Homogenous and heterogeneous catalytic activity of Azo-linked Schiff base complexes of Mn(II), Cu(II) and Co(II)

Article abstract of DOI:10.1007/s10562-011-0709-9

Azo linked Schiff-base[L] complexes of Mn(II)(1), Cu(II)(2) and Co(II)(3) obtained by template method, in the reaction of 4-(benzeneazo) salicylaldehyde with 1,2-propanediamine in the present of metal acetate, respectively. Complexes are used as catalyst

Full text of DOI:10.1007/s10562-011-0709-9

Catal Lett (2011) 141:1698–1702
DOI 10.1007/s10562-011-0709-9
Homogenous and Heterogeneous Catalytic Activity of Azo-Linked
Schiff Base Complexes of Mn(II), Cu(II) and Co(II)
•
Maryam Lashanizadegan Zeinab Zareian
Received: 15 July 2011 / Accepted: 20 September 2011 / Published online: 1 October 2011
Ó Springer Science+Business Media, LLC 2011
Abstract Azo linked Schiff-base[L] complexes of
Mn(II)(1), Cu(II)(2) and Co(II)(3) obtained by template
method, in the reaction of 4-(benzeneazo) salicylaldehyde
with 1,2-propanediamine in the present of metal acetate,
respectively. Complexes are used as catalyst for oxidation
of cyclohexene with tert-butylhydroperoxide (TBHP);
oxidation of cyclohexene catalyzed by these complexes
gave 2-cyclohexene-1-one and 2-cyclohexene-1-ol as
major products. Conversion of cyclohexene achieved was
95–100% with (1), (2) and (3), with selectivity of 57, 92
and 100% for 2-cyclohexene-1-one, respectively. The
encapsulated Cu(II) complex (Cu–NaY) catalyzes the
oxidation of cyclohexene using TBHP as oxidant in good
yield. (Cu–NaY) under optimized reaction condition gave
three reaction products. A maximum of 100% conversion
of cyclohexene has been achieved where selectivity of
2-cyclohexene-1-one was 83%.
to analyze the catalytic activity of various metal complexes
[6–10]. The activity of these complexes varied with the
type of ligands, coordination sites and metal ions. There
have been many reports on application of metal complexes
in homogenous and heterogeneous catalysis for allylic
oxidation of alkenes [11, 12]. Different reaction pathways
have been employed for the allylic oxidation of alkenes
with molecular oxygen, tert-butylhydroperoxide (TBHP),
H2O2 and transition metal catalysts. Iqbal and co-workers
carried out the oxidation of cyclohexene using cobalt(II)
Schiff base complex, in the presence of molecular oxygen
and 2-methylpropanal where the cyclohexenone and
cyclohexenol (2:1,70%) are obtained as major compounds
[13]. The chiral manganese Schiff base complex has been
shown to catalyze the oxidation of cyclohexene into a
mixture of cyclohexenol (15%), cyclohexenone (27%) and
cyclohexenyl hydroperoxide (32%) without a coreductant
under a flow of oxygen [14]. Copper (II) Schiff base
complexes supported on SiO2 [15] and Al2O3 [16] were
studied with TBHP for the oxidation of cyclohexene. These
reactions provided a mixture of cyclohexenone (58, 48%
respectively) and cyclohexenol (17, 9% respectively) as
major products along with a trace of hydroperoxide in
moderate yield.
Keywords Catalysis Á Homogenous Á Heterogeneous Á
Oxidation Á Zeolite Á Azo linked
1 Introduction
Many Schiff base complexes derived from salicylaldehyde
show excellent catalytic activity in various homogenous
and heterogeneous reactions [1–5].
Salavati-Niasari and co-workers carried out allylic oxi-
dation of cyclohexene using Schiff base complexes of
Cu(II), Ni(II), Co(II) and Mn(II) supported on alumina with
TBHP and H2O2. The result showed allylic oxidation of
cyclohexene with TBHP gave 2-cyclohexene-1-one,
2-cyclohexene-2-ol and 1-(tert-butylperoxy)-2-cyclohex-
ene whereas, oxidation with H2O2 resulted in the formation
of cyclohexene oxide and cyclohexene-1,2-diol. The reac-
tion was catalyzed more successfully with Schiff base
complex of manganese(II) ion supported on alumina than
other Schiff base complexes [17–21].
The oxidation of hydrocarbons using Schiff base com-
plexes has been in field of academic and industrial interest
M. Lashanizadegan (&) Á Z. Zareian
Department of Chemistry, Faculty of Sciences, Alzahra
University, Vanak, P. O. Box 1993891176, Tehran, Iran
e-mail: m_lashani@alzahra.ac.ir
123

Homogenous and Heterogeneous Catalytic Activity
1699
Azo-linked Schiff base are being increasingly used in
the textile, leather, and plastic industries [22–24]. Also azo
derivatives have been utilized as indicators and radical
reaction indicators. In addition, azo derivatives have the
potential for use in electronic and drug delivery applica-
tions [25, 26]. A few Schiff base azo linked complexes are
reported to be catalytically active towards oxidation [27].
Therefore, it is interesting to study azo linked compounds
as catalysts.
50 °C overnight. Yield: 82%. Anal. cacld for C29H26N6O2 :
C 71.23, H 5.30, N 17.14. Found: C 70.49, H 5.23, N 17.23.
FT-IR (KBr, cm-1): 3,444br, 3,064w, 2,968w, 2,924w,
1,631 (C=N), 1,583sh, 1,490m, 1,438w, 1,369w, 1,283m,
1,105w, 835m, 767m, 688m. UV/VIS (CH2Cl2, k, nm) 345,
1
280. H NMR (CDCl3, d): 13.28 (s, 2H, OH), 8.46, 8.5 (s,
2H, –CH=N–), 7–7.9(m, 16H, aromatic H) 3.7–3.8 (m, 2H,
CH2), 3.8–4 (m, 1H, CH), 1.51 (s, 3H, CH3).
In this study, we synthesized Mn(II), Cu(II) and Co (II)
complexes containing azo-Schiff-base [L]derivatives of 1,2
propane diamine and 4-phenylazosalicylaldehyde, we
studied their catalytic activity in the oxidation of cyclo-
hexene by TBHP. In mobilization of copper(II) azo-Schiff
base complexes (2) onto zeolite has been adopted to pre-
pare heterogeneous catalyst and activities of these hybrids
toward oxidation of cyclohexene by TBHP were studied.
2.4 Template Preparation of the Complexes (ML)
All complexes were prepared by template reaction in one
step, 1 M hydrated metal acetate, 1 M 1,2-propanediamine
and 2 M 4-(benzeneazo) salicylaldehyde in 30 mL ethanol,
refluxed for 4 h. The precipitated solid were filtered off
from the ice-cooled reaction mixture. The solid were
washed with ethanol and then dried at 50 °C [29]. Analysis
of complex 1. Anal. calcd for C29H24MnN6O2: C 63.0, H
4.53, N 15.22. Found: C 63.1, H 4.3, N 15.0. FT-IR (KBr,
cm-1): 3,428br, 3,044w, 2,924w, 1,609s (C=N), 1,541sh,
1,463w, 1,379m, 1,297s, 1,224w, 1,151w, 1,115w, 1,046w,
1,017w, 920w, 827m, 764m, 687m, 658w. UV/VIS
(CH2Cl2, k, nm) 384, 257. Complex 2. Anal. calcd for
C29H24CuN6O2: C 61.2, H 4.21, N 14.76. Found: C 60.94,
H 4.26, N 14.51. IR (KBr, cm-1): 3,445br, 2,964w,
2,924w, 2,854w, 1,631s (C=N), 1,606s, 1,530w, 1,467m,
1,416w, 1,382s, 1,326m, 1,256w, 1,190w, 1,155w, 1,112m,
890w, 834m, 759m, 687m. UV/VIS (CH2Cl2, k, nm) 381,
280. Complex 3. Anal. calcd for C29H27CoN6O3.5: C 63.63,
H 4.73, N 14.6. Found: C 60.0, H 4.4, N 14.4. FT-IR (KBr,
cm-1): 3,421br, 3,042w, 2,970w, 2,927w, 1,634s (C=N),
1,603s, 1,523m, 1,460m, 1,419w, 1,372m, 1,255w,
1,223 m, 1,143w, 1,133 m, 810 m, 766 m, 667 m. UV/VIS
(CH2Cl2, k, nm) 384, 280.
2 Experimental
2.1 Instruments and Reagents
Infrared spectra were recorded as KBr pellets using Bruker
Tensor 27 spectrometer. The visible spectra were deter-
mined using a Perkin Elmer, Lambda 35 UV/VIS. 1H NMR
spectra were obtained on a Bruker Avance 300 MHz
spectrometer using TMS as internal standard spectrometer.
The reaction products of oxidation were determined and
analyzed by GC–MS (Agilent Series 6890). X-ray dif-
fractograms of the catalysts were recorded using XRD,
Seifect, 3003 PTS diffractometer with a Cu-Ka target. The
metal contents were measured by using PU900 Philips
atomic absorption.
Analytical reagents grade cyclohexene, 1,2-propanedi-
amine, salicylaldehyde, TBHP (solution 80% in di-tert-
butylperoxide) were procured from Merck. Other reagents
and solvents used were also of AR grade. Y-zeolite (Si/Al
4.5) was obtained in our laboratory.
2.5 Incorporation of Copper(II) in NaY (Metal
Exchanged Y-Zeolite)
Na–Y zeolite (2 g) was suspended in 100 mL distilled
water which contained copper(II) nitrate (2 mmol). The
mixture was then stirred for 24 h. The solid was filtered
and washed with de-ionized water and dried at room
temperature to give a light blue powder of Cu–NaY [30].
Calcination of the prepared copper(II)-incorporated zeolite
was avoided to arrest the migration of copper (II) ions from
the vicinity of the super cage [31].
2.2 Preparation of 4-(benzeneazo) Salicylaldehyde
4-(benzeneazo) salicylaldehyde was prepared using stan-
dard procedure [28].
2.3 Preparation of Ligand (H2L)
0.05 mol of 1,2-propanediamine was slowly added to a
solution of 0.03 mol of 4-(benzeneazo) salicylaldehyde in
30 mL ethanol after refluxing the reaction mixture for 2 h.
The solution was left at room temperature and the red pre-
cipitate was collected by filtering and washing with 15 mL
of ethanol and then recrystallized from ethanol and dried at
2.6 Immobilization of CuL in Cu–NaY
Cu–NaY (1 g) and H2L (2 g) in acetonitrile solution was
mixed in a round bottom flask. The reaction mixture was
heated at 100 °C for 5 h in an oil bath with constant stir-
ring. The resulting material was taken out and extracted
123

1700
M. Lashanizadegan, Z. Zareian
Scheme 1
O
N
N
N
N
O
M
N
N
H3C
M= Cu, Mn, Co
with acetonitrile using soxhlet extractor till the complex
was free from un-reacted ligand. The non-complexed metal
ions present in the zeolite were removed by exchanging
with aqueous 0.01 M NaCl solution. The resulting solid
was finally washed with hot distilled water till no precip-
itation of AgCl was observed in reacting filtrate with
AgNO3 solution. This was then dried at 150 °C for several
hours till constant weight was achieved.
with Na(I) of Na–Y followed by reaction of metal
exchanged zeolite-Y with H2L in solution. The flexible
Schiff base ligand was allowed to react with Cu–NaY
(scheme 2).
It is expected that the CuL complex will be formed in the
super cage as well as on the surface of the Y zeolite. It
seems soxhlet extraction with CH3CN effectively washes
the hybrid material. The non complexed Cu(II) ions in
zeolite were removed by exchanging with aqueous 0.01 M
NaCl solution. The resulting solid was finally washed with
distilled water till no precipitation of AgCl was observed on
reacting the filtrate with AgNO3 solution. The intensity of
the peaks in encapsulated CuL–NaY is, though, weak due to
their low concentration in zeolite matrix. Comparison of
spectra of Cu–NaY, CuL–NaY with the complex (2) pro-
vides evidence for the coordinating mode of catalyst. IR
spectra of the hybrid material showed an intense band at
1,011 cm-1 attributable to the asymmetric stretching of Al–
O–Si chain of zeolite. The symmetric stretching and
bending frequency bands of Al–O–Si framework of zeolite
appear at 723 and 458 cm-1, respectively [34]. The dif-
fraction patterns of encapsulated copper complex and Na–Y
are essentially similar except a slight change in intensity of
the band in encapsulated complex. This observation indi-
cates that the framework of the zeolite has not structurally
changed during encapsulation.
2.7 Homogeneous Oxidation of Cyclohexene
To a solution of cyclohexene (10 mmol), metal complex
(0.1 g) in CH3CN (10 mL), was added TBHP (25 mmol).
The resulting mixture was refluxed under nitrogen atmo-
sphere, the products were collected at different time
intervals, identified and quantified by GC and verified by
GC–MS. The concentrations of products were determined
using benzyl chloride as internal standard.
2.8 Heterogeneous Oxidation of Cyclohexene
TBHP (25 mmol) cyclohexene (10 mmol) and catalyst
(0.2 g) were mixed in 10 mL of CH3CN and the reaction
mixture was heated at 84 °C with continuous stirring in an
oil bath under nitrogen atmosphere. The products were
collected at different time intervals and identified and
quantified by GC and verified by GC–MS. The concen-
tration of products were determined, using benzyl chloride
as internal standard.
Ligand (H2L)
Cu(NO3)2 in H2O
in solution
CuL-NaY
NaY-Zeolite
Cu-NaY
CuL formation
ion-exchange Cu(II)
Scheme 2
3 Results and Discussion
Table 1 Effect of different catalysts on the oxidation of cyclohexene
and product selectivity in acetonitrile
The complexes (Scheme 1) are air-stable colored solids,
insoluble in water, partly soluble in ethanol and methanol
and soluble in DMSO and DMF. Analytical data suggest
that the metal–ligand stoichiometry is 1:1.
Catalyst
Conversion (%) TON Product selectivity (%)
Ketone Alcohol Others
CuL(2)
MnL(1)
CoL(3)
95
100
100
105
109
110
149
92
57
6
16
0
2
27
0
The complexes (1), (2) and (3) showed a sharp band in
the range 1,608–1,634 cm-1 attributable to the azomethine
group of Schiff base ligand [32, 33].
100
83
CuL–NaY 100
17
0
Synthesis of complex CuL encapsulated in the nano
cavity of zeolite-Y involved the exchange of copper(II) ion
Ketone 2-cyclohexene-1-one, alcohol 2-cyclohexene-1-ol
123

Homogenous and Heterogeneous Catalytic Activity
1701
60
The oxidation of cyclohexene catalyzed by complexes
(1–3) with TBHP gives excellent conversion of 95–100%
(selectivity, 57–100%) of 2-cyclohexene-1-one under
homogeneous conditions.
ketone
alcohol
50
peroxide
40
30
20
10
0
others
The effect of various reaction media on oxidation of
cyclohexene catalyzed by complexes 2 has been studied. A
graphical representation of the relative efficacies of the
catalysts in different solvents has been given in Fig, 1. The
efficiency of the catalysts in different solvents decreases in
the order acetonitrile [ dichloromethane [ chloroform.
The effect of amount of catalyst and TBHP on the
oxidation of cyclohexene catalyzed by complex 2 has been
studied. A graphical representation of these effects is
shown in Fig 2a–b. Therefore, an amount of 0.1 g of cat-
alyze and as shown in Fig. 2b the 3.5:1 molar ratio is the
best to obtain the optimum cyclohexene conversion of
100% in 4 h reaction time.
acetonitrile
dichloromethane
chloroform
Fig. 1 Effect of solvent on the selectivity in cyclohexene oxidation
reactions catalyzed by complex (2)
80
(a)
70
60
The effect of various reaction media on the oxidation of
cyclohexene catalyzed by CuL–NaY also has been studied.
In all the oxidation reactions, 2-cyclohexene-1-one was
formed as major product. In acetonitrile and dichloro-
methane the conversion of cyclohexene are 100 and 98%,
respectively, but the selectivity of 2-cyclohexene-1-one in
CH3CN and CH2Cl2 is 83 and 74%, respectively. There-
fore, for the best solvent, CH3CN, polarity, hydrophilicity
and size of the solvent molecule may also play some role
on the reaction rate [35].
50
40
30
20
10
0
ketone
alcohol
peroxide
0.05g
0.1g
0.15g
90
80
70
60
50
40
30
20
10
0
(b)
ketone
alcohol
peroxide
others
(CH3)3C- OOH
+
LCu2+
LCu3+
+
(CH3)C- O
1.0
1.5
2.0
3.0
3.5
(CH3)3C- OOH
Fig. 2 Effect of amount of catalyst (a), and TBHP (b); on the
selectivity in cyclohexene oxidation reactions catalyzed by complex
(2)
(CH3)3C- OO
3.1 Catalytic Activities
LCu3+-OH
The oxidation of cyclohexene with TBHP was carried out
to test the efficiency of the prepared catalysts. The results
of the reactions are given in Table 1. The hybrid catalyst
showed good catalytic activity. It is noteworthy that neither
the mother zeolite NaY nor the Cu–NaY exhibited any
noticeable catalytic activities. It should be noted that
atomic absorption spectroscopic analysis shows copper is
not leaching out during oxidation reactions, as no copper
was detected in the liquid phase of the reaction mixture
after completion of the reaction.
O
OC(CH3)3
OH
O
+ LCu2+
+ LCu3+-OH
Scheme 3
123

1702
M. Lashanizadegan, Z. Zareian
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4 Conclusion
Complexes MnL, CuL and CoL have been synthesized and
used as catalysts in oxidation of cyclohexene. All com-
plexes are found to be catalytically active under homoge-
nous conditions. Reaction conditions have been optimized
considering different parameters to get maximum conver-
sion of substrate. A maximum of 100% conversation has
been obtained with CoL under inert atmosphere. The
selectivity of the major product of 2-cyclohexene-1-one
was 88%.
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Complex CuL has been encapsulated in the super cages
of zeolite-Y. Its encapsulation has been ensured by dif-
ferent studies. CuL–NaY has potential catalytic activity for
oxidation of cyclohexene. Reaction conditions have been
optimized considering different parameters to get maxi-
mum conversion of cyclohexene. 100% conversion of
cyclohexene has been achieved with CuL–NaY using
TBHP as oxidant. The selectivity of 2-cyclohexene-1-one
and 2-cyclohexene-1-ol are 83 and 17%, respectively.
Heterogeneous catalysis is stable and free from leaching as
confirmed by testing the filtrate for the corresponding metal
ion.
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