Polymer and non-polymer-grafted dioxidomolybdenum(VI) complexes having ONO donor ligand and their catalytic activities for the oxidative bromination of organic substrates

Article abstract of DOI:10.1016/j.molcata.2014.05.002

The ligand H₂sal-iah (I), derived from salicylaldehyde and indole-3-acetic hydrazide, reacts with [Mo^VIO₂(acac) ₂] in methanol to give dioxidomolybdenum(VI) complex [Mo ^VIO₂(sal-iah)(MeOH)]

Full text of DOI:10.1016/j.molcata.2014.05.002

Accepted Manuscript
Title: Polymer and non-polymer-grafted
dioxidomolybdenum(VI) complexes having ONO donor
ligand and their catalytic activities for the oxidative
bromination of organic substrates
Author: Mannar R. Maurya Naveen Kumar Fernando Avecilla
PII:
S1381-1169(14)00199-X
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2014.05.002
MOLCAA 9102
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
18-3-2014
4-5-2014
6-5-2014
Please cite this article as: M.R. Maurya, N. Kumar, F. Avecilla, Polymer
and non-polymer-grafted dioxidomolybdenum(VI) complexes having ONO
donor ligand and their catalytic activities for the oxidative bromination of
organic substrates, Journal of Molecular Catalysis A: Chemical (2014),
http://dx.doi.org/10.1016/j.molcata.2014.05.002
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Polymer and non-polymer-grafted dioxidomolybdenum(VI) complexes having
ONO donor ligand and their catalytic activities for the oxidative bromination
of organic substrates
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Mannar R. Maurya a,*, Naveen Kumar a, Fernando Avecilla b
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a Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
b Departamento de Química Fundamental, Universidade da Coruña, Campus de A Zapateira,
15071 A Coruña, Spain
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Keywords: Molybdenum complexes; Polymer-grafted molybdenum complex; Crystal structure;
Oxidative bromination of styrene; Oxidative bromination of trans–stilbene.
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* Corresponding author. Tel.: +91 1332 285327; fax: +91 1332 273560.
E-mail address: rkmanfcy@iitr.ac.in (M.R. Maurya).
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ABSTRACT
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The ligand H2sal-iah (I), derived from salicylaldehyde and indole-3-acetic hydrazide, reacts with
[MoVIO2(acac)2] in methanol to give dioxidomolybdenum(VI)
complex [MoVIO2(sal-
iah)(MeOH)] (1). Drop wise addition of 30% aqueous H2O2 to the methanolic solution of 1
yields complex [MoVIO(O2)(sal-iah)(MeOH)] (2). Complex 1 has been grafted via covalent
bonding through imino nitrogen of the indole to chloromethylated polystyrene cross-linked with
5% divinylbenzene {now abbreviated as PS-[MoVIO2(sal-iah)(MeOH)] (3)}. All these complexes
1
are characterized by various spectroscopic techniques (IR, electronic, H and 13C NMR) and
thermal as well as field-emission scanning electron micrographs (FE-SEM) studies. The crystal
structure of 1 has been determined, confirming the ONO binding mode of I. The polymer-grafted
complex 3 catalyzes the oxidative bromination, by H2O2, of styrene and trans-stilbene. Under the
optimized reaction conditions, the oxidative bromination of styrene gave 98 % conversion in 2 h
time where 2-bromo-1-phenylethane-1-ol and 1,2-dibromo-1-phenylethane are the main products
and 1-phenylethane-1,2-diol is the product obtained by the attack of nucleophile water on the α-
carbon of 2-bromo-1-phenylethane-1-ol. Oxidative bromination of trans-stilbene gave 96%
conversion with 2,3-diphenyloxirane (trans-stilbene oxide), 1,2-dibromo-1,2-diphenylethane
and 2-bromo-1,2-diphenylethanol as the products. Suitable reaction mechanisms for both
reactions have been suggested. Neat complex [MoVIO2(sal-iah)(MeOH)] (1) is equally active but
the recyclability and heterogeneity tests of polymer-grafted complex makes it better over neat
analog.
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1. Introduction
Catalytic applications of molybdenum complexes in oxidation and oxygen-transfer
reactions including oxidation of sulfides [1-22] have extensively been studied. Immobilizations
of these homogeneous catalysts on solid support find limited mention in the literature though
such catalysts have potential prospect for technological applications [23, 24] because solid
supported catalysts meet the industrial demand of recyclability and thermal stability along with
high turnover rates and environment-friendly synthetic routes to fine chemicals [25-29].
Recently our attention was drawn on the oxidative bromination of organic substrates by
vanadium complexes, a reaction normally promoted by vanadium haloperoxidase enzymes [30-
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32]. These homogeneous as well as heterogeneous vanadium complexes satisfactorily catalyze
the oxidative bromination of styrene, trans-stilbene and salicylaldehyde [33-40]. Such functional
similarities have also been demonstrated by some homogeneous molybdenum complexes [41-
43].
We have recently immobilized dioxidovanadium(V) complex of indole-derived ONO
donor ligand H2sal-iah (I, Scheme 1) onto chloromethylated polystyrene cross-linked with
divinyl benzene (PS-CH2Cl) for the development of more environmentally benign heterogeneous
catalyst and have explored their use as possible functional model for haloperoxidase enzymes.
Insertion of spacer (extra CH2 group) between polymer support and catalyst improved the
performance of the catalyst by allowing the better interaction of catalytic centre with substrates
and oxidant during catalytic reaction [44]. We now report the immobilization of
dioxidomolybdenum(VI) complex of H2sal-iah (I, Scheme 1) onto chloromethylated polystyrene.
Its characterization and catalytic potential towards the oxidative bromination of styrene and
trans-stilbene are reported here. The corresponding non polymer-grafted molybdenum complex
has also been prepared for comparing its catalytic performance.
O
HO
C
N
N
C
N
H
H
H
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Scheme 1. Structure of ligand H2sal-iah (I)
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2. Experimental
2.1. Materials
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Chloromethylated polystyrene [18.9 % Cl (5.35 mmol Cl per gram of resin)] cross-linked
with 5 % divinylbenzene was obtained from Thermax Limited, Pune, India. Analytical reagent
grade ammonium molybdate, molybdenum trioxide (S. D. Fine, India), salicylaldehyde (Sisco
Research, India), trans-stilbene (Lancaster, England), indole-3-acetic hydrazide, styrene
(Aldrich, USA) and 30 % aqueous H2O2, (Rankem, India) were used as obtained. H2sal-iah (I)
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[44] and [MoVIO2(acac)2] [45] were prepared according to methods reported in the literature.
Other chemicals and solvents of analytical reagent grades were used without purifications.
2.2. Physical methods and analysis
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Molybdenum content in polymer-grafted complex was obtained by Inductively Coupled
Plasma spectrometry (ICP; Labtam 8440 plasma lab). C, H and N analyses of the neat complex
were obtained with an Elementar model Vario-EL-III. Thermogravimetric analysis was carried
out using Perkin Elmer (Pyris Diamond) having weight sensitivity of 0.2 μg under oxygen
atmosphere. IR spectra were recorded (16 scans) as KBr pellets on a Nicolet NEXUS Aligent
1100 FT-IR spectrometer having a resolution of 4 cm–1. Electronic spectra of the polymer-
grafted complexes were recorded with a medium scan speed in Nujol on a Shimadzu 1601 UV-
Vis spectrophotometer having 0.1 nm wavelength accuracy by layering a mull of the sample on
the inside of one of the cuvettes while keeping the other one layered with Nujol as reference.
Spectra of ligand and neat complexes were recorded in methanol. 1H and 13C NMR spectra were
obtained using Bruker Avance III 500 MHz spectrometer. The energy dispersive X-ray analysis
(EDX) of anchored complex was obtained on a FEI Quanta 200 FEG. The samples were coated
with a thin film of gold to prevent surface charging, to protect the surface material from thermal
damage by the electron beam and to make the sample conductive. A Shimadzu 2010 plus gas-
chromatograph fitted with an Rtx-1 capillary column (30 m × 0.25 mm × 0.25 μm) and a FID
detector was used to analyze the reaction products and their quantifications were made on the
basis of the relative peak area of the respective product. The identity of the products was
confirmed using a GC-MS Perkin-Elmer, model Clarus 500 and comparing the fragments of each
product with the library available.
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2.3. Synthesis
2.3.1. [MoVIO2(sal-iah)(MeOH)] (1)
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A stirred solution of [MoVIO2(acac)2] (0.329 g, 1 mmol) dissolved in methanol (15 mL)
was added to a solution of H2sal-iah (0.293 g, 1 mmol) in methanol (25 mL) and the resulting
reaction mixture was stirred for ca. 6 h at room temperature. After reducing the solvent volume
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to ca. 10 mL and standing the solution in air for 24 h, the orange crystalline compound
precipitated which was filtered off, washed with methanol and dried in vacuo. Yield 0.42 g
(93%) Anal. Cal. for C18H17N3O5Mo (451.29): C, 47.91; H, 3.80; N, 9.31; Mo. Found: C, 47.8;
H, 4.0; N, 8.9%.
2.3.2. [MoVIO(O2)(sal-iah)(MeOH)] (2)
Aqueous 30% H2O2 (ca. 2 mL) was added dropwise to complex 1 (0.451 g, 1 mmol)
dissolved in methanol (50 mL) with constant stirring at ambient temperature. After ca. 4 h, the
solvent was slowly reduced to 10 mL by passing air through the solution and kept at room
temperature for slow precipitation of complex. The precipitated solid was filtered, washed with
cold methanol (2 × 4 mL) and dried in air. Yield 0.23 g (50%) Anal. Cal. for C18H17N3O6Mo
(467.29): C, 46.27; H, 3.67; N, 8.99. Found: C, 46.1; H, 3.7; N, 8.8%.
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2.3.3. PS-[MoVIO2(sal-iah)(MeOH)] (3)
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Chloromethylated polystyrene (1.0 g) was allowed to swell in DMF (8 mL) for 2 h. A
solution of [MoVIO2(sal-iah)(MeOH)] (1.0 g, 2.2 mmol) in DMF (8 mL) was added to the above
suspension followed by triethylamine (1.33 g) in ethylacetate (7 mL), and the obtained reaction
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mixture was heated at 80 C for 24 h with continuous but slow stirring. After cooling to room
temperature, the polymer-grafted complex was separated by filtration, washed with hot DMF,
followed by hot methanol and dried in an oven in air at 110 oC.
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2.4. X-Ray crystal structure determination
Three-dimensional X-ray data for 1 were collected on a Bruker SMART Apex CCD
diffractometer at room temperature, using a graphite monochromator and Mo-Kα radiation (λ =
0.71073 Å) by the φ-ω scan method. Reflections were measured from a hemisphere of data
collected from frames each of them covering 0.3º in ω. Of the 33032 reflections measured, all
were corrected for Lorentz and polarization effects and for absorption by multi-scan methods
based on symmetry-equivalent and repeated reflections, 4475 independent reflections exceeded
the significance level (⏐F⏐/σ⏐F⏐) > 4.0. Complex scattering factors were taken from the
program package SHELXTL [46]. The structures were solved by direct methods and refined by
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full matrix least-squares on F2. Hydrogen atoms were left to refine freely, except to C(4) and
C(18) which were included in calculation positions and refined in the riding mode. Refinements
were done with allowance for thermal anisotropy of all non-hydrogen atoms. Further details of
the crystal structure determination are given in Table 1. A final difference Fourier map showed
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no residual density outside: 0.432 and –0.464 e.Å-3. A weighting scheme w = 1/[σ2(Fo ) +
(0.046900 P)2 + 0.172800 P] was used in the latter stages of refinement.
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Table 1
Crystal data and structure refinement for [MoVIO2(sal-iah)(MeOH)](1).
Formula
C18H17MoN3O5
451.29
Formula weight
T, K
293(2)
Wavelength, Å
0.71073
Crystal system
Monoclinic
P21/c
Space group
a/Å
b/Å
c/Å
β/º
15.3299(4)
15.1955(4)
7.8411(2)
103.8140(10)
1773.72(8)
4
V/Å3
Z
F000
912
D
calc/g cm–3
1.690
μ/mm–1
0.776
1.37 to 31.89
0.0418
θ/ (º)
Rint
Crystal size/ mm3
0.21 × 0.18 × 0.16
1.093
Goodness-of-fit on F2
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R1[I>2σ(I)] a
wR2 (all data) b
0.0311
0.0971
Largest differences peak and hole (eÅ-3)
0.432 and -0.464
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aR1 = Σ⏐⎜Fo⎟ - ⎢Fc⎟⏐/Σ⏐Fo⏐. bwR2 = {Σ[w(⏐⎜Fo⎟2 -⎢Fc⎟2⏐)2]⏐/Σ[w(Fo )]}1/2
2.5. Catalytic activity
The catalytic oxidation bromination of styrene and trans-stilbene was carried out in a 100
ml flask at ca. 40 oC. Polymer-grafted catalyst was kept in MeOH for 1 h before use.
2.5.1. Oxidative bromination of styrene
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Catalyst (0.015 g), styrene (1.04 g, 10 mmol), KBr (2.38 g, 20 mmol), aqueous 30 %
H2O2 (2.27 g, 20 mmol) and 70 % aqueous HClO4 (2.86 g, 20 mmol, added in four equal portions
o
at t = 0, 30, 60 and 90 min.) were stirred at 40 C in a biphasic dichloromethane–water (40 mL
50%, v/v) mixture) system for 2 h. At every 15 minutes small aliquot of the reaction mixture
present in organic layer was withdrawn and analyzed quantitatively by gas chromatography.
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2.5.2. Oxidative bromination of trans-stilbene
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Catalyst (0.015, g) trans-stilbene (0.90 g, 5 mmol), KBr (2.38 g, 20 mmol), aqueous 30 %
H2O2 (2.27 g, 20 mmol) and 70 % aqueous HClO4 (2.86 g, 20 mmol, added in four equal portions
at t = 0, 30, 60 and 90 min.) were stirred at 40 oC in a biphasic chloroform–water (40 mL 50%,
v/v) mixture) system for 2 h. After 2h the reaction mixture was washed with water and the
organic layer was separated. Various reaction products were analyzed by gas chromatography
using this organic layer. The separation and identification of the reaction products were done as
reported earlier [44].
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3. Results and discussion
3.1. Synthesis and characterization
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Reaction between equimolar amounts of ligand H2sal-iah (I) and [MoVIO2(acac)2] in
refluxing MeOH gave [MoVIO2(sal-iah)(MeOH)] (1) [Eq. (1)]. Its reaction with 30 % aq. H2O2 in
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methanol gave complex [MoVIO(O2)(sal-iah)(MeOH)] (2) [Eq. (2)]. Both the complexes are
fairly soluble in methanol, DMF and DMSO. Scheme 2 presents the structures proposed for these
complexes, which are based on the elemental analyses, spectroscopic characterization (IR,
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electronic, H and C NMR), thermogravimetric patterns and single crystal X-ray analysis of 1.
The ligand coordinates through its dianionic (ONO) functionalities.
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[MoVIO2(acac)2] + H2sal-iah + MeOH → [MoVIO2(sal-iah)(MeOH)] + 2Hacac
[MoVIO2(sal-iah)(MeOH)] + H2O2 → [MoVIO(O2)(sal-iah)(MeOH)] + H2O
(1)
(2)
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The reaction of chloromethylated polystyrene (cross linked with 5% divinylbenzene) with
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dioxidomolybdenum(VI) complex 1 in DMF at 80 C in the presence of triethylamine leads to
the formation of polymer-anchored complex PS-[MoVIO2(sal-iah)(MeOH)] (3). During this
process, the labile proton of NH group of the indole reacts with CH2Cl group of polymer. The
whole synthetic procedures are presented in Scheme 2. The ICP-MS analysis of molybdenum in
the polymer-grafted complexes suggests molybdenum loading of 0.45 mmol g−1 of polymer in 3.
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H
O
H
O
O
O
O O
Mo
Me
O
Me
O
O
O
Mo
O
C
C
N
N
N
N
C
C
N
N
H
H
H
H
[MoVIO(O2)(sal-iah)(MeOH)] (2)
[MoVIO2(sal-iah)(MeOH)] (1)
H
O
O
O
Me
O
O
DMF, 80 oC
Mo
[MoVIO2(sal-iah)(MeOH)] (1)
C
N
Cl
Triethylamine,
Ethyleacetate
N
C
Chloromethylated polystyrene
[PS]
N
H
PS-[MoVIO2(sal-iah)(MeOH)] (3)
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Scheme 2. Proposed structures of complexes 1, 2 and 3, and synthetic route to prepare 3; PS (or
ball) represents the backbone of the chloromethylated polystyrene.
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3.2. Structure description
The ORTEP diagram for the compound [MoVIO2(sal-iah)(MeOH)] (1) is shown in Fig. 1.
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Fig. S1 (see supporting information) presents the intermolecular hydrogen bonds and π-π
interactions. Selected bond distances and angles are given in Table 2. The structure of the
complex is mononuclear and adopts a six-coordinated distorted octahedral geometry. In this
complex phenolic oxygen, alcohol oxygen and azomethine nitrogen atoms of the ligand, which
acts as tridentate, and two oxo groups coordinate to molybdenum centre. One methanol molecule
completes the coordination sphere. The O=Mo=O angle is 106.05(9)º and Mo=O distances are
1.6851(18) and 1.7024(15) Å. The Mo–O–C angle and Mo–O distance for Mo–OHCH3 in 1 are
125.13(16)° and 2.3794(17) Å, respectively, similar to other examples in literature [47].
The asymmetric unit of complex 1 contains only single molecule of [MoVIO2(sal-
iah)(MeOH)]. The indole groups of the two complexes interact by π-π interactions (see Fig. S1).
The distances between centroids is: dc1-c2 = 3.750 Å {c1 [N(3O), C(10O), C(11O), C(12O),
C(17O)], c2 [C(12A)-C(13A)-C(14A)-C(15A)-C(16A)-C(17A)]}. Intermolecular hydrogen
bonds are present in the crystal packing (see Table 3).
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Fig. 1. ORTEP plot of complex [MoVIO2(sal-iah)(MeOH)] (1). All the non-hydrogen atoms are
presented by their 30% probability ellipsoids.
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Table 2
Bond lengths [Å] and bond angles [°] for [MoVIO2(sal-iah)(MeOH)](1).
Bond lengths
1
Mo(1)-O(1)
Mo(1)-O(2)
Mo(1)-O(3)
Mo(1)-O(4)
Mo(1)-O(5)
Mo(1)-N(1)
1.9157(16)
1.6851(18)
1.7024(15)
2.3794(17)
2.0133(14)
2.2364(18)
Bond angles
1
O(2)-Mo(1)-O(3)
O(2)-Mo(1)-O(1)
O(3)-Mo(1)-O(1)
O(2)-Mo(1)-O(5)
O(3)-Mo(1)-O(5)
O(1)-Mo(1)-O(5)
O(2)-Mo(1)-N(1)
O(3)-Mo(1)-N(1)
O(1)-Mo(1)-N(1)
O(5)-Mo(1)-N(1)
O(2)-Mo(1)-O(4)
O(3)-Mo(1)-O(4)
O(1)-Mo(1)-O(4)
O(5)-Mo(1)-O(4)
N(1)-Mo(1)-O(4)
106.05(9)
100.68(10)
103.42(8)
95.32(9)
96.32(7)
149.90(7)
96.36(8)
155.51(7)
81.51(6)
71.45(6)
171.04(8)
81.90(7)
81.07(8)
79.46(7)
75.13(6)
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Table 3
Hydrogen bonds for complex [MoVIO2(sal-iah)(MeOH)] (1).
D-H...A
d(D-H)
0.75(3)
0.71(2)
d(H...A)
2.42(3)
2.05(3)
d(D...A)
3.098(3)
2.751(2)
<(DHA)
151(3)
170(3)
N(3)-H(3N)...O(3)#1
O(4)-H(4O)...N(2)#2
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Symmetry transformations used to generate equivalent atoms: #1 -x+1,-y,-z+1
#2 x,-y+1/2,z-1/2
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3.3. Field Emission-scanning Electron Micrograph (FE-SEM) and Energy Dispersive X-Ray
Analysis (EDX) studies
The images of field emission-scanning electron micrographs (Fe-SEM) of single beads of
pure chloromethylated polystyrene and polymer-grafted complex PS-[MoVIO2(sal-iah)(MeOH]
(3) are presented in Fig. 2. The pure chloromethylated polystyrene bead has smooth and flat
surface while anchored complex shows slight roughening of the top layer suggesting the
incorporation of metal complex into polymer matrices. However, the poor loading of the metal
complex does not allow extracting any accurate information on the morphological changes in
terms of exact orientation of ligand coordinated to the metal ion. The estimation of ca. 9.2 weight
percentage of molybdenum content for PS-[MoVIO2(sal-iah)(MeOH] (3) by energy dispersive X-
ray analysis (EDX), however, confirms the grafting of metal complex onto polystyrene beads.
This observation further suggests that part of the covalently bonded complexes is present on the
surface while remaining is at various sites.
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Fig. 2. Scanning electron micrographs (SEM) of chlomethylated polystyrene (left) and PS-
[MoVIO2(sal-iah)(MeOH)] (3) (right).
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3.4. Thermogravimetric study
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Thermogravimetric analysis profile of [MoVIO2(sal-iah)(MeOH)] (1) under an oxygen
atmosphere shows that it is stable up to ca. 120 oC and then loses 7 % (Anal. Cal. 7.1%) weight
o
between 120 to 180 C equivalent to one coordinated methanol. On further increasing the
temperature, the solvent free complex decomposes in two major fragments with exothermic
o
weight loss which completes at ca. 540 C. The obtained residue at this temperature is 31%
which is close to the theoretical value of 31.9%. The polymer-grafted complex PS-[MoVIO2(sal-
o
o
iah)(MeOH)] (3) starts losing weight at ca. 80 C and this step` completes at ca. 170 C with a
total loss of ca. 9% suggesting the presence of coordinated as well as trapped solvent. Thereafter,
it decomposes in several fragments with exothermic weight loss at higher temperature.
Quantitative measurement of weight loss and distinction between decomposition pattern of
complex and polymer matrix at various stages were not possible due to overlapping nature of the
decompositions. However, the final residues of 6.7 % (equivalent to 0.47 mmol g−1 of Mo in 3)
at ca. 520 oC suggest the formation of MoO3 and metal complex is grafted into polymer support.
3.5. IR spectral studies
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IR spectral data of the ligand and its neat and anchored complexes are presented in Table
4. The neat complex 1 exhibits two sharp bands at 911 and 940 cm−1 due to νsym(O=Mo=O) and
νasym(O=Mo=O) modes, respectively [48]. The corresponding polymer-bound molybdenum
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complex displays these bands at 903 cm−1 and 957 cm−1. Complex [MoVIO(O2)(sal-iah)(MeOH)]
(2) exhibits a sharp band at 965 cm–1 which is assigned due to ν(Mo=O) stretch. In addition, it
exhibits three IR active vibrational modes associated with the peroxido moiety [Mo(O2)]2+ at
910, 635 and 556 cm–1 which are assigned due to the O–O intra stretching, asymmetric Mo(O2)
stretching and symmetric Mo(O2) stretching, respectively [49]. These bands confirmed the η2-
coordination of the peroxo group to the molybdenum.
Ligand H2sal-iah (I) exhibits four distinct bands at 3400, 3186, 1670 and 1618 cm–1 due
to ν(OH), ν(NH), ν(C=O) and ν(C=N) modes, respectively. The presence of sharp bands due to
ν(NH) and ν(C=O) is indicative of its ketonic nature in the solid state. The absence of these
bands in the spectra of all complexes is consistent with the enolisation of the amide functionality
and subsequent coordination of enolic oxygen to the metal ion after proton replacement. A new
band appearing at ca. 1270 cm−1 is assigned to the ν(C–O)(enolic) stretching of the coordinated
hydrazone fragment. The band due to azomethine group moves towards lower wave number by
11 cm−1 (in 1), 5 cm−1 (in 2) and 9 cm−1 (in 3) indicating the coordination of azomethine nitrogen
to the molybdenum. The band corresponding to the free –OH group present in H2sal-iah is also
present in complexes 1 and 2 possibly suggesting the presence of coordinated methanol. The
presence of multiple bands of medium intensity observed in the region 2800–2900 cm−1 in all
complexes suggests the existence of –CH2 group.
The chloromethylated polystyrene displays strong peaks at 1264 and 673 cm−1 [50]. The
absence of these peaks in PS-[MoVIO2((sal-iah)(MeOH)] (3) suggests the covalent bonding of
chloromethylated polystyrene with [MoVIO2((sal-iah)(MeOH)] (cf. Scheme 2) through nitrogen
of the indole ring. This is further supported by the absence of ν(NH) band that appears at 3250
cm−1 in 1.
3.6. UV-visible spectral study
Fig. 3 (A and B) reproduces spectra of ligand, neat and polymer-grafted complexes and
Table 5 includes UV-visible spectral data. Ligand H2sal-iah (I) exhibits three spectral bands at
220, 279 and 321 nm in the UV region corresponding to σ→σ *, π→π* and n→π* transitions,
respectively. The additional band at 289 nm having intensity similar to π→π* transition is
possibly due to its splitting. All these bands also appear in the spectra of complexes 1 and 2 with
13
Page 13 of 33

308
309
310
311
312
313
314
315
316
slight variations. In addition, they also exhibit a low intense band at 380 (in 1) and ca. 400 nm (in
2) originating due to the transfer of charge from phenolate oxygen atom to an empty d-orbital of
the molybdenum atom (LMCT). Spectrum of 3 recorded in Nujol® has very similar but broad
electronic spectral patterns [Fig. 3(B)]. The expected LMCT transition in 3 could only be
observed around 386 nm as a weak shoulder in Nujol possibly due to poor loading of complex in
polymer matrix while bands in the UV region are similar to that observed in 1 and 2.
Table 4
IR spectral data (cm–1) of compounds
Compound
υ(OH)
3400
υ(NH)
3186
3250
3250
-
υ(C=O) υ(C=N υ(Mo=O)
H2sal-iah (I)
[MoVIO2((sal-iah)(MeOH)] (1)
[MoVIO(O2)(sal-iah)(MeOH)] (2) a 3400
PS-[MoVIO2(sal-iah)(MeOH] (3)
3400
1670
1618
1607
1613
1609
3400
-
-
-
911(s), 940(s)
965
903(s), 957(s)
317
318
a Bands due to the peroxido group: 910, 635 and 556 cm–1.
219
2.0
1.5
1.0
0.5
0.0
1.5
1.2
0.9
0.6
0.3
0.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
(B)
400
(A)
(c)
(b)
278
380
315
(a)
350
400
450
500
386
(c)
(b)
200
300
400
500
600
200
250
300
350
400
450
500
Wavelength (nm)
Wavelength (nm)
319
320
321
322
323
Fig. 3. (A): Electronic spectra of (a) H2sal-iah (I), (b) [MoVIO2(sal-iah)(MeOH)] (1) and (c)
[MoVIO(O2)(sal-iah)(MeOH)] (2) recorded in methanol. (B): Electronic spectrum of PS-
[MoVIO2(sal-iah)(MeOH)] (3) recorded after despersing it in nujol®.
14
Page 14 of 33

324
325
Table 5
Electronic spectral data of ligand and complexes.
Compound
Solvent
MeOH
λmax / nm (ε/ M-1cm-1)
220(5.98×104), 279(3.42×104), 289(3.04×104),
321(1.48×104)
H2sal-iah (I)
[MoVIO2(sal-iah)(MeOH)] (1)
MeOH
220(4.56×104), 279(2.30×104), 289(2.06×104),
320(0.96×104), 380(2.06×103)
[MoVIO(O2)(sal-iah)(MeOH)] (2) MeOH
218(3.91×104), 279(2.33×104), 289(2.16×104),
322(1.37×104), 400(2.55×103)
PS-[MoVIO2(sal-iah)(MeOH)] (3) Nujol
219, 278, 315, 386
326
327
328
3.7. 1H and 13C NMR studies
329
330
331
332
333
334
335
336
337
338
339
340
341
The 1H NMR spectra of H2sal-iah (I) and [MoVIO2(sal-iah)(MeOH)] (1) are shown in Fig.
1
4 and their typical chemical shifts are presented in Table 6. The H NMR spectrum of ligand
exhibits single singlet for phenolic –OH proton while two sets of singlet with about 1:2 ratio
each for azomethine (–CH=N–), methylene (–CH2–), NH (of –C(O)–NH– group) and NH (of
indole) protons, indicating its existence in two isomeric forms. The absence of signal due to NH
of –C(O)–NH– group in the complexes supports the enolisation of the ketonic group and
consequent replacement of H by the metal ion. Similarly, absence of phenolic proton signal in
complexes indicates the coordination of the phenolic oxygen after proton replacement. The two
azomethine signals appearing at 8.38 and 8.41 ppm merge into one and resonate at down field
due to the coordination of the azomethine nitrogen. Protons associated with aromatic, methyl and
NH (of indole group) groups appear at nearly same positions in ligand as well as in complexes.
Thus, 1H NMR data supplement the inference obtained by IR spectral study.
15
Page 15 of 33

*
-CH3
[MoVIO2(sal-iah)(MeOH)] (1)
-CH2
-CH=N
Ar-H
-NH
-OH
H2sal-iah (I)
-CH2
Ar-H
-CH=N
-NH
Ph-OH
*
342
343
344
345
346
347
Fig. 4. 1H NMR spectra of H2sal-iah (I) and [MoVIO2(sal-iah)(MeOH)](1).
Table 6
1H NMR chemical shifts [δ in ppm] of ligand and complexes recorded in DMSO-D6.
Compd a –OH
–NH–
–NH–
–CH=N–
–CH2 –
–CH3
Aromatic
–OH
(phenolic) (hydrazide)
(indole)
(alcoholic)
I
11.80
(br, 1H)
-
11.17, 11.27 10.88,10.94 8.38, 8.41 3.66, 4.02
6.86-7.72
(m, 9H)
(s, 1H)
-
(s, 1H)
10.94
(s, 1H)
8.79
(s, 2H)
3.80
1
2
3.17
6.88-7.67
4.09
(s, 1H)
10.90
(s, 1H)
8.90
(s, 2H)
3.82
(s, 3H) (m, 9H)
3.12 6.88-7.80
(s, 3H) (m, 9H)
(br, 1H)
4.05
(s, 1H)
(s, 1H)
(s, 2H)
(br, 1H)
348
349
350
aLetters given in parentheses indicate the signal structure: s = singlet, m = multiplet, br = broad
(unresolved).
16
Page 16 of 33

351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
The 13C NMR spectra of H2sal-iah (I) and [MoVIO2(sal-iah)](1) have been recorded which
1
also supplement H NMR spectral information for the elucidation of the structure of the
complex. Table 7 provides 13C NMR spectral data and Fig. S2 reproduces their spectra.
Assignments of the peaks are based on the intensity patterns of the chemical shift and on the
coordination-induced shifts (Δδ) of the signals for carbon atoms in the vicinity of the
1
coordinating atoms [51]. Similar to the H NMR spectrum, H2sal-iah (I) exhibits two sets of
signal for most carbons while complex resonates single set of signal for each carbon except to
those carbons where centre of symmetry exist. For carbons where centre of symmetry exist e.g.
aromatic carbons, they exhibit less number of signals. A large coordination-induced shift for C1
(carbon bearing phenolic oxygen), C7 (carbon bearing azomethine nitrogen) and C8 (carbon
bearing enolic oxygen) atoms demonstrate the coordination of these functionalities to the
molybdenum. A considerable up field shift of methylene (C9) carbon has also been noticed in
complex. A new signal at 49 ppm suggests the coordination of methanol to the molybdenum.
Table 7
13C NMR spectral data of ligand and complexes
H
O
O
18
OMe
O
Mo
N
O
16
9
15
14
2
1
C
8
17
369
370
3
10
11
N
C
6
7
13 12
4
N
H
5
H
Compound
C1
C2-C5
C6
C7
C8
C9
C10,C11, C12
C13- C17
C18
-
156.8, 116.6, 116.8, 131.3,
118.8, 141.4, 167.5, 29.7, 108.3, 108.4, 111.80, 111.89, 119.07,
I
157.8
131.6, 119.9, 120.5,
127.8, 129.9
118.9
118.9
147.4
155.7
172.7
174.5
31.8
28.3
124.3, 124.4, 119.09, 119.1, 119.7, 121.4,
136.5, 136.6 121.5, 127.3, 127.6
108.5, 124.5, 111.8, 120.5, 121.8, 119.2,
136.6 127.6
159.7
118.9,135.1,121.5,
134.5
49.0
1
371
372
3.8. Catalytic activity studies
3.8.1. Oxidative bromination of styrene
373
374
375
Vanadium (neat as well as polymer supported) and neat molybdenum complexes have
been used as catalyst to study oxidative bromination of styrene [33,34,37-40,43]. We have
17
Page 17 of 33

376
377
378
379
380
381
382
384
considered polymer supported complex PS-[MoVIO2(sal-iah)(MeOH)] (3) to carry out the
oxidative bromination of styrene using 30 % aqueous H2O2 as an oxidant and three products
namely 1,2-dibromo-1-phenylethane, 2-bromo-1-phenylethane-1-ol and 1-phenylethane-1,2-diol
were obtained along with small amount of un-identified product; Scheme 3. The main products
1
were identified and confirmed by H NMR spectroscopy as well as by GC–MS after their
separation, and are the same as reported earlier [33,34,37-40,43].
HO
Br
HO
386
OH
Br
Br
Catalyst
388
+
+
H2O2, KBr, HClO4
390
1,2-dibromo-1-
phenylethane
Styrene
2-bromo-1-
phenylethane-1-ol
1-phenylethane-
1,2-diol
392
393
Scheme 3. Oxidative bromination products of styrene.
394
395
396
397
398
399
400
401
402
403
404
405
406
407
With the objective to conclude suitable reaction conditions for the maximum conversion
of styrene different parameters, namely, the amounts of catalyst, oxidant (mol of H2O2 per mol of
styrene), HClO4 and KBr were tested. Acid was found to be essential to carry out the catalytic
bromination.
In order to optimize the catalyst amount, three different amounts of catalyst i.e. 0.010,
0.015 and 0.020 g were taken for the fixed amount of styrene (1.04 g, 10 mmol), H2O2 (2.27 g,
20 mmol), KBr (2.38 g, 20 mmol) and HClO4 (1.43 g, 10 mmol, added in four equal portions at t
= 0, 15, 30 and 45 min of the reaction time) in CH2Cl2–H2O (40 mL, v/v) solvent system and the
reaction was carried out at 40 oC for 2 h. As shown in Fig. 5(a), a maximum of 67 % conversion
was achieved with 0.010 g of catalyst. Upon increasing catalyst amount to 0.015 g the
conversion of styrene improved to 75 % but no appreciable improvement was noted with 0.020 g
of catalyst. Therefore, 0.015 g of catalyst was considered optimum for the maximum conversion
of styrene.
18
Page 18 of 33

408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
The amount of HClO4 was optimized by taking substrate to HClO4 ratios of 1:1, 1:2 and
1:3 under above reaction conditions; Fig. 5 (b). The addition of HClO4 to the catalytic reaction
mixture in four equal portion at t = 0, 15, 30 and 45 min for each set of reaction was the
minimum condition to avoid decomposition of the catalyst. At a substrate to HClO4 ratio of 1:1,
only 75% conversion was obtained in 2 h of reaction time but this conversion reached 96% at
molar ratio of 1:2. On increasing this ratio further to 1:3 reduced the conversion time but the
overall conversion of styrene remained nearly constant. Therefore, styrene to HClO4 molar ratio
of 1:2 was taken for further optimization of other parameters. Other acid like H2SO4 could also
be used successfully with nearly same result.
To understand the effect of oxidant, three different styrene : aqueous 30 % H2O2 molar
ratios viz. 1:1, 1:2, and 1:3 were considered for a fixed amount of styrene (1.04 g, 10 mmol) and
catalyst (0.015 g). As illustrated in Fig. 5 (c), increasing the styrene to oxidant ratio from 1:1 to
1:2 increases the conversion from 67 to 96%. However, further increasing this ratio to 1:3 shows
no predominant conversion. Thus substrate to H2O2 ratio of 1:2 was considered the best one for
the maximum oxidative bromination of styrene.
Similarly, for styrene (1.04 g, 10 mmol), catalyst (0.010 g), CH2Cl2–H2O2 (40 mL, v/v),
H2O2 (2.27 g, 20 mmol) and aqueous HClO4 (2.86 g, 20 mmol, added as mentioned above), three
different amounts of KBr i.e.10, 20 and 30 mmol were taken and the reaction was carried out at
40 oC. The obtained conversion was only 44 % with 10 mmol KBr but increasing the amount to
20 mmol improved this conversion to 96% which further improved to 99% at 30 mmol KBr as
shown in Fig. 5 (d). Therefore, 20 mmol KBr was considered the best one for the maximum
conversion of styrene.
Table 8 provides conversion of styrene under different reaction conditions and selectivity of
different reaction products under particular condition after 2 h of reaction time. From the data
presented in Table 8, it is clear that the best suited reaction conditions for the maximum
oxidative bromination of 10 mmol of styrene are (entry no. 4): PS-[MoVIO2(sal-iah)(MeOH]
(0.015 g), HClO4 (2.86 g, 20 mmol ), aqueous 30% H2O2 (2.27 g, 20 mmol) and KBr (2.38 g, 20
mmol) (for GC traces see Fig. S3).
437
19
Page 19 of 33

100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
(a)
1:1
1:2
1:3
(b)
0.010 g
0.015 g
0.020 g
0
15
30
45
60
75
90 105 120
0
15
30
45
60
75
90 105 120
Time (min.)
Time (min.)
100
100
90
80
70
60
50
40
30
20
10
0
(c)
(d)
1:1
1:2
1:3
90
80
70
60
50
40
30
20
10
0
1:1
1:2
1:3
0
15
30
45
60
75
90 105 120
0
15
30
45
60
75
90 105 120
Time (min.)
Time (min.)
438
439
440
441
Fig. 5. (a) Effect of amount of catalyst on the oxidative bromination of styrene. (b) Effect of
amount of HClO4 on the oxidative bromination of styrene. (c) Effect of amount of H2O2 (H2O2/
styrene molar ratio) on the oxidative bromination of styrene. (d) Effect of amount of KBr on the
oxidative bromination of styrene. For reaction conditions refer to Table 8.
20
Page 20 of 33

0
20
100
80
60
40
20
0
Styrene
2-Bromo-1-phenylethane-1-ol
1,2-Dibromo-1-phenylethane
1-Phenylethane-1,2-diol
Others
40
60
80
100
15
30
45
60
75
90
105 120
Time (min.)
442
443
444
Fig. 6. Consumption of styrene and variation in the selectivity of different reaction products as a
function of time.
445
446
Table 8
447
448
Results of oxidative bromination of styrene (1.04 g, 10 mmol) using catalyst PS-[MoVIO2(sal-
iah)(MeOH)] (3) after 2 h of reaction time.
Entry
No.
KBr
(g, mmol,
eq.) a
H2O2
(g, mmol,
eq.)
HClO4
(g, mmol,
eq.)
Catalyst
(g)
CH2Cl2/H2O
% Conv.,
TOF (h-1)
% selectivity
% Mono-
bromo
% Di-
bromo
% Di-ol
%
(v/v, mL)
others
1
2
3
4
5
6
7
8
9
2.38, 20, 2 2.27, 20, 2 1.43, 10, 1
2.38, 20, 2 2.27, 20, 2 1.43, 10, 1
2.38, 20, 2 2.27, 20, 2 1.43, 10, 1
2.38, 20, 2 2.27, 20, 2 2.86, 20, 2
2.38, 20, 2 2.27, 20, 2 4.29, 30, 3
2.38, 20, 2 1.13, 10, 1 2.86, 20, 2
2.38, 20, 2 3.39, 30, 3 2.86, 20, 2
1.19, 10, 1 2.27, 20, 2 2.86, 20, 2
3.57, 30, 3 2.27, 20, 2 2.86, 20, 2
0.010
0.015
0.020
0.015
0.015
0.015
0.015
0.015
0.015
20 /20
20/20
20/20
20/20
20/20
20/20
20/20
20/20
20/20
67, 1506
75, 1124
76, 854
35.4
37.2
39.2
45.0
13.5
38.3
29.2
55.0
24.7
1.9
2.7
1.4
2.0
2.8
2.9
2.2
2.3
1.9
59.9
59.1
56.8
51.2
81.4
57.6
66.2
41.9
71
2.7
1.1
2.6
1.7
2.3
1.2
2.5
0.8
2.4
96, 1439
99, 1484
67, 1004
99, 1484
44, 659
99, 1484
449
450
451
452
453
a eq. = equivalent amount
For 96% conversion of styrene after 2 h of reaction time under these conditions, the selectivity of
the reaction products follows the order: 1-phenylethane-1,2-diol (51.2%) > 2-bromo-1-
phenylethane-1-ol (45.0%) > 1,2-dibromo-1-phenylethane (2.0%). The consumption of styrene
21
Page 21 of 33

454
455
456
457
458
459
460
461
and the selectivity of different products under the optimized reaction conditions have also been
analyzed as a function of time and are presented in Fig. 6. The selectivity of the formation of 1-
phenylethane-1,2-diol and 2-Bromo-1-phenylethane-1-ol starts with ca. 46 and 48%,
respectively. With time these conversions slowly change and end up at 51.2 and 45.0%,
respectively. The selectivity of the formation of 1,2-dibromo-1-phenylethane and other un-
identified products always remains below 2% during these periods. Catalytic potential of 3
compares well with the activities shown by other molybdenum and vanadium complexes
[33,34,37-40,43].
462
463
The catalytic activity of the recovered catalyst from two fresh runs, after washing with
acetonitrile and drying, was also carried out and result shows about 95% conversion, indicating
the recyclability of the catalyst. Under the above reaction conditions the catalytic activity of neat
complex [MoVIO2(sal-iah)(MeOH)] (1) gave 92% conversion where selectivity of the reaction
products is similar to the one obtained by supported complex. Thus, catalytic potential of
supported as well as neat complexes both are good but the recyclability of the supported catalyst
makes it better over the non-supported one. In the absence of catalyst, the reaction mixture gave
ca. 45% conversion of styrene under above optimized reaction conditions.
464
465
466
467
468
469
470
471
3.8.2. Oxidative bromination of trans-stilbene
472
473
474
475
476
477
478
479
480
481
482
483
A biphasic chloroform-water system was found to be suitable to carry out oxidative
bromination of trans-stilbene. Oxidative bromination of trans-stilbene gave mainly three
products: i) 2,3-diphenyloxirane (trans-stilbene oxide), ii) 2-bromo-1,2-diphenylethanol and iii)
1,2-dibromo-1,2-diphenylethane; Scheme 4. About 2 h was required to acquire equilibrium with
maximum conversion. The reaction conditions for the maximum oxidative bromination of trans-
stilbene were also optimized considering all these parameters stated above such as amounts of
catalyst, aqueous 30% H2O2, KBr and 70% HClO4. Details of the reaction conditions, the
corresponding oxidative brominated and other products, and % selectivity of different products
under various conditions are summarized in Table 9. It is clear from the table that the optimized
reaction conditions (entry no. 5) for this reaction are: trans-stilbene (0.90 g, 5 mmol)), KBr (2.36
g, 20 mmol) aqueous 30 % H2O2 (2.27 g, 20 mmol) catalyst precursor (0.015 g), aqueous 70%
HClO4 (2.86 g, 20 mmol) and CHCl3/H2O (40 mL, 50% v/v). Under these conditions, a
22
Page 22 of 33

484
485
486
487
maximum of 96 % conversion of trans-stilbene was obtained where selectivity of the reaction
products follows the order: 2-bromo-1,2-diphenylethanol (49.0%) > 1,2-dibromo-1,2-
diphenylethane (47.5%) > 2,3-diphenyloxirane (trans-stilbene oxide) (1.9%) (for GC traces see
Fig. S4).
488
489
490
491
492
493
The catalytic activity obtained here compares well with the literature. NH4VO3 catalyzed
oxidative bromination of trans–stilbene with moderate conversion in aqueous medium in the
presence of H2O2, KBr and HBr has been reported by Hirao et al. [52]. A maximum of 91%
conversion of trans–stilbene with the selectivity order of 2,3-diphenyloxirane (trans–stilbene
oxide) (66%) > 1,2-dibromo-1,2-diphenylethane (24%) > 2-bromo-1,2-diphenylethanol (8%)
was obtained by PS–im[VVO2(pan)] (Hpan = 1-(2-pyridylazo)-2-naphthol) [40].
494
495
496
497
498
499
500
501
502
503
The catalytic activity of the recovered catalyst shows almost similar (93 %) conversion
and neat complex [MoVIO2(sal-iah)(MeOH)] gave 90% conversion with essentially similar
selectivity of reaction products. Control experiment without catalyst under above reaction
conditions gave only 51 % conversion of trans–stilbene while only 2 % conversion of was
obtained in the absence of KBr. In the absence of oxidant and KBr, no formation of trans–
stilbene oxide confirms that dioxido group of catalyst does not transfer its oxygen to the
substrate directly. Thus, neat as well as supported catalyst both enhances the reaction while the
recyclability of the supported catalyst makes it better over the non-supported one.
OH
Br
H2O2, KBr
HClO4
504
505
506
507
508
509
510
511
O
Br
Br
trans-stilbene
2,3-diphenyloxirane
2-bromo-1,2-diphenyl
ethanol
1,2-dibromo-1,2-diphenyl
ethane
Scheme 4. Oxidative bromination products of trans-stilbene.
23
Page 23 of 33

512
513
514
Table 9
Results of oxidative bromination of trans-stilbene (0.90 g, 5 mmol) using catalyst PS-[MoVIO2(sal-
iah)(MeOH)] (3) after 2 h of reaction time.
Entry
No.
KBr
(g, mmol,
eq.) a
H2O2
(g, mmol,
eq.)
HClO4
(g, mmol,
eq.)
Catalyst
(g)
CHCl3/H2O
(v/v, mL)
% Conv.,
TOF (h-1)
% selectivity
% Di-
% Mono-
bromo
%
%
bromo
T.S.O.b
others
1
2
3
4
5
6
7
8
9
2.38, 20, 4 2.27, 20, 4 4.29, 30, 6
2.38, 20, 4 2.27, 20, 4 4.29, 30, 6
2.38, 20, 4 2.27, 20, 4 4.29, 30, 6
2.38, 20, 4 2.27, 20, 4 1.43, 10, 2
2.38, 20, 4 2.27, 20, 4 2.86, 20, 4
2.38, 20, 4 1.13, 10, 2 2.86, 20, 4
2.38, 20, 4 1.70, 15, 3 2.86, 20, 4
1.19, 10, 2 2.27, 20, 4 2.86, 20, 4
1.79, 15, 3 2.27, 20, 4 2.86, 20, 4
0.015
0.020
0.025
0.015
0.015
0.015
0.015
0.015
0.015
20 /20
20/20
20/20
20/20
20/20
20/20
20/20
20/20
20/20
97, 727
97, 545
98, 441
57, 427
96, 720
80, 600
81, 607
40, 300
78, 585
35.5
39.4
40.8
46.4
49.0
43.7
46.2
55.9
56.5
56.4
56.3
55.6
50.6
47.5
48.3
36.9
33.1
36.8
4.3
3.2
2.2
2.6
1.9
4.4
10.6
6.9
3.4
3.8
1.0
1.5
0.4
1.6
3.6
6.0
4.2
3.3
515
516
a eq. = equivalent amount
b T.S.O. = trans-stlbene oxide
517
518
519
3.9. Reactivity of [MoVIO2(sal-iah)(MeOH)](1) with H2O2 and possible reaction pathway of the
catalyst
520
521
522
523
524
525
526
527
528
529
530
531
The formation of [MoO(O2)]2+ intermediate using [MoO2]2+ complexes has been
established in the literature. We have been able to isolate peroxido complex [MoVIO(O2)(sal-
iah)(MeOH)] (2) by the reaction of H2O2 and characterize it. Its in-situ formation has also been
established here by electronic absorption spectroscopy. Thus, the titration of a methanolic
solution of 1 (3.64 × 10–4 M) with 30 % H2O2 (one drop) dissolved in 10 ml of MeOH results in
the shift of 380 nm band to 400 nm along with increase in intensity (inset of Fig. 7) . The
intensities of other bands i.e. bands at 320, 289, 279 and 220 nm in diluted methanolic solution
(7.2 × 10–5 M) increases regularly without shifting (Fig. 7). The shape of final spectrum is
similar to the spectrum of peroxide complex 2, thus verifying the formation of similar
oxidoperoxido species in solution as well.
24
Page 24 of 33

2.0
1.5
1.0
0.5
0.0
3.6
3.0
2.4
1.8
1.2
0.6
0.0
400
350 400 450 500 550
200
300
400
500
Wavelength (nm)
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
Fig. 7. UV-Vis spectral changes observed during titration of [MoVIO2(sal-iah)(MeOH)] (1) with
H2O2. The spectra recorded after successive addition of one drop portions of dilute H2O2 (1 drop
of 30% H2O2 in 10 ml MeOH) to 22 mL of 7.2× 10–5 M methanolic solution of 1. Inset shows
similar spectral changes with 3.64 × 10–4 M solution of 1 in methanol.
It is normally accepted that V-dependent bromoperoxidase enzymes (V-BrPOs)
[33,34,40,53,54] in the presence of hydrogen peroxide [55], forms a peroxido intermediate
derivative which oxidizes the bromide ion to bromine equivalent intermediate. This intermediate
then either brominates an organic substrate or reacts with another molecule of Br− to form
bromine. The peroxide [MoO(O2)]2+ intermediate species form here may similarly oxidize the
−
bromide (to Br2, Br3 and/or HOBr), which may react with styrene to give bromonium ion as
intermediate. The attack of nucleophile Br– on the α-carbon of the intermediate gives 1,2-
dibromo-1-phenylethane while attack of H2O gives 2-bromo-1-phenylethane-1-ol. The
nucleophile H2O may further attack on the α-carbon of 2-bromo-1-phenylethane-1-ol to give 1-
phenylethane-1,2-diol (Scheme 5) [40]. The poor selectivity of dibromo product is possibly due
to its fast sequential conversion into the mono-bromo derivative, which in turn converts into diol.
We have also tested the conversion of monobromo derivative alone under the optimized reaction
conditions and observed the formation of 1-phenylethane-1,2-diol (Fig. S5). Thus the formation
of good amount of 1-phenylethane-1,2-diol is justified under any experimental conditions
25
Page 25 of 33

552
553
554
555
556
557
mentioned in Table 8. The presence of acid in the aqueous phase is possibly promoting the
protonation of the peroxido moiety and the presence of KBr is essential to get reasonable amount
of brominated product(s).
Following similar mechanisms (Scheme 6) may also be proposed for the formation of
different products upon oxidative bromination of trans-stilbene [40].
Br
Br
Br
Br
Br
Br
Br
H
OH
OH2
OH2
δ
HO
Br
Br
HBr
OH2
δ
OH
OH
OH2
OH
558
559
560
561
562
Scheme 5. Proposed mechanisms for the formation of three main products, after the bromonium
ion is formed by action of catalytically generated HOBr on styrene.
26
Page 26 of 33

Br
Br
H
H
H
Br
H
Br
1,2-dibromo-1,2-diphenylethane
Br
Br
H
Br
H
H
H
H2O
H
HO
H
H
OH2
2-bromo-1,2-diphenylethanol
Br
H
H
intramolecular
H
H
HO
SN2
Br
H
H
O
H
O
H
2,3-diphenyloxirane
563
564
Scheme 6. Proposed mechanisms for the formation of products, after the bromonium ion is
formed by action of catalytically generated HOBr on trans-stilbene.
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
4. Conclusions
Complex [MoVIO2(sal-iah)(MeOH)] (1) with dibasic tridentate ONO donor ligand H2sal-
iah (I) derived from salicylaldehyde and indole-3-acetic hydrazide has been prepared which can
also be converted, by treatment with H2O2, to the corresponding peroxido-complex
[MoVIO(O2)(sal-iah)(MeOH)] (2). Complex 1 has also been grafted successfully through
covalent bonding of the nitrogen of the indole group to chloromethylated polystyrene cross-
linked with 5% divinylbenzene {now abbreviated as PS–[[MoVIO2(sal-iah)(MeOH)] (3)}.
Oxidative bromination of styrene and trans-stilbene has been successfully carried out
using 1 and 3 as catalyst precursor. The presence of some of the metal centers on the surface of
the polymer in 3 due to insertion of spacer between polymer support and catalyst possibly
allowed its better interaction with substrates and oxidant during catalytic reaction, also observed
earlier [44], resulting in better performance of the catalyst. Further, the recyclability of 3 over
non-polymer analog makes it useful functional model analog of haloperoxidases. A moderate
conversions of the substrates in the absence of the catalyst has also been obtained but the
selectivity profiles of the reaction products differ significantly. The peroxido species, similar to
27
Page 27 of 33

582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
[MoVIO(O2)(sal-iah)(MeOH)] (2) isolated in the solid state, has also been demonstrated to form
in solution which oxidizes bromide, in the presence of acid, which in turn reacts with styrene and
trans-stilbene to give corresponding bromonium ion as intermediate. This intermediate is
responsible for different reaction products of substrates.
Acknowledgements
MRM and NK thank the Council of Scientific and Industrial Research, New Delhi for
financial support. Gas chromatograph used in this study was procured from the financial
assistance provided by Department of Science and Technology (DST), Government of India,
New Delhi (SR/S1/IC-32/2010).
Appendix A. Supplementary data
CCDC 990876 contains the supplementary crystallographic data for the structure reported
in this paper. These data can be obtained free of charge vihttp://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 doi: $$$$$.
Fragment of the crystal packing of complex [MoVIO2(sal-iah)(MeOH)] (1) and 13C NMR spectra
of H2sal-iah (I) and [MoVIO2(sal-iah)(MeOH)] (1) are presented in the supporting Information.
References
[1] M.M. Farahani, F. Farzaneh, M. Ghandi, Catal. Commun. 8 (2007) 6.
[2] M.M. Farahani, F. Farzaneh, M. Ghandi, J. Mol. Catal. A: Chem. 248 (2006) 53.
[3] K. Ambroziak, R. Pelech, E. Milchert, T. Dziembowska, Z. Rozwadowski, J. Mol. Catal.
A: Chem. 211 (2004) 9.
[4] Y. Sui, X. Zeng, X. Fang, X. Fu, Y. Xiao, L. Chen, M. Li, S. Cheng, J. Mol. Catal. A:
Chem. 270 (2007) 61.
[5] J. Zhao, X. Zhou, A.M. Santos, E. Herdtweck, C. C. Romao, F.E. Kühn, Dalton Trans.
(2003) 3736.
[6] X. Zhou, J. Zhao, A.M. Santos, F.E. Kühn, Z.Naturforsch. 59b (2004) 1223.
28
Page 28 of 33

612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
[7] J. M. Sobczak, J. J. Ziόlkowski, Appl. Catal. A 248 (2003) 261.
[8] M. Bagherzadeh, R. Latifi, L. Tahsini, V. Amani, A. Ellern, L. K. Woo, Polyhedron 28
(2009) 2517.
[9] A. Rezaeifard, I. Sheikhshoaie, N. Monadi, M. Alipour, Polyhedron 29 (2010) 2703.
[10] J. Pisk, D. Agustin, V. Vrdoljak, R. Poli, Adv. Synth. Catal. 353 (2011) 2910.
[11] J. Pisk, B. Prugovečki, D. Matković-Čalogović, R. Poli, D. Agustin, V. Vrdoljak,
Polyhedron 33 (2012) 441.
[12] K.C. Gupta, A.K. Sutar, Coord. Chem. Rev. 252 (2008) 1420.
[13] M. E. Judmaier, C. Holzer, M. Volpe, N. C. Mösch-Zanetti, Inorg. Chem. 51 (2012) 9956.
[14] X. Lei, N. Chelamalla, Polyhedron, 49 (2013) 244–251.
[15] J.M. Mitchell, N.S. Finney, J. Am. Chem. Soc. 123 (2001) 862.
[16] M.R. Maurya, U. Kumar, P. Manikandan, Dalton Trans. (2006) 3561.
[17] M. R. Maurya, A. Arya, P. Adão, J. Costa Pessoa, Appl. Catal. A: Gen. 351 (2008) 239.
[18] K. Jeyakumar, D.K. Chand, J. Chem. Sci. 121 (2009) 111.
[19] Z. Hu, X. Fu, Y. Li, Inorg. Chem. Commun. 14 (2011) 497.
[20] M. Bagherzadeh, M. M. Haghdoost, M. Amini, P.G. Derakhshandeh, Catal. Commun. 23
(2012) 14.
[21] R. D. Chakravarthy, K. Suresh, V. Ramkumar, D. K. Chand, Inorg. Chim. Acta 376
(2011) 57.
[22] I. Sheikhshoaie, A. Rezaeifard, N. Monadi, S. Kaafi, Polyhedron 28 (2009) 733.
[23] M.R. Maurya, Curr. Org. Chem. 16 (2012) 73.
[24] G. Grivani, A. Akherati, Inorg. Chem. Commun. 28 (2013) 90.
[25] J.H. Clark, D.J. Macquarrie, Org. Process Res. Dev. 1 (1997) 149.
[26] D. C. Sherrington in: Supported Reagents and Catalyst in Chemistry (Ed.: B. K. Hodnett,
A. P. Keybett, J. H. Clark, K. Smith), Royal Society of Chemistry, Cambridge (1998), p.
220.
[27] L. Canali, D. C. Sherrington, Chem. Soc. Rev. 28 (1999) 85.
[28] D.C. Sherrington, Catal. Today 57 (2000) 87.
[29] N. E. Leadbeater, M. Marco, Chem. Rev. 102 (2002) 3217.
[30] A. Butler, M. J. Clague, G. E. Meister, Chem. Rev. 94 (1994) 625.
29
Page 29 of 33