Synthesis, structural, spectral, electrochemical and catalytic properties of VO (IV) complexes containing N, O donors

Article abstract of DOI:10.1016/j.molstruc.2014.06.086

Complexes of the general formula M (X-DPMP)₂[where, (M = VO^IV), DPMP = 2-[(2,6-Diisopropyl-phenylimino)-methyl]-phenol and X = Br, BrCl, Ph] have been synthesized and characterized by IR, electronic, ESR spectral, magnetic and cyclic voltammetry measurements. The newly synthesized Schiff bases act as monobasic bidentate ligand in their complexes. The spectral data indicate that the ligand coordinates through the phenolic oxygen and azomethine nitrogen atoms. The observed parameters, hyperfine splitting constant (A) and Landé splitting energy (g) are found to be in good agreement with the values generally observed for the vanadyl complex with square pyramidal geometry. The cyclic voltammetric redox potentials of VO (IV) complexes suggest the existence of irreversible pairs in acetonitrile. The vanadium complexes were screened for sulfide oxidation studies and VO (C₁₉H₂₁BrON)₂or [VO (Br-DPMP)₂] was found to be an efficient catalyst for the oxidation of various sulfides to sulfoxides with PhIO terminal oxidant. Both aryl and alkyl sulfides were selected and converted into sulfoxides in good to excellent yields.

Full text of DOI:10.1016/j.molstruc.2014.06.086

Journal of Molecular Structure 1075 (2014) 227–233
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structural, spectral, electrochemical and catalytic properties
of VO (IV) complexes containing N, O donors
c
d
e
a,
K. Kanmani Raja b, , L. Lekha , R. Hariharan , D. Easwaramoorthy , G. Rajagopal
⇑
⇑
a Department of Chemistry, Madras Medical College, Chennai 600 003, Tamil Nadu, India
b Department of Chemistry, Government Art College for Men (A), Nandanam, Chennai 600 035, Tamil Nadu, India
c Department of Chemistry, Saveetha School of Engineering, Thandalam, Chennai 602 105, Tamil Nadu, India
d Department of Chemistry, Pachaiyappa’s College, Chennai 600 030, Tamil Nadu, India
e Department of Chemistry, B.S. Abdur Rahman University, Vandalur, Chennai 600 048, Tamil Nadu, India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
ꢀ
Various OV (IV) Schiff base complexes
have been synthesized.
Complexes are characterized by
spectral techniques.
Oxidation of various sulfides to
sulfoxides with PhIO.
Vanadyl complex with square
pyramidal geometry.
Crystal structure of Br,Cl-DPMP
O
O
R1
S
R2
VO(BrDPMP)2
(V)
PhIO
R1
S
R2
VO(BrDPMP)2
(IV)
PhI
Scheme for the oxidation of sulfide to sulfoxide using VO(C19H21BrON)2 as catalyst
a r t i c l e i n f o
a b s t r a c t
Complexes of the general formula M (X-DPMP)2 [where, (M = VOIV), DPMP = 2-[(2,6-Diisopropyl-phenyli-
mino)-methyl]-phenol and X = Br, BrCl, Ph] have been synthesized and characterized by IR, electronic,
ESR spectral, magnetic and cyclic voltammetry measurements. The newly synthesized Schiff bases act
as monobasic bidentate ligand in their complexes. The spectral data indicate that the ligand coordinates
through the phenolic oxygen and azomethine nitrogen atoms. The observed parameters, hyperfine split-
ting constant (A) and Landé splitting energy (g) are found to be in good agreement with the values gen-
erally observed for the vanadyl complex with square pyramidal geometry. The cyclic voltammetric redox
potentials of VO (IV) complexes suggest the existence of irreversible pairs in acetonitrile. The vanadium
complexes were screened for sulfide oxidation studies and VO (C19H21BrON)2 or [VO (Br-DPMP)2] was
found to be an efficient catalyst for the oxidation of various sulfides to sulfoxides with PhIO terminal oxi-
dant. Both aryl and alkyl sulfides were selected and converted into sulfoxides in good to excellent yields.
Ó 2014 Elsevier B.V. All rights reserved.
Article history:
Received 25 March 2014
Received in revised form 26 June 2014
Accepted 26 June 2014
Available online 3 July 2014
Keywords:
Schiff base
Oxovanadium (IV)
Cyclic voltammetry
Oxidation
PhIO
Sulfoxide
Introduction
coordination chemistry for developing stereochemical models in
main group, inner-transition and transition metal coordination
The design, synthesis and structural characterization of Schiff
base complexes are widely employed as privileged ligands in
chemistry [1,2]. This is mainly due to their ease of preparation,
good solubility in common solvents, structural diversities, mag-
netic, spectral, redox and catalytic properties [3–8]. Transition
metal complexes contain oxygen and nitrogen donor Schiff base
ligands, which can be modified by choosing the appropriate amine
precursors and ring substituents due to its versatility [9]. Bidentate
⇑
Corresponding authors. Cell: +91 9840712397 (K.K. Raja), +91 9444644661
(G. Rajagopal).
E-mail addresses: kkanmaniraja@gmail.com (K. Kanmani Raja), rajagopal18@
yahoo.com (G. Rajagopal).
http://dx.doi.org/10.1016/j.molstruc.2014.06.086
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

228
K. Kanmani Raja et al. / Journal of Molecular Structure 1075 (2014) 227–233
ligands containing imine groups have also been used as the modu-
lators of structural, electronic and catalytic properties of transition
metal centers [7,10].
addition of 5-chloro-salicylaldehyde [2 mmol]. The reaction mix-
ture was then refluxed for 3 h. Upon cooling to 0 °C, yellow solid
precipitated from the reaction mixture. The solid precipitate was
filtered, washed with ice cold ethanol and dried in vacuum over
a hydrous CaCl2.
The coordination chemistry of oxovanadium is highly ligand
dependent and more important in biological systems [11–13] as
well as catalytic systems [14,15]. Due to the d1 configuration, vana-
dium (IV) ionic species are easily identified by EPR spectroscopy.
Typical eight-line patterns are observed due to hyperfine interac-
tion of the V nucleus (I = 7/2) [16]. Due to less toxicity [17], the
Schiff base complexes of vanadyl ion are topic of many research
reports [14,18,19]. In continuation of our work [20–22], the pre-
ceding communication complex formation of VO (IV) with the
derivatives of 2-[(2,6-Diisopropyl-phenylimino)-methyl]-phenol
(Fig. 1), which contain nitrogen and oxygen donor atoms where
synthesized, investigated using different physio-chemical tech-
niques and used for catalytic system due to its increasing
importance.
2,4-Bromo-2-chloro-6-[(2,6-Diisopropyl-phenylimino)-methyl]-
phenol[Br,Cl-DPMP]
Overall yield 75%. Anal. Calc. C19H21BrClON: C, 57.82; H, 5.33; N,
3.55. Found: C, 57.68; H, 5.22; N, 3.45%. ppm: 14.1 (s, 1H), 8.23 (s,
1H), 7.68–7.70 (d, 1H), 7.33–7.34 (d, 1H), 7.22–7.28 (m, 3H), 2.91–
2.98 (m, 2H), 1.18–1.21 (d, 12H).
4-Bromo-2-[(2,6-Diisopropyl-phenylimino)-methyl]-phenol [Br-
DPMP]
Overall yield 75%. Anal. Calc. C19H22BrON: C, 63.35; H, 6.11; N,
3.89. Found: C, 63.25; H, 6.25; N, 3.99%. ppm: 12.95 (s,1H), 8.28
(s, 1H), 7.03 (d, 1H), 7.23–7.41 (m, 5H), 2.95–3.02 (m, 2H), 1.20–
1.23 (d, 12H).
Experimental
Material
1-[(2,6-Diisopropylphenylimino)methyl] naphthalen-2-ol [Np-DPMP]
Overall yield 75%. Anal. Calc. C23H25ON: C, 83.34, H, 7.60; N,
4.23. Found: C, 83.23; H, 7.64; N, 4.21%. ppm: 13.11 (s, 1H), 8.30
(s, 1H), 7.34–7.44 (m, 2H), 7.18 (s, 3H), 7.05–7.08 (d, 1H), 6.94–
6.99 (m, 2H), 1.16–1.19 (d, 12H).
Chemicals used for the preparation of the ligands and com-
plexes were purchased from Aldrich and used as such. The purity
of ligands and metal complexes was checked by TLC.
Physical measurements
Synthesis of VO (X-DPMP)2 complexes
The magnetic susceptibilities of the complexes in the solid state
were measured on a Gouy balance at room temperature using
Hg[Co(SCN)4] as calibrant. The IR spectra of the ligands and com-
plexes in KBr (4000–400 cmꢁ1) were recorded on a Perkin Elmer
577 grating spectrophotometer. The electronic spectra in MeCN were
obtained on a Shimadzu-160 UV–Vis. Spectrophotometer. Microa-
nalyses for the carbon, hydrogen and nitrogen content of the new
complexes were carried out by the CDRI, Lucknow, India. The metal
contents of the complexes were estimated by incinerating them to
their oxides in the presence of ammonium oxalate. 1H NMR spectra
were recorded in CDCl3 with TMS as an internal standard on a Bruc-
ker 300 MHz spectrometer. X-band e.s.r. spectra were recorded on a
Varian-E-12 spectrometer with a quartz Dewar for measurements at
the liquid N2 temperature and the spectra were calibrated with
DPPH. Cyclic voltammetric measurements were made in MeCN
(HPLC grade) using BAS-CV50 electrochemical analyzer. The three
electrode cell comprised a reference Ag/AgCl, auxiliary Pt and the
working glassy carbon electrodes. Bu4NClO4 was used as supporting
electrolyte. The single crystal XRD data collection have been
obtained using APEX2 (Bruker, 2004), IIT Madras, Chennai, India.
All the complexes were prepared using the following procedure
(Fig. 2). Methanolic solution (20 mL) of the Schiff base (1 mmol)
and the Vanadyl acetylacetonate (0.5 mmol) in methanol (10 mL)
were mixed thoroughly and boiled under reflux for 4 h, and then
cooled to room temperature. The resulting green colored precipi-
tate was filtered, washed in the ice cold methanol and dried ‘in
vacuum’.
Typical procedure for sulfoxidation
VO (BrDPMP)2 (0.1 mmol) and sulfide (1 mmol) were dissolved
in CH2Cl2 (3 ml) and the solution was stirred for five minutes. To
this solution PhIO was added (1.1 mmol) at once. The reaction
was monitored by TLC at regular intervals and continued for stip-
ulated reaction time. After removal of the solvent, the residue was
purified by Silica gel flash chromatography to afford sulfoxide. All
the sulfoxides thus obtained were identified by comparing NMR
data with values reported in the literature [8] and those of the
authentic samples.
Synthesis of ligands
Results and discussion
An ethanolic solution of 2,6-diisopropylaniline [2 mmol] was
magnetically stirred in a round bottom flask followed by drop wise
The color, magnetic moments and absorption maxima of the
ligands and their complexes are given in Table 1. The metal to
ligand ratio of all the complexes was found to be 1:2. The chelates
are soluble in CH3CN, DMSO and CHCl3 but insoluble in water.
N
Magnetic measurements
CH
OH
The magnetic susceptibility measurements in the solid state
show that the oxovanadium complexes are paramagnetic at room
temperature. The
fall in the 1.9–2.1 B.M. range corresponding to one unpaired
leff. value of the oxovanadium (IV) complexes
X
Fig. 1. The chemical structure of Schiff base Ligand [X-DPMP] [X = Br, BrCl, Ph].
electron.

K. Kanmani Raja et al. / Journal of Molecular Structure 1075 (2014) 227–233
229
X
O
N
CH3OH
O
V
N
VO(acac)2
CH
N
CH
CH
reflux
4h
OH
O
X
X
VO(X-DPMP)2
X = Br, BrCl, Ph
Fig. 2. Scheme of synthesis of VO (X-DPMP)2 complex.
Table 1
Colour, magnetic moment and absorption maxima of metal complexes.
Complexes (mole. formula)
Colour
F.W.
Found % (calculated)
leff, (B.M.)
kmax. (cmꢁ1
)
C
H
N
M
VO (C19H21BrON)2
Green
Green
785.50
854.39
58.10
58.25
5.39
5.26
3.57
3.69
6.49
6.59
2.0
1.9
16,611
VO (C19H20BrClON)2
53.42
53.55
4.72
4.85
3.28
3.39
5.96
5.84
40,160
37,878
29,069
39,840
75.91
75.80
6.65
6.55
3.85
3.72
7.00
7.15
2.1
VO (C23H24NO)2
Green
727.83
31,847
26,385
IR spectra
frequency of enol form of phenolic AOH from the region
1280 cmꢁ1 confirms the participation of oxygen in the CAOAM
bond. The reaction of the enolic Schiff bases with VO2+ ion with
the elimination of a proton revealed by the presence of a new band
in the complexes around 1300 cmꢁ1 due to (CAO) [26]. Oxovana-
dium complexes show two new bands at 525–450 cmꢁ1 and
415–400 cmꢁ1 assigned to (MAO) and (MAN) [27] respectively.
This is further evidence for the square pyramidal geometry
proposed for VO2+ complex [28].
Infrared spectral bands for the ligands and their metal
complexes are shown in Table 2. All of the Schiff base ligands in
the present investigation exhibit a broadband centered at 3410–
3450 cmꢁ1 (Fig. 3). This suggests the presence of a strongly hydro-
gen bonded OH group [23]. This indicates the involvement of the
AOH group in intramolecular hydrogen bonding with the lone pair
of azomethine nitrogen [24].
All the Schiff base ligands show a sharp and strong band in the
range of 1610–1630 cmꢁ1 due to azomethine group. The IR spectra
of the oxovanadium complexes exhibit strong band near
1000 cmꢁ1, which can be assigned to the (V@O) [25]. This is indic-
ative of its monomeric form [19]. The observed C@N stretching
vibration of the ligands have been shifted towards the low energy
in the metal complexes and appearing at 1600–1607 cmꢁ1, which
suggests the coordination of the azomethine nitrogen with the
central metal atom [24,25]. The disappearance of characteristic
peak for the AOH group and the increase of shift towards higher
Electronic spectra
The electronic spectra of the oxovanadium were recorded in
10ꢁ3 molar DMF solutions in the range of 12,500–5000 cmꢁ1. The
kmax of electronic spectral peaks and respective molar extinction
coefficient along with their tentative assignments are given in
Table 1. Besides high intensity charge transfer transitions, all the
oxovanadium complexes displayed one low intensity d–d transi-
tion which may be assigned to b2 ? 1a*1 [29–31] transition in each
case assumes idealized C2v symmetry. The representative
electronic spectrum of the complex has been shown in Fig. 4. The
electronic spectra of all the complexes show three bands in the
region 40,000–25,000 cmꢁ1. These bands may be assigned to three
transitions as shown in Table 1 [32]. An absorption band in the
range 30,959–27,548 cmꢁ1 was observed, which may be associated
Table 2
Infrared spectral bands for the ligands and their metal complexes.
S. no.
Ligands and complexes
t
(OH)
t
(V@O)
t
(CH@N)
t(CAO)
with a
p ?
p* transition originating mainly in the azomethine
Free ligand
chromophore [33]. In the UV region, a strong band around
1
2
3
4
Br-DPMP
Br, Cl-DPMP
I-DPMP
3444
3436
3435
3444
–
–
–
–
1624
1623
1623
1623
1272
1293
1272
1172
37,174–36,764 cmꢁ1 attributed to the
ring [34].
p ? p
* transition of benzene
Np-DPMP
Oxovanadium complex
EPR spectra
1
2
3
VO (C19H21BrON)2
VO (C19H20BrClON)2
VO (C23H24NO)2
–
–
–
995
1008
993
1607
1605
1601
1300
1300
1300
The X-band EPR spectra of VO2+ complex were recorded in
acetonitrile solution without DPPH (Fig. 5). These complexes are

230
K. Kanmani Raja et al. / Journal of Molecular Structure 1075 (2014) 227–233
Fig. 3. Comparative IR spectra of (a) Br-DPMP Schiff base ligand (b) VO (Br-DPMP)2 complex.
paramagnetic and gave typical axial EPR spectra for solid sample at
room temperature. The complex shows an eight line pattern,
characteristic of an unpaired electron being coupled with a vana-
dium nuclear spin [I = 7/2]. Thus, all the compounds show well
resolved axial anisotropy with g|| < g\ and A|| > A\ relationship
characteristic of an axially compressed d1xy configuration [35]. The
observed spectral parameters for this compound are tabulated in
Table 3. The range of g\ = 1.8320–1.8386, g|| = 1.7948–1.8446 and
giso = 1.8196–1.8362. The observed gav value deviates from the free
ion value 2.0036, and this suggests that the complex is appreciably
covalent [36]. Ligand nitrogen super hyperfine splitting is not
observed in the complex. This indicates the unpaired electron to
be in b2g (dxy,
2B2 ground state) orbital localized on metal, thus
excluding the possibility of its direct interaction with the ligand
[37]. The parameters A and g are found to be in agreement with
the values generally observed for the vanadyl complex with square
pyramidal geometry [38].
Cyclic voltammetry
Fig. 4. UV-representative spectra of VO (NpDPMP)2 complex.
The electro chemical behaviors of VO (IV) were studied using
cyclic voltammetric [CV] technique in acetonitrile solution con-
taining 0.1 tetrabutylammonium perchlorate [TBAP] as the sup-
porting electrolyte. All CVs and their data are presented in Fig. 6
and Table 4.
CV data of the oxovanadium which exhibit an irreversible redox
value with an additional oxidation wave. The CV shows that two
electron reduction and two step oxidation reactions. This reduction
wave refers to the VO (II)/VO (0) couples and the corresponding
oxidation reaction occurs as VO (0) ? VO (I) ? VO (II).
The redox behavior of VO (IV) at glassy carbon electrode surface
follows diffusion controlled process which is evident from the plot
p
of SR [Square root of Scan Rate] Vs Peak current. A straight line
was obtained for different scan rates 25–200 mV sꢁ1 (Fig. 7).
X-ray crystallography
The representative crystal structure of the ligand Br, Cl-DPMP is
shown in Fig. 8 and there are two molecules in the asymmetric unit
of the compound, with dihedral angles between the aromatic rings
of 70.0 (2) and 81.9 (3)°. The crystal structure is stabilized by inter-
Fig. 5. Representative ESR spectra of VO (C19H21BrON)2 in LNT.
molecular CAHꢂ ꢂ ꢂ
p
and CABrꢂ ꢂ ꢂ
p interactions. In additional, the

K. Kanmani Raja et al. / Journal of Molecular Structure 1075 (2014) 227–233
231
Table 3
ESR spectral parameters of the Oxovanadium(II) complexes.
S. no.
Oxovanadium complexes
A|| ꢄ 10ꢁ4 (cmꢁ1
)
A\ ꢄ 10ꢁ4 (cmꢁ1
)
g||
g\
giso
Aiso ꢄ 10ꢁ4 (cmꢁ1
)
1
2
3
VO (C19H21BrON)2
VO (C19H20BrClON)2
VO (C23H24NO)2
165.43
163.14
161.14
46
46
55
1.8246
1.7948
1.8069
1.8320
1.8320
1.8386
1.8362
1.8196
1.8280
85.81
85.05
90.38
The amount of catalyst appeared to be an important parameter
for the reduction of reaction time. With increased quantity of cat-
alyst, the reaction took place more rapidly (entries 1 and 2). It was
found that 2 mol% of vanadium catalyst is the optimal condition for
a good yield (ꢃ90%) at room temperature. Further, reduction in
catalytic loading requires longer reaction time (entry 1).
The scope of vanadium complex catalyzed sulfoxidation has
been explored by using substituted aromatic sulfides. Table 6
summarizes the most significant results obtained under optimized
conditions. In all cases, sulfides were converted into the corre-
sponding sulfoxides in moderate to good yields. Various sulfides
were subject to oxidation under the stoichiometric condition given
in Table 6. Unsubstituted and substituted thioanisoles (entries 1–
4) underwent very smooth oxidation with over 90% yield. The
substituents on the phenyl group showed no significant effect on
reaction time (entries 2–4). But, nitro and cyano substituents show
little rate retardation due to their electron withdrawing property
(entries 5 and 6). Diphenyl sulfide underwent clean oxidation to
the corresponding sulfoxide with longer reaction time due to steric
hindrance (entry 7).
Fig. 6. Representative CV of VO (C19H20BrClON)2 complex.
Such rate retardation has already been clearly observed in the
oxidation of diphenyl sulfide with longer reaction time giving
low yield. The insertion of methylene group into diphenyl sulfide
reduced the steric hindrance as indicated by a little shorter
stacked molecules exhibit intramolecular OAHꢂ ꢂ ꢂN hydrogen
bonds [39].
Sulfoxidation study
The selective oxidation of organic compounds catalyzed by
transition metal ions is one of the most productive and elegant
techniques for the oxo functionalization of organic substrates
[40,41].
Many metal-salen complexes have been used as an efficient cat-
alyst, like Fe-Salen [42], Oxovanadium-Salen [43] and Ru-Salen
[41] for the oxidation of organic sulfides to sulfoxides. A variety
of oxovanadium complexes have been shown to catalyze the
oxidation of sulfides [44]. The report shows [45] that the asymmet-
ric oxidation of methyl phenyl sulfide to chiral sulfoxide has been
carried out using cumene hydroperoxide as an oxidant and
oxovanadium (IV) ligated by the tetra dentate Schiff base obtained
by double condensation of chiral 1,2 diaminocyclohexane with sal-
icylaldehyde or its substituted derivatives as catalyst.
The catalytic activity of VO (C19H21BrON)2 was tested with
methylphenyl sulfide as a model substrate (Table 5). A mixture
of methylphenyl sulfide (1 mmol) and PhIO (1 mmol) was treated
with various amounts of vanadium complex (1–5 mol%) at room
temperature, the sulfide oxidation occurs smoothly (entries 1–5).
p
Fig. 7. Scan rate Vs Peak current.
Table 4
Electrochemical data of Oxovanadium complexes.
S. no.
1
Oxovanadium complex
VO (C19H21BrON)2
Eap (mV)
Ecp (mV)
ꢁ972
D
Ep
Ep/2
Icp Eꢁ5
Iap Eꢁ6
ꢁ2.96
Icp/Iap
ꢁ613
359
1387
ꢁ792.5
1.41
ꢁ4.76
1387
2
3
VO (C19H20BrClON)2
VO (C23H24NO)2
ꢁ590
692
1363
ꢁ1030
440
576
1363
ꢁ810
1.36
1.28
ꢁ2.66
ꢁ2.81
ꢁ5.11
ꢁ4.55
404
116
460
ꢁ554
118
ꢁ1080
342
526
289
ꢁ817

232
K. Kanmani Raja et al. / Journal of Molecular Structure 1075 (2014) 227–233
Fig. 8. Crystal structure of 2-Bromo-4-chloro-6-[(2,6-diisopropylphenyl)iminomethyl]phenol [Br, Cl-DPMP].
Table 5
Oxidation of methylphenyl sulfide using VO (BrDPMP)2/PhIO system at room
temperature.
O
S
O
R1
R2
VO(BrDPMP)2
(V)
PhIO
O
S
S
CH3
VO(BrDPMP)2,PhIO
CH3CN, r.t.
CH3
Entry
Catalyst (mol%)
Solvent
Time (min.)
Yield (%)
1
2
3
4
5
1
2
5
2
2
CH3CN
CH3CN
CH3CN
CH2Cl2
THF
180
100
90
120
140
90
93
92
85
86
R1
S
R2
VO(BrDPMP)2
(IV)
PhI
Fig. 9. Proposed scheme for the oxidation of sulfide to sulfoxide.
reaction time (entries 8 and 9). Some linear dialkyl sulfides (entries
10–11) underwent smooth oxidation very quickly (60–70 min)
with excellent yield. To test the catalytic activity of the present
catalyst, a model run was carried out with thioanisole without
catalyst and was found that there was no sulfoxidation reaction
taking place with the typical reaction time.
The possible reaction pathway of the catalyst during catalytic
action by reacting methanolic solution of Vanadium Schiff base
complex with PhIO dissolved in methanol has been given as per
the earlier report [46,47]. The catalytic pathway suggests the
formation of peroxo species on the interaction of OV (IV) with
PhIO. The in situ formation of peroxo species has been observed
previously by OV (IV) on interaction with the oxidant like PhIO,
H2O2, tert-butylhydroperoxide etc. This insitu generated peroxo
species finally transfer oxygen to the substrates to give oxidized
products. Thus, the reversible intermediate formation of facile
peroxo species may be responsible for the catalytic performance
of the catalyst [46]. This hypervalent V (V)@O state transfers oxy-
gen to the substrate for the sulfoxidation (Fig. 9).
Table 6
Oxidation of sulfide into sulfoxides.
O
VO(BrDPMP)2,PhIO
CH3CN, r.t.
R1
S
R2
R1
S
R2
Entry
Sulfide
R1
Time (min.)
Yield (%)a
R2
1
2
3
4
5
6
7
8
9
Ph
Me
Me
Me
Me
100
100
95
93
91
92
90
88
90
88
90
91
88
90
92
p-MeC6H4
p-BrC6H4
p-ClC6H4
95
p-NO2C6H4
p-CNC6H4
Ph
Me
Me
Ph
160
150
300
120
110
60
PhCH2
PhCH2
Me(CH2)2
Me(CH2)3
Me(CH2)7
Ph
PhCH2
Me(CH2)2
Me(CH2)3
Me(CH2)7
10
11
12
70
70
a
Isolated yields.

K. Kanmani Raja et al. / Journal of Molecular Structure 1075 (2014) 227–233
233
[14] D.M. Boghaei, S. Mohebi, J. Mol. Catal. A: Chem. 179 (2002) 41–51.
[15] J.-Q. Wu, Y.-S. Li, Coord. Chem. Rev. 255 (2011) 2303–2314.
[16] G. Micera, D. Sanna, in: J.O. Nriagu (Ed.), Vanadium in the Environment, Part
Conclusions
Oxovanadium complexes of multisubstituted Schiff base
ligands have been prepared and characterized. The magnetic and
spectral evidence shows that the complexes are formed through
the coordination of phenolic oxygen and the azomethine nitrogen
atoms. Newly synthesized OV (IV) complexes are found to be
square pyramidal. The vanadium complex, VO (C19H21BrON)2 was
found to be an efficient catalyst for the oxidation of various sulfides
to sulfoxides with PhIO terminal oxidant (Fig. 9).
One: Chemistry and Biochemistry, John Wiley
(Chapter 7).
& Sons, New York, 1998
[17] F.T.G. Hudson, Vanadium Toxicology and Biological Significance, Elsevier,
NewYork, 1996. p. 140.
[18] R.C. Maurya, S. Rajput, J. Mol. Stuct. 794 (2006) 24–34.
[19] D.M. Boghaei, A. Bezaatpour, M. Behzad, J. Mol. Catal. A: Chem. 245 (2006) 12–
16.
[20] L. Lekha, K. Kanmaniraja, D. Easwaramoorthi, G. Rajagopal, J. Mol. Struct.
1056–1057 (2014) 307–313.
[21] L. Lekha, K.K. Raja, G. Rajagopal, D. Easwaramoorthy, J. Organomet. Chem. 753
(2014) 72–80.
[22] K. Kanmaniraja, L. Lekha, D. Easwaramoorthi, G. Rajagopal, J. Mole. Struct.
1060 (2014) 49–57.
Acknowledgements
[23] S. Konar, A. Jana, K. Das, S. Ray, S. Chatterjee, James A. Golen, Arnold L.
Rheingold, S.K. Kar, Polyhedron 30 (2011) 280–288.
[24] R.C. Maurya, H. Singh, A. Pandey, Sunth. React. Inorg. Met. Org. Chem. 32
(2002) 231–233.
[25] J. Selbin, Coord. Chem. Rev. 1 (1996) 293–314.
[26] C. Yuan, L. Lu, Y. Wu, Z. Liu, M. Guo, S. Xing, X. Fu, M. Zhu, J. Inorg. Biochem.
104 (2010) 978–986.
[27] A.M. Dona, H.A. El-Boraey, M.F. El-Samalehy, J. Therm. Anal. Calorim. 73 (2003)
987–995.
[28] N.M. El-Metwaly, R.M. El-Shazly, I.M. Gabr, A.A. El-Asmy, Spectrochim. Acta 61
(2005) 1113–1119.
The authors thank the Management, Correspondent and the
Principal of BS Abdur Rahman University, Chennai 600048, The
Principal, Staff members of department of Chemistry, Government
Arts College for men, Nandanam, Chennai – 600 035, The Principal,
Staff members of department of Chemistry, Saveetha School of
Engineering, Chennai – 602 105 and The Dean, Madras Medical
College, Rajivgandhi Government General Hospital, Chennai –
600 003 for providing research facilities.
[29] A.B.P. Lever, Inorganic Electronic Spectroscopy, second Ed., Elsevier,
Amsterdam, 1984. 387.
[30] R.C. Maurya, S. Rajput, J. Mol. Struct. 687 (2004) 35–44.
[31] S. Sarkara, K. Dey, Spectrochim. Acta Part A 77 (2010) 740–748.
[32] S.R. Aswale, P.R. Mandlik, A.S. Aswar, J. Ind. Chem. Soc. 79 (2002) 722–729.
[33] W. Guangbin, Spect. Lett. 32 (1999) 679–688.
[34] K.K. Raja, L. Lekha, D. Easwaramoorthy, G. Rajagopal, J. Mol. Struct. 1060
(2014) 49–57.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.2014.06.
086.
[35] G.R. Hausan, T.A. Kabanos, A.D. Kkera,idas, D. Mentazafos, A. Terzis, Inorg.
Chem. 31 (1992) 2587–2594.
[36] R.L. Dutta, A. Syamal, Elements of Magnetochemistry, second ed., Affiliated
East-West Press Pvt. Ltd, New Delhi, 1993. 225.
References
[37] B.T. Thaker, R.S. Barvalia, Spectrochim. Acta Part A 84 (2011) 51–61.
[38] R. Ando, H. Inden, M. Sugino, H. Ono, D. Sakaeda, T. Yagyu, M. Maeda, Inorg.
Chim. Acta 357 (2004) 1337–1344.
[39] K.K. Raja, I.M. Bilal, S. Thambidurai, G. Rajagopal, A. Subbiahpandi, Acta Cryst.
E64 (2008) o2265.
[40] B. Meunier (Ed.), Metal-oxo and metal-peroxo species in catalytic oxidations,
Struct. Bond., vol. 97, Springer, Berlin, 2000.
[41] N.S. Venkataramanan, G. Kuppuraj, S. Rajagopal, Coord. Chem. Rev. 249 (2005)
1249–1268.
[42] M. Baghezadeh, M. Amini, Inorg. Chem. Commun. 12 (2009) 21–25.
[43] I. Lippold, J. Becher, D. Klemm, W. Plass, J. Mol. Catal. A: Chem. 299 (2009) 12–
17.
[44] C. Bolm, Coord. Chem. Rev. 237 (2003) 245–256.
[45] K. Nakajima, M. Kojima, Bull. Chem. Soc. Jpn. 63 (1990) 2620–2630.
[46] M.R. Maurya, A.K. Chandrakar, S. Chand, J. Mol. Catal. A: Chem. 274 (2007)
192–201.
[1] R. Hernández-Molina, A. Mederos, in: J.A. McCleverty, T.J. Meyer (Eds.),
Comprehensive Coordination Chemistry II, vol. 1, Elsevier, Amsterdam, 2004,
pp. 411–446.
[2] A.K. Sharma, S. Chandra, Spectrochim. Acta A 78 (2011) 337–342.
[3] P.C. Wikins, J.M. Berg, Inorganic Chemistry in Biology, Oxford University Press,
Oxford, 1997.
[4] S. Yamada, Coord. Chem. Rev. 537 (1999) 190–192.
[5] D.E. Fenton, Chem. Soc. Rev. 28 (1999) 159–168.
[6] P.G. Cozzi, Chem. Soc. Rev. 33 (2004) 410–421.
[7] P.A. Vigato, S. Tamburini, Coord. Chem. Rev. 248 (2004) 1717–2128.
[8] B. Samanta, J. Chakraborty, S. Shit, S.R. Batten, P. Jensen, J.D. Masuda, S. Mitra,
Inorg. Chim. Acta 360 (2007) 2471–2484.
[9] B. De Clereq, F. Lefebvre, F. Verpoort, Appl. Catal. A 247 (2003) 345–364.
[10] P.A. Vigato, S. Tamburini, L. Bertolo, Coord. Chem. Rev. 251 (2007) 1311–1492.
[11] H. Sakurai, A. Tamura, J. Fugono, H. Yasui, T. Kiss, Coord. Chem. Rev. 245 (2003)
31–37 (and reference therein).
[12] T.S. Smith, R. LoBrutto, V.L. Pecoraro, Coord. Chem. Rev. 228 (2002) 1–18.
[13] M. Kalanithi, D. Kodimunthiri, M. Rajarajan, P. Tharmaraj, Spectrochim. Acta
Part A: Mol. Biomol. Spec. 82 (2011) 290–298.
[47] A. Rayati, M. Koliaei, F. Ashouri, S. Mohebbi, A. Wojtczak, A. Kozakiewicz, Appl.
Catal. A: Gen. 346 (2008) 65–71.