.K. Bansal et al. / Applied Catalysis A: General 381 (2010) 8–17
11
Scheme 1.
plexes due to their low concentration in zeolite cavities. The IR
spectrum of [Ni{Me4(Bzo)2[14]tetraeneN4] showed three intense
bands at 1547 (N C–C), 1462 (C C) and 1396 ( C–H) while
and [Cu{Me4(Bzo)2[14]tetraeneN4] showed bands at 1566 cm−l
mentioned intense bands were observed in the IR spectra of zeo-
lite encapsulated tetraazamacrocycle complexes. The IR spectrum
of neat zeolite-Y showed a strong broad band at 1634 cm−1 due
to zeolite frame-work. In acylated zeolite encapsulated tetraaza-
macrocycle complexes this band shifts to a higher frequency due
to merging of C O bands (shown in Table 2). These IR bands were
observed slightly frequency shifted by ∼ 4–6 cm−1. These vari-
ations in the band frequency might be due to distortion in the
complexes or to interactions with the zeolite matrix. These obser-
(N C–C), 1447 cm−l (C C) and 1403 cm−l
( C–H). Upon acylation
of these complexes, a strong band due to C O was observed at 1646
and 1662 cm−1 respectively along with three intense bands with
a slight shift. When acylated and precursor tetraazamacrocycle
complexes are encapsulated in the zeolite cavity, the three above
Table 1
Chemical composition, physical and analytical data.
Compound
Metal content (wt.%)
Color
Cu-NaY
Ni-NaY
3.91
4.16
2.23
2.38
2.22
2.37
Light blue-green
Light green
Light-yellow
Greenish-yellow
Light-yellow
Greenish-yellow
[Cu(Me4(Bzo)2[14]tetraeneN4)]-NaY
[Ni(Me4(Bzo)2[14]tetraeneN4)]-NaY
7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY
7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY
Table 2
IR and electronics data of neat and zeolite encapsulated tetraazamacrocycle complexes.
Compound
ꢀmax (nm)
IR (cm−1
)
[Cu{Me4(Bzo)2[14]tetraeneN4}
637, 414, 383, 315, 288, 250
586, 429sh, 395, 337, 270
636, 412, 380, 314, 285, 252
585, 416sh, 392, 335, 267
642, 387, 286, 242
1566, 1447, 1403
1547, 1462, 1396
[Ni{Me4(Bzo)2[14]tetraeneN4}]
7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}
7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]
[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY
[Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY
1662, 1531, 1448, 1386
1646, 1535, 1434, 1380
1635, 1538, 1456, 1401
1634, 1544, 1458, 1394
1654, 1532, 1448, 1382
1643, 1533, 1426, 1378
590, 397, 265
642, 383, 286, 242
7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY
7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY
590, 397, 265

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V.K. Bansal et al. / Applied Catalysis A: General 381 (2010) 8–17
Fig. 1. Electronic spectra of neat 7,16-diacetyl[CuMe4(Bzo)2[14]tetraeneN4)] (A)
and 7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY (B).
vations confirm not only the acylation but also the presence of
metal tetraazamacrocycle complexes in the cavities of zeolite.
3.4. Field emission scanning electron micrograph study
Field emission scanning electron micrographs (FE-SEM) of zeo-
lite encapsulated tetraazamacrocycle complexes recorded before
and after soxhlet extraction are shown in Fig. 2, which shows well
defined crystals of zeolite encapsulated tetraazamacrocycle com-
plexes after soxhlet extraction, free from any shadow of metal
complex present on the external surface of zeolite. During the pro-
cess of encapsulation and soxhlet extraction, the framework of the
zeolite-Y was not damaged.
3.5. Powder X-ray diffraction studies
The powder X-ray diffraction (XRD) patterns of all zeo-
lite encapsulated tetraaza macrocycle metal complexes, metal
exchanged zeolite and zeolite-Y were recorded at 2Â val-
Fig.
2. Field
emission
scanning
electron
micrograph
of
7,16-
diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY of before (A) and after (B) soxhlet
extraction.
ues between
5
and 40◦ to see their crystallinity and to
ensure encapsulation of metal complexes in the cavity of zeo-
lite .The powder X-ray diffraction patterns of zeolite-Y, metal
exchanged zeolite Cu(II)-NaY and zeolite encapsulated 7,16-
diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY metal complexes are
shown in Fig. 3. The diffraction patterns of encapsulated tetraaza-
macrocycle complexes, Cu(II)-NaY and zeolite-Y are almost identi-
cal similar with only very slight changes. One new peak in the XRD
pattern of 7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY and
[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY was detected at 2Â value of
7.7. XRD patterns of 7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-
NaY, [Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY, Ni(II)-Y and NaY were
nearly identical. This new peak, observed in the XRD patterns of
zeolite encapsulated metal macrocycle complexes may be due to
encapsulation of metal complexes in the cavity of zeolite. Further,
a little change occurred in the relative peak intensities of 3 3 1,
3 1 1 and 2 2 0 upon introducing the metal ions or macrocycle com-
plexes. In neat zeolite-Y intensity values were found in the order
I3 3 1 > I2 2 0 > I3 1 1. Upon exchanging the metal or after, the encapsu-
lation process affects the relative peak intensities of the 3 1 1and
2 2 0 peaks, the intensity being in the order I3 3 1 > I3 1 1 > I2 2 0. This
was attributed to a redistribution of intrazeolite charge balancing-
cations [39–41]. These observations indicate that the crystallinity
of the zeolite has not undergone any significant change during the
process of encapsulation. The analysis of FE-SEM image also sup-
ports the assertion that all the modified zeolite has retained the
crystallinity of the zeolite-Y.
3.6. Thermo gravimetric analysis
The
representative
TG-DTA
thermogram
of
7,16-
diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY is shown in Fig. 4.
The thermal decomposition of all the zeolite encapsulated
tetraazamacrocycle complexes occurs in two major steps.
The first step corresponds to removal of physically adsorbed
Fig. 3. XRD patterns of zeolite-Y (c), Cu(II)-NaY (b), 7,16-diacetyl
[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY (a).

V.K. Bansal et al. / Applied Catalysis A: General 381 (2010) 8–17
13
Scheme 2.
7,16-diacetyl-[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY as a represen-
Fig. 4. TG (blue line) and DTG (red line) thermogram of 7,16-
diacetyl[Ni{Me4(Bzo)2[14]-tetraeneN4}]-NaY.
tative catalyst for further studies.
3.7.1.1. Effect of temperature. The effect of temperature
water and intrazeolite water molecules and the second step
is ascribable to the decomposition of the chelating ligand. In
the first step, an endothermic weight loss of ca. 12.1, 16.8, 8.7
and 15.6% in [M{Me4(Bzo)2[14]tetraeneN4}]-NaY and 7,16-
diacetyl[M{Me4(Bzo)2[14]tetraeneN4}]-NaY (where M = Ni(II)
and Cu(II)) take place respectively in the temperature range
90–260 ◦C. The second step of decomposition starts imme-
diately after the first and in this an exothermic weight loss
was observed in several sub-steps in the temperature range
260–900 ◦C. Weight losses of 13.9, 12.1, 17.3 and 15.0% were
observed in [M{Me4(Bzo)2[14]tetraeneN4}]-NaY and 7,16-
diacetyl[M{Me4(Bzo)2[14]tetraeneN4}]-NaY (where M = Ni(II) and
Cu(II)) respectively between 260 and 900 ◦C. In the second step,
the weight loss of zeolite encapsulated metal complexes in each
case was in close agreement with the metal content recorded by
atomic absorption spectroscopy
on
the
oxidation
of
benzyl
alcohol
using
7,16-
diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY as catalyst was
investigated at four different temperatures viz. 60, 70, 75 and
80 ◦C, keeping the other parameters fixed: namely benzyl alcohol
(3.24 g, 30 mmol), 30% H2O2 (5.10 g, 45 mmol), catalyst (30 mg)
and reaction time (6 h). The results are shown in Fig. 5, which
reveals that 16.7, 26.9, 29.9 and 30.1% conversion were found
corresponding to 60, 70, 75 and 80 ◦C respectively. On increasing
the temperature from 75 to 80 ◦C, only very little improvement
(0.2%) in conversion was observed, so that a temperature of 75 ◦C
was considered to be optimum.
3.7.1.2. Effect of catalyst amount. The amount of catalyst has a sig-
nificant effect on the oxidation of benzyl alcohol. Four different
amounts of catalyst viz., 10, 20, 30 and 40 mg were used, keep-
ing with all other reaction parameters fixed: namely temperature
(75 ◦C), benzyl alcohol (3.24 g, 30 mmol) to H2O2 (5.10 g, 45 mmol)
and reaction time (6 h). The results are shown in Fig. 6, indicating
12.8, 19.7, 29.9 and 30.3% conversion corresponding to 10, 20, 30
and 40 mg catalyst respectively. Lower conversion of benzyl alcohol
into benzaldehyde with 10 and 20 mg catalyst may be due to fewer
catalytic sites. The maximum percentage conversion was observed
with 40 mg catalyst but there was no remarkable difference in the
3.7. Catalytic activity studies
3.7.1. Oxidation of benzyl alcohol
Solvent free catalytic oxidation of benzyl alcohol was stud-
ied using H2O2 as oxidant [Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY
and 7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4]-NaY as catalysts.
Benzyl alcohol (3.24 g, 30 mmol), 30% H2O2 (5.10 g, 45 mmol)
and catalyst (30 mg) were taken in a 50 ml round bottom flask
and the reaction mixture was heated at 75 ◦C for 6 h. Gener-
ally, benzyl alcohol on oxidation gives benzaldehyde, benzoic
acid and benzyl benzoate. However, benzaldehyde was char-
acterized as the major oxidation product in the present case
(Scheme 2). Catalysts [Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY and
7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY showed 27.1
and 29.9% conversion of benzyl alcohol in 6 h, respectively. Selec-
tivity values for benzaldehyde, benzoic acid and benzyl benzoate
were found to be 94.1, 1.6 and 4.3% respectively, in the case of
[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY and 96.3, 1.2 and 2.5% in the
case of 7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY, while
turn-over frequency values [TOF = moles of substrate converted per
mole of metal (in zeolite encapsulated catalyst) per hour] were
found to be 110 and 123 h−1 respectively. The reaction carried out
using Cu(II)-NaY as catalyst under the same reaction conditions
showed nearly 1.4% conversion of benzyl alcohol. Furthermore in
the absence of catalyst, no significant amount of benzaldehyde was
produced indicating that H2O2 alone is unable to oxidize benzyl
alcohol to benzaldehyde. In order to obtain optimum reaction con-
ditions for maximum conversion of benzyl alcohol, we used catalyst
Fig. 5. Effect of temperature on the oxidation of benzyl alcohol, reaction condi-
tions: benzyl alcohol = 30 mmol, 30% H2O2 = 45 mmol, catalyst = 30 mg and reaction
time = 6 h.

14
V.K. Bansal et al. / Applied Catalysis A: General 381 (2010) 8–17
Fig. 6. Effect of amount of catalyst on the oxidation of benzyl alcohol, reaction condi-
tions: benzyl alcohol = 30 mmol, H2O2 = 45 mmol, reaction temperature = 75 ◦C and
reaction time = 6 h.
Scheme 3.
progress of reaction when 30 or 40 mg of catalyst was employed.
Therefore, 30 mg amount of catalyst was taken to be optimal.
ing the reaction of benzyl alcohol (3.24 g, 30 mmol) with 30% H2O2
(5.10 g, 45 mmol) in the presence of 30 g of catalyst at 75 ◦C with
constant stirring. The percentage of conversion was monitored at
different reaction times. It was seen that 29.9% conversion was
observed at 6 h; when the reaction was allowed to continue for
20 h, 31.2% conversion was observed.
3.7.1.3. Effect of H2O2 concentration. In order to determine the
effect of H2O2 on the oxidation of benzyl alcohol to benzaldehyde,
we studied the using three different benzyl alcohol: H2O2 molar
ratios (1:1, 1:1.5 and 1:2) keeping other parameter fixed: namely
catalyst (30 mg), temperature (75 ◦C) and reaction time (6 h). The
results are shown in Fig. 7. A benzyl alcohol to H2O2 molar ratio
of 1:1 resulted in 21.4% conversion, and when benzyl alcohol to
H2O2 molar ratio was changed to 1:1.5, conversion increased to be
nearly 29.9%, keeping all other conditions similar. However, con-
version was found to be almost the same at 30.7% when the benzyl
alcohol to H2O2 molar ratio was further changed to 1:2. The H2O2
efficiency [H2O2 efficiency (%) = (mol of H2O2 used in product for-
mation/mol of H2O2 added) × 100] was found to be 21.6, 67.3 and
51.8%. Therefore, 1:1.5 molar ratio of benzyl alcohol to H2O2 was
found to be the optimum in terms of conversion as well as H2O2
efficiency.
3.7.2. Oxidation of styrene
Oxidation of styrene was carried out using [Ni{Me4(Bzo)2
[14]tetraeneN4}]-NaY and 7,16-diacetyl[Ni{Me4(Bzo)2[14]tetrae-
neN4}]-NaY as catalysts in the presence of H2O2. Oxidation of
styrene gives five oxidation products styreneoxide, benzaldehyde
benzoic acid, phenylacetaldehyde and 1-phenylethane-1,2-diol
(Scheme 3). These products are very common and also have
been identified earlier [42–45]. However, styreneoxide and ben-
zaldehyde were characterized as the major oxidation products
in the present case. Styrene (1.56 g, 15 mmol), 30% H2O2 (3.52 g,
30 mmol) and catalyst (35 mg) were taken in 10 ml of acetoni-
trile in a round bottom flask and the reaction mixture was heated
at 75 ◦C. Catalysts 7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-
NaY and [Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY showed 53.5 and
44.2% conversion of styrene in 6 h respectively. Turn-over
frequencies and product selectivities are shown in Table 3.
The highest yield of benzaldehyde might be due to fur-
ther oxidation of styreneoxide by the nucleophilic attack of
H2O2 on styrene oxide, followed by cleavage of the inter-
mediate species hydroxy-hydroperoxistyrene [29]. In order to
obtain optimum reaction conditions for maximum conversion
of styrene, catalyst 7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-
NaY was used as a representative catalyst for the following
studies.
3.7.1.4. Effect of reaction time. The time dependence of catalytic
solvent free oxidation of benzyl alcohol was studied by perform-
3.7.2.1. Effect of temperature. In order to determine the
optimum temperature for the oxidation of styrene, we
investigated the oxidation of styrene using catalyst 7,16-
diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY and 30% H2O2 as
oxidant in 10 ml acetonitrile was investigated at four different
temperatures 65, 70, 75 and 80 ◦C, keeping the other parame-
ters fixed, namely styrene (1.56 g, 15 mmol), 30% H2O2 (3.52 g,
30 mmol) and catalyst (35 mg) and reaction time (6 h). The results
(Fig. 8) show that 30.9, 45.6, 53.5 and 54.1% conversions were
found corresponding to 60, 70, 75 and 80 ◦C respectively. Only a
Fig. 7. Effect of benzyl alcohol: H2O2 molar ratios on the oxidation of benzyl alcohol,
reaction conditions: benzyl alcohol = 30 mmol, catalyst amount = 30 mg, reaction
temperature = 75 ◦C and reaction time = 6 h.

V.K. Bansal et al. / Applied Catalysis A: General 381 (2010) 8–17
15
Table 3
Product selectivity, % conversion, TOF values of styrene after 6 h reaction time using H2O2 as oxidant.
Catalyst
Conversion (%)
TOFf (h−1
)
Product selectivity (%)
Soa
Bzab
Bzacc
Phedd
Phaae
Others
7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY
[Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY
Cu(II)-NaY
53.5
44.2
6.2
95
78
63
18.5
17.4
14.4
58.2
61.9
77.8
4.8
8.0
1.1
5.4
6.1
–
12.3
5.3
7.1
0.8
1.3
–
a
Styreneoxide.
Benzaldehyde.
Benzoic acid.
Phenylacetaldehyde.
b
c
d
e
1-Phenyl-ethane-1,2-diol.
f
turn-over frequency = mole of styrene converted per mole of metal (in zeolite encapsulated catalyst) per hour.
negligible improvement in conversion was observed on increasing
the temperature from 75 to 80 ◦C. So the temperature of 75 ◦C was
found optimal for the maximum conversion of styrene.
when 35 and 40 mg of catalyst was used. Therefore, 35 mg amount
of catalyst was found to be optimum.
3.7.2.3. Effect of H2O2 concentration. The effect of H2O2 concen-
tration on the oxidation of styrene is illustrated in Fig. 10. It was
studied using three different molar ratios of styrene: H2O2 viz.,
1:1, 1:2 and 1:3. Other parameters were kept fixed during the reac-
tion: namely styrene (1.56 g, 15 mmol) and catalyst (35 mg) in 10 ml
CH3CN, temperature (75 ◦C) and reaction time (6 h). Styrene: H2O2
molar ratio 1:1 and 1:2 showed 38.4 and 53.5% conversion respec-
tively. When the styrene to H2O2 molar ratio was increased to 1:3,
the conversion was found to 52.3% under all other similar condi-
tions. The reason for decreasing % conversion of styrene might be
due to dilution of the reaction mixture, since 30% H2O2 has consid-
erable amount of water. Therefore, 1:2 molar ratio of benzyl alcohol
to H2O2 was found the optimum in terms of conversion as well as
cost of H2O2.
3.7.2.2. Effect of catalyst amount. The amount of catalyst has a
considerable effect on the oxidation of styrene. Four different
amounts of catalyst viz., 20, 30, 35 and 40 mg were used keeping all
other reaction parameters fixed: namely styrene (1.56 g, 15 mmol),
30%H2O2 (3.52 g, 30 mmol), temperature (75 ◦C) and reaction time
(6 h). Fig. 9 shows the results of percent conversion as a function of
time, indicating 25.1, 44.9, 53.5 and 54.7% conversions correspond-
ing to 20, 30, 35 and 40 mg of catalyst, respectively. The maximum
percentage conversion was observed with 40 mg of catalyst but
there was no considerable difference in the styrene conversion
3.7.2.4. Effect of reaction time. The time dependence of the catalytic
oxidation of styrene was studied by performing the reaction of
styrene (1.56 g, 15 mmol), 30% H2O2 (3.52 g, 30 mmol) and cata-
lyst (35 mg) in 10 ml CH3CN at 75 ◦C for 6 h with constant stirring.
The percentage of conversion was monitored at different reaction
times. It is seen that 53.5% conversion was observed. When the
reaction was allowed to continue for 20 h, 55.0% conversion was
observed.
3.8. Test for heterogeneity and recycle ability
The recyclability of used encapsulated catalysts has been tested
in both the catalytic reactions. The reaction mixture was filtered
after a contact time of 6 h. The catalysts were activated by washing
with hot acetonitrile and drying at 90 ◦C in an oven. Each catalyst
was used in further catalytic oxidation reactions under similar con-
Fig. 8. Effect of temperature on the oxidation of styrene, reaction conditions:
styrene = 15 mmol, 30% H2O2 = 30 mmol, CH3CN = 10 ml, catalyst = 35 mg and reac-
tion time = 6 h.
Fig. 9. Effect of amount of catalyst on the oxidation of styrene, reaction
conditions: styrene = 15 mmol, 30%H2O2 = 30 mmol, CH3CN = 10 ml, reaction tem-
perature = 75 ◦C and reaction time = 6 h.
Fig. 10. Effect of styrene: H2O2 molar ratios on the oxidation of styrene, reaction
conditions: styrene = 15 mmol, catalyst amount = 35 mg, CH3CN = 10 ml, reaction
temperature = 75 ◦C and reaction time = 6 h.

16
V.K. Bansal et al. / Applied Catalysis A: General 381 (2010) 8–17
Fig. 12. Spectral change during titration of 7,16-diacetyl[Cu{Me4(Bzo)2
[14]tetraeneN4}] with methanolic solution of 30% H2O2.
Fig. 11. Spectral change during titration of 7,16-diacetyl[Ni{Me4(Bzo)2
[14]tetraeneN4}] with methanolic solution of 30% H2O2.
species of the complexes is present, the formation of [7,16-
diacetyl[M{Me4(Bzo)2[14]tetraeneN4}]-(OOH)] {M = Cu(II), Ni(II)}
intermediate is expected [45,48,49]. The intermediate species
finally transfers oxygen atoms to the substrates to give the prod-
ucts. Thus, the catalytic performance of encapsulated catalyst could
be attributed to the facile formation of reversible intermediate
species.
ditions. It was found that the conversion was nearly the same as for
the first cycle and there was only a minor loss in catalytic activity for
the second cycle. In the case of styrene the reaction times increased.
This may be due to the blocking of zeolite channels during the reac-
tion. IR spectra of recycled catalysts were found be nearly identical
to that of fresh catalysts, pointing to the stability and recyclability
of the catalysts. The heterogeneity of the catalysts has been tested
in both the catalytic reactions by atomic absorption spectroscopy.
The filtrate collected after separating the catalysts were placed in a
reaction flask and the reactions were continued after adding fresh
H2O2 for another 6 h under conditions similar to those used ear-
lier. The gas chromatographic analysis showed no improvement in
conversion after 6 h. The absence of metal in the filtrate of reac-
tion mixtures was confirmed by AAS. This showed that there was
no metal leaching during the catalytic reactions, therefore both the
reactions were found to be heterogeneous in nature.
4. Conclusion
In summary, neat 7,16-diacetyl[M{Me4(Bzo)2[14]tetraeneN4}]
{M = Cu(II), Ni(II)} have been synthesized and characterized. These
square planar complexes have also been encapsulated by the
template synthesis method in the super cages of zeolite-Y, and
their encapsulation was ensured by different studies. Furthermore,
the spectroscopic data suggest that the encapsulated tetraaza-
macrocycle complex experienced very little distortion in the super
cages of zeolite and that chemical ligation to the zeolite surface
is minimal. Catalyst 7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]-
NaY is a better catalyst for the solvent free oxidation of benzyl
alcohol compared to [Cu{Me4(Bzo)2[14]tetraeneN4}]-NaY. Ben-
zaldehyde was found as the major oxidation product along
with benzoic acid and benzylbenzoate as minor products. For
the oxidation of styrene by H2O2 as oxidant, the catalyst
7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY showed the best
performance as compared to [Ni{Me4(Bzo)2[14]tetraeneN4}]-NaY.
Benzaldehyde and styreneoxide were found as major products. All
catalysts are stable and reusable. These catalysts do not leach dur-
ing the reaction, so they can be used as heterogeneous catalysts.
3.9. Possible pathway of the catalyzed reactions
To establish the possible path of reactions,
a
10−5 M
7,16-
solution
of
neat
tetraazamacrocycle
complexes
diacetyl[M{Me4(Bzo)2[14]tetraeneN4}]
{M = Cu(II),
Ni(II)}
(complexes were first dissolved in minimum amount of chlo-
roform then diluted by methanol) were treated with a methanolic
solution of 30% H2O2. Spectral changes in the electronic spectra of
neat complexes were monitored using a UV–vis spectrophotome-
ter. Gradual addition of methanolic solution of 30% H2O2 to the
solution of 7,16-diacetyl[Ni{Me4(Bzo)2[14]tetraeneN4}] resulted
in a decrease in intensity of the 585, 416 and 392 nm peaks while
the intensity of the peaks at 335 and 267 nm gradually increased.
The spectral changes are shown in Fig. 11. Three isosbestic points
were found at 525, 450 and 353 nm. When small drop portions
of a methanolic solution of 30% H2O2 were gradually added to
10−5 M solution of 7,16-diacetyl[Cu{Me4(Bzo)2[14]tetraeneN4}]
spectral changes also occurred as shown in Fig. 12. The intensity of
peaks observed at 636, 412, 380 and 314 nm decreased on gradual
addition of H2O2 while the intensity of the peaks at 285 and
252 nm increased. An isosbestic point was also found at 302 nm.
These changes indicate the interaction of hydrogen peroxide with
Cu(II) and Ni(II) metal center.
Acknowledgements
One of the authors V.K.B. thanks CSIR, New Delhi for the grant
of a Senior Research fellowship. The authors are also thankful to
the Head, RSIC CDRI, Lucknow (India) for the Mass Spectra of the
complexes.
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