Synthesis, structural characterization, encapsulation in zeolite y and catalytic activity of an oxidovanadium(V) complex with a tribasic pentadentate ligand

Article abstract of DOI:10.1016/j.poly.2013.02.036

Reaction of [V^IVO(acac)₂] with H₃hap-dahp (I: Schiff base derived from 2-hydroxyacetophenone and 1,3-diamino-2- hydroxypropane) in methanol under aerobic conditions resulted in the formation of the complex [V^VO(hap-dahp)] (1). Treatment of I with vanadium(IV) exchanged zeolite Y followed by aerial oxidation gave the encapsulated oxidovanadium(V) complex [V^VO(hap-dahp)]-Y (2) in the nanocavity of zeolite Y. Elemental analysis, spectroscopic (IR, electronic, ¹H and ⁵¹V NMR) studies, scanning electron micrographs and X-ray diffraction patterns have been used to characterize these complexes, which have a distorted octahedral structure, confirming the tribasic O₃N₂ binding mode of the ligand. The encapsulated complex [V^VO(hap-dahp)]- Y (2) catalyzes the oxidation of styrene, methyl phenyl sulfide and diphenyl sulfide using H₂O₂ as an oxidant in good yield (82%, 98% and 81%, respectively). Styrene, under optimized reaction conditions, gave five reaction products, namely styrene oxide, benzaldehyde, 1-phenylethane-1,2-diol, benzoic acid and phenylacetaldehyde, while the organic sulfides gave the corresponding sulfoxides as the major product. The neat complex [V ^VO(hap-dahp)] (1) also exhibits good catalytic activity for these substrates. The encapsulated complex showed a good recycling ability.

Full text of DOI:10.1016/j.poly.2013.02.036

Polyhedron 54 (2013) 180–188
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, structural characterization, encapsulation in zeolite Y and catalytic
activity of an oxidovanadium(V) complex with a tribasic pentadentate ligand
a
a
b
c
Mannar R. Maurya a, , Manisha Bisht , Nikita Chaudhary , Fernando Avecilla , Umesh Kumar ,
⇑
Hua-Fen Hsu c
a Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667, India
b Departamento de Química Fundamental, Universidade da Coruña, Campus de A Zapateira, 15071 A Coruña, Spain
c Department of Chemistry, National Cheng Kung University, #1 University Road, Tianan 701, Taiwan
a r t i c l e i n f o
a b s t r a c t
Reaction of [VIVO(acac)2] with H3hap-dahp (I: Schiff base derived from 2-hydroxyacetophenone and
1,3-diamino-2-hydroxypropane) in methanol under aerobic conditions resulted in the formation of the
complex [VVO(hap-dahp)] (1). Treatment of I with vanadium(IV) exchanged zeolite Y followed by aerial
oxidation gave the encapsulated oxidovanadium(V) complex [VVO(hap-dahp)]-Y (2) in the nanocavity of
zeolite Y. Elemental analysis, spectroscopic (IR, electronic, 1H and 51V NMR) studies, scanning electron
micrographs and X-ray diffraction patterns have been used to characterize these complexes, which have
a distorted octahedral structure, confirming the tribasic O3N2 binding mode of the ligand. The encapsu-
lated complex [VVO(hap-dahp)]-Y (2) catalyzes the oxidation of styrene, methyl phenyl sulfide and
diphenyl sulfide using H2O2 as an oxidant in good yield (82%, 98% and 81%, respectively). Styrene, under
optimized reaction conditions, gave five reaction products, namely styrene oxide, benzaldehyde, 1-phen-
ylethane-1,2-diol, benzoic acid and phenylacetaldehyde, while the organic sulfides gave the correspond-
ing sulfoxides as the major product. The neat complex [VVO(hap-dahp)] (1) also exhibits good catalytic
activity for these substrates. The encapsulated complex showed a good recycling ability.
Article history:
Received 14 August 2012
Accepted 9 February 2013
Available online 22 February 2013
Keywords:
Oxidovanadium(V) complex
Crystal structure
Zeolit-Y encapsulated complex
Oxidation of styrene
Oxidation of methyl phenyl sulfide
Oxidation of diphenyl sulfide
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
co-workers have used manganese(III) complexes of salen deriva-
tives encapsulated in the cavity of zeolite X and zeolite Y for the
The coordination chemistry of vanadium has been studied
extensively [1–3] due to its occurrence in the active site of en-
zymes (e.g. vanadate-dependent haloperoxidases and vanadium-
nitrogenases) that are involved in various catalytic actions [4–6].
Many vanadium complexes provide a suitable structural and/or
functional model for these enzymes [7]. Amongst the tetradentate
ligands, salen type (H2salen = N,N0-bis(salicylidene)ethane-1,2-dia-
mine) ligands find a key place in the literature as complexes of
such ligands have great potential as catalysts for oxido transfer
reactions and other processes [8–10]. Vanadium complexes of sal-
an (H2salan = ligand obtained by reducing H2salen) type ligands
have also shown good catalytic reactions for oxygen transfers
and E-H activations [11–13]. The flexible nature of salen-type
ligands has also provided opportunities to encapsulate various
transition-metal complexes in the nanocavity of zeolites and to
develop catalytic processes for various reactions [14–25].
Metallosalen complexes encapsulated in zeolite X have been used
as catalysts for the oxidation of cyclooctane [14]. Ratnasamy and
oxidation of styrene under aerobic conditions using tert-butylhy-
droperoxide as an oxidant. They have also studied the effect of
electron-withdrawing substituents, such as Cl, Br and NO2, present
on the aromatic ring on the rate of oxidation [15,16]. These
complexes also catalyze the oxidation of phenol and p-xylene
[26,27]. Zeolite Y encapsulated copper(II) [23], manganese(III)
[25] and oxidovanadium(IV) [24] complexes of ligands derived
from pyridoxal and various diamines have been reported from
our laboratory for various oxidation reactions.
We have designed a ligand derived from 2-hydroxyacetophe-
none and 1,3 diamino-2-hydroxypropane (H3hap-dahp, I;
Scheme 1), similar to salen type ligands but with one more coordi-
nating site whilst maintaining its flexible nature. The deprotona-
tion behavior of the additional functional group and its
participation or non-participation in coordination to metal ions
controls the oxidation state of central metal ion [26].
We report herein the oxidovanadium(V) complex of I, its encap-
sulation in the super cages of zeolite Y and its characterization. The
catalytic activities of neat as well as the encapsulated complex
have been tested for the liquid phase oxidation of styrene, methyl
phenyl sulfide and diphenyl sulfide. Styrene oxide, an oxidation
product of styrene, is an important intermediate in organic
⇑
Corresponding author. Tel.: +91 1332 285327; fax: +91 1332 273560.
E-mail address: rkmanfcy@iitr.ernet.in (M.R. Maurya).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.02.036

M.R. Maurya et al. / Polyhedron 54 (2013) 180–188
181
Table 1
HO
OH
Crystal data and structure refinement for [VVO(hap-dahp)] (1).
N
N
Formula
Formula weight
T, K
C19H19N2O4V
390.30
100(2)
OH
Wavelength (Å)
Crystal system
Space group
a (Å)
0.71073
orthorhombic
Pbca
13.9677(3)
13.0077(3)
18.1778(4)
3302.68(13)
8
H3hap-dahp (I)
Scheme 1. Structure of ligand.
b (Å)
c (Å)
synthesis and in the manufacture of the perfumery chemical phen-
ylethyl alcohol. Vanadium complexes are known to catalyze the
oxidation of organic sulfides to sulfoxides and sulfones [13], a reac-
tion also promoted by vanadium haloperoxidase enzymes.
V (Å3)
Z
F(000)
1616
1.570
0.630
Dcalc (g cmꢂ3
)
l
(mmꢂ1
)
h (°)
Rint
2.24–28.42
0.0314
2. Experimental
Crystal size (mm3)
0.36 ꢃ 0.26 ꢃ 0.18
Goodness-of-fit (GOF) on F2
1.050
a
2.1. Materials and methods
R1
0.0296
0.0831
wR2 (all data)b
Largest differences peak and hole
0.450 and ꢂ0.447
V2O5, VOSO4ꢀ5H2O, (Loba Chemie, India), zeolite NaY (Si/
Al = ꢁ10) acetylacetone, 1,3-diamino-2-hydroxypropane (Aldrich,
USA), 2-hydroxyacetophenone (Merck, Germany), methyl phenyl
sulfide (Alfa Aesar, USA), styrene (Acros Organics, USA) and 30%
aqueous H2O2 (Qualigens, India) were used as obtained. All other
chemicals and solvents used were of AR grade. [VIVO(acac)2] was
prepared according to the method reported in the literature [27].
Elemental analyses (C, H and N) of the ligand and the complex
were obtained by an Elementar model Vario-EL-III. IR spectra with
a resolution of 2 cmꢂ1 were recorded as KBr pellets on a Nicolet
1100 FT-IR spectrometer after grinding the sample with KBr. A total
of 32 scans were obtained to measure the spectra. Electronic spectra
of the ligand and the neat complex were recorded in methanol. The
electronic spectrum of the zeolite Y encapsulated complex was re-
corded in Nujol using a Shimadzu 1601 UV–Vis spectrophotometer
by layering the mull of the sample inside of one of the cuvettes,
(e Åꢂ3
)
a
R1
wR2 = {
=
R
|Fo ꢂ Fc|/R|Fo|.
2
b
R
[w(|Fo ꢂ Fc2|)2]|/
R .
[w(Fo4)]}1/2
for Lorentz and polarization effects and for absorption by semi-
empirical methods based on symmetry-equivalent and repeated
reflections, 3619 independent reflections exceeded the significance
level F/r(F) > 4.0. Complex scattering factors were taken from the
program package SHELXTL [28]. The structure was solved by direct
methods and refined by full-matrix least-squares methods on F2.
The non-hydrogen atoms were refined with anisotropic thermal
parameters in all cases. The hydrogen atoms were left to refine
freely. A final difference Fourier map showed no residual density
outside: 0.450 and ꢂ0.447 e Åꢂ3. Crystal data and details of the
data collection and refinement for the new compound are collected
in Table 1.
whilst keeping the other one layered with Nujol as a reference. 1
H
and 13C NMR spectra were obtained on a Bruker 200 spectrometer,
and 51V NMR spectra on a Bruker Avance III 400 MHz spectrometer,
with the common parameter settings. NMR spectra were usually re-
corded in DMSO-d6, and d (51V) values are referenced relative to neat
VVOCl3 as an external standard. X-ray powder diffractograms of the
zeolite containing samples were recorded using a Bruker AXS D8 ad-
2.3. Preparations
2.3.1. Preparation of H3hap-dahp (I)
vance X-ray powder diffractometer with a Cu Ka target. A scanning
A solution of 1,3-diamino-2-hydroxypropane (0.90 g, 10 mmol)
dissolved in methanol (50 ml) was added to a solution of 2-
hydroxyacetophenone (2.72 g, 20 mmol) dissolved in methanol
(20 ml) and the reaction mixture was stirred at room temperature
for 2 h. During this period a yellow solid slowly separated out. This
was filtered off, washed thoroughly with water, followed by cold
methanol and dried in a vacuum desiccator over silica gel. Yield
2.27 g (84%). Anal. Calc. for C19H22N2O3 (326.40): C, 69.92; H,
6.79; N, 8.58. Found: C, 70.0; H, 6.8; N, 8.4%. 1H NMR (DMSO-d6,
d/ppm): 13.56 (br, 2H, phenolic OH), 6.15–7.61 (m, 8H), 5.23 (br,
1H, –OH), 4.19 (m, 1H, –CH), 3.27 (m, 4H, –CH2), 2.13 (s, 6H, CH3).
electron micrograph (SEM) of the catalyst was recorded on a Leo
instrument, model 435VP. The sample was dusted on alumina and
coated with a thin film of gold to prevent surface charging and to
protect the surface material from thermal damage by the electron
beam. A uniform thickness of about 0.1 mm was maintained. A con-
stant voltage of 20 kV was applied so that only the outer surface of
the zeolite Y was accessible. A Thermax Nicolet gas chromatograph
with an HP-1 capillary column (30 m ꢃ 0.25 mm ꢃ 0.25
lm) was
used to analyze 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.
The percent conversion of the substrate and selectivity of the
products were calculated from the GC data using the formulae pre-
sented elsewhere [25].
2.3.2. Preparation of [VVO(hap-dahp)] (1)
2.3.2.1. Method A. A filtered solution of VOSO4ꢀ5H2O (0.506 g,
2 mmol) in 10 ml methanol was added to a solution of H3hap-dahp
(I) (0.652 g, 2 mmol) and triethylamine (0.606 g, 6 mmol) prepared
in 10 ml of methanol, and the obtained reaction mixture was stir-
red for 2 h while bubbling air through it. The separated dark brown
and off-white solid mixture was filtered off, washed with water,
followed by cold methanol and dried in a vacuum desiccator over
silica gel. Yield: 0.479 (59%). Anal. Calc. for C19H19N2O4V
(390.31): C, 58.47; H, 4.91; N, 7.18. Found: C, 58.6; H, 4.9; N,
7.6%. For other details see Method B.
2.2. X-ray crystal structure determination
Three-dimensional X-ray data for [VO(hap-dahp)] (1) were col-
lected on a Bruker SMART Apex CCD diffractometer at 100(2) K, using
a graphite monochromator and Mo K
the /– scan method. Reflections were measured from a hemi-
sphere of data collected of frames each covering 0.3 degrees in
. Of the 31174 reflections measured, all of which were corrected
a radiation (k = 0.71073 Å) by
x
x

182
M.R. Maurya et al. / Polyhedron 54 (2013) 180–188
2.3.2.2. Method B. A stirred solution of H3hap-dahp (0.652 g,
2 mmol) in methanol (10 ml) was treated with [VIVO(acac)2]
(0.530 g, 2 mmol) dissolved in methanol (10 ml), and the obtained
reaction mixture was stirred while bubbling air through it. After
2 h of stirring, the separated dark brown solid was filtered, washed
with cold methanol and dried. It was crystallized from methanol.
Yield: 0.593 g (73%). Anal. Calc. for C19H19N2O4V (390.31): C,
58.47; H, 4.91; N, 7.18. Found: C, 58.2; H, 4.8; N, 7.4%. 1H NMR
(DMSO-d6, d/ppm): 6.73–7.64 (m, 8H), 4.21 (m, 1H, –CH), 3.69
(m , 4H, –CH2), 2.35 (s, 6H, CH3). 13C NMR (DMSO-d6, d/ppm):
173.6 (C@N), 164.3, 132.8, 129.2, 119.43, 118.6, 117.0 (aromatic
carbon), 53.3 (–CH), 39.3 (–CH2), 15.0 (–CH3).
O
V
O
O
V
O
O
N
O
N
O
N
O
N
Y
(1)
(2)
Scheme 2. Proposed structures for [VVO(hap-dahp)] (1) and the encapsulated
complex [VVO(hap-dahp)]-Y (2).
complex [VVO(hap-dahp)] (1) (Scheme 2), where H3hap-dahp be-
haves as a tribasic pentadentate ligand; Eqs. (1) and (2):
2.3.3. Preparation of [VVO(hap-dahp)]-Y (2)
2½VIVOðacacÞ ꢄ þ 2H3hap ꢂ dahp þ 1=2O2
[VIVO]-Y [oxidovanadium(IV)-exchanged zeolite-Y] [24] (3.0 g)
and H3hap-dahp (2.0 g) were mixed in methanol (100 ml) and
the reaction mixture was heated under reflux for 14 h in an oil bath
with stirring. After filtering, the resulting solid was Soxhlet ex-
tracted with methanol to remove any unreacted ligand. It was fi-
nally treated with hot DMF while stirring for 1 h, filtered and
washed with DMF, followed by hot methanol. The uncomplexed
metal ions present in the zeolite were removed by stirring with
aqueous 0.1 M NaCl (150 ml) for 10 h. The resulting light brown so-
lid was filtered, washed with hot methanol, followed by distilled
water until no precipitate of AgCl was observed in the filtrate on
treating with AgNO3. Finally it was dried at 120 °C for several
hours. Recovered amount: 2.7 g. Found V (ICP-MS): 1.62%.
2
! 2½VVOðhap ꢂ dahpÞꢄ þ 4Hacac þ H2O
ð1Þ
ð2Þ
VOSO4 þ H3hap ꢂ dahp þ 1=2O2 þ Et3N
! ½VVOðhap ꢂ dahpÞꢄ þ Et3HNSO4 þ H2O
The synthesis of the encapsulated complex in the nanocavity of
zeolite Y involves: (i) exchange of [VIVO]2+ with Na+ of Na-Y in
aqueous solution to form [VIVO]-Y and (ii) reaction of vanadium ex-
changed zeolite Y, i.e. [VIVO]-Y, with excess H3hap-dahp in metha-
nol, where the ligand slowly enters into the super cages of zeolite Y
due to its flexible nature and interacts with the vanadyl ion to
give the vanadium(IV) complex, which on aerial oxidation gives
[VVO(hap-dahp)]-Y (2) (Scheme 2). Extraction of the impure sam-
ple with methanol using a Soxhlet extractor removed any excess
free ligand and the neat metal complex formed on the surface of
the zeolite, if any. The remaining uncomplexed metal ions in
zeolite were removed by exchanging with aqueous 0.1 M NaCl
solution. As the impure sample was extracted well, the vanadium
content (1.62%) found in 2 is only due to encapsulation of the
vanadium complex in the cavities of zeolite-Y. Complex 1 is
characterized on the basis of elemental analysis, spectroscopic
(IR, UV–Vis, 1H and 51V NMR) data and single crystal X-ray diffrac-
tion analysis. Complex 2 is additionally characterized by FE-SEM,
EDX and X-ray powder diffraction patterns.
2.4. Catalytic activity studies
Zeolite Y encapsulated, [VVO(hap-dahp)]-Y (2) as well as the
neat complex [VVO(hap-dahp)] (1) have been used as catalysts to
carry out the oxidation of styrene, methyl phenyl sulfide and di-
phenyl sulfide. All reactions were carried out in a 50 ml two-
necked glass reaction flask fitted with
condenser.
a water circulated
2.4.1. Oxidation of styrene
In a typical reaction, styrene (1.04 g, 10 mmol) and aqueous 30%
H2O2 (2.27 g, 20 mmol) were taken in 10 ml of acetonitrile and
temperature of the reaction mixture was raised to 80 °C. After
addition of catalyst (0.010 g) to the above reaction mixture, it
was stirred and the obtained oxidized products were analyzed
quantitatively by gas chromatography during the reaction by with-
drawing small aliquots of the reaction mixture at one hour inter-
vals. The identities of the products were confirmed by GC–MS
and their quantifications were made on the basis of the relative
peak area of the respective product.
3.2. Structure description of [VVO(hap-dahp)] (1)
Fig. 1 shows an ORTEP representation of [VVO(hap-dahp)] (1).
The asymmetric unit contains one neutral vanadium complex. In
the molecular structure, the vanadium center adopts a distorted
six-coordinated octahedral geometry with the (hap-dahp) ligand
coordinated through the two Ophenoxy, two Nimine and one Ohydroxyl
atoms. The ligand acts as a pentadentate phenol-containing ligand
with (O,N,O,N,O)-donor atoms. Another (O,N,O,N,O)-donor ligand
containing phenol groups presents a different coordination chemis-
try with the (VV@O) ion [29], forming a dinuclear complex, perhaps
due to the position of the imine group. The V@O bond [V(1)–O(3):
1.6023(10) Å] is characteristic of an oxo-type O atom with strong
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 H2O2 (1.14 g, 10 mmol) and cata-
lyst (0.0075 g) in acetonitrile were stirred at room temperature
and the reaction was monitored by withdrawing samples at differ-
ent time intervals and analyzing them quantitatively by gas chro-
matography. The identities of the products were confirmed as
mentioned above.
p
bonding (see Table 2). The N@CH lengths [N(1)–C(7):
1.2824(18) Å and N(2)–C(11): 1.2968(18) Å] are consistent with
N@C double-bonds, the O–C bonds [O(1)–C(1): 1.3438(16) Å,
O(2)–C(17): 1.3228(16) Å and O(4)–C(9): 1.4184(16) Å] with a sin-
gle O–C character of these bonds, while the N–C bond lengths
[N(1)–C(8): 1.4616(18) Å and N(2)–C(10): 1.4784(18) Å] are consis-
tent with their single-bond character. The V–Nimine bond, which is
3. Results and discussion
3.1. Synthesis and solid state characteristics
trans to the l-oxo atom, is significantly longer [V(1)–N(1):
2.2734(11) Å] than the other Nimine atom, which is trans to the Ophen-
oxy atom [V(1)–N(2): 2.1220(12) Å] [12,26]. The tetragonal plane is
best defined by O(1)–O(2)–-N(2)–O(4) (mean deviation from the
plane = 0.0371(5) Å), leaving the oxo atom, O(3), and the other
The reaction between equimolar amounts of [VIVO(acac)2] or
VOSO4 (in the presence of triethylamine) and H3hap-dahp (I) fol-
lowed by aerial oxidation gives the brown oxidovanadium(V)

M.R. Maurya et al. / Polyhedron 54 (2013) 180–188
183
3.3. IR spectral studies
Complex 1 displays one sharp band at 945 cm–1 due to the
(V@O) mode. The zeolite Y framework displays major IR bands
m
at 1140, 1040, 960, 785 and 740 cmꢂ1 [13,17,30] and because of
these bands, the band due to
m
(V@O) stretching in [VVO(hap-
dahp)]-Y (2) could not be assigned unambiguously. However, other
bands appearing in complex 2 are similar to 1. The supporting
information provides further details on the IR discussion.
3.4. Field-emission-scanning electron micrograph (FE-SEM) and
energy dispersive X-ray analysis (EDX) studies
The field emission scanning electron micrograph of [VVO(hap-
dahp)]-Y (2), along with the energy dispersive X-ray analysis
(EDX) profile, is presented in Fig. 2. Accurate information on the
morphological changes in terms of the exact orientation of the li-
gand coordinated to the metal ion has not been possible due to
poor loading of the metal complex. However, it is clear from the
micrograph that the vanadium complex entrapped zeolite has well
defined crystals and there is no indication of the presence of any
metal ions or complex on the surface. An energy dispersive X-ray
analysis plot, evaluated semi-quantitatively, supports this conclu-
sion as no vanadium or nitrogen contents were noted on the spot-
ted surface in the plot for the catalyst. Only a small amount of
carbon (ca. 6%) and no nitrogen on the spotted surface suggests
the presence of a trace amount of solvent (methanol), with which
it was finally washed after Soxhlet extraction. The amount of ca. 2%
sodium suggests the exchange of the remaining free vanadium ion
by the sodium ion during the re-exchange process (see Section 2).
Fig. 1. ORTEP plot of the complex [VVO(hap-dahp)] (1). All non-hydrogen atoms are
presented by their 30% probability ellipsoids. Hydrogen atoms are omitted for
clarity.
Table 2
Bond lengths [Å] and angles [°] for [VO(hap-dahp)] (1).
Bond lengths
Bond angles
V(1)–O(3)
V(1)–O(4)
V(1)–O(1)
V(1)–O(2)
V(1)–N(2)
V(1)–N(1)
O(1)–C(1)
O(2)–C(17)
N(1)–C(7)
N(1)–C(8)
N(2)–C(11)
N(2)–C(10)
O(4)–C(9)
1.6023(10)
1.8627(10)
1.8776(11)
1.8931(9)
2.1220(12)
2.2734(11)
1.3438(16)
1.3228(16)
1.2824(18)
1.4616(18)
1.2968(18)
1.4784(18)
1.4184(16)
O(3)–V(1)–O(4)
O(3)–V(1)–O(1)
O(4)–V(1)–O(1)
O(3)–V(1)–O(2)
O(4)–V(1)–O(2)
O(1)–V(1)–O(2)
O(3)–V(1)–N(2)
O(4)–V(1)–N(2)
O(1)–V(1)–N(2)
O(2)–V(1)–N(2)
O(3)–V(1)–N(1)
O(4)–V(1)–N(1)
O(1)–V(1)–N(1)
O(2)–V(1)–N(1)
N(2)–V(1)–N(1)
95.74(5)
99.41(5)
109.19(4)
100.65(5)
153.92(5)
88.06(4)
100.33(5)
77.11(4)
158.53(4)
80.08(4)
169.67(5)
75.35(4)
79.07(4)
89.54(4)
82.97(4)
3.5. Powder X-ray diffraction studies
The powder X-ray diffraction patterns of Na-Y, [VIVO]-Y and
encapsulated oxidovanadium(V) complex [VVO(hap-dahp)]-Y (2)
were recorded at 2h values between 5° and 70°, and the patterns
are presented in Fig. 3. Essentially similar diffraction patterns of
Na-Y, [VIVO]-Y and encapsulated complex have been noticed, ex-
cept for a slightly weaker intensity of the zeolite Y having the me-
tal complex encapsulated. These observations indicate that the
framework of the zeolite has not undergone any structural change
during incorporation of the catalyst, hence the crystallinity of the
zeolite Y is preserved during the encapsulation. No new peaks
due to the encapsulated complex were detected in the zeolite Y
Nimine atom, N(1), in the axial positions. The torsion angle of the
plane containing C(5)–C(6)–C(7)–N(1) presents a sizeable deviation
to 180°: ꢂ149.77(13)°, while N(2)–C(11)–C(12)–C(13) is closer to
180°: ꢂ165.91(13)°. The presence of methyl groups bonded to the
carbon atoms of the imine bonding obstructs the formation of
hydrogen bonds between the complexes in the crystal packing.
Fig. 2. Scanning electron micrograph (left) of [VVO(hap-dahp)]-Y (2) and energy dispersive X-ray analysis (EDX) (right). Asterisk in EDX shows the signal for gold.

184
M.R. Maurya et al. / Polyhedron 54 (2013) 180–188
2.0
1.5
[VVO(hap-dahp)]-Y
1.0
0.5
0.0
VIVO-Y
Na-Y
10
20
30
40
50
60
70
2θ
200
400
600
800
1000
Fig. 3. XRD patterns of Na-Y, [VIVO]-Y and [VVO(hap-dahp)]-Y.
Wavelength/ nm
Fig. 4. Electronic spectrum of [VVO(hap-dahp)]-Y (2) recorded after dispersal in
Nujol.
encapsulated samples, possibly due to a very low percentage load-
ing of the metal complex.
We have also recorded the 51V NMR spectrum of [VVO(hap-
dahp)] (1) in DMSO-d6 using VOCl3 as an external standard. The
51V NMR spectrum of 1 dissolved in DMSO-d6 (ca. 4 mM) shows
a strong resonance at d = ꢂ543 ppm, characteristic of an O/N coor-
dinated vanadium complex [31]. Owing to the quadrupole moment
(spin 7/2) of the 51V nucleus, the resonance is slightly broadened;
the line width at half-height is typically ca. 200 Hz, which may be
considered comparatively narrow [31,32]. In order to see the effect
of MeOH on the 51V NMR signal observed in DMSO-d6, initially
0.25 eq (v/v) of MeOH was added, which resulted in two new sig-
nals at ꢂ503 and ꢂ534 ppm. Increasing the amount of MeOH to 0.5
and 0.75 eq (v/v) increased the intensity of these bands, slowly at
the expense of the ꢂ543 ppm resonance. Finally, this resonance
completely disappeared upon addition of 1 eq (v/v) of MeOH and
the resonances at ꢂ503 (91.4%) and ꢂ534 ppm (8.6%) became the
main ones.
3.6. Electronic absorption spectral studies
Table 3 includes electronic spectral data of the ligand and the
complexes, and Fig. 4 provides the spectrum of the encapsulated
complex. H3hap-dahp (I) exhibits four absorption bands in the
UV region. The extinction coefficients of these bands suggest their
interpretation as
p ?
p⁄ (260 and 280 nm) and n ? p⁄ (321 and
389 nm) transitions. The additional bands in the ligand are possi-
bly due to splitting of these transitions. All these bands also appear
in the spectrum of complex 1 with slight variations, while 2 exhib-
its only two bands at 222 and 279 nm, with a shoulder band at
370 nm. In addition, both complexes exhibit a ligand-to-metal
charge transfer (LMCT) transition from the phenolate oxygen atom
to an empty d-orbital of the vanadium atom at 485 nm (in 1) and
480 nm (in 2). As VV-complexes have a 3d0 configuration, no d ? d
bands are not expected.
3.7. 1H, 13C and 51V NMR Studies
3.8. Reactivity of [VVO(hap-dahp)] towards H2O2
The coordinating mode of H3hap-dahp (I) was also confirmed by
comparing its 1H NMR spectral patterns with those of the complex.
The spectral data are presented in the experimental section.
H3hap-dahp shows two signals at 13.56 (s, 2H) and 5.35 ppm
(broad, 1H) due to the phenolic and alcoholic OH, respectively.
The absence of both signals in the complexes is in conformity with
the coordination of the phenolic and alcoholic oxygen atoms to
vanadium. Signals due to CH3, CH, CH2 and aromatic protons of
the ligand, as well as the complex, appear well within the expected
regions.
It is known that vanadium ([VIVO]2+, [VVO]3+ or [VVO2]+) com-
plexes react with H2O2 to give the corresponding [VVO(O2)]+-com-
plexes, and it is normally assumed that the corresponding
hydroperoxido-complex is the active catalyst which mediates
oxygenation, including the oxidation of sulfides to sulfoxides and
sulfones and the epoxidation of alkenes [33,34]. We have applied
UV–Vis and 51V NMR spectroscopic studies and showed that
addition of H2O2 to a solution of [VVO2(hap-dahp)] in methanol/
DMSO-d6 yields the oxidoperoxido species.
The changes in the absorption spectra during the dropwise
addition of a 30% H2O2 solution diluted in methanol to a methano-
lic solution of [VVO(hap-dahp)] (1) are shown in Fig. 5. The charge
transfer band appearing at ca. 485 nm slowly disappears with a de-
crease in intensity. Simultaneously, the weak shoulders appearing
at 388 and 320 nm shift slightly to 392 and 325 nm, respectively,
along with a slight increase in their intensities. These bands also
The 13C NMR spectrum recorded for complex 1 contains 10 sig-
nals corresponding to the 19 carbon atoms of the molecules. The
resonances at 15.0, 39.3, 53.3 and 173.6 ppm are due to the carbon
atoms of CH3, CH2, CH and C@N, respectively. Due to symmetry,
only six signals are observed for the aromatic carbons in the ex-
pected regions, which is compatible with the proposed structure.
Table 3
Electronic spectral data of the compounds.
a
Compound
Solvent
kmax (nm)/e )
(liter molꢂ1 cmꢂ1
H3hap-dahp (I)
MeOH
MeOH
Nujol
218(3.98 ꢃ 104), 255(1.55 ꢃ 104), 268(1.37 ꢃ 104), 320(5.09 ꢃ 103), 390(6.6 ꢃ 103)
223(8.2 ꢃ 103), 250(sh)(5.77 ꢃ 103), 275(3.22 ꢃ 103), 320(1.6 ꢃ 103), 388(1.08 ꢃ 103), 485(0.93 ꢃ 103)
222, 279, 370(sh), 480
[VVO(hap-dahp)] (1)
[VVO(hap-dahp)]-Y (2)
a
sh = Shoulder band.

M.R. Maurya et al. / Polyhedron 54 (2013) 180–188
185
assign the resonance at ꢂ594 ppm as being due to [VVO(O2)(Hhap-
dahp)]ꢂ [35]. The formation of such a seven coordinated peroxido-
vanadium(V) species upon addition of aqueous 30% H2O2 to a
methanolic solution of an oxidovanadium(IV) complex of a tetra-
dentate ligand has been established by 51V NMR as well as in a the-
oretical study [12]. The solution acquires the original spectrum on
either addition of 1 eq. of methyl phenyl sulfide or standing at
room temperature for ca. 24 h, suggesting the reversibility of the
system.
3
2
1
0
3.9. Catalytic activity studies
3.9.1. Oxidation of styrene
200
300
400
500
600
The catalytic potential of the complex [VVO(hap-dahp)]-Y (2)
was tested for the oxidation of styrene. Its catalytic oxidation in
the presence of H2O2 gave styrene oxide, benzaldehyde, 1-phenyle-
thane-1,2-diol, benzoic acid and phenylacetaldehyde; Scheme 3.
These products of styrene oxidation were previously observed by
us and others as well [24,36–39].
Wavelength/ nm
Fig. 5. Spectral changes observed during addition of aqueous 30% H2O2 dissolved in
5 ml of methanol to 20 ml of ca. 10ꢂ3 M solution of [VVO(hap-dahp)] in methanol.
In order to achieve suitable reaction conditions for a maximum
oxidation of styrene, four different parameters, viz. amount of oxi-
dant (mol of H2O2 per mol of catalyst), catalyst, solvent and tem-
perature of the reaction were tested. Table 4 (and Figs. S1 to S3
of the supporting information) summarizes the various conditions
and conversions obtained.
Thus, for the maximum oxidation of 10 mmol of styrene, the
following conditions were considered an adequate: catalyst
(0.010 g), H2O2 (2.27 g, 20 mmol), CH3CN (15 mL) and 80 °C reac-
tion temperature (i.e. entry No. 7 of Table 4). Under the optimized
reaction conditions, the selectivity of the different oxidation prod-
ucts formed varies in the order: benzaldehyde (49%) > 1-phenyle-
thane-1,2-diol (25%) > benzoic acid (15 %) > styrene oxide
(6%) > phenylacetaldehyde (5%); Table 5. The formation of benzal-
dehyde with the highest yield may be due to the nucleophilic at-
tack of H2O2 on 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 mech-
anism. The formation of 1-phenylethane-1,2-diol is possible
result in the formation of two isosbestic points centered at 315 and
420 nm. With a marginal increase in the intensity, the band at 275
shifts to 268 nm while the extremely weak shoulder at ca. 250 nm
sharpens with a decrease in intensity. Again these shifts generate
two isosbestic points at 261 and 282 nm. These changes indicate
the interaction of [VVO(hap-dahp)] (1) with H2O2 and the plausible
formation of [VVO(O2)(hap-dahp)]2ꢂ/[VVO(O2)(Hhap–dahp)]ꢂ in
MeOH. However, among these possible peroxide species, the for-
mation of [VVO(O2)(Hhap-dahp)]ꢂ, where the alcoholic oxygen of
the amine residue remains protonated without coordinating to
vanadium, is more likely as an oxidovanadium(IV) complex with-
out a coordinating alcoholic oxygen is known [26].
The addition of 1 equiv of 30% aqueous H2O2 to [VVO(hap-
dahp)] dissolved in DMSO-d6 (ca. 4 mM) results in the broadening
of the resonance at ꢂ543 ppm. Upon further addition of 1 equiv of
H2O2, a new resonance at ꢂ594 ppm becomes visible along with
the original peak. The original peak completely disappears after
the addition of 3 equiv of H2O2 and additions of 4 and 5 equiv of
30% H2O2 make no difference in the spectra (Fig. 6). We tentatively
Fig. 6. Spectral changes observed during addition of 30% H2O2. (a) Spectrum of [VVO(hap-dahp)] (1) dissolved in DMSO-d6 (ca. 4 mM), (b) after addition 1 eq. of 30% H2O2, (c)
after addition of 2 eq. of 30% H2O2, (d) after addition of 3 eq. of 30% H2O2, (e) after addition of 4 eq. of 30% H2O2, (f) after addition of 5 eq. of 30% H2O2 and (g) after adding 1 eq.
methyl phenyl sulfide to a solution of (f) or keeping the solution of (f) for 24 h.

186
M.R. Maurya et al. / Polyhedron 54 (2013) 180–188
benzaldehyde
styrene oxide
phenyl acetaldehyde
benzoic acid
phenylethylene1,2-diol
O
90
90
80
70
60
50
40
30
20
10
0
Conversion
Phenylacetaldehyde
(phaa)
80
70
60
50
40
30
20
10
O
HO
OH
Catalyst
H2O2
1-phenylethane-1,2-diol
(phed)
Styreneoxide
(s o)
Styrene
O
HO
O
1
2
3
4
5
6
7
8
Time/ h
Benzoic acid
(bzac)
Benzaldehyde
(bza)
Fig. 7. Conversion of styrene and variation in the selectivity of different reaction
products as a function of time using [VVO(hap-dahp)]-Y as the catalyst.
Scheme 3. Oxidation products of styrene with H2O2 catalyzed by [VVO(hap-dahp)]-
Y(2).
The encapsulated catalyst, separated from the reaction mixture
after catalytic action, was washed with acetonitrile, dried and sub-
jected to further catalytic reaction for the oxidation of styrene un-
der similar conditions. The obtained results are presented in
Table 5. It is clear from the table that the catalyst partially loses
its catalytic activity during the recycling process. Nevertheless,
the selectivity order is nearly maintained.
Table 4
Conversion of 10 mmol (1.04 g) of styrene using [VVO(hap-dahp)]-Y (2) as catalyst in
a reaction time of 8 h under different reaction conditions.
Entry
No.
Catalyst
(g)
Temp.
(°C)
H2O2 (g,
mmol)
CH3CN
(ml)
Conv.
(%)
1
2
3
4
5
6
7
8
9
0.010
0.010
0.010
0.005
0.015
0.010
0.010
0.010
0.010
80
80
80
80
80
80
80
60
70
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
10
10
10
10
10
5
15
15
15
53.2
71.5
75.9
34.3
75.3
52.7
82.0
48.3
69.0
The neat complex [VVO(hap-dahp)] (1), taking the same mole
concentration as that used for the encapsulated complex, also
exhibits a very comparable conversion of 78%, with a very similar
selectivity of the different products (Table 5) as obtained by the
encapsulated complex. A blank reaction under the above reaction
conditions gave around 4% conversion. Thus, the neat complex as
well as the encapsulated complex show good performance, but
the possibility of the formation of oligomeric inactive species
[40] and easier hydrolysis of the neat complex in the presence of
aqueous H2O2 relative to the encapsulated counterpart, and the
recyclable nature as well as higher stability along with higher
TOF value of the encapsulated complex make it significantly better
over the neat complex.
through hydrolysis of styrene oxide with water present in H2O2
[13].
The conversion of styrene and the selectivity of the different
reaction products using [VVO(hap-dahp)]-Y as a catalyst under
the optimized reaction conditions have been analyzed as a function
of time and the results are presented in Fig. 7. It is clear from the
plot that a selectivity of 80% of benzaldehyde has been obtained
at a conversion of 15% of styrene in 1 h of reaction time. This selec-
tivity slowly decreases with time and reaches 50% with an increase
of the conversion of styrene to 82.0% in 8 h. The selectivity of sty-
rene oxide (5%) and benzoic acid (3%) are relatively low and re-
mains nearly constant over the conversion of styrene with time,
while the formation of the other two products (i.e. 1-phenyle-
thane-1,2-diol and phenyl acetaldehyde) are initially low, but
slowly improve and reach 25% and 15%, respectively after 8 h of
reaction time.
3.9.2. Oxidation of methyl phenyl sulfide and diphenyl sulfide
The sulfur atom of the organic sulfide is electron rich and
undergoes electrophilic oxidation catalyzed by several vanadium-
dependent haloperoxidases [6,41,42] and model vanadium com-
plexes [24]. Such oxidations of methyl phenyl sulfide and diphenyl
sulfide were tested using [VVO(hap-dahp)]-Y (2) as the catalyst and
the corresponding sulfoxide as well as the sulfone were obtained,
as shown in Scheme 4.
Again, the reactions were carried out under various conditions
using 10 mmol (1.24 g) of methyl phenyl sulfide while varying
the amount of catalyst (0.005, 0.0075 and 0.010 g), aqueous 30%
Table 5
Effect of catalysts on the oxidation of styrene, TOF and the product selectivity.
Catalyst
Substrate: oxidant ratio
Conv. (%)
TOF (hꢂ1
)
Selectivity (%)a
bza
so
phea
bzac
phed
[VVO(hap-dahp)] (neat)
[VVO(hap-dahp)]-Y
[VVO(hap-dahp)]-Yb
[VVO(hap-dahp)]-Yc
Without catalyst
1:2
1:2
1:2
1:2
1:2
78
82
79
77
4
308
323
–
–
–
50
49
55
59
82
2
6
5
5
4
15
15
14
12
7
7
5
4
5
3
26
25
22
19
4
a
b
c
For abbreviations see Scheme 3.
First cycle of used catalyst.
Second cycle of used catalyst.

M.R. Maurya et al. / Polyhedron 54 (2013) 180–188
187
Table 7
O
S
O
O
Oxidation of methyl phenyl sulfide, conversion, TOF and product selectivity using the
encapsulated and neat catalysts.
S
S
Catalyst
H2O2
R
R
R
+
Catalyst (g)
TOF (hꢂ1
)
Conversion (%)
Selectivity (%)a
R = CH3, C6H5
mpso
mpsn
[VVO(hap-dahp)]-Y
[VVO(hap-dahp)]-Yb
[VVO(hap-dahp)]-Yc
[VVO(hap-dahp)]
Blank
1036
–
–
1000
–
98
97
96
95
20
77
74
75
78
79
23
26
25
22
21
Scheme 4. Oxidation of methyl phenyl sulfide and diphenyl sulfide with H2O2
catalyzed by [VVO(hap-dahp)]-Y (2).
Table 6
a
b
c
Abbreviations: mpso = methyl phenyl sulfoxide, mpsn = methyl phenyl sulfone.
First cycle of used catalyst.
Second cycle of used catalyst.
Conversion of methyl phenyl sulfide (1.24 g, 10 mmol) using [VO(hap-dahp)]-Y (2) as
the catalyst in 3 h of reaction time under different reaction conditions.
Entry No.
Catalyst (g)
H2O2 (g, mmol)
CH3CN (ml)
Conversion (%)
1
2
3
4
5
6
7
8
0.0075
0.0075
0.0075
0.0075
0.005
0.010
0.010
0.010
1.14, 10
1.71, 15
2.27, 20
2.84, 25
2.27, 20
2.27, 20
2.27, 20
2.27, 20
10
10
10
10
10
10
05
15
68
73
82
83
70
98
82
98
Table 8
Conversion of diphenyl sulfide (1.86 g, 10 mmol) using [VO(hap-dahp)]-Y (2) as the
catalyst in a reaction time of 7 h under different reaction conditions.
Entry No.
Catalyst (g)
H2O2 (g, mmol)
CH3CN (ml)
Conversion (%)
1
2
3
4
5
6
7
0.005
0.0075
0.010
0.0075
0.0075
0.0075
0.0075
1.14, 10
1.14, 10
1.14, 10
1.14, 10
1.14, 10
1.71, 15
2.27, 20
10
10
10
15
20
15
15
48.0
66
55
81
71
59
39
H2O2 (10, 15, 20 and 25 mmol) and solvent (acetonitrile) volume
(5, 10 and 15 ml), and the reaction was carried out at room temper-
ature to obtain the maximum oxidation of the substrate. Table 6
(and Figs. S4 and S5 of the Supporting information) summarizes
all the conditions and the conversion obtained under a particular
set of conditions.
overall selectivity of sulfone is only 23% and of sulfoxide it is 77% at
a conversion of 98% at the end of 3 h.
Entry 6 of Table 6 presents the optimized reaction conditions
for 10 mmol of methyl phenyl sulfide, which are: substrate
(1.24 g, 10 mmol), H2O2 (2.27 g, 20 mmol), [VVO(hap-dahp)]-Y
(0.010 g) and CH3CN (10 ml). The percent conversion of methyl
phenyl sulfide under the optimized reaction conditions and the
selectivity of the reaction products as a function of time are shown
in Fig. 8. It is clear from the plot that both the products start to
form with the conversion of methyl phenyl sulfide. However, the
initial selectivity of 78% for methyl phenyl sulfoxide at 71% conver-
sion of methyl phenyl sulfide in first half an hour moves towards
the lower side for the initial 2 h and then partly improves and
reaches 77% after 3 h of reaction time. Thus, the initially formed
sulfoxide further reacts with H2O2 present in the reaction mixture
to give sulfone, but this reaction slowly suppresses after ca. 2 h and
the selectivity for the formation of sulfoxide further improves. The
The recycled encapsulated catalyst, after reactivating, was fur-
ther used for the oxidation of methyl phenyl sulfide under similar
conditions as mentioned above and the obtained results are pre-
sented in Table 7. It is clear from the table that the catalyst only
partially loses its catalytic activity during recycling process. A
blank reaction under similar conditions gave only 20% conversion.
The neat complex [VVO(hap-dahp)] (1) also exhibits very good con-
version (95%) of methyl phenyl sulfide, with a very similar selectiv-
ity of the different products as obtained by the encapsulated
complex. However, the recyclable nature and higher turnover fre-
quency (TOF) value of the encapsulated catalyst make it better over
the neat complex.
Similarly for the oxidation of diphenyl sulfide, three different
amounts of catalyst [VVO(hap-dahp)]-Y, oxidant and volume of sol-
vent (acetonitrile) (see Table 8 and Figs. S6–S8) were considered
100
95
90
85
80
75
70
80
70
60
50
40
30
20
100
80
70
60
90
80
70
% Conversion
methyl phenyl sulfoxide
methyl phenyl sulfone
60
50
40
30
20
10
% Conversion
Diphenyl sulfoxide
50
40
30
20
Diphenyl sulfone
30
60
90
120
150
180
1
2
3
4
5
6
7
Time/ min
Time/ h
Fig. 8. Plots showing the percentage conversion of methyl phenyl sulfide, and the
selectivity of the formation of methyl phenyl sulfoxide and methyl phenyl sulfone
as a function of time. Reaction conditions: methyl phenyl sulfide (1.24 g, 10 mmol),
H2O2 (2.27 g, 20 mmol), [VVO(hap-dahp)]-Y (0.010 g) and acetonitrile (10 ml).
Fig. 9. Plot showing the percentage conversion of diphenyl sulfide and the
selectivity of diphenyl sulfoxide and dipheny sulfone formation as a function of
time. Reaction conditions: diphenyl sulfide (1.86 g, 10 mmol), H2O2 (1.14 g,
10 mmol), [VVO(hap-dahp)]-Y (0.0075 g) and 15 ml acetonitrile.

188
M.R. Maurya et al. / Polyhedron 54 (2013) 180–188
Table 9
S1/IC-32/2010). MB acknowledges the Council of Scientific and
Industrial Research (CSIR) for a NET–Junior Research fellowship.
Effect of different catalysts on the oxidation of diphenyl sulfide, conversion, TOF and
product selectivity.
Catalyst (g)
TOF (hꢂ1
)
Conversion (%)
Selectivity (%)a
Appendix A. Supplementary material
dpso
dpsn
[VVO(hap-dahp)]-Y
[VVO(hap-dahp)]-Yb
[VVO(hap-dahp)]-Yc
[VVO(hap-dahp)]
Blank
488
–
–
450
–
81
77
75
75
5
82
80
79
85
90
18
20
21
15
10
CCDC 888645 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: +44 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.poly.2013.02.036.
a
b
c
Abbraviations: dpso = diphenyl sulfoxide, dpsn = diphenyl sulfone.
First cycle of used catalyst.
Second cycle of used catalyst.
References
and the reaction was carried out at room temperature. For
10 mmol (1.86 g,) of diphenyl sulfide, 0.075 g of catalyst and a H2-
O2:diphenyl sulfide molar ratio of 1:1 in 15 mL of acetonitrile, the
reaction was found to give a maximum of 81% conversion of diphe-
nyl sulfide in 7 h of reaction time at room temperature. The selec-
tivity of sulfoxide and sulfone at this conversion is 82% and 18%,
respectively.
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4. Conclusions
The oxidovanadium(V) complex [VVO(hap-dahp)] (1), where
H3hap-dahp is the O3N2 donor Schiff base obtained by the conden-
sation of 2-hydroxyacetophenone and 1-3-diamino-2-hydroxypro-
pane, has been synthesized and its molecular structure determined
by single-crystal X-ray diffraction, confirming its distorted octahe-
dral geometry. Complex 1 has been encapsulated in the super
cages of zeolite Y and used as a catalyst for the oxidation of sty-
rene, methyl phenyl sulfide and diphenyl sulfide with aqueous
H2O2 as an oxidant. A maximum of 82% conversion of styrene
has been achieved under optimized reaction conditions, where
the selectivity of the obtained five reaction products varies in the
order: benzaldehyde (49%) > 1-phenylethane-1,2-diol (25%) > ben-
zoic acid (15%) > styrene oxide (6%) > phenylacetaldehyde (5%).
Under the optimized reaction conditions, a maximum of ca. 98%
conversion of methyl phenyl sulfide, and ca. 81% of diphenyl sul-
fide has been achieved with significant amounts of the correspond-
ing sulfoxide. The neat complex [VVO(hap-dahp)] is also a good
catalyst for these substrates, along with a similar selectivity for
the various products, but with significantly lower turnover fre-
quencies. The encapsulated complex is recyclable at least up to
two cycles of catalytic oxidation, but with a partial loss of activity.
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Acknowledgements
M.R.M. is thankful to the Department of Science and Technol-
ogy, Government of India, New Delhi for financial assistance (SR/