[bipy.H] hosted by Al-MCM-41: An efficient dibenzo[b,f][1,4]oxazepine (CR) decontamination nano-reactor

Article abstract of DOI:10.1039/c5ra04565g

Encapsulation of [Fe(bipy)Cl₄][bipy.H] (1) (where bipy is 2,2′-bipyridine) in the Al-MCM-41 molecular sieve by using a "ship in a bottle synthesis" approach was achieved and the product characterized by X-ray diffraction, FTIR, DRS, TG, EDS and BET analysis. Encapsulation of the complex into the channels of Al-MCM-41, did not affect the morphology of the host as is evident from SEM and TEM micrographs. The obtained nanocatalyst in combination with K₂S₂O₈ as the oxidant, was successfully used in selective catalytic conversion of dibenzo[b,f][1,4]oxazepine (CR, riot control agent) to dibenzo[b,f][1,4]oxazepin-11(10H)-one as a potential decontamination route. Good selectivity was also obtained toward formation of benzil in the oxidation of trans-stilbene. This journal is

Full text of DOI:10.1039/c5ra04565g

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[Fe(bipy)Cl4][bipy.H] hosted by Al-MCM-41: an
efficient dibenzo[b,f][1,4]oxazepine (CR)
decontamination nano-reactor
Cite this: RSC Adv., 2015, 5, 32804
*
Alireza Khorshidi and Sirous Heidari
Encapsulation of [Fe(bipy)Cl4][bipy.H] (1) (where bipy is 2,20-bipyridine) in the Al-MCM-41 molecular sieve by
using a “ship in a bottle synthesis” approach was achieved and the product characterized by X-ray
diffraction, FTIR, DRS, TG, EDS and BET analysis. Encapsulation of the complex into the channels of Al-
MCM-41, did not affect the morphology of the host as is evident from SEM and TEM micrographs. The
obtained nanocatalyst in combination with K2S2O8 as the oxidant, was successfully used in selective
catalytic conversion of dibenzo[b,f][1,4]oxazepine (CR, riot control agent) to dibenzo[b,f][1,4]oxazepin-
11(10H)-one as a potential decontamination route. Good selectivity was also obtained toward formation
of benzil in the oxidation of trans-stilbene.
Received 15th March 2015
Accepted 30th March 2015
DOI: 10.1039/c5ra04565g
www.rsc.org/advances
Due to the steric constraint of these hosts, however, inter-
esting changes in the physicochemical properties of such
encapsulated complexes have been reported.10–13
1. Introduction
Encapsulation of transition metal complexes inside inorganic
structures makes it possible to design catalysts which combine
the advantages of homogeneous and heterogeneous catalytic
systems.1 Molecular sieves are attractive hosts, as they combine
high thermal and chemical stability with a quite regular crys-
talline framework structure. The well-dened and ordered
structure of them provides an ideal environment to entrap
active metal complexes, and the connement leads to higher
stability by reducing dimerization of active sites. These modi-
ed systems can be exploited as catalysts. Both zeolites and
mesoporous material such as MCM-41 have been used for this
purpose. For example, Balkus et al. reported zeolite encapsu-
lated metal complexes,2 Xavier et al., prepared intrazeolite
cobalt(II), nickel(II) and copper(II) complexes of 3-formylsalicylic
acid for oxidation reactions3 and Yamaguchi et al., recently
reported selective hydroxylation of cyclohexene over Fe-
Mixed ligand complexes, on the other hand, can be a
synthetic challenge to tune properties of transition metal
complexes. Metal complexes containing diimine ligands such
as 1,10-phenanthroline and bipyridine have attracted attention
because of their versatile roles as building blocks for the
synthesis of metallodendrimers and as molecular scaffolding
for supramolecular assemblies, and in analytical chemistry,
catalysis, electrochemistry, ring-opening metathesis polymeri-
zation (ROMP) and biochemistry. However, most diimine
complexes reported so far, are homo ligand compounds of the
general formula M(N–N)3 or to a lesser extent M(N–N)2X2. To the
best of our knowledge, little attention has been paid to the
incorporation of hetero ligand complexes into the molecular
sieves. Dibenzo[b,f][1,4]oxazepine (CR), on the other hand, is an
incapacitating and a lachrymatory agent. CR was rst synthe-
sized in 1962 (ref. 14) and is a pale yellow crystalline solid with a
pepper-like odor. It is chemically stable and does not degrade
with time. The dibenzo[b,f][1,4]oxazepine moiety is present in
the typical antipsychotic drug loxapine (Fig. 1), but, unlike CR,
loxapine is not reactive and is not an irritant.
bipyridine complexes encapsulated into zeolite
Y under
environment-friendly conditions.4 In addition to zeolites, mes-
oporous structures such as MCM-41 also, have been studied.
Some reports in this context include trimethylstannyl molyb-
denum complex hosted by MCM-41,5 Fe(III)-salen encapsulated
Al-MCM-41 as a catalyst in polymerization of bisphenol-A,6
metallo octamethylcalix pyridine complexes encapsulated in
MCM-41,7 Zn(II) phthalocyanines immobilized in mesoporous
silica Al-MCM-41 for photocatalytic degradation of pesticides8
and dinuclear iron 1,10-phenanthroline complex encapsulated
in MCM-41 for oxidation of benzyl alcohol.9
Department of Chemistry, Faculty of Sciences, University of Guilan, P. O. Box:
41335-1914, Iran. E-mail: Khorshidi@guilan.ac.ir
Fig. 1 Dibenzo[b,f][1,4]oxazepine and loxapine.
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Our interest in the study of ion-exchanged zeolites and
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In order to encapsulate [Fe(bipy)Cl4][bipy.H] in the host, 2,20-
encapsulated species,15,16 prompted us to evaluate [Fe(bipy)Cl4]- bipyridine (0.155 g, 1 mmol, excess) was dissolved in 10 mL of a
[bipy.H] encapsulated in molecular sieves as a selective oxida- 1 : 1 mixture of ethanol and water and titrated by 0.1 M HCl to
tion catalyst and the results were satisfying.
pH of 7.0. To this solution, 500 mg of the corresponding ion-
exchanged host was added and the mixture was stirred at
55–60 ꢀC for 3 h. The orange product was then ltered and
washed with hot deionized water three times, then Soxhlet
extracted with acetonitrile. The iron content of the catalyst
(Al-MCM-41–[Fe(bipy)Cl4][bipy.H]) was determined by using
inductively coupled plasma (ICP) as 1.848%.
2. Experimental
2.1 Reagents and materials
All materials were purchased from Merck and used without
further purication. [Fe(bipy)Cl4][bipy.H] was synthesized
according to Safari et al.17 In brief, 2,20-bipyridine (0.155 g,
1 mmol) was dissolved in 0.1 M HCl (10 mL). FeCl3$6H2O
2.2 General procedure for the oxidation reactions
(0.135 g, 0.5 mmol) in water (10 mL) was added to this solution, Caution: dibenzo[b,f][1,4]oxazepine is highly irritating.
ꢀ
and the resulting red solution was stirred at 55–60 C for 3 h.
Dibenzo[b,f][1,4]oxazepine (1.0 mmol) was dissolved in
The product was obtained from CH3CN as orange prismatic 5.0 mL of ethanol and potassium persulfate (0.5 mmol in 5.0 mL
crystals aer 3 days (yield: 0.195 g, 76.3%). M.p.: 216 ꢀC, IR of dimethylformamide) was added to the solution. Then 20 mg
(KBr, cmꢁ1): 3060, 1615, 1599, 1583, 1443, 1311, 1270, 1248, of the catalyst was added and the mixture stirred at 50 ꢀC under
1229, 1174, 1158, 1021, 764, 733, 652, 630, 357, 333, 309 (Fe–Cl), reux condition. Progress of the reaction was monitored by TLC
291 (Fe–Cl), 258 (Fe–N).
(n-hexane/ethyl acetate: 10/4). Aer 1 h, the reaction mixture
Al-MCM-41 with a Si/Al ratio of 39 was synthesized and was ltered and quenched with 10 mL of cold water. The gray
characterized according to the literature.18 The Fe3+ ion- precipitate was ltered and recrystallized from ethyl acetate to
exchanged molecular sieve was obtained by overnight stirring provide pure dibenzo[b,f][1,4]oxazepin-11(10H)-one.
of the Al-MCM-41 with 0.05 M solution of FeCl3$6H2O
Dibenzo[b,f][1,4]oxazepin-11(10H)-one. Gray solid, M.P. 208–
(15 mL gꢁ1 of Al-MCM-41), then ltration and washing with hot 211 ꢀC, FTIR (KBr, n/cmꢁ1): 3062, 2931, 1676, 1607, 1448, 1204
deionized water to remove any physisorbed species, as was and 767. 1H NMR (400 MHz, DMSO-d6): d 11.21 (s, 1H), 8.03
monitored by a conductometer. The whole process repeated (d, 1H, J ¼ 7.6 Hz), 7.85 (br, 2H), 7.53 (t, 1H, J ¼ 7.6 Hz), 7.48–
three times and Soxhlet extraction with acetonitrile removed 7.44 (m, 2H), 7.14 (d, 2H, J ¼ 8.4 Hz), 7.09 (t, 1H, J ¼ 7.6 Hz)
the ions located on the host's surface. Finally, the ion- ppm. 13C NMR (100 MHz, DMSO-d6): d 162.8, 158.2, 149.3,
exchanged material was subsequently ltered and calcined at 139.9, 134.4, 128.1, 126.3, 125.8, 120.4, 119.7, 117.6, 111.5,
ꢀ
550 C.
110.9 ppm.
Fig. 2 The labeled diagram of [Fe(bipy)Cl4][bipy.H] (left), and its unit cell structure with hydrogen bonds shown as dashed lines (right).19
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trans-Stilbene (1.0 mmol) and KIO4 (0.5 mmol) were added to
10 mL of a mixture of acetonitrile and dimethylformamide
(1 : 9), and then 30 mg of the catalyst was added. The reaction
mixture was stirred at 60 ꢀC under reux condition. Progress of
the reaction was monitored by TLC (n-hexane/ethyl acetate:
10/2). Aer 1 h, the reaction mixture was ltered and the
products were puried by using preparative TLC (n-hexane/ethyl
acetate: 10/2), and characterized from their FTIR spectra in
comparison with authentic samples.
2.3 Instrumentation
X-ray powder diffraction (XRD) measurements were performed
by using a Philips diffractometer of X'pert Company with mono
chromatized Cu Ka radiation. IR spectra were recorded on a
Shimadzu FTIR-8400S spectrometer. Morphology of the
synthesized samples was characterized with a scanning electron
microscope (SEM) from Philips Company (XL30 ESEM). TEM
images were obtained on a transmission electron microscope
(TEM-PHILIPS MC 10) with an acceleration voltage of 80 kV.
Fig. 3 FT-IR spectrum of [Fe(bipy)Cl4][bipy.H] (a) and Al-MCM-41 loaded [Fe(bipy)Cl4][bipy.H] (b).
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1H NMR spectra were obtained on a Bruker DRX-400 Avance
spectrometer and 13C NMR spectra were obtained on a Bruker
1
DRX-100 Avance spectrometer. Chemical shis of H and 13C
NMR spectra were expressed in ppm downeld from tetrame-
¨
thylsilane. Melting points were measured on a Buchi Melting
Point B-540 instrument and are uncorrected.
3. Results and discussion
Treatment of one equivalent of FeCl3$6H2O with 2 equivalents
of the bidentate chelating ligand, bipy, in the presence of HCl
solution affords a compound with the formula [Fe(bipy)Cl4]-
[bipy.H]. The structure of complex 1 is unambiguously identi-
ed.19 Considering our interest in the transition metal catalytic
systems and difficulty of recovering homogeneous transition
metal complexes, we decided to encapsulate complex 1 in
mesoporous Al-MCM-41, as a potential heterogeneous alterna-
˚
tive. The unit cell parameters of the complex 1 (a ¼ 15.938(2) A,
b ¼ 9.3068(15) A, c ¼ 14.513(3) A, z ¼ 4, R1 ¼ 0.0406, Fig. 2),19 are
˚
˚
proportional to the Al-MCM-41 pore size.
To do so, a “ship in a bottle synthesis” approach was
selected. Fe3+ loaded Al-MCM-41 (FeIII–Al-MCM-41) is yellow in
color. Upon diffusion of the 2,20-bipyridine ligand into the
channels of Al-MCM-41, however the color changed to red,
which is the rst characteristic of formation of the desired
complex. Feasibility of the synthesis however, was approved by
FT-IR spectra and XRD patterns. Fig. 3a shows the FT-IR spectra
of 1, and Fig. 3b shows FT-IR spectra of the Al-MCM-41 loaded
[Fe(bipy)Cl4][bipy.H]. No peaks associated to stretching vibra-
tions mode of Fe–O in the region of 580–640 cmꢁ1 were
observed, which diminished the formation of iron(III) oxide
during calcination.
While little could be deduced from these spectra, which is
due to broad and strong absorption bands of the host, IR
spectroscopy in the region of 200–400 cmꢁ1 provided more
useful details. As it is obvious from Fig. 4a, complex 1 shows
three characteristic bands at 309 (Fe–Cl), 291 (Fe–Cl) and 258
(Fe–N) cmꢁ1 17 The same vibrations were observed for Al-MCM-
.
41 loaded [Fe(bipy)Cl4][bipy.H] (Fig. 4b).
XRD patterns of free and Al-MCM-41-encapsulated complex
1, also conrm feasibility of the synthesis (Fig. 5). Four index
peaks of the complex 1 (Fig. 5a) at 2q ¼ 12, 25.5, 26 and 29.2ꢀ
reoccurred in the XRD pattern of the encapsulated complex
(Fig. 5b). Inset of the Fig. 5b, also, shows low angle pattern for
the Al-MCM-41-encapsulated complex 1, indicating that the
crystal structure of Al-MCM-41 was retained aer
incorporation.20
Incorporation of the complex 1 into the channels of Al-MCM-
41 did not affect morphology of the host as it is evident from
SEM micrographs. As shown in Fig. 6, the Al-MCM-41 crystal-
lites of about 1 mm, preserved their size and shape aer hosting
the complex, and a close-up image also showed that the struc-
ture of channels were preserved, too. TEM image taken with the
electron beam parallel to the pore direction showed a highly
ordered hexagonal structure with slight occlusion (Fig. 6d). In
the other images there was no evidence of the formation of
complex nanoparticles outside the pores. EDS analysis of the
Fig. 4 FT-IR spectrum of complex 1 (a) and Al-MCM-41 loaded
complex 1 (b) in the region of 200–400 cmꢁ1
.
composite (Fig. 6f), on the other hand, conrmed the presence
of complex 1, probably with a uniform distribution inside the
channels rather than formation of aggregates or nanocrystals.
The N2 adsorption–desorption isotherms of calcined
Al-MCM-41 and Al-MCM-41 loaded [Fe(bipy)Cl4][bipy.H] exhibit
type IV behavior, typical for mesoporous materials with two
dimensional hexagonal structure (Fig. 7). As it is obvious from
Fig. 7b, in the case of Al-MCM-41 loaded [Fe(bipy)Cl4][bipy.H] the
amount of adsorbed nitrogen decreases and the small hysteresis
loop observed at relative pressures about 0.3 for Al-MCM-41
shis to lower values. The decrease in the absorption amount
may be attributed to the reduced surface area, and shi of the
inection point may be resulted from pore lling effect due to
incorporation of the complex into the mesoporous structure.
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Fig. 5 XRD patterns of [Fe(bipy)Cl4][bipy.H] (a) and Al-MCM-41-encapsulated [Fe(bipy)Cl4][bipy.H] (b). Inset shows low angle pattern for the
Al-MCM-41-encapsulated complex [Fe(bipy)Cl4][bipy.H].
BET surface area of Al-MCM-41 dropped from 930.0 m2 gꢁ1 to to transitions from 1A1 / 1T1 for a d6 conguration in a pseudo-
703.9 m2 gꢁ1 for impregnated host. Drop in pore volume was octahedral eld which results in the orange color of the
from 0.88 mL gꢁ1 to 0.69 mL gꢁ1, and as expected, BJH maxima complex. The same transitions were observed in the DRS spec-
of the pore size distribution decreased from 3.8 to 2.6 nm.
Thermogravimetric (TG) analysis of the as-synthesized
trum of Al-MCM-41–[Fe(bipy)Cl4][bipy.H].
Having encapsulated complex in hand, we decided to eval-
product (Fig. 8a) consists of distinct parts: (a) loss of phys- uate its application in selective oxidative transformations. The
isorbed water from 80 to 180 ꢀC, which corresponds to the water chemistry of CR derivatives has attracted attention due to their
molecules absorbed on the external surface and those hosted in importance in biologically active compounds.21,22
the pores, (b) collapsing of the complex molecules from 215 to
3-ring heterocyclic compounds, to which the CR belongs,
ꢀ
250 C and (c) condensation of silanol groups from 350 to 600 have widespread application in medicine as anti-depressant
ꢀC. It could be deduced that the obtained catalyst has enough agents. The CR itself, however, is chemically stable and little
thermal stability to endure recycling processes or harsh reaction has been reported on its reactions such as chlorination and
conditions up to 200 ꢀC. The TG curve of the [Fe(bipy)Cl4]- oxidation, thus far.23–25
[bipy.H] complex is also shown for comparison in Fig. 8b.
Brewster et al.26 reported the oxidation of CR derivatives in
To further conrm the presence of complex inside the glacial acetic acid by using H2O2 overnight, which provided a
channels of mesoporous material, the diffuse reectance mixture of lactam, phenoxazine, benzoxazole and other prod-
spectra were obtained. As shown in Fig. 9, the Al-MCM-41 shows ucts. Harrison et al., on the other hand, reported the metabo-
no absorbance in the visible range (Fig. 9a). [Fe(bipy)Cl4]- lism of CR and its in vivo hydroxylation which provided a
[bipy.H] complex on the other hand, exhibited a broad mixture of lactam, 4-hydroxylactam and 7-hydroxylactam.27 Due
absorption in the range of 450–500 nm (Fig. 9b), corresponding to application of dibenzo[b,f][1,4]oxazepin-11(10H)-one
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Fig. 6 SEM images of Al-MCM-41 (a) and Al-MCM-41 loaded [Fe(bipy)Cl4][bipy.H] (b and c), TEM image of Al-MCM-41 loaded [Fe(bipy)Cl4]-
[bipy.H] (d and e), EDS analysis of Al-MCM-41 loaded [Fe(bipy)Cl4][bipy.H].
derivatives as intermediates in the synthesis of loxapine and
amoxapine,28,29 selectivity in the oxidation of CR toward lactam
product would be of great interest.
In order to achieve selective transformation of the CR
substrate to the lactam product, in presence of the Al-MCM-41
loaded [Fe(bipy)Cl4][bipy.H] as a heterogeneous catalyst, rst
the reaction conditions were optimized with regard to the
catalyst type, catalyst loading, oxidant and solvent. As shown in
Table 1, by using KIO4 as the oxidant, in the absence of the
catalyst, no formation of the desired product was observed and
the optimum loading was 20 mg of the catalyst per mmol of the
substrate (entry 3). Although under the same condition, free
[Fe(bipy)Cl4][bipy.H] resulted in excellent yield of 99%, but
recycling of the catalyst was problematic. To optimize the
reaction time and exclude the equilibrium of the reaction, and
to clarify the performance, shorter reaction times were tested
(entries 5–10). It was found that the homogeneous catalyst had
superiority against the heterogeneous counterpart in terms of
the reaction time. Heterogeneous catalyst, on the other hand,
Fig. 7 N2 adsorption–desorption isotherms of Al-MCM-41 (a) and
had the advantage of easy recycling which promises minimi-
Al-MCM-41 loaded [Fe(bipy)Cl4][bipy.H] (b).
zation of the waste. Fe(III)-ion exchanged Al-MCM-41 was also
Fig. 8 TG curve for the Al-MCM-41-encapsulated [Fe(bipy)Cl4][bipy.H] (a), and [Fe(bipy)Cl4][bipy.H] complex (b).
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Fig. 9 Diffuse reflectance spectra (DRS) of Al-MCM-41 (a), [Fe(bipy)Cl4][bipy.H] (b) and Al-MCM-41-encapsulated [Fe(bipy)Cl4][bipy.H] (c).
tested and a lower yield was obtained under the same condition pure Al-MCM-41 host. This may conrm heterogeneity of our
(entry12). The Al-MCM-41 host itself, however, resulted in no catalyst and success of encapsulation. With regard to the
desirable product. It was also found that the yield of the product oxidant, K2S2O8 was also tested and resulted in excellent yield of
was solvent dependant, and the best solvent was found to be a 98%. The optimized conditions are summarized in Scheme 1.
1 : 1 mixture of ethanol and dimethylformamide. The catalytic
Although the precise mechanism of the reaction awaits
performance of Al-MCM-41 loaded [Fe(bipy)Cl4][bipy.H] was further studies, a proposed mechanistic pathway which ratio-
compared with a mixture of Al-MCM-41 and [Fe(bipy)Cl4]- nalizes the selective product formation, is presented in Scheme 2.
[bipy.H] with exactly the same metal to host ratio (1.8% w/w Fe).
As it is shown, a four-membered ring intermediate may be
Although the excellent yield of 92% was obtained in 45 min involved in the reaction, which in turn provides the lactam
(entry 14), but ltration of the reaction mixture only resulted in product upon rearrangement. Encouraged by these results, we
Table 1 The effect of various parameters on the oxidation reaction of dibenzo[b,f][1,4]oxazepine
Entrya
Catalyst
Catalyst loading (mg)
Time (min)
Yieldb (%)
1
2
3
4
5
6
7
8
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
[Fe(bipy)Cl4][bipy.H]
0
10
20
30
20
20
20
20
10
10
10
20
20
20d
20
60
60
60
60
10
20
30
45
10
30
60
60
60
60
60
0c
84c
95c
95c
32
45
64
78
68
91
99c
73c
0c
9
10
11
12
13
14
15
[Fe(bipy)Cl4][bipy.H]
[Fe(bipy)Cl4][bipy.H]
FeIII–Al-MCM-41
Al-MCM-41
Al-MCM-41 + [Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
92
98e
All reactions were carried out at 50 ꢀC under reux condition. b Isolated yields. c KIO4 as the oxidant. d 1.8% w/w Fe/Al-MCM-41. e K2S2O8 as the
a
oxidant.
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Scheme
1 Selective oxidation of dibenzo[b,f][1,4]oxazepine to
dibenzo[b,f][1,4]oxazepin-11(10H)-one.
decided to evaluate efficiency of this protocol in the oxidation of
trans-stilbene. Generally, oxidation of trans-stilbene may
produce a mixture of products such as epoxide, benzil, benz-
aldehyde and benzoic acid. Under catalysis of Al-MCM-41–
[Fe(bipy)Cl4][bipy.H] by using KIO4 as the oxidant however, no
epoxide was observed (Scheme 3), and selectivity toward benzil
was obtained as follows (Table 2):
The optimum catalyst loading was determined at room
temperature in a 1 : 1 mixture of CH3CN and DMF by using KIO4
as the oxidant. This resulted in 64% selectivity toward benzil
(Table 2, entry 3). At elevated temperature the ratio of the
products was changed and the best selectivity toward benzil was
obtained at 60 ꢀC. Finally it was found that increasing the
CH3CN/DMF ratio to 9 : 1 results in excellent selectivity of 88%.
A comparison was also made between Al-MCM-41–[Fe(bipy)Cl4]-
[bipy.H], Al-MCM-41, [Fe(bipy)Cl4][bipy.H] and Al-MCM-41
mixed with [Fe(bipy)Cl4][bipy.H] under optimized conditions
(entries 7–10). It was found that Al-MCM-41–[Fe(bipy)Cl4]-
[bipy.H] has superiority in terms of recyclability and selectivity
Scheme 3 Selectivity in the oxidation of trans-stilbene.
toward benzil. [Fe(bipy)Cl4][bipy.H], on the other hand, resulted
in lower reaction time and lower selectivity, and in the case of
Al-MCM-41 mixed with [Fe(bipy)Cl4][bipy.H] with exactly the
same metal to host ratio (1.8% w/w Fe), lower selectivity and
difficulty of catalyst recovery were major drawbacks.
One of the main aims of the study was to evaluate reusability
of the catalyst. To do so, the oxidation reaction of dibenzo[b,f]-
[1,4]oxazepine to dibenzo[b,f][1,4]oxazepin-11(10H)-one was
carried out in presence of the recycled catalyst in successive
runs. From reaction run 1 to 5, the yields were 98%, 95%, 91%,
89% and 81%, respectively. Therefore aer ve runs, 17%
decrease in the efficiency of the catalyst was observed. This
result shows that Al-MCM-41–[Fe(bipy)Cl4][bipy.H] can be
utilized as a moderate and recyclable catalyst for the oxidative
transformation of dibenzo[b,f][1,4]oxazepine to dibenzo[b,f][1,4]-
oxazepin-11(10H)-one. In order to conrm heterogeneity of the
catalyst, the iron content of the catalyst was determined for the
recycled catalyst of the 5th run and a similar result (1.81%) was
obtained, which conrmed that no considerable leaching was
occurred during the course of reaction. To further approve this
assumption, the oxidation reaction of dibenzo[b,f][1,4]oxaze-
pine was interrupted halfway (30 min) and the catalyst was
removed by ltration. The reaction was then continued for the
rest of time (up to 60 min). At the end of this period only 65% of
the product was obtained, which may further approve the
success of encapsulation.
Scheme 2 Proposed mechanism for the oxidation of CR.
Table 2 The effect of various parameters on the oxidation reaction of trans-stilbene
Yieldb (%)
Entrya
Catalyst
Catalyst loading (mg)
Temperature (ꢀC)
Benzaldehyde
Benzil
Benzoic acid
1
2
3
4
5
6
7
8
9
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41–[Fe(bipy)Cl4][bipy.H]
Al-MCM-41
10
20
30
35
30
30
30
30
10
30
25
25
25
25
60
90
60
60
60
60
31
26
24
20
11
5
4
8
31
33
49c
59c
64c
63c
68c
60c
88d
6d
16
12
11
11
19
34
8
3
28
27
[Fe(bipy)Cl4][bipy.H]
Al-MCM-41 + [Fe(bipy)Cl4][bipy.H]
40d,e
39d
10
a
All reactions were carried out according to general experimental procedure. b Isolated yields. c CH3CN/DMF ¼ 1 : 1. d CH3CN/DMF ¼ 9 : 1. e 30
min reaction time.
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Paper
´
10 M. Alvaro, V. Fornes, S. Garcia, H. Garcia and J. C. Scaiano,
4. Conclusion
J. Phys. Chem. B, 1998, 102, 8744.
11 Y. Umemura, Y. Minai, N. Koga and T. Tominaga, J. Chem.
Soc., Chem. Commun., 1994, 893.
In conclusion, we have successfully incorporated the complex
[Fe(bipy)Cl4][bipy.H] into the channels of mesoporous Al-MCM-
41 with no considerable change in the properties of the host.
The whole assembly was used as an array of nanoreactors for
selective oxidation of dibenzo[b,f][1,4]oxazepine and trans-stil-
bene. Further investigation in this context is currently under
way in our laboratory.
12 S. Ray and S. Vaudevan, Inorg. Chem., 2003, 42, 1711.
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16 M. A. Zanjanchi, K. Tabatabaeian and A. Khorshidi, Russ. J.
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Acknowledgements
Partial support of this study by the research council of university
of Guilan is gratefully acknowledged. A. Khorshidi is grateful to
Dr S. Sohrabnejad for her generous support.
19 V. Ahmadi, N. Safari and H. R. Khavasi, Polyhedron, 2007, 26,
4257.
20 J. M. Kim, J. H. Kwak, S. Jun and R. Ryoo, J. Phys. Chem.,
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32812 | RSC Adv., 2015, 5, 32804–32812
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