Synthesis and characterisation of polymer-anchored oxidovanadium(IV) complexes and their use for the oxidation of styrene and cumene

Article abstract of DOI:10.1002/ejic.200601130

The Schiff bases H₂fsal-ea (I), H₂fsal-pa (II) and H₂fsal-amp (III), derived from 3-formylsalicylic acid and 2-aminoethanol, 3-aminopropanol and 2-amino-2-methylpropanol, respectively, have been connected, by means of covalent bonds, to chloromethylated polystyrene cross-linked with 5% divinylbenzene. On treatment with [VO(acac)₂] in dimethylformamide (DMF), these polymer-anchored ligands PS-H₂fsal-ea (IV), PS-H₂fsal-pa (V) and PS-H₂fsal-amp (VI) gave the oxidovanadium(IV) complexes, PS-[VO(fsal-ea)·DMF] (4), PS-[VO(fsal-pa)·DMF) (5) and PS-[VO(fsal-amp)·DMF] (6), respectively. The corresponding neat complexes [VO(fsal-ea)]₂ (1), [VO(fsal-pa)]₂ (2) and [VO(fsal-amp)]₂ (3) have also been similarly prepared. These complexes all exhibit a medium intensity band between 964 and 993 cm^-1 in their IR spectra resulting from the V=O stretch. The EPR spectra of the polymer-anchored complexes are characteristics of monomelic V^IV centres with a simple S = 1/2 electronic spin and with an axial pattern typical of square pyramidal geometry. Broad features for the neat complexes along with magnetic susceptibility studies suggest the presence of antiferromagnetic exchange interactions between two vanadium centres in close proximity. These catalysts have been tested for the oxidation of styrene and cumene and were found to be efficient. Styrene gives five reaction products namely styrene epoxide, benzaldehyde, 1-phenylethane-1,2-diol, benzoic acid and phenylacetaldehyde, whereas cumene gives acetophenone, 2-phenylpropanal, α-methyl styrene epoxide, 2-phenyl-2-propanol, 2-isopropyl-1,4- benzoquinone and α-methyl styrene. The polymer-anchored heterogeneous catalysts are recyclable. The catalytic activities of the neat complexes have also been examined and compared with the corresponding anchored analogues. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200601130

FULL PAPER
DOI: 10.1002/ejic.200601130
Synthesis and Characterisation of Polymer-Anchored Oxidovanadium(IV)
Complexes and Their Use for the Oxidation of Styrene and Cumene
[a]
[a]
[b]
Mannar R. Maurya,* Umesh Kumar, and P. Manikandan
Keywords: Vanadium(IV) complexes / Polymer support / Heterogeneous catalysts / Oxidations
The Schiff bases H
2
fsal-ea (I), H
2
fsal-pa (II) and H
2
fsal-amp
with an axial pattern typical of square pyramidal geometry.
Broad features for the neat complexes along with magnetic
susceptibility studies suggest the presence of antiferromag-
netic exchange interactions between two vanadium centres
in close proximity. These catalysts have been tested for the
oxidation of styrene and cumene and were found to be ef-
ficient. Styrene gives five reaction products namely styrene
epoxide, benzaldehyde, 1-phenylethane-1,2-diol, benzoic
acid and phenylacetaldehyde, whereas cumene gives aceto-
phenone, 2-phenylpropanal, α-methyl styrene epoxide, 2-
phenyl-2-propanol, 2-isopropyl-1,4-benzoquinone and α-
methyl styrene. The polymer-anchored heterogeneous cata-
lysts are recyclable. The catalytic activities of the neat com-
plexes have also been examined and compared with the cor-
responding anchored analogues.
(
III), derived from 3-formylsalicylic acid and 2-aminoethanol,
3-aminopropanol and 2-amino-2-methylpropanol, respec-
tively, have been connected, by means of covalent bonds, to
chloromethylated polystyrene cross-linked with 5% divi-
nylbenzene. On treatment with [VO(acac)
amide (DMF), these polymer-anchored ligands PS-H
IV), PS-H fsal-pa (V) and PS-H fsal-amp (VI) gave the ox-
idovanadium(IV) complexes, PS-[VO(fsal-ea)·DMF] (4), PS-
VO(fsal-pa)·DMF] (5) and PS-[VO(fsal-amp)·DMF] (6),
respectively. The corresponding neat complexes [VO(fsal-
ea)] (1), [VO(fsal-pa)] (2) and [VO(fsal-amp)] (3) have also
2
] in dimethylform-
2
fsal-ea
(
2
2
[
2
2
2
been similarly prepared. These complexes all exhibit a me-
dium intensity band between 964 and 993 cm– in their IR
spectra resulting from the V=O stretch. The EPR spectra of
the polymer-anchored complexes are characteristics of mo-
1
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
IV
nomeric V centres with a simple S = ½ electronic spin and
Introduction
The catalytic potential of [VO(sal-ohyba)] and [K(H O)][-
2
VO (sal-ohyba)] (H sal-ohyba = Schiff base derived from
salicylaldehyde and o-hydroxybenzylamine) for the oxi-
Advances in the coordination chemistry of vanadium
with multidentate ligands stem from the discovery of the
vanadium containing enzymes, namely vanadate-dependent
2
2
dation and oxidative bromination of organic substrates has
[
9]
[
1]
[2]
been recently investigated in our group. The stability and
potential of these complexes to be recycled were improved
remarkably by immobilizing them onto a polymer support.
For the development of industrial processes, such modifica-
tions to homogeneous catalysts would be very important
and this, in addition, would lead to operational flexibility
haloperoxidases, vanadium nitrogenases and vanadium
containing nitrate reductases.[3] Vanadate-dependent halo-
peroxidases catalyse the peroxide mediated oxidation of ha-
lides to hypohalous acid which further halogenates hydro-
carbons in a non-enzymatic process.[4] Many vanadium
complexes provide a suitable structural and/or functional
[
10]
model for these enzymes.[
5,6]
of the catalyst as well.
Recently, Ando et al. reported
Oxidations of aliphatic as well
oxidovanadium(IV) complexes covalently bonded to Merri-
field resin as a heterogeneous catalysts for the oxidation of
as aromatic substrates including (prochiral) organic sulfides
to (chiral) sulfoxides, catalysed by vanadium complexes,
[
11]
have also been achieved in excellent yield.[
7,8]
organic sulfide selectively.
In continuation of our efforts on the development of
polymeric supported/anchored vanadium complexes and
their catalytic potential, we report herein the preparation
and characterisation of polymer-anchored oxidovanadi-
[
[
a] Department of Chemistry, Indian Institute of Technology
Roorkee,
Roorkee 247667, India
E-mail: rkmanfcy@iitr.ernet.in
b] Catalysis and Inorganic Chemistry Division, National Chemi- um(IV) complexes of ligands I, II and III, Scheme 1, along
cal Laboratory,
Pune 411008, India
with their neat complexes. The catalytic potential of these
complexes has been demonstrated by studying the oxidation
of styrene and cumene.
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2007, 2303–2314
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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M. R. Maurya, U. Kumar, P. Manikandan
FULL PAPER
These anchored ligands react with [VO(acac) ] in DMF
2
at ca. 90 °C to give the polymer-anchored oxidovanadi-
um(IV) complexes PS-[VO(fsal-ea)·DMF] (4), PS-[VO(fsal-
pa)·DMF] (5) and PS-[VO(fsal-amp)·DMF] (6) which are
dark green in colour. Equation (1) represents the synthetic
procedure.
(
1)
Scheme 1.
Similarly, the reaction of [VO(acac) ] with an equimolar
2
amount of the neat ligands I, II and III in acetonitrile at
reflux yields the neat oxidovanadium(IV) complexes
Results and Discussion
[
(
VO(fsal-ea)]2 (1), [VO(fsal-pa)]2 (2) and [VO(fsal-amp)]2
3), respectively. The neat complexes exhibit effective mag-
Synthesis, Reactivity and Solid-State Characteristics
The elemental and spectroscopic data (IR, H and 13C netic moments of 1.31 (for 1), 1.34 (for 2) and 1.49 µ (for
1
B
NMR) of the ligands H fsal-ea (I), H fsal-pa (II) and 3) at 298 K which are lower than the expected value of
2
2
1
H fsal-amp (III) used in the present study, described in the 1.73 µ for a d (S = ½) system. We have also studied the
2
B
experimental section, confirm the structures of ligands. The magnetic susceptibilities of these complexes as a function
chloromethylated polystyrene, cross-linked with 5% divi- of temperature in the 298–90 K range. Figure 1 shows a plot
corr
nylbenzene, reacts with these ligands in DMF in the pres- of the magnetic susceptibility χM
as a function of tem-
ence of triethylamine to give the polymer-anchored ligands perature for 1. The χMcorr values show a slight dependence
PS-H fsal-ea(IV), PS-H fsal-pa (V) and PS-H fsal-amp on temperature, the observed magnetic moment values
2
2
2
(
VI), respectively. During this process the -COOH group varied in the range 1.31–1.15 µ and the Curie–Weiss plot
B
corr
of 3-formylsalicylic acid reacts with the -CH Cl group of [1/χM
vs. T], as shown in Figure 2, was found to be a
2
polystyrene. Covalent bonding through the -COOH group straight line with a Weiss constant of –40. Similarly, the
of the ligand has been further demonstrated by treating magnetic moment values of 2 and 3 varied in the ranges
benzylchloride with H fsal-ea (I) under the above reaction 1.34–1.10 and 1.49–1.23 µ , respectively, with Weiss con-
2
B
conditions. Scheme 2 depicts the structures of the ligands stant values of ca. –50. These data all indicate an antiferro-
isolated; a representative synthetic procedure for IV is also magnetic interaction possibly due to dimerisation of the
[
12,13]
shown. The remaining chlorine content of 1.7% (0.49 mmol complexes.
Based on the variations in magnetic mo-
Cl/g of resin) in PS-H fsal-ea, 1.8% (0.51 mmol Cl/g of ments with temperature and the spectroscopic studies of,
2
resin) in PS-H fsal-pa and 2.2% (0.62 mmol Cl/g of resin) for example, complexes [VO(X-sal-ea)] (where X-sal-ea =
2
2
in PS-H fsal-amp suggested roughly a 90% load of the li- Schiff bases derived from salicylaldehyde and 2-amino-
2
gands.
ethanol or 3-aminopropanol, X = 5-Cl, 5-Br, 5-NO , 3-NO ,
2 2
Scheme 2. Synthetic procedure for IV only; PS represents the backbone of chloromethylated polystyrene.
2304
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 2303–2314

Polymer-Anchored Oxidovanadium(IV) Complexes
FULL PAPER
5
-OMe, 3-OMe), Syamal et al. suggested antiferromagnetic
[14]
exchange interactions along with a dimeric structure.
Thus, the dimeric structure as shown in Scheme 3 for the
neat complexes may also be proposed here. A dimeric struc-
ture for [VO(sal-ea)] has been confirmed by a single-crystal
2
[
15]
X-ray diffraction study.
Scanning Electron Micrograph
Scanning electron micrographs (SEM) for a single bead
of pure chloromethylated polystyrene, the polymer-an-
chored ligand and the polymer-anchored vanadium com-
plexes were recorded in order to observe the morphological
changes. Images of PS-H fsal-ea (IV) and PS-[VO(fsal-ea)·
2
DMF] (4) are reproduced in Figure 3. As expected, the pure
polystyrene bead has a smooth and flat surface while the
anchored ligands and complexes show a very slight rough-
ening of the top layer. This roughening is relatively greater
in the complexes possibly due to the interaction of vana-
dium with the anchored ligand which resulted in the forma-
tion of complexes with a fixed geometry. Accurate infor-
mation on the morphological changes in terms of the exact
orientation of the ligands coordinated to the metal ion has
not been possible due to poor loading of the metal complex.
corr
Figure 1. Plot of the magnetic susceptibility χ
for [VO(fsal-ea)] (1).
m
vs. temperature
2
Figure 3. Scanning Electron Micrographs (SEM) of PS-H
2
fsal-ea
corr
Figure 2. Curie–Weiss plot [1/χ
m
2
vs. T] for [VO(fsal-ea)] (1).
(
IV) and PS-[VO(fsal-ea)·DMF] (4); magnification ca. ϫ200.
TGA Study
Thermogravimetric analyses in an oxygen atmosphere
showed good stabilities for polymer-anchored complexes 4,
5
and 6 up to ca. 175 °C. The first weight loss starting just
above 175 °C is possibly due to the loss of coordinated
DMF. The complexes, thereafter, decompose in multiple
steps. Quantitative measurement of weight loss at various
stages was not possible due to the overlapping nature of the
decompositions. However, the stabilities of the final resi-
dues at ca. 700 °C suggest the formation of V O . The metal
2
5
content calculated from the final residue in each case was
close to that recorded by atomic absorption spectroscopy.
IR Spectroscopic Study
The experimental section contains a partial list of the IR
spectroscopic data of all ligands and complexes. The chlo-
romethylated polystyrene exhibits strong peaks at 1264 and
Scheme 3. Proposed structure for neat oxidovanadium(IV) com-
plexes.
Eur. J. Inorg. Chem. 2007, 2303–2314
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2305

M. R. Maurya, U. Kumar, P. Manikandan
FULL PAPER
6
73 cm–1 due to CH Cl group and the absence of these
2
peaks in the polymer-anchored ligands suggests covalent
bonding of the chloromethylated polystyrene to the li-
[
16]
gands.
A sharp band due to ν(C=O) of the carboxylate
–
1
group appears at 1670–1676 cm in the polymer-anchored
ligands and complexes. In the corresponding neat ligands
and complexes, this band appears at either the same or a
slightly lower wavenumber. The ν(C=N) (azomethine)
stretch of the neat ligands mostly appears along with the
ν(C=O). However, a sharp peak due to the ν(C=N) (azo-
methine) stretch is observable in the spectra of the corre-
sponding complexes at a lower wavenumber. The polymer-
anchored ligands show a medium intensity band at 1630–
–
1
1
635 cm and this band shifts to a lower wavenumber by
–
1
ca. 30 cm in the complexes thereby indicating the coordi-
nation of the azomethine nitrogen atom. The coordination
Figure 4. Emission spectra of complexes [VO(fsal-ea)]
2
(1),
of phenolic oxygen could not be assigned unequivocally in [VO(fsal-pa)] (2) and [VO(fsal-amp)] (3) recorded in methanol at
2
2
ambient temperature.
most complexes because of the appearance of a weak broad
–
1
band in the 3400 cm region. Similarly, coordination of
DMF in 4, 5 and 6 could not be possible because of the
strong ν(C=O) absorption band of the carboxylate in the
same region. In addition to this, all the complexes exhibit a
sharp ν(V=O) band in the 964–993 cm–1 region.[6]
EPR Spectroscopic Study
The room temperature X-band EPR spectra of the poly-
mer-anchored samples are reproduced in Figure 5. They are
characteristics of monomeric V centres with a simple S =
IV
½
electronic spin and a typical axial pattern for a possible
square pyramidal geometry, Scheme 4. The hyperfine fea-
tures are well resolved in both the parallel and perpendicu-
lar regions. These resolved hyperfine features reflect the fact
that the vanadium centres are well separated by the polymer
backbones which causes least dipolar vanadium–vanadium
coupling. Such arrangements generally broaden the EPR
pattern. The hyperfine lines are typical for an interaction of
the unpaired electron of the vanadium(IV) ion with its nu-
cleus, 51V having a high abundance of 99.75% and a nuclear
Electronic and Fluorescence Spectroscopic Studies
The electronic spectra of the neat and anchored com-
plexes in Figure S1 and relevant data in Table S2 are given
in the Supporting Information (see also the footnote on the
first page of this article). The spectroscopic patterns shown
by the neat as well as the supported ligands are essentially
the same except for the broadness of the bands in nujol.
The expected charge-transfer band at ca. 400 nm could not
be distinguished due to the appearance of an nǞπ* transi-
tion in the same region. In addition, two additional weak
bands at ca. 570 and 690 nm were observed for neat com-
plexes in DMF due to d-d transitions thus indicating the
presence of a vanadium(IV) ion at the centre.
The fluorescence excitation and emission spectra of
1
0–6  methanolic solution of oxidovanadium(IV) com-
plexes 1, 2 and 3 were recorded at room temperature and
are presented in Figure 4. All neat complexes have approxi-
mately the same chromophore units and exhibit similar
spectroscopic patterns. On excitation at 257 nm (in the UV
region) complex 1 exhibited a strong band at λmax = 483 nm
(
in the visible region) with a shoulder band at 556 nm and,
on excitation at 387.5 nm, exhibited a broad peak with λmax
501 nm. In the case of complexes 2 and 3, excitation at
58 (in 2) and 255 (in 3) nm gave emission bands at 464
=
2
and 466 nm, respectively, along with weak shoulder bands
at 517 and 554 nm. Similarly, broad peaks at 503 (in 2) and
5
3
5
02 nm (in 3) were obtained with excitation at 382 and
85.5 nm, respectively. As, expected, the overtone at ca.
10 nm was observed as a sharp band in all complexes. All
Figure 5. Room temperature EPR spectra of polymer-anchored
complexes (a) PS-[VO(fsal-ea)·DMF] (4), (b) PS-[VO(fsal-pa)·
DMF] (5), (c) PS-[VO(fsal-amp)·DMF] (6) and (d) PS-[VO(fsal-pa)·
DMF] (5) (recovered); the microwave frequency was 9.4458 GHz.
these spectroscopic patterns hint towards the photo-cata-
lytic utility of these complexes.
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Polymer-Anchored Oxidovanadium(IV) Complexes
spin I = 7/
FULL PAPER
. The anisotropic EPR spectrum of the VIV ion
The EPR spectra for the neat compounds were also re-
2
with g Ͻ g and A Ͼ A is characteristic of square pyram- corded and are reproduced in Figure 6. The broad spectro-
ʈ
Ќ
ʈ
Ќ
idal complexes with possible C4v symmetry in which the scopic features are typical for dimeric or polymeric species
V=O bond is along the z axis and the other four coordinat- with dipolar interactions or exchange interactions with
ing atoms are along the x and y axes.[ Simulation of the V –V pairs with spin S = 1.
17]
4+
4+
[18]
In the absence of any
EPR spectra was carried to extract the Hamiltonian param- hyperfine features, the spectra could be best fitted by super-
4+
4+
eters and the resultant parameters are given in Table 1. As imposing features of at least two V –V pairs having
seen in the table and Figure 5, the Hamiltonian parameters slightly different environments with different zero-field
are more or less the same for the all three polymer-anchored splitting parameters, D and E, and the resultant parameters
samples indicating that local symmetry and environments are given in Table 1. As seen in the table, one of the V –
around the V centres are more or less the same.
4+
4+
V
pairs has a D value in the range 1850–1900 MHz and
an E value of 500 MHz indicating a strong rhombic distor-
tion site. The other species could be fitted with D in the
range 1250–1350 MHz with no E splitting thus indicating
less distortion. The broad features in the EPR spectra for
the complexes [VO(X-sal-ea)] (X = 5-Cl, 5-Br, 5-NO , 5-
2
2
OMe, 3-OMe) have also been noted previously and inter-
preted on the basis of the presence of antiferromagnetic ex-
change interactions between two vanadium centres in close
[
12–14]
proximity.
Scheme 4. Possible structure for polymer-anchored complexes.
After carrying out the catalytic reactions, the polymer-
anchored catalysts were filtered, washed with acetonitrile
and dried. The EPR spectra were then recorded under iden-
tical conditions. The EPR spectrum for one of the recovered
catalysts, PS-[VO(fsal-amp)·DMF] (6), is also reproduced in
Figure 5 as a representative example. The EPR spectra of
the recovered (spent) samples were only slightly different
from the fresh samples indicating the environment and co-
ordination geometry of the vanadium centres is retained to
the maximum extent after the catalytic reaction. A slight
increase in the A component for the recovered catalyst can
ʈ
be observed from 18.6 mT to 18.8 mT. A higher A value is
ʈ
generally due to reduced delocalisation of the paramagnetic
electron density of the V centre indicating a slight displace-
ment in the coordinating atom of the ligand. In other
words, the vanadium–nitrogen bond is slightly weaker than
that in the neat compound.
Figure 6. Room temperature EPR spectra of neat complexes (a)
[VO(fsal-ea)] (1), (b) [VO(fsal-pa)] (2) and (c) [VO(fsal-amp)] (3).
2
2
2
Table 1. Spin Hamiltonian parameters for the calculated EPR spectra: g-tensors (g
parameters (D, E).
ʈ
, g
Ќ
), hyperfine tensors (A
ʈ
Ќ
, A ), zero-field splitting
Compound
Spectrum
g
ʈ
(giso
)
g
Ќ
A
(
ʈ
(Aiso
mT)
)
A
(mT)
Ќ
D
(MHz)
E
(MHz)
PS-[VO(fsal-ea)·DMF] (4)
1
1
1
1
1
2
1
2
1
2
1.945
1.945
1.945
1.943
1.955
1.940
1.975
1.940
1.975
1.940
1.999
1.999
1.999
1.999
–
–
–
–
–
–
18.6
18.4
18.6
18.8
–
–
–
–
–
–
7
7
7
7
–
–
–
–
–
–
–
–
–
–
1250
1190
1150
1850
1350
1850
–
–
–
–
0
500
0
500
0
PS-[VO(fsal-pa))·DMF] (5)
PS-[VO(fsal-amp))·DMF] (6)
PS-[VO(fsal-pa))·DMF] (5) (recovered)
[
[
[
VO(fsal-ea)]
2
(1)
VO(fsal-pa)]
2
(2)
VO(fsal-amp)]
2
(3)
500
Eur. J. Inorg. Chem. 2007, 2303–2314
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2307

M. R. Maurya, U. Kumar, P. Manikandan
FULL PAPER
Catalytic Activity Study
97.3%, respectively, at the end of the 6 h. Thus, at the ex-
pense of H O , 0.040 g of catalyst was found to be sufficient
2
2
The catalytic potential of the polymer-anchored as well
as the neat complexes were studied for the oxidation of sty-
rene and cumene.
to carry out the reaction. The temperature of the reaction
mixture also influenced the performance of the catalyst.
Figure 9 shows the effect of the reaction temperature on the
performance of the catalysts and at 80 °C a much better
conversion was achieved.
Oxidation of Styrene
Oxidation of styrene catalysed by the polymer-anchored
complexes PS-[VO(fsal-ea)·DMF] (4), PS-[VO(fsal-pa)·
DMF] (5) and PS-[VO(fsal-amp)·DMF] (6) gave styrene ox-
ide, benzaldehyde, benzoic acid, phenylacetic acid and 1-
phenylethane-1,2-diol as indicated in Scheme 5. These reac-
tion products are common and have also been identified
earlier by other workers.[
19–21]
Figure 7. Effect of amount of H
Reaction conditions: styrene (1.04 g, 10 mmol), PS-[VO(fsal-pa)·
DMF] (5) (0.040 g), CH CN (10 mL) and temp. (80 °C).
2 2
O on the oxidation of styrene.
3
Scheme 5.
Complex 5 was taken as a representative amongst these
catalysts and its catalytic activity was studied as a function
of the amount of H O (mol of H O per mol of styrene)
2
2
2
2
and catalyst as well as the temperature of the reaction mix-
ture. These parameters were varied in order to obtain suit-
able reaction conditions for the maximum oxidation of sty-
rene. Reactions were carried out with three different molar Figure 8. Effect of amount of catalyst on the oxidation of styrene.
Reaction conditions: styrene (1.04 g, 10 mmol), H
2 2
O (2.27 g,
ratios of 1:1, 1:1.5 and 1:2 of styrene to aqueous 30% H O2
for a fixed amount of styrene (1.04 g, 10 mmol) and catalyst
2
2
0 mmol), CH CN (10 mL) and temp. (80 °C).
3
(
0.040 g) in CH CN (10 mL) at 80 °C. The results were ana-
3
lysed periodically for up to 6 h. As illustrated in Figure 7,
a maximum conversion of 42% was achieved in 6 h with a
styrene to H O molar ratio of 1:1. On increasing the ratio
2
2
to 1:1.5 the conversion was improved to 65% while a 1:2
molar ratio showed a maximum conversion of 95%. No
further improvement in the oxidation was observed on in-
creasing the molar ratio to 1:3 (not shown in Figure) which
suggests that a large amount of oxidant is not an essential
condition for improving the oxidation of styrene. In another
experiment, three different catalyst loadings, viz. 0.030,
0
1
.040 and 0.070 g, were varied at styrene to H O ratios of
:2 under the above reaction conditions and the results are
2 2
shown in Figure 8. As seen in the figure, 0.030 g of catalyst
gave only a 52.5% conversion while catalyst loadings of
Figure 9. Effect of temperature on the oxidation of styrene. Reac-
tion conditions: styrene (1.04 g, 10 mmol), PS-[VO(fsal-pa)·DMF]
0.040 and 0.070 g showed maximum conversions of 95 and (5) (0.040 g), H
2 2 3
O (2.27 g, 20 mmol) and CH CN (10 mL).
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Polymer-Anchored Oxidovanadium(IV) Complexes
FULL PAPER
Other catalysts e.g. 4 and 6 were tested under the reac-
tion conditions as optimised above. Thus, for 10 mmol of
substrate, aqueous 30% H O (20 mmol) and catalyst
2
2
(
0.040 g) were added in CH CN (10 mL) and the reaction
3
was carried out at 80 °C. Table 2 shows a comparison of
percent conversion of styrene and the selectivity of various
reaction products along with the turnover frequency of the
catalysts. Catalyst 4 exhibits a 90% conversion of styrene
while 6 exhibits only an 82% conversion. Thus, the per-
formances of these catalysts follow the order: 5 (95%) Ͼ 4
(90%) Ͼ 6 (82%). The good performance of these catalysts
is possibly due to easy formation of peroxo species in the
presence of H O (vide infra) as well as the ease in transfer-
2
2
ring oxygen from the intermediate peroxo species to the
substrate.
We also tested the catalytic activity of the neat complexes
for the oxidation of styrene. Their performances after 6 h rene (1.04 g, 10 mmol), catalyst (0.040 g for polymer anchored and
Figure 10. Catalytic comparison of polymer-anchored and neat
complexes for the oxidation of styrene. Reaction conditions: sty-
are also presented in Table 2. Figure 10 provides conversion 0.020 g for neat complexes), H
2 2 3
O (1.27 g, 20 mmol), CH CN
(
10 mL) and temp. (80 °C).
percentages for each catalyst as a function of time. For
.020 g of each the neat vanadium complexes 1, 2 and 3,
0
and with reaction conditions fixed as above, the obtained
conversions were 65, 70 and 62%, respectively. Their calcu-
to 1-phenylethane-1,2-diol to some extent. Low formation
of styrene oxide, an important product, is understandable
because of its further conversion into other products.
–1
lated turnover frequencies vary in the range 15.3–17.6 h .
Thus, the catalytic performances of the neat complexes are
also good. However, in the light of special features e.g. easy
recovery, no leaching and the ability of the polymer-an-
chored complexes to be recycled, it may be concluded that
polymer-anchored vanadium complexes are better catalysts.
The product selectivity for the polymer-anchored com-
plexes follows the order: benzaldehyde Ͼ 1-phenylethane-
1,2-diol Ͼ benzoic acid Ͼ styrene oxide Ͼ phenylacetalde-
hyde while for the neat complexes the order is: benzalde-
hyde Ͼ benzoic acid Ͼ1-phenylethane-1,2-diol Ͼ styrene
oxide Ͼ phenylacetaldehyde. The formation of benzalde-
hyde in the highest yield is possibly due to a nucleophilic
attack of H O on styrene oxide formed in the first step
Scheme 6.
2
2
followed by a cleavage of the intermediate hydroperoxysty-
Several other polymer-anchored oxidovanadium(IV)
rene as shown in Scheme 6. Benzaldehyde formation may complexes e.g. PS-[VO(hmbmz) ] [where PS-Hhmbmz =
2
also be facilitated by direct oxidative cleavage of the styrene polymer-anchored 2-(α-hydroxymethyl)benzimidazole],[
22]
side chain double bond by a radical mechanism.[ Forma- PS-K[VO(O ) (2-pybzm)] [where 2-pybzm = 2-(2-pyridyl)-
19]
2
2
[
20]
[9]
tion of other products such as benzoic acid from benzalde- benzimidazole]
and PS-[VO(sal-ohyba)·DMF]
have
hyde is rather slow in all reactions. Similarly the formation been used as catalysts in our laboratory for the oxidation
of phenylacetaldehyde, a product formed by isomerisation of styrene. Though all these catalysts gave all five products
of styrene oxide, is less in all cases. Water present in H O2 with nearly similar selectivity patterns, the conversions with
2
is probably responsible for the hydrolysis of styrene oxide the catalysts reported here are higher.
Table 2. Turn over frequencies of various catalysts, percent conversion of styrene and product selectivities.
Catalyst
Conv. /mol-%
TOF /h–1
Selectivity /mol-%
so[a]
phaa[b]
bza
[c]
bzac
[d]
phed[e]
8.8
8.8
8.9
23.5
17.3
18.3
Others
[
[
[
VO(fsal-ea)]
VO(fsal-pa)]
VO(fsal-amp)] (3)
2
PS-[VO(fsal-ea)·DMF (4)
PS-[VO(fsal-pa)·DMF] (5)
PS-[VO(fsal-amp)·DMF] (6)
2
(1)
(2)
65
70
62
90
95
82
15.3
16.4
17.6
22.5
25.5
24.0
3.9
3.6
3.9
4.1
3.8
4.3
3.1
3.8
3.4
2.9
3.5
3.9
61.7
62.5
60.4
58.4
62.8
60.6
18.3
4.3
4.2
4.6
3.5
3.8
4.0
2
17.2
18.8
7.6
8.7
9.0
[
a] Styrene epoxide. [b] Phenylacetaldehyde. [c] Benzaldehyde. [d] Benzoic acid. [e] 1-Phenylethane-1,2-diol. Reaction conditions as men-
tioned in Figure 10.
Eur. J. Inorg. Chem. 2007, 2303–2314
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2309

M. R. Maurya, U. Kumar, P. Manikandan
FULL PAPER
Oxidation of Cumene
Similarly, for a cumene to H O ratio of 1:2, three dif-
2
2
ferent amounts of catalyst were used, viz. 0.040, 0.060 and
.080 g, under above reaction conditions and the results are
Oxidation of cumene by the polymer-anchored com-
plexes 4, 5 and 6 gave acetophenone, 2-phenylpropanal, α-
methylstyrene epoxide, 2-phenyl-2-propanol, 2-isopropyl-
0
summarised in Figure 12. An amount of 0.040 g of catalyst
gave only a 29% conversion while 0.060 g and 0.080 g of
catalyst showed maximum conversions of 41 and 44%,
respectively. Since the conversion is not significantly higher
using 0.080 g of catalyst, an amount of 0.060 g of catalyst
can be considered sufficient to carry out the oxidation.
Moreover, the turnover rates of the catalyst for the catalytic
1,4-benzoquinone and α-methylstyrene, as indicated in
Scheme 7.
conversions using 0.060 g and 0.080 g are comparable
7.32 h–1 for 0.060 g and 5.9 h for 0.080 g). As observed
–1
(
in the case of styrene oxidation, a temperature of at least
0 °C was required to carry out the above reaction effec-
8
tively. Moreover, time required in achieving the maximum
conversion was also reduced on carrying out the reaction
at 80 °C.
Scheme 7. a = acetophenone, b = 2-phenylpropanal, c = α-methyl-
styrene epoxide, d = 2-phenyl-2-propanol, e = 2-isopropyl-1,4-
benzoquinone and f = α-methylstyrene.
In order to achieve suitable reaction conditions for the
maximum oxidation of cumene, complex 5 was taken as a
representative catalyst and three different parameters were
varied, viz. the amounts of H O (mol of H O per mol of
2
2
2
2
cumene) and catalyst as well as the temperature of the reac-
tion mixture. The effect of H O concentration on the oxi-
2
2
dation of cumene is illustrated in Figure 11. A conversion
of about 13% was achieved at a cumene to 30% H O mo-
2
2
lar ratio of 1:1 in 6 h when cumene (1.20 g, 10 mmol), 30%
H O (1.14 g, 10 mmol) and catalyst (0.060 g) were placed Figure 12. Effect of amount of catalyst PS-[VO(fsal-pa)·DMF] on
2
2
the oxidation of cumene. Reaction conditions: cumene (1.20 g,
0 mmol), H (2.27 g, 20 mmol), CH CN (10 mL) and temp.
80 °C).
in acetonitrile (10 mL) and the reaction was carried out at
0 °C. This conversion improved to ca. 18% on increasing
1
(
2
O
2
3
8
the ratio to 1:1.5 and to 41% at a cumene to 30% H O2
2
molar ratio of 1:2. This oxidation remained nearly constant
on further increasing the amount of oxidant which suggests
Thus, suitable reaction conditions for the maximum oxi-
that a 1:2 (cumene to oxidant) ratio is sufficient enough to dation of cumene were fixed as follows: cumene (1.20 g,
maximise the oxidation of cumene.
10 mmol), 30% H O (2.27 g, 20 mmol), catalyst (0.060 g),
2
2
acetonitrile (10 mL) and a temperature of 80 °C. Catalysts
4
and 6 were also tested under the above optimised reaction
conditions and results are summarised in Table 3. Figure 13
shows a comparison of the percentage conversions of all
three catalysts as a function of time. The conversion per-
centages of cumene after 6 h follow the order: 5 (41%) Ͼ 4
(39%) Ͼ 6 (35%). Independent of the type of catalyst, the
percent yield of various products follow the order: aceto-
phenone Ͼ 2-phenyl-2-propanal Ͼ α-methylstyrene epoxide
Ͼ 2-phenylpropanol Ͼ 2-isopropyl-1,4-benzoquinone ≈ α-
methylstyrene.
We have also compared the catalytic activity of these
polymer-anchored complexes with their respective neat
ones. Table 3 shows a comparison of the percentage conver-
sion of cumene as well as product selectivity of various cat-
alysts obtained after a reaction time of 6 h. For 0.030 g of
each of the neat vanadium complexes and keeping other
reaction conditions fixed as above, oxidation of cumene in
Figure 11. Effect of amount of H
Reaction conditions: cumene (1.20 g, 10 mmol), PS-[VO(fsal-pa)·
DMF] (5) (0.060 g), CH CN (10 mL) and temp. (80 °C).
2 2
O on the oxidation of cumene.
3
2310
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Eur. J. Inorg. Chem. 2007, 2303–2314

Polymer-Anchored Oxidovanadium(IV) Complexes
FULL PAPER
Table 3. Percent conversion of cumene and selectivity of various oxidation products.
Catalyst
Conv. /mol-%
TOF /h–1
Selectivity /mol-%
d
a[a]
b
c
e
f
Others
[
[
[
VO(fsal-ea)]
VO(fsal-pa)]
VO(fsal-amp)]
2
(1)
(2)
25
27
21
39
41
35
3.92
4.46
3.52
6.50
7.32
6.83
62
63
66
60
63
59
18
19
17
13
13
12
10
9
8
17
14
17
4
3
3
3
4
3
3
2
2
2
2
3
2
2
3
3
2
2
1
2
1
3
1
3
2
2
(3)
PS-[VO(fsal-ea)·DMF (4)
PS-[VO(fsal-pa)·DMF] (5)
PS-[VO(fsal-amp)·DMF] (6)
[
a] a = acetophenone, b = 2-phenylpropanal, c = α-methylstyrene epoxide, d = 2-phenyl-2-propanol, e = 2-isopropyl-1,4-benzoquinone,
f = α-methylstyrene.
Proposed Mechanism
As observed earlier, the reaction of cumene proceeds by
means of a radical mechanism if molecular oxygen is used
as the oxidant. The cumene radical, formed by abstracting
the tertiary hydrogen of the cumene by a metal ion, reacts
with molecular oxygen to produce an alkyl peroxide, which
in turn abstracts hydrogen from cumene to form hydroper-
[
28,31]
oxide (Scheme 8).
The oxidant H O is likely to form
2 2
peroxidovanadium(V) species with the oxidovanadium(IV)
complexes reported here, which finally transfer oxygen to
the substrate to give the various products. As cumene hy-
droperoxide was not observed among the reaction products,
the reaction pathway either does not follow any secondary
mechanism, e.g. through radical formation, or the cumene
Figure 13. Catalytic comparison of catalysts for the oxidation of hydroperoxide, if formed at all, decomposes catalytically to
cumene. Reaction conditions: cumene (1.20 g, 10 mmol), catalyst
yield acetophenone and other products.
2 2 3
(0.060 g), H O (2.27 g, 20 mmol), CH CN (10 mL), temp. (80 °C).
the 21–27% range was observed which is less than the cor-
responding values recorded for the anchored complexes.
The percentage yields of various products follow the order:
acetophenone Ͼ 2-phenylpropanal Ͼ α-methylstyrene ep- Scheme 8.
oxide Ͼ 2-phenyl-2-propanol ≈ 2-isopropyl-1,4-benzoqui-
none ≈ α-methylstyrene. Thus, the yield of α-methylstyrene
Similarly, the formation of styrene oxide may proceed
epoxide is slightly better than 2-phenyl-2-propanal in the through the transfer of oxygen from oxidoperoxidovanadi-
case of the neat complexes. However, the selectivity as well um(V) species to styrene. The oxidoperoxido species is fi-
as the yield of the major product acetophenone is compar- nally converted to dioxidovanadium(V) and the catalytic cy-
able in all cases.
Homogeneous catalysts such as metal complexes
metalloporphyrins,
cle moves through these intermediates. These are the most
and common species observed during the catalytic action of ox-
and heterogeneous catalysts such as idovanadium(IV)/dioxidovanadium(V) complexes for most
[
23]
[
24]
[
25]
[26]
platinum metals, metal oxides, metal oxides supported oxidation reactions carried out in the presence of perox-
[
27]
[5a,7b]
on alumina
MCM-41
and metals or metal oxides supported ide.
have been used for the oxidation of cumene. that dioxidovanadium(V) species are slowly converted to
Only limited literature deals with the oxidation of cumene oxidovanadium(IV) during the washing and drying pro-
As the recovered species is EPR active, it seems
[
28]
[
29]
using polymer-supported catalysts e.g. metal salts
and cesses and exhibit EPR spectroscopic patterns similar to
supported on a that of the neat oxidovanadium(IV) complex (cf. Figure 5).
polymer. Catalytic activity of the complexes reported here To support the reaction mechanism through peroxidova-
2
+
[30]
[
Fe(phen)2] (phen = phenanthroline)
compares well with the literature data. However, cumene nadium(V) species formation, we tried the isolation of neat
hydroperoxide, in most cases, has been reported to be the peroxidovanadium(V) complexes with ligands I, II and III
major product amongst the various products formed but were unsuccessful possibly due to their poor stability
whereas we observed the formation of acetophenone with a at ambient temperature. Nevertheless, the generation of the
selectivity of 59–66%. This difference is possibly due to the oxido-monoperoxidovanadium(V) complex, [VO(O )(fsal-
2
–
use of different oxidants as well as different metal centres pa)] has been established in methanol by electronic absorp-
in catalysts.
tion spectroscopy. In a typical reaction, 10 mL of a ca.
Eur. J. Inorg. Chem. 2007, 2303–2314
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2311

M. R. Maurya, U. Kumar, P. Manikandan
FULL PAPER
1
ϫ10–4  solution of [VO(fsal-pa)] (2) was treated with catalyst during the catalytic reaction. No further oxidation
2
one drop portions of 30% H O dissolved in methanol and of substrates on removal of the solid catalysts is consistent
2
2
the resultant spectroscopic changes are presented in Fig- with a heterogeneous process.
ure 14 Thus, the intensity of the 390 nm band increases
slowly along with a corresponding shift to 399 nm by drop-
wise addition of H O dissolved in methanol. The shoulder Conclusions
2
2
band at 279 nm does not change its position but undergoes
an increase in intensity. Two other bands centred at 255 and
Polymer-anchored oxidovanadium(IV) complexes with
polymer-anchored ligand PS-H fsal-ea, PS-H fsal-pa and
212.5 nm remain constant while a shoulder band at 223 nm
2
2
PS-H fsal-amp, having potential catalytic activities for the
slowly appears. We have interpreted this result in terms of
2
oxidation of styrene and cumene, have been isolated and
characterised. The oxidation of styrene follows the order:
PS-[VO(fsal-pa)·DMF] (95%) Ͼ PS-[VO(fsal-ea)·DMF]
the formation of the oxidoperoxidovanadium(V) complex
–
[
VO(O )(sal-pa)] .
2
(90%) Ͼ PS-[VO(fsal-amp)·DMF] (82%) where the selectiv-
ity of the five different products follows the order: benzalde-
hyde Ͼ 1-phenylethane-1,2-diol Ͼ benzoic acid Ͼ phenyl-
acetaldehyde Ͼ styrene oxide. The oxidation of cumene
gives at least six different products with the following order
of selectivity: acetophenone Ͼ 2-phenyl-2-propanal Ͼ α-
methylstyrene epoxide Ͼ 2-phenylpropanol Ͼ 2-isopropyl-
1,4-benzoquinone and α-methylstyrene. The good perform-
ance of these catalysts is possibly due to the facile formation
of peroxido species in the presence of H O as well as the
2
2
ease in transferring oxygen from the intermediate peroxido
species to the substrate. However, complexes slowly convert
back to the oxidovanadium(IV) species since the recycled
species exhibit similar EPR spectroscopic patterns. The
catalytic activities of these complexes have also been com-
pared with the corresponding neat complexes and it was
observed that the neat complexes are, however, good cata-
lyst but exhibit less catalytic activity than the anchored
ones. The easy separation of the polymer anchored com-
plexes from the reaction mixture and their ability to be recy-
cled makes them better catalyst compared wit the neat ones.
They can pass through up to three cycles without signifi-
Figure 14. Titration of [VO(fsal-pa]
tra were recorded after the successive addition of 1-drop portions
dissolved in methanol to 10 mL of ca. 10–4  solution of
of H
in methanol.
2 2 2
(2) with 30% H O ; the spec-
2
O
2
2
Similar spectroscopic patterns were also observed for cant loss in their catalytic activities.
complexes 1 and 3. Oxidoperoxidovanadium(V) complexes
have also been generated previously on treatment of, for
[9]
example, complexes [VO(sal-ohyba)] and K[VO (sal-inh)- Experimental Section
2
[
32]
(
H O)] with H O in methanol.
2 2 2
Materials: Analytical reagent grade V
salicylaldehyde, acetylacetone (Ranbaxy, India), styrene, cumene,
-aminopropanol (Acros organics, USA), 2-aminoethanol, 2-
amino-2-methylpropanol (S.D. Fine Chemicals, India), aqueous
0% H (Qualigens, India) were used as obtained. Other chemi-
cals and solvents were of AR grade. Chloromethylated polystyrene
18.9% Cl (5.3 mmol Cl per gram of resin)] cross-linked with 5%
divinylbenzene was obtained as gift from Thermax limited, Pune,
2 5
O , (Loba Chemie, India),
3
Leaching and Heterogeneity of the Catalytic Reaction and
Potential of the Catalyst to be Recycled
3
2 2
O
[
The polymer-anchored complexes 4, 5 and 6 have been
tested for their ability to be recycled. The reaction mixture
was filtered after a contact time of 6 h. The catalysts sepa-
rated from the reaction mixture after catalytic action in all
three cases were washed with acetonitrile, dried and sub-
jected to further catalytic reactions under similar condi-
tions. No appreciable loss in the activity in all cases suggests
that catalysts were active even after the first cycle. During
catalytic oxidation of styrene and cumene, the solid catalyst
was separated from the reaction mixture by filtration after
[33]
[34]
India. [VO(acac)
2
]
and 3-formylsalicylic acid
were prepared
following the methods reported in the literature.
Methods: Elemental analyses of the ligands and complexes were
obtained using an Elementar model Vario-EI-III instrument. IR
spectra were recorded as KBr pellets on a Nicolet NEXUS Aligent
1100 FT-IR spectrometer. Electronic spectra of the polymer-an-
chored compounds were recorded in Nujol on a Shimadzu1601
UV/Vis spectrophotometer by layering a mull of the sample inside
one of the cuvettes while keeping other one layered with Nujol as
2
h and the reaction was continued for a further 4 h. The
a reference. The spectra of other ligands and complexes were re-
1
gas chromatographic analyses showed barely a 1% in- corded in methanol or DMF. H NMR spectra were obtained using
crement in the conversion. This confirms no leaching of the a Bruker 500 NMR spectrometer in [D
312 Eur. J. Inorg. Chem. 2007, 2303–2314
6
]DMSO. EPR spectra were
2
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Polymer-Anchored Oxidovanadium(IV) Complexes
FULL PAPER
recorded at room temperature on a Bruker EMX X-band spec-
trometer operating at 100-kHz field modulation at room tempera-
ture. The microwave frequency was calibrated using a frequency
counter of the Microwave Bridge ER 041 XG-D. The Bruker Sim-
fonia software package was used in the spectroscopic simulations
and to calculate hyperfine coupling constant. The magnetic suscep-
tibilities of simple oxidovanadium(IV) complexes were measured at
ture was heated in an oil bath at 80 °C for 20 h with mechanical
stirring. After cooling to room temperature, the yellow resins were
filtered, washed thoroughly with hot DMF followed by hot meth-
anol and dried in an air oven at 120 °C. Found: C 70.76, H 8.64,
–
1
N 3.16. IR (KBr): ν˜ max = 1675 (νC=O), 1635 (νC=N) cm .
PS-H fsal-pa (V) and PS-H fsal-amp (VI): The ligands PS-H
pa and PS-H fsal-amp were prepared by following the procedure
out lined for PS-H fsal-ea.
Data for V: Found: C 71.58, H 8.63, N 3.25. IR (KBr): ν˜ max = 1675
2
2
2
fsal-
2
298 K with a Vibrating Sample Magnetometer model 155, using
2
nickel as a standard. Diamagnetic corrections were carried out
using Pascal’s increments.[ Thermogravimetric analyses of the
complexes were carried out using a Perkin–Elmer (Pyris Diamond)
instrument. Scanning Electron Micrographs (SEM) of polymer an-
chored ligands and complexes were recorded on a Leo instrument
model 435 VP. The samples were coated with a thin film of gold
to prevent the surface changing and to protect the surface material
from thermal damage by the electron beam.
35]
–
1
(νC=O), 1637 (νC=N) cm .
Data for VI: Found: C 69.21, H 7.43, N 3.05. IR (KBr): ν˜ max
=
–1
1673 (νC=O), 1630 (νC=N) cm .
[
VO(fsal-ea)]
2
(1): A stirred solution of H
2
fsal-ea (1.05 g, 5 mmol)
in acetonitrile (30 mL) was added with stirring to [VO(acac)
2
]
(
1.33 g, 5 mmol) dissolved in acetonitrile (25 mL) and the resultant
Preparations
reaction mixture was heated to reflux on a water bath for 3 h. After
cooling to room temperature, a green precipitate of 1 was filtered,
washed with acetonitrile and dried in vacuo. Yield 78%.
H
2
fsal-ea (I): A stirred solution of 2-aminoethanol (0.61 g,
10 mmol) in acetonitrile (10 mL) was added to a solution of 3-
C
10
H
9
5
NO V (274.13): calcd. C 43.80, H 3.31, N 5.11, V 18.59;
formylsalicylic acid (1.66 g, 10 mmol) in hot acetonitrile (30 mL)
and the reaction mixture was heated to reflux on a water bath for
found C 43.62, H 3.42, N 5.05, V 18.06. IR (KBr): ν˜ max = 1670
–
1
(
ν
C=O), 1607 (νC=N), 987 (νV=O) cm .
VO(fsal-pa)] (2) and [VO(fsal-amp)]
prepared analogously to 1, replacing H
fsal-amp, respectively.
Data for 2: Yield 76%. C H NO V (288.15): calcd. C 45.83, H
5
h. After reducing the solvent volume to ca. 10 mL, the flask was
kept at room temperature. A yellow solid of I slowly separated out
overnight. This was filtered, washed with petroleum ether and dried
[
2
2
(3): Complexes 2 and 3 were
fsal-ea for H fsal-pa and
2
2
in vacuo. Yield 72%. C10
4
H11NO (209.2): calcd. C 57.40, H 5.30,
H
2
N 5.70; found C 57.43, H 5.32, N 5.68. IR (KBr): ν˜ max = 1658
–
1 1
(
ν
C=O) cm . H NMR ([D
ylic –OH), 5.20 (br., 1 H, phenolic OH), 8.37 (s, 1 H, –CH=N–),
.09 (d, 1 H, aromatic), 7.69 (d, 1 H, aromatic), 6.75 (t, 1 H, aro-
6
]DMSO): δ = 12.89 (br., 1 H, carbox-
11 11
5
3
.85, N 4.86, V 17.69; found C 45.91, H 3.65, N 4.74, V 17.14. IR
–
1
(
KBr): ν˜ max = 1673 (νC=O), 1603 (νC=N), 985 (νV=O) cm .
Data for 3: Yield 70%. C12 13NO V (302.18): calcd. C 47.68, H
.34, N 4.64, V 16.87; found C 47.30, H 4.54, N 4.41, V 16.36. IR
8
2 2
–), 3.70 (s, 2 H, –CH
–) ppm. 1 C NMR
3
matic), 3.77 (s, 2 H, –CH
[D ]DMSO): δ = 190.1 (carboxyl), 175.2 (azomethine), 168.4 (phe-
H
5
(
6
4
nolic), 141.1, 139.9, 119.5, 116.1, 114.2 (aromatic), 59.3, 54.2 (alkyl
chain) ppm.
–1
(
KBr): ν˜ max = 1674 (νC=O), 1600 (νC=N), 988 (νV=O) cm .
PS-[VO(fsal-ea)·DMF] (4): Polymer-anchored ligand PS-H
(
2
fsal-ea
2.0 g) was allowed to swell in DMF (30 mL) for 2 h. A solution
H
2
fsal-pa (II) and H
following the above procedure using 3-formylsalicylic acid (1.66 g,
0 mmol) and 3-aminopropanol (0.89 g, 10 mmol) or 2-amino-2-
methylpropanol (0.89 g, 10 mmol).
2
fsal-amp (III): These ligands were prepared
2
of [VO(acac) ] (5.30 g, 20 mmol) in DMF (20 mL) was added to
1
the above suspension and the reaction mixture was heated at 90 °C
in an oil bath for 15 h while slow mechanical stirring. The blackish
green beads of polymer-anchored complex 4 were filtered off,
washed with hot DMF followed by hot methanol and dried at
120 °C in an air oven. Found: C 67.08, H 7.74, N 5.04, V 8.5. IR
Data for II: Yield 55%. C11
4
H13NO (223.2): calcd. C 59.17, H 5.87,
N 6.28; found C 59.39, H 5.84, N 6.23. IR (KBr): ν˜ max = 1657
–1
1
6
(νC=O) cm . H NMR ([D ]DMSO): δ = 12.09 (br., 1 H, car-
–
1
(
KBr): ν˜ max = 1655 (νC=O), 1607 (νC=N), 977 (νV=O) cm .
boxylic –OH), 4.80 (br., 1 H, phenolic –OH), 8.76 (s, 1 H, –CH =
N–), 8.08 (d, 1 H, aromatic), 7.65 (d, 1 H, aromatic), 6.67 (t, 1 H,
PS-[VO(fsal-pa)·DMF] (5) and PS-[VO(fsal-amp)·DMF] (6): Com-
aromatic), 3.81 (t, 2 H, –CH
2
–), 3.53 (t, 2 H, –CH
2
–), 1.89 (quin, plexes 5 and 6 were prepared by following the procedure out lined
2
1
1
H, –CH
2
) ppm. 13C NMR ([D
6
]DMSO): δ = 190.8 (carboxyl), for 4.
75.2 (azomethine), 168.4 (phenolic), 141.0, 139.8, 119.5, 116.1,
14.1 (aromatic), 58.4, 49.7, 32.1 (alkyl chain) ppm.
Data for 5: Found: C 68.18, H 7.86, N 4.83, V 7.93. IR (KBr): ν˜ max
–
1
=
1659 (νC=O), 1609 (νC=N), 993 (νV=O) cm .
Data for III: Yield 60%. C12
H
15NO
4
(237.2): calcd. C 60.73, H
Data for 6: Found: C 64.19, H 7.31, N 4.66, V 7.26. IR (KBr): ν˜ max
6
1
.38, N 5.91; found C 60.60, H 6.31, N 5.94. IR (KBr): ν˜ max
680 (νC=O) cm . H NMR ([D ]DMSO): δ = 13.57 (br., 1 H,
6
=
–
1
=
1675 (νC=O), 1609 (νC=N), 964 (νV=O) cm .
–1
1
carboxylic –OH), 5.57 (br., 1 H, phenolic –OH), 8.81 (s, 1 H, –CH =
N–), 8.84 (d, 1 H, aromatic), 7.79 (d, 1 H, aromatic), 6.71 (t, 1 H,
Catalytic Activity Studies
Oxidation of Styrene: The oxidation of styrene was carried out in
a 50 mL reaction flask fitted with a water condenser. All anchored
catalysts were allowed to swell in acetonitrile for 2 h prior to their
use. In a typical oxidation reaction, styrene (1.04 g, 10 mmol) and
aromatic), 3.49 (s, 2 H, –CH
2 3
–), 1.42 (s, 3 H, –CH ), 1.17 (s, 3 H,
–
CH ]DMSO): δ = 190.1 (carboxyl), 168.2
3
) ppm. 13C NMR ([D
6
(
(
azomethine), 165.7 (phenolic), 141.2, 139.7, 119.4, 116.2, 114.2
aromatic), 68.0, 61.2 (alkyl chain), 23.2 (methyl) ppm.
2 2
aqueous 30% H O (2.27 g, 20 mmol) were mixed in acetonitrile
PS-H
prepared following the procedure developed by Syamal et al.
Chloromethylated polystyrene (3.0 g) was allowed to swell in DMF
2
fsal-ea (IV): The polymer-anchored ligand PS-H
2
fsal-ea was
(10 mL) and the reaction mixture was heated to 80 °C with stirring.
The appropriate catalyst (0.040 g) was added to the reaction mix-
ture and stirred for 6 h. The progress of the reaction was monitored
by withdrawing small amounts of the reaction mixture at different
time intervals and analysing them quantitatively by gas chromatog-
raphy. The identities of the products were confirmed by GC–MS
[
36]
(30 mL) for 2 h. A solution of H
2
fsal-ea (9.96 g, 45 mmol) in DMF
(30 mL) was added to the above suspension followed by triethyl-
amine (4.50 g, 45 mmol) in ethyl acetate (50 mL). The reaction mix-
Eur. J. Inorg. Chem. 2007, 2303–2314
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2313

M. R. Maurya, U. Kumar, P. Manikandan
FULL PAPER
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Received: November 29, 2006
Published Online: April 24, 2007
2314
www.eurjic.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 2303–2314