Effective and selective direct aminoformylation of nitroarenes utilizing palladium nanoparticles assisted by fibrous-structured silica nanospheres

Article abstract of DOI:10.1007/s11164-020-04206-8

Abstract: Palladium nanoparticles (~ 1–3?nm, 0.4?wtpercent Pd) were uniformly distributed over the surface of fibrous silica nanospheres (KCC-1) modified via aminopropyltriethoxysilane using a fast and cost-effective palladium (II) chloride reduction process. The Pd nanoparticles (Pd NPs) distribution over the ensuing catalyst Pd/KCC-1-NH₂ showed much more uniform distribution, and smaller size compared with the tedious hydrothermal reduction method. The morphological, chemical, and size analyses of Pd/KCC-1-NH₂ by BET, UV–Vis spectra, XRD, HR-TEM, EDS and XPS analysis revealed that the succeeding material consist of a distinct fibrous silica nanospheres support adorn with Pd NPs. The resultant nanocatalyst was tested for the one-step reductive aminoformylation of aromatic nitro compounds using formic acid. A wide range of substituted nitroarenes including electron withdrawing, releasing, sterically hindered and multifunctional groups have been converted to corresponding aryl formamide in quantitative yields (yields up to 98percent) at moderate temperature (70?°C). Optimization study has proved that the 6 equivalent of formic acid is required and toluene was found to be the better solvent. The established practice is beneficial due to the use of formic acid as H₂ source and formylating agent, easiness in handling of the catalyst and simple workup procedure with efficient catalyst reusability. Graphic abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s11164-020-04206-8

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-020-04206-8
Efective and selective direct aminoformylation
of nitroarenes utilizing palladium nanoparticles assisted
by fbrous‑structured silica nanospheres
Ziyauddin S. Qureshi1 · E. A. Jaseer1
Received: 14 May 2020 / Accepted: 26 June 2020
© Springer Nature B.V. 2020
Abstract
Palladium nanoparticles (~1–3 nm, 0.4 wt% Pd) were uniformly distributed over the
surface of fbrous silica nanospheres (KCC-1) modifed via aminopropyltriethoxysi-
lane using a fast and cost-efective palladium (II) chloride reduction process. The
Pd nanoparticles (Pd NPs) distribution over the ensuing catalyst Pd/KCC-1-NH2
showed much more uniform distribution, and smaller size compared with the tedious
hydrothermal reduction method. The morphological, chemical, and size analyses of
Pd/KCC-1-NH2 by BET, UV–Vis spectra, XRD, HR-TEM, EDS and XPS analysis
revealed that the succeeding material consist of a distinct fbrous silica nanospheres
support adorn with Pd NPs. The resultant nanocatalyst was tested for the one-step
reductive aminoformylation of aromatic nitro compounds using formic acid. A wide
range of substituted nitroarenes including electron withdrawing, releasing, sterically
hindered and multifunctional groups have been converted to corresponding aryl for-
mamide in quantitative yields (yields up to 98%) at moderate temperature (70 °C).
Optimization study has proved that the 6 equivalent of formic acid is required and
toluene was found to be the better solvent. The established practice is benefcial due
to the use of formic acid as H2 source and formylating agent, easiness in handling of
the catalyst and simple workup procedure with efcient catalyst reusability.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4-020-04206-8) contains supplementary material, which is available to authorized users.
*
Ziyauddin S. Qureshi
zqureshi@kfupm.edu.sa
E. A. Jaseer
jaseer@kfupm.edu.sa
1
Center for Refning and Petrochemicals, King Fahd University of Petroleum & Minerals, P.O.
Box 5040, Dhahran 31261, Saudi Arabia
Vol.:(0123456789)
1 3

Z. S. Qureshi, E. A. Jaseer
Graphic abstract
Keywords Fibrous silica, KCC-1 · Palladium nanoparticles · Aminoformylation ·
Nitroarenes
Introduction
The reduction of nitroarenes into the corresponding anilines and their conversion
to N-formyl derivatives (formanilides) is one of the most versatile organic trans-
formation due to their widespread application in diferent felds [1], such as in the
production of polymer, dyes, pigments, synthesis of agrochemicals like N,N-dia-
ryl ureas [2], synthesis of pharmaceuticals like cancer chemotherapeutic agents
[3], quinolone antibiotics [4]. Formanilide moiety constitutes very important pre-
cursors for the preparation of herbicides and fungicides [5]. Additionally, N-for-
myl compounds are also been used in the perfume industry as scented fowers
[6]. Synthesis of amino-formyl derivatives from nitro compounds is a two-step
reaction involving the reduction of functional nitro group to an amine followed
by N-formylation [7]. There have been several studies on improving the catalytic
performance and selectivity for selective reduction of aryl nitro compounds to
anilines [8] as well as N-formylation of anilines with various formylating agents
[9–17]. Conventionally, stoichiometric amounts of metallic reagents is used for
the reduction of nitroarenes, such as iron [18, 19], tin [20], zinc [21, 22] in the
presence of an acid, Raney nickel-based systems [23, 24], and hydrogen gas as
reducing agent [25–28]. Although convenient, the major concern with these sys-
tems is stoichiometric amount of metallic reagents which are not environmentally
benign, use of fery hydrogen gas under drastic conditions of high pressure and
temperature, difculties in handling H2 gas on an industrial scale, and/or poor
selectivity of the reaction process in multi-reducible functional nitroarenes. How-
ever, developing new clean, facile, fast, cost-efective, and chemoselective pro-
cedures for the direct conversion [29] of aryl nitro compounds to amino-formyl
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Efective and selective direct aminoformylation of nitroarenes…
derivatives would be an ideal choice for this class of important compounds.
Eforts have been made by utilizing in situ generated hydrogen using Au/TiO2
catalyst under hazardous and toxic carbon monoxide atmosphere [30, 31]. Among
the alternative reduction protocols catalytic transfer hydrogenation (CTH) [32,
33] has emerged among the most feasible approach as it employs economy, safe,
and easily available reducing agents, such as formic acid or formate salts, or iso-
propanol and dienes as hydrogen sources under either homogeneous [34–37] or
heterogeneous [38, 39] conditions. CTH also eludes the use of fammable and
explosive molecular H2 gas and is more globally friendly compared to stoichio-
metric reductions.
Recently, some groups have proposed formic acid as a biomass resource as a
harmless replacement for the conversion of hydrogenation of nitroarenes to the pro-
duction of aryl amines [40]. Later formylation of amine will be achieved out in sepa-
rate rung. However, this reaction is highly sensitive toward temperature and requires
an inert atmosphere. Low temperature (~70 °C) restricts the reaction to amines
while high temperature produces N,N-dimethylated amine product [40, 41]. Some of
the CTH methods for this reduction-formylation process of nitroarenes includes the
use of Pd/C HCOONH4 [32], Fe/HCOOH [33], Sn/HCOOH [29], Zn/HCOONH4
[42], P/I2/HCOOH [43], Au/TiO2/HCOONH4 [44], [Cp*RhCl2]2/HCOOH [45],
CH(OEt)3/β-CD-TiO2 [46], Mag-IL-Pd/HCOONH4 [40], Au/rutile/HCOOH [41],
AgPd@g-C3N4/HCOOH [47], and Pd(TFA)2/HCOOH [48]. However, regardless of
their potential added value, all potential methods experienced from advantages and
drawbacks such as the use of costly, moisture/air-sensitive catalysts and problems
accompanying with catalyst and product separation, which restrict its applications.
Similarly, in most cases homogeneous catalysts are used, and therefore they are
more difcult to recycle. The loss of such metal catalysts, at even ppm level is not
appropriate as of its high price and acute harmfulness for pharmaceutical solicita-
tions. Hence, the exploration for a single heterogeneous and recyclable catalyst that
might efectively catalyze both reduction-formylation process of nitroarenes is the
subject of the current work.
Recently, KCC-1 fbrous silica nanospheres emerged as attractive material with
excellent textural, mechanical properties and good thermal, hydrothermal properties
even with the absence of a conventional porous structure. These silica nanosphere
shows high surface area and approachability due to its unique fbrous morphology,
which results in good performance as a catalyst support. Because of these excep-
tional KCC-1 properties, which have recently been applied to energy, sustainability
and environment such as gas adsorption, catalysis and sensors [49–53]. Continuing
our ongoing work on the development of transition-metal catalysts for olefn CTH
and conjugate reduction of carbonyl-unsaturated carbonyl compounds [54], CO oxi-
dation [55], here we report an simple and cost-efective method for the preparation
of fbrous silica nanospheres KCC-1 supported monodispersed Pd NPs catalyst (Pd/
KCC-1-NH2) and there application for the one-step reductive formylation of aro-
matic nitro compounds (as shown in Scheme 1). The catalyst showed outstanding
activity, and the current system allows a wide range of nitroarenes to convert to cor-
responding formanilides. The catalyst also displays excellent reusability up to seven
successive cycles without any substantial cost in activity.
1 3

Z. S. Qureshi, E. A. Jaseer
Scheme 1 Schematic diagram of the overall procedure synthesis of Pd-KCC-1-NH2 catalyst and its
application for N-Formylation of nitroarenes
Experimental
General
Both solvents and substrates have been obtained from Sigma-Aldrich, Saudi Arabia
and used without further purifcation (nitroarenes 99%, toluene 99.8%, formic acid
98–100%). The specifc surface area of as synthesized silica supports and of the sil-
ica supported palladium nanocatalysts were determined using the Brunauer Emmet
and Teller (BET) gas adsorption and desorption method on ASAP 2020, Micromer-
itics, USA. The Barrett, Joyner, and Halenda (BJH) nitrogen gas absorption method
was used to collect average pore diameter and pore volume. Transmission electron
microscopy (TEM) images were recorded using JEOL JEM-2100F transmission
electron microscopy at 200 kV JEOL JSM-6610LV at 20 kV, respectively. Images
were taken from scanning electron microscopy (SEM) over JEOL JSM-6610LV
functioning at 20 kV. The energy dispersed X-ray spectroscopy (EDXS) analysis
and elemental mapping had been employed to evaluate the elementary composi-
tion of catalyst. Particle size distributions were achieved by investigation of more
than hundreds of nanoparticles. The sample pattern of X-ray difraction (XRD) was
investigated from 2θ ranges of 5°–90° using Rigaku Minifex II desktop X-ray dif-
fractometer and by means of Cu Kα radiation (wavelength λ=1.5406 Å) and 15 mA
and 30 kV as functional parameters, the step size is 0.02° and the speed is 2° min−1.
The UV–Vis difuse refectance spectrum (DRS) (JASCO V-670 Spectrophotom-
eter) was logged to detect the existence of zero valent palladium by a wavelength
of 220–500 nm. XPS studies were carried out on ESCALAB™ XI+ X-ray Photo-
electron Spectrometer (XPS) Microprobe armed by a monochromatic Al Kα X-ray
source (hα=1486.68 eV) operational at 150 W, Multi-channel detector plate and
line delay below 1×10−9 Torr vacuum. The survey and the high-resolution spectra
were reported at 160 and 20 eV, respectively, passing energy via fxed analysis. Sam-
ples were afxed to avoid contrast charging in foating mode. Charge neutralization
for all the samples was necessary. Binding energy for C was thought to be 1 s bind-
ing energy of random carbon contamination that was supposed to be at 284.08 eV.
The results were examined with commercially accessible software, CASAXPS.
Metallic peak were fxed with a Asymmetric Lorentzian Function with Gaussian
Convolution, whereas nonmetallic peaks were fxed with combination of Gauss-
ian (70%)-Lorentzian (30%) (GL30) function afterward Shirley type background
1 3

Efective and selective direct aminoformylation of nitroarenes…
subtraction. Advancement of the reaction was monitored by the GC system 7890A
armed with 5975C inert MSD with Triple-Axis Detector aimed for the mass inves-
tigation of products (30 m×320 μm×1 μm) (column fow 1.8 mL min−1, 80 °C to
250 °C at 5 °C min−1 rise). The analysis was calibrated using commercial samples
of starting materials and products. The Pd content of the nanocatalyst was calculated
using the inductively coupled plasma spectrometer of Horiba Scientifc (ULTIMA 2,
ICP-OES). The reaction products have been validated by the GC–MS analysis.
Preparation of fbrous‑structured silica nanospheres (KCC‑1)
The KCC-1 was synthesized by amending the previously reported procedure
involves template-mediated hydrolysis–polycondensation of tetraethyl orthosilicate
(TEOS) precursor [54]. In a typical synthesis, TEOS (35 mL) has been dissolved
in the cyclohexane (300 mL) and pentanol (15 mL) solution. A solution of cetyltri-
methylammonium bromide (CTAB; 13.33 g) in water (500 mL) was slowly added to
the above solution. The resulting mixture was stirred at room temperature for 30 min
and then heated in a microwave at 120 °C for 30 min. The white precipitate obtained
was centrifuged, washed with excess water and dried in the oven at 100 °C for 2 h in
the air. Calcination was performed at 550 °C for 6 h to remove the residual organic
template in a continuous airfow. The obtained material is labeled as KCC-1.
Functionalization of KCC‐1 (KCC‐1‐NH2)
KCC-1 (10 g), anhydrous toluene (150 mL), and 3‐aminopropyltriethoxysilane (3‐
APTES; 40 mL, 171 mmol) were mixed in a 250 mL round-bottom fask and heated
for 24 h at refux temperature. The solution was fltered and the precipitated white
solid was washed with acetone and chloroform. The obtained solid cake was dried
overnight in the oven at 60 °C to allow the silica support to be functionalized by the
amino groups (KCC‐1‐NH2).
Pd/KCC‑1‑NH2 synthesis
Round-bottom fask (100 mL) was added with 1.0 g of KCC-1-NH2 nanocomposite
in 60 mL deionized water and well dispersed ultrasonically for 0.5 h. To this solu-
tion 0.2 g of PdCl2 was added, ultrasonically dispersed (0.5 h) and continued stirring
(500 rpm) at room temperature for 24 h. To this mixture 1.46 g of NaBH4 was added
pinch by pinch within 0.5 h, and resulting solution was further stirred for next 24 h.
The resulting product has been isolated by centrifugation, splashed repeatedly with
deionized water (3×50 mL), methanol (3×50 mL), acetone (3×50 mL) and later
dried up in a vacuum at 65 °C for about 6 h.
Experimental procedure for aminoformylation of nitroarenes
The nanocatalyst Pd/KCC-1-NH2 (10 mg, 0.4 wt% Pd) and formic acid (6 equiva-
lent) were mixed to a stirred solution of nitroarene (1 mmol) in toluene (3 mL). The
1 3

Z. S. Qureshi, E. A. Jaseer
resultant reaction mixture was continued to stir at 70 °C for 3 h in a 25 mL fask
attired with a refuxing condenser and covered through a CaCl2 stopcock. The GC
investigated the progress of the reaction. The reaction mixture was allowed to cool
down to RT after completion and the catalyst was extracted by centrifugation. Prod-
ucts have been mined using ethyl acetate (3×5 mL) and dried above Na2SO4 and
subsequently solvent was removed under vacuum in order to obtain a crude prod-
uct. Subsequently, the crude product was analyzed using gas chromatographic tech-
niques for the calculation of yield and selectivity.
Recyclability study
The reaction was performed as indicated above in the typical experimental proce-
dure. After the completion of reaction, reaction mixture cooled to RT. The catalyst
has been extracted by quick centrifugation and washed thoroughly with methanol
(5×10 mL) and acetone (5×10 mL) for eliminating all traces of the reactant or
products existing and further centrifuged. The recovered catalyst was vacuum-dried
at 65 °C and held for 4 h before the successive process. This dried catalyst was used
for catalyst recyclability study.
Results and discussion
Catalyst characterization
The BET surface area, Barrett–Joyner–Halenda (BJH) pore volume and pore size
for the Pd/KCC-1-NH2 catalyst and its precursors KCC-1 and KCC-1-NH2 sil-
ica nanospheres were determined by N2 physisorption measurements. The results
are summarized in Table 1. The BET surface area of KCC-1 is calculated to be
602 m2 g−1. After the functionalization and immobilization of Pd, the BET surface
areas decreased to 326, and 308 m2 g−1 in KCC-1-NH2 and Pd/KCC-1-NH2, respec-
tively. This decrease in surface properties are from the resulting efect of lining from
the walls of the pores with the (3-Aminopropyl)triethoxysilane (APTES) organic
ligand and immobilization of Pd NPs on and inner surface of the support [54–57].
Table 1 Physicochemical properties of parent KCC-1, and modifed KCC-1-NH2, Pd/KCC-1-NH2
Entry
Material
SaBET (m2/g−1
)
PVb (cm3 g−1
)
PSb (nm)
Pd
Contentc
(wt%)
1
2
3
KCC-1
KCC-1-NH2
Pd/KCC-1-NH2
602
326
308
1.439
0.70
0.46
9.2
7.5
5.5
–
–
0.4
aSurface area measured from the adsorption isotherms by BET equation
bTotal pore size and pore volume measured using the nitrogen adsorption at p/p0 =0.99
cDetermined by ICP-OES
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Efective and selective direct aminoformylation of nitroarenes…
Figure 1a shows the N2 adsorption–desorption isotherms of KCC-1, KCC-1-NH2
and Pd/KCC-1-NH2. The N2 adsorption–desorption isotherms of all samples could
be defned as Type IV, which specifes the mesoporous structures of the all three
samples. The pore size distribution for parent (KCC-1) and modifed (KCC-1-NH2
and Pd/KCC-1-NH2) observed to remain same, with a major pore size of distribu-
tion at 3.6 nm and other larger mesopores (Fig. 1b). Thus, the overall reaction of
KCC-1-NH2 with PdCl2 followed by a simple reduction with NaBH4 is an easier,
and efective method for the preparation of well-distributed Pd NPs with average
particle size of ~1–3 nm. The Pd content of Pd/KCC-1-NH2 nanocatalyst obtained
by ICP analysis is 0.4 wt%.
Construction of Pd NPs over the KCC-1-NH2 was studied using UV–vis spectros-
copy. During reduction, changes in the color of the reaction mixture were observed
from yellow to dark brown. As displayed in Fig. 2, the characteristic absorption peak
of Pd2+ or PdCl42− at λmax 260–320 nm disappeared completely during the reaction
Fig. 1 N2 adsorption–desorp-
tion isotherm (a) and pore size
distribution (b) curves for parent
KCC-1 and modifed KCC-
1-NH2 and Pd/KCC-1-NH2
(a)
400
KCC-1
KCC-1-NH2
Pd/KCC-1-NH2
350
300
250
200
150
100
50
0
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (p/p°)
(b)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
KCC-1
KCC-1-NH2
Pd/KCC-1-NH2
0
5
10
15
20
25
30
35
40
Pore Diameter (nm)
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Z. S. Qureshi, E. A. Jaseer
1
0.8
0.6
0.4
0.2
0
Fig. 2 UV-vis spectra of a
KCC-1, b KCC-1-NH2, c Pd/
KCC-1-NH2, and d PdCl2
314
268
(d)
(c)
(b)
(a)
220
270
320
370
420
470
Wavelength (nm)
progression, this clearly shows the divalent palladium Pd(II) was reduced com-
pletely to zero valent palladium Pd(0) and the development of the plasmic absorp-
tion spectrum for the Pd NPs [58].
X-ray difraction patterns (XRD) spectrum was measured to determine the crys-
tallinity of the parent KCC-1, and modifed KCC-1-NH2, Pd/KCC-1-NH2 nanocat-
alysts (Fig. 3). XRD spectra of Pd/KCC-1-NH2 nanocatalyst present an extensive
difraction peak at 2θ=23.1 consistent with KCC-1 and KCC-1-NH2 ascribed to
amorphous silica [59]. As shown in Fig. 3c, the major difraction peaks at 40.2°,
46.6°, 67.5°, 80.8° and 85° should be allocated to the (111), (200), (220), (311)
and (222) planes for face centered cubic (fcc) palladium crystals, respectively, this
revealed that the Pd NPs were made (JCPDS#5-0681). No other difraction peaks
from impurities were detected; this advises that Pd/KCC-1-NH2 is highly pure.
Surface morphology and size of Pd NPs within the KCC-1 nanosphere fb-
ers were further examined by high-resolution transmission electron microscopy
(HR-TEM) via low accelerating voltage was carried out; this allowed the deter-
mination of the particle size dispersion by quantifying the diameter of more than
Fig. 3 XRD spectra of a KCC-
1, b KCC-1-NH2, and c Pd/
KCC-1-NH2 nanocatalyst
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Efective and selective direct aminoformylation of nitroarenes…
100 Pd NPs (Fig. 4). HR-TEM images outcomes endorse the development of uni-
formly distributed Pd NPs (∼ 1–3 nm) not only over the surface but also inside
the fbers of KCC-1 support compared to prepared through a tedious hydrother-
mal reduction method (> 5 nm) (Fig. 4a, b). The size of Pd NPs (∼ 1–3 nm) dis-
tribution histogram over Pd/KCC-1-NH2 is shown in Fig. 4c. The EDS elemental
mapping analysis confrmed the presence of elements C, N, Pd, and Si in Pd/
KCC-1-NH2 indicating the successful development of palladium nanoparticles
over KCC-1 support (Figs. 4d, S1). This is direct evidence for the attachment of
Pd onto the amine functionalized silica nanospheres KCC-1 and successful crea-
tion of the Pd/KCC-1-NH2.
The most surface sensitive practice XPS was made to study the reduction of
the divalent Pd2+ or PdCl42− into a Pd0 species (Fig. 5). XPS measurement shows
that, the Pd NPs exist in Pd(0) state in agreement with the observed binding
energies of 334.38 eV (Pd0 3d5/2) and 339.58 eV (Pd0 3d3/2), the interval for two
peaks is about 5.2 eV which is in contract with the literature value (5.2 eV) [60,
61]. In specifc, the Pd 3d (3d5/2 = 334.38 eV) binding energy of the Pd/KCC-
1-NH2 nanocatalyst is negatively shifted ca. 0.72 eV as compared with the nor-
mal values for bulk Pd (3d5/2 = 335.10 eV), this is attributed to the interaction
between APTES and metal atom [62, 63]. This resulting shift of elemental bind-
ing energy is due to the development of electrostatic interaction between APTES
and the added Pd precursor ions, as a lone pair of electrons from NH2 groups
from APTES, they efciently donate their electrons to Pd.
Fig. 4 a, b HR-TEM images, c Pd NPs size distribution histogram, and EDS of Pd/KCC-1-NH2 (d)
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Z. S. Qureshi, E. A. Jaseer
Fig. 5 XPS spectra of Pd/KCC-1-NH2 nanosphere
Study of optimization parameters for reductive formylation of nitrobenzene
The catalytic evaluation of nanocatalyst Pd/KCC-1-NH2 commenced by studying its
activity and selectivity in the reductive formylation of nitrobenzene using formic
acid as a reducing as well as a formylating agent and the results are summarized in
Table 2. It was noted that the selectivity of the reaction was infuenced by the exist-
ence of the solvent. Reaction works efciently in the presence of nonpolar solvent as
compared to the polar solvents. Nitrobenzene reaction with formic acid (5–10 mmol)
in polar aprotic solvents such as CH3CN (69%) and THF (65%) results in moderate
yield of the reductive-formylated product (Table 2, entries 1 and 3). Interestingly,
when acetonitrile was used as solvent with double amount of HCOOH (10 mmol),
the selectivity shifted toward N-ethylaniline (68%) (Table 2, entry 2). This could
be due to the competitive reaction between intermediate aniline and solvent ace-
tonitrile. A polar protic solvent for example methanol was likewise found to lower
selectivity (26%) (Table 2, entry 4). Whereas, nonpolar solvent toluene was found to
be very efective giving exceptional yield of selective reductive-formylated product
(Table 2, entry 5). The efect of HCOOH as a reductive formylating source; using
6 mmol of HCOOH provided 99% conversion and 100% selectivity of the antici-
pated product (Table 2, entry 6), whereas 3 mmol of HCOOH shows almost same
conversion (97%) with slight decline chemoselectivity (96%) toward the desired
product (Table 2, entry 7). More optimization of the conditions for the reaction
revealed that, Pd/KCC-1-NH2 shows high catalytic activity even at reduced reaction
temperature of 70 °C (Table 2, entries 8–10). So as to explore the efect of palladium
concentration on reaction outcome, reactions were carried out at diferent palladium
concentration ranging from 25 to 5 mg of Pd/KCC-1-NH2 (Table 2, entries 11–13).
It has been observed that at 10 mg of catalyst is sufcient for the complete con-
version toward desired product. While reaction did not work at all without catalyst
(Table 2, entry 14), clearly signifying the role of Pd/KCC-1-NH2. A reaction time of
3 h was enough to achieve a complete conversion of the starting material (Table 2,
entries 15–16). The Pd/KCC-1-NH2 nanocatalyst’s catalytic behavior was com-
pared with our previously prepared heterogeneous palladium catalysts, such as, Pd/
KCC-1-NH2, Pd/SBA-15-NH2 [54], and 10% Pd/C (Table 2, entries 15, 17–19), but
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Efective and selective direct aminoformylation of nitroarenes…
1 3

Z. S. Qureshi, E. A. Jaseer
1 3

Efective and selective direct aminoformylation of nitroarenes…
among them our newly prepared small size (∼1–3 nm) nanocatalyst Pd/KCC-1-NH2
was identifed as the best catalyst providing excellent conversion (99%), selectivity
toward the desired product in toluene (Table 2, entry 15). Furthermore, when the
same reaction was conducted under sonication at room temperature, a substantial
rate increase was observed and completed within 1.5 h, resulting in 99% conversion
and selectivity (100%) to N-phenylformamide (Table 2, entry 20).
With most favorable conditions in hand, we explore further the general applica-
bility of present practice for the reductive-formylation of various nitroarenes using
HCOOH and Pd/KCC-1-NH2 nanocatalyst. Nitroarenes with diferent functional-
ity undergo reductive-formylation giving excellent yields of the respective N-aryl
formamide within 2–6 h at 70 °C (Table 3). Nitrobenzene converted into N-phenyl
formamide with excellent yield of 99% within 3 h (Table 3, entry 1 or Table 2 entry
15 or Fig. 6 cycle 1). Alkyl substituted nitrobenzenes such as o-, m- and p-nitroben-
zenes transforms into the respective formamides at excellent yields (Table 3, entries
2–4). Subsequently, we have also studied the present protocol for reductive formyla-
tion of o-nitro and p-nitro phenol. Interestingly, it has been observed that o-nitro
phenol shows 84% selectivity toward corresponding product and 16% toward benzo-
xazole [64]; while p-nitro phenol provided good yield of the respective N-aryl for-
mamide product within 3 h (Table 3, entries 5 and 6). The p-nitroacetophenone was
reductive-formylated giving parallel product in good yield 83% (Table 3, entry 7).
We have also screened p- and m-nitrobenzaldehyde under the same conditions, very
low yields of the desired products were observed, this may be due to more electron
defcient carbonyl group (Table 3, entries 8 and 9). The reduction of p-nitrobenzoic
acid and methyl 3-nitrobenzoate (Table 3, entries 10 and 11) is smooth, giving mod-
erate to high yields of the expected products with total chemo selectivity toward the
reductive formation of the nitro group. The Pd/KCC-1-NH2 nanocatalyst was also
found active for 3-nitrostyrene, where it frst undergoes the hydrogenation of sub-
stituted double bond followed by the reductive-formylation of nitro group and the
resulting product was aforded in quantitative yield (Table 3, entry 12). 3-Nitroph-
thalic anhydride proved a more difcult substrate, resulting in a mixture of amine
products (84%) and a reductive formylated product (16%) (Table 3, entry 13). It was
observed that sterically hindered 5-nitrosalicylaldehyde is not favorable under the
present reaction condition (Table 3, entry 14). Moreover, the generality of present
catalytic system was explored further for tandem synthesis of benzimidazole from
o-dinitrobenzene, which are building block in natural products and pharmaceutical
agents [65]. The o-dinitrobenzene efciently undergoes reductive-formylation fol-
lowed by cyclization giving excellent yield of benzimidazole (Table 3, entry 15).
Recently Lei et al. reported the gold-based solid catalyst (Au/rutile), as versatile
catalyst for the direct conversion of o-dinitroarenes to respective benzimidazoles
from readily available formic acid [41]. In the case of larger 3,5-dinitrobenzoic
acid, nanocatalyst Pd/KCC-1-NH2 shows selective reduction of only one of the nitro
group into corresponding amine (3-amino-5-nitrobenzoic acid, 100% selectivity),
also no other products were noticed even with a prolong reaction time (Table 3,
entry 16). Similarly 1-fuoro-2,4-dinitrobenzene under present condition shows a
very low conversion (10%) and moderate selectivity (70%) toward the desired reduc-
tive-formylated product without afecting halogen group (Table 3, entry 17).
1 3

Z. S. Qureshi, E. A. Jaseer
Table 3 Reductive N-formylation of various nitroarenes using Pd/KCC-1-NH2
Entry
Nitroarenes
Time
(h)
Product
Conv.:Selec.:Yield
(%)[a]
H
N
NO2
H
1
2
3
4
5
6
3
3
3
3
3
3
99:100:99
O
H
N
NO2
CH3
H
99:97:96
99:99:98
92:99:91
99:84:81
99:98:96
O
CH3
H
N
H3
C
NO2
H
3C
H
H
O
H
N
NO2
O
H3
C
H3
C
H
N
NO2
H
O
OH
OH
H
NO2
N
H
O
HO
HO
H
NO2
N
H
H3
C
7
3
99:84:83
H3C
O
O
O
H
NO2
N
H
H
8[b]
9[b]
6
6
6
05:83:4.2
04:99:4.0
99:70:68
O
O
OHC
OHC
OHC
OHC
H
N
NO2
NO2
H
N
H
10[b]
O
HOOC
HOOC
O
O
H
NO2
N
H
H3CO
H3CO
11
3
93:99:92
O
H
NO2
N
H
12
1
6
99:96:95
86:16:14
O
O
O
O
O
13[b]
O
O2
N
N
H
O
O
O
H
N
OHC
HO
NO2
OHC
HO
H
14
6
3
00:00:00
99:97:96
N
NO2
NO2
15[b]
N
H
O2
N
NO2
O2
N
NH2
16
17
9
6
99:100:97
10:70:7.0
COOH
COOH
H
O2
N
NO2
F
O2N
N
H
O
F
1 3

Efective and selective direct aminoformylation of nitroarenes…
Table 3 (continued)
Nitroarenes (1 mmol), Toluene (3 mL), Pd/KCC-1-NH2 (10 mg, 0.038 mol%), formic acid (6 mmol),
temperature (70 °C), stirring 500 rpm
aYield of N-formylated products determined by GC–MS; else specifed, no other products were detected
bTHF (3 mL) as solvent
100%
80%
60%
40%
20%
0%
1
2
3
4
5
6
7
Catalytic cycle
Fig. 6 Reusability of Pd/KCC-1-NH2 nanocatalyst for the reductive formylation of nitrobenzene.
Nitrobenzene (1 mmol), toluene (3 mL), Pd/KCC-1-NH2 (10 mg, 0.038 mol%), formic acid (6 mmol),
temperature (70 °C), Time 3 h, stirring 500 rpm
Results of the Pd/KCC-1-NH2 recycling run are shown in Fig. 6. The reduc-
tive-formylation of nitrobenzene in toluene was selected to test the reusability of
the efcient nanocatalyst, Pd/KCC-1-NH2. After completion of the frst reaction,
the nanocatalyst was retrieved by simple centrifugation, washed with methanol
and acetone consecutively and dried under vacuum for 4 h at 65 °C. The recov-
ered catalyst was recycled seven times under the same reaction conditions and
was found to maintain high activity and selectivity with no noticeable reduction
in catalytic efciency (98% yield at the seventh cycle, Figure S2), thus endors-
ing the highly robustness of the catalyst.
At the end of the reaction and after the catalyst separation, palladium leach-
ing into the reaction media was analyzed by the product’s inductively coupled
plasma—optical emission spectrometry (ICP-OES). Palladium concentration
in the solution was found to be negligible, i.e., below the observable value of
0.01 ppm, which clearly show no substantial leaching of palladium. This may
be attributed to the anchorage of APTES amino groups with the metal particles
over the KCC-1 surface, which prevent the leaching and agglomeration [66]. To
conclude, whether the catalysis initiated from heterogeneous nanocatalyst Pd/
KCC-1-NH2 or from the homogeneous palladium bits leaked during progress of
reaction, a hot-flter check was performed. In hot conditions, the Pd/KCC-1-NH2
catalyst was fltered out when the reaction time is 1 h and later allows the fltrate
to react more, Pd/KCC-1-NH2 catalyst has been fltered out when the reaction
time is 1 h and later allows the flter to react more, no further substrate conver-
sion has been detected [67].
1 3

Z. S. Qureshi, E. A. Jaseer
Conclusions
In conclusion, we have successfully prepared a fbrous silica nanospheres KCC-1
supported Pd NPs catalyst (Pd/KCC-1-NH2) by a simple and cost efcient method
with average size of the monodispersed Pd NPs about ~1–3 nm. The Pd/KCC-
1-NH2 nanocatalyst has been found to be an impressive catalyst for the one step
reductive-formylation of nitroarenes during short reaction time. Pd/KCC-1-NH2
nanocatalyst efciently catalyzed for the variety of nitroarenes giving good to the
excellent yields of the desired reductive-formylated products. Without any loss of
activity and selectivity the catalytic process could be efectively cycled seven times.
Acknowledgements The research reported in this publication was supported by center for refning and
petrochemicals, King Fahd University of Petroleum & Minerals (KFUPM), Saudi Arabia.
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