Oxidation of styrene and cyclohexene with TBHP catalyzed by copper(II) complex encapsulated in zeolite-Y

Article abstract of DOI:10.1080/00958972.2012.706281

Reaction of monobasic tridentate Hacpy-oap (Hacpy-oap=Schiff base derived from 2-acetylpyridine and o-aminophenol) with Cu^IICl₂ in refluxing methanol results in formation of [Cu^II(acpy-oap)Cl]. DFT calculations have been used to optimize structure of the complex. [Cu ^II(acpy-oap)Cl] has also been encapsulated in the nanocavity of zeolite-Y and its encapsulation ensured by various physico-chemical techniques. Neat as well as encapsulated complexes are active catalysts for oxidation of styrene and cyclohexene using tert-butylhydroperoxide. Reaction conditions for oxidation of these substrates have been optimized by concentration of oxidant, amount of catalyst, volume of solvent and temperature of the reaction mixture. [Cu^II(acpy-oap)Cl] does not leach metal ion during catalytic activity and is recyclable.

Full text of DOI:10.1080/00958972.2012.706281

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Oxidation of styrene and cyclohexene
with TBHP catalyzed by copper(II)
complex encapsulated in zeolite-Y
Mannar R. Maurya a , Priyanka Saini a , Chanchal Haldar a , Anil K.
Chandrakar b & Shri Chand b
a Department of Chemistry , Indian Institute of Technology
Roorkee , Roorkee 247 667, Uttarakhand , India
b Department of Chemical Engineering , Indian Institute of
Technology Roorkee , Roorkee 247 667, Uttarakhand , India
Accepted author version posted online: 25 Jun 2012.Published
online: 10 Jul 2012.
To cite this article: Mannar R. Maurya , Priyanka Saini , Chanchal Haldar , Anil K. Chandrakar
& Shri Chand (2012) Oxidation of styrene and cyclohexene with TBHP catalyzed by copper(II)
complex encapsulated in zeolite-Y, Journal of Coordination Chemistry, 65:16, 2903-2918, DOI:
10.1080/00958972.2012.706281
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Journal of Coordination Chemistry
Vol. 65, No. 16, 20 August 2012, 2903–2918
Oxidation of styrene and cyclohexene with TBHP catalyzed
by copper(II) complex encapsulated in zeolite-Y
MANNAR R. MAURYA*y, PRIYANKA SAINIy, CHANCHAL HALDARy,
ANIL K. CHANDRAKARz and SHRI CHANDz
yDepartment of Chemistry, Indian Institute of Technology Roorkee,
Roorkee 247 667, Uttarakhand, India
zDepartment of Chemical Engineering, Indian Institute of Technology Roorkee,
Roorkee 247 667, Uttarakhand, India
(Received 17 January 2012; in final form 11 May 2012)
Reaction of monobasic tridentate Hacpy-oap (Hacpy-oap ¼ Schiff base derived from
2-acetylpyridine and o-aminophenol) with CuIICl2 in refluxing methanol results in formation
of [CuII(acpy-oap)Cl]. DFT calculations have been used to optimize structure of the complex.
[CuII(acpy-oap)Cl] has also been encapsulated in the nanocavity of zeolite-Y and its
encapsulation ensured by various physico-chemical techniques. Neat as well as encapsulated
complexes are active catalysts for oxidation of styrene and cyclohexene using tert-
butylhydroperoxide. Reaction conditions for oxidation of these substrates have been optimized
by concentration of oxidant, amount of catalyst, volume of solvent and temperature of the
reaction mixture. [CuII(acpy-oap)Cl] does not leach metal ion during catalytic activity and is
recyclable.
Keywords: Zeolite-Y; [CuII(acpy-oap)Cl]; [CuII(acpy-oap)Cl]-Y; Catalyst; Oxidation of
cyclohexene; Oxidation of styrene
1. Introduction
Catalytic properties of transition metal complexes are controlled by metal and their
electronic and structural properties [1, 2]. Oxygen transformations catalyzed by
transition metal complexes to produce more valuable organic compounds, such as
alcohols, aldehydes, and ketones, require selective oxidation of strong C–H bonds. In
homogeneous systems the catalytic activity of the complexes slowly decreases with time
due to their slow decomposition, dimerization, or formation of oxo- or peroxo-bridged
complexes. Heterogenization of homogeneous catalysts has been sought to avoid such
complications [3–5]. Zeolite encapsulated metal complexes (ZEMC) hold a key place
and are suggested as model compounds for enzyme mimicking [6, 7]. Encapsulations of
complexes in the nano-cavity of zeolite-Y is a process that does not require interactions
between the catalyst and the support, and thus maintain inherent advantages of
homogeneous catalytic systems [4]. Such ZEMC have provided the opportunity to
*Corresponding author. Email: rkmanfcy@iitr.ernet.in
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.706281

2904
M.R. Maurya et al.
N
OH
N
H3C
Scheme 1. Structure of (Hacpy-oap; I).
develop catalytic processes for selective oxidation of various substrates and produce
important intermediates and industrial products [2, 4, 6–11]. Most encapsulated
complexes show better activity than their respective non-encapsulated counterparts.
In many cases these are more active, easily recyclable and maintain activity after several
cycles of catalytic use.
We have encapsulated copper(II) complex of the Schiff base derived from
2-acetylpyridine and o-aminophenol (scheme 1) in the super cages of zeolite-Y.
Its catalytic potential has been tested for oxidation of styrene and cyclohexene.
The oxidation of styrene is of great interest because styrene oxide and benzaldehyde are
important and versatile synthetic intermediates in chemical industry [12, 13]. Selective
oxidation of styrene has been reported using various homogeneous catalysts, e.g., metal
complexes [14–17] and supported heterogeneous catalysts such as mixed metal oxides
[18], zeolites [19], ZEMC [20], metal complexes supported on mesoporous materials
[21, 22], etc. Copper complexes encapsulated in the cavity of zeolite-Y have been used as
catalyst for oxidation of cyclohexene where various oxidation products such as
cyclohexene oxide, 2-cyclohexene-1-one, 2-cyclohexene-1-ol, cyclohexane-1,2-diol, etc.
have been identified [23–27].
2. Experimental
2.1. Materials and methods
Copper(II) nitrate (Qualigens, India), 2-acetylpyridine, o-aminophenol, cyclohexene
(Himedia, India), styrene (Acros Organics, USA), 70% (w/v) tert-butylhydroperoxide
(TBHP) (E. Merck, India) were used as obtained. Y-zeolite (Si/Al ¼ 10) was obtained
from Indian Oil Corporation (R&D), Faridabad, India. Copper exchanged zeolite-Y
[CuII-Y] was prepared as reported previously [28]. Found: Cu (ICP-MS), 7.6%. All
other chemicals and solvents used were of AR grade.
Elemental analyses of the ligand and complex were obtained by an Elementar model
Vario-EL-III. Electronic spectrum of encapsulated complex was recorded in Nujol
using a Shimadzu 1601 UV-Vis spectrophotometer by layering the mull of the sample
inside a cuvette while keeping the other one layered with Nujol as reference. Spectra of
neat complex and ligand were recorded in methanol. IR spectra were recorded as KBr
pellets on a Nicolet NEXUS Aligent 1100 series FT-IR spectrometer after grinding the
sample with KBr. Thermogravimetric analysis of the encapsulated complex was carried
out using a Perkin Elmer (Pyris Diamond) instrument in air with a heating rate of
10ꢀC minꢁ1. Scanning electron micrographs (SEMs) of Na-Y and encapsulated catalyst
were recorded on a Leo instrument model 435VP; the samples were dusted on alumina
and coated with a thin film of gold to prevent surface charging and to protect the

Oxidation of alkenes
2905
surface material from thermal damage by the electron beam. In all analyses a uniform
thickness of about 0.1 mm was maintained. X-ray powder diffractograms of solid
catalyst were recorded using a Bruker AXS D8 Avance X-ray powder diffractometer
with a Cu-Ka target. A thermoelectron gas-chromatograph with an HP-1 capillary
column (HP-1, 30 m ꢂ 0.25 mm ꢂ 0.25 mm) was used to analyze the reaction products.
The identity of the products was confirmed by GC-MS using a Perkin-Elmer
Clarus 500.
Full geometry optimization of the complex was carried out using the density
functional theory method at the (U)B3LYP level [29]. All elements except Cu were
assigned the 6-31G(d) basis set. LanL2DZ with an effective core potential for Cu was
used. The vibrational frequency calculations were performed to ensure that the
optimized geometries represent the local minima and that there are only positive
eigenvalues.
2.2. Preparations
2.2.1. Preparation of Hacpy-oap (I). A filtered solution of o-aminophenol (0.504 g,
5 mmol) in methanol (25 mL) was added to a solution of 2-acetylpyridine (0.605 g,
5 mmol) in methanol (25 mL) with stirring and the resulting reaction mixture was
refluxed for 4 h. The volume of solvent was reduced to ca 20 mL and in situ formed light
brown ligand was used for further reaction. Yield: 64%. Anal. Calcd for C13H12N2O
1
(212.25) (%): C, 73.57; H, 5.70; N, 13.20. Found (%): C, 73.50; H, 5.78; N, 13.16. H
NMR (DMSO-d6(ppm)): 8.7(b, 1H), 7.7(d, 1H, aromatic), 7.47(m, 2H, aromatic),
7.41(t, 1H, aromatic), 6.82(b, 2H, aromatic), 6.39(s, 2H, aromatic), 1.60(s, 3H, ꢁCH3).
Signal due to methyl protons could be seen well in CDCl3.
2.2.2. Preparation of [CuII(acpy-oap)Cl] (1). A solution of I (equivalent to 5 mmol)
was prepared as mentioned above in 50 mL of methanol. A filtered solution of
CuCl2 ꢃ 2H2O (0.852 g, 5 mmol) prepared in 100 mL methanol was added to the above
solution and the resulting reaction mixture was stirred at room temperature for 4 h.
After reducing the solvent volume to ca 20 mL, the flask was kept at ambient
temperature overnight where brown mass separated. This was filtered, washed with
methanol and dried in vacuum over silica gel. Yield: 56%. Anal. Calcd for
C13H11N2OClCu (310.04) (%): C, 50.32; H, 3.55; N, 9.03; Cl, 11.45. Found (%):
C, 50.5; H, 3.4; N, 9.2; Cl, 11.3.
2.2.3. Preparation of [CuII(acpy-oap)Cl]-Y (2). A methanolic solution of o-aminophe-
nol (1.64 g, 15 mmol) in 15 mL was added to a solution of 2-acetylpyridine (1.82 g,
15 mmol) already dissolved in 25 mL of methanol. The obtained reaction mixture was
refluxed for 4 h in an oil bath; 1.0 g of [CuII]-Y was suspended to the solution and the
reaction mixture was heated under reflux for 15 h in an oil bath while stirring. The
resulting light brown material was filtered, dried and Soxhlet extracted with methanol
followed by acetone to remove excess ligand and metal complex on the surface of the
zeolite if any. The uncomplexed metal ions in zeolite were removed by treating with
aqueous 0.1 mol Lꢁ1 NaCl solution (200 mL) with stirring for 8 h. It was then washed
with doubly distilled water until no precipitate of AgCl was observed in the filtrate on

2906
M.R. Maurya et al.
treating with AgNO3. Finally it was dried at 120ꢀC to constant weight. Found: Cu
(ICP-MS), 2.6%.
2.3. Catalytic activity studies
2.3.1. Oxidation of styrene. The catalytic oxidation of styrene was carried out in a
50 mL flask fitted with a water-circulated condenser. An aqueous solution of 70%
TBHP (2.56 g, 20 mmol) and styrene (1.04 g, 10 mmol) were mixed in 20 mL of CH3CN
and the reaction mixture was heated at 80ꢀC with continuous stirring in an oil bath. The
reaction was considered to begin after addition of [CuII(acpy-oap)Cl]-Y (0.035 g).
During the reaction, the products were analyzed quantitatively by gas chromatography
by withdrawing small aliquots after specific intervals of time. The identities of the
products were confirmed by GC-MS.
2.3.2. Oxidation of cyclohexene. An aqueous solution of 70% TBHP (2.56 g,
20 mmol), cyclohexene (0.82 g, 10 mmol) and catalyst (0.035 g) were mixed in 20 mL
of CH3CN and the reaction mixture was heated at 75ꢀC with continuous stirring in an
oil bath. The progress of the reaction was monitored as mentioned above and identity
of the various products confirmed by GC-MS.
3. Results and discussion
Reaction between equimolar amounts of CuIICl2 and Hacpy-oap (I) in dry, refluxing
methanol yields the brown [CuII(acpy-oap)Cl] (1). The ligand coordinates out as
monoanionic (ONN(1 -)) form; equation (1).
Â
Ã
CuIICl2 þ Hacpyꢁoap ! CuIIðacpyꢁoapÞCl þ HCl
ð1Þ
Encapsulation of [CuII(acpy-oap)Cl] (1) in the nanocavity of zeolite-Y involved the
interaction of [CuII]-Y with excess Hacpy-oap in methanol where ligand slowly enters
into the cavity of zeolite-Y due to its flexible nature and interacts with copper. Soxhlet
extraction using methanol/acetone purified the impure complex. The remaining
uncomplexed metal ions in zeolite were removed by exchanging with aqueous
0.1 mol Lꢁ1 NaCl solution. As one extra anionic ligand would be required to balance
the overall charges on the CuII, Clꢁ of NaCl used during exchanged process fulfills this
requirement. The presence of chloride in complex has been confirmed qualitatively.
Hence, the formula of the encapsulated CuII complex may also be written as [CuII(acpy-
oap)Cl]; the encapsulated complex is abbreviated as [CuII(acpy-oap)Cl]-Y (2).
As impure sample of 2 was extracted with methanol and acetone, the copper content
(2.6%) after encapsulation is only due to the presence of [CuII(acpy-oap)Cl] in the super
cages of zeolite-Y. Due to space constraint in the cavity of zeolite-Y, 1 will exist in its
monomeric form in the nanocavity. The observed surface area of [CuII]-Y and
[CuII(acpy-oap)Cl]-Y are 752 and 510 m2 gꢁ1, respectively. Thus, encapsulation of
metal complex in zeolite-Y led to an apparent reduction in the surface area and pore
volume. This decrease depends on the amount of incorporated complex as well as its

Oxidation of alkenes
2907
Figure 1. Fully optimized structure of [CuII(acpy-oap)Cl] (1).
Table 1. Selected bond lengths and angles (ꢀ) calculated for [CuII(acpy-oap)Cl] compared
with literature data.
Present article
Literature value
Cu–Cl
2.282
1.998
1.997
1.913
2.248b
N(az)–Cu–Cla
N(r)–Cu–O
163.465
159.868
101.305
83.907
81.308
96.697
Cu–N(r)a
Cu–N(az)a
Cu–O
2.0511(17)b, 1.995(6)c
1.9549(18)b
Cl–Cu–O
1.9293(15)b
N(az)–Cu–Oa
N(az)–Cu–N(r)a
N(r)–Cu–Cla
ar represents ring nitrogen and az represents azomethine nitrogen.
bRef. [26].
cRef. [30].
molecular size and geometrical conformation inside the zeolitic host. Similarity the
spectral properties of neat as well as encapsulated complex (vide infra) suggests a
distorted square planar structure for encapsulated complex as well.
3.1. DFT studies
The fully optimized DFT structure of [CuII(acpy-oap)Cl] is presented in figure 1 and
computed bond lengths and angles are presented in table 1. The coordination
polyhedron around copper, where pyridinic ring nitrogen, enolic oxygen, azomethine
nitrogen, and Cl– are involved, is a much distorted square plane. The DFT structural
˚
˚
data reveal that Cu–Nring bond lengths (1.998 A), Cu–Nazomethine (1.997 A), Cu–Oenolic
˚
˚
(1.913 A), and Cu–Cl (2.282 A) are within the values normally found (table 1) for these
types of bonds [26, 30]. Similarly, various bond angles around copper compare well with
values reported for such complexes. The steric requirements of the molecule,

2908
M.R. Maurya et al.
Figure 2. Mapped surface of the total electron density showing the steric requirements of [CuII(acpy-
oap)Cl] (1).
Table 2. IR and electronic spectral data of ligand, pure, and encapsulated complexes.
IR (cm–1
)
Compound
ꢀ(C¼N)
ꢁmax (nm)
Hacpy-oap (I)
[CuII(acpy-oap)Cl] (1)
[CuII(acpy-oap)Cl]-Y (2)
1587
1633, 1583
1631, 1585
208, 236, 273, 428
228, 235, 268, 435, 500
235, 270, 440
considering mapped surface of the total electron density (figure 2), suggests that
chloride deviates from the plane containing the four donor atoms. Calculated ꢀ(OH)
band at 3670 cmꢁ1 in ligand is absent in the complex while the band at 1652 cmꢁ1 in the
complex for Cu–Nring/azomethine is close to the observed value (1633 cmꢁ1).
These complexes were further characterized by spectroscopic (IR and UV-Vis) data,
elemental analysis, FE-SEM, X-ray powder diffraction pattern, and thermogravimetric
analysis.
3.2. IR spectral studies
A partial list of IR spectral data is presented in table 2. The intensities of peaks in
encapsulated complex are weak due to their low concentration in zeolite matrix, but
show similar bands. Comparison of spectra of these catalysts with ligand provides
evidence for the coordination mode of the ligand. Ligand exhibits ꢀ(C ¼ N)
(azomethine) at 1640 cmꢁ1 and this band moves to lower wavenumbers in complexes
(1633 cmꢁ1 in 1 and 1631 cmꢁ1 in 2), indicating participation of the azomethine nitrogen
in coordination. A weak band at ca 1585 cmꢁ1 is assigned to coordinated pyridine.
Absence of band due to hydroxyl group in [CuII(acpy-oap)Cl] (1) indicates
deprotonation followed by coordination of oxygen to copper while presence of such
band in [CuII(acpy-oap)Cl]-Y (2) is due to the presence of intra-zeolite water.

Oxidation of alkenes
2909
(c)
(b)
(a)
5
10
15
20
25
30
35
40
2θ
Figure 3. XRD patterns of (a) Na-Y, (b) CuII-Y, (c) [CuII(acpy-oap)Cl]-Y.
3.3. Electronic spectral studies
Table 2 also presents electronic spectral data of ligand and complexes. The electronic
spectrum of the ligand exhibits four bands at 208, 236, 273, and 428 nm. The low energy
band (428 nm) is assigned to n–ꢂ* transition, the bands at 236 and 273 nm are due to
split band of ꢂ–ꢂ* while 208 nm band is due to ’–’* transition. All these bands are also
present in [CuII(acpy-oap)Cl] (1) with slight variations. A broad band at 432 nm is
assigned to ligand-to-metal charge transfer (LMCT) from the phenolate oxygen to an
empty d orbital of copper. The n–ꢂ* band merges with this band. In addition, a broad
and less intense band at ca 500 nm also appears and is assigned to d–d transition,
characteristic of copper(II) in a distorted square planar geometry [31, 32]. Encapsulated
[CuII(acpy-oap)Cl]-Y (2) displays only bands at 206 and 270 nm in Nujol in the UV
region. The d–d transition band could not be located due to poor loading of 1 in the
zeolite-Y. However, a LMCT band at 440 nm in the visible region clearly suggests the
encapsulation of metal complex.
3.4. Powder X-ray diffraction studies
The powder X-ray diffraction patterns of Na-Y, [CuII]-Y and encapsulated metal
complex [CuII(acpy-oap)Cl]-Y (2) were recorded at 2ꢃ values between 5ꢀ and 40ꢀ. The
diffraction patterns of encapsulated metal complex, [CuII]-Y and Na-Y are similar
except a slight change in intensity of the bands in encapsulated complex (figure 3).
These observations indicate that the framework of the zeolite has not undergone
significant structural change during encapsulation. No new peaks were detected in the
zeolite having encapsulated complex due to poor loading of metal complex in the
nanocavity of zeolite-Y.
3.5. Field-emission-SEM and energy dispersive X-ray analysis studies
Figure 4 presents the field emission SEM of [CuII(acpy-oap)Cl]-Y (2) (left) along with
the respective energy dispersive X-ray (EDX) analysis plot (right). It is clear from the

2910
M.R. Maurya et al.
Figure 4. Field emission SEM (Fe-SEM) of [CuII(acpy-oap)Cl]-Y (2) (left) along with the respective EDX
analysis plot (right).
micrograph that copper complex entrapped in zeolite has well-defined crystals and there
is no indication of metal ion or complex on the surface. EDX analysis plot supports this
conclusion as no copper or nitrogen contents were noted on the spotted surface in the
plot. The average silicon and aluminum percentage obtained on the spotted surfaces
were ca 28% and ca 11%, respectively. Sodium, ca 3%, suggests the exchange of
remaining free copper by sodium during re-exchange process (Experimental section).
Only a small amount of carbon (ca 4%) and no nitrogen suggest the presence of trace
amount of solvent (methanol) from which it was finally washed after Soxhlet extraction.
No morphological changes on the surface upon encapsulation of the complexes in the
cavity are seen due to their poor loading.
3.6. Thermogravimetric analysis
The thermogravimetric analysis data of [CuII(acpy-oap)Cl]-Y (2) along with the percent
weight loss at different steps and their assignments are presented here. The thermogram
of encapsulated complex indicates its decomposition in three steps, though these steps
are overlapping. The first step involves removal of trapped water of ca 3.8% up to
150ꢀC, while the loss of water of ca 9.8% is associated with the structural framework
and occurs at 170–350ꢀC. The third step involves the slow but exothermic weight loss of
ca 19.2% in a wider temperature range (350–800ꢀC) due to decomposition of the
chelating ligand.
3.7. Catalytic activity studies
3.7.1. Oxidation of styrene. The oxidation of styrene, catalyzed by [CuII(acpy-
oap)Cl]-Y, was carried out using 70% TBHP as an oxidant to give styrene oxide and
benzaldehyde along with only minor amounts of unidentified products, scheme 2.
These are common products and have been identified by others as well [7, 9–11].

Oxidation of alkenes
2911
O
O
Catalyst
TBHP
Styrene
Benzaldehyde
(bza)
Styreneoxide
(so)
Scheme 2. Oxidation products of styrene.
In the presence of H2O2, further oxidation of styrene oxide to other products has also
been reported [33, 34].
In search of reaction conditions to achieve maximum oxidation of styrene, the effect
of amount of oxidant (moles of TBHP per mole of styrene), catalyst (amount of catalyst
per mole of styrene), and temperature of the reaction were studied.
The effect of TBHP on oxidation of styrene is illustrated in figure 5(a). Three
different styrene/TBHP molar ratios of 1 : 1, 1 : 2, and 1 : 3 were considered where the
mixture of styrene (1.04 g, 10 mmol), catalyst (0.050 g), and oxidant were taken in 20 mL
of CH3CN and the reaction was carried out at 80ꢀC (entry nos. 1–3 of table 3).
Increasing the styrene/TBHP ratio from 1 : 1 to 1 : 2 increases the conversion from
34.7% to 50.8%. Further increasing the ratio to 1 : 3 brings the conversion down to
47.5%. The reason for this may be due to the dilution of the reaction mixture by the
presence of larger amount of water molecules in TBHP solution. It is, therefore,
concluded that the 1 : 2 molar ratio is best to obtain the maximum styrene conversion of
50.8% in 7 h reaction time.
Amount of catalyst also affects on the conversion. In order to optimize it, four
different amounts of catalyst namely, 0.020, 0.035, 0.050, and 0.075 g were taken for the
fixed operating conditions of styrene (1.04 g, 10 mmol) and TBHP (2.56 g, 20 mmol) in
20 mL of CH3CN at 80ꢀC. As shown in figure 5(b) (entry nos. 2, 5–7 of table 3),
increasing the catalyst amount from 0.020 g to 0.035 g improved the styrene conversion
from 36.6% to 60.2%. However, increasing the catalyst amount to 0.050 and 0.075 g
did not improve the conversion, thereby suggesting that 0.035 g of catalyst is sufficient
to effect maximum conversion. The reason for lower conversion at higher catalyst
amount may be due to adsorption/chemisorptions of two reactants on separate catalyst
particles, thereby reducing the chance to interact.
Figure 5(c) (entry nos. 5, 7, and 8 of table 3) shows the effect of temperature on the
oxidation of styrene while keeping amount of catalyst and styrene/TBHP ratio
optimized in 20 mL of CH3CN. Increasing temperature increases the conversion
and running the reaction at 80ꢀC is the best to obtain 60.2% conversion in 7 h of
reaction time.
Thus, for maximum oxidation of 10 mmol of styrene optimized parameters (entry no.
5 of table 3) are: [CuII(acpy-oap)Cl]-Y (0.035 g), TBHP (2.56 g, 20 mmol), CH3CN
(20 mL) and temperature (80ꢀC).
A maximum of 60.2% conversion of styrene with turnover frequency (TOF) of 61 hꢁ1
has been obtained under optimized conditions after 7 h of reaction time. The styrene
oxide, an important product, is obtained in 78.2% selectivity while benzaldehyde is
obtained with only 18.2% selectivity. Other minor products (ca 3.6%) could not be
identified. Higher selectivity of styrene oxide can be explained from the fact that TBHP

2912
M.R. Maurya et al.
(a)
(b)
60
50
40
30
20
10
0
0.020 g
0.035 g
0.050 g
0.075 g
50
40
30
20
10
0
1:1
2:1
3:1
0
60
120 180 240 300 360 420
Time (min)
0
60
120 180 240 300 360 420
Time (min)
(c)
(d)
[CuII(acpy-oap)Cl]-Y (2)
[CuII(acpy-oap)Cl] (1)
60
50
40
30
20
10
0
60
50
40
30
20
10
0
50 oC
65 oC
80 oC
0
60
120 180 240 300 360 420
Time (min)
60
120 180 240 300 360 420
Time (min)
Figure 5. (a) Effect of TBHP concentration (TBHP : styrene) on oxidation of styrene. (b) Effect of amount
of catalyst per unit weight of styrene. (c) Effect of temperature on the oxidation of styrene. (d) Effect of
different catalysts [CuII(acpy-oap)Cl] (1) and [CuII(acpy-oap)Cl]-Y (2) on oxidation of styrene. See text for
reaction conditions of each plot.
Table 3. Conversion of styrene (1.04 g, 10 mmol) using [CuII(acpy-oap)Cl]-Y as catalyst in 7 h under different
reaction conditions.
Entry No.
Catalyst (g)
TBHP (g, mmol)
Temperature (ꢀC)
MeCN (mL)
Conv. %
1
2
3
4
5
6
7
8
0.050
0.050
0.050
0.020
0.035
0.075
0.035
0.035
1.28, 10
2.56, 20
3.84, 30
2.56, 20
2.56, 20
2.56, 20
2.56, 20
2.56, 20
80
80
80
80
80
80
50
65
20
20
20
20
20
20
20
20
34.7
50.8
47.5
36.6
60.2
44.4
14.7
38.6
is a milder oxidant leading to the formation of styrene oxide in better yield and does not
oxidize further. After washing with acetonitrile and drying, the used catalyst was further
used under similar conditions to check its recyclability. About 59.6% conversion of
styrene obtained at the end of 7 h with similar selectivity of products suggests its
recyclability.

Oxidation of alkenes
2913
O
OH
OH
TBHP
Catalysts
+
O
+
+
OH
2-Cyclohexene-1-ol 2-cyclohexene-1-one
Cyclohexeneoxide
Cyclohexane-1,2-diol
Scheme 3. Oxidation products of cyclohexene.
Neat complex [CuII(acpy-oap)Cl] has been used as a catalyst precursor using same
mole concentration of copper as in its zeolite encapsulated complex to compare its
catalytic activity. Interestingly, this exhibited 38.6% conversion (figure 5d) when
complex (0.0028 g, 0.009 mmol), styrene (1.04 g, 10 mmol), TBHP (2.56 g, 20 mmol), and
CH3CN (20 mL) were used and the reaction was carried out at 80ꢀC. Here, the
selectivity of different products is styrene oxide (73.4%) 4 benzaldehyde (20.7%).
Thus, the order is the same as obtained by encapsulated complex and the selectivity of
individual products differs only slightly. Blank reaction under above reaction
conditions gave 3% conversion. Thus, neat as well as encapsulated complexes are
good catalysts. However, the recyclable nature and no leaching of [CuII(acpy-oap)Cl]-Y
makes it better.
Catalytic activity of [CuII(acpy-oap)Cl]-Y compares well with other catalysts. Metal
complex [MnII(salen)] encapsulated in zeolite-Y exhibits ca 30% conversion of styrene
using molecular oxygen as an oxidant with excess TBHP as initiator [14]. Zeolite-Y
encapsulated [VIVO(salphen)] exhibits 34.8% conversion of styrene using TBHP as
oxidant [15]. Other zeolite encapsulated catalysts such as [MnII(3-MeOsalen)]-Y
(H2salen ¼ bis(salicylaldehyde)-1,2-diaminoethane),
[MnII(3-MeOsalpn)]-Y
and
[MnII(salpn)]-Y (H2salpn ¼ bis(salicylaldehyde)-1,3-diaminopropane) exhibit only
17%, 8.7%, and 7.4% conversions, respectively, using TBHP as oxidant [35].
A maximum of 56.7% conversion of styrene was reported using closely related catalyst
[CuII(sal-ambmz)Cl]-Y (Hsal-ambmz ¼ Schiff base derived from salicylaldehyde and
2-aminomethylbenzimidazole) using H2O2 as oxidant while [VO2(sal-ambmz)] showed
much better conversion of ca 97% [28].
3.7.2. Oxidation of cyclohexene. [CuII(acpy-oap)Cl]-Y also catalyzes the oxidation of
cyclohexene by 70% TBHP as oxidant to give cyclohexene oxide, 2-cyclohexene-1-ol,
2-cyclohexene-1-one, and cyclohexane-1,2-diol as presented in scheme 3. Reaction
conditions have also been optimized for cyclohexene.
In order to achieve optimum amount of 70% TBHP for maximum oxidation of
cyclohexene, four different cyclohexene to aqueous 70% TBHP molar ratios namely
1 : 1, 1 : 2, and 1 : 3 were considered for a fixed amount of cyclohexene (0.82 g, 10 mmol)
and catalyst (0.035 g) in 20 mL of MeCN and reaction was carried out at 75ꢀC.
As illustrated in figure 6(a) (entry nos. 1–3 of table 4), a maximum of 41.1% conversion
was achieved in 6 h at a cyclohexene to TBHP molar ratio of 1 : 1. Increasing the ratio to
1 : 2 improved the conversion to 61.3%, while further increasing the ratio to 1 : 3 brings
the conversion back to 58.5%.
Under the operating conditions above, i.e. cyclohexene (0.82 g, 10 mmol), TBHP
(2.56 g, 20 mmol), MeCN (20 mL) and temperature (75ꢀC), the effect of catalyst using
0.015, 0.025, 0.035, and 0.045 g as a function of time was studied (entry nos. 2, 4–6

2914
M.R. Maurya et al.
(a)
(b) 70
60
60
50
40
30
20
10
0
0.015 g
0.025 g
0.035 g
0.045 g
1:1
2:1
3:1
50
40
30
20
10
0
0
60
120
180
240
300
360
0
60
120
180
240
300
360
Time (min)
Time (min)
(c) 70
60
(d) 70
60
[CuII(acpy-oap)Cl]-Y (2)
[CuII(acpy-oap)Cl] (1)
55 oC
65 oC
75 oC
50
50
40
40
30
30
20
20
10
10
0
0
0
60
120
180
240
300
360
0
60
120
180
240
300
360
Time (min)
Time (min)
Figure 6. (a) Effect of TBHP concentration (TBHP:cyclohexene) on oxidation of cyclohexene. (b) Effect
of amount of catalyst on oxidation of cyclohexene. (c) Effect of reaction temperature on oxidation of
cyclohexene. (d) Effect of different catalysts [CuII(acpy-oap)Cl] (1) and [CuII(acpy-oap)Cl]-Y (2) on oxidation
of cyclohexene.
Table 4. Conversion of cyclohexene (0.82 g, 10 mmol) using [CuII(acpy-oap)Cl]-Y as catalyst in 6 h under
different reaction conditions.
Entry No.
Catalyst (g)
TBHP (g, mmol)
Temperature (ꢀC)
MeCN (mL)
Conv. %
1
2
3
4
5
6
7
8
0.035
0.035
0.035
0.015
0.025
0.045
0.035
0.035
1.28, 10
2.56, 20
3.84, 30
2.56, 20
2.56, 20
2.56, 20
2.56, 20
2.56, 20
75
75
75
75
75
75
55
65
20
20
20
20
20
20
20
20
41.4
61.3
58.5
32.3
44.1
65.3
11.9
36.5
of table 4) and results are illustrated in figure 6(b). A maximum of 32.3% oxidative
conversion was achieved in 6 h of reaction time with 0.015 g of catalyst. This conversion
increases on further increasing the catalyst amount, i.e. 44.1% with 0.025 g, 61.3% with
0.035 g, and 65.6% with 0.045 g. However, 0.035 g of catalyst can be considered the
suitable one as increasing the amount increases the conversion as well as turnover rates,
only marginally.

Oxidation of alkenes
2915
Figure 7. UV-Vis spectral changes observed during titration of [CuII(acpy-oap)Cl] with TBHP. The spectra
were recorded after successive addition of one drop portions of TBHP in minimum methanol to 10 mL of ca
10ꢁ4 mol Lꢁ1 solution of [CuII(acpy-oap)Cl] in methanol.
After optimizing the cyclohexene to TBHP molar ratio and catalyst amount,
temperature was also varied in the range 55–75ꢀC (entry nos. 2, 7, and 8 of table 4)
while keeping other parameters as optimized above. It is evident from figure 6(c) that
increasing the temperatures increases the conversion and 75ꢀC is the best to obtain
61.3% conversion in 6 h of reaction time.
Thus, for the maximum oxidation of 10 mmol of cyclohexene optimized parameters
are: [CuII(acpy-oap)Cl]-Y (0.035 g), TBHP (2.56 g, 20 mmol), CH3CN (20 mL) and
temperature (75ꢀC). Under the optimized reaction conditions, a maximum of 61.3%
conversion of cyclohexene with TOF of 72 hꢁ1 was obtained in 6 h of reaction time.
At 6 h, the selectivity of different products is cyclohexane-1,2-diol (77.7%) 4 2-cyclo-
hexene-1-ol (11.1%) 4 cyclohexene epoxide (4.7%) 4 2-cyclohexene-1-one (4.6%).
After washing with acetonitrile and drying, the used catalyst was further used under
similar conditions. About 60% conversion of cyclohexene was obtained at the end of
6 h while maintaining the selectivity of reaction products. A maximum of 42.1%
conversion of cyclohexene was obtained with neat catalyst precursor [CuII(acpy-oap)Cl]
under similar conditions (Figure 6d) where product selectivity varied in the order:
cyclohexane-1,2-diol (73.5%) 4 2-cyclohexene-1-ol (9.2%) 4 cyclohexene epoxide
(6.8%) 4 2-cyclohexene-1-one (3.4%). Thus, neat complex also maintains the selectiv-
ity obtained for the encapsulated complex, though conversion is relatively lower.
Catalytic potential of the encapsulated complex presented here compares well with
similar encapsulated complexes. For example, [Cu(2-pyrazinecarboxylate)2]-Y exhibited
as high as 90.5% conversion of cyclohexene at a substrate to oxidant (30% H2O2) ratio

2916
M.R. Maurya et al.
of 1 : 2 where no formation of cyclohexene epoxide was observed and selectivity of the
other oxidation products varied, 2-cyclohexene-1-one (51%) 4 2-cyclohexene-1-ol
(42.4%) 4 cyclohexane-1,2-diol (6.6%) [24]. [Cu(sal-oaba)(H2O)]-Y, however, exhib-
ited only 45.8% conversion with the formation of only 2-cyclohexene-1-one and
2-cyclohexene-1-ol [23]. Cyclohexene was oxidized very slowly by TBHP using
[Cu(pan)Cl)]-Y (where Hpan ¼ 1 -(2-pyridylazo)-2-naphthol) under aerobic conditions
and only 28% conversion was obtained. Here, the percent selectivity of products varied,
1-tert-butylperoxy-2-cyclohexene 89% 4 2-cyclohexene-1-one (11%) [25]. Under opti-
mized conditions nearly quantitative oxidation (99.6%) of cyclohexene with [Cu(hap-
inh)Cl]-Y was achieved using H2O2 as oxidant where the selectivity of different
products followed the order, 2-cyclohexene-1-ol (44%) 4 2-cyclohexene-1-one (40%)
cyclohexene epoxide (12%) 4 cyclohexane-1, 2-diol (4%) [26].
3.8. Possible reaction mechanism
To propose a mechanism for the catalytic reaction, we studied the interaction of
[CuII(acpy-oap)Cl] (1) with TBHP. Addition of one drop portions of TBHP in
minimum amount of methanol to 10 mL of ca 10ꢁ4 mol Lꢁ1 solution of [CuII(acpy-
oap)Cl] in methanol results in slow reduction of intensity of the d–d band at 500 nm
without changing its position (figure 7). The charge transfer band at 435 nm also
experienced decrease in intensity, while the bands at 268, 235, and 228 nm (last two
bands not shown in figure) slowly gain intensity and finally disappear. All these suggest
the interaction of TBHP with Cu(II) center.
At least three types of intermediates having copper–oxygen interaction namely side-
on CuIII–(ꢄ-ꢅ2–peroxo)–CuIII, bis(ꢄ–oxo–CuIII) and CuIIIꢁOꢁO–H (copper-hydro-
peroxide) have been discussed in the literature during catalytic action [36, 37]. As
[CuII(acpy-oap)Cl] exists monomeric in the cavity of zeolite-Y due to space constraints,
facile formation of [(HOO)–CuIII(acpy-oap)Cl] is expected in the cavity due to the
vacant site on copper complex. A decrease in the intensities of d–d and charge transfer
bands along with major changes in UV bands may be due to formation of
hydroperoxide [HOO)–CuIII(acpy-oap)Cl] intermediate of the neat complex. Similar
observations have also been noted earlier for [CuII(hap-inh)Cl]-Y [26] and [CuII(sal-
aebmz)Cl)] [28]. Hydroperoxocopper complexes exhibit a charge transfer band at ca
600 nm [38]. The decrease in intensity of ca 500 nm band without any isosbestic point in
neat complex may be due to merging of this additional charge transfer band with the
d–d transition. The intermediate finally transfers coordinated oxygen atoms to the
substrates to give the products. Thus, catalytic performance of encapsulated catalyst
could be attributed to formation of facile and reversible intermediate species.
4. Conclusions
Hacpy-oap, an ONN donor, has been used to prepare [CuII(acpy-oap)Cl]. Its
encapsulation in the super cages of zeolite-Y gave [CuII(acpy-oap)Cl]-Y.
Spectroscopic along with chemical and thermal studies confirmed their structures.
The encapsulated complex is active for oxidation of styrene and cyclohexene. Oxidation

Oxidation of alkenes
2917
of styrene gives 60.2% conversion in 7 h with two main products, styrene oxide (78.2%)
and benzaldehyde (18.2%). Oxidation of cyclohexene requires 6 h to attain equilibrium
with 61.3% conversion and selectivity cyclohexane-1,2-diol (77.7%) 4 2-cyclohexene-
1-ol (11.1%) 4 cyclohexene epoxide (4.7%) 4 2-cyclohexene-1-one (4.6%). No
leaching of metal ion during catalytic reactions, recyclability and heterogeneous
nature are advantages of the catalyst. Neat analog [CuII(acpy-oap)Cl] is also active but
exhibits less conversion than encapsulated. Oxidation of cyclohexene proceeds through
[(HOO)–CuIII(acpy-oap)Cl], formation of which has been demonstrated by electronic
absorption spectroscopy.
Supplementary material
1
Figures having HOMO, LUMO, IR (ligand and complex), and H NMR spectrum of
ligand and complex are submitted as supporting materials.
Acknowledgments
Authors are thankful to Council of Scientific and Industrial Research, New Delhi, for
financial support.
References
[1] E.N. Jacobsen, W. Zhang, M. Guler. J. Am. Chem. Soc., 113, 6703 (1991).
[2] M.S. Niasari. Microporous Mesoporous Mater., 92, 173 (2006).
[3] M.R. Maurya, J. Costa Pessoa. J. Organomet. Chem., 696, 244 (2011).
[4] M.R. Maurya, A. Kumar, J. Costa Pessoa. Coord. Chem. Rev., 255, 2315 (2011).
[5] K.C. Gupta, A.K. Sutar, C.-C. Lin. Coord. Chem. Rev., 253, 1926 (2009).
[6] P.P. Knops-Gerrits, D. De Vos, F. Thibault-Starzyk, P.A. Jacobs. Nature, 369, 543 (1994).
[7] S.P. Verkey, C. Ratnasamy, P. Ratnasamy. Microporous Mesoporous Mater., 22, 465 (1998).
[8] N. Herron. Inorg. Chem., 25, 4714 (1986).
[9] G.S. Rafelt, J.H. Clark. Catal. Today, 57, 33 (2000), and references therein.
[10] R.A. Sheldon, I.W.C.E. Arends, A. Dijksman. Catal. Today, 57, 157 (2000).
[11] G.J. Hutchings. Chem. Commun., 301 (1999).
[12] G. Grigoropoulou, J.H. Clark, J.A. Elings. Green Chem., 5, 1 (2003).
[13] B.S. Lane, K. Burgess. Chem. Rev., 103, 2457 (2003).
[14] W. Zeng, J. Li, S. Qin. Inorg. Chem. Commun., 9, 10 (2006).
[15] B.M. Choudary, P.N. Reddy. J. Mol. Catal. A Chem., 103, L1 (1995).
[16] S.S. Kurek, P. Michorczyk, A.-M. Balisz. J. Mol. Catal. A Chem., 194, 237 (2003).
[17] J.-Y. Liu, X.-F. Li, Y.-Z. Li, W.-B. Chang, A.-J. Huang. J. Mol. Catal. A Chem., 187, 163 (2002).
[18] N. Ma, Y. Yue, W. Hua, Z. Gao. Appl. Catal. A: Gen., 251, 39 (2003).
[19] L.M. Kustov, A.L. Tarasov, V.I. Bogdan, A.A. Tyrlov, J.W. Fulmer. Catal. Today, 61, 123 (2000).
[20] T. Joseph, D. Srinivas, C.S. Gopinath, S.B. Halligudi. Catal. Lett., 83, 209 (2002).
[21] T. Joseph, S.B. Halligudi. J. Mol. Catal. A Chem., 229, 241 (2005).
[22] Y. Luo, J. Lin. Microporous Mesoporous Mater., 86, 23 (2005).
[23] M.R. Maurya, A.K. Chandrakar, S. Chand. J. Mol. Catal. A Chem., 274, 192 (2007).
[24] P. Chutia, S. Kato, T. Kojima, S. Satokawa. Polyhedron, 28, 370 (2009).
[25] I. Kuzniarska-Biernacka, K. Biernacki, A.L. Magalha
102 (2011).
[26] M.R. Maurya, C. Haldar, S. Behl, N. Babu, F. Avecilla. J. Coord. Chem., 64, 2995 (2011).
˜
es, A.M. Fonseca, I.C. Neves. J. Catal., 278,

2918
[27] M.R. Maurya, B. Singh, P. Ada
M.R. Maurya et al.
˜
o, F. Avecilla, J. Costa Pessoa. Eur. J. Inorg. Chem., 5720 (2007).
[28] M.R. Maurya, A.K. Chandrakar, S. Chand. J. Mol. Catal. A Chem., 263, 227 (2007).
[29] D. Andrae, U. Haußermann, M. Dolg, H. Stoll, H. Preuß. Theor. Chim. Acta, 77, 123 (1990).
[30] C.S. Sarkar, A. Mondal, J. Ribas, M.G.B. Drew, K. Pramanik, K.K. Rajak. Inorg. Chim. Acta, 358, 641
(2005).
[31] R. Kumar, K. Mahiya, P. Mathur. Indian J. Chem., 50A, 775 (2011).
[32] G. Batra, P. Mathur. Inorg. Chem., 31, 1575 (1992).
[33] M.R. Maurya, M. Bisht, A. Kumar, M.L. Kuznetsov, F. Avecilla, J. Costa Pessoa. Dalton Trans., 40,
6968 (2011).
[34] M.R. Maurya, M. Bisht, F. Avecilla. J. Mol. Catal. A Chem., 344, 18 (2011).
[35] M. Silva, C. Freire, B. de Castro, J.L. Figueiredo. J. Mol. Catal. A Chem., 258, 327 (2006).
[36] E.I. Solomon, P. Chen, M. Metz, S.-K. Lee, A.E. Palner. Angew. Chem. Int. Ed., 40, 4570 (2001).
[37] J.P. Klinman. Chem. Rev., 96, 2541 (1996).
[38] K.D. Karlin, J.C. Hayes, Y. Gultneh, R.W. Cruse, J.W. McKown, J.P. Hutchinson, J. Zubieta. J. Am.
Chem. Soc., 106, 2121 (1984).