A. Arora et al.
Inorganica Chimica Acta 522 (2021) 120267
in catalyst development. In comparison to commonly used capping li-
gands [1], negligible work has been done on exploring the potential of
such compounds as stabilizers of NPs [15,16]. Except a few reports on Pd
NPs for coupling reactions [15,16], no other metal NPs have been
developed using organoselenium compounds as stabilizers.
refined by full matrix least-squares with SHELXL-97, refining on F2. The
image was created using the program Diamond. High resolution mass
spectrometry (HRMS) was carried out with Bruker High Impact HD
spectrometer on the sample prepared in acetonitrile. Kinetics studies
were carried out using Shimadzu UV-1900 Spectrophotometer. A Philips
CM200 operated at 200 kV was used for HRTEM (High Resolution
Transmission Electron Microscopic) studies and the sample for such
studies was prepared by dispersing the nanocatalyst in ethanol. The SEM
(Scanning Electron Microscopic) and EDX (Energy Dispersive X-Ray
spectroscopy) system (model JSM 6100) has been used for studying the
morphology and elemental composition of NPs. Powder X-ray diffrac-
tion (PXRD) studies were carried out on Panalytical XPert diffractometer
with Cu filtered radiation using a scan speed of 2 degrees per min and
scan step of 0.02◦. Raman studies have been carried out on Horiba LAB
RAM HR evolution raman spectrometer. FTIR (Fourier Transform
Infrared) spectroscopic studies were performed on Shimadzu IRSpirit
QATR-S spectrophotometer. Thermogravimetric (TG) analysis was car-
ried out using Netzsch DSC 204 F1 Phoenix with a heating rate of 10 ◦C
minute per. Inductively coupled plasma (ICP) analysis was carried out
on Leeman Prodigy XP instrument. L1′ [pyren-1-yl-CH=N-(CH2)2-SePh]
which is required as a precursor for synthesis of L1 was synthesized
using the previously reported method [19].
The reduction of nitroarenes is a widely employed route in the syn-
theses of amino–aromatics [20-27] and also in the removal of nitro-
arenes from waste water. As nitrophenol is highly soluble in water (a
green solvent), researchers have shown interest in the development of
such catalytic systems which may be applied in aqueous medium [22].
For this purpose, non-noble 3d metals (Cu, Fe, Ni, Co) based catalytic
systems have also drawn significant attention due to their high abun-
dance, non-toxic nature and low cost [23]. These include monometallic,
bimetallic, multi metallic and solid-supported nanocatalysts [22].
Though copper has constituted an important class of catalysts for
various other chemical transformations [24], only a few copper based
systems have been used for reduction of nitroarenes.
In the past the chitosan coated magnetite has been used as a very
interesting solid support for obtaining some user-friendly heterogeneous
catalytic systems [27]. In such systems, magnetite remains present in the
form of some nanosized crystalline phases and structures such as Fe3O4
and Fe2O3 (α, γ) [28,29]. Presence of magnetic character in the catalyst
offers many advantages [30-36]. The work-up procedures become easy,
ease in reusability gets enhanced [25,37] due to separation of the
maximum quantity of catalyst with the help of an external magnet and
the loss in the quantity of the catalyst during the recycling becomes
minimum. In addition, the layering with chitosan (i.e. a linear poly-
saccharide) renders some interesting characteristics [27,38]. It is an
environment-friendly, economical and less toxic polymer support. Due
to its presence, the chemical stability and biocompatibility of magnetite
is improved. It also protects this magnetic support from oxidation and
agglomeration. It has free amino and alcoholic groups [27,38] due to
which it is capable of forming covalent as well as non-covalent
interactions.
2.2. Synthesis of stabilizer (L1)
To a solution of L1′ (0.207 g, 0.5 mmol) in 15 mL of ethanol, 0.074 g
of NaBH4 (2.0 mmol) was added. The reaction mixture was refluxed for
12 h. Thereafter, the reaction mixture was cooled and subjected to sol-
vent extraction with chloroform and distilled water. Organic layer was
separated and dried over anhydrous sodium sulphate. Solvent was
evaporated under vacuo to obtain a yellowish solid. Recrystallization
was done in ethanol to obtain the needle shaped yellow-coloured single
crystals of L1.
Yield (0.373 g, 90%) NMR: 1H (CDCl3, 25 ◦C, TMS) δ (ppm) 8.38 (1H,
d, J = 10.0 Hz), 8.21 (2H, t, J = 5.0 Hz), 8.13–8.17 (2H, m), 8.02–8.07
(3H, m), 7.97 (1H, d, J = 5.0 Hz), 7.45 (2H, d, J = 2.5 Hz), 7.16–7.21
(3H, m), 4.51 (2H, s), 3.15 (2H, t, J = 2.5 Hz), 3.06 (2H, t, J = 5.0 Hz).
13C{1H} (CDCl3, 25 ◦C, TMS), δ (ppm): 133.70, 133.11, 131.41, 130.92,
129.49, 129.14, 129.12, 129.10, 127.80, 127.57, 127.22, 127.13,
127.11, 126.02, 125.23, 125.16, 124.99, 124.77, 124.27, 51.39, 48.63,
28.74. 77Se{1H} (CDCl3, 25 ◦C, Me2Se), δ (ppm): 264.71.
Having considered all the aforementioned factors and the fact that,
to the date, there are only a few examples of metal-chitosan anchored
onto the magnetic NPs with the catalytic applications in the organic
transformations in general and the reduction of nitroarenes in particular
[27], an easily synthesizable and hybrid organoselenium ligand (L1),
having a combination of hard N and soft Se donors, has been designed
and used as a stabilizer for obtaining pre-synthesized Cu nanoparticles.
The group (pyren-1-yl-) is envisaged to minimize the surface deactiva-
tion of Cu NPs by restricting the number of stabilizer molecules on the
surface. Subsequently, these pre-formed NPs were immobilised on chi-
tosan coated magnetite for obtaining a stable, reusable and efficient
catalyst which is user-friendly and offers the advantage of its easy sep-
aration from the reaction mixture with an external magnet.
2.3. Synthesis of L1-stabilized copper nanoparticles
(L1ꢀ stabilizedꢀ CuNPs)
1.0 mmol of L1 was dissolved in 10 mL of dichloromethane. It was
added to a solution of 1.0 mmol of CuCl2 in 10 mL methanol and was
stirred vigorously for about 30 min. To this mixture, 2.0 mmol of NaBH4
was added and stirred further for 2 h. The reaction mixture was then
centrifuged at 5000 rpm and the Cu NPs were obtained as black powder
which were then dried under vacuum. NMR: 77Se{1H} (25 ◦C, Me2Se), δ
(ppm): 331.17.
2. Experimental section
2.1. Materials and methods
1–Pyrene carboxaldehyde, diphenyl diselenide, 2–chloroethylamine
hydrochloride, ferrous chloride, ferric chloride, chitosan, and cupric
chloride (anhydrous) were obtained from Sigma Aldrich. Solvents and
other common reagents were obtained from local suppliers and used
further without purification. All the experiments regarding analytical
thin layer chromatography were carried out on Merck silica gel coated
on aluminium sheets and a UV-light chamber containing lamp of
265–280 nm was used for viewing them. 1H and 13C NMR studies have
been performed on JNM ECX–500 NMR spectrometer at 500 and 125
MHz respectively. 77Se NMR was carried out on ECZR Series 600 MHz
NMR spectrometer. X-ray diffraction studies were performed on Super-
nova X-ray diffractometer system at 150 K using Mo Ka radiation (0.710
A). CrysalisPro Software (online version) was used for data collection.
The structure was solved by direct methods using olex2, SHELXS-97 and
2.4. Synthesis of magnetic support (Fe3O4) in particulate form
Different solutions of FeCl2 (1.0 mol) and FeCl3 (2.0 mol) were
prepared in 10 mL of distilled water. Both the solutions were stirred for
10 min. Solutions were mixed and the mixture was stirred further for 20
min. Thereafter, the saturated solution of sodium hydroxide was added
until the pH 10 was achieved. Mixture was again refluxed at 80 ◦C for 30
min with continuous stirring. The reaction mixture was then cooled and
the precipitate was filtered and washed with three portions of 10 mL of
distilled water. It was left for drying, and the product was sintered at
200 ◦C in a muffle furnace for 2 h.
2