G Model
CRAS2C-3731; No. of Pages 7
2
S. Rayati, P. Abdolalian / C. R. Chimie xxx (2013) xxx–xxx
end of reaction as well as its good activity and selectivity
for epoxide formation.
O
Br
O
N
O
N
Br
Mo
O
2. Experimental
2.1. Instruments and reagents
H
H
Infrared spectra were recorded on KBr pellets using a
Unicam Matson 1000 FT-IR.
A Bruker FT-NMR 500
Me
Me
(500 MHz) spectrometer was utilized to obtain the NMR
spectra. A Varian AA240 atomic absorption spectrometer
was used for molybdenum determination. The high-power
ultrasonic cleaning unit Bandelin Super Sonorex RK-100H
with ultrasonic peak output 320 W and HF power 80 Weff
has been used. The melting points were measured on an
Electro thermal 9100 apparatus. X-ray powder diffraction
(XRD) was carried out on a Philips X’Pert diffractometer
Fig. 1. General structure of the used dioxomolybdenum complex.
temperature under N2 atmosphere. The magnetic MCM-
41 was prepared by adding 20 mL of the Fe3O4 colloid after
sonication to a 1 L solution with molar composition 292
NH4OH:1 CTABr:2773 H2O under vigorous mixing and
sonication. Then, sodium silicate (16 mL) was added, and
the mixture was allowed to react at room temperature for
24 h under consecutive mixed conditions. The magnetic
MCM-41 was filtered and washed. The surfactant template
was then removed from the synthesized material by
calcination at 450 8C for 4 h and so (Fe3O4)–MCM-41 was
using the Cu Ka radiation. Scanning electron microscopy
(SEM) images were obtained on a Hitachi S-1460 field
emission scanning electron microscope using an ACC
voltage of 15 kV. Transmission electron microscopy (TEM)
image were obtained with a Zeiss EM-900 transmission
electron microscopy device using an ACC voltage of 80 kV.
The oxidation products were analyzed with
a
gas
converted to (a-Fe2O3)–MCM-41[10]. (a-Fe2O3)–MCM-41
chromatograph (Shimadzu, GC-14B) equipped with a
SAB-5 capillary column (phenyl methyl siloxane 30
m ꢀ 320 mm ꢀ 0.25 mm) and a flame ionization detector.
2,20-Dimethylpropylenediamine, 5-bromo-2-hydroxy-
benzaldehyde, molybdenyl acetylacetonate and hydrogen
peroxide (solution 27% in water) were used as received
from commercial suppliers. The solvents were dried and
distilled by standard methods before use. Other chemicals
were purchased from Merck or Fluka chemical companies.
(3 g) was suspended in 60 mL of chloroform with sonica-
tion. To this mixture, an excess amount of Mo(O)2L was
added, and the resulting mixture was stirred for 12 h with a
mild magnetic agitator at room temperature, then filtered
to obtain a brick-red precipitate, which was washed with
chloroform as a Mo(O)2L solvent, and finally dried in air.
The preparation of (
in Fig. 2.
a-Fe2O3)–MCM-41–Mo(O)2L is shown
2.5. General heterogeneous green oxidation procedure
2.2. Preparation of the Schiff base ligand (H2L)
Catalytic experiments were carried out in a 10-mL glass
flask fitted with a water condenser. In a typical procedure,
0.5 mmol cyclooctene, 0.015 g of (a-Fe2O3)–MCM-41–
The Schiff base ligand was prepared by the reported
methods [41,42].
Mo(O)2L and 2 mL (20 mmol) of H2O2 were added in
3 mL of ethanol. The reaction mixture was refluxed for 8 h.
The reaction products were monitored at periodic time
intervals using gas chromatography (GC). The oxidation
products were identified by comparison with authentic
samples (retention times in GC).
2.3. Preparation of molybdenum(VI) complex
The molybdenum complex (Fig. 1) was prepared as
follows: the Schiff base ligand, H2L (0.468 g, 1 mmol) was
dissolved in 20 mL of ethanol. An ethanolic solution of
molybdenyl acetylacetonate (0.326 g, 1 mmol) was added
and the reaction mixture was refluxed for 1 h. The light
orange solution was concentrated to yield orange powders.
The products were washed with warm ethanol. Mo(O)2L:
3. Results and discussion
3.1. Characterization of the ligand and of the
dioxomolybdenum(VI) complex
Yield: 83%, 0.493 g, D.p.: > 295, Selected FT-IR data,
(cmꢁ1): 2922 (C–H), 1614 (C5N), 1520 (C5C), 826 and 913
(Mo–O). 1H NMR (
): 0.75, 1.17 (s, 6H, NCH2C(CH3)2CH2N),
y
d
3.1.1. IR spectral studies
1.18 (s, 2H, N5CH), 3.38–4.63 (4H, NCH2C(CH3)2CH2N),
6.54–7.60 (m, 6H, ArH), 8.04–8.12 (s, 2H, N5CH).
A practical list of IR spectral data is presented in Table 1.
The comparison of the spectra of the complex with the
ligand provides evidence for the coordination mode of the
ligand in the dioxomolybdenum(VI) complex. A sharp
2.4. Preparation of the (a-Fe2O3)–MCM-41–Mo(O)2L
band appearing at 1626 cmꢁ1
, due to y(C5N) (azo-
Fe3O4 magnetic nanoparticles were prepared by the
chemical co-precipitation method reported in the litera-
ture [10,43]. Briefly, a solution with molar composition of
3.2 FeCl3:1.6 FeCl2:1 CTABr:39 NH4OH:2300 H2O was used
for the preparation of Fe3O4 nanoparticles at room
methine), shifts towards the lower wave numbers by
12 cmꢁ1 and appears at 1614 cmꢁ1. This observation
indicates the involvement of the azomethine nitrogen in
coordination with the molybdenum center [44]. The IR
spectra of the Mo complex showed two characteristic
Please cite this article in press as: Rayati S, Abdolalian P. Heterogenization of a molybdenum Schiff base complex as a
magnetic nanocatalyst: An eco-friendly, efficient, selective and recyclable nanocatalyst for the oxidation of alkenes. C.