Palladium(II) complexes assembled on solid materials: as catalysts for the –NO2 (nitro) to –NH2 (amine) reactions

Article abstract of DOI:10.1007/s00706-020-02679-2

Abstract: Herein, a new series of [PdCl₂(L)₂] complexes where ligands are monodentate amine ligands bearing sulfonamide groups were synthesized, characterized using various techniques such as NMR, FT-IR, UV–Vis, and sc-XRD and invest

Full text of DOI:10.1007/s00706-020-02679-2

Monatshefte für Chemie - Chemical Monthly
https://doi.org/10.1007/s00706-020-02679-2
ORIGINAL PAPER
Palladium(II) complexes assembled on solid materials: as catalysts
for the –NO2 (nitro) to –NH2 (amine) reactions
Serkan Dayan1 · Nilgün Kayacı2 · Namık Özdemir3 · Osman Dayan4 · Nilgun Kalaycioglu Ozpozan2
Received: 1 May 2020 / Accepted: 1 September 2020
© Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract
Herein, a new series of [PdCl2(L)2] complexes where ligands are monodentate amine ligands bearing sulfonamide groups
were synthesized, characterized using various techniques such as NMR, FT-IR, UV–Vis, and sc-XRD and investigated for
their catalytic performance for the reduction of nitroarenes (2-nitroaniline, 4-nitroaniline, and nitrobenzene) in the presence
of NaBH4 in water under heterogeneous conditions. Because the results show that the synthesized complexes are very efcient
catalysts, materials using the selected palladium(II) complex supported by multiwall carbon nanotubes, silicon dioxide, and
iron(II,III) oxide (Fe3O4) were fabricated by a simple-impregnation methodology, characterized by FT-IR, BET, TEM, and
XRD techniques and investigated for their catalytic performance for the same reaction. Thus, a series of supported catalysts
was designed with the aim of both enhancing catalytic activity and reducing noble-metal contents. Our fndings serve to
develop simple catalytic systems and this system can be easily used for catalytic reduction reactions which are the cornerstone
of the production of important chemicals.
Graphic abstract
Keywords Palladium(ii) complexes · Supported catalysts · Nitrobenzene · Hydrogenation
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s00706-020-02679-2) contains
supplementary material, which is available to authorized users.
Introduction
Nitro compounds are widely regarded as contaminants found
in industrial waste and they pose a serious problem for both
living organisms and the ecosystem. Also, amine compounds
formed by the hydrogenation of nitro compounds are used in
many areas as qualifed chemicals; for example, as chelating
agents in pharmaceuticals, polymers, pesticides, explosives,
fbers, dyes, and cosmetics, etc. [1–7]. The most suitable
method to produce aromatic amines which belong to the
group of compounds that are more useful than nitroben-
zene derivatives is an efcient, environmentally friendly,
catalytic system operating in mild conditions. In this case,
many processes have been developed, including adsorption/
* Serkan Dayan
serkandayan@erciyes.edu.tr
1
Drug Application and Research Center, Erciyes University,
38039 Kayseri, Turkey
2
Department of Chemistry, Faculty of Science, Erciyes
University, 38039 Kayseri, Turkey
3
Department of Mathematics and Science Education, Faculty
of Education, Ondokuz Mayıs University, 55139 Samsun,
Turkey
4
Department of Chemistry, Faculty of Science, Çanakkale
Onsekiz Mart University, 17020 Çanakkale, Turkey
Vol.:(0123456789)
1 3

S. Dayan et al.
desorption, photoactive catalysts, electrochemical treatment,
the e-Fenton method, electrocoagulation, hydrogenation, etc.
[8–13]. The development of a catalytic system undergoes
several reaction optimizations steps. Among these, sub-
strate-related screening tests, as well as the development of
suitable catalysts and, studies about increasing the activity
of existing catalysts can be quite valuable. In general, the
catalytic hydrogenation of nitrobenzene derivatives is made
possible by catalysts containing many metals. For example,
palladium, platinum, gold, and silver are the most common
ones, and their catalytic performances are excellent. How-
ever, the high price of noble metals used during the cata-
lytic process is the main disadvantage of these conventional
noble-metal catalysts and limit their large-scale applications.
The catalysts including other metals may also lose catalytic
performance. Therefore, the idea of adding materials that
can add a synergistic efect to catalysts consisting of noble
metals has also been investigated by researchers. Of course,
many parameters come to the fore in these catalytic systems;
for example, solvent, hydrogen source, amount of substrate,
amount of catalyst, etc. [14–17].
materials containing diferent characteristic properties are
combined with a simple method. These new materials can
also show synergistic efects in diferent application areas.
Because of all these reasons, there is increasing attention
in the literature about the preparation of simple, novel, efec-
tive, and reusable catalysts for catalytic reduction of nitro
compounds in aqueous media. For these purposes, herein,
we report a new series of synthesized Pd(II) complexes
C1–C6 bearing monodentate N-(2-aminophenyl)benzene-
sulfonamides ligands which can easily interact with sup-
porting materials via secondary chemical bonding and tested
as catalysts for the reduction of nitrobenzenes. Herein the
sulfonamides ligands are easily synthesizable compounds,
and the sulfonamide compounds support the immobiliza-
tion methodology with the functional groups. In addition,
sulfonamide derivative ligands and their complexes are often
used in catalytic reactions [48–50].
Then, to reduce noble-metal (Pd) content, the MWCNT,
SiO2, and Fe3O4-supported C4 materials M1–M3 were also
prepared and screened for their efciency as catalysts in the
reduction of nitroarenes. The catalytic results for the sup-
ported materials clearly show that although the palladium
content is reduced, the catalytic efciencies are higher than
for the complexes.
Also, avoiding the use of organic solvents and the
improvement of suitable processes for hydrogenation of
nitrobenzenes in aqueous media under mild conditions are
still necessary. Likewise, some quite remarkable studies have
been carried out with compounds bearing palladium for the
hydrogenation of nitro-compounds [18–27].
Results and discussion
Complexes or materials containing palladium are also
widely used during the application of reduction processes
[28], C–C or C–N bond formation reactions [29, 30], oxida-
tion works [31, 32], hydrogenation studies [33], anti-cancer
drugs [34, 35], as biosensors [36], in solar cells [37], etc.
Especially, palladium complexes or materials have been the
focus of intense research in catalyst chemistry as a homo-
geneous/heterogeneous catalyst [38–40]. From most of the
research about palladium complexes in the literature, it
is seen that at least bidentate ligands were used, because
electronic and steric parameters are one of the most impor-
tant cases in catalysis chemistry. The research about Pd(II)
complexes with monodentate ligands is rare. On the other
hand, the preparation conditions for Pd(II) complexes bear-
ing N-donor ligands generally does not require a specifc
atmosphere such as argon or nitrogen gas. Recently, palla-
dium-based catalysts, in particular, those supported by car-
bon [41], zeolite [42], silica [43], alumina [44], and poly-
mer [45], have been fabricated by diferent methods (such as
deposition–precipitation, impregnation and co-precipitation,
immobilization, etc.) and used as catalysts in many organic
transformations (C–C bond formation, hydrogenation, oxi-
dation, etc.).
The details of analytical methods
The synthesis of monoamine aromatic sulfonamide ligands
L1–L6 was performed in a simple one-step reaction, start-
ing from commercially available arylsulfonyl chlorides and
1,2-diaminobenzene. Their amine-coordinated Pd(II) com-
plexes C1–C6 were isolated as yellow solids with high yields
and were stable in the solid-state and solution. The structures
of Pd(II) complexes C1–C6 were elucidated by FT-IR, NMR,
and UV–Vis spectrophotometer.
1
In H NMR spectra recorded from a Bruker 400 NMR
spectrometer at 297 K, the methoxy and 2,4,6-trimethyl
protons for C2 and C4 were assigned at 3.81 ppm as singlet
for –OCH3 group, at 2.24 ppm as singlet for -p-CH3 and
2.38 ppm as singlet for o-CH3 for 2,4,6-trimethyl protons,
respectively. Also, the aromatic ring protons as multiplet
peaks were located at 6.72–7.99 ppm for C1, 6.49–7.60 ppm
for C2, 6.46–8.37 ppm for C3, 6.45–7.09 ppm for C4,
6.75–8.02 ppm for C5, and 6.75–7.95 ppm for C6. In the 13
C
NMR spectra for the N-coordinate Pd(II) complexes C1–C6,
the peaks belonging in (c) position to the -p-OCH3, -p-CH3
carbons were located at 55.6 ppm and 22.6 ppm, respec-
tively. Additionally, the carbons belonging to aromatic rings
were obtained at 117.1–147.2 ppm for C1, 113.8–162.3 ppm
for C2, 124.2–149.7 ppm for C3, 116.7–147.3 ppm for C4,
The studies of combining molecular and material struc-
tures with immobilization methods have been frequently
seen in recent years [26, 37, 46–48]. In this way, the
1 3

Palladium(II) complexes assembled on solid materials: as catalysts for the –NO2 (nitro) to…
115.7–147.0 ppm for C5, and 121.0–146.9 ppm for C6. All
NMR chemical shifts and integrations of signals were con-
sistent with the proposed structures (Fig. S1–8). FT-IR was
measured with a Perkin-Elmer Spectrum 400 FTIR system.
For the palladium(II) complexes C1–C6, the –N–H stretch-
ing frequency peaks belonging to the sulfonamide groups
appeared at 3098 cm−1, 3131 cm−1, 3147 cm−1, 3153 cm−1,
3109 cm−1, and 3152 cm−1 and -NH2 stretching frequency
peaks were observed at 3252–3148 cm−1, 3279–3165 cm−1,
3300–3216 cm−1, 3269–3185 cm−1, 3221–3153 cm−1, and
3247–3185 cm−1, respectively.
complexes [54, 55]. The N−Pd−Cl cis angles
[89.66(4)–90.34(4)°] are very close to the optimal angle
of 90°, while the Cl−Pd−Cl and N−Pd−N trans angles
are exactly equal to 180°. The bond distances for Pd−N
[2.0623(14) Å] and Pd−Cl [2.2850(4) Å] are comparable
with those published in the literature for related complexes
of general formula PdCl2L2, where L denotes the amino-
ligands [54–61]. The square plane makes dihedral angles of
86.22(5)° and 65.53(6)° with the planes of the C1–C6 and
C7–C12 benzene rings, while the dihedral angle between
the two benzene rings is 64.30(7)°. In the benzenesulfona-
mide ligand, the N1−C7 and N2−C12 bond distances of
1.414(2) and 1.442(2) Å agree well with the single bond
value, and the S1−O1 and S1−O2 distances of 1.4351(19)
and 1.4213(19) Å are consistent with S=O double bond-
ing. Atom S1 has a distorted tetrahedral confguration which
is evident from the angles changing from 105.21(10)° to
120.49(13)°.
The UV–Vis spectra of Pd(II) complexes C1–C6 in dime-
thyl sulfoxide (DMSO) (1 × 10–4 mol dm−3) solvent were
recorded within the 260–560 nm range, and a representative
spectrum is shown in Fig. S9. In the spectra of the com-
plexes, there are two main transition bands excluding C6
complex. The frst bands (280–301 nm) are attributed to
the π→π* transition and the second bands in the range of
326–335 nm are attributed to the n → π* transition of the
Pd(II) complexes.
In the molecular structure of the complex, there are two
intramolecular interactions of N−H···Cl type (Fig. 1), form-
ing seven-membered rings with graph-set descriptor S(7)
[62]. The 2D supramolecular structure of the complex can
readily be analyzed in terms of two one-dimensional sub-
structures. In the frst substructure, amino atom N2 in the
molecule at (x, y, z) acts as a hydrogen-bond donor, via atom
H2B, to sulfonyl atom O1 in the molecule at (x − 1, y, z),
Description of the crystal structure of C1
X-ray data were collected with an STOE IPDS II difractom-
eter at room temperature using graphite-monochromated Mo
Kα radiation by applying the ω-scan method. Data collection
and cell refnement were carried out using X-AREA, while
data reduction was applied using X-RED32 (X-AREA Ver-
sion 1.18 and X-RED32 Version 1.04, Stoe & Cie, Darm-
stadt, Germany, 2002). The structure was solved by direct
methods using SHELXS-2013 and refned with full-matrix
least-squares calculations on F2 using SHELXL-2014 [51,
52] implemented in WinGX [53] program suit. H atoms
bonded to C atoms were assigned C–H distances of 0.93 Å,
with Uiso(H) = 1.2Ueq(C). The nitrogen-bound hydrogens
were in a diference Fourier map and refned freely. Crys-
tal data, data collection and structure refnement details are
summarized in Table 1, while relevant geometric parameters
are collected in Table 2. PLATON was used for the structure
analysis. Molecular graphics were generated using ORTEP-3
[53].
thereby forming an R2(18) ring. The propagation of this
2
hydrogen-bonding motif generates a chain of rings running
parallel to the [100] direction (Fig. 2a). In the second sub-
structure, benzene carbon atom C10 in the molecule at (x, y,
z) acts as a hydrogen-bond donor to chlorido ligand Cl1 in
the molecule at (− x − 1, − y + 1, − z + 1), so forming an
R2(14) ring. Propagation of this hydrogen-bonding motif
2
generates another chain of rings running parallel to the
[
]
−
1
0 direction (Fig. 2b). Full details of the hydrogen-bond-
1
ing geometry are given in Table 3.
Materials’ characterization
The infrared spectrum of multiwall carbon nanotubes
(MWCNTs)–, SiO2–, and Fe3O4– supported M1–M3 materi-
als and C4 are shown in Fig. 3. For M1 (Fig. 3a), the carbonyl
(C=O), the C=C stretching, and the –OH bending absorption
bands were associated with ≈ 1800 and 1100–1300 cm−1,
≈ 1500–1600 cm−1 and ≈ 3500–3800 cm−1 and were
compatible with bare MWCNTs-COOH, respectively. For
M2 (Fig. 3b), the bare SiO2 has two major peaks at 794
and 1047 cm−1 which are attributed to Si–O bending and
Si–O–Si asymmetric stretching, respectively and the related
major peaks were also observed in the FT-IR spectra of M2
material. For M3, the absorption band at 529 cm−1 belongs to
the Fe–O vibration (magnetic phase). Hereby, the formation
The molecular structure of complex C1 was confrmed
using the X-ray crystallography. The compound crystallizes
in the triclinic space group P− with a single molecule in the
1
unit cell and is shown in Fig. 1.
The asymmetric unit of the compound contains one-half
of the molecule, because the palladium atom occupies a
special position in the crystallographic center of inversion.
The Pd(II) cation is coordinated to two chlorido ligands
and the nitrogen atoms of two N-(2-aminophenyl)-benze-
nesulfonamide ligands, in an almost perfect square-planar
geometry. The molecule adopts the trans disposition, which
is commonly observed for bis(amino)-dihalopalladium(II)
1 3

S. Dayan et al.
Table 1 Crystal data and
structure refnement parameters
for C1
CCDC depository
Color/shape
1,483,076
Dark orange/prism
[PdCl2(C12H12N2O2S)2]
673.89
Chemical formula
Formula weight
Temperature/K
Wavelength/Å
Crystal system
Space group
296
0.71073 Mo Kα
Triclinic
P
− (No. 2)
1
Unit cell parameters
a, b, c/Å
7.2484(4), 8.2098(5), 12.3917(8)
73.068(5), 82.842(5), 72.361(5)
671.74(7)
α, β, γ/°
Volume/Å3
Z
1
Dcalc/g cm−3
1.666
1.084
μ/mm−1
Absorption correction
Tmin, Tmax
F000
Integration
0.5652, 0.7390
340
0.56×0.49×0.33
STOE IPDS II/ω scan
−9≤h≤9,−11≤k≤11,−16≤l≤16
2.702≤θ≤28.639
10,635
Crystal size/mm3
Difractometer/measurement method
Index ranges
θ range for data collection/°
Refections collected
Independent/observed refections
Rint
Refnement method
Data/restraints/parameters
Goodness-of-ft on F2
Final R indices [I>2σ(I)]
R indices (all data)
Δρmax, Δρmin /e Å−3
3431/3282
0.102
Full-matrix least-squares on F2
3431/0/181
1.061
R1 =0.0228, wR2 =0.0597
R1 =0.0307, wR2 =0.0604
0.473, − 0.311
Table 2 Selected geometric parameters for C1
of peaks belonging to the C4 complex does not appear in
the initial curve of the support materials (MWCNT, SiO2,
Fe3O4).
Bond lengths/Å
Pd1–Cl1
Pd1–N2
S1–O1
S1–O2
2.2850(4)
2.0623(14)
1.4351(19)
1.4213(19)
S1–N1
S1–C6
N1–C7
N2–C12
1.6286(17)
1.7592(19)
1.414(2)
The bare MWCNT, SiO2, and Fe3O4 support appear as
(a), (b), and (c) in Fig. 3, respectively, and the formation of
peaks belonging to Pd(II) complex C4 is seen in Fig. 3. In
brief, it was found that the Pd(II) complex C4 is supported
by MWCNT, SiO2, and Fe3O4 after the use of the impregna-
tion method.
1.442(2)
Bond angles/°
Cl1–Pd1–Cl1i
N2–Pd1–N2i
N2–Pd1–Cl1
N2–Pd1–Cl1i
O2–S1–O1
O2–S1–N1
180.0
180.0
90.34(4)
89.66(4)
120.49(13)
108.01(11)
O1–S1–N1
O2–S1–C6
O1–S1–C6
N1–S1–C6
C7–N1–S1
105.21(10)
107.96(11)
107.35(10)
107.16(8)
Transmission electron microscopy (TEM) images were
taken by the JEOL TEM-1400-EDX model device. Fig-
ure 4a–c and S10 show a representative TEM image of the
prepared M1–M3 materials, respectively. When investigating
the TEM image, it can be concluded that the characteristic
shapes belonging to MWCNT, SiO2, and Fe3O4 were pre-
served after impregnation. Also, the EDX images are given
in Fig. S11 as supporting information.
122.29(13)
Symmetry code: i −x, −y, −z+1
The Barrett–Joyner–Halenda (BJH) pore volume
(cm3 g−1), Brunauer–Emmett–Teller (BET) surface area
1 3

Palladium(II) complexes assembled on solid materials: as catalysts for the –NO2 (nitro) to…
(m2 g−1), and BJH pore width (Å) were calculated by the N2
adsorption–desorption (BET) isotherms for M1–M3 using a
Micromeritics Gemini VII Surface Area and Porosity sys-
tem. The results indicate that the BET isotherms of M1–M3
materials were identified as typical type IV isotherms
according to IUPAC (Fig. 5). The BET surface areas (SBET
)
of M1–M3 were found as 125.59 m2 g−1, 2.989 m2 g−1, and
54.815 m2 g−1, respectively. The SBET surface area of M1 is
high compared to M2 and M3 (Table 4). Table 4 shows the
corresponding BJH pore widths of 531.375 Å, 484.197 Å,
and 152.692 Å, respectively. Also, all the N2 adsorption–des-
orption (BET) isotherms data is give in the supporting infor-
mation as Table S1. As expected, the surface area of the
carbon nanotube structure (MWCNTs) was observed higher
than other solid support materials. It is well known that the
surface area is an important parameter in catalyst systems
and has catalytic efciency increasing efect. Likewise, the
surface area of the Fe3O4 solid support is well and it is pre-
dicted that it contributes positively to the catalytic yield.
X-ray powder difraction (XRD) analyses were measured
with a Bruker AXS D8 Advance Model difractometer which
Fig. 1 Molecule of C1 showing the atom-labeling scheme. Displace-
ment ellipsoids are drawn at the 30% probability level. Hydrogen
bonds are shown as dashed lines. For the sake of clarity, only hydro-
gen atoms involved in hydrogen bonding have been included
Fig. 2 a Part of the crystal structure of C1 showing the formation of a
For the sake of clarity, H atoms not involved in the motif shown have
been omitted
chain of R2(18) rings along [100]. b Part of the crystal structure of
[
]
−
2
C , showing the formation of a chain of R2(14) rings along 1 0 .
1
1
2
1 3

S. Dayan et al.
Table 3 Hydrogen-bonding geometry for C1
D–H···A
D–H/Å
H···A/Å
D···A/Å
D–H···A/°
N1–H1A···Cl1i
N2–H2B···O1ii
C10–H10···Cl1iii
0.80(2)
0.83(2)
0.93
2.49(2)
2.14(2)
2.73
3.2490(18)
2.966(2)
3.626(2)
159(2)
175(2)
161
Symmetry codes: i −x,−y,−z+1; iix−1, y, z; iii −x−1,−y+1,−z+1
Fig. 4 Representative TEM images of M1 (a), M2 (b), and M3 (c)
was run at 20–60 kV and 6–80 mA, 2Ө=10°–90°, and a step
of 0.002° using CuKα X-ray. Powder XRD studies were per-
formed to analyze the formation of patterns. The XRD spec-
tra demonstrated that all the Pd(II)-impregnated MWCNT,
Fig. 3 FT-IR spectra prepared materials
1 3

Palladium(II) complexes assembled on solid materials: as catalysts for the –NO2 (nitro) to…
Table 4 Adsorption–desorption characteristics of M1–M3 materials
Materials
BET surface
area/m2 g−1
BJH pore vol-
ume/cm3 g−1
BJH pore width/Å
M1
M2
M3
125.590
2.989
54.815
1.588485
0.015653
0.136632
531.375
484.197
152.692
Fig. 6 XRD patterns of M1 (a), M2 (b), and M3 (c)
material (MWCNT, SiO2, Fe3O4). The structure confrms
the efectiveness of the simple wet impregnation method
for the synthesis MWCNT-, SiO2-, and Fe3O4-supported C4
materials M1–M3.
Catalytic studies
We investigated the catalytic activity of C1–C6 complexes
using the hydrogenation of 2-nitroaniline (2-NA) to o-phe-
nylenediamine in the presence of BH4− ion in the water at
ambient temperature as a precursor reaction. The functional
groups of the synthesized complexes are designed to com-
pare steric, electron-donating and electron-withdrawing
groups.
The reaction was easily followed spectrophotometrically
due to the reactant (2-NA) and product having diferent
absorption bands such as λmax = 410 nm [63, 64] (–NO2
group of 2-NA). Initially, the 2-NA (2.5×10–4 mol dm−3)
mixture has a yellow color which is the color of the adsorp-
tion band belonging to the nitro group, this color gradually
vanished because of the formation of the o-phenylenedi-
amine product. Briefy, the absorption peak at 410 nm gradu-
ally decreased in intensity during this reaction. The percent
conversions were monitored at diferent times between 30
and 90 s. It is well known that when the times were increased
from minimum time to maximum time. The catalytic ef-
ciencies of C1–C6 found as 93.2%, 94.4%, 93.8%, 94.9%,
Fig. 5 BET isotherms of M1 (a), M2 (b), and M3 (c)
SiO2, and Fe3O4 materials produced characteristic peaks
similar to those of MWCNT [JCDPS card no: 75–1621,
26.29° (002), 43.12° (200), SiO2 and Fe3O4 [JCDPS card
no: 19-0629, 30.1° (220), 35.5° (311), 43.1° (400), 57.0°
(511), 62.9° (440)] in Fig. 6. Likewise, all the XRD data
have new peaks, in addition to the data for pure supporting
1 3

S. Dayan et al.
1.2
1
Fig. 7 Time-dependent UV–
Vis absorption spectra of the
2-nitroaniline reduced by
NaBH4 catalyzed by the C1–C6
complexes
C1 as catalyst
1.2
1
C2 as catalyst
2-nitroaniline
2-nitroaniline
30 s
60 s
90 s
30 s
60 s
90 s
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
200
300
400
500
600
700
200
300
400
500
600
700
Wavelength / nm
Wavelength / nm
C3 as catalyst
1.2
1
C4 as catalyst
1.2
1
2-nitroaniline
2-nitroaniline
30 s
60 s
90 s
30 s
60 s
90 s
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
200
300
400
500
600
700
200
300
400
500
600
700
Wavelength / nm
Wavelength / nm
1.2
1.2
C5 as catalyst
C6 as catalyst
2-nitroaniline
2-nitroaniline
1
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
30 s
60 s
90 s
30 s
60 s
90 s
200
300
400
500
600
700
200
300
400
500
600
700
Wavelength / nm
Wavelength / nm
97.0%, and 94.1% at the end of 90 s, respectively (Fig. 7). It
is seen that all catalytic reactions were almost complete in
90 s, and so the synthesized Pd(II) complexes C1–C6 were
showed excellent catalytic activity under these conditions.
A diference in the functional groups could not be deter-
mined in all the catalytic activity results obtained. However,
the positive contribution of the -F group, an electron-with-
drawing group, was detected. Also, the C4 complex, which
shows an average activity in complex selection, was chosen
as the representative of the synthesis group. In recent years,
the catalytic activity of hybrid materials has been remark-
able in the literature [65–70]. In light of this information,
we envisaged that the catalytic activity of the tested pal-
ladium complexes C1–C6 can be combined with a diferent
type of solid support material such as MWCNTs, SiO2, and
Fe3O4 and the performance of these new hybrid materi-
als will be high for the reduction of nitroarenes. Thus, we
selected one of the efective palladium complexes (bis[N-
(2-aminophenyl)-2,4,6-trimethylbenzenesulfonamide]-di-
chloro-palladium(II), C4) as randomly (not having the best
activity) for the impregnation method into MWCNTs, SiO2,
and Fe3O4 materials. Herein, the solid support materials
selected were selected from diferent types and their poten-
tials were compared, and the C4 was chosen for the prepa-
ration of solid-supported catalysts, because the supporting
material generally increases the efciency of catalysts syner-
gistically and we also want to clearly demonstrate this efect
in this paper. The materials were chosen SiO2 as the most
common material, Fe3O4 as a metal oxide with magnetic
properties, and MWCNTs as a carbon based and commonly
used material.
To demonstrate the success of this methodology, the cata-
lytic performances of bare solid support materials (MWC-
NTs, SiO2, and Fe3O4) were tested as catalysts under the
same conditions which were followed by UV–Vis spectro-
photometer in the presence of NaBH4 in water with 2-NA
1 3

Palladium(II) complexes assembled on solid materials: as catalysts for the –NO2 (nitro) to…
Fig. 8 Time-dependent
MWCNT as catalyst
1.2
1
1.2
1
SiO2 as catalyst
UV–Vis absorption spectra
of the 2-nitroaniline reduced
by NaBH4 catalyzed by the
MWCNT, SiO2, and Fe3O4 sup-
ported materials
2-nitroaniline
5 min.
10 min.
2-nitroaniline
5 min.
10 min.
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
15 min.
15 min.
200
300
400
500
600
700
200
300
400
500
600
700
Wavelength / nm
Wavelength / nm
1.2
1
Fe3O4 as catalyst
2-nitroaniline
5 min.
0.8
0.6
0.4
0.2
0
10 min.
15 min.
200
300
400
500
600
700
Wavelength / nm
(Fig. 8). When the time-dependent spectrophotometer meas-
urement results are evaluated, the catalytic performances
were 50.2% (5 min), 51.4% (10 min), and 58.2% (15 min)
for MWCNTs, 37.1% (5 min), 41.3% (10 min), and 54.7%
(15 min) for SiO2, 6.7% (5 min), 16.1% (10 min), and 20.9%
(15 min) for Fe3O4. In light of these results, it can be said
clearly that the catalytic conversion of bare Fe3O4 material is
lower than other selected solid support materials. However,
as known, catalysts bearing Fe3O4 can be recovered easily
due to the magnetic properties of Fe3O4 (via a simple mag-
net). Therefore, eforts to improve the catalytic performance
power belonging to Fe3O4 material can be quite valuable.
Based on the above results, we tested the catalytic activ-
ity of M1–M3 nanomaterials for the catalytic hydrogenation
Fig. 9 Time-dependent UV–
Vis absorption spectra of the
2-nitroaniline reduced by
[PdCl2(L4)2]@SiO2 as catalyst
2-nitroaniline
[PdCl2(L4)2]@MWCNT as catalyst
2-nitroaniline
1.2
1
1.2
1
30 s
60 s
90 s
30 s
60 s
90 s
NaBH4 catalyzed by the M1–M3
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
200
300
400
500
600
700
200
300
400
500
600
700
Wavelength / nm
Wavelength / nm
[PdCl2(L4)2]@Fe3O4 as catalyst
2-nitroaniline
1.2
1
30 s
60 s
90 s
0.8
0.6
0.4
0.2
0
200
300
400
500
600
700
Wavelength / nm
1 3

S. Dayan et al.
of 2-nitroaniline (2-NA). As shown in Fig. 9, the specifc
absorption band belonging to 2-nitroaniline is observed
410 nm and when M1–M3 nanomaterials were added to the
reaction media, the corresponding peak intensity showed
a quick decline. The catalytic performances of M1–M3
nanomaterials for the hydrogenation of 2-NA were 96.8%
(30 s), 96.9% (60 s), 97.7% (90 s); 94.5% (30 s), 96.7%
(60 s), 97.6% (90 s); and 93.7% (30 s), 96.0% (60 s), 96.1%
(90 s), respectively. A signifcant improvement in the
catalytic performance of the nanomaterials M1–M3 was
observed compared to bare materials. Interestingly, the
best-enhanced catalyst was recorded as M3 compared to
bare Fe3O4. These results are compatible with the litera-
ture [71]. However, the success of hybrid materials formed
by molecular metal complexes is limited [63]. When the
catalytic performances of C4, the bare solid support mate-
rials and the hybrid nanomaterials M1–M3 are examined
in detail, it is evident that the hybrid nanomaterials have
higher catalytic conversions than both the palladium(II)
complex C4 and the solid support materials (MWCNTs,
SiO2, Fe3O4). This situation may be related to the syner-
gistic efect.
97.8% (60 s), 98.1% (90 s) for M1, 96.0% (30 s), 97.1%
(60 s), 97.5% (90 s) for M2, and 96.0% (30 s), 96.8%
(60 s), 97.4% (90 s) for M3 (Fig. 10).
Moreover, M1–M3 nanomaterials were used as catalysts
for the hydrogenation of nitrobenzene under the optimized
conditions. The band disappeared after hydrogenation at
265 nm from the –NO2 group. The performance of cata-
lysts (M1–M3) were 89.7% (30 s), 90.3% (60 s), 93.3%
(90 s) for M1, 89.2% (30 s), 90.4% (60 s), 90.6% (90 s)
for M2, and 90.3% (30 s), 90.5% (60 s), 91.3% (90 s) for
M3 (Fig. 11).
Furthermore, the magnetic catalyst M3 could be recov-
ered from the reaction mixture by fltration with the help
of a magnet and used again in the next cycle. According to
Fig. 12, the recovered M3 magnetic catalyst exhibited good
catalytic efciency for at least fve cycles in the hydro-
genation of 2-NA with the conversion of 96.1–83.5% dur-
ing the 90 s.
Herein, the kinetic equation for the reduction
of nitrobenzenes to anilines can be represented as
ln(Ct/C0) = − kt, where t is time for the reaction and, k
is the apparent frst‐order rate constant (s−1) in Table 5.
Also, the k′ = k/M parameter (M: the amount of the cata-
lyst) is introduced for quantitative comparison and the
parameter is defned as the ratio of the rate constant k
to the weight of the catalyst added [72]. In Table 5, the
catalytic activity rate constant parameters were compared
for the palladium(II) complexes C1–C6 and the nanoma-
terials M1–M3 and summarized. The table showed that
the parameters k and k’ for the nanomaterials M1–M3 are
We also studied the hydrogenation of 4-nitroaniline
(4-NA) using M1–M3 under the same conditions. The
characteristic absorption band of the pure 4-nitroaniline
arises at 380 nm from the –NO2 group. After the addition
of catalysts M1–M3, the characteristic band of 4-NA at
380 nm gradually decreased in intensity and the color of
the solution gradually vanished as the reaction proceeded.
The catalytic activities were found to be 96.7% (30 s),
Fig. 10 Time-dependent
[PdCl2(L4)2]@MWCNT as catalyst
[PdCl2(L4)2]@SiO2 as catalyst
4-nitroaniline
4
3
2
1
0
4
3
2
1
0
UV–Vis absorption spectra of
the 4-nitroaniline reduced by
NaBH4 catalyzed by the M1–M3
4-nitroaniline
30 s
60 s
90 s
30 s
60 s
90 s
200
300
400
500
600
700
200
300
400
500
600
700
Wavelength / nm
Wavelength / nm
[PdCl2(L4)2]@Fe3O4 as catalyst
4-nitroaniline
4
3
2
1
0
30 s
60 s
90 s
200
400
600
Wavelength / nm
1 3

Palladium(II) complexes assembled on solid materials: as catalysts for the –NO2 (nitro) to…
Fig. 11 Time-dependent UV–
Vis absorption spectra of the
nitrobenzene reduced by NaBH4
catalyzed by the M1–M3
[PdCl2(L4)2]@MWCNTs as catalyst
nitrobenzene
[PdCl2(L4)2]@SiO2 as catalyst
nitrobenzene
3
2
1
0
3
2
1
0
30 s
60 s
90 s
30 s
60 s
90 s
200
300
400
500
600
700
200
400
600
Wavelength / nm
Wavelength / nm
[PdCl2(L4)2]@Fe3O4 as catalyst
nitrobenzene
3
30 s
60 s
90 s
2
1
0
200
400
600
Wavelength / nm
Fig. 12 Reusability of M3
magnetic catalyst for the hydro-
genation of 2-NA with NaBH4
(at 90 s intervals). % Conver-
sion=[(Ao − At)/Ao] × 100, Ao
is the absorbance at time t=0
higher than the corresponding palladium(II) complexes
and this also supports the synergistic efect during the
reduction reaction of nitrobenzenes.
intermediates [25, 76]. The catalyzed process/cycle began
immediately by adding M1–M3 nanomaterials to the reaction
mixture. The nitrobenzenes and ions belonging to NaBH4
are difused from the reaction solution to the active surface
of M1–M3 nanomaterials and especially, around the Pd(II)
ion.
As a general concept, the catalytic activity in any reac-
tion depends on both the composition-type of catalyst and
substrate which is detailed in the literature. A catalyzed
process is controlled by diferent parameters in the cata-
lytic system such as particle size (micro or nano), recovery,
active surface area, reusability, surface morphology, active
functional groups, the redox and electron charge potential
of metal center [73]. Materials containing metal ion can
appear to be especially efcient catalysts for the reduction
of nitroarene or nitrobenzene compounds to aminobenzenes
[15, 17, 74, 75]. The hydrogenation or reduction of nitroben-
zenes has diferent mechanisms or pathways and potential
Hence, the metal center (palladium(II)) and other regions
(ligand and solid material) act as a tool for electron trans-
fer from hydride ions to the nitro group which achieves
the formation of the amino group. With this route, the H+
ions are exposed in the reaction medium for the reduction
of nitrobenzenes to aminobenzenes and as the cycle rate
increases, the reaction rate constant also rises. With this
operation, it is clear that the catalytic cycle was rapid with
the M1–M3 nanomaterials compared to bare MWCNTs,
1 3

S. Dayan et al.
Table 5 Catalytic activity rate
Catalysts
Substrate
k/s−1a
k/M/s−1 g−1 b
constant of catalysts
30 s
60 s
90 s
30 s
60 s
90 s
(10–2)
(10–2)
(10–2)
(10+1
)
(10+1
)
(10+1
)
C1
2-NA
2-NA
2-NA
2-NA
2-NA
2-NA
2-NA
2-NA
2-NA
4-NA
4-NA
4-NA
Nitrobenzene
Nitrobenzene
Nitrobenzene
7.24
9.10
6.16
6.91
9.63
7.69
11.60
9.68
9.19
11.40
10.80
10.70
7.56
7.42
7.77
3.76
4.56
3.63
3.59
5.55
4.27
5.79
5.69
5.37
6.36
5.94
5.72
3.89
3.91
3.91
2.98
3.20
3.10
3.31
3.91
3.15
4.17
4.15
3.59
4.40
4.11
4.04
3.00
2.63
2.72
3.62
4.55
3.08
3.46
4.82
3.85
5.80
4.84
4.60
5.70
5.40
5.35
3.78
3.71
3.89
1.88
2.28
1.82
1.80
2.78
2.14
2.90
2.85
2.69
3.18
2.97
2.86
1.95
1.96
1.96
1.49
1.60
1.55
1.66
1.96
1.58
2.09
2.08
1.80
2.20
2.06
2.02
1.50
1.32
1.36
C2
C3
C4
C5
C6
M1
M2
M3
M1
M2
M3
M1
M2
M3
aThe reaction rate constant
bThe reaction rate constant per total weight of tested catalyst (2 mg)
SiO2, Fe3O4 materials. There was also a diference in cata-
lytic activity according to the type of substrate. In this reac-
tion medium and conditions, we would recommend that
these types of hybrid materials (M1–M3) are preferable for
the hydrogenation of nitro groups (nitrobenzenes, etc.)
Experimental
All chemicals (reagents and solvents) were purchased from
chemical companies (Sigma-Aldrich, Merck, and Alfa
Aesar) and used as received unless otherwise stated. Ligands
L1–L3 [32] and L4 [77] were synthesized according to the
literature.
The 400 MHz 1H NMR and 100.56 MHz 13C NMR spec-
tra were recorded at ambient temperature on a Bruker 400
NMR spectrometer. A Perkin-Elmer Spectrum 400 FT-IR
system with universal ATR sampling accessory was used
to obtain the FT-IR spectra. For melting point determina-
tion, an Electrothermal 9100 instrument was used with open
capillary tubes. X-ray difraction (Bruker AXS D8 Advance
Model) was used to confrm for immobilization methodol-
ogy. The SEM–EDX analysis employed a Leo 440 Computer
Controlled Digital for surface morphological characteriza-
tion. The UV–Vis spectrophotometer (Perkin-Elmer Lambda
25 UV/Vis spectrophotometers) measurements were used for
monitoring the reduction of nitrophenols and dyes.
Conclusion
Herein, the fabrication of a series of simple N-coordinate
palladium(II) complexes C1–C6 and [PdCl2(L4)2]@MWC-
NTs (M1), [PdCl2(L4)2]@SiO2 (M2), and [PdCl2(L4)2]@
Fe3O4 (M3) nanomaterials and their use as catalysts for
the hydrogenation of nitrobenzenes to aminobenzenes
was defined. Using a basic impregnation methodology,
palladium(II) complexes were immobilized on the surface of
MWCNTs, SiO2, and Fe3O4 and detailed structural analysis
of the complex and materials was carried out using NMR,
UV–Vis, FT-IR, single-crystal X-ray difraction for C1, BET,
TEM, and XRD methods. The materials M1–M3 are highly
efcient at room temperature for catalysis of the reduction
of nitroanilines (>95% conversion in<1 min) with NaBH4
as the hydrogen source in water. Moreover, the M3 catalyst
is highly durable under the optimized conditions for at least
fve cycles without a signifcant loss of activity. The catalytic
studies carried out with this method have the advantages
of high yields, simple synthesis methodology, and easy
workup. This type of catalyst is simple and stable, and it
can be recovered by an external magnet.
General procedure for the synthesis of ligands L5
and L6
A solution of 1,2-diaminobenzene (1 mmol) and trieth-
ylamine (2 mmol) in 10 cm3 tetrahydrofuran (THF) was
stirred at ambient temperature for 30 min. To this, a solu-
tion of aromatic sulfonyl chlorides (1 mmol) in 5 cm3 THF
was added slowly under ambient temperature overnight.
The resulting solution was fltered, and the volatiles were
1 3

Palladium(II) complexes assembled on solid materials: as catalysts for the –NO2 (nitro) to…
removed in vacuo. The material was taken up in 20 cm3
dichloromethane (DCM), washed with water (3 × 5 cm3)
and brine (2×5 cm3), dried over MgSO4, and concentrated
under reduced pressure. The product was recrystallized
from DCM/diethyl ether (Scheme 1).
930, 902, 840, 814, 755, 744, 726, 703, 667, 649, 621, 567,
555, 534, 486, 469 cm−1.
General procedure for the synthesis of Pd(II)
complexes C1–C6
N‑(2‑Aminophenyl)‑4‑fluorobenzenesulfonamide (L5,
C14H15FN2S) Color: orange; yield: 75%; m.p.: 96–97 °C;
1H NMR (400 MHz, CDCl3): δ=4.00 (br., 2 H, –NH2), 6.52
(d, 1H, J=8 Hz, –H1), 6.51 (t, 2H, J=8 Hz, –H3), 6.73 (d,
1H, J=8 Hz, –H4), 7.05 (t, 1H, J=8 Hz, –H2), 7.12 (t, 2H,
J=8 Hz, –Hb), 7.77 (d, 2H, J=8 Hz, –Ha) ppm; 13C NMR
(100 MHz, CDCl3): δ=116.1, 117.1, 118.6, 120.7, 128.5,
129.1, 130.3, 134.9, 144.5, 165.3 (d, J = 260 Hz) (–C–F)
ppm; FT-IR (ATR): v = 3445, 3338, 3275, 3103, 3071,
3038, 2988, 1621, 1590, 1491, 1463, 1406, 1383, 1330,
1312, 1292, 1261, 1228, 1211, 1164, 1151, 1124, 1088,
1030, 1013, 930, 899, 834, 817, 787, 745, 726, 708, 685,
670 cm−1.
A solution of PdCl2 (0.2 mmol) in 5 cm3 methanol was
slowly transferred to a solution of N-(2-aminophenyl)benze-
nesulfonamides (0.4 mmol) in 5 cm3 methanol. The mixture
was slowly warmed to 50 °C for 30 min, cooled to ambient
temperature, and stirred overnight before the removal of
the volatiles in vacuo. The crude product was washed with
diethyl ether (3×10 cm3) and dried under reduced pressure
to give C1–C6 (Scheme 1).
Bis[N‑(2‑aminophenyl)benzenesulfonamide]‑dichloro‑
palladium(II) (C1, C28H32Cl2N4PdS2) Color: light yel-
1
low; yield: 79%; m.p.: 310–311 °C; H NMR (400 MHz,
DMSO-d6): δ = 6.58 (s, 4H, –NH2), 6.72 (t, 2H, J = 8 Hz,
–H3), 6.94 (t, 2H, J= 8 Hz, –H2), 7.07 (d, 2H, J= 8 Hz, –
H1), 7.46 (d, 2H, J = 8 Hz, –H4), 7.51 (d, 4H, J = 8 Hz, –
Hb), 7.99 (d, 4H, J=8 Hz, –Ha) ppm; 13C NMR (100 MHz,
DMSO-d6): δ = 117.1, 121.1, 126.8, 128.8, 129.9, 131.5,
133.8, 138.1, 143.0, 147.2 ppm; FT-IR (ATR): v=3252 (–
NH2), 3148 (–NH2), 3098 (-NH), 3030, 1608, 1570, 1488,
1454, 1445, 1303, 1286, 1264, 1243, 1208, 1174, 1161,
1141, 1117, 1107, 1081, 1039, 1022, 999, 978, 958, 862,
848, 818, 773, 749, 719, 703, 686 cm−1; UV–Vis (DMSO,
c = 1 × 10–4 mol dm−3): λmax (ε) = 280 (9831), 327 (5611)
nm (mol−1 dm3 cm−1).
N‑(2‑Aminophenyl)‑4‑chlorobenzenesulfonamide (L6,
C14H15ClN2S) Color: brown; yield: 77%; m.p.: 106–107 °C;
1H NMR (400 MHz, CDCl3): δ=3.90 (br., 2 H, –NH2), 6.50
(d, 1H, J=8 Hz, –H1), 6.56 (t, 2H, J=8 Hz, –H3), 6.76 (d,
1H, J = 8 Hz, –H4), 7.07 (t, 1H, J = 8 Hz, –H2), 7.44 (d,
2H, J = 8 Hz, –Hb), 7.70 (d, 2H, J = 8 Hz, –Ha) ppm; 13C
NMR (100 MHz, CDCl3): δ = 117.2, 118.7, 120.6, 128.5,
129.0, 129.2, 129.3, 137.3, 139.6, 144.4 ppm; FT-IR (ATR):
v =3477, 3379, 3255, 3094, 3074, 2998, 2954, 2904, 1616,
1587, 1574, 1498, 1476, 1464, 1387, 1335, 1308, 1280,
1253, 1214, 1159, 1124, 1084, 1028, 1014, 1007, 973, 941,
CCDC 1,483,076 contains supplementary crystallo-
graphic data for the compound C1 reported in this article.
Scheme 1
1 3

S. Dayan et al.
These data can be obtained free of charge via https://www.
ccdc.cam.ac.uk/conts/retrieving.html, or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
1052, 1043, 1038, 1023, 958, 894, 864, 853, 792, 753, 716,
672, 660 cm−1; UV–Vis (DMSO, c = 1 × 10–4 mol dm−3):
λmax (ε)=289 (13,725), 335 (6553) nm (mol−1 dm3 cm−1).
Bis[N‑(2‑aminophenyl)‑4‑fuorobenzenesulfonamide]‑
dichloro‑palladium(II) (C5, C28H30Cl2F2N4PdS2) Color:
1
Bis[N‑(2‑aminophenyl)‑4‑methox ybenzene ‑
s u l f o n a m i d e ] ‑ d i c h l o r o ‑ p a l l a d i u m ( I I ) (C 2 ,
C30H36Cl2N4O2PdS2) Color: yellow; yield: 71%; m.p.:
308–309 °C; 1H NMR (400 MHz, DMSO-d6): δ=3.43 (br.,
2H, –NH), 3.82 (s, 6H, –OCH3), 6.50 (t, 2H, J=8 Hz, –H3),
6.58 (s, 4H, -NH2), 6.64 (d, 2H, J = 8 Hz, –H1), 6.70 (d,
2H, J=8 Hz, –H4), 6.92 (t, 2H, J=8 Hz, –H2), 7.07 (d, 4H,
J=8 Hz, –Hb), 7.60 (d, 4H, J=8 Hz, –Ha) ppm; 13C NMR
(100 MHz, DMSO-d6): δ = 55.6 (–OCH3), 113.8, 114.1,
126.9, 127.4, 128.7, 129.0, 131.5, 135.2, 141.9, 162.3 ppm;
FT-IR (ATR): v = 3279 (–NH2), 3216 (–NH2), 3165 (–
NH2), 3131 (–NH), 3072, 2996, 2974, 1593, 1574, 1496,
1463, 1445, 1406, 1332, 1311, 1282, 1261, 1248, 1182,
1149, 1129, 1088, 1030, 1009, 982, 945, 906, 835, 802,
794, 761, 750, 724, 669 cm−1; UV–Vis (DMSO, c=1×10–
4 mol dm−3): λmax (ε)=300 (12,902), 326 (6934) nm (mol−1
dm3 cm−1).
dark yellow; yield: 73%; m.p.: 260–261 °C; H NMR
(400 MHz, DMSO-d6): δ=6.56 (s, 4H, –NH2), 6.75 (t, 2H,
J = 8 Hz, –H3), 6.96 (t, 2H, J = 8 Hz, –H2), 7.07 (d, 2H,
J = 8 Hz, –H1), 7.35 (4H, –Hb), 7.50 (d, 2H, J = 8 Hz, –
H4), 8.02 (4H, –Ha) ppm; 13C NMR (100 MHz, DMSO-d6):
δ=115.7, 120.9, 125.9, 126.6, 129.6, 135.7, 139.5, 141.3,
147.0, 163.6 (d, J = 240 Hz) (–C–F) ppm; FT-IR (ATR):
v =3221 (–NH2), 3153 (–NH2), 3109 (–NH), 3081, 3013,
2829, 2781, 1615, 1590, 1574, 1539, 1492, 1455, 1403,
1306, 1296, 1289, 1272, 1252, 1235, 1216, 1192, 1166,
1144, 1127, 1112, 1098, 1081, 1042, 1029, 1012, 981, 960,
858, 843, 830, 813, 763, 743, 709, 701, 679, 664 cm−1; UV–
Vis (DMSO, c=1×10–4 mol dm−3): λmax (ε)=301 (13,291),
335 (7698) nm (mol−1 dm3 cm−1).
Bis[N‑(2‑aminophenyl)‑4‑chlorobenzenesulfonamide]‑
dichloro‑palladium(II) (C6, C28H30Cl4N4PdS2) Color:
1
light yellow; yield: 71%; m.p.: 331–332 °C; H NMR
Bis[N‑(2‑aminophenyl)‑4‑nitrobenzenesulfonamide]‑
dichloro‑palladium(II) (C3, C28H30Cl2N6O4PdS2) Color:
(400 MHz, DMSO-d6): δ = 6.55 (s, 4H, –NH2), 6.75 (t,
2H, J = 8 Hz, –H3), 6.97 (t, 2H, J = 8 Hz, –H2), 7.06 (d,
2H, J = 8 Hz, –H1), 7.51 (d, 2H, J = 8 Hz, –H4), 7.58 (d,
4H, J = 8 Hz, –Hb), 7.95 (d, 4H, J = 8 Hz, –Ha) ppm; 13C
NMR (100 MHz, DMSO-d6): δ=121.0, 121.4, 125.9, 126.5,
128.6, 128.8, 135.7, 136.1, 142.0, 146.9 ppm; FT-IR (ATR):
v =3247 (–NH2), 3185 (–NH2), 3152 (–NH), 3102, 2908,
1612, 1574, 1489, 1476, 1456, 1394, 1306, 1293, 1266,
1240, 1208, 1169, 1142, 1115, 1107, 1080, 1037, 1014, 983,
949, 865, 847, 821, 811, 774, 748, 709, 648 cm−1; UV–Vis
(DMSO, c=1×10–4 mol dm−3): λmax (ε)=287 (12,236) nm
(mol−1 dm3 cm−1).
1
dark yellow; yield: 79%; m.p.: 311–312 °C; H NMR
(400 MHz, DMSO-d6): δ = 6.99 (s, 4H, –NH2), 6.48 (t,
2H, J = 8 Hz, –H3), 6.68 (d, 2H, J = 8 Hz, –H1), 6.99 (d,
2H, J = 8 Hz, –H4), 7.16 (t, 2H, J = 8 Hz, –H2), 7.91 (d,
4H, J = 8 Hz, –Hb), 8.37 (d, 4H, J = 8 Hz, –Ha) ppm; 13C
NMR (100 MHz, DMSO-d6): δ=124.2, 124.4, 126.4, 127.1,
127.5, 128.0, 128.5, 141.3, 145.7, 149.7 ppm; FT-IR (ATR):
v =3300 (–NH2), 3246 (–NH2), 3216 (–NH2), 3147 (-NH),
3103, 3072, 1607, 1578, 1527, 1498, 1478, 1466, 1414,
1401, 1367, 1351, 1340, 1318, 1303, 1292, 1280, 1249,
1238, 1167, 1117, 1088, 1044, 1031, 1014, 949, 938, 914,
853, 832, 796, 764, 748, 738, 716, 699, 682, 663 cm−1; UV–
Vis (DMSO, c=1×10–4 mol dm−3): λmax (ε)=295 (1668),
336 (6314) nm (mol−1 dm3 cm−1).
General procedure for the preparation of MWCNT,
SiO2, and Fe3O4‑supported C4 (M1–M3)
C4@MWCNTs (M1), C4@SiO2 (M2), and C4@Fe3O4 (M3)
materials were prepared by modifying the published pro-
cedure [37, 63, 78]. Raw MWCNTs (698,849 Aldrich)
was refuxed with a magnetic stirrer in a mixture of HNO3
(78%) and H2SO4 (98%) (1/3 v/v) at 130 °C. This process
ensured the formation of the carboxylic acid (R–COOH)
groups on the sidewalls of MWCNTs. The fnal product
MWCNTs–COOH was fltered and washed with pure water
(5 cm3, fve times), and dried under reduced pressure at
40 °C [37].
Bis[N‑(2‑aminophenyl)‑2,4,6‑trimethylbenzene‑
s u l f o n a m i d e ] ‑ d i c h l o r o ‑ p a l l a d i u m ( I I ) (C 4 ,
C34H44Cl2N4PdS2) Color: yellow; yield: 75%; m.p.: 256–
1
257 °C; H NMR (400 MHz, DMSO-d6): δ = 2.24 (s, 6H,
-p-CH3), 2.38 (s, 12H, o-CH3), 6.45 (d, 2H, J=8 Hz, –H1),
6.60 (t, 2H, J=8 Hz, –H3), 6.75 (d, 2H, J=8 Hz, –H4), 6.81
(t, 2H, J = 8 Hz, –H2), 6.98 (s, 4H, –Hb) ppm; 13C NMR
(100 MHz, DMSO-d6): δ=20.5, 22.6, 116.7, 119.8, 127.7,
131.6, 134.2, 137.1, 138.8, 140.4, 141.7, 147.3 ppm; FT-IR
(ATR): v =3269 (–NH2), 3185 (–NH2), 3153 (–NH), 3070,
2987, 2940, 1599, 1494, 1465, 1453, 1408, 1393, 1382,
1332, 1299, 1274, 1246, 1191, 1161, 1138, 1117, 1105,
In a 20 cm3 glass tube, 90 mg of MWCNTs, SiO2, or
Fe3O4 (from FeCl3·6H2O and FeSO4·4H2O with stoichio-
metric ratios in the presence of ammonia in water [71]) was
1 3

Palladium(II) complexes assembled on solid materials: as catalysts for the –NO2 (nitro) to…
dispersed in 10 cm3 of diethyl ether via an ultrasonic device,
and then 10 mg of C4 complex as a model complex (this
weight ratio was selected to set the amount of catalyst used
in each catalytic experiment) was added to the pot. The fnal
mixture was sonicated for 3 h to form a stable suspension at
ambient temperature. Then, the volatiles were evaporated
in vacuo and dried under reduced pressure. The prepared
materials were structurally analyzed by FT-IR, TEM, BET,
and XRD.
14. Baran T (2019) J Mol Struct 1182:213
15. Liu ZY, Wang XG, Zou XJ, Lu XG (2018) ChemistrySelect
3:5165
16. Jia WG, Ling S, Zhang HN, Sheng EH, Lee R (2018) Organo-
metallics 37:40
17. Cui XL, Zhou X, Dong ZP (2018) Catal Commun 107:57
18. Oh SG, Mishra V, Cho JK, Kim BJ, Kim HS, Suh YW, Lee H,
Park HS, Kim YJ (2014) Catal Commun 43:79
19. Schabel T, Belger C, Plietker B (2013) Org Lett 15:2858
20. Fan GY, Huang WJ, Wang CY (2013) Nanoscale 5:6819
21. Nasrollahzadeh M, Sajadi SM, Rostami-Vartooni A, Alizadeh
M, Bagherzadeh M (2016) J Colloid Interf Sci 466:360
22. Naseem K, Begum R, Farooqi ZH (2017) Environ Sci Pollut Res
24:6446
Catalytic reduction of nitroarenes
23. Dong BQ, Li YH, Ning XM, Wang HJ, Yu H, Peng F (2017)
Appl Catal A Gen 545:54
The catalytic activities of C1–C6 and M1–M3 were exam-
ined for the reduction of nitroarenes (2-nitroaniline, 2-NA,
4-nitroaniline, 4-NA, nitrobenzene, NB) to aminoarenes in
the presence of NaBH4 as a hydrogen source in the water at
ambient temperature.
24. Jiang T, Du SC, Jafari T, Zhong W, Sun Y, Song WQ, Luo Z,
Hines WA, Suib SL (2015) Appl Catal A Gen 502:105
25. El-Hout SI, El-Sheikh SM, Hassan HMA, Harraz FA, Ibrahim
IA, El-Sharkawy EA (2015) Appl Catal A Gen 503:176
26. Dayan S, Altinkaynak C, Kayaci N, Dogan SD, Özdemir N,
Ozpozan NK (2020) Appl Organomet Chem 34:e5381
27. Dayan S, Kayaci N, Dayan O, Ozdemir N, Ozpozan NK (2020)
Polyhedron 175:114181
In a typical reduction reaction, 2.5 mg of the catalysts
were added to nitroarenes (2.5×10–4 mol dm−3) and NaBH4
(0.015 M, freshly) in aqueous solution (10 mol dm−3) and
stirred at ambient temperature for a period of the desired
time. It is important that the reaction started instantly after
the addition of the catalyst. At the end of the period fol-
lowed, the samples are taken from the reaction and fltered
through the micro column. The progress of the reaction was
monitored using an ultraviolet–visible (UV–Vis) spectro-
photometer (Perkin-Elmer Lambda 25). The catalytic activi-
ties of all the materials were monitored by comparing the
bands which appeared and disappeared after reduction on
the UV–Vis spectrum.
28. Dongil AB, Pastor-Perez L, Fierro JLG, Escalona N, Sepulveda-
Escribano A (2016) Appl Catal A Gen 513:89
29. Areephong J, Huo B, Mbaezue II, Ylijoki KEO (2016) Tetrahe-
dron Lett 57:3124
30. Khan RI, Pitchumani K (2016) Green Chem 18:5518
31. Ji R, Zhai SR, Zheng W, Xiao ZY, An QD, Zhang F (2016) RSC
Adv 6:70424
32. Dayan S, Kalaycioglu NO (2013) Appl Organomet Chem 27:52
33. McCue AJ, Guerrero-Ruiz A, Rodriguez-Ramos I, Anderson JA
(2016) J Catal 340:10
34. Dahm G, Bailly C, Karmazin L, Bellemin-Laponnaz S (2015)
J Organomet Chem 794:115
35. Marquise N, Chevallier F, Nassar E, Frederich M, Ledoux A,
Halauko YS, Ivashkevich OA, Matulis VE, Roisnel T, Dorcet
V, Mongin F (2016) Tetrahedron 72:825
36. Rezaei B, Shams-Ghahfarokhi L, Havakeshian E, Ensaf AA
(2016) Talanta 158:42
References
37. Dayan S, Ozdemir N, Ozpozan NK (2019) Appl Organomet
Chem 33:e4710
38. Charbonneau M, Addoumieh G, Oguadinma P, Schmitzer AR
(2014) Organometallics 33:6544
1. Dell’Anna MM, Intini S, Romanazzi G, Rizzuti A, Leonelli C,
Piccinni F, Mastrorilli P (2014) J Mol Catal A Chem 395:307
2. Hu XW, Long Y, Fan MY, Yuan M, Zhao H, Ma JT, Dong ZP
(2019) Appl Catal B Environ 244:25
39. Dang TT, Zhu YH, Ngiam JSY, Ghosh SC, Chen AQ, Seayad
AM (2013) ACS Catal 3:1406
40. Kim SW, Kim M, Lee WY, Hyeon T (2002) J Am Chem Soc
124:7642
3. Shokouhimehr M, Kim T, Jun SW, Shin K, Jang Y, Kim BH, Kim
J, Hyeon T (2014) Appl Catal A Gen 476:133
4. Das P, Ghosh S, Baskey M (2019) J Mater Sci Mater Electron
30:19731
41. Zeng MF, Wang YD, Liu Q, Yuan X, Feng RK, Yang Z, Qi CZ
(2016) Int J Biol Macromol 89:449
42. Choi J, Chan S, Yip G, Joo H, Yang H, Ko FK (2016) Water Res
101:46
5. Qu YM, Chen T (2020) Chem Eng J 382:122911
6. Liu Q, Tadrent S, Proust C, Gomez F, Khelfa A, Luart D, Len C
(2020) Chem Eng Sci 211:115275
43. Pahlevanneshan Z, Moghadam M, Mirkhani V, Tangestaninejad
S, Mohammadpoore-Baltork I, Loghmani-Khouzani H (2016) J
Organomet Chem 809:31
7. Du JT, Shi J, Sun Q, Wang D, Wu H, Wang JX, Chen JF (2020)
Chem Eng J 382:122883
44. Morisse CGA, McInroy AR, Anderson C, Mitchell CJ, Parker
SF, Lennon D (2017) Catal Today 283:110
8. Marais E, Nyokong T (2008) J Hazard Mater 152:293
9. Modirshahla N, Behnajady MA, Mohammadi-Aghdam S (2008)
J Hazard Mater 154:778
45. Yadav D, Awasthi SK (2020) New J Chem 44:1320
46. Subodh, Mogha NK, Chaudhary K, Kumar G, Masram DT
(2018) ACS Omega 3 :16377
10. Canizares P, Saez C, Lobato J, Rodrigo MA (2004) Ind Eng Chem
Res 43:1944
47. Subodh, Chaudhary K, Prakash K, Masram DT (2020) Appl
Surf Sci 509:144902
11. Chiou JR, Lai BH, Hsu KC, Chen DH (2013) J Hazard Mater
248:394
48. Dayan S, Kayaci N, Ozpozan NK, Dayan O (2017) Appl Orga-
nomet Chem 31:e3699
12. Khan F, Pandey J, Vikram S, Pal D, Cameotra SS (2013) J Hazard
Mater 254:72
13. Jayabal S, Ramaraj R (2014) Appl Catal A Gen 470:369
1 3

S. Dayan et al.
49. Kayaci N, Dayan S, Ozdemir N, Dayan O, Ozpozan NK (2018)
Appl Organomet Chem 32:e4558
67. Zhang N, Cao LY, Feng LL, Huang JF, Kajiyoshi K, Li CY, Liu
QQ, Yang D, He JJ (2019) Nanoscale 11:11542
68. Yao YJ, Yu MJ, Yin HY, Wei FY, Zhang J, Hu HH, Wang SB
(2019) Appl Surf Sci 489:44
50. Gunnaz S, Ozdemir N, Dayan S, Dayan O, Cetinkaya B (2011)
Organometallics 30:4165
51. Sheldrick GM (2015) Acta Crystallogr A 71:3
52. Sheldrick GM (2015) Acta Crystallogr C 71:3
53. Farrugia LJ (2012) J Appl Crystallogr 45:849
54. Vicente J, Saura-Llamas I, Garcia-Lopez JA (2010) Organometal-
lics 29:4320
69. Xu C, Wang J, Gao BR, Dou MM, Chen R (2019) J Mater Sci
54:8892
70. Tamakloe W, Agyeman DA, Park M, Yang J, Kang YM (2019) J
Mater Chem A 7:7396
71. Abbas M, Torati SR, Kim C (2015) Nanoscale 7:12192
72. Baghbamidi SE, Hassankhani A, Sanchooli E, Sadeghzadeh SM
(2018) Appl Organomet Chem 32:e4251
55. Accadbled F, Tinant B, Henon E, Carrez D, Croisy A, Bouquillon
S (2010) Dalton Trans 39:8982
56. Grazul M, Sigel R, Maake C, Besic-Gyenge E, Lorenz IP, Mayer
P, Czyz M, Budzisz E (2014) Polyhedron 67:136
57. Sabater S, Mata JA, Peris E (2013) Organometallics 32:1112
58. Wu QX, Wu LL, Zhang L, Fu HY, Zheng XL, Chen H, Li RX
(2014) Tetrahedron 70:3471
73. Goyal A, Bansal S, Singhal S (2014) Int J Hydrogen Energy
39:4895
74. Begum R, Naseem K, Ahmed E, Sharif A, Farooqi ZH (2016)
Colloid Surf A 511:17
75. Huang HG, Tang MW, Wang XG, Zhang M, Guo SQ, Zou XJ, Lu
XG (2018) ACS Appl Mater Inter 10:5413
59. Tessier C, Rochon FD (2010) Inorg Chim Acta 363:2652
60. Heinrich F, Kessler MT, Dohmen S, Singh M, Prechtl MHG,
Mathur S (2012) Eur J Inorg Chem 36:6027
76. Mahata N, Cunha AF, Orfao JJM, Figueiredo JL (2008) Appl
Catal A Gen 351:204
61. Grirrane A, Garcia H, Corma A, Alvarez E (2012) Chem Eur J
18:14934
77. Dayan S, Arslan F, Kayaci N, Kalaycioglu NO (2014) Spectrochim
Acta A 120:167
62. Bernstein J, Davis RE, Shimoni L, Chang NL (1995) Angew
Chem Int Ed 34:1555
78. Dayan S, Kalaycioglu NO, Dayan O, Ozdemir N, Dincer M, Buy-
ukgungor O (2013) Dalton Trans 42:4957
63. Dayan S, Arslan F, Ozpozan NK (2015) Appl Catal B Environ
164:305
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional afliations.
64. Dayan S, Ozturk S, Kayaci N, Ozpozan NK, Ozturk E (2015) B
Mater Sci 38:1651
65. Kilic A, Gezer E, Durap F, Aydemir M, Baysal A (2019) J Orga-
nomet Chem 896:129
66. Zheng Y, He F, Wu JM, Ma DL, Fan HL, Zhu SF, Li X, Lu YZ,
Liu Q, Hu X (2019) ACS Appl Nano Mater 2:3538
1 3