Clay-anchored non-heme iron-salen complex catalyzed cleavage of C{double bond, long}C bond in aqueous medium

Article abstract of DOI:10.1016/j.tet.2006.08.011

Clay-anchored iron[N,N′-ethylenebis(salicylideneaminato)] complex, synthesized by direct exchange, oxidizes various olefins and chalcones in aqueous acetonitrile using hydrogen peroxide as terminal oxidant. Aldehyde and its derivatives are obtained as oxidation products by the cleavage of C{double bond, long}C double bond. In comparison with the catalysis by iron-salen complex in solution, the clay catalyzed pathway not only increases the rate of reaction significantly, but also provides selective oxidation toward the aldehyde. Some chalcones also give very good yield in water, compared to the solution and clay catalyzed pathways.

Full text of DOI:10.1016/j.tet.2006.08.011

Tetrahedron 62 (2006) 9911–9918
Clay-anchored non-heme iron–salen complex catalyzed
cleavage of C]C bond in aqueous medium
*
Amarajothi Dhakshinamoorthy and Kasi Pitchumani
School of Chemistry, Madurai Kamaraj University, Madurai 625 021, India
Received 18 May 2006; revised 24 July 2006; accepted 3 August 2006
Available online 22 August 2006
Abstract—Clay-anchored iron[N,N0-ethylenebis(salicylideneaminato)] complex, synthesized by direct exchange, oxidizes various olefins
and chalcones in aqueous acetonitrile using hydrogen peroxide as terminal oxidant. Aldehyde and its derivatives are obtained as oxidation
products by the cleavage of C]C double bond. In comparison with the catalysis by iron–salen complex in solution, the clay catalyzed path-
way not only increases the rate of reaction significantly, but also provides selective oxidation toward the aldehyde. Some chalcones also give
very good yield in water, compared to the solution and clay catalyzed pathways.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
various approaches include covalent binding to organic
polymers,9 layered double hydroxides,8–10 ion exchange
into the intracrystalline space of zeolite Y, Al-MCM-41,11
and encapsulation in zeolite using ship in a bottle method-
ology.12 Although immobilization shows increase in the
catalytic activity of homogeneous catalysts,13 it is often
accompanied by a decrease in enantioselectivity. Although
a few reports are available on immobilization of both achiral
and chiral manganese–salen complexes onto the interlayers
of montmorillonite clays14 for enantioselective epoxidation
of nonfunctionalized olefins using NaOCl as oxidant,
attempts have not been made to oxidize olefins to the
corresponding aldehydes. To achieve this objective, clay-
supported iron–salen complexes are prepared and used in
the present study.
In recent years, methods available for high-yielding, selec-
tive transformations of organic compounds have increased
tremendously. Most of these reactions also lay emphasis
on catalysis and ‘atom-economy’.1 Iron–salen complexes
are used as catalysts in allylic oxidation of olefins,2 epoxida-
tion of unfunctionalized olefins with iodosylbenzene,3 and
oxidation of adamantane in the presence of oxygen.4 Fur-
thermore, m-oxo-bisiron–salen complexes are also used in
the cyclopropanation of olefins.5 Iron-catalyzed asymmetric
oxidation of sulfides to sulfoxides has been achieved with
high enantioselectivity using hydrogen peroxide as terminal
oxidant.6
The progress in heterogeneous asymmetric synthesis, partic-
ularly in the asymmetric synthesis on chiral catalysts immo-
bilized in porous materials by various approaches such as
chemical grafting, encapsulation, organic–inorganic hybrid
synthesis, intercalation in layered materials, ionic interac-
tion for asymmetric reactions like epoxidation, hydrogena-
tion, hydroformylation, carbon–carbon bond formation,
ring opening of epoxides, and cyanohydrin synthesis was
recently reviewed by Li.7
Oxidative cleavage of olefins is one of the often used reac-
tions in organic chemistry. The various reagents used for
the cleavage of C]C bond are cobalt(II)–Schiff base com-
plexes,15 KMnO4 under acidic conditions,16 thiyl radical,17
OsO4–oxone,18 OsO4–NaIO4,19 Ru(II),20 and Au(I).21 Al-
though good results are obtained, the high cost of many of
these catalysts is a drawback. An alternative and under-
explored option is the use of iron catalysts, which possess
many advantages over traditional catalysts due to their non-
toxic and inexpensive nature.
Immobilization of homogeneous catalysts has attracted sig-
nificant interest because it could combine the advantages
of both homogeneous and heterogeneous catalysis.8 The
2. Results and discussion
Keywords: Iron–salen complex; K10-montmorillonite; Aldehyde; Aqueous
medium; Cleavage of C]C bond.
* Corresponding author. Tel.: +91 452 2456614; fax: +91 452 2459181;
e-mail: pit12399@yahoo.com
In the present work, the catalytic activity of the clay-
supported iron–salen complexes is studied in the oxidative
cleavage of olefins and chalcones (Scheme 1) using hydrogen
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.08.011

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A. Dhakshinamoorthy, K. Pitchumani / Tetrahedron 62 (2006) 9911–9918
O
peroxide as oxidant. To study the influence of ligand, ferric
chloride, iron–salen complex, and oxidant in the oxidation
of C]C bond, control experiments are carried out with
styrene using hydrogen peroxide in the presence of oxygen
(air). The results show that the oxidation is very slow when
only the ligand/FeCl3/complex is present.
(a)
(b)
O
+
H
O O H
O2
H
H
R3
R3
R1
R2
R1
R2
clay catalyst
+
+
C O
H2O2
C O
C
C
H
RT, MeCN/H2O
Scheme 2.
Where, R1= Ph
R2 = H, CH3, Ph
R3 = H, NO , CHO, COOH, COOCH3
B and the yields are 98 and 76%, respectively. When the oxi-
dationisextendedtob-nitrostyrene, theyieldofbenzaldehyde
decreases marginally when method B is employed in contrast
to method A. All other olefins (namely trans-cinnamalde-
hyde, trans-cinnamic acid, and trans-methyl cinnamate)
give a much better yield by method B. These results amply
demonstrate that this method for C]C double bond cleavage
is also effective with unsaturated compounds bearing elec-
tron-withdrawing substituents. Furthermore, the competing
allylic oxidation of the methyl group in a-methylstyrene (by
a radical route) is not observed under the present conditions.
In addition, this efficient and mild oxidizing system does
not disturb the functionalities such as aldehyde and esters.
2
Scheme 1.
Cleavage of C]C double bond was studied with olefins such
as styrene, a-methylstyrene, b-nitrostyrene, 1,1-diphenyl-
ethylene, cinnamicacidderivatives,andchalcones. InTable 1
the results of the oxidation of these olefins by 30% hydrogen
peroxide as oxidant in the presence of iron–salen complex
and clay-supported iron–salen complex are presented and
a significant increase in yield of aldehydes is noticed in the
clay-supported iron–salen complex oxidations. Oxidation
by iron–salen complex is monitored by threeways. In method
A, only iron–salen complex, without any clay support, is
used. Methods B and C employ clay-supported iron–salen
complex in acetonitrile and in acetonitrile–water mixture
(0.5:2.5 mL), respectively. Method C is adopted to explore
the potential utility of this novel oxidant in an ecofriendly
solvent (water). The observedresults provideveryinteresting
features. For example, when the reaction is performed in ace-
tonitrile at room temperature with 30% hydrogen peroxide in
the presence of molecular oxygen and iron–salen complex,
the conversion of styrene to benzaldehyde is only 14% (in-
complete even after 48 h and which also furnishes benzoic
acid). Under these conditions, no epoxide and diol are ob-
served. The same reaction also fails to furnish aldehyde
with nonpolar solvents such as diethyl ether and hexane.
Organometallic catalysts in aqueous systems offer exciting
prospects, both from academic and industrial points of
view. The use of transition metal catalysts in water or in
a two-phase system offers the same advantages as in an
organic medium. However, they simplify the separation of
the catalyst from the products, eventually for its recycling
and this is significant in large scale chemical processes.
The use of water as solvent can also exhibit different selec-
tivities to those shown in organic medium. Wacker oxidation
of olefins to ketones catalyzed by palladium complexes is
a well known process, which has been applied to numerous
olefins.23 However, selective oxidation of C8–C16 a-olefins
remains a challenge. Mortreux et al. have developed a new
catalytic system for the quantitative and selective oxidation
of higher a-olefins in aqueous medium.24–26
When clay iron–salen complex (heterogenized onto the
layers of clay) is used as catalyst, with the objective of im-
proving the stability of the metal complex under the reaction
conditions by preventing the catalytic active species from
aggregating and also to fine-tune the selectivity of the reac-
tion on the interlayers of clay solid via steric constraints, the
reaction proceeds more rapidly, affording benzaldehyde and
substituted benzaldehydes in moderate to good yield. Other
advantages are the absence of over oxidized product (benz-
oic acid) and a typical GC and GC–MS analysis shows the
absence of epoxide and phenylacetaldehyde also. Reactions
of various olefins with heterogeneous catalysts by method B
are examined and the results are shown in Table 1. Two
different pathways are likely in the oxidation of styrene.22
First pathway (a) leads to epoxidation of styrene to form
styrene oxide and is not dependent on oxygen, whereas the
second (b) leads to the formation of benzaldehyde and is
dependent on oxygen (Scheme 2). When the oxidation is
performed in air under the reaction conditions, benzalde-
hyde is obtained as the sole product.
These exciting results of organic reactions in water have
prompted us to study the oxidation of olefins, using hydrogen
peroxide as oxidant in acetonitrile–water mixture with a het-
erogeneous catalyst (method C). As anticipated, selective
oxidation of olefin is achieved to yield aldehyde or ketone
as the sole products as indicated by GC and GC–MS. The
ratio of acetonitrile–water is fixed in such a way that the
substrate dissolves completely. It is also observed that the
oxidation is slowed down when 100% water is used as sol-
vent. a-Methylstyrene, 1,1-diphenylethylene, and cinnamic
acid are also oxidized by method C in a moderate yield.
On the other hand, excellent yields of 94 and 92% are
observed in the oxidation of dibenzylidenecyclohexanone
and 4,40-dimethoxydibenzylideneacetone, respectively. For
these two substrates the rate of the reaction is accelerated
when compared to methods A and B. The lower reactivity
of methyl cinnamate, benzylideneacetone, and 4-methyl-
chalcone is probably due to their poor solubility in water.
In an analogous manner, other olefins such as 1,1-diphenyl-
ethylene and a-methylstyrene are also oxidized by method
These interesting results have prompted an extension of the
study to chalcones and its derivatives for oxidative cleavage

A. Dhakshinamoorthy, K. Pitchumani / Tetrahedron 62 (2006) 9911–9918
9913
Table 1. Oxidation of C]C double bond in olefins and chalcones by hydrogen peroxide, catalyzed by iron–salen complex under various reaction conditions
Entry
Substrate
Methoda
Product
Yield (%)b
TONc
O
1
2
3
A
B
C
14
30
10
09
20
07
H
O
4
5
6
A
B
C
27
76
43
18
51
26
CH3
O
7
8
9
A
B
C
34
32
23
23
22
15
NO2
H
10
11
12
A
B
C
68
27
38
16
Ph
Ph
Ph
98, 86d
41
CH2
O
Ph
O
O
O
O
13
14
15
A
B
C
32
53
16
22
36
11
CHO
COOH
H
H
H
H
16
17
18
A
B
C
50
34
44
36
65, 58d
53
19
20
21
A
B
C
23
65
09
15
44
06
COOCH3
22
23
24
A
B
C
34
70
45
23
47
30
O
C
CH CH
25
26
27
A
B
C
27
82
60
14
42
31
O
C
CH
Cl
OHC
CH
Cl
O
O
28
29
30
A
B
C
44
22
06
30
15
04
O
C
H
H
CH
CH3
CH
31
32
33
A
B
C
—
87
—
59
67
O
100, 91,e 96d
H3C
CH
CH
34
35
36
A
B
C
32
92
68
19
55
40
O
CH3
OHC
H3C
CH CH
H3CO
H3CO
CH
CH
37
38
39
A
B
C
38
85
20
45
53
O
OHC
OHC
OCH3
CH3
100, 94,e 97d
CH CH
O
40
41
42
A
B
C
47
45
05
28
27
03
CH
H3C
CH
C
a
Method A: olefin (50 mg), iron–salen complex (10 mg), 30% H2O2 (0.6 mL), MeCN (3 mL); method B: olefin (50 mg), clay-anchored iron–salen complex
(30 mg), 30% H2O2 (0.6 mL), MeCN (3 mL); method C: olefin (50 mg), clay-anchored iron–salen complex (30 mg), 30% H2O2 (0.6 mL), MeCN (0.5 mL)–
H2O (2.5 mL). All reactions are carried out in the presence of oxygen.
Determined by GC; error limit ꢀ3%.
b
c
d
e
Turnover number (TON): millimole of product/millimole of catalyst.
Catalyst reused.
Isolated yield.
in solution as well as on clay-supported iron–salen complex.
The yield has increased in a heterogeneous medium when
compared to solution reaction except in the case of benzyl-
ideneacetone. It is likely that the interaction of hydrogen
peroxide with the heterogeneous catalyst in the presence
of oxygen has prompted the formation of active oxygenating
As expected, chalcones also undergo oxidative cleavage to
corresponding aldehydes by method A (Table 1). Oxidations
of chalcones are also extended to method B using 30% hy-
drogen peroxide as oxidant in presence of molecular oxygen.

9914
60
A. Dhakshinamoorthy, K. Pitchumani / Tetrahedron 62 (2006) 9911–9918
counterpart are the increase in complex stability in reaction
media and the possibility of reusing the catalyst by simple
filtration, without neither loss of selectivity nor activity. In
some cases, the catalyst is reused in the oxidation of olefins
and chalcones (by methods B and C) and the results are given
in Table 1. It is also observed that this oxidation is inhibited
to a greater extent by the addition of sodium azide, which
suggests a radical pathway. It is relevant to note that in the
presence of hydrogen peroxide, azide ion interacts with fer-
ric native state of catalase to generate azidyl radical, which
in turn reacts with the heme group of catalase thus inactivat-
ing the enzyme.27
Method A
Method B
Method C
50
40
30
20
10
0
Complete mechanistic interpretation of these results requires
consideration of two main pathways in which the O–O bond
of hydrogen peroxide can be cleaved upon reaction with the
catalyst (Scheme 3). Hydrogen peroxide typically reacts
with a metal complex to form an initial metal–allylperoxo
intermediate (a). The O–O bond of the coordinated peroxide
can then cleave heterolytically to form high-valent metal oxo
complex and water (b) or homolytically to form OH radicals
and a metal hydroxide complex (c).
1-3
4-6
7-9
10-12
13-15
16-18
19-21
Substrates
Figure 1. Oxidation of C]C double bond in olefins with molecular oxygen
in various reaction conditions as a function of turnover number (TON).
species. Also the clay interlayer localizes the substrate and
the active oxo complex in close proximity, which is not
the case in solution reaction. Increased steric hindrance to
oxidation in the case of chalcone may also have contributed
to the lower reactivity. In some cases, it is very interesting to
note that oxidation of chalcone by clay-supported iron–salen
complex is even faster in aqueous acetonitrile (entries 33 and
39, method C) than with only acetonitrile (method B). More-
over, various functional groups such as alkyl, alkoxy, and
halide groups on phenyl rings are well tolerated under this
oxidizing system. With methyl group at para position of
chalcone, potential byproducts from the radical oxidation
of the methyl group are not observed (entries 34–36 and
40–42, Table 1).
O
(n+2)+
OH
M
+ H2O
(b)
HO
M
(a)
n+
n+
M
+
H
O O H
OH
M(n+1)
+
(c)
+
OH
Scheme 3. Possible pathways of O–O bond cleavage in hydrogen peroxide.
In the proposed mechanism (Scheme 4), the active oxidizing
species (formed upon reaction of hydrogen peroxide with
the catalyst) is described as high-valent Fe(V)]O.28 It
can add onto the double bond leading to a carbon radical
intermediate (proposed by Tuynman et al.).29 This carbon
radical intermediate is trapped by molecular oxygen fol-
lowed by the abstraction of hydrogen or by the reaction
between the carbon radical and activated hydrogen per-
oxide, which finally rearranges to give benzaldehyde as the
sole product.
The catalyst turnover number (TON, the ratio between num-
ber of millimoles of product formed and number of milli-
moles of catalyst used), increases for methods B and C in
contrast to method A (Figs. 1 and 2). The most important ad-
vantages of heterogeneous catalysis over the homogeneous
80
Method A
Method B
Method C
70
60
50
40
30
20
10
0
O
IV
Fe
O
H2O2
IV
Fe
III
H2O2
Fe
or
O2/H2O
O
O
O
H
22-24
25-27
28-30
31-33
34-36
37-39
40-42
IV
Substrates
CHO
Fe
Figure 2. Oxidation of C]C double bond in chalcones with molecular
oxygen in various reaction conditions as a function of turnover number
(TON).
Scheme 4. Possible mechanism for the oxidative cleavage of C]C double
bond in presence of molecular oxygen.

A. Dhakshinamoorthy, K. Pitchumani / Tetrahedron 62 (2006) 9911–9918
9915
3. Conclusion
with diethyl ether, and the organic layer dried over anhy-
drous sodium sulfate.
In summary, we have developed a novel method to oxidize
olefins and chalcones to ketones/aldehydes in aqueous
medium using hydrogen peroxide as oxidant within the mi-
croenvironment of clay interlayer wherein the local concen-
tration of active oxygenating species and substrate are more
localized. In almost all the cases where selective catalytic
oxidations of olefin are carried out, second- or third-row
transition metal complexes are involved. This is the first
report wherein the first-row transition metal is utilized for
oxidation of olefin to carbonyl compounds in aqueous
medium. In addition, the present study highlights the activa-
tion of oxygen and its subsequent transfer to the substrate. A
range of functional groups, which includes electron-with-
drawing groups can be tolerated and this oxidation proceeds
under mild conditions in water. Turnover number has in-
creased from method A to B for most of the substrates and
method B to C for 4,40-dimethoxydibenzylideneacetone
and dibenzylidenecyclohexanone. As the polarity of the
reaction medium is increased by water–acetonitrile mixture,
more substrates may be intercalated into the layers of clay to
increase their local concentration in a heterogenous medium
with faster reaction rate. The catalyst can also be reused
without any loss in the selectivity and activity.
4.1.2. Heterogeneous oxidation of olefin (method B or C).
To a solution of olefin (50 mg) in 3 mL of acetonitrile, the
heterogeneous catalyst was added followed by the addition
of 30% hydrogen peroxide as terminal oxidant. Then the re-
action mixture was stirred for 24 h at room temperature. The
reactants were extracted from the heterogeneous catalyst,
upon stirring with diethyl ether for 8 h and filtered. The fil-
trate was washed with water and the organic layer was dried
over anhydrous sodium sulfate.
4.1.3. Synthesis of iron(III)–salen complex. The Schiff
base salen ligand was prepared according to the established
procedure.31 To an ethanolic (15 mL) solution of salicylalde-
hyde (2.40 g) was added an ethanolic (15 mL) solution of
ethylenediamine (0.67 g) and the resulting mixture was
allowed to reflux for 1 h. The progress of the reaction was
monitored by TLC. This mixture was allowed to cool at
about 10 ꢁC. The yellow crystalline product was filtered
and dried and the formation of the ligand was confirmed
by FTIR analysis.
An ethanolic (15 mL) solution of anhydrous iron(III) chlo-
ride (0.8 g) was added to a solution of salen ligand
(1.34 g) in absolute ethanol (25 mL). The resulting dark
brown suspension was refluxed for 1 h and allowed to cool
to room temperature. Then it was filtered, washed with
ethanol, and dried at 50–60 ꢁC for 1 h.
4. Experimental
4.1. General methods
All reagents were obtained commercially and used without
further purification unless otherwise noted. The starting ma-
terials (chalcones and its derivatives) were synthesized by
following previous procedures.30 Proton nuclear magnetic
resonance (1H NMR) spectra were recorded on Bruker
300 MHz and carbon nuclear magnetic resonance (13C
NMR) were recorded on 75 MHz Bruker instrument using
TMS as an internal standard. UV–visible spectra for com-
plexes were recorded using Jasco V-550 instrument. IR spec-
tra for neat and immobilized complexes were recorded as
KBr pellet in a Shimadzu FT-IR (8400 S) instrument. TGA
analyses were carried out using Netzsch STA 409 PC model
instrument. The percentage conversion, purity, and relative
yields of the final products were confirmed and their charac-
terization were carried out using gas chromatograph (Shi-
madzu GC-17A model, ZB-5 (10%) capillary column with
FID detector and high purity nitrogen as carrier gas). The
products were identified by comparing with authentic sam-
ples and the retention time of the starting material was taken
as internal reference. In most cases the mass balance is
>80%. GC–MS analyses were also carried out in a Finnigan
GC–MS with RTX5-MS capillary column and high purity
helium as the carrier gas.
4.1.4. Preparation of heterogeneous Fe(salen) catalyst.
To a solution of iron(III)–salen complex in acetonitrile
(250 mg), 500 mg of K10-montmorillonite was added and
the resulting suspension was stirred for 30 h at room temper-
ature. This heterogeneous catalyst was filtered, washed with
acetonitrile, and dried at 60 ꢁC prior to use. The filtrate was
concentrated and it was found that around 95–98% of the
complexes were anchored onto the interlayer of the clay as
shown in Scheme 5.
4.1.5. Characterization. The UV–visible spectra of salen
ligand recorded in acetonitrile medium show two character-
istic absorptions at 253 and 326 nm, which are attributed
to ligand n/p* and p/p* charge transfer bands,
respectively. Iron–salen complex exhibits a broad band
around 473 nm and the absence of 253 and 326 nm bands
confirm the absence of ligand in the complex (Fig. 3a).
The diffuse reflectance spectra of clay-anchored iron–salen
complex too exhibit a band at 473 nm, which confirms the
presence of iron–salen complex onto the layers of clay
(Fig. 3b).
IR spectra were recorded for salen ligand, iron–salen
complex, and heterogeneous catalyst using preactivated
KBr as standard. As seen from Figure 4, the spectrum
of the salen–Fe(III) clay complex coincided with that of
the chloride salt of the same complex, thus establishing the
purity and identity of salen–Fe(III) clay. In addition, the
most characteristic band associated with the salen ligand
appearing at 1500 cmꢂ1 was absent for clay sample, indicat-
ing that all the ligands had reacted with metal to form
complex.
4.1.1. Procedure for C]C bond cleavage in homoge-
neous medium (method A). To a solution of olefin
(50 mg) in 3 mL acetonitrile iron–salen complex (10 mg),
30% hydrogen peroxide (0.6 mL) was added. The reaction
mixture was stirred for 24 h at room temperature. The prog-
ress of the reaction was monitored by the color change from
dark pink to pale pink as the reaction time increased. Then
the reaction mixture was quenched with water, extracted

9916
A. Dhakshinamoorthy, K. Pitchumani / Tetrahedron 62 (2006) 9911–9918
O
N
N
(a)
+
OH
H2N
NH2
HO
OH
Salen
Salicylaldehyde
Ethylenediamine
(b)
T
N
N
N
N
O
Fe
Fe
I
(c)
O
O
O
Cl
T
T = Tetrahedral layer
I = Interstitial space
Scheme 5. Reagents and conditions: (a) salicylaldehyde (2 equiv), ethylenediamine (1 equiv), ethanol, reflux 1 h, 90–93%; (b) anhydrous ferric chloride
(1 mol), salen ligand (1 mol), ethanol, 85–90%; (c) K10-montmorillonite, iron–salen complex, acetonitrile, 30 h.
Figure 4. FTIR spectra of (a) iron–salen complex and (b) iron–salen com-
plex immobilized on clay matrix.
(Fig. 5b). The increase in temperature observed for immobi-
lized sample is due to stabilization of the complex inside the
interlayer of clays.
Direct evidence for the +3 oxidation state of iron–salen
complex was obtained by cyclic voltammetry technique.
Figure 3. (a) UV–visible spectrum of iron–salen complex in acetonitrile and
(b) diffused reflectance spectra of clay-supported iron–salen complex.
Thermogravimetric analysis (TGA) in air profile showed the
decomposition of iron–salen complex and iron–salen clay
complex with residues amounting iron oxide. As seen
from Figure 5a, the decomposition was complete for iron–
salen complex at 610 ꢁC. However on immobilization,
the final decomposition temperature was shifted to 720 ꢁC
Figure 5. Thermogravimetric analysis (TGA) of (a) iron–salen complex and
(b) iron–salen complex immobilized in the clay matrix.

A. Dhakshinamoorthy, K. Pitchumani / Tetrahedron 62 (2006) 9911–9918
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-1000
200
0
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-400
-600
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-1000
E (mV)
Figure 6. (a) Cyclic voltammogram of iron–salen complex in acetonitrile
containing LiClO4 and (b) cyclic voltammogram of iron–salen complex
immobilized onto the clay interlayer and graphite composite (1:1, w/w) in
acetonitrile as solvent.
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The electrochemical behavior of the iron–salen complex
in acetonitrile showed reduction potential of ꢂ0.360 V vs
Ag/AgCl (Fig. 6a). Also, cyclic voltammogram was re-
corded for iron–salen complex immobilized onto the inter-
layer of clay by mixing equal amount (w/w) of iron–salen
immobilized complex and graphite with a small amount of
paraffin liquid as binder, which shows a quasi reversible be-
havior with single reduction potential at ꢂ0.75 V (Fig. 6b).
The existence of single redox process for the salen complex
immobilized in clay implies that the complex exist as mono-
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Acknowledgements
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Financial assistance from Department of Science and Tech-
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