In situ synthesis of CuO nanoparticles over functionalized mesoporous silica and their application in catalytic syntheses of symmetrical diselenides

Article abstract of DOI:10.1039/c9dt03418h

A versatile and novel catalyst, CuO nanoparticles immobilized over functionalized mesoporous silica (nCuO-FMS), has been synthesized over an organically modified mesoporous silica framework following a facile synthetic route. The surface of the silica support (SBA-15) is first grafted with the 3-aminopropyl silane group and then further functionalized with tris(4-formylphenyl)amine. The reaction is performed in such a way that a few -CHO groups remain free for further functionalization. Finally, the CuO nanoparticles immobilized on mesoporous silica are obtained by a one pot reaction between the functionalized silica, 2-aminophenol and CuCl₂. The product obtained has been used as a catalyst for the syntheses of symmetrical diselenides in the presence of KOH as the base and dimethyl sulphoxide (DMSO) as the solvent. The materials have been characterized thoroughly by X-ray powder diffraction, nitrogen adsorption-desorption studies, transmission electron microscopy, thermal analysis and different spectroscopic techniques. The Cu content of the sample has been determined by atomic absorption spectrophotometry (AAS). The products of the catalytic studies have been identified and estimated by NMR spectroscopy. Almost 78% isolated yield could be achieved at 363 K within 3 hours of the reaction and the catalyst, nCuO-FMS, can be recycled at least up to five catalytic cycles.

Full text of DOI:10.1039/c9dt03418h

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
In situ synthesis of CuO nanoparticles over
functionalized mesoporous silica and their
application in catalytic syntheses of symmetrical
diselenides†
Cite this: Dalton Trans., 2019, 48,
17874
c
Trisha Das, a Rana Chatterjee, b Adinath Majee, b Hiroshi Uyama,
a
David Morgan d and Mahasweta Nandi
*
A versatile and novel catalyst, CuO nanoparticles immobilized over functionalized mesoporous silica
(nCuO-FMS), has been synthesized over an organically modified mesoporous silica framework following a
facile synthetic route. The surface of the silica support (SBA-15) is first grafted with the 3-aminopropyl
silane group and then further functionalized with tris(4-formylphenyl)amine. The reaction is performed in
such a way that a few –CHO groups remain free for further functionalization. Finally, the CuO nano-
particles immobilized on mesoporous silica are obtained by a one pot reaction between the functiona-
lized silica, 2-aminophenol and CuCl2. The product obtained has been used as a catalyst for the syntheses
of symmetrical diselenides in the presence of KOH as the base and dimethyl sulphoxide (DMSO) as the
solvent. The materials have been characterized thoroughly by X-ray powder diffraction, nitrogen adsorp-
tion–desorption studies, transmission electron microscopy, thermal analysis and different spectroscopic
techniques. The Cu content of the sample has been determined by atomic absorption spectrophotometry
(AAS). The products of the catalytic studies have been identified and estimated by NMR spectroscopy.
Almost 78% isolated yield could be achieved at 363 K within 3 hours of the reaction and the catalyst,
nCuO-FMS, can be recycled at least up to five catalytic cycles.
Received 21st August 2019,
Accepted 18th November 2019
DOI: 10.1039/c9dt03418h
rsc.li/dalton
reaction. To overcome this problem, the metal ion should
strongly interact with the heterogeneous support so that it
Introduction
It is known that metal containing heterogeneous catalysts are does not get detached from the solid framework during the
advantageous over their homogeneous counterparts due to liquid phase catalytic process. Different types of solid supports
multiple reasons like recyclability, easy recovery and high e.g. polymers,1 zeolite,2 alumina,3 silica,4 graphene,5 meso-
surface accessibility and are often economical with respect to porous carbon,6 carbon nanotubes,7 metal–organic frame-
conventional catalysts which can be used only once. However, works,8 metal oxide nanoparticles,9 etc.10–12 have been used
leaching is a typical problem for heterogeneous catalytic for the successful syntheses of heterogeneous catalysts. Among
systems and in such cases it becomes difficult to ascertain these, mesoporous silica is often chosen as the solid support
whether the metal ion bound to the solid support or the metal because of its better interaction with the metal centers and
ion leached into the solution is responsible for catalyzing the accessibility to the substrates. These take place due to its large
surface area13 which significantly increases the efficiency of
the catalysts. Apart from this, it is also possible to tune the
pore size of the mesoporous silica matrix as per the specific
requirements. Silicate-based structures are generally robust,
aIntegrated Science Education and Research Centre, Siksha Bhavana,
Visva-Bharati University, Santiniketan 731 235, India.
E-mail: mahasweta.nandi@visva-bharati.ac.in
bDepartment of Chemistry, Siksha Bhavana, Visva-Bharati University,
Santiniketan 731235, India
cDepartment of Applied Chemistry, Graduate School of Engineering,
Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
dCardiff Catalysis Institute, School of Chemistry, Cardiff University, Park Place,
Cardiff CF10 3AT, UK
and thermally and chemically stable. Functionalization of
their framework can be done easily to introduce hydrophobi-
city through the insertion of various organic moieties.
Moreover, if such organic functionalities are heteronuclear
molecules, then various heteroatoms like N, O and S can be
introduced into the materials, taking into account their advan-
tage. The introduction of such groups can modify the affinities
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
C9DT03418H
17874 | Dalton Trans., 2019, 48, 17874–17886
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
of the functionalized silica based materials towards specific
substrates and tune the overall acid base character of the
framework. Metal centers can interact and attach to such
modified frameworks via covalent interaction or hard–soft
interaction based on the heteroatoms that can be chosen judi-
ciously for this purpose.
Over the last two decades and also at present, a consider-
able amount of interest has been focused on research based
on the use of nanostructured metal based catalysts. Such cata-
lysts have shown their potential utility and played a pivotal role
in several types of organic syntheses and methodologies.
Nanoparticle based metal catalysts exhibit special properties
and have distinctive physical, chemical, magnetic and optical
properties that are completely different from those of their
bulk counterparts.14 This can be attributed to their relatively
larger surface area compared to the same mass in bulk form
and the quantum effects that begin to dominate their behavior
at the nanoscale. Due to these characteristics, nanoparticles
have been used extensively for applications in the fields of cat-
alysis, electronics and photonics. In the field of organic syn-
thesis, metal oxide nanoparticle based catalysts are known to
be very effective and fruitful due to their various advantages as
a heterogeneous catalyst.15–17 They are superior over conven-
tional metal catalysts because of their greater surface exposure,
high reactivity and high thermal resistance, thereby exhibiting
higher product yields with better atom economy. Copper oxide
(CuO) nanoparticles are one of these important classes of
materials that have been used as catalysts for the development
of a number of organic transformations. The effectiveness of
using CuO nanoparticle-based catalysts in the area of organic
synthesis is well documented in the literature.18–23
Organochalcogen compounds are known to function as bio-
logically active molecules24,25 and have been used as reaction
intermediates and reagents in various organic syntheses.26–28
Apart from these, the organoseleno compounds have found
important applications as antioxidants, anti-ulcer and anti-
inflammatory agents.29–31 Several organoseleno compounds
have been used as therapeutic agents in the treatment of
cancer and various infectious diseases and as apoptosis
inducers.32,33 These compounds also play a vital role in the
fields of materials science and nanotechnology.34,35 Owing to
such immense contribution of the organoseleno compounds
(especially the diselenides) across several fields of application,
there is considerable demand for the preparation of these
compounds both in academia and industry. Accordingly,
several methods have been developed for the synthesis of di-
selenide compounds.36–43 Among these, a method developed
by Braga et al. is particularly interesting where diselenide com-
Scheme 1 Synthesis of nCuO-FMS.
strategy (Scheme 1). The CuO nanoparticles are spontaneously
formed in situ under the reaction conditions in the presence of
tris(4-formyl phenyl)amine grafted mesoporous silica,
2-aminophenol and CuCl2. nCuO-FMS has been used as a cata-
lyst for the cost effective synthesis of diselenide compounds,
including diaryl diselenides. It could be established that the
presence of a catalytic amount of this CuO nanoparticle-
based catalyst highly influences the progress of the reaction,
whereas in the absence of the catalyst the reaction does not
proceed. To the best of our knowledge, this is the first report
of a CuO nanoparticle based heterogeneous catalyst for the
syntheses of diselenides using a neat, facile and innovative
technique.
Experimental details
Materials and physical measurements
pounds have been synthesized using powder CuO nano- All the chemicals used in the synthesis have been obtained
particles as a catalyst.44 In line with this, we have tried to from commercial sources and used without further purifi-
design a mesoporous silica based heterogeneous catalyst con- cation. The FT-IR spectra of the samples have been collected
taining immobilized CuO nanoparticles instead of the com- on a PerkinElmer Spectrum Two spectrometer using the atte-
mercially available CuO nanoparticle powder to perform cata- nuated total reflectance (ATR) method. Thermogravimetric
lytic reactions leading to the formation of diselenides. We have analyses (TGA) have been performed under N2 atmosphere
prepared CuO nanoparticles immobilized over functionalized (flow rate: 50 cc min−1) from room temperature to 1073 K (at
mesoporous silica (nCuO-FMS) through a one-pot synthetic heating rate of 2 K min−1) using a PerkinElmer STA-6000
This journal is © The Royal Society of Chemistry 2019
Dalton Trans., 2019, 48, 17874–17886 | 17875

View Article Online
Paper
Dalton Transactions
thermal analyzer. Low and high angle powder X-ray diffraction was added to it. The mixture was vigorously stirred until all the
patterns of the samples have been collected on a Bruker D-8 P123 dissolved and a clear solution was obtained. Then 6 g of
Advance diffractometer using Ni-filtered Cu-Kα radiation (λ = 35% HCl solution was added to the mixture and kept again
1.5406 Å) at 40 kV and 40 mA. N2 sorption isotherms of the under stirring for 15 min. Finally, 3.5 g of tetraethyl ortho-
samples have been measured using a NOVA 2200e Surface Area silane was added dropwise to the resulting clear solution and
and Pore Size Analyzer, Quantachrome Instruments, USA at the reaction mixture was stirred for another 20 h at 313 K. The
77 K. Before performing the measurements, the samples have resulting white gel was heated at 373 K for 20 h without stir-
been degassed for 8–12 h at 353, 393 or 423 K depending on ring in the polypropylene bottle under air-tight conditions.
the nature of the samples and the specific surface areas have Then the white mixture was cooled to room temperature, fil-
been obtained by using the Brunauer–Emmett–Teller (BET) tered and washed with water several times followed by 2–3
method. For obtaining the pore size distributions, the non- washings with ethyl alcohol. The white product was dried
local density functional theory (NLDFT) model has been used. under vacuum and then calcined at 773 K for 10 hours in a
The transmission electron microscopic (TEM) images have flow of air to obtain the mesoporous SBA-15.
been recorded on a JEOL JEM-1400 transmission electron
In the next step, 3-aminopropyl units were grafted onto the
microscope. The sample grids for TEM have been prepared by surface of SBA-15 by stirring 1.0 g of the mesoporous silica
putting one drop of the dispersion of the samples in ethyl with 1.5 g of 3-aminopropyl triethoxy silane (3-APTES) over-
alcohol on an amorphous carbon coated copper grid of night in chloroform at room temperature under N2 atmo-
400 mesh. Solid state 13C CP and 29Si MAS NMR spectra have sphere. The mixture was then filtered and the product was
been recorded on a CHEMAGNETICS 300 MHz CMX 300 washed repeatedly with chloroform and then dichloro-
spectrometer. A Kratos Axis Ultra DLD system has been used to methane. Finally, –NH2 functionalized SBA-15 was obtained
collect X-ray photoelectron spectra (XPS) using a monochro- after drying the product under vacuum. Further modification
matic Al Kα X-ray source operating at 120 W (10 mA × 12 kV). of the amine functionalized silica was carried out with tris(4-
Data have been collected with pass energies of 160 eV for formyl phenyl)amine, a trialdehyde (Scheme 1), which was pre-
survey spectra and 20 eV for the high-resolution scans with pared through the Vilsmeier–Haack formylation reaction of tri-
step sizes of 1 eV and 0.1 eV, respectively. The system has been phenylamine and phosphorus oxychloride following a reported
operated in the Hybrid mode, using a combination of mag- procedure.46 In this step, the trialdehyde and the –NH2 func-
netic and electrostatic lenses and acquired over an area of tionalized SBA-15 were refluxed for 4 h in methanol and the
approximately 300 × 700 µm2. A magnetically confined charge molar ratio was kept at 1 : 1, so that two –CHO groups of the
compensation system has been used to minimize the charging trialdehyde remain free for further functionalization.47 The
of the sample surface, and all the spectra have been recorded resulting light yellow coloured product was filtered and
with a 90° take off angle. A base pressure of ca. 1 × 10−9 Torr washed repeatedly with methanol until the filtrate became
has been maintained during the collection of the spectra. Data colourless.
have been analysed using CasaXPS (v2.3.23) after the subtrac-
For synthesizing nCuO-FMS, the tris(4-formyl phenyl)amine
tion of a Shirley background and using modified Wagner sen- functionalized SBA-15, 2-aminophenol and CuCl2 were taken
sitivity factors as supplied by the manufacturer. Atomic in methanol in a round bottom flask. The molar ratio of the
absorption spectrophotometric (AAS) studies have been carried reactants was maintained at 1 : 2 : 2. Then the reaction mixture
out by using a PinAAcle 900F, PerkinElmer atomic adsorption was refluxed for 4 h when the colour of the solution gradually
spectrometer. For preparing the sample solution, 0.04 g of darkened due to the in situ formation of CuO nanoparticles.
nCuO-FMS has been dispersed in 2 ml of DTPA (diethyl- The solid product was then isolated through filtration and
enetriaminepentaacetic acid) solution and the volume has washed repeatedly with methanol to remove any excess reac-
been made up to 20 ml by the addition of distilled water. Then tants. Finally, the brown coloured CuO nanoparticles immobi-
the solution has been shaken for 2 hours and filtered to lized over functionalized mesoporous silica (nCuO-FMS) were
obtain a colorless filtrate and this filtrate has been used for obtained after drying the product under vacuum.
1
the analysis. H NMR spectra have been collected in a CDCl3
solvent using a 400 MHz Bruker spectrometer with tetra-
Catalysis
methylsilane (δ = 0) as the internal standard. The chemical In a typical catalytic reaction batch, 0.5 mmol iodo benzene,
shifts have been expressed in parts per million (δ). Mass 1 mmol Se0 powder and 1 mmol KOH were taken together in a
spectra have been obtained by using a Thermo ISQ QD EI Gas round bottom flask in the presence of 2.0 ml of DMSO as the
Chromatograph-Mass Spectrometer (GC-MS) System.
solvent at 363 K and under nitrogen atmosphere. The reaction
was initiated with the addition of 20 mg of nCuO-FMS as the
catalyst into it. The reaction was allowed to continue for the
Synthesis of nCuO-FMS
Mesoporous silica, SBA-15, was used as the solid support for desired time and the solid catalyst was separated from the
the preparation of the nCuO-FMS catalyst. For the synthesis of reaction mixture by centrifugation and washed repeatedly to
SBA-15,45 1.7 g of Pluronic P123 (poly(ethylene glycol)-block- remove the organic product from it. Then, the product was
poly(propylene glycol)-block-poly(ethylene glycol) block copoly- extracted in ethyl acetate and washed thoroughly with brine
mer) was taken in a polypropylene bottle and 62 ml of water solution and water for complete removal of the inorganic com-
17876 | Dalton Trans., 2019, 48, 17874–17886
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
ponents. The solid product was isolated through evaporation
Thermogravimetric analyses have been carried out with the
of the solvent and purified by column chromatography in a powder samples of SBA-15, 3-APTES functionalized SBA-15, tri-
petroleum ether/ethyl acetate mixture. The isolated yield of the aldehyde loaded SBA-15 and nCuO-FMS in the temperature range
final product in pure form was obtained after solvent evapor- of 303–1073 K to examine the thermal stability of the frame-
ation. The structure of the isolated product was characterized works (Fig. 2). The high thermal stability of the silica support,
1
by H and 13C NMR spectroscopy in CDCl3 and its percentage SBA-15 (Fig. 2a), is quite clear from the curve, where only 4%
conversion, turnover frequency and turnover number were weight loss takes place up to 1073 K, mostly due to the loss of
determined. To examine the recyclability of the catalyst, it was adsorbed solvent and other molecules. Such high stability
separated out from the reaction mixture after the completion makes SBA-15 a potential candidate to act as the catalyst
of the reaction by centrifugation. The recovered catalyst was support. The thermal stabilities of the other samples can be
washed repeatedly with ethyl acetate, dried and used again for ascertained from their corresponding TGA plots.50,51 All the
another catalytic cycle of Se–Se coupling.
organically modified materials (Fig. 2b–d) show a stepwise
weight loss corresponding to the nature and amount of the func-
tional groups present and the mass loss continues to take place
at 1073 K. For all the samples, the first step of weight loss of ca.
3–4% takes place at around 373 K which can be attributed to the
physisorbed water molecules. For the 3-APTES functionalized
Results and discussion
FT-IR spectra and thermal studies
The FT-IR spectra of SBA-15, 3-APTES functionalized SBA-15, SBA-15 (Fig. 2a), there is another step of weight-loss corres-
trialdehyde loaded SBA-15 and nCuO-FMS have been recorded ponding to the removal of 3-aminopropyl moieties in the
by the ATR technique with the powdered samples and the sample, between the temperature range of 530 and 820 K. The
results are shown in Fig. 1. The spectrum of 3-APTES functio- TGA profile of the trialdehyde loaded SBA-15 (Fig. 2c) also shows
nalized SBA-15 (Fig. 1(A)b) shows a broad band in the region a similar trend, but the weight-loss is higher in this case due to
of 3747–2929 cm−1 which may appear due to the presence of the removal of 3-aminopropyl and the trialdehyde units. The
amine group and methylene moieties of the aminopropyl catalyst, nCuO-FMS (Fig. 2d), loses more weight in this tempera-
group.48 For the trialdehyde loaded SBA-15 (Fig. 1(A)c), two ture region due to the removal of the 2-aminophenol units, in
additional peaks arise at 1643 cm−1 and 1698 cm−1, which addition to the other organic functionalities, which plays an
indicate the formation of azomethine bond and the presence important role in stabilization of the CuO nanoparticles. It can
of free aldehyde groups, respectively, in the material.49 For also be seen from the plot that the material loses only ca. 5.5%
nCuO-FMS (Fig. 1(A)d), the peak at 1698 cm−1 disappears indi- of its weight up to 413 K and thus can be considered to be
cating the complete conversion of free –CHO groups to CvN. stable at least up to this temperature for its use as a catalyst. The
The band at 1647 cm−1 indicates the retention of azomethine percentage of functionalization in each step can be calculated
moiety. The peak at ca. 1595 cm−1 may be due to the presence from the data. The studies also give the amount of organic
of aromatic CvC units which are present both in trialdehyde loading on the silica framework for each material. It can be cal-
loaded SBA-15 and nCuO-FMS. For clarity, the region of inter- culated that 0.76 mmol of 3-APTES has been loaded on 1.0 g of
est for trialdehyde loaded SBA-15 and nCuO-FMS is shown in SBA-15 and the amount of trialdehyde and 2-aminophenol is
Fig. 1(B).
0.18 mmol g−1 and 0.345 mmol g−1, respectively.
Fig. 1 (A) FT-IR spectra of (a) SBA-15, (b) 3-APTES functionalized SBA-15, (c) trialdehyde loaded SBA-15 and (d) nCuO-FMS; (B) magnified region of
plot (c) and (d).
This journal is © The Royal Society of Chemistry 2019
Dalton Trans., 2019, 48, 17874–17886 | 17877

View Article Online
Paper
Dalton Transactions
Fig. 2 Thermogravimetric study of (a) SBA-15, (b) 3-APTES functiona-
lized SBA-15, (c) trialdehyde loaded SBA-15 and (d) nCuO-FMS.
Fig. 4 Wide angle powder X-ray diffraction pattern of nCuO-FMS.
Mesoporosity and microstructure
The powder X-ray diffraction patterns of SBA-15, 3-APTES func-
tionalized SBA-15, trialdehyde loaded SBA-15 and nCuO-FMS
are given in Fig. 3. All the samples are found to show a 2D-
ordered hexagonal mesostructure which is evident from the
presence of the three distinct diffraction peaks assigned to the
(100), (110) and (200) planes along with a very weak one for the
(210) plane.52,53 However, the intensities of the peaks get
lowered and the ordering of pores are affected in the materials
with gradual functionalization. In addition, a reduction in
pore size takes place which is indicated by the shifting of the
peaks to higher 2θ values. The wide angle diffraction pattern
of nCuO-FMS is shown in Fig. 4. Several diffraction peaks can
be observed which are indexed in the figure and correspond to
the characteristic planes of CuO.54 Thus, it is conclusive from
the figure that CuO nanoparticles have formed in the material.
Nitrogen physisorption analysis can be used to determine
the total surface area, pore size and pore volume of nanopor-
ous materials. Nitrogen adsorption/desorption isotherms have
been measured at 77 K for SBA-15 and all the other samples
obtained after each step of functionalization. From the iso-
therms shown in Fig. 5, it is possible to establish the meso-
porous structures of SBA-15, 3-APTES functionalized SBA-15,
trialdehyde loaded SBA-15 and nCuO-FMS. The BET surface
area, pore volume and pore size of all the samples are pre-
sented in Table 1. By comparing these data, we can conclude
that a gradual decrease in the BET surface area takes place
with gradual functionalization over the mesoporous SBA-15
support. This is expected as the surfaces become occupied by
various organic and inorganic moieties with every step of
functionalization. The pattern of the isotherms for all the
samples is type IV with a steep increase in the higher pressure
region because of capillary condensation. This is a character-
istic of the mesoporous nature of the materials.52,55 The iso-
therms of all the samples exhibit H1 type hysteresis loops
between the P/P0 values of 0.6 and 1.0 which is attributed to
Fig. 3 Powder X-ray diffraction patterns of (a) SBA-15, (b) 3-APTES
functionalized SBA-15, (c) trialdehyde loaded SBA-15 and (d) nCuO-FMS. the presence of well-defined cylindrical pore channels56 and
17878 | Dalton Trans., 2019, 48, 17874–17886
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
decreased to some extent (Fig. 6b), however, the basic hexag-
onal structure is retained quite well. The TEM image of
nCuO-FMS is shown in Fig. 6c. Spherical CuO particles with a
diameter of ca. 6–7 nm could be seen dispersed throughout
the matrix of mesoporous silica confirming the in situ gene-
ration of the nanoparticles. Thus, the powder X-ray diffraction,
N2 sorption experiments and TEM image analyses of the
samples establish their microstructure and mesoporosity. In
addition, the formation of CuO nanoparticles over the functio-
nalized silica support can also be established from the studies.
The amount of Cu2+ present in nCuO-FMS has been ascer-
tained from the atomic absorption spectrophotometric study.
It has been found that 1.0 g of nCuO-FMS contains 2.096 ×
10−4 mol or 13.32 mg of Cu2+.
Solid state NMR studies
The chemical environments around the silicon atom in the
synthesized materials have been studied by 29Si MAS NMR and
the results are given in Fig. 7. For SBA-15, peaks are obtained
at ca. −111.65 and −103.17 ppm (Fig. 7a) which can be
assigned to the Q4 and Q3 silica centers of the Si(OSi)n(OH)4−n
units. For the 3-APTES functionalized SBA-15 (Fig. 7b), apart
from the peaks for Q4 and Q3 silica species, additional peaks
appear at −67.0 and −58.06 ppm due to the incorporation of
the aminopropyl group in the matrix. The chemical environ-
ment of the starting silica support changes due to such
addition of aminopropyl groups and the new peaks can be
attributed to the T3 ((SiO)3Si-R-Si(OSi)3) and T2 ((HO)2(OSi)Si-
R-Si(OSi)2(OH)) species,58,59 respectively. The spectra for the
other two samples, trialdehyde loaded SBA-15 and nCuO-FMS
(Fig. 7c and d, respectively), show similar patterns to 3-APTES
modified SBA-15 which indicates the formation and retention
of imine bonds in both the samples. A marginal shifting of the
peak position is observed for nCuO-FMS (Fig. 7d) due to the
formation of CuO nanoparticles which are stabilized by the N
and O groups of the functionalized silica framework through
noncovalent interactions.60,61
Fig. 5 Nitrogen adsorption–desorption isotherms of (a) SBA-15, (b)
3-APTES functionalized SBA-15, (c) trialdehyde loaded SBA-15 and (d)
nCuO-FMS. For clarity, the Y-axis values have been increased by 100,
100 and 50 cc g−1 for plots a, b and c, respectively. Adsorption points
are marked by filled symbols and desorption points by empty symbols.
Inset: NLDFT pore size distribution of (a’) SBA-15, (b’) 3-APTES functio-
nalized SBA-15, (c’) trialdehyde loaded SBA-15 and (d’) nCuO-FMS.
Y-axis values have been increased by 0.3, 0.25 and 0.15 cc nm−1 g−1, for
plot (a’), (b’) and (c’), respectively.
Table 1 Surface area, pore volume and pore size of the samples at
various stages
BET surface
area (m2 g−1
Pore volume Pore size
Sample
)
(cc g−1
)
(nm)
(a) SBA-15
(b) 3-APTES
732
366
0.966
0.652
8.15
7.45
functionalized SBA-15
(c) Trialdehyde loaded
SBA-15
13C CP MAS NMR studies have been performed with the
materials having organic contents and the spectra are shown
in Fig. 8. The spectrum for 3-APTES functionalized SBA-15
(Fig. 8a) shows peaks at 9.71, 22.39, 29.17 and 42.86 ppm. The
signal at 42.86 ppm may be attributed to the carbon adjacent
243
133
0.315
0.205
5.95
4.75
(d) nCuO-FMS
intercrystallite adsorption.57 The average pore diameter of the to the amine group, the signals at 29.17 and 22.39 ppm may
starting mesoporous SBA-15 from the NLDFT model is appear due to the α and β carbon atoms with respect to the
7.86 nm (inset of Fig. 5). The pore sizes of the functionalized –NH2 group and the signal at 9.71 ppm may be attributed to
materials follow a gradual descending trend as the incorpor- the other aliphatic carbon atoms. For trialdehyde loaded
ation of functional groups on the pore walls of the silica SBA-15 (Fig. 8b), several new peaks emerge at 10.47, 21.84,
support inhibits the access of nitrogen gas molecules into the 42.86 and 63.98 ppm for the aliphatic carbon atoms and at
pores. A similar decreasing trend is also observed for the pore 151, 164.84 and 128.95 ppm for the aromatic carbon atoms.
volume of the samples.
Two characteristics peaks at 183.72 and 199.78 ppm appear
The transmission electron microscopic (TEM) images of due to the formation of the CvN bond (imine bond) and the
SBA-15, trialdehyde loaded SBA-15 and nCuO-FMS are shown free aldehyde group, respectively. From this spectrum, we can
in Fig. 6. The image for SBA-15 (Fig. 6a) confirms the for- conclude that Schiff base reaction has taken place between the
mation of a well-formed hexagonally arranged mesoporous trialdehyde and 3-APTES loaded silica and at the same time
structure as desirable for an appropriate solid support. Upon residual free aldehyde groups are also present. For nCuO-FMS
functionalization, the long range ordering of the pores is (Fig. 8c), the peaks corresponding to the aliphatic and aro-
This journal is © The Royal Society of Chemistry 2019
Dalton Trans., 2019, 48, 17874–17886 | 17879

View Article Online
Paper
Dalton Transactions
Fig. 6 TEM images of (a) SBA-15, (b) trialdehyde loaded SBA-15, (c) nCuO-FMS and (d) reused nCuO-FMS.
Fig. 7 Solid state 29Si MAS NMR spectra of (a) SBA-15, (b) 3-APTES
functionalized SBA-15, (c) trialdehyde loaded SBA-15 and (d) nCuO-FMS.
Fig. 8 Solid state 13C CP-MAS NMR spectra of (a) 3-APTES functiona-
lized SBA-15, (b) trialdehyde loaded SBA-15 and (c) nCuO-FMS.
17880 | Dalton Trans., 2019, 48, 17874–17886
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
matic regions are found to remain almost intact. However, two reveal two states with binding energies of 934.6 eV and 932.1
new peaks appear at 147.76 and 163.67 ppm which may be eV and assigned to the Cu 2p3/2 states, for Cu(II), in CuO and
attributed to the aromatic carbon attached to the phenolic reduced Cu, respectively; the lower binding energy species can
–OH group and imine bond formation, respectively. The peak be attributed to the reduction of the Cu(II) species during
at 163.67 ppm confirms the complete conversion of the analysis.62,63 Fig. 9c and d show the multiple states of oxygen
residual –CHO groups of trialdehyde to CvN after conden- and carbon present within the material. The peak at 532.7 eV
sation with 2-aminophenol.
is assigned primarily to Si–O bonds, although the presence of
carbon–oxygen functions at this energy also cannot be dis-
counted. The peaks at 531.1 and 533.8 eV can be ascribed to
inorganic (Cu–O)64 and organic oxygen, respectively. The
binding energies of different types of carbon present in the
sample are illustrated in Fig. 9d. Four distinct peaks appear at
284.3, 284.7, 286 and 287.1 eV and can be attributed to the
XPS analysis
The wide scan and fitted XPS spectra of nCuO-FMS are shown
in Fig. 9. The survey spectrum (Fig. 9a) reveals the presence of
Si, C, O, N and Cu in the material, in agreement with the
expected elemental distribution. The Cu(2p) spectra (Fig. 9b)
Fig. 9 XPS spectra of nCuO-FMS (a) wide scan, (b) Cu 2p core-level, (c) O 1s core-level and (d) C 1s core-level.
This journal is © The Royal Society of Chemistry 2019
Dalton Trans., 2019, 48, 17874–17886 | 17881

View Article Online
Paper
Dalton Transactions
presence of the CvC, C–C, C–O and CvO species in carried out for different time periods (Table 3). It can be seen
nCuO-FMS, respectively.65
that the conversion increases marginally as the reaction time
is increased from 3 h to 6, 9 and 12 h. After 12 h, the isolated
yield obtained is 83% (entry 4) which is a little better than the
78% yield that is obtained within 3 h (entry 1) of the reaction.
So, it can be concluded that if the reaction time is increased
the yields do not increase significantly, and thus in the
present study, the reaction time has been optimized at 3 h.
However, it should be noted that isolated yields are always
lower than the actual conversion in a reaction since some
amount of the product is lost during the process of work-up,
isolation and purification of the final reaction mixture.
After determining the optimized reaction conditions, the
conversions have been carried out using various substituted
iodobenzenes to produce the corresponding 1,2-diphenyl di-
selenide derivatives (Table 4). When 4-methyl iodobenzene and
3-methyl iodobenzene are used, the products, 1,2-di-p-tolyl-
diselane (3b) and 1,2-di-m-tolyldiselane (3c), are obtained with
very good yields of 77 and 75%, respectively. To explore the
scope of substrate for the reactions, substituted iodobenzenes
with different groups (–F, –Cl, –Br, –CF3) have been studied.
4-Fluoro iodobenzene reacted to form 1,2-bis(4-fluorophenyl)
diselenide (3d) with a 74% yield, 4-chloro iodobenzene formed
1,2-bis(4-chlorophenyl)diselenide (3e) with a 76% yield and
4-bromo iodobenzene formed 1,2-bis(4-bromophenyl)disele-
nide (3f) with a 75% yield. 3-Trifluoromethyl iodobenzene
gives 1,2-bis(3-(trifluoromethyl)phenyl)diselenide (3g) as the
product with a 72% yield. A heterocyclic iodo compound,
2-iodothiophene, has also been used for the study. The
product, 1,2-di(thiophen-2-yl)diselenide (3h), is obtained and
the yield is 73%. Thus, it is observed that iodobenzene with no
substituent gives the finest result among the substrates.
The 1H NMR, 13C NMR, 77Se NMR and mass spectra are
given in the ESI† with the structure of the corresponding
compounds.
Catalytic studies
The catalytic efficiency of nCuO-FMS has been studied for
Se–Se coupling reaction under different reaction conditions
(Table 2). To begin with, different amounts of nCuO-FMS are
used to study the reaction between iodobenzene (0.5 mmol),
Se0 powder (1.0 mmol) and KOH (1.0 mmol) in 2.0 ml of
dimethyl sulphoxide (DMSO) at 363 K under nitrogen atmo-
sphere to ascertain the maximum yield. The product obtained
is 1,2-diphenyl diselenide (3a). The reaction does not produce
significant amounts of the product when 1 mg of nCuO-FMS
is used for the catalytic reaction (entry 1). With a gradual
increase in the amount of the catalyst to 2, 5 and 10 mg
(entries 2–4), the yield is found to increase slowly to 25, 46 and
64%, respectively. When the amount of nCuO-FMS is increased
to 20 mg, the yield reaches 78% (entry 5), and this is the
maximum value at the given temperature. When the amount
of catalyst is increased further to 30 mg, product formation is
not affected much and the yield is 79% (entry 6). Thus, it can
be established that 20 mg of nCuO-FMS is sufficient for achiev-
ing the best yield of 3a for this optimization reaction under
the specified conditions. In the next step, the base is altered;
KOH is replaced by NaOH and the yield is found to be lower at
67% (entry 7). Then the reaction is carried out by changing the
solvent to dimethyl formamide (DMF) and acetonitrile
(CH3CN), and the yields reduce to 73 and 63% (entries 8 and
9), respectively. Finally, the reaction is performed at different
temperatures. Increasing the temperature to 373 K does not
improve the product yield (78% yield, entry 10), while by
decreasing the temperature to 333 K a lower yield (55%, entry
11) is obtained.
To study the time dependent conversion of iodobenzene to
1,2-diphenyl diselenide, the reaction in DMSO solvent is then
Table 2 Optimization of the catalytic conditionsa
nCuO-FMS
(in mg)
Temperature
(K)
Isolated
Entry
Base
Solvent
yieldb (%)
TON
TOF
1
2
3
4
5
6
7
8
1
2
5
KOH
KOH
KOH
KOH
KOH
KOH
NaOH
KOH
KOH
KOH
KOH
363
363
363
363
363
363
363
363
363
373
333
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
Trace
25
46
64
78
79
67
73
63
—
—
9.940
29.82
54.87
76.35
93.03
94.23
79.91
87.07
75.14
93.03
65.60
18.288
25.445
31.011
31.409
26.638
29.023
25.05
10
20
30
20
20
20
20
20
9
10
11
CH3CN
DMSO
DMSO
78
55
31.011
21.867
a All the reactions are carried out for 3 h with 0.5 mmol of substrate, 1.0 mmol Se0 and 1.0 mmol of base. b Yields determined by NMR
spectroscopy.
17882 | Dalton Trans., 2019, 48, 17874–17886
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
Table 3 Time dependent conversion of iodobenzene in the catalytic
Se–Se coupling reactiona
the substrate has been studied under the optimized conditions.
In each cycle, 0.5 mmol iodobenzene, 1.0 mmol Se0 powder and
1.0 mmol KOH are taken in 2.0 ml of DMSO and the reaction
is carried out at 363 K under nitrogen atmosphere for 3 h.
Then the catalyst is recovered, regenerated and reused in the
subsequent run. The conversion (%) against the number of
reaction cycles for the coupling is given in Fig. 10. The percen-
tage conversions for five cycles are 78, 78, 75, 70 and 68%,
respectively. It can be seen that the efficiency of the catalyst
remains more or less the same in the first two cycles. After
that there is a marginal drop in the percentage of conversion
in each step and after five cycles it is 68%. The gradual drop in
conversion from the first to the fifth cycle may be attributed to
the partial damage of the mesoporous structure of the catalyst
when it remains in the matrix of the catalytic system for a pro-
longed period during the reactions. Thus, it can be inferred
that the catalyst has a good recycling efficiency. The TEM
image of recycled nCuO-FMS is illustrated in Fig. 6d. It shows
that the porous structure of the mesoporous silica matrix is
retained even after the catalytic performance and the immobil-
ization of the CuO nanoparticles over it also remains intact. In
addition, the surface area of the recycled catalyst is also not
reduced to a large extent which adds to the reusability of the
material as a catalyst.
Time
(h)
Isolated
Entry
yieldb (%)
TON
TOF
1
2
3
4
3
6
9
12
78
80
81
83
93.03
95.42
96.61
99.00
31.01
31.81
32.20
33.00
a The reactions have been carried out in 2 ml of DMSO as the solvent
with 0.5 mmol of iodobenzene, 1.0 mmol of Se0 powder and 1.0 mmol
of KOH, at 363 K using 20 mg of nCuO-FMS as the catalyst. b Yields
determined by NMR spectroscopy.
Table 4 Catalytic Se–Se coupling reactions using different substratesa
Mechanism
A plausible mechanism66 can be proposed for the Se–Se coup-
ling reaction and it is shown in Scheme 2. In the presence of a
base, selenium gives selenide or selenite anion and in a super
basic DMSO/KOH medium a reductive dimsyl species is pro-
duced. The dimsyl species is responsible for the formation of
the desired diselenide anion. This preformed anion is con-
sidered to be the active species involved in the catalytic cycle.
The formation of species a and b takes place by the ligand
exchange with the diselenide anion and may further generate
complex c. Then, species c may undergo reductive elimination
via the formation of the initial coupling product d and the
CuO nanoparticles in nCuO-FMS are regenerated. Then d prob-
ably reacts with another unit of b to form a new complex e.
Finally, the desired diselenide compound f is formed by
another step of reductive elimination and the other unit of
Isolated
Entry
R/substrate
yieldb (%)
TON
TOF
3a
3b
3c
3d
3e
3f
—
4-CH3
3-CH3
4-F
4-Cl
4-Br
78
77
75
74
76
75
72
73
93.03
91.84
89.46
88.26
90.65
89.46
85.88
87.07
31.01
30.61
29.82 CuO nanoparticles of nCuO-FMS could be regenerated. The
29.42
30.22
29.82
28.63
29.02
CuO nanoparticles thus recovered can be used in the next cata-
lytic cycle.
3g
3h
3-CF3
2-Iodothiophene
The amount of copper present in 1 g of nCuO-FMS as deter-
mined by AAS study is 2.096 × 10−4 mol or 13.32 mg of Cu. We
have optimized the amount of catalyst at 20 mg for all the reac-
tions, which means 0.041 mmol or 0.266 mg of Cu is used in
each cycle to catalyse 1 mmol of substrate. On the other hand,
when commercially available CuO nanoparticles have been
used,40,44 the amounts of Cu used for the catalysis have been
found to be 3.2–6.4 mg of Cu for 1 mmol of substrate. Clearly,
the amount of active copper centers in nCuO-FMS is much less
a The reactions have been carried out for 3 h in 2 ml of DMSO as the
solvent with 0.5 mmol of the respective substrates, 1.0 mmol of Se0
powder and 1.0 mmol of KOH at 363 K using 20 mg of nCuO-FMS as
the catalyst. b Yields determined by NMR spectroscopy.
Recyclability
The ability to recycle is the most attractive feature of a hetero- compared to that in the reported studies. This is the advantage
geneous catalyst. In this work, to study the recyclability of of a heterogeneous framework where more active sites are
nCuO-FMS in Se–Se coupling, the reaction of iodobenzene as exposed on the surface of the catalyst and thus a very small
This journal is © The Royal Society of Chemistry 2019
Dalton Trans., 2019, 48, 17874–17886 | 17883

View Article Online
Paper
Dalton Transactions
Fig. 10 Recycling efficiency of nCuO-FMS for Se–Se coupling using iodobenzene.
Conclusions
In this article, we have synthesized a mesoporous silica based
catalyst with immobilized CuO nanoparticles nCuO-FMS,
using a facile synthetic route. The generation of CuO nano-
particles takes place in situ in the presence of 2-amino-
phenol, which also acts as a stabilizing support to the metal
oxide particles. The silica support, SBA-15, and all the other
subsequent organically functionalized frameworks, includ-
ing the catalyst, have been characterized thoroughly to estab-
lish their structure. These CuO nanoparticles containing
porous silica with good specific surface area are found to
catalyze the Se–Se coupling reaction to produce symmetrical
diselenides with high yields. Thus, it provides a simple and
efficient method for the preparation of diselenides through
the cross-coupling reaction between selenium and aryl
iodides. The process is chemoselective and can be used to
prepare a wide range of substituted symmetrical diselenides
containing e.g. methoxy, carboxylate, hydroxyl, amino, alde-
hyde and bromo groups. The superior activity of the catalyst
can be attributed to the nanoscale dimension of the CuO
particles and the high surface area of the silica matrix
which predisposes the substrates better at the catalytically
active metal centres. The catalyst is cheaper than the com-
mercially available CuO nanopowder and due to its hetero-
geneous nature it can be economically used for several reac-
tion cycles.
Scheme 2 Plausible mechanism for organo diselenide synthesis.
amount of the catalyst is sufficient to catalyse the reactions.
This is also beneficial from an environmental point of view. In
addition, the CuO nanopowder based catalytic systems
reported in the previous studies40,44 do not provide any data
on the reusability of the catalyst. In this respect, the supported
heterogeneous catalyst reported in this work can be recycled
several times and is thus more economical compared to as-
purchased CuO nanoparticle based catalytic systems.
Conflicts of interest
There are no conflicts to declare.
17884 | Dalton Trans., 2019, 48, 17874–17886
This journal is © The Royal Society of Chemistry 2019

View Article Online
Dalton Transactions
Paper
22 N. K. Ojha, G. V. Zyryanov, A. Majee, V. N. Charushin,
O. N. Chupakhin and S. Santra, Coord. Chem. Rev., 2017,
353, 1.
Acknowledgements
MN thanks the DST-SERB, India (SB/FT/CS-004/2014 dated 27/
06/2014) and the WB-DST, India (ST/P/S&T/15G-20/2018) for 23 A. Fihri, M. Bouhrara, B. Nekoueishahraki, J.-M. Basset and
financial support. The authors are thankful to N. Pradhan and V. Polshettiwar, Chem. Soc. Rev., 2011, 40, 5181.
J. Guin of the Indian Association for the Cultivation of Science 24 G. Mugesh, W. W. du Mont and H. Sies, Chem. Rev., 2001,
for providing TEM and GC-MS facilities and G. Ghosh of Visva-
Bharati for AAS studies.
101, 2125.
25 C. W. Nogueira and J. B. T. Rocha, Arch. Toxicol., 2011, 85,
1313.
26 K. Didehban, E. Vessally, A. Hosseinian, L. Edjlali and
E. S. Khosroshahi, RSC Adv., 2018, 8, 291.
27 V. Nascimento, E. E. Alberto, D. W. Tondo, D. Dambrowski,
M. R. Detty, F. Nome and A. L. Braga, J. Am. Chem. Soc.,
2012, 134, 138.
References
1 K. C. Gupta, A. K. Sutar and C.-C. Lin, Coord. Chem. Rev.,
2009, 253, 1926.
2 D. R. Godhani, H. D. Nakum, D. K. Parmar, J. P. Mehta and 28 D. M. Freudendahl, S. Santoro, S. A. Shahzad, C. Santi and
N. C. Desai, J. Mol. Catal. A: Chem., 2017, 426, 223. T. Wirth, Angew. Chem., Int. Ed., 2009, 48, 8409.
3 M. Trueba and S. P. Trasatti, Eur. J. Inorg. Chem., 2005, 17, 29 A. Gucchait, N. Joardar, P. K. Parida, P. Roy, N. Mukherjee,
3393.
A. Dutta, R. Yesuvadian, S. P. SinhaBabu, K. Jana and
A. K. Misra, Eur. J. Med. Chem., 2018, 143, 598.
30 D. Plano, Y. Baquedano, D. Moreno-Mateos, M. Font,
A. Jiménez-Ruiz, J. A. Palop and C. Sanmartín, Eur. J. Med.
Chem., 2011, 46, 3315.
31 P. G. Geiger, F. Lin and A. W. Girotti, Free Radical Biol.
Med., 1993, 14, 251.
32 E. E. Alberto, V. Nascimento and A. L. Braga, J. Braz. Chem.
Soc., 2010, 21, 2032.
4 E. L. Margelefsky, R. K. Zeidan and M. E. Davis, Chem. Soc.
Rev., 2008, 37, 1118.
5 A. Zarnegaryan, M. Moghadam, S. Tangestaninejad,
V. Mirkhani and I. Mohammdpoor-Baltork, New J. Chem.,
2016, 40, 2280.
6 Y. Zhang, A. Wang and T. Zhang, Chem. Commun., 2010, 46,
862.
7 J. M. Planeix, N. Coustel, B. Coq, V. Brotons,
P. S. Kumbhar, R. Dutartre, P. Geneste, P. Bernier and 33 C. W. Nogueira, G. Zeni and J. B. T. Rocha, Chem. Rev.,
P. M. Ajayan, J. Am. Chem. Soc., 1994, 116, 7935. 2004, 104, 6255.
8 A. Dhakshinamoorthy and H. Garcia, Chem. Soc. Rev., 2014, 34 E. R. T. Tiekink, Dalton Trans., 2012, 41, 6390.
43, 5750.
35 G. I. Dzhardimalieva and I. E. Uflyand, J. Coord. Chem.,
2019, 72, 1.
36 T. Manna and A. K. Misra, SynOpen, 2018, 2, 229.
9 S. Zhou, M. Johnson and J. G. C. Veinot, Chem. Commun.,
2010, 46, 2411.
10 H. Noh, Y. Cui, A. W. Peters, D. R. Pahls, M. A. Ortuñ, 37 D. Tanini, A. Degl’Innocenti and A. Capperucci, Eur. J. Org.
N. A. Vermeulen, C. J. Cramer, L. Gagliardi, J. T. Hupp and
O. K. Farha, J. Am. Chem. Soc., 2016, 138, 14720.
11 C. M. A. Parlett, K. Wilson and A. F. Lee, Chem. Soc. Rev.,
2013, 42, 3876.
Chem., 2015, 357.
38 M. A. Rizvi, S. Guru, T. Naqvi, M. Kumar, N. Kumbhar,
S. Akhoon, S. Banday, S. K. Singh, S. Bhushan,
G. M. Peerzada and B. A. Shah, Bioorg. Med. Chem. Lett.,
2014, 24, 3440.
12 T. Toyao, K. Miyahara, M. Fujiwaki, T.-H. Kim, S. Dohshi,
Y. Horiuchi and M. Matsuoka, J. Phys. Chem. C, 2015, 119, 39 Z. Li, F. Ke, H. Deng, H. Xu, H. Xiang and X. Zhou, Org.
8131. Biomol. Chem., 2013, 11, 2943.
13 R. M. Rioux, H. Song, J. D. Hoefelmeyer, P. Yang and 40 G. V. Botteselle, M. Godoi, F. Z. Galetto, L. Bettanin,
G. A. Somorjai, J. Phys. Chem. B, 2005, 109, 2192.
14 C. Xu, X. Wang, J. Zhu, X. Yang and L. Lu, J. Mater. Chem.,
2008, 18, 5625.
D. Singh, O. E. Rodrigues and A. L. Braga, J. Mol. Catal. A:
Chem., 2012, 365, 186.
41 A. Krief, W. Dumont and C. Delmotte, Angew. Chem., Int.
Ed., 2000, 39, 1669.
15 G. B. Shul’pin, Catalysts, 2016, 6, 50.
16 K. C. Gupta and A. K. Sutar, Coord. Chem. Rev., 2008, 252, 42 F. Tian, Z. Yu and S. Lu, J. Org. Chem., 2004, 69, 4520.
1420. 43 P. Salama and C. Bernard, Tetrahedron Lett., 1998, 39, 745.
17 M. B. Thathagar, J. Beckers and G. Rothenberg, J. Am. 44 D. Singh, A. M. Deobald, L. R. S. Camargo, G. Tabarelli,
Chem. Soc., 2002, 124, 11858.
O. E. D. Rodrigues and A. L. Braga, Org. Lett., 2010, 12,
18 T. Kamal, Polym. Test., 2019, 77, 105896.
3288.
19 L. Xu, J. Zhang, Z. Li, Q. Ma, Y. Wang, F. Cui and T. Cui, 45 D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson,
New J. Chem., 2019, 43, 520. B. F. Chmelka and G. D. Stucky, Science, 1998, 279, 548.
20 X. Xiong, C. You, Z. Liu, A. M. Asiri and X. Sun, ACS 46 T. Mallegol, S. Gmouh, M. A. A. Meziane, M. B.-Desce and
Sustainable Chem. Eng., 2018, 6, 2883. O. Mongin, Synthesis, 2005, 1771.
21 S. Vásquez-Céspedes, K. M. Chepiga, N. Möller, 47 T. Das, H. Uyama and M. Nandi, New J. Chem., 2018, 42,
A. H. Schäfer and F. Glorius, ACS Catal., 2016, 6, 5954.
6416.
This journal is © The Royal Society of Chemistry 2019
Dalton Trans., 2019, 48, 17874–17886 | 17885

View Article Online
Paper
Dalton Transactions
48 D. Singha, T. Das, L. Satyanarayana, P. Roy and M. Nandi, 59 S. Inagaki, S. Guan, T. Ohsuna and O. Terasaki, Nature,
New J. Chem., 2019, 43, 15563. 2002, 416, 304.
49 K. Sarkar, K. Dhara, M. Nandi, P. Roy, A. Bhaumik and 60 C. Sarkar, S. Pendem, A. Shrotri, D. Q. Dao, P. P. T. Mai,
P. Banerjee, Adv. Funct. Mater., 2009, 19, 223.
50 C. Sarkar, P. Koley, I. Shown, J. Lee, Y.-F. Liao, K. An,
J. Tardio, L. Nakka, K.-H. Chen and J. Mondal, ACS
Sustainable Chem. Eng., 2019, 7, 10349.
51 S. K. Verma and V. K. Singh, J. Coord. Chem., 2015, 68,
1072.
T. N. Ngoc, D. R. Chandaka, T. V. Rao, Q. T. Trinh,
M. P. Sherburne and J. Mondal, ACS Appl. Mater. Interfaces,
2019, 11, 11722.
61 S. C. Shit, R. Singuru, S. Pollastri, B. Joseph, B. S. Rao,
N. Lingaiah and J. Mondal, Catal. Sci. Technol., 2018, 8,
2195.
52 A. P. Wight and M. E. Davis, Chem. Rev., 2002, 102, 3589.
53 O. Olkhovyk and M. Jaroniec, J. Am. Chem. Soc., 2005, 127, 60.
54 V. V. T. Padil and M. Černík, Int. J. Nanomed., 2013, 8, 889.
55 A. Stein, Adv. Mater., 2003, 15, 763.
62 L. Xu, J. Zhang, Z. Li, Q. Ma, Y. Wang, F. Cui and T. Cui,
New J. Chem., 2019, 43, 520.
63 T. L. Freeman, S. D. Evans and A. Ulman, Thin Solid Films,
1994, 244, 784.
56 M. Thommes, K. Kaneko, A. V. Neimark, J. P. Olivier, 64 H. Wang, J.-Z. Xu, J.-J. Zhu and H.-Y. Chen, J. Cryst. Growth,
F. Rodriguez-Reinoso, J. Rouquerol and K. S. Sing, Pure
Appl. Chem., 2015, 87, 1051.
57 T. Tanev and T. J. Pinnavaia, Science, 1996, 271, 1267.
2002, 244, 88.
65 Y. Liu, L. Ma, D. Zhang, G. Han and Y. Chang, RSC Adv.,
2017, 7, 12027.
58 S. Inagaki, S. Guan, Y. Fukushima, T. Ohsuna and 66 V. P. Reddy, A. V. Kumar, K. Swapna and K. R. Rao, Org.
O. Terasaki, J. Am. Chem. Soc., 1999, 121, 9611. Lett., 2009, 11, 951.
17886 | Dalton Trans., 2019, 48, 17874–17886
This journal is © The Royal Society of Chemistry 2019