Synthesis, characterization and catalytic activities of vanadium complexes containing ONN donor ligand derived from 2-aminoethylpyridine

Article abstract of DOI:10.1016/j.molcata.2011.04.017

Reaction between [V^IVO(acac)₂] and the ONN donor Schiff base Hpydx-aepy (I) (Hpydx-aepy = Schiff base obtained by the condensation of pyridoxal and 2-aminoethylpyridine) resulted in the formation of a complex [V^IVO(acac)(pydx-aepy)] (1). Addition of aqueous 30% H₂O₂ to 1 yields the poor stable oxidoperoxidovanadium(V) complex [V^VO(O₂)(pydx-aepy)] (2). Its formation has also been demonstrated in solution by treating 1 with H₂O₂ in methanol. Reaction of vanadium exchanged zeolite-Y with I in methanol followed by aerial oxidation gave zeolite-Y encapsulated dioxidovanadium(V) complex, abbreviated as [V^VO₂(pydx-aepy)]-Y (4). The crystal and molecular structure of 1 has been determined, confirming the ONN binding mode of the ligand. The encapsulated complex [V^VO₂(pydx-aepy)]-Y (4) catalyses the oxidation of styrene, cyclohexene, methyl phenyl sulfide and diphenyl sulfide using H₂O₂ as oxidant in good yield. Styrene under optimised reaction conditions gave four reaction products namely, styrene oxide, benzaldehyde, 1-phenylethane-1,2-diol and benzoic acid while organic sulfides gave the corresponding sulfoxide as the major product. Cyclohexene gave cyclohexene epoxide, 2-cyclohexene-1-one, 2-cyclohexene-1-ol and cyclohexane-1,2-diol. Neat complex [V^IVO(acac)(pydx-aepy)] has been used as catalyst precursor to compare its catalytic activities with the encapsulated one.

Full text of DOI:10.1016/j.molcata.2011.04.017

Journal of Molecular Catalysis A: Chemical 344 (2011) 18–27
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Synthesis, characterization and catalytic activities of vanadium complexes
containing ONN donor ligand derived from 2-aminoethylpyridine
Mannar R. Maurya , Manisha Bisht , Fernando Avecillab
a,∗
a
a
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
Departamento de Química Fundamental, Universidade da Coru ˜n a, Campus de A Zapateira, 15071 A Coru ˜n a, Spain
b
a r t i c l e i n f o
a b s t r a c t
Reaction between [VIVO(acac) ] and the ONN donor Schiff base Hpydx-aepy (I) (Hpydx-aepy = Schiff base
Article history:
2
Received 15 February 2011
Received in revised form 23 April 2011
Accepted 25 April 2011
obtained by the condensation of pyridoxal and 2-aminoethylpyridine) resulted in the formation of a
IV
complex [V O(acac)(pydx-aepy)] (1). Addition of aqueous 30% H2O2 to 1 yields the poor stable oxi-
V
doperoxidovanadium(V) complex [V O(O2)(pydx-aepy)] (2). Its formation has also been demonstrated
Available online 7 May 2011
in solution by treating 1 with H2O2 in methanol. Reaction of vanadium exchanged zeolite-Y with I
in methanol followed by aerial oxidation gave zeolite-Y encapsulated dioxidovanadium(V) complex,
Keywords:
V
abbreviated as [V O2(pydx-aepy)]-Y (4). The crystal and molecular structure of 1 has been determined,
Vanadium complexes
Encapsulated complex
Catalytic activity
Oxidation of styrene
Oxidation of cyclohexene
Oxidation of organic sulfides
V
confirming the ONN binding mode of the ligand. The encapsulated complex [V O2(pydx-aepy)]-Y (4)
catalyses the oxidation of styrene, cyclohexene, methyl phenyl sulfide and diphenyl sulfide using H2O2
as oxidant in good yield. Styrene under optimised reaction conditions gave four reaction products namely,
styrene oxide, benzaldehyde, 1-phenylethane-1,2-diol and benzoic acid while organic sulfides gave the
corresponding sulfoxide as the major product. Cyclohexene gave cyclohexene epoxide, 2-cyclohexene-
IV
1
-one, 2-cyclohexene-1-ol and cyclohexane-1,2-diol. Neat complex [V O(acac)(pydx-aepy)] has been
used as catalyst precursor to compare its catalytic activities with the encapsulated one.
©
2011 Elsevier B.V. All rights reserved.
1
. Introduction
but catalyst also became recyclable for further use [15]. The advan-
tages of immobilised metal complexes promoted several research
groups to investigate the catalytic properties of various metal com-
plexes entrapped within the nano-cavities of zeolite-Y [16–25].
In this paper, we describe the synthesis and characterization of
oxidovanadium(IV) complex of ligand I (Scheme 1). Its reactivity
Modeling the structure and properties of vanadium-containing
bio-molecules has influenced research on vanadium coordina-
tion chemistry. Vanadate-dependent haloperoxidases (V-HPOs) are
important examples amongst bio-molecules in this context [1–5].
Vanadium haloperoxidases not only catalyse the oxidative halo-
genation, they accelerate the oxidation of aliphatic as well as
aromatic substrates in the presence of hydrogen peroxide, organic
hydroperoxides or molecular oxygen [6–10]. Several models and
other vanadium complexes have been shown to catalyse all these
reactions as well [4–14]. Solution studies on model complexes
have also been performed to provide knowledge on the under-
standing of the role of enzymes and mechanism of the catalytic
reactions [10–14]. We reported structural and functional models
of VHPO considering benzimidazole and imidazole derived ligands
with H O2 has also been described. Dioxidovanadium(V) complex
2
has been encapsulated in the nano cavity of zeolite-Y and its cat-
alytic activity has been demonstrated considering the oxidation,
by peroxide, of styrene, cyclohexene, methyl phenyl sulfide and
diphenyl sulfide. For comparison, we have used oxidovanadium(IV)
complex as catalyst precursor and tested for all the above reac-
tions.
2. Experimental
[
11,12] and have explored their catalytic potential for the oxidation
of styrene, benzoin, methyl phenyl sulfide and diphenyl sulfide.
Encapsulation of such complexes in nano-cavities of zeolite-Y not
only improved its catalytic activity with high turn over frequency
2.1. Materials and methods
V2O5, VOSO4·5H2O (Loba Chemie, Mumbai, India), acetylace-
tone (Hacac) (Aldrich, U.S.A.), pyridoxal hydrochloride, cyclohex-
ene (Himedia, India), methyl phenyl sulfide (Alfa Aesar, U.S.A.),
styrene and 2-(2-aminoethyl)pyridine (Acros Organics, U.S.A.), 30%
∗ Corresponding author. Tel.: +91 1332 285327; fax: +91 1332 273560.
E-mail address: rkmanfcy@iitr.ernet.in (M.R. Maurya).
aqueous H O2 (Qualigens, India) were used as obtained. Zeolite-
Y (Si/Al = ca. 10) was obtained as gift from National Chemical
2
1
381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.04.017

M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 344 (2011) 18–27
19
V
2
.2.3. Preparation of [V O(O )(pydx-aepy)] (2)
2
OH
N
IV
N
Complex [V O(acac)(pydx-aepy)] (0.872 g, 2 mmol) was dis-
N
solved in 40 ml of hot methanol and cooled to room temperature
after filtration. An aqueous 30% H O2 (2 ml dissolved in 5 ml of
2
HO
methanol) was added drop wise to the above solution within 15 min
under stirring. Stirring was continued where yellow solid slowly
separated out within 30 min. This was filtered off, washed with
methanol and dried in vacuo. This complex is poor stable (it looses
oxygen at room temperature) and therefore only IR, electronic
and 5 V NMR spectra could be recorded with the sample. Yield:
0.650 g (75%). 5 V NMR (DMSO-d6, ı/ppm): −497 (minor) and −519
(major).
Hpydx-aepy (I)
Scheme 1.
1
laboratory, Pune, India. All other chemicals and solvents used
were of AR grade. [VO(acac) ] was prepared according to method
reported in the literature [26].
1
2
Elemental analyses of the ligand and complexes were obtained
by an Elementar model Vario-EL-III. IR spectra were recorded as
KBr pellets on a Nicolet 1100 FT-IR spectrometer after grinding
the sample with KBr. Electronic spectra of ligand and complexes
were recorded in methanol or DMF. Electronic spectrum of zeolite-
Y encapsulated complex was recorded in Nujol using Shimadzu
2.2.4. Preparation of [VIVO]-Y (3)
A filtrated solution of VOSO4.5H2O (9.0 g, 36 mmol) dissolve in
100 ml of distilled water was added to a suspension of Na-Y zeolite
(15.0 g) in 900 ml of distilled water and the reaction mixture was
◦
heated at 90 C with stirring for 24 h. The light bluish solid was
1
601 UV–vis spectrophotometer by layering the mull of the sample
filtered, washed with hot distilled water until filtrate was free from
any vanadyl ion content and dried at 150 C for 12 h. Yield: 14.9 g
(99.2%). Found: V (ICP-MS), 4.6%.
◦
to inside of one of the cuvettes while keeping the other one lay-
ered with Nujol as reference. 51V NMR spectrum of peroxo complex
was recorded on a Bruker Avance 400 MHz spectrometer with the
51
2.2.5. Preparation of [VVO (pydx-aepy)]-Y (4)
common parameter settings in DMSO-d . ı( V) values are quoted
2
6
IV
relative to VOCl as external standard. X-ray powder diffractograms
[V O]-Y (3.0 g) and Hpydx-aepy (prepared in situ from 5 mmol
3
of zeolite containing samples were recorded using a Bruker AXS D8
advance X-ray powder diffractometer with a Cu K␣ target. Scan-
ning electron micrographs (SEMs) of samples were recorded on a
Leo instrument model 435VP. The samples were dusted on alu-
mina and coated with thin film of gold to prevent surface charging
and to protect the surface material from thermal damage by elec-
tron beam. In all analyses, a uniform thickness of about 0.1 mm
was maintained. A constant voltage of 20 kV was applied so that
only outer surface of the zeolite-Y was accessible. Magnetic sus-
ceptibility of oxidovanadium(IV) complex was determined at 298 K
with a Vibrating Sample Magnetometer model 155, using nickel as
a standard and diamagnetic corrections were done with Pascal’s
constants [27]. A Thermo Nicolet gas chromatograph with a HP–1
capillary column (30 m × 0.25 mm × 0.25 ␮m) was used to analyse
the reaction products. The identity of the products was confirmed
using a GC–MS model Perkin-Elmer, Clarus 500 by comparing the
fragments of each product with the library available.
each of pyridoxal and 2-aminoethyl pyridine) were mixed in
methanol (50 ml) and the reaction mixture was heated under reflux
for 14 h in an oil bath with stirring. The resulting material was
filtered and then Soxhlet extracted with methanol to remove unre-
acted ligand. It was finally treated with hot DMF while stirring
for 1 h, filtered, washed with DMF followed by hot methanol. The
uncomplexed metal ions present in the zeolite were removed by
stirring with aqueous 0.01 M NaCl (150 ml) for 10 h. The resulting
greenish-yellow solid was filtered, washed with hot methanol fol-
lowed by distilled water until no precipitate of AgCl was observed in
the filtrate on treating with AgNO3. The solid was further suspended
in methanol and oxidised by passing air while stirring at room tem-
perature for 24 h. Finally the obtained cream solid was dried at
◦
120 C for several hours. Yield: 2.3 g (76.7%). Found: V (ICP-MS),
2.6; N, 2.2%.
2.3. Crystal structure determination
Three-dimensional X-ray data for 1 H O were collected on
a Bruker SMART Apex CCD diffractometer at 153(2) K, using a
graphite monochromator and Mo–K␣ radiation (ꢀ = 0.71073 A˚ ) by
2
2
2
.2. Preparations
.2.1. Preparation of Hpydx-aepy (I)
Pyridoxal hydrochloride (0.406 g, 2 mmol) was dissolved in
the ꢁ–ω scan method. Reflections were measured from a hemi-
◦
sphere of data collected of frames each covering 0.3 in ω. Of
absolute methanol (15 ml) in the presence of KOH (0.112 g, 2 mmol)
with stirring. After 1 h of stirring, the separated white solid (KCl)
was filtered and the obtained clear solution was added to a solution
of 2-(2-aminoethyl)pyridine (0.244 g, 2 mmol) in methanol (15 ml)
with stirring and the resulting reaction mixture was refluxed for 2 h.
The volume of solvent was reduced to ca. 10 ml and in situ formed
yellow-orange ligand was used as such for further reaction.
the 19025 reflections measured, all of which were corrected for
Lorentz and polarization effects, and for absorption by semi-
empirical methods based on symmetry-equivalent and repeated
reflections, 2894 independent reflections exceeded the significance
level |F|/ꢂ(|F|) > 4.0. Complex scattering factors were taken from
the program package SHELXTL [28]. The structure was solved by
direct method and refined by full-matrix least-squares method on
2
F . The non-hydrogen atoms were refined with anisotropic ther-
2
.2.2. Preparation of [VIVO(acac)(pydx-aepy)] (1)
mal parameters in all cases. The hydrogen atoms were placed in
idealised positions and refined by using a riding mode, except
the hydrogen atoms from the water molecule, two hydrogen
atoms of carbon atoms and the hydrogen atom from the hydroxyl
group. One hydrogen atom (H1WB) and the hydrogen atom of the
A solution of in situ generated Hpydx-aepy (equivalent to
2
mmol) as mentioned above in dry methanol (10 ml) was treated
IV
with [V O(acac) ] (0.530 g, 2 mmol) dissolved in dry methanol
2
(
10 ml) and the resulting reaction mixture was refluxed on a water
bath for 3 h. After cooling to room temperature and adding distilled
water (10 ml), the flask was kept at room temperature for ca. 10 h.
The separated brown crystals of 1 were filtered off, washed with
methanol (10 ml) and dried in vacuum over silica gel at room tem-
hydroxyl group (H O) were located from a difference electron den-
2
sity map and fixed to the oxygen atoms. The other hydrogen atom
(H1WA) of the water molecule and the two hydrogen atoms of
the carbon atoms (C6 and C16) were left to refine freely. A final
difference Fourier map showed no residual density outside: 0.310
perature. Yield: 0.65 g (86.0%). Anal. Calc. for C20H23N O5V (436.4):
3
−
3
C, 55.1; H, 5.3; N, 9.6. Found: C, 55.0; H, 5.4; N, 9.4%.
and −0.261e. A˚ . CCDC No. 795727 contains the supplementary

2
0
M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 344 (2011) 18–27
Table 1
Crystal data and structure refinement for [VO(acac)(pydx-aepy)]·H2O (1) .
stirring. The reaction products were analyzed and identified as
mentioned above.
a
Formula
C20H25N3O6V
Mr
T [K]
454.37
153.2
3. Results and discussion
ꢀ
, A˚ [Mo, K␣]
Crystal system
Space group
a [ A˚ ]
0.71073
Monoclinic
P1¯
3
.1. Synthesis and solid state characteristics
Reaction between equimolar amounts of [VIVO(acac) ] and the
6.8719(11)
13.305(2)
13.325(2)
118.381(8)
91.570(8)
97.907(8)
2
1055.7(3)
1.429
0.511
2
b [ A˚ ]
ligand Hpydx-aepy (I) in dry, refluxing methanol yields the brown
oxidovanadium(IV) complex [V O(acac)(pydx-aepy)] (1). The lig-
and coordinates out of its monoanionic (ONN(1-)) form; Eq. (1):
c [ A˚ ]
IV
◦
˛
[ ]
◦
ˇ [ ]
◦
ꢃ [ ]
VIVO(acac) ] + Hpydx-aepy → [VIVO(acac)(pydx-aepy)]
[
2
Z
Volume [A˚
3
]
+
Hacac
(1)
−
3
ꢄcalcd[gcm
]
−
1
ꢅ mm
Reflections measured
Independent reflections
R (int)
19025
2894
0.0392
1.079
0.0401
0.1056
Complex 1 exhibits a magnetic moment of 1.72 ␮B at ambi-
b
ent temperature; the normal spin only value for a d1 system
2
being 1.73 ␮ . The addition of H O to 1 yields the oxidoperox-
Goodness-of-fit on F
B
2
2
c
R1
ido vanadium(V) complex 2, as shown by Eq. (2). Aerial oxidation
c
wR2 (all data)
IV
of [V O(acac)(pydx-aepy)] in solution ended up with diamagnetic
a
The structure was solved using SHELXS Program for Crystal Structure Determi-
nation and refined with SHELXL Program for Crystal Structure Refinement.
vanadium(V) species but this could not be isolated in the solid
state:
b
I > 2ꢂ(I).
c
R1 = ˙||F0| − |Fc||/˙|F0|, wR2 = {˙[w(||F0| − |Fc| |) ]/˙[w(F0 )]}1/2.
2
2
2
4
[VIVO(acac)(pydx-aepy)] + 3H O2 → 2[V O(O )(pydx-aepy)]
V
2
2
2
+
2Hacac + 2H O
(2)
2
crystallographic data for this paper. This data can be obtained free
of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data request/cif. Crystal data and details of
the data collection and refinement for the new complex is collected
in Table 1.
Synthesis of dioxidovanadium(V) complex encapsulated in the
nano-cavity of zeolite-Y involves two steps: (i) the exchange of
IV
V
O with Na-Y in aqueous solution and (ii) the reaction of vana-
IV
dium exchanged zeolite i.e. [V O]-Y (3) with excess Hpydx-aepy
in methanol where ligand slowly enters into the cavity of zeolite-
Y due to its flexible nature and interacts with metal ions to
give possibly oxidovanadium(IV) complex loaded zeolite-Y. Extrac-
tion of impure samples with methanol using Soxhlet extractor
removed excess free ligand and stirring in DMF removed neat
metal complex formed on the surface of the zeolite, if any. The
initially formed oxidovanadium(IV) species slowly oxidises by
2.4. Catalytic activity studies
V
We have used [V O (pydx-aepy)]-Y as catalyst to carry out the
2
oxidation of styrene, methyl phenyl sulfide, diphenyl sulfide and
cyclohexene. All reactions were carried out in a 50 ml two-necked
reaction flask fitted with a water condenser.
V
2.4.1. Oxidation of styrene
air in solution to give dioxidovanadium(V) complex [V O2(pydx-
In a typical reaction, styrene (0.52 g, 5 mmol) and aqueous 30%
aepy)]-Y (4). The remaining uncomplexed metal ions in zeolite
were removed by exchanging with aqueous 0.01 M NaCl solu-
tion. As impure sample was extracted well, the vanadium (2.6%)
and nitrogen (2.2%) contents found after encapsulation is only
due to the presence of dioxidovanadium(V) complex in the cavi-
ties of the zeolite-Y. As pyridoxal containing dioxidovanadium(V)
complex may have tendency to stabilize as polynuclear species
H O (1.14 g, 10 mmol) were taken in 5 ml of acetonitrile and tem-
2
2
◦
perature of the reaction mixture was raised to 80 C. The catalyst,
V
[
V O (pydx-aepy)]-Y (0.0125 g) was added to the above reaction
2
mixture and stirred. Oxidised products were analysed quantita-
tively by gas chromatography during the reaction by withdrawing
small aliquots of the reaction mixture at every 30 min intervals. The
identities of the products were confirmed by GC–MS. The effects of
various parameters, such as amounts of oxidant, catalyst and sol-
vent as well as temperature of the reaction medium were studied
in order to see their effect on the conversion and selectivity of the
reaction products.
V
e.g. complex [K(H2O)2][V O2(pydx-inh)] [29], the encapsulation of
V
dioxidovanadium(V) complex [V O2(pydx-aepy)] in the cavity of
zeolite-Y presents an example of stabilisation of monomeric dioxi-
dovanadium(V) complex of this type. Scheme 2 provides structures
of the complexes described here and characterized on the basis of
spectroscopic (IR, UV/vis and 51V NMR) data, elemental analyses,
FE-SEM, X-ray powder diffraction patterns and single crystal X-ray
diffraction analysis of complex 1.
2
.4.2. Oxidation of methyl phenyl sulfide and diphenyl sulfide
Methyl phenyl sulfide (1.24 g, 10 mmol) or diphenyl sulfide
(
(
1.86 g, 10 mmol), 30% aqueous H O (1.14 g, 10 mmol) and catalyst
0.020 g) in acetonitrile were stirred at room temperature and the
2 2
3.2. Structure description of [VIVO(acac)(pydx-aepy)]·H O (1)
2
reaction was monitored by withdrawing samples at different time
intervals and analysing them quantitatively by gas chromatogra-
phy. The identities of the products were confirmed as mentioned
above.
The molecular structure of [VIVO(acac)(pydx-aepy)]·H O (1)
2
together with the atom-numbering scheme is shown in Fig. 1;
Table 2 provides selected bond lengths and bond angles. In complex
IV
1
, the V centre is six-coordinated with an octahedral geometry.
2
.4.3. Oxidation of cyclohexene
Cyclohexene (0.82 g, 10 mmol), aqueous 30% H O2 (2.27 g
0 mmol) and catalyst (0.010 g) were mixed in acetonitrile (10 ml),
The ONN monobasic tridentate ligand, terminal oxygen atom (O3)
and two oxygen atoms of the acac group complete the coordina-
tion sphere. The presence of acac ions obstructs the formation of
dinuclear species [30]. The V1–O3 bond has typical V O distance of
2
2
◦
and the reaction mixture was heated at 80 C with continuous

M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 344 (2011) 18–27
21
O
O
O
O
O
O
O
O
V
O
O
V
O
V
N
N
N
N
N
N
Y
N
N
N
HO
V
HO
HO
IVO(acac)(pydx-aepy)] (1) [V O(O )(pydx-aepy)] (2) [V O (pydx-aepy)]-Y (4)
V
[V
2
2
Scheme 2. Structures of complexes prepared in this paper. Y represents zeolite-Y frame work.
3.3. IR spectral studies
Table 4 presents IR spectral data of compounds. IR spectrum
IV
of complex, [V O(acac)(pydx-aepy)] exhibits a sharp band at
−
1
9
43 cm which is characteristic of ꢆ(V O) stretch. The peroxido
V
complex [V O(O )(pydx–aepy)] is poor stable and looses oxy-
2
gen at room temperature. However, the freshly prepared complex
exhibits three IR active vibrational modes associated with the per-
3
+
−1
oxido moiety {V(O ) } at 830, 756 and 590 cm , and are assigned
2
to the O–O intra-stretch (ꢆ ), the antisymmetric V(O ) stretch (ꢆ ),
1
2
3
and the symmetric V(O ) stretch (ꢆ ), respectively. The presence
2
2
2
of these bands confirms the common ␩ -coordination of the per-
oxido group. In addition, a sharp band appearing at 934 cm is
−
1
assigned to the ꢆ(V O) stretch. These peaks agree well with those
V
reported for several [V O(O )L] complexes [31]. Location of bands
2
due to cis-VO2 structure in zeolite-Y encapsulated vanadium com-
plex has not been possible due to appearance of a strong and
−
1
broad band at ca. 1000 cm due to zeolite frame work. The lig-
and Hpydx-aepy was not isolable in the solid state, however, its
in situ prepared methanolic solution exhibited two sharp bands at
−
1
1
631 and 1595 cm due to the ␯(C N) of the azomethine and ring
Fig. 1. ORTEP plot (at 30% probability level) of [VIVO(acac)(pydx-aepy)] (1).
stretch, respectively. The band due to azometnine nitrogen nor-
mally shifts towards lower wavenumber while that of ring nitrogen
moves towards higher side. All the complexes also exhibit one or
−
1
two sharp bands in the 1600–1637 cm , indicating the coordina-
tion of the azomethine/ring nitrogen to the vanadium. The presence
1
.599(2) A˚ . The V1–O4 and V1–O5 distances [V1–O4, 1.9897(19) A˚
−
1
and V1–O5, 2.159(2) A˚ ] are similar to those reported for other V(V)-
of multiple bands of medium intensity covering 2800–2900 cm
regions is consistent with the presence of –CH2 groups.
acac compounds [11,12,14]. The remaining three coordination sites
are occupied by the phenolate O atom [V1–O1, 1.9457(19) A˚ ],
imine N atom [V1–N2, 2.077(2) A˚ ] and pyridine N atom [V1–N3,
3.4. Field-emission-scanning electron micrograph (FE-SEM) and
energy dispersive X-ray analysis (EDX) studies
2
.193(2) A˚ ]. Again, these bond lengths are similar to other com-
pounds with similar groups bonding to V(IV) centre [11,12,14].
Hydrogen bonds data and symmetry operations are presented in
Table 3.
The field emission scanning electron micrograph (FE-SEM) of
V
[V O (pydx-aepy)]-Y along with their energy dispersive X-ray
2
analysis (EDX) profile are presented in Fig. 2. Accurate information
Table 3
Table 2
Selected bond lengths [ A˚ ] and angles [ ] for the complex [VO(acac)(pydx-aepy)]·H2O
◦
Hydrogen bonds data and symmetry operations.
(
1).
D–H
H· · ·A
D· · ·A
<(DHA)
Lengths ( A˚ )
0
1
0
.94
.02
.77(4)
1.93
1.85
2.03(5)
2.774(4)
2.830(4)
2.780(4)
148.5
161.2
165(5)
O(2)–H(2O)· · ·O(1W)
V(1)–O(1)
V(1)–O(3)
V(1)–O(4)
V(1)–O(5)
V(1)–N(2)
1.9457(19)
1.599(2)
1.9897(19)
2.159(2)
V(1)–N(3)
C(1)–O(1)
N(2)–C(6)
N(2)–C(7)
2.193(2)
1.302(3)
1.277(4)
1.466(3)
O(1W)–H(1WB)· · ·O(2) $1
O(1W)–H(1WA)· · ·N(1) $2
Symmetry transformations used to generate equivalent atoms:
$
1 [−x, −y−1, −z].
2.077(2)
◦
$2 [x − 1, y, z].
Angles ( )
O(3)–V(1)–O(1)
O(3)–V(1)–O(4)
O(1)–V(1)–O(4)
O(3)–V(1)–N(2)
O(1)–V(1)–N(2)
O(4)–V(1)–N(2)
O(3)–V(1)–O(5)
O(1)–V(1)–O(5)
O(4)–V(1)–O(5)
N(2)–V(1)–O(5)
O(3)–V(1)–N(3)
103.48(10)
98.61(9)
86.55(8)
96.17(10)
86.58(9)
164.80(9)
171.91(9)
84.40(8)
83.53(8)
82.32(8)
91.77(9)
O(1)–V(1)–N(3)
O(4)–V(1)–N(3)
N(2)–V(1)–N(3)
O(5)–V(1)–N(3)
C(1)–O(1)–V(1)
C(6)–N(2)–C(7)
C(6)–N(2)–V(1)
C(7)–N(2)–V(1)
C(13)–N(3)–C(9)
C(13)–N(3)–V(1)
C(9)–N(3)–V(1)
164.73(9)
92.05(8)
91.02(9)
80.34(8)
128.74(17)
117.5(2)
124.42(19)
117.81(18)
117.8(2)
118.03(18)
123.99(19)
Table 4
IR spectral data (cm−1) of complexes.
Compound
ꢆ(C N)
ꢆ(V O)
Hpydx-aepy (I)
1631, 1595
1634, 1600
1637, 1618
1635
IV
[V O(acac)(pydx-aepy)] (1)
943
934
–
V
a
[V O(O2)(pydx-aepy)] (2)
V
[V O2(pydx-aepy)]-Y (4)
a
−1
.
Bands due to the peroxido group at 830, 756 and 590 cm

2
2
M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 344 (2011) 18–27
V
Fig. 2. Scanning electron micrograph (left) and energy dispersive X-ray analysis (EDX) profile (right) of [V O2(pydx-aepy)]-Y. Asterisk in EDX shows signal for gold.
on the morphological changes in terms of exact orientation of lig-
and coordinated to the metal ion has not been possible due to poor
loading of the metal complex. However, it is clear from the micro-
graph that zeolite having encapsulated vanadium complex has well
defined crystals and there is no indication of the presence of any
metal ion or complex on the surface. Energy dispersive X-ray anal-
ysis plot, evaluated semi-quantitatively, supports this conclusion
2
.0
1.5
1.0
as no vanadium or nitrogen contents were noted on the spotted
V
surface in the plot for [V O (pydx-aepy)]-Y. Only small amount of
2
carbon (ca. 9.6%) but no nitrogen on the spotted surfaces suggest
the presence of trace amount of adsorbed solvent (methanol) from
which it was finally washed after Soxhlet extraction. An amount of
ca. 2.6% sodium suggests the exchange of remaining free vanadium
ion by sodium ion during re-exchange process. The average silicon
and aluminum percentage obtained were ca. 38.5% and ca. 12.2%,
respectively.
0
0
.5
.0
3
00
400
500
600
700
Wave length/ nm
V
Fig. 4. Electronic spectrum of [V O2(pydx-aepy)]-Y (5) recorded after dispersing in
Nujol.
3.5. Powder X-ray diffraction studies
The powder X-ray diffraction patterns of Na-Y, [VIVO]-Y and
V
3.6. Electronic absorption spectra
encapsulated complex [V O (pydx-aepy)]-Y were recorded at 2Â
2
◦
values between 5 and 70 , and patterns are presented in Fig. 3.
The electronic spectral profile of encapsulated complex is pre-
sented in Fig. 4 and the corresponding data along with other
Essentially similar diffraction patterns in encapsulated complex,
IV
[
V
O]-Y and Na-Y were noticed except a slightly weaker intensity
compounds are presented in Table 5. The electronic spectrum of
for the encapsulated complex. These observations indicate that the
framework of the zeolite has not undergone any structural change
during incorporation of the complex i.e. crystallinity of the zeolite-Y
is preserved during encapsulation. No new peaks due to encapsu-
lated complex were detected in the zeolite encapsulated sample
possibly due to very low percentage loading of metal complex.
V
[
V O (pydx-aepy)]-Y (4) exhibits a lmct band at 410 nm along
2
with two UV bands compatible with dioxidovanadium(V) species
in the super cages of the cavity of the zeolite-Y. Other complexes
exhibit lmct band at ca. 400 nm along with four UV bands. The
lower energy (less intense) bands appearing at 535 and 768 nm
in [VO(acac)(pydx-aepy)] (1) are assigned due to d–d transitions.
As complex 4 has 3d0 configuration, d → d bands are not expected.
3
.7. 51V NMR spectrum
The 51V NMR spectrum of [V O(O )(pydx-aepy)] could only
V
2
be recorded with the freshly prepared complex in DMSO-
V
[
V O (pydx-aepy)]-Y
d . The resonance was broadened as a consequence of the
2
6
51
quadrupolar interaction
moment = −4.8 fm); line widths at half height were approximately
00 Hz, which is still considered narrow in 51V NMR spectroscopy
( V: nuclear spin = 7/2, quadrupole
IV
[
V O]-Y
2
Na-Y
Table 5
Electronic spectral data of complexes.
Compounds
Solvent
ꢀmax (nm)
1
0
20
30
40
50
60
70
IV
2
θ
[V O(acac)(pydx-aepy)] (1)
MeOH
MeOH
Nujol
225, 258, 305, 395, 535, 768
225, 258, 337, 435
267, 293, 410
V
[
V O(O2)(pydx-aepy)] (2)
V
Fig. 3. XRD patterns of Na-Y, [VIVO]-Y and [V O2(pydx-aepy)]-Y.
V
[V O2(pydx-aepy)]-Y (4)

M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 344 (2011) 18–27
23
[
32,33]. The complex did not show clean 51V NMR signal due to its
O
HO
poor stability. In fact, it exhibits two sharp peaks at −497 (minor)
OH
V
and −519 ppm (major) which seems to be due to [V O (pydx-
Catalyst
H O
2
V
aepy)(DMSO)] and [V O (pydx-aepy)]. This is based on the recently
2
V
2 2
reported very similar complex e.g. [V O (sal-aepy)] that exhibits
2
1
-phenylethane-1,2-diol
(phed)
Styrene
Styreneoxide
two resonances at −491 and −517 ppm in DMSO-d6 [12] All these
results affirm the poor stability of peroxide species and its conver-
sion into a mixture of vanadium(V) complexes in DMSO. However,
(
so)
O
HO
O
addition of one drop of 30% aqueous H O2 to the above solution
2
gives rise to an additional weak signal at −575 ppm along with the
reduction of the intensity of originally appeared two resonances
and this is indicative of the formation of peroxide species at the
expense of the two species existed in solution [12].
Benzoic acid
Benzaldehyde
bza)
(
bzac)
(
3
.8. Reactivity of [VIVO(acac)(pydx-aepy)] (1) with H O2
V
2
Scheme 3. Oxidation of styrene with H O catalysed by [V O (pydx-aepy)]-Y.
2
2
2
IV
Treatment of complex [V O(acac)(pydx-aepy)] with H O2 at
2
catalyst (amount of catalyst per mole of styrene), temperature and
solvent amount of the reaction mixture in detail.
◦
ca 10 C yielded poor stable oxidoperoxidovanadium(V) complex
V O(O )(pydx-aepy)], the generation of which in solution has also
V
[
2
The effect of oxidant was studied considering styrene: aque-
been established by electron absorption spectroscopy. Changes in
ous 30% H O2 molar ratios of 1:1, 1:2, and 1:3 where the mixture
2
the absorption spectra during titration of the methanolic solution
of styrene (0.52 g, 5 mmol), catalyst (0.0125 g) and oxidant were
IV
of [V O(acac)(pydx-aepy)] with aqueous 30% H O2 dissolved in
2
◦
taken in 5 ml of CH CN and the reaction was carried out at 80 C. As
3
methanol are shown in Fig. 5. The d–d bands appearing at 535
and 768 nm slowly disappeared (Fig. 5a and in set there in). The
charge transfer band appearing at 395 nm shifted to 435 nm along
with decrease in intensity while band due to n–␲* transition at
illustrated in see Fig. S1 (supporting information) and presented in
entry nos. 1, 2 and 3 of Table 6, the percent conversion of styrene
improved from 79.7% to 94.0% on increasing the styrene: oxidant
ratio from 1:1 to 1:2. Further increasing this ratio to 1:3, though
affected the conversion but not very significantly (96.6%), sug-
gesting that 1:2 (styrene:H O ) molar ratio is sufficient enough to
3
05 nm shifted to 337 nm with decrease in intensity. With increase
in the maxima, bands at 225 and 258 nm remained nearly constant
2
2
(
Fig. 5b). The features of the final spectrum is similar to that of the
perform the reaction with good conversion.
V
isolated peroxido complex [V O(O )(pydx-aepy)].
2
Similarly, for three different amounts viz. 0.010, 0.0125 and
0
.015 g of catalyst and styrene to H O2 molar ratio of 1:2 under
2
3
.9. Catalytic activity studies
.9.1. Oxidation of styrene
above reaction conditions, 0.010 g catalyst gave only 54.1% conver-
sion while 0.0125 and 0.015 g catalyst produced 94.0% and 97.6%
conversions, respectively (Fig. S2 and entry nos. 2, 4 and 5 of
3
V
Oxidation of styrene, catalysed by [V O (pydx-aepy)]-Y using
Table 6). However, at the expense of H O , 0.0125 g catalyst can be
2
2 2
aqueous 30% H O as oxidant gave four oxidation products namely,
considered sufficient enough to carry out the reaction. Further, the
2
2
−
1
styrene oxide, benzaldehyde, 1-phenylethane-1,2-diol and benzoic
acid along with small amount of unidentified product (Scheme 3).
Hulea and Dumitriu [34] have reported some of these product dur-
ing the oxidation of styrene using TS-1 and MCM-41. At least five
oxidation products have been obtained using polymer-anchored
turn over rates (TOF h = moles of substrate converted per mole of
catalyst per hour) is also higher for 0.0125 g catalyst (TOF = 105.4)
to achieve 94.0% conversion of styrene.
Temperature of the reaction mixture has also influenced on
the performance of the catalyst. Amongst three different tem-
IV
V
◦
catalysts PS-[V O(sal-ohyba)·DMF] [35] and PS-K[V O(O )(L)]
peratures of 60, 70 and 80 C for the fixed operating condition
2
V
[
L = 2-(2-pyridyl)benzimidazole and 2-(3-pyridyl)benzimidazole]
36].
of styrene (0.52 g, 5 mmol), H O2 (1.14 g, 10 mmol), [V O (pydx-
2
2
◦
[
aepy)]-Y (0.0125 g) and MeCN (5 ml), running the reaction at 80 C
gave much better conversion (Fig. S3 and entry nos. 2, 6 and 7
of Table 6). More over, time required in achieving the maximum
The reaction conditions were optimised for the maximum oxi-
dation of styrene by studying four different parameters viz. the
◦
effect of amount of oxidant (moles of H O2 per mole of styrene),
conversion was also reduced on carrying out the reaction at 80 C.
2
(
a) 3.0
(
b) 3.0
2.5
0
.30
2
2
1
1
0
0
.5
.0
.5
.0
.5
.0
0.25
0
0
0
0
0
.20
.15
.10
.05
.00
2.0
1.5
650 700 750 800 850 900
1.0
0.5
0.0
5
00
600
700
800
900
200
250
300
350
400
450
500
Wave length / nm
Wave length / nm
Fig. 5. UV–vis spectral changes observed during titration of [VIVO(acac)(pydx-aepy)] with H2O2. (a) The spectra were recorded after successive additions of one drop portions
−
3
IV
of H2O2 (ca. 12 mmol of 30% H2O2 dissolved in 10 ml of methanol) to 50 ml of ca. 10 M solution of [V O(acac)(pydx-aepy)] in methanol at every 5 min interval. (b) The
IV
−4
equivalent titration, but with lower concentrations of a [V O(acac)(pydx-aepy)] solution (ca. 10 M).

2
4
M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 344 (2011) 18–27
Table 6
V
Conversion of styrene (0.52 g, 5 mmol) using [V O2(pydx-aepy)]-Y as catalyst in 7 h of reaction time under different reaction conditions.
◦
Entry no.
Catalyst (g)
Temp. ( C)
H2O2 (g, mmol)
CH3CN (ml)
Conversion %
1
2
3
4
5
6
7
8
9
0.0125
0.0125
0.0125
0.010
80
80
80
80
80
60
70
80
80
0.57, 5
5
5
5
5
5
5
5
2
79.7
94.0
96.6
54.1
97.6
54.8
77.0
87.7
54.9
1.14, 10
1.71, 15
1.14, 10
1.14, 10
1.14, 10
1.14, 10
1.14, 10
1.14, 10
0.015
0.0125
0.0125
0.0125
0.0125
7.5
Complex [VIVO(acac)(pydx-aepy)] has been used as a catalyst
precursor to compare its catalytic activity with encapsulated com-
plex. Interestingly, this exhibited 85.9% conversion when complex
Variation in the volume of the solvent was also studied by tak-
ing 2, 5 and 7.5 ml of CH CN (Table 6). It was observed that 5 ml
3
of CH CN was sufficient enough for styrene (0.52 g, 5 mmol), H O
3
2
2
V
(
1.14 g, 10 mmol) and [V O (pydx-aepy)]-Y (0.0125 g) to get good
(0.0028 g, 0.007 mmol), styrene (0.52 g, 5 mmol) and 30% H O2
2
2
◦
transformation of styrene while running the reaction at 80 C. Thus,
all reaction conditions as concluded above were considered essen-
tial and applied for the maximum transformation of styrene into a
mixture of oxidation products.
(1.14 g, 10 mmol) were taken in 5 ml of acetonitrile and the reaction
◦
was carried out at 80 C. Here, the selectivity of different products
follow the order: benzaldehyde (60.5%) > 1-phenylethane-1,2-diol
(24.4%) > benzoic acid (10.9%) > styrene oxide (3.2%). Thus, the order
is same as obtained by encapsulated complex but the selectivity of
individual products differs in two cases. Blank reaction under above
reaction conditions gave 3% conversion. Thus, neat as well as encap-
The conversion of styrene and the selectivity of different reac-
V
tion products using [V O (pydx-aepy)]-Y as catalyst under the
2
optimised reaction conditions (entry no. 2 of Table 6) have been
analysed as a function of time and are presented in Fig. 6. It is clear
from the plot that a selectivity of 80.7% of benzaldehyde has been
obtained at a conversion of 22.8% of styrene in 1 h of the reaction
time. This selectivity decreases slowly with time and reaches to
sulated complexes both are good in catalytic activity. However, the
V
recyclable nature and no leaching of [V O (pydx-aepy)]-Y makes
2
it better over neat one.
.
5
8.3% with the increase of the conversion of styrene to 94.0% in 7 h.
Starting with 6.9% in first hour, the selectivity of 1-phenylethane-
,2-diol increases considerably with the conversion of styrene and
reaches to 29.6%. The selectivity of other two products styrene
oxide and benzoic acid is poor in the beginning but the former one
slowly decreases while later one increases. However, their overall
formations are not much even after 7 h of the reaction time. After
3
.9.2. Oxidation of methyl phenyl sulfide and diphenyl sulfide
It is known that vanadium dependent haloperoxidases [5,37]
1
and model complexes catalyse the oxidation, by H O , of sulfides
2
2
(thioethers) to sulfoxides and further to sulfones [38,39]. We have
V
tested the catalytic potential of [V O (pydx-aepy)]-Y to mimic the
sulfoxidation considering methyl phenyl sulfide and diphenyl sul-
2
7
h only minor changes have been observed in the selectivity of the
different reaction products.
Under optimised reaction conditions, the selectivity of the
different oxidation products formed varies in the order: ben-
zaldehyde (58.3%) > 1-phenylethane-1,2-diol (29.6%) > benzoic acid
O
S
O
O
R
S
S
H O
Catalyst
2
2
R
R
+
(
6.6%) > styrene oxide (4.3%). The formation of benzaldehyde in
highest yield may be due to the nucleophilic attack of H O2 on
2
R = CH : Methyl phenyl sulfide
the styrene oxide formed in the first step, followed by the cleavage
of the intermediate hydroperoxy styrene. Benzaldehyde formation
may also be facilitated by direct oxidative cleavage of the styrene
side chain double bond via a radical mechanism [34]. The formation
of 1-phenylethane-1,2-diol formation is possible through hydroly-
sis of styrene oxide by water present in H O .
3
R = C H : Diphenyl sulfide
6
5
Scheme 4.
% Conversion
%
%
2
2
100
80
Sulfoxide
Sulfone
9
8
0
0
7
6
5
4
3
0
0
0
0
0
1
00
8
7
6
5
4
3
2
0
0
0
0
0
0
0
Benzaldehyde
Styrene oxide
Benzoic acid
8
6
4
2
0
0
0
0
70
60
1
-Phenylethane-1,2-diol
Conversion
%
5
4
3
0
0
0
20
210
10
0
3
0
60
90
120
150
180
Time / min
1
2
3
4
5
6
7
Time / h
Fig. 7. Plots showing percentage selectivity of methyl phenyl sulfoxide and methyl
phenyl sulfone formation, and percentage conversion of methyl phenyl sulfide as a
function of time. Reaction condition: methyl phenyl sulfide (1.24 g, 10 mmol), H2O2
Fig. 6. Conversion of styrene and variation in the selectivity of different reaction
V
V
products as a function of time using [V O2(pydx-aepy)]-Y as catalyst.
(2.27 g, 20 mmol), [V O2(pydx-aepy)]-Y (0.020 g) and CH3CN (5 ml).

M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 344 (2011) 18–27
25
Table 7
V
Conversion of methyl phenyl sulfide (1.24 g, 10 mmol) or diphenyl sulfide (1.86, 10 mmol) using [V O2(pydx-aepy)]-Y as catalyst in 7 h of reaction time under different
reaction conditions.
Entry No.
Catalyst (g)
Substratea
H2O2 (g, mmol)
CH3CN (ml)
Conversion %
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
0.020
0.020
0.020
0.020
0.025
0.030
0.035
0.015
0.015
0.015
0.010
0.020
0.025
0.020
0.020
mps
mps
mps
mps
mps
mps
mps
dps
dps
dps
pds
dps
dps
dps
dps
1.14, 10
1.70, 15
2.27, 20
3.41, 30
2.27, 20
2.27, 20
2.27, 20
1.14, 10
2.27, 20
3.41, 30
1.14, 10
1.14, 10
1.14, 10
1.14, 10
1.14, 10
5
5
5
5
5
82.9
87.9
93.1
96.9
95.0
75.4
68.4
48.9
27.0
23.7
35.9
63.0
63.6
63.6
67.0
5
5
10
10
10
10
10
10
5
1
1
1
1
1
1
15
a
mps: methyl phenyl sulfide and dps: diphenyl sulfide.
V
fide. The oxidation of these sulfides gave a mixture of two products;
Scheme 4
The reaction conditions were optimised for the maximum
oxidation of methyl phenyl sulfide by studying three different
Similarly, four different amounts of [V O (pydx-aepy)]-Y viz.
2
0.020, 0.025, 0.030, 0.035 g were taken under the above optimised
reaction conditions i.e. methyl phenyl sulfide (1.24 g, 10 mmol), 30%
H O (2.27 g, 20 mmol) and CH CN (5 ml) to see the effect of amount
2
2
3
parameters viz. the effect of amount of oxidant (moles of H O2 per
of catalyst on the reaction and results are shown in Fig. S5 and
presented in entry nos. 1 and 5–7 of Table 7. It was observed that
increasing the amount of catalyst from 0.020 g to 0.025 g improved
the conversion from 93.1% to 95.0% but further increment of cat-
alyst resulted in the lower conversion. As TOF value for 0.020 g
(TOF = 260.8 h ) catalyst is higher than for 0.025 g (TOF = 213 h ),
while conversion difference for these amounts is not much (ca. 4%),
an amount of 0.020 g catalyst was considered to be optimum for
best result. The amount of solvent also has influence on the oxi-
2
mole of methyl phenyl sulfide) and catalyst (amount of catalyst per
mole of methyl phenyl sulfide) and solvent of the reaction mixture
in detail.
The effect of oxidant was studied by considering substrate to
−
1
−1
oxidant ratios of 1:1, 1:1.5, 1:2 and 1:3 for the fixed amount of
V
[
V O (pydx-aepy)]-Y (0.020 g) and methyl phenyl sulfide (1.24 g,
2
1
0 mmol) in 5 ml of acetonitrile and reaction was monitored at
room temperature. As shown in Fig. S4 and presented in entry
nos. 1–4 of Table 7, the oxidation of methyl phenyl sulfide depen-
dents upon the amount of oxidant (30% aqueous H O ) used in
dation of methyl phenyl sulfide. It was concluded that 5 ml CH CN
3
2
2
was sufficient enough to effect maximum conversion under above
optimised reaction conditions.
the reaction. At a H O :methyl phenyl sulfide molar ratio of 1:1, a
2
2
maximum of 82.9% conversion was achieved in ca. 3.5 h. This con-
version goes on increasing on further increasing this ratio. At lowest
Therefore, from these experiments, the best reaction condi-
tions for the maximum oxidation of methyl phenyl sulfide are:
V
H O :methyl phenyl sulfide concentration of 1:1, the selectivity for
substrate (1.24 g, 10 mmol), H O2 (2.27 g, 20 mmol), [V O (pydx-
2
2
2
2
the formation of methyl phenyl sufoxide was highest (74.2%) and
this takes up decreasing trend on increasing this ratio i.e. 73.1% at
aepy)]-Y (0.020 g) and CH CN (5 ml). The percent conversion of
3
methyl phenyl sulfide under the optimised reaction conditions and
the selectivity of reaction products as a function of time are shown
in Fig. 7. It is clear from the plot that both the products started
to form with the conversion of methyl phenyl sulfide. However,
their selectivity (70.6% for methyl phenyl sulfoxide and 29.2% for
methyl phenyl sulfone) after 1 h remained nearly constant while
conversion increased from 32.3 to 93.1% in 3.5 h.
1
:1.5, 71.2% at 1:2 and 63.4% at 1:3 ratio. However, H O :methyl
2 2
phenyl sulfide molar ratio of 1:2 with methyl phenyl sulfide conver-
sion of 93.1% and TOF of 261 seems to be the best one as increasing
this ratio to 1:3 increases TOF only marginally while decreases the
formation of sulfoxide sharply.
IV
Using [V O(acac)(pydx-aepy)] as catalyst precursor and consid-
V
% Conversion
80
ering its same mole concentration as of [V O (pydx-aepy)]-Y under
2
1
00
%
%
Sulfoxide
Sulfone
IV
above reaction conditions (i.e. [V O(acac)(pydx-aepy)] (0.0045 g,
90
80
70
60
50
40
30
0.01 mmol), methyl phenyl sulfide (1.24 g, 10 mmol), 30% H O2
70
60
50
40
30
2
(2.27 g, 20 mmol) and acetonitrile (5 ml)), a maximum of 96.3% con-
version of methyl phenyl sulfide was achieved. Here selectivity of
sulfoxide and sulfone were 65% and 35%, respectively.
V
The catalytic action of [V O (pydx-aepy)]-Y towards the oxi-
2
dation of diphenyl sulfide was found to be different from methyl
phenyl sulfide. Here, at a diphenyl sulfide to oxidant molar
ratio of 1:1 for the fixed amount of diphenyl sulfide (1.86 g,
V
1
0 mmol), [V O (pydx-aepy)]-Y (0.015 g) and CH CN (10 ml), reac-
2
3
20
OH
O
3
0
60
90
120
150
180
210
OH
OH
H O
2
2
Time / min
O
+
+
+
Catalyst
Cyclohexene
Fig. 8. Plots showing percentage selectivity of diphenyl sulfoxide and diphenyl
sulfone formation and percentage conversion of diphenyl sulfide as a function of
(a)
(b)
(c)
(d)
time. Reaction condition: diphenyl sulfide (1.86 g, 10 mmol), H2O2 (1.14 g, 10 mmol),
Scheme 5. (a) Cyclohexeneoxide, (b) 2-cyclohexene-1-ol, (c) 2-cyclohexene-1-one
and (d) cyclohexane-1,2-diol.
V
[V O2(pydx-aep)]-Y (0.020 g) and acetonitrile (15 ml).

2
6
M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 344 (2011) 18–27
Table 8
V
Conversion of cyclohexene (0.82 g, 10 mmol) using [V O2(pydx-2aep)]-Y as catalyst in 6 h of reaction time under different reaction conditions.
◦
Entry No.
Catalyst (g)
Temp. ( C)
H2O2 (g, mmol)
CH3CN (ml)
10
10
10
10
10
2
5
5
5
5
Conversion %
1
2
3
4
5
6
7
8
0.010
0.010
0.010
0.005
0.015
0.010
0.010
0.010
0.010
0.010
0.010
80
80
80
80
80
80
80
60
70
80
80
1.14, 10
2.27, 20
3.41, 30
2.27, 20
2.27, 20
2.27, 20
2.27, 20
2.27, 20
2.27, 20
2.27, 20
2.27, 20
85.0
94.1
96.0
75.8
97.4
98.5
96.1
72.0
87.5
93.7
93.1
9
0
1
a
1
1
b
5
a
First recycle of used catalyst.
b
Second recycle of used catalyst.
tion required ca. 7 h to acquire equilibrium and only 48.9% dipheyl
sulfide was converted into products at room temperature. Increas-
ing this ratio only slightly influenced on the equilibrium towards
left but the over all conversion was decreased (Fig. S6 and entry
nos. 8–10 of Table 7). The selectivity of the formation of sulfoxide
was better (86.0%) at 1:1 ratio while at diphenyl sulfide to oxidant
Considering same mole concentration of neat catalyst precur-
IV
sor, [V O(acac)(pydx-aepy)] under above reaction conditions (i.e.
IV
[V O(acac)(pydx-aepy)] (0.0045 g, 0.01 mmol), diphenyl sulfide
(1.86 g, 10 mmol) and 30% H O2 (1.14 g, 10 mmol) and acetonitrile
2
(15 ml)), a maximum of 86.1% conversion of diphenyl sulfide was
achieved where selectivity of sulfoxide was 83.2%. Thus, neat as
well as encapsulated complexes both are good catalysts for the
oxidation of organic sulfides. However, the stability and recyclable
nature of zeolite-Y encapsulated complex make it better catalyst
over neat one.
(
H O ) molar ratios of 1:2 and 1:3, the selectivity decreased to 71.9
2 2
and 66.3%, respectively.
Four different amount of catalyst viz. 0.010, 0.015, 0.020, and
0
1
.025 g were used for the fixed amount of diphenyl sulfide (1.86 g,
0 mmol), H O (1.14 g, 10 mmol) and acetonitrile (10 ml) to see
2
2
the effect of catalyst and obtained results are plotted in Fig. S7
and presented in entry nos. 8 and 11–13 of Table 7 as a function
of time. Increasing the amount of catalyst increased the diphenyl
sulfide transformation and a maximum of 63.0% conversion was
achieved with 0.020 g of catalyst. Further increment of catalyst
amount to 0.025 g resulted in only marginal increase (63.6%) in
substrate conversion. This has been interpreted in terms of ther-
modynamic and mass transfer limitations at higher reaction rate.
In all cases reaction acquired steady state in ca. 7 h and the selectiv-
ity of the formation of diphenyl sulfoxide remained almost constant
3
.9.3. Oxidation of cyclohexene
V
Complex [V O (pydx-2aep)]-Y also catalyses the oxidation of
2
cyclohexene by H O2 efficiently to give cyclohexene epoxide, 2-
cyclohexene-1-one, 2-cyclohexene-1-ol and cyclohexane-1,2-diol
as presented in Scheme 5.
2
In order to achieve optimum conditions, three different cyclo-
hexene to aqueous 30% H O molar ratios viz. 1:1, 1:2 and 1:3 were
considered for the fixed amount of cyclohexene (0.82 g, 10 mmol)
and catalyst (0.010 g) in 10 ml of MeCN and reaction was carried
out at 80 C. Fig. S8 and entry nos. 1, 2 and 3 of Table 8 presents the
results obtained. A maximum of 85.0% conversion was obtained
2
2
◦
(
ca. 86%).
The influence of the volume of solvent (CH CN) on the rate of
3
for cyclohexene to H O2 molar ratio of 1:1 in 6 h of reaction time.
This conversion reached 94.1% on increasing this ratio to 1:2 while
2
reaction was also tested and 15 ml of acetonitrile was found to be
the best (entry no. 15 of Table 7) under the optimised reaction con-
1
:3 ratio has shown only marginal improvement (96.0%) in the
conversion.
Under the operating conditions as fixed above i.e. cyclohexene
0.82 g, 10 mmol), 30% H O (2.27 g, 20 mmol) in 10 ml of MeCN, the
ditions i.e. diphenyl sulfide (1.86 g, 10 mmol), 30% H O (1.14 g,
2
2
V
1
6
0 mmol), [V O (pydx-aepy)]-Y (0.020 g) to give a maximum of
2
7.0% conversion with 66.3% selectivity of diphenyl sulfoxide. How-
(
2
2
ever, the selectivity for the diphenyl sulfoxide was 86.0% at 63.6%
transformation of diphenyl sulfide in lower amount of solvent
(
5 ml), We have analysed the conversion of diphenyl sulfide as a
Conversion
function of time considering the best reaction conditions for the
maximum oxidation of diphenyl sulfide along with good selectiv-
ity towards the formation of diphenyl sulfoxide as concluded above
100
90
cyclohexeneoxide
90
80
2
2
-Cyclohexene-1-one
-Cyclohexene-1-ol
Cyclohexane-1, 2-diol
7
0
(
[
i.e. diphenyl sulfide (1.86 g, 10 mmol), H O (1.14 g, 10 mmol),
2 2
V
80
V O (pydx-aep)]-Y (0.020 g) and acetonitrile (15 ml)) and results
60
2
are presented in Fig. 8. About 25% conversion with 92% selectiv-
ity of diphenyl sulfoxide was achieved within 1 h. This conversion
improved with time and reached to 67% while the selectivity of sul-
foxide started going down with time and reached to 66.3% in 7 h,
5
4
3
0
0
0
7
6
5
4
0
0
0
0
accordingly, the selectivity of diphenyl sulfone reached to 33.8%.
V
20
10
0
Thus, the catalytic potential of [V O (pydx-aepy)]-Y varies with
2
the sulfide substrates, and different conditions are required to
observed effective catalytic activity. In the absence of the cata-
lyst, the reaction mixture gave 35.3% conversion of methyl phenyl
sulfide in 10 ml of acetoniitrile with 65.5% selectivity towards sul-
foxide, 34.2% towards sulfone and ca. 0.3% an unidentified product.
Blank reaction with diphenyl sulfide under the above reaction con-
ditions gave ca. 5% conversion with sulfoxide:sulfone selectivity
of 57:43. Thus, catalysts not only improve the conversion of sub-
strates, they alter the selectivity of the products as well.
1
2
3
4
5
6
Time / h
Fig. 9. Plots showing percentage selectivity of cyclohexene oxide, 2-cyclohexene-
-one 2-cyclohexene-1-ol, and cyclohexane-1,2-diol formation and percentage
conversion of cyclohexene as a function of time. Reaction condition: cyclohexene
1
(
(
0.82 g, 10 mmol), H2O2 (2.27 g, 20 mmol), [VO2(pydx-aepy)]-Y (0.010 g) acetonitrile
◦
5 ml) and temp. (80 C).

M.R. Maurya et al. / Journal of Molecular Catalysis A: Chemical 344 (2011) 18–27
27
effect of catalyst considering three different amounts viz. 0.005,
.010 and 0.015 g as a function of time was studied and results
are illustrated in Fig. S9 and presented in entry nos. 2, 4 and 5 of
Table 8. It is clear from the plot that 0.010 g catalyst was the best
one to obtain a maximum of 94.1% conversion of cyclohexene as
phenyl sulfide, diphenyl sulfide and cyclohexene using H O2 and
results are very encouraging. The encapsulated catalyst is stable,
recyclable and looses its activity only slightly.
2
0
Acknowledgements
0.015 g catalysts showed only marginal improvement in conver-
sion while 0.005 g catalyst gave much poor result. We have also
optimised the amount of solvent (acetonitrile, entry nos. 2, 6 and
MRM and MB are thankful to Department of Science and Tech-
nology, Government of India, and FA acknowledges Universidade
da Coru n˜ a for financial support.
7
) and temperature (entry nos. 7, 8 and 9) of the reaction and
◦
found that 5 ml of solvent and 80 C reaction temperature were
good to obtained 96.1% conversion under above reaction condi-
tions.
Appendix A. Supplementary data
The conversion of cyclohexene and selectivity of different reac-
tion products under the optimised reaction conditions (entry no.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molcata.2011.04.017.
7
of Table 8) have been analysed as a function of time and are
presented in Fig. 9. It is clear from the plot that at a conversion
of 44.5% of cyclohexene in 1 h of reaction time, 3.0% selectiv-
ity of cyclohexene epoxide, 71.0% of 2-cyclohexene-1-one, 20.8%
of cyclohexene-1-ol and 5.2% of 2-cyclohexe-1,2-diol have been
obtained. The selectivity of cyclohexene-1-ol and 2-cyclohexe-
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8
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