A zirconium Schiff base complex immobilized on starch-coated maghemite nanoparticles catalyzes heterogeneous condensation of 1,2-diamines with 1,2-dicarbonyl compounds

Article abstract of DOI:10.1007/s11243-015-0012-5

A magnetically separable zirconium Schiff base nanocatalyst was synthesized under ultrasonic agitation. TEM images revealed a uniform spherical particle shape with average size of 10-14 nm for the as-prepared catalyst. The catalytic performance of ZrOL₂@SMNP in the heterogeneous condensation of various 1,2-diamines and 1,2-dicarbonyls for the synthesis of heterocyclic compounds in ethanol has been explored.

Full text of DOI:10.1007/s11243-015-0012-5

Transition Met Chem
DOI 10.1007/s11243-015-0012-5
A zirconium Schiff base complex immobilized on starch-coated
maghemite nanoparticles catalyzes heterogeneous condensation
of 1,2-diamines with 1,2-dicarbonyl compounds
1
1
Maasoumeh Jafarpour
•
Abdolreza Rezaeifard
Received: 10 October 2015 / Accepted: 23 November 2015
Ó Springer International Publishing Switzerland 2015
Abstract A magnetically separable zirconium Schiff
base nanocatalyst was synthesized under ultrasonic agita-
tion. TEM images revealed a uniform spherical particle
shape with average size of 10–14 nm for the as-prepared
problems, magnetic nanoparticles, whose flocculation and
dispersion can be controlled reversibly by applying a
magnetic field, have been extensively employed as a
recyclable support matrix.
catalyst. The catalytic performance of ZrOL @SMNP in
2
Quinoxaline derivatives are an important class of hete-
rocyclic compounds. By modifying the core quinoxaline
structure, it is possible to obtain a wide variety of com-
pounds with various biological properties. In the last two
decades, several quinoxaline derivatives have been found
to have antimicrobial activity, particularly as antifungal [9,
10] and antibacterial agents [9–13]. Promising results have
also been obtained for their anticancer activity [14–16].
Antioxidant and anti-inflammatory activity has been
explored for quinoxaline derivatives [17, 18]. Some copper
and zinc quinoxaline complexes have presented antidia-
betic activity [19], such that N-arylcarbamoyl and N-aryl
thiocarbamoyl derivatives revealed hypoglycemic behavior
in Wister rats.
the heterogeneous condensation of various 1,2-diamines
and 1,2-dicarbonyls for the synthesis of heterocyclic
compounds in ethanol has been explored.
Introduction
Over the past decade, zirconium compounds have found an
ever-increasing role in organic synthesis, as revealed by the
extensive literature on zirconium compounds as catalysts
or reagents in synthetic organic chemistry [1]. Recently,
the use of nanomaterials with high activity under mild
conditions has been explored, because of their very large
surface area [2–6]. The control of chemical reactions by
changing the size, dimensionality, chemical composition
and morphology of the reaction centers is the central aim of
nanocatalysis [7]. However, the small size of nanoparticles
often makes their separation from the reaction solution and
subsequent recycling difficult, impeding their use in
industrial processes [8]. In order to circumvent such
With the aim of developing our ongoing research for
synthesis of new heterogeneous nanocatalysts for synthesis
of organic compounds [20–26], herein we report the syn-
thesis and catalytic performance of a new zirconium Schiff
base complex anchored on magnetic nanoparticles in the
condensation of aryl 1,2-diamines with 1,2-dicarbonyls for
synthesis of quinoxaline derivatives in ethanol under mild
conditions in good to high yields (Scheme 1).
&
&
Maasoumeh Jafarpour
mjafarpour@birjand.ac.ir
Experimental
Abdolreza Rezaeifard
rrezaeifard@birjand.ac.ir; rrezaeifard@gmail.com
General remarks
1
All chemicals were purchased from Merck or Fluka.
Powder X-ray diffraction (XRD) experiments were per-
formed on a Bruker D8-advance X-ray diffractometer with
Catalysis Research Laboratory, Department of Chemistry,
Faculty of Science, University of Birjand,
Birjand 97179-414, Iran
123

Transition Met Chem
Scheme 1 Synthesis of
quinoxaline derivatives and
pyrido pyrazines in the presence
O
O
R2
R2
2
of ZrOL @SMNP. The black
sphere surrounded by a white
layer represents starch-coated c-
MeO
O
N
O
Si
Si
O
N
N
R2
O
R1
2
Fe O
3
EtOH
Zr
O
O
MeO
X
R2
N
O
R1
NH2
NH2
X
˚
Cu Ka (k = 1.54178 A) radiation. FTIR spectra were
recorded on a NICOLET spectrometer. TEM images were
obtained with a 906 E instrument (Zeiss, Jena, Germany).
Samples for TEM experiment were prepared by dispersion
in ethanol, sonicating for 30 min and evaporating one drop
of the solution onto a 200-mesh formvar-coated copper
grid.
Preparation of zirconium Schiff base complex
A solution of ZrOCl O (0.806 g, 2.5 mmol) in ethanol
Á8H
2
2
(10 ml) was added to a solution the Schiff base (5 mmol,
0.25 g) in ethanol (10 ml) at 60 °C under ultrasonic agi-
tation. The same conditions were maintained for 3 h. The
zirconium Schiff base complex precipitated upon cooling
the reaction mixture; it was filtered off and washed with
cold ethanol, followed by drying at 100 °C under vacuum.
Progress of each reaction was monitored by TLC using
silica-gel SIL G/UV 254 plates and also by GC on a Shi-
madzu GC-16A instrument using a 25-m CBP1-S25
(
0.32 mm ID, 0.5 lm coating) capillary column. NMR
spectra were recorded on Bruker Avance DPX 250 and
00 MHz instruments.
Preparation of c-Fe
O
2 3
4
c-Fe MNPs were synthesized by a previously reported
O
2 3
chemical co-precipitation technique involving ferric and
ferrous ions in alkali solution with minor modifications [28,
The preparation of organosilicon aldehyde [27]
2
9]. Thus, FeCl Á4H O (1.99 g) and FeCl Á6H O (3.25 g)
2
2
3
2
To a solution of (3-chloropropyl) trimethoxy silane
were dissolved in deionized water (30 ml) under an Ar
atmosphere at room temperature. NH OH solution (0.6 M,
200 ml) was then added dropwise (drop rate = 1 ml min
(
0.74 ml, 4 mmol) in DMSO (0.35 ml, 5 mmol), NaHCO3
0.67 g, 8 mmol) was added, and the mixture was refluxed
4
-
1
(
)
at 155 °C for 2 h. Then, water (50 ml) was added to the
to the stirring mixture at room temperature such that the
reaction pH reached 11. The resulting black dispersion was
stirred for 1 h at room temperature and then heated to reflux
for 1 h to yield a brown dispersion. The magnetic nanopar-
ticles were then separated by an external magnet and washed
with deionized water until neutral. The as-synthesized
reaction mixture, and the product was extracted with Et O
2
(
2 9 50 ml). The organic layer was separated, dried over
anhydrous CaCl and filtered. Evaporation of the solvent
2
afforded the desired product (yellow oil, 70 % isolated
yield). Structural assignments of the product are based on
1
its FTIR and H NMR spectra.
-1
sample was heated at 2 °C min up to 250 °C and then kept
in a furnace at 200 °C for 3 h to give a reddish-brown
powder.
The preparation of Schiff base [27]
To a solution of (3-oxopropyl) trimethoxy silane (0.8 ml,
Preparation of starch-coated c-Fe
O @SMNP [27]
2 3
5
mmol) in ethanol (10 ml), a solution of ethanolamine
(
0.3 ml, 5 mmol) in ethanol (10 ml) was gradually added
To 1.0 g of c-Fe particles dispersed in 15 ml of bidis-
O
2 3
at 60 °C under ultrasonic agitation. The same conditions
were maintained for 60 min. The product which precipi-
tated after 24 h at room temperature was filtered off,
washed with ethanol and dried in a desiccator (85 % iso-
lated yield). Structural assignments of the product are
tilled water, a hot aqueous solution of starch (2 g) was
gradually added under ultrasonic agitation, which was then
maintained for additional 15 min. After stirring at room
temperature for 8 h, the starch-coated maghemite
nanoparticles (SMNP) were separated by an external
magnetic field, washed with water and dried.
1
based on its FTIR and H NMR spectra.
1
23

Transition Met Chem
O
N
NaHCO , DMSO
H N
OH
3
2
(
MeO) Si
Cl
OH
3
(MeO) Si
H
3
reflux , 2 h
EtOH , )))
(MeO)3Si
ZrOCl 8H O EtOH, )))
2.
2
MeO
O
(
MeO) Si
N
O
O
Si
N
O
O
3
O
O
Zr
Zr
O
O
SMNP
Si
N
O
(MeO) Si
3
N
MeO
2 3
@SMNP. The black sphere surrounded by white layer represents starch-coated Fe O
Scheme 2 Preparation of ZrOL
2
2 3 2
Fig. 1 XRD patterns of bare c-Fe O (left) and ZrOL @SMNP (right)
Immobilization of ZrOL on SMNP
2
(ZrOL @SMNP)
2
To 1.0 g of SMNP in 30 ml absolute ethanol, [ZrOL2]
2 mmol) (over period of 10 min) was added under ultra-
(
sonic agitation at room temperature and the resulting mixture
was refluxed for 14 h. The final sample (ZrOL @SMNP)
2
was separated by an external magnetic field, washed three
times with ethanol and dried under vacuum.
General procedure for the synthesis of quinoxalines
and pyrido pyrazines
A mixture of the required 1,2-dicarbonyl (1 mmol) and
ZrOL @SMNP (0.004 g) in ethanol (0.5 ml) was stirred at
2
2
5 °C for 2 min. Then, the required 1,2-diamine
1.5 mmol) was added to the mixture, which was stirred at
0 °C for the appropriate reaction time. The progress of the
(
6
reaction was monitored by TLC or GC. After completion of
the reaction, the precipitate was dissolved by adding
ethanol, and ZrOL @SMNP was separated by decantation
2
of the reaction mixture in the presence of an external
magnet. Most of the product was precipitated purely by
Fig. 2 FTIR spectra of
c ZrOL @SMNP
2 3 2 3
a c-Fe O , b c-Fe O @starch and
2
123

Transition Met Chem
used as an appropriate linker for a new heterogeneous
supported catalyst. Condensation with ethanolamine gave a
new Schiff base [27]. The zirconyl Schiff base complex
was prepared (ZrOL ) by condensation of the Schiff base
2
(
HL) with ZrOCl Á8H O. The as-prepared ZrOL complex
2
2
2
was then immobilized on magnetic nanoparticles (MNP)
28, 29] coated with a dense starch layer (SMNP) [27] by
[
the use of ultrasonic agitation (ZrOL @SMNP).
2
The XRD pattern of ZrOL @SMNP (Fig. 1, right)
2
exhibits characteristic peaks at the same 2h values as pure
c-Fe O itself, demonstrating that the crystalline structure
of the iron oxide remains intact after attachment to the
2
3
Schiff base complex.
The FTIR spectra of pure c-Fe O nanoparticles, SMNP
2
3
and ZrOL @SMNP are depicted in Fig. 2. Comparison of
2
2
Fig. 3 TEM image of ZrOL @SMNP nanoparticles
the FTIR spectra of ZrOL @SMNP (Fig. 2c) with those of
2
MNP (Fig. 2a) and SMNP (Fig. 2b) confirms the succes-
sive formation of the respective composites. Major bands at
concentrating and cooling the ethanolic solution. The
remaining product was isolated from an excess of 1,2-di-
amine by plate chromatography eluted with n-hexane–
EtOAc (10/2). Structural assignments of the products were
-
625 cm are attributed to the imine group and a strong
1
1
-
peak at 1122 cm to the Si–O bonds. The absorption
1
-
1
bands at 700 and 490 cm
can be assigned to the
1
13
based on their H and C NMR spectra.
stretching vibrations of the Zr=O and Zr–N bonds,
respectively.
Inductively coupled plasma atomic emission (ICP)
analysis revealed that the content of Zr in the supported
catalyst was 0.089 wt%. Therefore, each gram of hetero-
geneous catalyst contains 9.7 lmol Zr. Transmission
electron microscopy (TEM) images clearly show spherical
Results and discussion
Synthesis and characterization of the catalyst
As shown in Scheme 2, organosilicon aldehyde prepared
by oxidation of (3-chloropropyl) trimethoxy silane was
ZrOL @SMNP nanocatalyst particles, with size ranging
2
between 12–14 nm (Fig. 3).
Table 1 Condensation of o-
phenylenediamine and 4,4-
dimethoxybenzil under different
a
conditions
Entry
Catalyst
Solvent
EtOAc
Temp (°C)
Time (min)
Isolated yield %
1
2
3
4
5
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
SMNP@ZrOL
2
2
2
2
2
2
2
2
2
2
2
2
2
2
60
60
60
60
60
60
70
50
40
25
60
60
60
60
60
60
60
30
120
80
90
80
20
20
70
85
80
20
60
20
20
20
20
20
94
44
53
74
54
94
94
83
84
59
94
80
74
94
54
46
55
2
H O
S.F
C
2
H
Cl
4 2
CH
3
CN
b
6
EtOH (0.5 ml)
EtOH
7
8
9
EtOH
EtOH
1
1
1
1
1
1
1
1
a
0
1
3
4
5
6
7
8
EtOH
EtOH (1 ml)
EtOH (1.5 ml)
EtOH (0.5 ml)
EtOH (0.5 ml)
EtOH
(0.009 lmol)
(0.066 lmol)
2 3
Fe O
SMNP
Starch
EtOH
EtOH
Reaction condition: molar ratio of diamine/diketone/catalyst 1.5/1/.004 g (0.038 lmol) in 0.5 ml solvent
b
Optimized conditions
1
23

Transition Met Chem
Table 2 Synthesis of quinoxalines and pyrido pyrazines in the presence of ZrOL
2
@SMNP
R1
NH2
NH2
O
O
R2
R2
R1
N
R2
R2
ZrOL2@SMNP
+
EtOH
X
X
N
a
Product X, R
Entry
Diamine X, R
C, H
1
1,2-Diketone R
2
1
, R
2
Time (min.)
Isolated yield (%)
1
2
3
4
5
6
7
8
9
Ph
Ph
Ph
C, H, Ph
2
2
97
95
96
94
93
85
96
95
94
95
96
78
97
C, CH
3
C, CH
C, NO
C, H, p-OCH
C, CH , p-OCH
C, NO , p-OCH
C, H, CH
C, CH , CH
C, NO , CH
C, H, Furyl
C, CH , Furyl
3
, Ph
C, NO
C, H
2
2
, Ph
60
20
20
90
3
p-OCH
p-OCH
p-OCH
3
-Ph
3
-Ph
3
-Ph
3
-Ph
-Ph
-Ph
C, CH
3
3
3
C, NO
C, H
2
2
3
CH
CH
CH
3
3
3
3
C, CH
3
3
3
3
C, NO
C, H
2
2
3
15
4
10
11
12
13
Furyl
Furyl
C, CH
3
3
3
C, NO
C, H
2
Furyl
O
C, NO , Furyl
2
100
3
O
N
N
O
O
1
4
C, NO
2
60
88
O2N
N
N
15
16
17
18
19
N, Br
N, Br
N, Br
N, Br
N, Br
Ph
N, Br, Ph
5
90
5
94
73
94
95
94
p-OCH
CH
3
-Ph
3
N, Br, p-OCH -Ph
3
N, Br, CH
3
Furyl
O
N, Br, Furyl
12
35
O
Br
N
N
N
The reactions were run at 60 °C in 0.5 ml ethanol, and the molar ratio of 1,2-dicarbonyl/1,2 diamine/catalyst was 100:120:0.004
a
All products were identified by their spectroscopic data [24]
Catalytic activity of ZrOL @SMNP
2
condensed with 4,4-dimethoxybenzil (1 mmol) in ethanol
(
0.5 ml) at 60 °C to give the desired product in 94 % yield
The catalytic potential of the ZrOL @SMNP was evalu-
2
within 20 min (Table 1, entry 6).
ated in the condensation of various 1,2-diamines and 1,2-
dicarbonyls for the synthesis of quinoxalines and pyrido
pyrazines. Initially, blank experiments were addressed to
the condensation of o-phenylenediamine (1.5 mmol) and
Moreover, the yield of the condensation product
decreased for the above-mentioned reaction when the
nanocatalyst was replaced by c-Fe O (54 %), SMNP
2
3
(46 %) or starch (55 %) under the same conditions.
4
,4-dimethoxybenzil (1 mmol) as a model reaction under
The optimized reaction conditions were applied for the
condensation of various aryl 1,2-diamines and 1,2-dicar-
bonyls, giving promising results (Table 2). The yields of
products were highly dependent on the electronic demands
of the substrate used. For instance, condensation of a dia-
mine bearing a strongly electron-withdrawing group
(Table 2, entries 3, 6, 9, 12 and 14) or a dicarbonyl
neat conditions which gave 45 % yield (by NMR) after 7 h.
To find the optimum reaction conditions, the influence of
different factors such as solvent nature and amount, tem-
perature and catalyst amount were investigated (Table 1).
Under the optimized conditions in the presence of
0
.004 g of nanocatalyst, o-phenylenediamine (1.5 mmol)
123

Transition Met Chem
Table 3 Catalytic activity of
ZrOL @SMNP in comparison
Entry
Catalyst
Catalyst (mol%)
Time (min)
Yield (%)
Ref.
2
with other catalysts used for the
condensation of 4-nitro-o-
phenylenediamine and 4,4-
dimethoxybenzil
1
2
3
4
5
6
a
ZrOL
Zr(salphen)Cl
ZrL Cl /EtOH
ZrOCl O/EtOH
Á8H
ZrCl /Methanol
Zr(DS) /H
2
@SMNP/EtOH
0.004
1
90
180
180
180
240
110
85
[a]
2
/EtOH
40
[30]
[31]
[32]
[33]
[34]
2
2
1
\10
2
2
10
5
No reaction
4
96
83
4
2
O
2.5
This work
Table 4 Recyclability of the catalytic system in the condensation of o-phenylenediamine and 4,4-dimethoxybenzil
Run
Conversion % (5 min)
Conversion % (10 min)
Conversion % (15 min)
Conversion % (20 min)
Run 1
Run 2
Run 3
Run 4
70
70
65
65
80
80
75
75
90
90
90
90
100
98
98
96
The reactions were run under conditions mentioned in Table 2
compound substituted with a strongly electron-donating
group proceeded slowly (Table 2, entries 4–6 and 16).
Under similar reaction conditions, 5-bromo-2,3-di-
aminopyridine reacted efficiently with a variety of 1,2-
diketones to give high yields of pyrido[2,3-b] pyrazines,
albeit in longer reaction times than those for the aryl 1,2-
diamines (Table 2, entries 15–19).
protected c-Fe O nanoparticle component, allows the
2
3
catalyst to be recovered and reused at least four times in
the condensation of o-phenylenediamine and 4,4-
dimethoxybenzil (Table 4).
This high yielding condensation method offered ready
scalability. For example, the condensation of o-
phenylenediamine and benzil in a 20 mmol scale in the
presence of the nanocatalyst was investigated. The reaction
proceeded similarly to the smaller scale, and the desired
product was obtained in almost the same isolated yield and
reaction time.
Table 3 shows the merit of this protocol for the con-
densation of 4-nitro-o-phenylenediamine and 4,4-
dimethoxybenzil as normally inactive substrates in com-
parison with ZrOCL and other similar catalysts, in terms
2
of conversion rate, and especially catalyst mol% used in
the reactions.
Conclusions
The catalyst reuse and stability
The ZrOL @SMNP nanocatalyst (12-14 nm) was prepared
2
by immobilizing a new zirconium Schiff base complex on
The high yields of condensation products obtained by this
catalytic system demonstrate the high stability and activity
starch-coated c-Fe O nanoparticles. Heterogeneous con-
2
3
densation of various 1,2-diamines and 1,2- dicarbonyls in
of the prepared ZrOL @SMNP. This was further evalu-
2
ethanol was efficiently catalyzed by the ZrOL @SMNP
2
ated by the recovery potential of the nanocatalyst in the
condensation of o-phenylenediamine and 4,4-dimethoxy-
benzil under the conditions given in Table 2. Recovery of
nanoparticles. A variety of products were obtained in good/
excellent yields by using a low catalyst loading of
0.004 mol%, while its initial activity was preserved after
ZrOL @SMNP catalyst was easy and efficient. When
2
several recoveries, regardless of the type of selected reac-
tion. Thus, our method is cost-effective and could enable
industrially important reactions to be carried out efficiently
under safe and practically attainable conditions.
magnetic stirring was stopped, the catalyst simply aggre-
gated on the magnetic stirring bar. The catalyst was then
recovered by decantation of the reaction mixture in the
presence of an external magnet. The recovered nanocat-
alyst was washed with ethyl acetate or ethanol, dried
under vacuum and used directly for the next round of
reaction without further purification. The ease of recovery,
combined with the intrinsic stability of the starch-
Acknowledgments Support for this work by Research Council of
University of Birjand under Project 1389/D/870 is highly appreciated.
We thank Miss Fahimeh Feizpour for her assistance in some parts of
this project.
1
23

Transition Met Chem
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