A highly effective green catalyst Ni/Cu bimetallic nanoparticles supported by dendritic ligand for chemoselective oxidation and reduction reaction

Article abstract of DOI:10.1007/s11696-020-01480-z

The highly active Ni/Cu bimetallic nanoparticles (NPs) of the different molar ratios of Ni and Cu (1:1, 1:3, 3:1) assisted by dendritic ligand 2,4,6-Tris (di-4-chlorobenzamido)-1,3-diazine were synthesized successfully confirmed by Scanning Electron Microscopy (SEM), Electron Diffraction X-ray (EDX), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM) analysis. These NPs were studied as a heterogeneous catalyst for the chemoselective oxidation of alcohol to the corresponding aldehyde at 30?min and chemoselective reduction of aromatic nitro substituents to the corresponding amino substituents at 20?min, while the Ni/Cu (3:1) NPs were found to be the most effective among other Ni/Cu?(1:1)?and Ni/Cu?(1:3)?NPs at room temperature under mild conditions. The Ni/Cu (3:1) NPs can be recycled for at least five successive runs with no perceptible decrease in catalytic activity. Graphic abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s11696-020-01480-z

Chemical Papers (2021) 75:2353–2369
https://doi.org/10.1007/s11696-020-01480-z
ORIGINAL PAPER
A highly efective green catalyst Ni/Cu bimetallic nanoparticles
supported by dendritic ligand for chemoselective oxidation
and reduction reaction
Md. Sayedul Islam1 · Md. Wahab Khan1
Received: 25 May 2020 / Accepted: 18 December 2020 / Published online: 6 January 2021
© Institute of Chemistry, Slovak Academy of Sciences 2021
Abstract
The highly active Ni/Cu bimetallic nanoparticles (NPs) of the diferent molar ratios of Ni and Cu (1:1, 1:3, 3:1) assisted
by dendritic ligand 2,4,6-Tris (di-4-chlorobenzamido)-1,3-diazine were synthesized successfully confrmed by Scanning
Electron Microscopy (SEM), Electron Difraction X-ray (EDX), X-ray fuorescence spectroscopy (XRF), X-ray difraction
(XRD), and Transmission Electron Microscopy (TEM) analysis. These NPs were studied as a heterogeneous catalyst for
the chemoselective oxidation of alcohol to the corresponding aldehyde at 30 min and chemoselective reduction of aromatic
nitro substituents to the corresponding amino substituents at 20 min, while the Ni/Cu (3:1) NPs were found to be the most
efective among other Ni/Cu (1:1) and Ni/Cu (1:3) NPs at room temperature under mild conditions. The Ni/Cu (3:1) NPs
can be recycled for at least fve successive runs with no perceptible decrease in catalytic activity.
Graphic abstract
Ar-NO2
R-CH2OH/ R2-CHOH
H2O, Room temp., 20 min
H2O, Room temp., 30 min
Ni/Cu (3:1) 4c NPs (4.0 mol%)
Ni/Cu (3:1) 4c NPs (4.0
Ar-NH2
mol%)
10 Examples, up to 97 % yield
R-CHO/ R2-CO
Ni/Cu (3:1) 4c NPs
11 Examples, up to 94 % yield
Keywords Dendritic · Nickel/copper bimetallic nanoparticles · Chemoselective · Oxidation · Reduction
Introduction
One of the signifcant chemical procedures for the synthe-
sis of specifc compounds is chemoselective oxidation of
alcohols; it provides essential synthetics such as aldehydes,
ketones, and carboxylic acids. Stoichiometric oxidation pro-
cedures applying homogeneous oxidants such as KMnO4,
K2Cr2O7, and also the oxidation process catalyzed by the
metal-complexes (Gong et al. 2016; Harada et al. 2010) have
a long tradition of the oxidation reaction.
Supplementary Information The online version contains
supplementary material available at https://doi.org/10.1007/s1169
6-020-01480-z.
* Md. Wahab Khan
mwkhan@chem.buet.ac.bd
Md. Sayedul Islam
sayedulbuet98@gmail.com
Also, in the chemical, petroleum, pharmaceutical, and
agricultural industries, the chemoselective reduction of nitro
compounds to the resulting amines is a crucial procedure
1
Department of Chemistry, Faculty of Engineering,
Bangladesh University of Engineering and Technology
(BUET), Dhaka 1000, Bangladesh
Vol.:(0123456789)
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Chemical Papers (2021) 75:2353–2369
(Hosseini-Sarvari and Razmi 2015); as a consequence of
ordinarily using amines and their derivatives as intermedi-
ate for colorants of azo dyes, pigments in industrial chemi-
cals and also in bioactive substances, medicinal, pesticides,
insecticides, and fungicides (Yang et al. 2012a, b; Mondal
and Purkait 2017; Harraz et al. 2012).
as palladium, gold, platinum, etc. assisted by other ligands.
These are crucial challenges from the eco, economic, and
safety perspectives (Chalker et al. 2009; Chatterjee and
Ward 2016).
Moreover, dendrimers are efective stabilizers in NPs’
formation as they stabilize the nanoparticles through steric
efects and create the NPs surface availability for catalytic
reactions and also form size-specifc dispersed NPs (Islam
and Khan 2019). Also, the dendritic ligands can prevent
agglomeration during the catalytic run and avoid oxidation
of the sensitive active metal surface and enhance the cata-
lytic activity of nanoparticles (Islam and Khan 2020).
However, such noble metals are expensive as rare sup-
plies, and, nevertheless their extraordinary specifcities, the
high price of noble metals creates unattractive to use as a
catalyst. This paved the way for developing the most efec-
tive, cheap, non-noble nanometal-based catalysts which will
be immensely proftable (Rezaei et al. 2018; Lee et al. 2010).
In recent times, Ni-based bimetallic NPs such as Ni–Cu,
Ni–Co, and Ni–Sn were applied as an extremely active cata-
lyst in the various reactions (Sharma et al. 2019).
However, after forming the products, these general meth-
ods have noteworthy drawbacks resulting from the removal
of salts, the separation of catalysts, and the refning of the
yields. Therefore, it is essential to improve green catalytic
methods under benign conditions to synthesis pure alde-
hydes, ketones, and amines through selective oxidation and
reduction reactions.
Signifcantly, heterogeneous bimetallic NPs have revealed
tremendous interest as catalysts in recent times. Bimetal-
lic NPs are typically formed to lower the cost of a catalyst
(An and Somorjai 2015; Shao et al. 2006) and/or to raise a
monometal catalyst’s characteristics (Dimitratos et al. 2012;
Yang et al. 2012a, b). Maximum bimetallic NPs consist of
a transition metal and a precious metal such as Au, and Pt,
and a 3d transition metal involving Fe, Co, Ni, or Cu (An
and Somorjai 2015; Yang et al. 2012a, b). These kinds of
particles are used to catalyze several reactions including
oxidation (Pritchard et al. 2010; Alhumaimesset al.2012;
Balcha et al. 2011) and hydrogenation (Liuet al. 2016). The
advantages of using bimetallic NPs as catalysts due to their
vast surface area and tuning efect increase the number of
active sites on which reaction can take place, as a result,
increases the rate of a reaction (Balcha et al. 2011).
Herein, we have studied rapid chemo-selective oxidation
of alcohol into aldehyde and reduction of the nitro group into
the amino group in the presence of another sensitive group
of the same compound in the presence of water as solvent
catalyzed by the more active dendritic ligand supported Ni/
Cu (3:1) 4c bimetallic NPs than other Ni/Cu (1:1) 4a and
Ni/Cu (1:3)4b at room temperature under green reaction
conditions. The Ni/Cu (3:1) 4c bimetallic NPs were found
as a heterogeneous catalyst and can be recycled at least fve
consecutive runs without any loss of activity.
Recently, the noble bimetallic catalyst such as Au–Pd,
Au–Ag, Au–Ni, Cu–Ni, and Ni–Co have been stated to be
highly catalytic active in selective benzyl alcohol oxidation
to benzaldehyde under moderate conditions (Sun et al. 2017;
Alshammari et al. 2017; Liu et al. 2018; Kimi et al.2018).
Furthermore, metal NPs based on noble metals (Pt, Pd, Au,
etc.) have shown the extraordinary activity for reduction of
the nitro group using H2, NaBH4, N2H4·H2O, etc. conditions
(Zhang et al. 2016; Wuet al. 2012).
Experimental section
Materials
All reagents are reagent graded and used without purifca-
tion unless otherwise stated. Reaction solvent was deionized
water used in the experiment. All the used reagents 2,4,6-Tri-
aminopyrimidine (97%), 4-Chlorobenzoyl chloride (99%),
Benzyl alcohol (anhydrous, 99.8%), 4-Methylbenzyl alcohol
(98%), 4-Chlorobenzyl alcohol (99%), 4-Fluorobenzyl alco-
hol (97%), Furfuryl alcohol (98%), 2-Thiophenemethanol
(98%), 1-(p-Tolyl)ethanol (≥ 97.0%), 1-(4-chlorophenyl)
ethanol (98%), 1-(4-(hydroxymethyl)phenyl)ethanol (98%),
4-Nitrophenol (≥ 99%), Nitrobenzene (99%), 2-Nitroben-
zaldehyde (98%), 4-nitrobenzoic acid (98%), 4-nitroben-
zaldehyde (98%), 1-azido-4-nitrobenzene (98%), methyl
4-nitrobenzoate (99%), 1-Fluoro-4-nitrobenzene (99%),
Copper(I) iodide (98%), Hydrazine monohydrate (rea-
gent grade, 98%), Nickel(II) chloride hexahydrate (99.9%
trace metals basis) from Sigma-Aldrich/Merck, USA, and
Noticeably, dendritic ligands based on diazine, particu-
larly pyrimidine, have been drawn among other dendritic
molecules owing to cheap cost, selective molecular reactiv-
ity recognition, and synthetic versatility (Yagai et al. 2019;
Vollhardt et al. 2005). Most notably, pyrimidine’s molecular
recognition can defne certain molecules through donation
and acceptance of hydrogen bonds, metal chelation, and
interactions with π–π. This capability has enabled many
supramolecular structures and various forms of attractive
oligomers and polymers that are needed to support metal
nanoparticles (Vollhardt et al. 2005; Zimmerman and
Lawless 2001). Low-priced bimetallic nickel–copper NPs
catalytic systems supported by pyrimidine-based dendritic
ligand make recyclable and reusable catalysts, minimizing
particulate leaching relative to other costly metal NPs such
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Chemical Papers (2021) 75:2353–2369
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1-(4-nitrophenyl) ethanone (98%), 1-nitro-4-thiocyanatoben-
zene (98%) from Finetech Industry Limited, England, and
also 2-(p-Tolyl)ethanol (98.0+%) from TCI America, USA
were purchased.
water was added and the crude product was extracted with
CHCl3. After removing the solvent under reduced pressure,
the crude product was run through silica gel column chroma-
tography (n-hexane/ethylacetate 1:8). Finally, the dendritic
product (3) was obtained after further purifcation by recrys-
tallization with ethanol.
Methods
White crystalline solid, 90% yield, mp. 308–310 °C,
A melting point system (Model BUCHI, B-540) was used
to calculate melting points through open capillary tubes.
Purifcation of dendritic ligand and other products was per-
formed by silica gel column chromatography on silica gel
60 N (neutral, 40–100 μM). Analytical thin-layer chroma-
tography (TLC) of silica gel 60 F254 coated on 25 TCC
aluminum sheets (20 × 20 cm) was used to monitor the
reaction. Shimadzu’s new-generation GC-2025 capillary
gas chromatography was used to measure the percentage of
conversion of alcohol and diferent substituted aromatic nitro
compounds. The Shimadzu FT-IR 8400S Fourier Transform
Infrared spectrophotometer was used to detect the IR spec-
tra with KBr pellets (400–4000 cm−1). 1H NMR (400 MHz,
Bruker) and 13C NMR (100 MHz, Bruker) were recorded
at 400 MHz and 100 MHz, respectively. Chemical shifts
related to TMS were calculated. Elemental analyses of den-
dritic ligand and all solid products were carried out with
a Fisons EA 1108 CHNS-O apparatus. JEOL-JSM-7600F
was used to take surface morphology and elemental com-
position of all Ni/Cu of bimetallic NPs through SEM and
EDX investigation. The X-RAY FLUORESCENCE (XRF)
analysis to study the ratio of the metal composition of all
Ni/Cu NPs was carried out by LAB CENTER XRF-1800
SEQUENTIAL X-RAY FLUORESCENCE SPECTROM-
ETER. The TEM analysis of all nanoparticles was done
by Thermo Scientifc Talos F200X Transmission Electron
Microscope (TEM) to measure the average nanosize of the
particles and phase was observed by a PANANALYTICAL
X-ray difractometer (XRD). Perkin Elmer ELAN DRC E
ICP/MS was used to study the leaching of Ni and Cu after a
catalytic run of the Ni/Cu NPs catalyst.
Mol. Wt.: 956.44, IR (KBr): µmax (cm−1) 3094.89,
1
1680.20, 1592.29, 1424.489, 1092.71, 780.20. H NMR
(400 MHz, CDCl3): δH (ppm) 4.62 (s, 1H, Ar–H), 7.65 (d,
12H, J=8.8 Hz, Ar–H), 8.28 (d, 12H, J=8.8 Hz, Ar–H). 13
C
NMR (100 MHz, CDCl3): δC (ppm) 71.88, 126.65, 129.62,
133.25, 138.25, 167.24, 170.16, 172.42. Anal. Calcd. for
C46H25Cl6N5O6: C, 57.77; H, 2.63; N, 7.32; Found: C, 57.70;
H, 2.60; N, 7.30.
Synthesis of Ni/Cu (1:1) 4a, Ni/Cu (1:3) 4b, and Ni/Cu
(3:1) 4c bimetallic NPs by co‑complexation method
General procedure—nickel chloride (0.5 g, 0.0038 M)
and copper iodide (0.734 g, 0.0038 M) (molar ratio
1:1)/0.0038 M nickel chloride (0.5 g) and 0.0114 M copper
iodide (2.204 g) (molar ratio 1:3)/nickel chloride (1.020 g,
0.0078 M) and copper iodide (0.5 g, 0.00262 M) (molar ratio
3:1) were dissolved and stirred separately in 10 mL ethanol
containing dendritic ligand 3 (0.5 g) in three R.B fask by
the addition of 10 mL hydrazine hydrate. A few drops of 1 M
KOH were introduced with continuous stirring for main-
taining pH=11.0, and then, the temperature of the reaction
mixture was maintained at 120 °C for 2 h. The precipitation
of these bimetallic nanoparticles was separated, washed with
ethanol, and dried at 100 °C overnight.
General procedure for the selective oxidation
of alcohol to the aldehyde using Ni/Cu (3:1) 4c
bimetallic NPs as a catalyst
In a round-bottom fask, alcohol (1.0 mmol) and Ni/Cu
(3:1) 4c of 4.0 mol% catalyst were added to water (5.0 mL)
and the mixture was stirred for 30 min at room temperature.
The reaction progress and conversion of the reactants were
monitored by gas chromatography (GC). The reaction mix-
ture was centrifuged at 4,000 rpm after the complete conver-
sion of alcohol into aldehyde or ketone due to isolating the
catalyst and was fltered. Finally, the desired pure products
were obtained from the run through silica gel column chro-
matography (n-hexane/ethylacetate 10:1).
Synthesis and characterization of dendritic ligand
2,4,6‑Tris (di‑4‑chlorobenzamido)‑1,3‑diazine (3)
and Ni/Cu (1:1) 4a, Ni/Cu (1:3) 4b, and Ni/Cu
(3:1) 4cbimetallic NPs
Dendritic ligand 2,4,6‑tris
(di‑4‑chlorobenzamido)‑1,3‑diazine (3)
In a round-bottom fask, the mixture of 2,4,6-triaminopy-
rimidine (0.2 g, 0.00159 mmol) 1 and 4-Chlorobenzoyl
chloride 2 (3 mL, 9.50 mmol) was introduced in 10 mL of
DMF was stirred at 90 °C temperature for 9 h. The reac-
tion advancement was observed by thin-layer chromatogra-
phy (TLC). After the complete reaction reactants, distilled
Benzaldehyde (13) (Pan et al. 2018)
Colorless oil, 90% yield (Table 3, entry 1), 1H NMR (CDCl3,
400 MHz): δH (ppm) 7.52–7.68 (m, 3H, Ar–H); 8.10 (d, 2H,
J=8.8 Hz, Ar–H); 9.18 (s, 1H, CHO).
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Chemical Papers (2021) 75:2353–2369
4‑Methylbenzaldehyde (14) (Pan et al. 2018)
(d, 1H, J = 4.8 Hz, Ar–H); 9.99 (s, 1H, CHO). 13C NMR
(CDCl3, 100 MHz): δC (ppm) 112.00, 121.70, 149.94,
153.22, 178.24.
Colorless oil, 94% yield (Table 3, entry 2), Mol. Wt.:
120.15,1H NMR (CDCl3, 400 MHz): δH (ppm) 2.62 (s,
3H, CH3); 7.76 (d, 2H, J = 8.0 Hz, Ar–H); 8.69 (d, 2H,
J = 8.0 Hz, Ar–H); 9.88 (s, 1H, CHO). 13C NMR (CDCl3,
100 MHz): δC (ppm) 25.45, 129.33, 129.47, 135.20,
144.24, 191.07.
Thiophene‑2‑carbaldehyde (20) (Pan et al. 2018)
Yellow oil, 81% yield (Table 3, entry 8), Mol. Wt.:
112.15, 1H NMR (CDCl3, 400 MHz):δH (ppm) 6.30 (t, 1H,
J=8.0 Hz, Ar–H); 7.38–7.43 (m, 2H, Ar–H); 9.50 (s, 1H,
CHO). 13C NMR (CDCl3, 100 MHz): δC (ppm) 127.70,
135.35, 137.32, 143.23, 182.24.
2‑p‑Tolylacetaldehyde (15)
Colorless oil, 85% yield (Table 3, entry 3), Mol. Wt.:
1
1‑p‑Tolylethanone (23)
134.18, H NMR (CDCl3, 400 MHz): δH (ppm) 2.20 (s,
3H, CH3), 3.76 (d, 2H, J = 8.0 Hz, CH2); 6.98 (s, 4H,
Ar–H); 9.87 (t, 1H, J = 4.0 Hz, CHO). 13C NMR (CDCl3,
100 MHz): δC (ppm) 25.00, 50.00, 129.00, 134.44, 137.24,
200.24.
Colorless liquid, 86% yield (Table 4, entry 1), Mol. Wt.:
134.18,1H NMR (CDCl3, 400 MHz):δH (ppm) 2.37 (s,
3H, CH3); 2.72 (s, 3H, CH3); 7.76 (d, 2H, J = 8.0 Hz,
Ar–H); 8.79 (d, 2H, J=8.0 Hz, Ar–H). 13C NMR (CDCl3,
100 MHz): δC (ppm) 24.45, 28.46, 128.33, 129.94, 134.12,
142.24, 200.00.
4‑Chlorobenzaldehyde (16) (Pan et al.2018)
Colorless solid, 84% yield (Table 3, entry 4), mp.
1‑(4‑Chlorophenyl)ethanone (24) (Addis et al. 2010)
1
45–47 °C (lit. 44–46 °C), Mol. Wt.: 140.57, H NMR
(CDCl3, 400 MHz): δH (ppm) 7.79 (d, 2H, J = 8.0 Hz,
Ar–H); 8.16 (d, 2H, J=8.0 Hz, Ar–H); 9.87 (s, 1H, CHO).
13C NMR (CDCl3, 100 MHz): δC (ppm) 129.00, 132.44,
135.45, 140.54, 192.00. Anal. Calcd. for C7H5ClO: C,
59.81; H, 3.59; Found: C, 59.78; H, 3.50.
Colorless solid, 85% yield (Table 4, entry 2), mp. 75–77 °C,
(lit. 74–76 °C), Mol. Wt.: 154.59,1H NMR (CDCl3,
400 MHz): δH (ppm) 2.28 (s, 3H, CH3); 2.72 (s, 3H, CH3);
7.67 (d, 2H, J = 7.6 Hz, Ar–H); 8.10 (d, 2H, J = 8.8 Hz,
Ar–H). 13C NMR (CDCl3, 100 MHz): δC (ppm) 30.00,
129.00, 130.00, 134.54, 137.34, 200.33.Anal. Calcd. for
C8H7ClO: C, 62.15; H, 4.56; Found: C, 62.15; H, 4.56.
4‑Fluorobenzaldehyde (17) (Pan et al. 2018)
Colorless oil, 82% yield (Table 3, entry 5), Mol. Wt.:
4(1‑Hydroxyethyl)benzaldehyde (26) (Jiang and Ma 2018)
1
124.11, H NMR (CDCl3, 400 MHz): δH (ppm) 6.89 (d,
2H, J = 8.0 Hz, Ar–H); 7.59 (d, 2H, J = 8.4 Hz, Ar–H);
9.86 (s, 1H, CHO). 13C NMR (CDCl3, 100 MHz): δC
(ppm) 116.72, 130.43, 133.43, 167.74, 192.23.
.Colorless oil, 82% yield (Table 5, entry 2), Mol. Wt.:
150.17, 1H NMR (CDCl3, 400 MHz): δH (ppm) 1.61 (s, 3H,
CH3); 2.11 (s, 1H, OH); 4.42–4.50 (m, 1H, CH), 7.76 (d, 2H,
J=8.0 Hz, Ar–H); 8.69 (d, 2H, J=8.0 Hz, Ar–H); 9.89 (s,
1H, CHO). 13C NMR (CDCl3, 100 MHz): δC (ppm) 22.77,
75.76, 116.76, 120.14, 130.23, 152.24, 166.24.
(Z)‑3,7‑Dimethylocta‑2,6‑dienal (18)
Colorless oil, 80% yield (Table 3, entry 6), Mol. Wt.:
1
General procedure for the selective reduction
of the nitro group of diferent compounds using Ni/
Cu (3:1) 4c bimetallic NPs as a catalyst
152.23, H NMR (CDCl3, 400 MHz): δH (ppm) 1.30 (s,
9H, CH3); 2.01 (d, 4H, J = 7.6 Hz, CH2); 5.00 (s, 1H,
CH), 5.63 (d, 1H, J=0.4 Hz, CH); 9.86 (d, 1H, J=0.4 Hz,
CHO). 13C NMR (CDCl3, 100 MHz): δC (ppm) 19.40,
22.40, 25.79, 33.46, 123.13, 128.24, 132.56, 164.07,
192.07.
In a round-bottom fask, 1.0 mmol of the nitro substrate was
provided in 5 ml of distilled water. By adding 0.5 mmol
hydrazine hydrate and catalyst Ni/Cu (3:1) 4c of 4.0 mol%
to this solution and stirring the reaction mixture at room
temperature for 20 min. Gas chromatography (GC) was
used to observe the movement of the reaction and to detect
the conversion of the reactants. The reaction mixture was
centrifuged at 4,000 rpm after completion of the reaction
and fltered to isolate the catalyst. Eventually, from the run
Furan‑2‑carbaldehyde (19) (Pan et al. 2018)
Yellow oil, 82% yield (Table 3, entry 7), Mol. Wt.:
96.08,1H NMR (CDCl3, 400 MHz):δH (ppm) 6.45 (t, 1H,
J = 7.6 Hz, Ar–H); 7.89 (d, 1H, J = 4.8 Hz, Ar–H); 8.10
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Chemical Papers (2021) 75:2353–2369
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through silica gel column chromatography (n-hexane/ethy-
lacetate 10:1), the targeted pure products were collected.
C7H7NO: C, 69.41; H, 5.82; N, 11.56; Found: C, 69.38; H,
5.79; N, 11.51.
4‑Aminophenol (37)
4‑Azidobenzenamine (42) (Pagoti et al.2013)
White solid, 96% yield (Table 7, entry 1), mp. 182–184 °C
(lit. 181–183 °C) (Takasaki et al. 2008).
Brown crystalline solid, 93% yield (Table 7, entry 6), mp.
1
164–166 °C (Lit. 165 °C), Mol. Wt.: 134.14, H NMR
Mol. Wt.: 109.13, 1H NMR (CDCl3, 400 MHz): δH (ppm)
4.00 (s, 2H, NH2); 5.20 (s, 1H, OH); 6.16–6.19 (dd, 2H,
J = 4.0, 2.0 Hz); 6.45–6.48 (dd, 2H, J= 6.8, 4.0 Hz). 13C
NMR (CDCl3, 100 MHz): δC (ppm) 17.74, 118.84, 141.13,
148.43. Anal. Calcd. for C6H7NO: C, 66.04; H, 6.47; N,
12.84; Found: C, 66.00; H, 6.40; N, 12.81.
(CDCl3, 400 MHz): δH (ppm) 4.00 (s, 2H, NH2); 6.45 (d,
2H, J=8.8 Hz, Ar–H); 7.63 (d, 2H, J=8.0 Hz, Ar–H). 13
C
NMR (CDCl3, 100 MHz): δC (ppm) 166.66, 130.23, 136.22,
149.24. Anal. Calcd. for C6H6N4: C, 53.72; H, 4.51; N,
41.77; Found: C, 53.70; H, 4.49; N, 41.70.
Methyl 4‑aminobenzoate (43) (Takasaki et al. 2008)
Aniline (38)
Slightly brown crystalline solid, 91% yield (Table 7, entry
7), mp. 101–102 °C (Lit. 102–103 °C); Mol. Wt.: 151.16, 1H
NMR (CDCl3, 400 MHz): δH (ppm) 3.66 (s, 3H, CH3), 4.16
(s, 2H, NH2); 6.66 (d, 2H, J=4.0 Hz, Ar–H); 7.75 (d, 2H,
J=8.0 Hz, Ar–H). 13C NMR (CDCl3, 100 MHz): δC (ppm)
50.77, 116.76, 120.14, 130.23, 152.24, 166.23. Anal. Calcd.
for C8H9NO2: C, 63.56; H, 6.00; N, 9.27; Found: C, 63.50;
H, 5.98; N, 9.21.
Colorless liquid, 88% yield (Table 7, entry 2), Mol. Wt.:
1
93.13, H NMR (400 MHz): δH (ppm) 4.00(s, 2H, NH2);
7.16 (d, 2H, J = 4.0 Hz); 7.41–7.56 (m, 1H); 8.04 (d, 2H,
J=8.0 Hz).
2‑Aminobenzaldehyde (39) (Reddy et al. 2015)
Yellow solid, 97% yield (Table 7, entry 3), mp. 33–35 oC,
(Lit. 32–34 °C).
1‑(4‑Aminophenyl)ethanone (44) (Currall and David
Jackson 2014)
Mol. Wt.: 121.14, 1H NMR (CDCl3, 400 MHz): δH (ppm)
4.00 (s, 2H, NH2); 6.86 (d, 1H, J = 2.8 Hz); 7.40 (t, 1H,
J=5.6 Hz); 7.70 (d, J=4.0, 1H); 10.40 (s, 1H, CHO). 13
C
Brown crystalline solid, 93% yield (Table 7, entry 8), mp.
104–106 °C, (Lit. 103–105 °C), Mol. Wt.: 135.6, 1H NMR
(CDCl3, 400 MHz): δH (ppm) 2.56 (s, 3H, CH3), 4.26 (s,
2H, NH2); 6.56 (d, 2H, J = 4.0 Hz, Ar–H); 7.66 (d, 2H,
J=8.0 Hz, Ar–H). 13C NMR (CDCl3, 100 MHz): δC (ppm)
30.77, 116.78, 127.77, 130.24, 152.14, 160.24.
NMR (CDCl3, 100 MHz): δC (ppm) 117.34, 119.00, 130.23,
131.34, 135.12, 150.23, 200.00. Anal. Calcd. for C7H7NO:
C, 69.41; H, 5.82; N, 11.56; Found: C, 69.39; H, 5.78; N,
11.50.
4‑Aminobenzoic acid (40) (Takasaki et al. 2008)
Anal. Calcd. for C8H9NO: C, 71.09; H, 6.71; N, 10.36;
Found: C, 71.00; H, 6.69; N, 10.30.
White–gray crystals, 91% yield (Table 7, entry 4), mp.
188–190 °C (Lit. 187–189 °C), Mol. Wt.: 137.14, 1H NMR
(CDCl3, 400 MHz): δH (ppm) 4.11 (s, 2H, NH2); 6.66 (d,
2H, J=4.0 Hz, Ar–H); 7.76 (d, 2H, J=8.4 Hz, Ar–H); 10.88
(s, 1H, COOH). 13C NMR (CDCl3, 100 MHz): δC (ppm)
116.33, 120.47, 132.33, 153.14, 170.24. Anal. Calcd. for
C7H7NO2: C, 61.31; H, 5.14; N, 10.21, Found: C, 61.28; H,
5.11; N, 10.18.
4‑Thiocyanatobenzenamine (45)
Brown crystalline solid, 95% yield (Table 7, entry 9), mp.
115–117 °C, Mol. Wt.: 150.2, 1H NMR (CDCl3, 400 MHz):
δH (ppm) 4.04 (s, 2H, NH2); 6.20 (d, 2H, J = 8.0 Hz,
Ar–H); 6.73 (d, 2H, J=8.0 Hz, Ar–H). 13C NMR (CDCl3,
100 MHz): δC (ppm) 112.33, 114.47, 117.77, 132.24,
151.14. Anal. Calcd. for C7H6N2S.
4‑Aminobenzaldehyde (41) (Sharif et al. 2014)
: C, 55.97; H, 4.03; N, 18.65; S, 21.35, Found: C, 55.90;
H, 4.00; N, 18.61; S, 21.31.
Yellow solid, 96% yield (Table 7, entry 5), mp. 34–36 oC,
1
(Lit. 33–35 °C), Mol. Wt.: 121.14, H NMR (CDCl3,
4‑Fluorobenzenamine (46) (Ishikawa 1994)
400 MHz): δH (ppm) 4.12 (s, 2H, NH2); 6.46 (d, 2H,
J=4.0 Hz, Ar–H); 7.46 (d, 2H, J=4.4 Hz, Ar–H); 9.88 (s,
1H, CHO). 13C NMR (CDCl3, 100 MHz): δC (ppm) 116.78,
126.67, 130.34, 154.44, 160.24, 190.24. Anal. Calcd. for
Oily Liquid, 87% yield (Table 7, entry 10), Mol. Wt.:
1
111.12, H NMR (CDCl3, 400 MHz): δH (ppm) 4.10 (s,
2H, NH2); 6.13–6.20 (m, 2H, Ar–H); 6.45–6.58 (m, 2H,
1 3

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Chemical Papers (2021) 75:2353–2369
Ar–H). 13C NMR (CDCl3, 100 MHz): δC (ppm) 116.76,
117.76, 142.23, 152.14.
Synthesis and characterization of Ni/Cu (1:1) 4a,
Ni/Cu (1:3) 4b, and Ni/Cu (3:1) 4c bimetallic
NPs supported by dendritic ligand 2,4,6‑Tris
(di‑4‑chlorobenzamido)‑1,3‑diazine (3)
Results and discussion
Dendritic ligand 2,4,6-Tris (di-4-chloro benzamido)-1,3-dia-
zine supported Ni/Cu (1:1) 4a bimetallic NPs were prepared
by adding NiCl2·6H2O:CuI (1:1) to the ligand (3) in the pres-
ence of NH2.NH2.H2O and KOH in ethanol at 120 °C for 2 h
with stirring the reaction mixture.
Synthesis and characterization of dendritic ligand
2,4,6‑Tris (di‑4‑chlorobenzamido)‑1,3‑diazine (3)
Dendritic ligand 2,4,6-Tris (di-4-chlorobenzamido)-1,3-di-
azine (3) was prepared with a reaction of 2,4,6-Triamino-
pyrimidine (1), 4-chlorobenzoyl chloride (2) in anhydrous
DMF at 90 °C for 9 h (Scheme 1) (Islam and Khan 2019).
The product (3) was analyzed by IR, 1H NMR, 13C NMR,
and elemental analysis.
Similarly, 2,4,6-Tris (di-4-chlorobenzamido)-1,3-diazine-
supported Ni/Cu (1:3) 4a bimetallic NPs were prepared by
introducing NiCl2·6H2O: CuI (1:3) to the ligand (3) in the
presence of NH2·NH2·H2O and KOH in ethanol at 120 °C
for 2 h with stirring.
Also, 2,4,6-Tris (di-4-chloro benzamido)-1,3-diazine-
supported Ni/Cu (3:1) 4a bimetallic NPs were synthesized
by loading NiCl2·6H2O: CuI (3:1) to the ligand (3) in the
presence of NH2.NH2.H2O and KOH in ethanol at 120 °C
for 2 h with stirring.
In the IR spectrum of dendritic ligand (3) (S1 in the
supplementary information), the band at 3094.89 cm−1
and 1592.29 cm−1 indicates the C-H (aro) and C=N (aro)
stretching absorption, respectively, while the bands at
1424.48 cm−1 and 1092.71 cm−1 stretching bands specify
the existence of C=C (aro) and C–N (aro) correspond-
ingly. Particularly, the sharp band at 1620.20 cm−1 and
780.20 cm−1 signifes the C=O group and the aromatic
However, the dendritic ligand 2,4,6-Tris (di-
4-chlorobenzamido)-1,3-diazine (3) assisted Ni/Cu bimetal-
lic NPs of diferent molar ratios (1:14a, 1:34b, and 3:14c)
were synthesized by co-complexation method (Schemes 2, 3,
4) and also described by particular physicochemical methods
such as SEM, EDX, XRF, TEM, and XRD. The SEM images
of surface morphology of all Ni/Cu bimetallic NPs 4a, 4b,
and 4c display almost similar aggregated globular size of the
particle as well as the dendritic shape (Figs. 1, 2, 3).
I
C–Cl bond individually. Also, the H NMR (S2 in the
supplementary information), and 13C NMR spectrum (S3
in the supplementary information), as well as elemental
analysis, confrms the formation of compound (3).
Scheme 1 Synthesis of 2,4,6-
O
N
O
O
Tris (di-4-chlorobenzamido)-
H
N
H
1,3-diazine (3)
COCl
ClC6H4
N
C6H4Cl
N
N
DMF, 90 oC, 9 hrs
ClC6H4
ClC6H4
O
O
+
H
H
N
N
N
C6H4Cl
C6H4Cl
N
H
N
H
Cl
O
2
1
3
Scheme 2 Synthesis of 2,4,6-
Tris (di-4-chlorobenzamido)-
1,3-diazine supported Ni/Cu
(1:1) 4a bimetallic NPs
O
O
O
N
O
O
ClC6H4
N
N
C6H4Cl
ClC6H4
N
N
C6H4Cl
NiCl2·6H2O:CuI (1:1)
NH2.NH2.H2O, KOH
O
O
N
O
N
O
O
EtOH, 120 oC, 2 hrs
ClC6H4
ClC6H4
N
C6H4Cl
ClC6H4
ClC6H4
N
N
C6H4Cl
C6H4Cl
O
C6H4Cl
O
3
4a
1 3

Chemical Papers (2021) 75:2353–2369
2359
Scheme 3 Synthesis of 2,4,6-
Tris (di-4-chlorobenzamido)-
1,3-diazine supported Ni/Cu
(1:3) 4b bimetallic NPs
O
N
O
O
O
O
N
O
O
O
ClC6H4
N
N
C6H4Cl
ClC6H4
N
N
C6H4Cl
NiCl2·6H2O:CuI(1:3)
NH2.NH2.H2O, KOH
O
O
N
O
O
N
EtOH, 120 oC, 2 hrs
ClC6H4
ClC6H4
N
C6H4Cl
ClC6H4
ClC6H4
N
C6H4Cl
C6H4Cl
C6H4Cl
3
4b
Scheme 4 Synthesis of 2,4,6-
Tris (di-4-chlorobenzamido)-
1,3-diazine supported Ni/Cu
(3:1) 4c bimetallic NPs
O
N
O
O
O
O
N
O
O
O
ClC6H4
N
N
C6H4Cl
ClC6H4
N
N
C6H4Cl
NiCl2·6H2O:CuI (3:1)
NH2.NH2.H2O, KOH
O
O
N
O
O
N
EtOH, 120 oC, 2 hrs
ClC6H4
ClC6H4
N
C6H4Cl
ClC6H4
ClC6H4
N
C6H4Cl
C6H4Cl
C6H4Cl
3
4c
Fig. 1 SEM of Ni/Cu (1:1) 4a
Fig. 3 SEM of Ni/Cu (3:1) 4c
The investigated EDX results of these synthesized Ni/Cu
bimetallic NPs have established the formation of the three
diferent molar ratios of nanoparticles. Figure 4 exhibits the
elemental composition, i.e., copper (40.69% of mass) and
nickel (39.80%% of mass) that specifes the formation of
Ni/Cu (1:1) 4a bimetallic NPs. Likewise, Fig. 5 displays
the amount of copper (17.12% of mass) and nickel (5.82%
of mass) that indicates the creation of Ni/Cu (1:3) 4b
NPs. Similarly, Fig. 6 shows the amount of element nickel
(17.82% of mass) and copper (5.12% of mass) that confrms
the growth of Ni/Cu (3:1) 4c.
However, Table 1 demonstrates the observed XRF results
of the synthesized three diferent Ni/Cu (1:1) 4a, Ni/Cu (1:3)
4b, and Ni/Cu (3:1) 4c bimetallic NPs which supports the
Fig. 2 SEM of Ni/Cu (1:3) 4b
1 3

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Chemical Papers (2021) 75:2353–2369
Fig. 4 EDX analysis of Ni/Cu (1:1)4a
Fig. 5 EDX analysis of Ni/Cu (1:3)4b
EDX result of these NPs and confrms that the preparation
method of these bimetallic NPs was successful.
cubic cuprous oxide phase in the three Ni/Cu (1:1) 4a, Ni/
Cu (1:3) 4b, and Ni/Cu (3:1) 4c bimetallic NPs. Conversely,
Fig. 7 shows that the nonappearance of any typical peaks of
CuO of XRD patterns, suggesting that a pure cuprous oxide
phase was formed in these NPs.
Figure 7 presents that the peaks at 2 theta (2Ɵ) values
of 36.20 and 61.30 degrees matching to the crystal planes
of (111) and (220), respectively, compared with the Inter-
national Center of Diffraction Data Card (JCPDS card
77–0199) for Cu2O powder of X-ray difraction analysis
(Lee et al. 2010) have proven the existence of the single
Also, Fig. 7 displays that the prominent XRD peaks at
43.50, 51.00, and 74.90 degrees relating to (111), (200), and
(220) planes specify the FCC phase of Cu NPs (JCPDS card
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Chemical Papers (2021) 75:2353–2369
2361
Fig. 6 EDX analysis of Ni/Cu (3:1) 4c
Table 1 Quantitative results of XRF analysis of three diferent Ni/Cu
(1:1) 4a, Ni/Cu (1:3) 4b, and Ni/Cu (3:1) 4c bimetallic NPs
with the JCPDS General Powder Difraction Card, Nickel
Record No (04—0850) (File, 1997) reveal the growth of
FCC nickel NPs (Yang et al. 2017).
Analytic metal Result (w/w)% Result (w/w)% Result (w/w)%
of Ni/Cu (1:1) of Ni/Cu (1:3) of Ni/Cu (3:1) 4c
Notably, Figs. 8 and 9 reveal the TEM analysis result
that demonstrates the maximum number of the average size
of the nanoparticles is 25–30 nm in the Ni/Cu (1:1) 4a and
Ni/Cu (1:3) 4b bimetallic NPs, whereas Fig. 10 exhibit
15–20 nm average size of the nanoparticles in the Ni/Cu
(3:1) 4c bimetallic NPs.
4a bimetallic
4b bimetallic
bimetallic NPs
(%)
NPs (%)
NPs (%)
Ni
Cu
50.2136
49.7864
24.1135
75.8865
74.7614
25.2386
Catalytic performance of Ni/Cu 4a, 4b, and 4c
bimetallic NPs for the chemoselective oxidation
of alcohol
Recently, various interesting studies of bimetallic NPs such
as Cu–Ni NPs assisted on activated carbon (Kimi et al. 2018)
and AuPd alloys embedded in MgO and MnO2 (Alsham-
mari et al. 2017), etc. for the chemoselective oxidation of
alcohol into aldehyde have been done. Metal nanoparticle
catalyzed high-temperature-based oxidation reaction of aro-
matic alcohol easily creates aromatic acid and ester due to
over oxidation of aromatic aldehyde and decreases selective
oxidation in the presence of another sensitive group and for
this problem, we avoided high temperature and also another
organic solvent.
Fig. 7 XRD analysis of Ni/Cu (1:1) 4a, Ni/Cu (1:3) 4b, Ni/Cu (3:1)
4c bimetallic NPs
no.85-1326) (Yang et al. 2017) in the three Ni/Cu (1:1) 4a,
Ni/Cu (1:3) 4b, and Ni/Cu(3:1) 4c bimetallic NPs. Further-
more, Fig. 7 demonstrates that the peaks at 2 theta values
of 42.20, 51.00, and 74.15 degrees associating with (111),
(200), and (220) nickel planes, respectively, those associated
However, the chemoselective oxidation of benzyl alcohol
to benzaldehyde catalyzed by the Ni/Cu bimetallic nanopar-
ticle (molar ratio 1:1/1:3/3:1) bimetallic NPs 4a, 4b, and
4c was examined as a model reaction (Scheme 5) due to
1 3

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Chemical Papers (2021) 75:2353–2369
Fig. 8 TEM analysis of Ni/Cu
(1:1) 4a bimetallic NPs
Fig. 9 TEM analysis of Ni/Cu
(1:3) 4b bimetallic NPs
Fig. 10 TEM analysis of Ni/Cu
(3:1) 4c bimetallic NPs
the determination of optimized reaction conditions and the
efect of the diferent molar ratio of Ni and Cu on the reac-
tion rate of the oxidation reaction under the aerobic condi-
tion at room temperature.
the maximal 75% yield for 77% of conversion or 82% of
benzaldehyde for 83% of conversion of benzyl alcohol
was found for catalyst Ni/Cu (3:1) 4c, respectively, while
another two Ni/Cu (1:1) 4a and for Ni/Cu (1:3) 4b NPs
gave less conversion with %yield (Table 2, entries 2, 3).
However, optimized reaction conditions were detected
with maximum 90% yield for 90% conversion, while the
reaction was carried out catalyzed by 4.0 mol% of the Ni/
Cu (3:1) 4c bimetallic NPs at room temperature at 30 min
(Table 2, entry 3). Moreover, no better yield was found by
increasing the catalyst loading (5.0 mol%) and reaction
time up to 40 min (Table 2, entry 5). Consequently, it was
revealed from this optimization that the reaction rate and
Initially, the oxidation reactions of benzyl alcohol in
the presence of H2O catalyzed by 2.5 mol% of three Ni/Cu
(1:1 4a/ 1:3 4b/ 3:1 4c) bimetallic NPs at room tempera-
ture about 10 min the maximum 55% yield of benzalde-
hyde for 56% conversion of benzyl alcohol was observed
for catalyst Ni/Cu (3:1) 4c, whereas minimum 35% yield
with conversion 35% for Ni/Cu (1:1) 4a (Table 2, entry 1).
Unexpectedly, by expanding the reaction time up to 20 min
or 30 min and catalyst loading 3.0 mol% or 3.5 mol%,
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Chemical Papers (2021) 75:2353–2369
2363
Table 2 Optimized conditions
of Ni/Cu 4a, 4b, and
Entry Catalyst Time (min) % Conva % Yielda % Convb % Yieldb % Convc % Yieldc
(mol%)
4c bimetallic NPs catalyzed
oxidation of benzyl alcohol to
benzaldehyde
1
2
3
4
5
2.5
3.0
3.5
4.0
5.0
10
20
30
30
40
35
51
60
55
56
35
50
59
55
55
47
57
68
57
58
47
56
68
56
57
56
77
83
90
91
55
75
82
90
90
Reaction conditions: catalyst 4.0 mol%, alcohol (1.0 mmol), time 30 min, solvent H2O (5 mL), room tem-
perature (RT), and atmospheric air (O2)
aStands for % conversion of benzyl alcohol determined by GC and % yield of benzaldehyde for catalyst Ni/
Cu (1:1) 4a
bStands for % conversion of benzyl alcohol determined by GC and % yield of benzaldehyde for catalyst Ni/
Cu (1:3) 4b
cStands for % conversion of benzyl alcohol determined by GC and % yield of benzaldehyde for catalyst Ni/
Cu (3:1) 4c
% yield depend on the amount of Ni NPs more than the
amount of Cu NPs of the Ni/Cu bimetallic NPs.
elemental analysis for solid products as well as compared
with literature data.
However, based on the observed optimized condition
of the oxidation of benzyl alcohol catalyzed by Ni/Cu
(3:1) 4c bimetallic nanoparticles and for checking chem-
oselectivity of the oxidation for diferent types alcohols,
we carried out this oxidation reaction of the broad scope
of alcohols containing diferent sensitive functional group
catalyzed by Ni/Cu (3:1) 4c NPs’ catalyst under above-
optimized conditions and the results are listed in the fol-
lowing Tables 3 (entries 1–8).
Catalytic activity of Ni/Cu 4a, 4b, 4c bimetallic NPs
for the chemoselective reduction of nitro groups
of aromatic compounds
In recent years, bimetallic NPs catalyzed selective reduction
of the aromatic nitro group at room temperature are also
studied (Yang et al. 2017).
However, for studying the optimized conditions for the
chemoselective reduction of the nitro group of aromatic sub-
stances into corresponding aniline derivatives catalyzed by
the Ni/Cu bimetallic nanoparticle of diferent molar ratios
(1:1 4a), (1:3 4b), and (3:1 4c), and also the efect of the
diferent molar ratio of Ni and Cu on the reaction rate of the
reaction, the reduction of the nitro group of 4-nitrophenol
catalyzed by the synthesized Ni/Cu (1:1) 4a, Ni/Cu (1:3) 4b,
and Ni/Cu (3:1) 4c nanoparticles with hydrazine hydrate as
a reducing agent under the aerobic conditions at room tem-
perature was considered as the model reaction (Scheme 6).
Initially, in the absence of a catalyst or hydrazine hydrate
in the presence of H2O at room temperature under aero-
bic conditions, the advancement of the reactions was not
observed (Table 6, entries 1, 2). Fascinatingly, by charging
with 2.0 mol% of the three diferent bimetallic Ni/Cu 4a,
4b, 4c NPs, when this reaction was continued individually
in 10 min, the % yield of 4-aminophenol was attained as
40% for 41% conversion of 4-nitrophenol for catalyst Ni/
Cu (1:1) 4a and 50% yield for 51% conversion for Ni/Cu
(1:3) 4b, and also 60% yield for 60% conversion for Ni/Cu
(3:1) 4c at room temperature in water under aerobic condi-
tions in the presence of hydrazine hydrate (Table 6, entry 3).
Also, by adding the amount of NPs catalyst from 3.0 mol%
to 3.5 mol% and increasing the reaction time up to 20 min,
the maximum yield 89% for 89% conversion of 4-nitrophenol
Furthermore, although the reaction rate of the conver-
sion of alcohol appeared to be slightly reduced with steri-
cally constrained and electron-withdrawing groups and
also a fve-membered ring containing primary alcohols
(Table 3, entries 1–8) in the case of a secondary alco-
hol, the full conversion was completed at 4 h under the
same reaction conditions and the % yield cited in Table 4
(entries 1, 2).
However, Table 5 exhibits that this catalytic method is
extremely chemoselective, because the oxidation reaction of
a 1:1 mixture of a primary alcohol with secondary alcohol
results in a quantitative conversion of the primary alcohol
into an aldehyde after 30 min, while Ketone was produced
only 5% of yield for 5% conversion of secondary alcohol
(Entry 1).
Signifcantly, a far better result of chemoselectivity was
observed when the oxidation of 1-(4-(hydroxymethyl)phe-
nyl)ethanol 25 containing primary and secondary hydroxyl
group on the same skeleton is carried out by this catalyst
Ni/Cu (3:1) 4c (Table 5, entry 2). After 30 min of the reac-
tion, the only obtained product was 4-(1-hydroxyethyl)ben-
zaldehyde without contamination of either the dicarbonyl
compound or the isomeric keto alcohol.
1
All the carbonyl products were evaluated by H, 13C
NMR (S4-S24 in the supplementary information), and also
1 3

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Chemical Papers (2021) 75:2353–2369
Table 3 Oxidation of primary
alcohols into the corresponding
carbonyl compounds catalyzed
by Ni/Cu (3:1) 4c NPs’ catalyst
Entry
1
Alcohol
Product
% Conv
91
% Yield
90
OHC
HO
13
5
2
94
94
OHC
HO
6
14
HO
O
3
86
86
85
84
7
15
O
HO
4
Cl
F
Cl
F
8
16
O
HO
5
6
83
80
82
80
17
9
O
OH
18
10
7
8
83
82
82
81
O
S
O
S
O
O
OH
OH
11
19
20
12
%Conversion of alcohols determined by GC and % yield calculated based on the respective alcohol.
Reaction conditions: catalyst 4.0 mol%, alcohol (1.0 mmol), time 30 min, solvent H2O (5 mL), room tem-
perature (RT), and atmospheric air (O2)
was isolated for catalyst Ni/Cu (3:1) 4c (Table 6, entries
4, 5). However, the optimized condition was ascertained
with maximal 96% yield for 97% conversion, while com-
pleting these reactions in 20 min with Ni/Cu nanoparticles
(3:1) 4c at room temperature in water under aerobic condi-
tions using hydrazine hydrate as a reducing agent (Table 6,
Entry 6). These outcomes indicate that Ni/Cu (3:1) 4c is
more active as a catalyst than Ni/Cu (1:1) 4a and Ni/Cu
(1:3) 4b.
Cu (3:1) 4c NPs’ catalyst under the above-optimized con-
ditions, this catalytic method was explored for a wide vari-
ety of substituted aromatic nitro-compounds for synthe-
sizing the corresponding aromatic amines. The obtained
results are included in Table 7. These results have shown
that completely unchanged are the easily reducible func-
tional groups such as CO, COMe, CO2Me, COOH, F, N3,
and SCN, and accorded well to moderate % yield of prod-
ucts (Table 7, entries 2–10). The products were separated
in a pure form directly by extraction with ethyl acetate.
From this observation, owing to checking the chem-
oselectivity for the reduction of the nitro group in difer-
ent aromatic compounds even in the presence of another
reducible group catalyzed by the most active catalyst Ni/
1
All the amine products were analyzed by the H and
13C NMR spectrum (S25-S43 in the supplementary
1 3

Chemical Papers (2021) 75:2353–2369
2365
Table 4 Oxidation of aromatic secondary alcohols into the corresponding carbonyl compounds catalyzed by catalyst Ni/Cu (3:1) 4c
Entry
Alcohol
Product
% Conv
% Yield
1
87
86
OH
O
21
22
23
2
86
85
Cl
Cl
OH
O
24
%Conversion of alcohols determined by GC and % yield calculated based on the respective alcohol. Reaction conditions: catalyst Ni/Cu (3:1)4c
4.0 mol%, alcohol (1.0 mmol), time 4 h, solvent H2O (5 mL), and room temperature (RT)
Table 5 Chemoselective
oxidation of alcohols catalyzed
by Ni/Cu (3:1) 4c
Entry
1
Alcohol
Product
% Conv
93
% Yield
93
CHO
OH
OH
+
+
+
5
+
5
O
2
83
82
CHO
HO
HO
OH
26
25
%Conversion determined by GC and % yield calculated based on the respective alcohol. Reaction condi-
tions: catalyst 4.0 mol%, alcohol (1.0 mmol), time 30 min solvent H2O (5 mL), room temperature (RT),
and atmospheric air (O2)
Table 6 Optimized conditions of Ni/Cu bimetallic NPs (1:1 4a), (1:3 4b), (3:1 4c) catalyzed reduction of 4-nitrophenol to 4-aminophenol
Entry
Catalyst
(mol%)
NH2-NH2. Time (min)
H2O
(%) Conva
(%) Yielda
(%) Convb
(%) Yielda
(%) Convc
(%) Yieldc
1
2
3
4
5
6
–
+
–
+
+
+
+
10
10
10
15
20
20
–
–
41
50
60
66
–
–
40
50
59
65
–
–
51
64
73
83
–
–
50
63
72
82
–
–
60
79
89
97
–
–
60
78
89
96
2.0
2.0
3.0
3.5
4.0
Reaction conditions: catalyst (4.0 mol%), solvent H2O (5.0 mL), 4-nitrophenol (1.0 mmol), NH2-NH2.H2O (0.5 mmol), time (20 min), room tem-
perature (RT), and atmospheric air (O2)
aStands for % conversion of 4-nitrophenol determined by GC and % yield of 4-aminophenol for catalyst Ni/Cu (1:1) 4a, similarly
bStands for % conversion of 4-nitrophenol determined by GC and % yield of 4-aminophenol for catalyst Ni/Cu (1:3) 4b
cStands for % conversion of 4-nitrophenol determined by GC and % yield of 4-aminophenol for catalyst Ni/Cu (3:1) 4c
1 3

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Chemical Papers (2021) 75:2353–2369
Table 7 Reduction of
Serial
no.
1
Substrate
Product
(%)
Conv
96
(%)
Yield
96
substituted nitro benzenes to
the corresponding anilines
catalyzed by Ni/Cu (3:1) 4c
HO
NO2
HO
NH2
27
37
2
89
88
NO2
NH2
38
28
CHO
CHO
3
97
97
NO2
NH2
29
30
39
4
92
91
HOOC
NO2
HOOC
OHC
NH2
40
5
6
96
94
96
93
NH2
OHC
NO2
31
41
O2N
N3
H2N
N3
32
42
7
8
92
94
91
93
O
O
O
O
O2N
H2N
33
43
O
O
NO2
NH2
34
35
44
45
9
95
88
95
87
NCS
O2N
NO2
F
NCS
H2N
NH2
10
F
36
46
%Conversion determined by GC and % yield calculated based on their respective nitro compound. Reac-
tion conditions: catalyst Ni/Cu (3:1)4c, (4.0 mol%), solvent H2O (5.0 mL), substituted nitro compounds
(1.0 mmol), NH2-NH2.H2O (0.5 mmol), time (20 min), and atmospheric air (O2)
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Chemical Papers (2021) 75:2353–2369
2367
O
C
H2
Ni/Cu NPs (mol%)
C
H
OH
Time, Temparature, Solvent
Scheme 5 Optimization of Ni/Cu 4a, 4b, and 4c bimetallic NPs cat-
alyzed oxidation of benzyl alcohol to benzaldehyde
Table 8 % Yield of
Run
Yield (%)
benzaldehyde for diferent
catalytic run by Ni/Cu (3:1) 4c
NPs
1
2
3
4
5
85
84
84
83
80
Fig. 11 SEM of the recovered catalyst Ni/Cu (3:1) 4c
information) and also elemental analysis for solid products
in addition to associated with the literature data.
Heterogeneity test of the catalyst Ni/Cu (3:1) 4c
Initially, a mixture of Ni/Cu (3:1) 4c NPs (4.0 mol%) and
benzyl alcohol (1.0 mmol) in water (5 mL) was stirred for
15 min at room temperature. Then, the reaction was stopped
and centrifuged of the reaction mixture and also fltered of
the catalyst. By analyzing the solution with 1H NMR, 50%
conversion of benzyl alcohol into benzaldehyde was found
and the experiment further proceeded for another 15 min
with that fltrate solution. The concentration of the benzal-
dehyde was not increased, as calculated by the study of 1H
NMR. Moreover, the leaching study of metal of heteroge-
neous catalyst is very signifcant, and for this, Ni and Cu
leaching analysis after separating of the catalyst was done
using ICP-OES and no leaching of Ni and Cu was observed.
Fig. 12 XRD of the recovered catalyst Ni/Cu (3:1) 4c
NH2
NO2
Ni/Cu NPs (mol%)
Time, RT, H2O
OH
OH
Scheme 6 Optimization of Ni/Cu bimetallic nanoparticles 4a, 4b,
and 4c catalyzed reduction of 4-nitrophenol to 4-aminophenol
Recoverability and reusability of the catalyst Ni/Cu
(3:1) 4c
benzyl alcohol under present reaction conditions (Fig. 12).
However, these detected results suggest that the catalyst is
not only actively satisfactory for the reaction but also very
stable (Scheme 6).
The recoverability and reusability of the catalyst 4c were
tested considering the reaction of oxidation of benzyl alco-
hol to benzaldehyde (Scheme 5), and the % yield of benza-
ldehyde is cited in Table 8. The catalyst was recovered by
centrifugation after each catalytic run followed by ethanol
and acetone washing (2 × 3 mL) and also reused to fur-
ther catalytic run. After recycling fve times, the results of
XRD and SEM analysis showed the necessary peaks for the
recovered catalyst’s FCC structure of the catalyst (Fig. 12)
and agglomerated spherical surface morphology (Fig. 11)
distinctly. The specifc peak intensity of the recycled catalyst
was reduced, suggesting that the structure of the recycled Ni/
Cu (3:1) 4c was slightly demolished during the oxidation of
Reaction conditions: Ni/Cu (3:1) 4c NPs (4.0 mol%), ben-
zyl alcohol (1.0 mmol) in water (5 mL), room temperature,
and time 30 min.
Conclusions
In summary, Ni/Cu bimetallic nanoparticles with molar
ratios (1:1) 4a, (1:3) 4b, (3:1) 4c supported by dendritic
ligand 2,4,6-Tris (di-4-chlorobenzamido)-1,3-diazine 3 were
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Chemical Papers (2021) 75:2353–2369
with crystal facet-enhanced catalytic efects for benzyl alcohol
aerobic oxidation. CrystEngComm 18:5110–5120
prepared. Among the diferent molar ratios of Ni and Cu
(1:1 4a or 1:3 4b), the catalyst Ni/Cu (3:1) 4c has shown
excellent activity for the rapid chemoselective oxidation of
primary alcohols to aldehydes at 30 min and reduction of
the nitro substrates in the vicinity of other easily reducible
functional groups to the corresponding anilines at 20 min in
an aqueous medium with a high degree of chemoselectivity
under very mild conditions. Also, this heterogeneous Ni/Cu
bimetallic nanocatalyst is easily recoverable and reusable at
least fve times without any signifcant loss of activity. How-
ever, selective oxidation and reduction of biologically active
organic compounds in an aqueous medium at room tem-
perature and various carbon–carbon cross-coupling reactions
such as Heck, Suzuki, Stille carbon–carbon cross-coupling
reactions can be studied by this green catalytic approach.
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nanoparticles stabilized by polyethylene glycol: Efcient, recy-
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Acknowledgements The authors would like to express their innermost
gratitude to the Ministry of Science and Technology, Government of
the People’s Republic of Bangladesh, Dhaka, Bangladesh (National
Science and Technology, Grant No.:39.00.0000.012.002.04.19-08
(2019-2020) and Bangladesh University of Engineering and Technol-
ogy (BUET), Dhaka, Bangladesh for providing fnancial support to
perform this research work.
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benzylic alcohols to carboxylic acids. Synthesis 50:1629–1639
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benzyl alcohol. J Phys Chem Solids 112:50–53
Compliance with ethical standards
Lee W, Piao L, Park C-H et al (2010) Facile synthesis and size con-
trol of spherical aggregates composed of Cu2O nanoparticles. J
Colloid Interface Sci 342:198–201
Conflict of interest The authors have no conficts of interest.
Liu L, Lou H, Chen M (2016) Selective hydrogenation of furfural to
tetrahydrofurfuryl alcohol over Ni/CNTs and bimetallic CuNi/
CNTs catalysts. Int J Hydrog Energy 41:14721–14731
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supported on zeolitic imidazolate framework-8 as highly active
heterogenous catalysts for selective oxidation of benzyl alcohol
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