A novel route for the synthesis of 5-substituted 1-: H tetrazoles in the presence of polymer-supported palladium nanoparticles

Article abstract of DOI:10.1039/c7nj02222k

A novel method for the synthesis of 5-substituted 1-H tetrazoles has been developed using one-pot tandem reactions of aryl halides with K₄[Fe(CN)₆] and sodium azide in the presence of cross-linked poly(4-vinylpyridine)-stabilized Pd(0) nanoparticles, [P₄-VP]-PdNPs. The catalyst was characterized using various techniques such as FT-IR and UV-vis spectroscopy, AAS, TEM, FESEM, EDX analysis, XRD and XPS. The results confirm a good dispersion of palladium nanoparticles on the polymer support. The catalyst is reusable many times without a significant loss in its activity.

Full text of DOI:10.1039/c7nj02222k

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A novel route for the synthesis of 5-substituted
1-H tetrazoles in the presence of polymer-supported
Cite this:DOI: 10.1039/c7nj02222k
palladium nanoparticles†
Seyed Shahab Addin Darbandizadeh Mohammad Abadi * and
Mohammad Ali Karimi Zarchi
A novel method for the synthesis of 5-substituted 1-H tetrazoles has been developed using one-pot
Received 21st June 2017,
Accepted 9th August 2017
tandem reactions of aryl halides with K
4
[Fe(CN)
6
] and sodium azide in the presence of cross-linked
poly(4-vinylpyridine)-stabilized Pd(0) nanoparticles, [P
4
-VP]-PdNPs. The catalyst was characterized using
various techniques such as FT-IR and UV-vis spectroscopy, AAS, TEM, FESEM, EDX analysis, XRD and
XPS. The results confirm a good dispersion of palladium nanoparticles on the polymer support. The catalyst
is reusable many times without a significant loss in its activity.
DOI: 10.1039/c7nj02222k
rsc.li/njc
catalysts, reagents and scavengers have been widely applied in
Introduction
3
2–35
organic transformations.
Also, there are many reports on
3
6–39
Tetrazoles are a singularly important class of heterocyclic polymer-supported palladium in the literature.
Poly(vinyl-
compounds and are well known as a magic moiety exhibiting pyrrolidone) (PVP) has been shown to be an effective matrix to
1
biologically attractive properties such as being antihypertensive,
stabilize palladium nanoparticles for use as a catalyst in cross-
2
3
4
5
40–43
anti-allergic, antibiotic, anti-diabetic, anti-arrhythmic, anti- coupling reactions such as Suzuki reactions,
inflammatory, anti-neoplastic and antiviral. These compounds reactions, Heck and carbonylation reactions,
also possess a broad spectrum of applications which have made genation of 2-ethyl-9,10-anthraquinone, electroless copper
Sonogashira
the hydro-
6,7
44
45–47
4
8
4
9
50
them privileged in heterocyclic compound research fields such as deposition, nitrate and nitrite reductions and H–D exchange
8
9
39
drug design, carboxylic acid surrogates, lipophilic spacers,
2
between N-heterocyclic compounds and D O. Palladium nano-
1
0,11
and especially explosives, rocket propellants,
and information recovery systems.
photography particles supported on poly(N-vinylpyrrolidone)-grafted silica as
8
a new recyclable catalyst for the Heck cross-coupling reaction
5
1
The conventional method for the synthesis of 5-substituted was also reported by Tamami et al. Also in 2011, Iyer and
-H tetrazole is via a [3+2] cycloaddition of nitriles to sodium co-workers reported the synthesis of palladium nanoparticles
1
1
2,13
14
15
azide,
sources.
trimethylsilylazide, hydroazoic acid or many azide assembled in a polymeric nanosphere as a catalyst for the
1
6–18
38
Various catalysts have been introduced for this Mizoroki–Heck cross-coupling reaction. In 2014, Kaur and
19
20
21
22
23
type of reaction such as BF
TBAF, montmorillonite K-10, BaWO
3
ÁOEt, AlCl
3
,
Cu
2
O, ZnO, clay,
Shah reported the microwave assisted fluoride-free Hiyama
1
4
24
25
26
37
4
,
3
FeCl –SiO
2
,
MoO
3
–
cross-coupling reaction catalyzed by Pd(0)–PVP nanoparticles.
2
7
28
SiO2, and sulfated zirconia. Many of the reported procedures In 2014, Lefferts and co-workers reported PVP-stabilized Pd
for the synthesis of tetrazoles suffer from disadvantages such as nanoparticles as a catalyst for nitrite hydrogenation in the
unsatisfactory yields, the use of toxic solvents and harsh recovery aqueous phase. The recent developments in polymer-supported
of the catalyst. Palladium nanoparticles, mainly used in C–C reactions have led to the propagation of combinatorial chemistry
coupling reactions, are usually formed by metal salt reductions as a method for the rapid and efficient preparation of novel
36
5
2
and are generally stabilized by polymeric molecules, tetraalkyl- functionalized molecules. A fast growing branch of this area
ammonium salts and ionic liquids. Very recently, palladium is polymer-supported catalysts, reagents and scavengers.
5
3
dispersions containing small metal particles have been of Considering the importance of tetrazoles, we report another
increasing scientific interest as a colloidal catalyst for organic novel method for the synthesis of 5-substituted 1-H tetrazoles
2
9–31
C–C bond formation reactions.
In recent years, polymeric by one-pot multicomponent reactions of aryl halides, K [Fe(CN) ]
4 6
and sodium azide in the presence of potassium carbonate
as a base and palladium nanoparticles supported on poly-
Department of Organic Chemistry, Faculty of Chemistry, Yazd University, Yazd,
Iran. E-mail: seyedshahabaddin@gmail.com, darbandi@stu.yazd.ac.ir
(4-vinylpyridine) cross-linked with 2% DVB as a reusable
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/c7nj02222k catalyst (Scheme 1).
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General procedure for the synthesis of 5-substituted
-H tetrazoles
A mixture of halobenzene (1 mmol), K
300 mg, 0.8 mmol), NaN (3 mmol), DMF (2 mL) and the [P
4
1
CO
2 3
(3 mmol), K
4
[Fe(CN)
6
]
(
3
-VP]-
PdNPs (20 mg) was taken in a 5 mL round bottomed flask and
heated at 120 1C. After completion of the reaction (monitored by
TLC), the catalyst was separated from the reaction mixture by an
external magnet. The solvent was removed under reduced pressure
and the residue was dissolved in water (5 mL) and acidified with
HCl, then a white solid was obtained.
Scheme 1 One-pot reaction for the synthesis of 5-substituted 1-H tetra-
4
zoles in the presence of [P -VP]-PdNPs.
Experimental
Materials
Physical and spectroscopic data for selected 5-substituted 1-H
tetrazole derivatives
All chemicals were commercial products. Poly(4-vinylpyridine)
cross-linked with 2% divinyl benzene (DVB), [P4-VP] 2% DVB,
À1
5-Phenyl-1H-tetrazole (2a). FT-IR (KBr); nmax (cm ) = 3467,
was purchased from Fluka Company (Busch, Switzerland) and 3083, 3046, 2981, 2918, 2848, 2768, 2698, 2612, 2577, 2475,
the [P4-VP]-PdNPs were prepared in our laboratory. The reactions 1890, 1614, 1570, 1505, 1434, 1404, 1285, 1258, 1187, 1164,
were monitored by thin layer chromatography (TLC) using silica 1125, 1086, 1054, 1027, 991, 823, 744, 711, 698, 615, 506, 486,
1
gel Poly Gram SIL G/UV 254 plates and all yields refer to the 475, 457, 440, 420. H NMR (500 MHz, DMSO-d
6
): d (ppm) = 7.61
1
3
isolated products. The FT-IR spectra were obtained using a (d, 3H, J = 7 Hz, ArH), 8.10 (m, 2H, J = 7 Hz, ArH) C NMR
Bruker Equinox (model 55, Germany), and the NMR spectra were (125 MHz, DMSO-d
): d (ppm) = 124.9, 127.8, 130.3, 132.1, 156.1.
6
À1
recorded on a Bruker (DRX-500 AVANCE) 500 MHz spectrometer
5-(3-Nitrophenyl)-1H-tetrazole (2c). FT-IR (KBr); nmax (cm ) =
1
13
at 500 MHz for H and at 125 MHz for C NMR in CDCl
3
(using 3101, 3079, 2998, 2909, 2862, 2695, 2608, 2483, 1988, 1931,
tetramethylsilane as the internal reference). Capacity measure- 1796, 1754, 1627, 1588, 1531, 1479, 1409, 1348, 1307, 1278,
ments were carried out with an Analytik Jena nova 300 (model 1251,1176, 1163, 1090, 1059, 1033, 992, 916, 870, 817, 765,
1
3
30, Germany) atomic absorption spectrometer utilizing an air- 738, 726, 709, 677, 655, 551, 523, 445, 424. H NMR (500 MHz,
6
acetylene flame atomizer. The UV-visible absorption spectra were DMSO-d ): d (ppm) = 7.79 (t, 1H, J = 8 Hz, ArH), 8.42 (d, 1H,
recorded on an avantes photodiode array spectrophotometer J = 8 Hz, ArH), 8.59 (d, 1H, J = 8 Hz, ArH), 8.10 (s, 1H, ArH)
1
3
model AvaSpec-2048 equipped with a source model of AvaLight-
DH-S-BAL. TEM images were recorded using a ZEISS 10A conven- 131.9, 133.8, 149.0, 157.7.
tional TEM model Carl Zeiss-EM10C-100 KV (Germany). FESEM
C NMR (125 MHz, DMSO-d
6
): d (ppm) = 122.2, 126.3, 126.9,
À1
2-(1H-Tetrazol-5-yl) phenol (2f). FT-IR (KBr); nmax (cm ) =
images were recorded using an FESEM MIRA 3-XMU with a high- 3096, 1597, 1526, 1472, 1449, 1375, 1344, 1287, 1255, 1233,
energy beam of electrons from the Razi Metallurgical Research 1205, 1160, 1143, 1096, 1059, 987, 911, 829, 762, 743, 716, 695,
1
Center. EDX analysis was performed using ZEISS (model SIGMA 668, 526, 466. H-NMR (500 MHz, DMSO-d
6
): d (ppm) = 7.13
VP-500, Germany) with an Oxford Instrument detector (England). (t, 1H, J = 7.5 Hz, ArH), 7.2 (d, 1H, J = 7.5 Hz, ArH), 7.33 (d, 1H,
XRD patterns were recorded on a PANalytical (model X’Pert PRO) J = 7.5 Hz, ArH), 7.51 (t, 1H, J = 7.5 Hz, ArH), 7.92 (s, 1H, OH)
1
3
X-ray diffractometer. The uncorrected melting points of the
C-NMR (125 MHz, DMSO-d ): d (ppm) = 111.4, 117.2, 120.6,
6
compounds were taken using a Buchi melting point B-540 B.V. 129.9, 133.5, 152.7, 156.2.
CHI apparatus.
Results and discussion
Preparation of the [P -VP]-PdNPs
4
4
The [P -VP]-PdNPs were prepared by the following procedure: in The palladium nanoparticles immobilized on cross-linked
the first step, an aqueous solution of H PdCl was prepared by poly(4-vinylpyridine) were easily prepared in a two-step procedure.
2
4
mixing 106.4 mg of PdCl (0.6 mmol), 6.0 mL of 0.2 M HCl, and In the first step, an aqueous solution of H PdCl was prepared by
2
2
4
2
94 mL of distilled water. In the second step, a mixture of 15 mL mixing PdCl , HCl and distilled water (step 1, Scheme 2). Then
2
of H
methanol and 0.2668 g of [P
00 mL flask for 1 h. In the final step, 15 mL of a 0.015 M solution of this solution shows that no reduction of the Pd species to
of sodium borohydride in methanol was added dropwise into the Pd(0) occurs during the reflux (Fig. 1).
2
PdCl
4
4
solution (prepared in the first step), 21 mL of methanol and [P -VP] 2% DVB were added to the above mixture
4
-VP] 2% DVB was refluxed in a and refluxed for 1 hour. The UV-vis electronic absorption spectrum
2+
1
above mixture immediately after 1 h of refluxing. The abrupt
color change from pale green to dark brown indicates that Pd
In order to study the effect of reflux time on the reduction of
the Pd species, the palladium solution (step 1, Scheme 2) was
2+
2+
was reduced to Pd(0) nanoclusters that were stabilized by [P -VP] refluxed for up to 3 h, but we did not observe any reduction of
4
2
+
2
% DVB and consequently, [P -VP]-PdNPs were formed. Methanol Pd . This experiment shows that refluxing in methanol is not
4
2
+
was removed from the solution by evaporation in a rotary evaporator enough to reduce the Pd species to zero valent palladium.
Heidolph Laborata-4000) and the [P -VP]-PdNPs were washed with Therefore, a sodium borohydride solution was added dropwise
(
4
excess acetone to remove the excess residuals.
to the mixture and an abrupt color change was observed from
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Scheme 2 Structures of [P
4
-VP] 2% DVB and [P
4
-VP]-PdNPs and the simplified structure of the [P
4
-VP]-PdNPs.
nanoclusters on the surface or in the pores of the polymer.
Also, in order to obtain more comparisons, reflux in ethanol
was performed instead of in methanol. We believe that the
2
+
reduction of Pd occurred during the reflux because in the
À1
FT-IR spectrum of the solution we observed a signal at 1655 cm
,
2+
indicating that the ethanol reduced Pd and oxidised itself to
acetaldehyde.
Fig. 1 shows the UV-vis absorption spectra of (a) H
-VP] 2% DVB after refluxing in methanol (for 1 h) in the
presence of H PdCl before the addition of sodium borohydride
2 4
PdCl , (b)
[P
4
2
4
[
(I) in Scheme 2] and (c) the polymer after the addition of
sodium borohydride, [P -VP]-PdNPs (Scheme 2). As Fig. 1 reveals,
two absorption bands were observed at 250 and 325 nm, which
4
2À
were attributed to the [PdCl
4
]
anions (a and b) that disappeared
when sodium borohydride was added to the mixture (c). This
2+
disappearance indicates that the reduction of the Pd precursor
to Pd(0) occurs and the reduced species is stabilized by [P -VP]
% DVB and consequently, the [P -VP]-PdNP catalyst is formed.
4
Fig. 1 UV-visible absorption spectra of (a) H
after refluxing (for 1 h) in H PdCl
borohydride [(I) in Scheme 2] and (c) the [P
2
4 4
PdCl , (b) [P -VP] 2% DVB
2
4
2
4
solution before the addition of sodium
-VP]-PdNPs.
The free pyridine pendant group of [P -VP] 2% DVB can also
4
4
be protonated by adsorbing the liberated HCl as toxic waste.
4 4
The structures of [P -VP] 2% DVB, the [P -VP]-PdNPs and
pale yellow to dark brown immediately upon addition of the simplified structure of the [P
sodium borohydride. This indicates the formation of Pd(0) Scheme 2.
4
-VP]-PdNPs are shown in
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4 4
Fig. 2 FT-IR spectra of [P -VP] 2% DVB (black line) and the [P -VP]-PdNPs (red line).
Vibrational spectroscopy is a suitable tool for the characteri- related to the asymmetric stretching of CQC and CQN, respectively.
2
+
zation of polymer–transition metal ion systems. It is known When a complex between a Pd ion and vinylpyridine forms,
that the CQN and CQC stretching frequencies in vinylpyridine the stretching frequencies of CQC and CQN shift to higher
5
7
polymers shift to higher frequencies upon complexation with frequencies, but the stretching frequencies of [P
4
-VP] 2% DVB
-VP]-PdNPs are the same. It can be concluded that
been studying palladium–nitrogen containing polymer inter- the Pd ions were reduced to Pd(0) and adsorbed on the surface
2
+ 54,55
2+
56
metal ions such as Cu
and Pd ions. Hasik et al. have and the [P
4
2
+
actions and they have found that, in PdCl
2
solutions with a high or in the pores of the polymer.
2
À
À
HCl concentration containing [PdCl
4
]
and [PdCl
3
(H
2
O)] as
Fig. 3 presents the image obtained using transmission electron
the major species, acid–base type reactions (protonation) along microscopy (TEM), which was analysed in order to investigate the
with the formation of the polymer salt as well as the coordination particle size and morphology of the catalyst. The TEM image of
2
+
of Pd ions by the nitrogen atoms of the polyvinylpyrrolidone the [P -VP]-PdNPs shows palladium nanoparticles. Also, the size
4
take place. Similarly, in the present study, the nitrogen atoms in
the pyridine rings in [P -VP] 2% DVB constitute potential sites for
4
interactions between polymer–palladium complexes and also can
be protonated by adsorbing liberated HCl as toxic waste to give
4
the corresponding salt (I) and the [P -VP]-PdNPs, shown in
Scheme 2. The formation of the polymer salt was attributed to
À1
the observation of the N–H stretching frequency at 3415 cm in
the FT-IR spectrum of the [P -VP]-PdNPs (Fig. 2).
4
During our study we found that one hour of reflux is
necessary for good dispersion of the polymer in the mixture
to provide a better interaction between the metal and the
stabilizer to prevent agglomeration after reduction. When the
2 4 4
H PdCl solution was refluxed in the presence of [P -VP] 2%
2
+
DVB, complexation was probably formed between the Pd ions
and the nitrogen atoms of the pyridine pendant group in the
polymer [(I) in Scheme 2]. This process can be used to prevent
the agglomeration of the nanoparticles after the reduction
2
+
4
of Pd to Pd(0). The FT-IR spectra of [P -VP] 2% DVB and the
[
[
P
P
4
4
-VP]-PdNPs are shown in Fig. 2. [P
-VP]-PdNPs show characteristic peaks at 1414 and 1595 cm
4
-VP] 2% DVB and the
À1
4
Fig. 3 TEM image of the [P -VP]-PdNPs.
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Fig. 4 Size distribution of the [P -VP]-PdNPs.
distribution of the palladium nanoparticles is shown in Fig. 4.
As can be seen, most of the nanoparticles are less than 10 nm
in size.
The XRD diffraction pattern of the [P
4
-VP]-PdNPs is shown
in Fig. 5. Three observed peaks in the XRD pattern at 2y = 391,
5
8
4
61 and 691 are attributed to elemental palladium. The
diffraction peaks were broad owing to very small crystallite size.
The morphology of the [P -VP]-PdNPs was studied using
4
FESEM (at a magnification of 100 KX) (Fig. 6). The FESEM
micrograph of [P -VP] 2% DVB after refluxing (for 1 h) in
4
2 4
methanol in the presence of H PdCl before the addition of
sodium borohydride does not show any Pd nanoparticles on the
surface of the polymer [(a) in Fig. 6]. However, when ethanol
was used as the reduction agent, the FESEM micrograph shows
the presence of Pd nanoparticles on the surface of the polymer
2
+
[
(b) in Fig. 6]. This means that Pd is reduced to Pd(0) by
ethanol which is stabilized by the polymer and consequently,
P -VP]-PdNPs are formed. But, when sodium borohydride is
[
4
2
+
added, the reduction of Pd to Pd(0) by sodium borohydride
and the stabilization of Pd(0) by the polymer occur faster and
4
consequently, the [P -VP]-PdNPs that are formed contain more
Pd nanoparticles and they are very small. In this case, the
FESEM micrograph [(c) in Fig. 6] shows a large number of
uniformly distributed Pd nanoparticles that have a very small
size distribution and rough surfaces. After immersing the
Fig. 6 FESEM images of (a) [P
methanol in the presence of H
borohydride; (b) [P -VP] 2% DVB after refluxing (for 1 h) in ethanol in
the presence of H PdCl before the addition of sodium borohydride,
-VP]-PdNPs and (c) [P -VP] 2% DVB after refluxing (for 1 h) in methanol
in the presence of H PdCl
-VP]-PdNPs.
4
-VP] 2% DVB after refluxing (for 1 h) in
2 4
PdCl before the addition of sodium
4
2
4
[
P
4
4
2
4
after the addition of sodium borohydride,
[P
4
4
Fig. 5 XRD diffraction pattern of the [P -VP]-PdNPs.
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valve (Rheodyne, CA, USA) with a loop of 100-lL capacity was
used for the effective control of the amount of sample and the
reproducibility of the measurements. The absorbance time
response was monitored on an x–t-chart recorder (L-250) and
consequently, the capacity of the catalyst was determined to be
0.10 mmol of Pd per gram of the catalyst.
Fig. 8 and 9 show the XPS elemental survey scans of the
[P -VP]-PdNPs. As shown in Fig. 8, the peaks corresponding to
4
palladium, chlorine, carbon and nitrogen are clearly observed.
Fig. 9 displays the palladium binding energy of the palladium
nanoparticles supported on poly(4-vinylpyridine), [P -VP]-PdNPs.
4
This spectrum exhibits two major peaks centered at 335.5 and
Fig. 7 EDX spectrum of the [P
4
-VP]-PdNPs.
39
341 eV, which are assigned to Pd(0) 3d5/2 and 3d3/2, respectively.
However, two peaks were observed at 337 and 342.5 eV, which
correspond to the higher oxidation state of Pd. Also, there are
catalyst in organic solvents for a few days and then repeatedly bands at 338.5 and 343.5 eV that are assigned to a higher
washing with water and organic solvents (ethanol, toluene and oxidation state of palladium, PdO , due to the oxidation of the
acetone), the FESEM images of these nanoparticles before and surface of the nanoparticles during the XPS sample preparation.
after the reaction are basically identical. To optimize the reaction, initially, the reaction of iodobenzene,
The EDX spectrum of the [P -VP]-PdNPs was used to analyze potassium carbonate, K [Fe(CN) ] and sodium azide was selected
x
59
4
4
6
the composition of the samples and is shown in Fig. 7. This as a model reaction. The reaction conditions have dramatic effects
analysis shows a considerable amount of Pd (2.3%). However, on the time and yield of a reaction due to the harsh reaction
the capacity of the [P
an Analytik Jena nova 300 (model 330, Germany).
4
-VP]-PdNPs was determined by AAS using conditions needed for the synthesis of tetrazoles. The model
reaction behavior was studied by adjusting various parameters
After filtration of the mixture in step 2 of the synthesis of the such as the solvent, temperature, base and amount of catalyst
4
[P -VP]-PdNPs, determination of the amount of excess palla- and the results are summarized in Table 1. To investigate the
dium ions in the filtrate was carried out using a Buck Scientific effect of temperature, the reaction was performed at 100, 110, 120
atomic absorption spectrometer (Model 210 VGP, USA) with a and 130 1C. The best result was obtained at 120 1C (Table 1,
hollow cathode lamp using an air-acetylene flame. The single- entries 1–4). We also found that the amount of catalyst had a
line flow-injection system consisting of a peristaltic pump significant effect on the reaction course (Table 1, entries 3 and
(Ismatic, MS-REGLO/8-100, Switzerland) and a rotary injection 5–7). It was found that 20 mg of catalyst gave the best result.
4
Fig. 8 Full XPS spectrum of the [P -VP]-PdNPs.
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Fig. 9 XPS spectrum of Pd 3d of the [P -VP]-PdNPs.
Table 1 Optimization of the reaction conditions for the synthesis of 5-phenyl 1H-tetrazole
a
Entry
Catalyst (mg)
Solvent
Base (mmol)
Temp. (1C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
[P
[P
[P
[P
[P
[P
[P
[P
[P
[P
[P
[P
[P
[P
[P
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
-VP]-PdNPs (20)
-VP]-PdNPs (20)
-VP]-PdNPs (20)
-VP]-PdNPs (20)
-VP]-PdNPs (15)
-VP]-PdNPs (25)
-VP]-PdNPs (30)
-VP]-PdNPs (20)
-VP]-PdNPs (20)
-VP]-PdNPs (20)
-VP]-PdNPs (20)
-VP]-PdNPs (20)
-VP]-PdNPs (20)
-VP]-PdNPs (20)
-VP]-PdNPs (20)
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
EtOH
K
K
K
K
K
K
K
2
2
2
2
2
2
2
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
3
(3)
(3)
(3)
(3)
(3)
(3)
(3)
100
110
120
130
120
120
120
120
120
120
120
120
120
Reflux
Reflux
120
12
8
6
5.8
9
6.4
8
70
91
96
83
82
97
95
84
73
81
80
93
—
60
—
20
Et
NaOH
KOH
3
N (3)
7
12
12
6.5
10
N.R.
36
N.R.
36
10
11
12
13
14
15
16
3 4
Na PO
K
K
K
K
K
2
2
2
2
2
CO
CO
CO
CO
CO
3
3
3
3
3
(2)
(3)
(3)
(3)
(3)
2
H O
DMF
H
2
PdCl
4
(0.68)
a
Yield refers to the pure isolated product.
The effect of base was also investigated by performing the in an oven at 120 1C for 2 h, and reused in the same reaction
model reaction with various bases such as triethylamine, sodium four times (Fig. 10). As Fig. 10 reveals, when the catalyst was
hydroxide, potassium hydroxide and trisodium phosphate reused after four runs in the same reaction and under identical
(Table 1, entries 8–11). The results show that potassium carbonate conditions, the isolated yield of the product only decreased by a
is very effective for this reaction. few percent (7.3%), which indicates the low leaching amount of
The scope and generality of this type of reaction with respect the Pd catalyst into the reaction mixture. No decomposition
to different aryl halides was illustrated using potassium carbonate, of the stabilizer was observed in the reaction and the [P -VP]-
4
K
4
[Fe(CN)
Table 2.
To study the reusability of the [P
6
] and sodium azide and the results are summarized in PdNPs were found to be stable to metal leaching throughout
the reaction.
4
-VP]-PdNPs, the recovered
4
In order to examine the palladium leaching of the [P -VP]-
catalyst from the model reaction was washed with DMF, dried PdNPs, we considered the model reaction conditions without
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Table 2 Synthesis of 5-substituted 1H-tetrazoles catalyzed by the [P -VP]-PdNPs
M.p. (1C)
a
ref.
Entry
Substrate
Product
Time (h)
Yield (%)
Found
Reported
6
0
0
2
2
a
6
96
79
214–215
214–215
212–214
212–214
6
b
9.6
6
1
2
2
c
8.2
90
145–146
145–146
d
13.5
15
80
65
245–248
223–225
Not found
62
2
2
e
221–224
6
2
0
f
6.5
98
72
223–225
241–243
221–224
242–245
6
2
g
12
a
Yield refers to the pure isolated product.
Table 3 Palladium leaching study of [P
4
-VP]-PdNPs
À1
Cycle
Residue palladium (mmol g
)
Pd leaching (%)
1
2
3
4
0.0990
0.99
0.88
0.68
0.1
0.09812
0.09745
0.09735
time, the catalyst was separated and the amount of palladium in
solution was determined for four cycles and summarized in
Table 3 and Fig. 11.
4
Fig. 10 Recovery study of the [P -VP]-PdNPs.
To show the merit of our method and the [P -VP]-PdNPs in
4
comparison to other reported methods, we summarized several
reagents as a new set of conditions. A mixture of K
DMF (2 mL) and [P -VP]-PdNPs (20 mg) was taken in a 5 mL round can be seen, our method has a good yield and shorter time than
bottomed flask and heated at 120 1C for 6 h. After this period of the other reported methods.
2 3
CO (3 mmol), results for the synthesis of 5-phenyl-1H-tetrazole in Table 4. As
4
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9
G. F. Holland and J. N. Pereira, J. Med. Chem., 1967, 10, 149–154.
1
1
1
0 P. Rhonnstad and D. Wensbo, Tetrahedron Lett., 2002, 43,
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4
Fig. 11 Palladium leaching of the [P -VP]-PdNPs.
Table 4 A comparison of our method with other reported methods
ref.
Entry Catalyst
Time (h) Yield (%) Conditions
1
4
1
2
3
4
TBAF
Cu-MCM-41
18
12
12
6
86
90
79
96
Solvent free, 85 1C 18 J.-J. Shie and J.-M. Fang, J. Org. Chem., 2007, 72, 3141–3144.
DMF, 140 1C
6
3
19 A. Kumar, R. Narayanan and H. Shechter, J. Org. Chem.,
6
4
FeCl
3
–SiO
2
DMF, 120 1C
DMF, 120 1C
1
996, 61, 4462–4465.
0 D. P. Matthews, J. E. Green and A. J. Shuker, J. Comb. Chem.,
000, 2, 19–23.
[P -VP]-PdNPs (this study)
4
2
2
Conclusions
21 T. Jin, F. Kitahara, S. Kamijo and Y. Yamamoto, Tetrahedron
Lett., 2008, 49, 2824–2827.
We introduced a novel route for the synthesis of 5-substituted
-H tetrazoles by one-pot multicomponent reactions of aryl
halides, K [Fe(CN) ] and sodium azide in the presence of
2
2
2
2
2
2 M. Lakshmi Kantam, K. Kumar and C. Sridhar, Adv. Synth.
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1
4
6
potassium carbonate as a base and palladium nanoparticles
supported on poly(4-vinylpyridine) 2% DVB as a reusable catalyst.
The catalyst was recycled several times with a mild decrease
in its activity. Also, high product yields and easy recovery are
some advantages of this catalyst.
2
011, 32, 4001.
5 J. He, B. Li, F. Chen, Z. Xu and G. Yin, J. Mol. Catal. A: Chem.,
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6 M. Nasrollahzadeh, Y. Bayat, D. Habibi and S. Moshaee,
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Conflicts of interest
2
2
7 S. M. Sajadi, Chem. Mater. Res., 2012, 2, 12–16.
8 A. Teimouri and A. Najafi Chermahini, Polyhedron, 2011, 30,
There are no conflicts to declare.
2606–2610.
2
9 A. R. Hajipour and Z. Tavangar-Rizi, Appl. Organomet.
Chem., 2017, e3701.
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