Oxidation of alkenes and sulfides catalyzed by a new binuclear molybdenum bis-oxazoline complex

Article abstract of DOI:10.1016/j.poly.2014.01.004

A novel bis(oxazoline) ligand derived from 1,3-dicyanobenzene was prepared and applied as a ligand for the preparation of a new binuclear molybdenyl complex. This ligand was characterized by UV-Vis, mass, ¹H NMR, and FT-IR spectroscopic methods, thermal and elemental analysis and X-ray diffraction. The molybdenum complex was prepared by the reaction of this ligand with MoO₂(acac)₂. The catalyst was also characterized by FT-IR, UV-Vis, and ICP spectroscopy, elemental and thermal analysis. This catalytic system was efficiently used for the oxidation of alkenes and sulfides in the presence of TBHP. The effect of different solvents and kind of oxygen donor was also studied in the oxidation reactions.

Full text of DOI:10.1016/j.poly.2014.01.004

Polyhedron 72 (2014) 19–26
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Oxidation of alkenes and sulfides catalyzed by a new binuclear
molybdenum bis-oxazoline complex
a,
Maedeh Moshref Javadi a, Majid Moghadam a, , Iraj Mohammadpoor-Baltork
⇑
⇑
,
Shahram Tangestaninejad a, Valiollah Mirkhani a, Hadi Kargar b, Muhammad Nawaz Tahir c
a Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-73441, Iran
b Department of Chemistry, Payame Noor University, Tehran 19395-3697, Iran
c Department of Physics, University of Sargodha, Punjab, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel bis(oxazoline) ligand derived from 1,3-dicyanobenzene was prepared and applied as a ligand for
the preparation of a new binuclear molybdenyl complex. This ligand was characterized by UV–Vis, mass,
1H NMR, and FT-IR spectroscopic methods, thermal and elemental analysis and X-ray diffraction. The
molybdenum complex was prepared by the reaction of this ligand with MoO2(acac)2. The catalyst was
also characterized by FT-IR, UV–Vis, and ICP spectroscopy, elemental and thermal analysis. This catalytic
system was efficiently used for the oxidation of alkenes and sulfides in the presence of TBHP. The effect of
different solvents and kind of oxygen donor was also studied in the oxidation reactions.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 16 November 2013
Accepted 4 January 2014
Available online 11 January 2014
Keywords:
Bis(oxazoline)
Molybdenum(VI) complex
Epoxidation
Sulfoxidation
1. Introduction
Since the first report on the synthesis of sulfoxides by Marcker
[7] in 1865, many processes for the conversion of sulfides to sulf-
The oxidation of organic substrates by transition metal
complexes has become an important research area in both organic
synthesis and bioinorganic modeling of oxygen transfer metalloen-
zymes. In the late 1960s, molybdenum complexes played a critical
role in homogeneous industrial catalysis in the Arco and Halcon
processes, involving the typical example of the industrial produc-
tion of propylene oxide using alkyl hydroperoxides as oxidants,
catalyzed by a homogeneous Mo(VI) (Scheme 1) [1].
Several oxomolybdenum(VI) complexes have recently been
explored as catalysts for liquid-phase olefin epoxidation, usually
employing tert-butyl hydroperoxide (TBHP) as the mono-oxygen
source [2–4]. Partial oxidation of alkenes to epoxides and reaction
products based on epoxides are both of academic and industrial
interest. Different epoxides are among the most widely used
intermediates in organic synthesis, pharmaceuticals together with
polymer production, and act as precursors for complex molecules
due to the strained oxirane ring [5]. They react to provide industri-
ally essential products such as surfactants, detergents, antistatic
agents and corrosion protection agents, lubricating oils, textiles
and cosmetics [6].
oxides [8] using nitric acid [7], hydrogen peroxide [9], dinitrogen
tetroxide [10], ozone [11], peracids [12], hydroperoxides [13] and
many other reagentshave been developed. Sulfoxides and sulfones
have found many applications in pharmacy [14,15] and other fields
such as engineering plastics and polymers [16]. Oxidation of sul-
fides is the most direct approach for the synthesis of sulfoxides
and sulfones [17]. Many different catalysts have been applied for
oxidation of organic substrates but in order to make this process
rapid, selective and consist of higher yields of products, the use
of catalysts is mandatory. As a result of the apparent interest in
the perfection of oxidation product synthesis, many explorations
have been commenced to develop catalysts for oxidation, e.g. sup-
ported metal oxides [18,19] as well as homogeneous transition
metal complexes [20,21]. Nevertheless, the reported methods
rarely offer the ideal combination of simplicity of method and
selectivity. Among all ligands used for example Schiff bases [22],
porphyrins [23], and other ligands, metal complexes of the oxazo-
line ligand bearing a N–O coordination sphere have been reported
[24,25] as one of the most efficient homogeneous catalysts. Their
functions have grown quickly and a broad range of catalytic reac-
tions has been described including oxidation, addition and reduc-
tion [26,27].
⇑
Corresponding authors. Tel.: +98 311 7932712; fax: +98 311 6689732
(M. Moghadam).
The aim of the present study is to find a highly active, selective,
and stable catalyst, based on the oxazoline moiety that can be used
under mild conditions.
E-mail addresses: moghadamm@sci.ui.ac.ir (M. Moghadam), imbaltork@sci.ui.
ac.ir (I. Mohammadpoor-Baltork).
http://dx.doi.org/10.1016/j.poly.2014.01.004
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

20
M. Moshref Javadi et al. / Polyhedron 72 (2014) 19–26
Scheme 1. Oxidation of propylene using alkyl hydroperoxides as oxidants, catalyzed by a homogeneous Mo(VI).
O
O
O
N
O
O
O
Mo
O
Mo
O
O
O
O
N
+ Oxidation products
or
O
R
O
or
S
O
S
O
O
TBHP, 1,2-DCE
S
+
R
R'
R
R'
R'
Scheme 2. Oxidation of alkenes and sulfides with TBHP catalyzed by [Mo2(O)4BOX(acac)2].
In this article, a novel binuclear molybdenum oxazoline com-
pound was synthesized and used as a homogeneous and efficient
catalyst for the epoxidation of olefins and oxidation of sulfides
with tert-BuOOH (Scheme 2). The effect of different solvents,
oxidants, and temperatures on the activity and selectivity of the
catalyst was also studied.
NC
HO
CN
OH
HO
OH
SSA
N
N
+
.
Reflux or
)
)
)
)
O
O
NH2
Mo(O)2(acac)2
Ethanol
2. Experimental
Reflux
All materials and chemicals were of commercial reagent grade
and prepared from Merck, Aldrich or Fluka chemical companies.
Alkenes were obtained from Merck or Fluka and were passed
through a column containing active alumina and/or silica to
remove peroxide impurities. 1H NMR spectra were recorded on a
Bruker Avance 400 MHz spectrometer using DMSO-d6 as solvent.
Elemental analysis was performed on a LECO, CHNS-932 analyzer.
Thermogravimetric analysis (TGA) were carried out on a Mettler
TG50 instrument under air flow at a uniform heating rate of
5 °Cminꢀ1 in the range 25–800 °C. FT-IR spectra were obtained as
potassium bromide pellets in the range of 400–4000 cmꢀ1 by a
JASCO 6300 spectrophotometer. Gas chromatography experiments
(GC) were performed on a Shimadzu GC-16A instrument using a
2 m column packed with silicon DC-200 or Carbowax 20 m.
UV–Vis spectra were obtained on a Shimadzu UV 265 spectrometer.
The Mo content of the catalyst was determined by a Jarrell-Ash
1100 ICP analysis. Mass spectra were recorded by a Platform II
spectrometer from Micromass, EI mode at 70 eV.
O
O
O
O
O
O
O-
Mo
O
Mo
O
=
O
O
O
O
O
O
N
N
O
Scheme 3. The synthesis route for BOX ligand and its Mo complex.
bis-oxazoline crystals were obtained as described above. Yield
91%; Mp 198 °C; Elemental Anal. Calc. for C14H16N2O4
(MW = 276.29) C, 60.86; H, 5.84; N, 10.14. Found: C, 58.69; H,
6.23; N, 10.16%. Exact Mass: 276.11; m/z: 276.11 (100.0%),
277.11 (15.9%), 278.12 (1.9%).
2.2. General procedure for synthesis of Mo complex
The bis-oxazoline was metallated as follows: a degassed ethanol
solution (40 ml) of the corresponding bis-oxazoline (0.276 g,
1 mmol) was added to a solution of Mo(O)2(acac)2 (1 mmol,
0.326 g) in absolute ethanol (20 ml) under argon atmosphere.
The reaction was stirred under reflux conditions for 24 h. The solu-
tion was then cooled, filtered and evaporated under reduced pres-
sure. Dissolving this crude product in methanol and evaporation
under reduced pressure for a second time, gave the pure product.
Yield: (0.257 g, 35%, light green powder). Elemental analysis: Anal.
Calc. for C24H28Mo2N2O12 (MW = 728.41): C, 39.57; H, 3.87; N, 3.85.
Found: C, 39.45; H, 3.76; N, 4.15%.
2.1. General procedure for ligand (BOX) synthesis
The novel bis-oxazoline ligand, BOX, was synthesized using our
previously reported methods with slight modifications [28,29]. A
mixture of 1,3-dicyanobenzene (4 mmol), 2-amino-1,3-propane-
diol (16 mmol) and silica sulphoric acid, SSA, (200 mg) was stirred
at 100 °C for 3 days. The progress of the reaction was monitored by
TLC (eluent:n-hexane/EtOAc, 2:1). After completion of the reaction,
the mixture was cooled to room temperature and dissolved in
methanol to remove the unreacted aminoalcohol. The mixture
was filtered and the solid material was dissolved in hot methanol,
and the bis-oxazoline light pink needle-like crystals were obtained
by the slow evaporation of methanol. The same reaction was
also carried out under ultrasonic irradiation as following: a mix-
ture of 1,3-dicyanobenzene (4 mmol), 2-amino-1,3-propanediol
(16 mmol) and SSA (200 mg) was exposed to ultrasonic irradiation
for 3 h (6 discontinuous 30 min. exposures). The reaction pro-
gress was monitored by TLC (eluent:n-hexane/EtOAc, 2:1). The
2.3. General procedure for oxidation of alkenes with TBHP catalyzed by
Mo BOX complex
In a round-bottom flask (25 mL) equipped with a reflux con-
denser, a gas inlet and a magnetic stirrer, a solution of alkene
(1 mmol) in 1,2-dichloroethane (4 mL) was prepared. The molyb-
denum BOX complex (8 mg, 0.01 mmol, 0.02 mmol Mo) and TBHP
(2 mmol) was added to this solution and the reaction mixture was

M. Moshref Javadi et al. / Polyhedron 72 (2014) 19–26
21
Fig. 1. (a) The crystal structure and (b) crystal packing for bis(oxazoline) ligand.
Table 1
Epoxidation of alkenes with TBHP catalyzed by [Mo2(O)4BOX(acac)2] in refluxing 1,2-dichloroethane.a
Row
1
Substrate
Product
Conversion (%)b
100
Epoxide yield (%)
100
Time (h)
3
TON
50
TOF (hꢀ1
16.7
)
O
2
3
87
50
8
6
43.5
50
5.4
8.3
O
O
H
100
(1,2-epoxide) 83
(8,9-epoxide) 17
O
O
4
53
53
10
26.5
2.7
O
5
6
7
44
30
18
44
30
18
10
10
10
22
15
9
2.2
1.5
0.9
O
O
O
a
Reaction conditions: Alkene (1 mmol), TBHP (2 mmol), catalyst (0.01 mmol, 0.02 mmol Mo), 1,2-dichloroethane (4 mL).
GC yield based on the starting alkene.
b
stirred under reflux conditions. The reaction progress was
monitored by GC. After completion of the reaction, the mixture
was directly passed through a short column of silica-gel (1:1,
n-hexane–ethyl acetate) to remove the catalyst. The elute was
evaporated under reduced pressure and the remaining residue
was purified by silica-gel plate chromatography (eluted with
CCl4:Et2O = 9:1) to afford the corresponding epoxide.
2.4. General procedure for oxidation of sulfides with TBHP catalyzed by
Mo BOX complex
In a 25 mL round-bottom flask equipped with a magnetic stir-
ring bar, a solution of sulfide (1 mmol), catalyst (6 mg, 0.008 mmol,
0.016 mmol Mo) in 1,2-dichloroethane (4 mL) was prepared. TBHP
(2 mmol) was added to this solution and the reaction mixture was

22
M. Moshref Javadi et al. / Polyhedron 72 (2014) 19–26
24hrs.
3hrs.
6hrs.
8hrs.
3hrs.
6hrs.
8hrs.
24hrs.
100
80
60
40
20
0
100
80
60
40
20
0
No catalyst
0.003
0.005
Catalyst Amount
0.008
0.01
Solvent
Fig. 4. The effect of various solvents in the oxidation of cyclooctene with TBHP
catalyzed by [Mo2(O)4BOX(acac)2].
Fig. 2. Optimization of the catalyst amount in the oxidation of cyclooctene with
TBHP catalyzed by [Mo2(O)4BOX(acac)2].
3 hrs.
6 hrs.
8 hrs.
24 hrs.
3hrs.
6hrs.
8hrs.
24hrs.
100
80
60
40
20
0
100
80
60
40
20
0
25 C
60 C
Temperature
Reflux
H2O2
NaIO4
UHP
Oxidant
KHSO5
TBHP
Fig. 5. The effect of temperature on the oxidation of cyclooctene with TBHP
catalyzed by [Mo2(O)4BOX(acac)2].
Fig. 3. The effect of various oxidants in the oxidation of cyclooctene with TBHP
catalyzed by [Mo2(O)4BOX(acac)2].
stirred under reflux conditions. The reaction progress was moni-
tored by TLC. After the reaction was completed, the isolation and
purification of the products were done as described above.
and the space group of the ligand is C2. In the absence of sufficient
anomalous dispersion (the absence of element heavier than Si in
case of normal sealed tube Mo X-ray radiation) the absolute struc-
ture of the compound could not be determined by Mo X-ray radi-
ation so the total 580 Friedel pairs were merged.
3. Results and discussion
3.1. Preparation and characterization of the BOX ligand
3.2. Preparation and characterization of the molybdenum oxazoline
complex
The synthetic route for ligand, [2,20-(1,3-phenylene)bis(4,5-
dihydrooxazole-4,2-diyl)]dimethanol, is shown in Scheme 3.
This ligand was characterized by elemental analysis, FT-IR, 1H
NMR and UV–Vis spectroscopic methods. All data was in agree-
ment with the structure of the synthesized ligand. Initial evidence
of the ligand is shown in the FT-IR spectra (Fig. S1). The very sharp
The prepared catalyst was characterized by elemental analysis,
FT-IR and UV–Vis spectroscopic methods. The FT-IR spectrum of
homogeneous [Mo2(O)4BOX(acac)2] (Fig. S5 shows a band at
1642 cmꢀ1 for
uted to the
m
(C@N), and two bands at 945 and 906 cmꢀ1 attrib-
m
(Mo@O) bonds. 1H NMR (400 MHz, DMSO-d6)
band at 2234 cmꢀ1, relating to
m
(C„N) disappears upon ligand
d = 8.31–7.52 (m, 6H, 4CHarom, 2 ꢁ CH3COCHCOCH3), 4.68 (m, 4H,
2 ꢁ CH2O), 4.00–3.98 (m, 4H, 2 ꢁ CH2O), 3.35 (br, m,12H, 2 ꢁ CH3
COCHCOCH3), 2.08–1.91 (m, 2H, 2 ꢁ CH–N).
synthesis. 1H NMR (Fig. S2) also confirmed the identity of the
desired ligand. 1H NMR (400 MHz, DMSO-d6) d = 8.34 (t, JH-H
=
4
4
3
1.6 Hz, 1H), 7.94 (dd, JH-H = 1.6 Hz, JH-H = 7.6 Hz, 2H), 7.55 (t,
3JH-H = 7.6 Hz, 1H), 4.84–4.80 (m, 2H, 2 ꢁ CHN@C), 4.45–4.29 (m,
4H, 2 ꢁ CH2O), 3.56–3.31 (m,4H, 2 ꢁ CH2OH). TG and DTG data
show that this ligand decomposes at about 400 °C (Fig. S3). This
ligand shows two absorption peaks in ethanol at kmax 224 and
250 nm (Fig. S4). The structure of this ligand was also confirmed
by X-ray crystallography. The crystal structure of the ligand (CCDC
926630) along with its crystal packing is shown in Fig. 1 (Also see
Tables S1, S2, and S3). The number of molecules in the unit cell is 2
As seen in Fig. S7, the [Mo2(O)4BOX(acac)2] shows a peak at
kmax = 310 nm which is attributed to the O(p )?Mo(d ) charge-
p
p
transfer transition [30].
TG and DTG data show that this complex decomposes at about
220 °C (Fig. S8). This is in accordance with the data obtained from
melting point studies.
According to the ICP and CHN analyses, the ratio between Mo
and the ligand was 2.07 that confirm that the catalyst consists of
two molybdenum metals and is therefore binuclear.

M. Moshref Javadi et al. / Polyhedron 72 (2014) 19–26
23
Table 2
Comparison of the results obtained for epoxidation of cyclooctene catalyzed by [Mo2(O)4BOX(acac)2] with some previously reported molybdenum systems.
Entry
Catalyst
Support
Oxidant
Conditions (°C)/Solvent
TOF (h–1
)
Refs.
1
2
3
4
Mo2O4(acac)2BOX
[MoI2(CO)3(trpH)]
[MoI2(CO)3(pheH)]
HT–trp–Mo
None
None
None
TBHP
TBHP
TBHP
TBHP
Reflux/DCE
55/DCE
55/DCE
16.7
9
2
This work
[31]
[31]
Amino acid intercalated clay
materials HT–trp)
Amino acid intercalated clay
materials HT–phe)
Silica
MCM-41
MCM-41
None
55/DCE
10
[31]
5
HT–phe–Mo
TBHP
55/DCE
17
[31]
6
7
8
9
MoO2(acac)2
MoO2(acac)2
MoO2(acac)2
MoO2[1,2-diphenylethylenebis
(3-oxyethylpyrrole)salicylideneiminate]
TBHP
TBHP
TBHP
TBHP
Reflux/DCE
Reflux/DCE
Reflux/DCE
Reflux/DCE
16.0
15.5
14.7
5
[32]
[33]
[34]
[35]
80
5 min.
15 min.
30 min.
45 min.
SO= Sulfoxide
SU= Sulfone
60
40
20
0
SO
SU
SO
SU
SO
SU
SO
SU
SO
SU
No Catalyst
0.003
0.005
0.008
0.01
Catalyst amount/ mmol
Fig. 6. Optimization of the catalyst amount in the oxidation of diphenyl sulfide with TBHP catalyzed by [Mo2(O)4BOX(acac)2], along with the ratios of products formed.
80
SO= Sulfoxide
SU= Sulfone
5 min.
10 min.
15 min.
20 min.
60
40
20
0
SO
SU
SO
SU
SO
SU
SO
SU
SO
SU
SO
SU
SO
SU
SO
SU
Acetonitrile
DCE
Tolouene
Methanol
DMF
Ethanol
DCM
Chloroform
Solvent
Fig. 7. The effect of various solvents in the oxidation of diphenyl sulfide with TBHP catalyzed by [Mo2(O)4BOX(acac)2].

24
M. Moshref Javadi et al. / Polyhedron 72 (2014) 19–26
80
60
40
20
0
presence of catalytic amounts of [Mo2(O)4BOX(acac)2]. The opti-
mum conditions used for the oxidation of cyclooctene by this cat-
alytic system was catalyst, substrate, and oxidant in a molar ratio
of 1:100:200, respectively (Table 1). In this reaction cyclooctene
oxide was produced with 100% selectivity.
First, we optimized the catalyst amount in the oxidation of
cyclooctene. The results showed that when 0.01 mmol (8 mg)
of catalyst was used in the oxidation of cyclooctene with
2 mmol of TBHP, the highest yield was obtained. Whereas trace
amounts of products (10%) was detected when the same reaction
was carried out in the absence of catalyst (Fig. 2).
The effect of different oxidants such as H2O2, NaIO4, tert-BuOOH
and H2O2/urea (UHP) was also investigated in the oxidation of
cyclooctene. The results showed that tert-BuOOH is the best
oxygen source (Fig. 3).
No Oxidant
1mmol
1.5 mmol
Oxidant
2 mmol
3 mmol
Different solvents were also used in the oxidation of cyclooc-
tene with tert-BuOOH and amongst them, 1,2-dichloroethane gave
the most conversion (Fig. 4).
Fig. 8. Time interval for the oxidation of diphenylsulfide with various TBHP
amounts in 20 min.
The reaction temperature was also optimized by repeating the
reaction in various temperatures. At room temperature (25 °C),
the product yields were low and with increasing the reaction
temperature better results and higher yields were obtained
(Fig. 5).
3.3. Catalytic alkene epoxidation with TBHP catalyzed by
[Mo2(O)4BOX(acac)2]
Under the optimized reaction conditions, different alkenes
including cyclic and linear ones were oxidized by this catalytic
In order to find the optimized conditions, cyclooctene was used
as a model substrate using tert-BuOOH as an oxidant and in the
Table 3
Sulfide oxidation with TBHP catalyzed by [Mo2(O)4BOX(acac)2] in refluxing 1,2-dichloroethane.a
Row
1
Sulfide
Time (min)
Conversion (%)b
Producta
TOF (hꢀ1
)
Sulfoxide (%)
Sulfone (%)
5
60
55
95
5
0
50
95
412.5
59.4
NO2
CH3
S
S
2
5
30
100
100
95
70
5
30
750.0
125.0
3
4
10
15
95
100
95
95
0
5
356.3
250.0
CH3
S
HO
5
20
90
100
90
0
0
100
675.0
187.5
S
OH
5
6
30
60
95
100
75
0
20
100
118.8
62.5
S
45
90
100
100
75
20
25
80
83.3
41.7
S
7
8
5
25
5
100
100
100
100
90
0
100
10
10
100
0
750.0
150.0
750.0
125.0
S
S
CH3
30
90
9
10
35
5
30
20
45
100
100
100
100
65
100
0
100
0
60
30
0
100
0
100
5
375.0
107.1
750.0
125.0
121.9
83.3
S
10
11
S
S
100
70
a
Reaction conditions: sulfide (1 mmol), TBHP (2 mmol), catalyst (0.008 mmol, 0.016 mmol Mo), 1,2-dichloroethane (4 mL).
GC yield based on the starting sulfide.
b

M. Moshref Javadi et al. / Polyhedron 72 (2014) 19–26
25
system. As can be seen in Table 1, both cyclic and linear alkenes
were converted to their corresponding epoxides with TBHP in the
presence of [Mo2(O)4BOX(acac)2] catalyst. In this catalytic system,
cyclooctene was completely converted to its corresponding epox-
ide with 100% selectivity. In the epoxidation of styrene, the major
product was styrene oxide (50%) and about 37% benzaldehyde was
also produced. This catalytic system exhibits a promising regiose-
lectivity in the epoxidation of (R)-(+)-limonene. The ratio among
1,2- and 8,9-epoxides was found to be 4.88. In the case of linear al-
kenes such as 1-heptene, 1-octene, 1-decene and 1-dodecene, the
corresponding epoxides were obtained in good to high yields with
100% selectivity.
of the peroxide to the sulfoxide sulfur ultimately facilitates the for-
mation of the sulfone. However electron-donating groups, e.g. CH3
tend to favor the first step and form the consistent sulfoxide.
4. Conclusion
In summary, we synthesized a new binuclear molybdenum
complex and demonstrated its high catalytic activity in the selec-
tive oxidation of various alkenes and sulfides under homogeneous
conditions using TBHP as the terminal oxidant. The excellent che-
moselectivity of this complex towards alkenes and the sulfur
group, as well as the high yields makes it a good choice for
oxidation.
The results obtained with this catalytic system were compared
with some of those reported in the literature (Table 2). As can be
seen, this catalytic system is an efficient system in the epoxidation
of alkenes.
Acknowledgments
We gratefully acknowledge The University of Isfahan Council of
Research for the support of this work. The authors also thank Dr.
Reza Kia for his valuable helps.
3.4. Oxidation of sulfides with tert-BuOOH catalyzed by
[Mo2(O)4BOX(acac)2]
The reaction conditions were also optimized in the oxidation of
sulfides with TBHP in which diphenyl sulfide was used as a model
substrate. In the optimization of catalyst amount, the best results
were obtained when 0.008 mmol (6 mg, 0.016 mmol Mo) of cata-
lyst was applied with 2 mmol of TBHP after 20 min. Under these
conditions, the conversion was 81% and the sulfoxide to sulfone ra-
tio was 4.4. No better results were obtained when higher amounts
of catalyst were used. When the reaction was continued for 45 min,
the amount of sulfoxide decreased to 30% and the amount of sul-
fone reached to 70%. Trace amounts of the products were detected
when the same reaction was carried out in the absence of catalyst
(Fig. 6).
In order to choose the reaction media, different solvents were
also tested and 1,2-dichloroethane was chosen as solvent because
of the higher amount of sulfoxide was produced (Fig. 7).
Various TBHP molar amounts were also tested. The results
showed that when 2 mmole of the oxidant were used, the highest
yields of sulfoxide were obtained (Fig. 8).
Appendix A. Supplementary data
The data corresponding to the FT-IR, 1H NMR, TG-DTG, and elec-
tronic absorption data of the BOX ligand are provided (Figs. S1, S2,
S3, and S4). The data corresponding to the FT-IR, TG-DTG, and elec-
tronic absorption data of the molybdenum complex are provided
(Figs. S5, S6, S7, and S8). Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.poly.2014.01.004.
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