Surface engineered Iridium-based magnetic photocatalyst paving a path towards visible light driven C-H arylation and cyanation reaction

Article abstract of DOI:10.1016/j.jcat.2021.08.014

The report presents the fabrication and application of a highly versatile, magnetic and robust iridium based photoredox nanocatalyst. Herein, Ir(PPy)₃ based photocatalyst sites have been chemically engineered over the magnetic nanoparticles to encompass the captivating features of homogeneous iridium photocatalyst with the magnetically recyclable core. A household photoreactor was designed and fabricated to achieve highly selective visible light driven oxidative C-H arylation and C-H cyanation under sustainable and ambient reaction conditions utilizing the Ir@PyBz@ASMNPs photoredox nanocatalyst. The environment friendly Ir@PyBz@ASMNPs shows excellent photocatalytic activity, broad substrate adaptability and outstanding recyclability compared to the analogous homogeneous catalysts. Indeed, the Ir@PyBz@ASMNPs possess some key features including high surface area, high iridium metal loading and excellent stability. This work is expected to enlighten and provide new insights in the rational design of high performance and recoverable photoredox nanocatalyst through surface engineering strategy.

Full text of DOI:10.1016/j.jcat.2021.08.014

Journal of Catalysis 401 (2021) 297–308
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Surface engineered Iridium-based magnetic photocatalyst paving a path
towards visible light driven C-H arylation and cyanation reaction
Pooja Rana a, Rashmi Gaur a, Bhawna Kaushik a, Pooja Rana a, Sneha Yadav a, Priya Yadav a, Priti Sharma c,
Manoj B. Gawande b, , Rakesh K. Sharma a,
⇑
⇑
a Green Chemistry Network Centre, Department of Chemistry, University of Delhi, New Delhi 110007, India
b Department of Chemistry and Engineering, Institute of Chemical Technology Mumbai-Marathwada Campus, Jalna 431213, Maharashtra, India
c Regional Centre of Advanced Technologies and Materials, Czech Advanced Technology and Research Institute, Palacky´ University, 779 00 Olomouc, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
The report presents the fabrication and application of a highly versatile, magnetic and robust iridium
based photoredox nanocatalyst. Herein, Ir(PPy)3 based photocatalyst sites have been chemically engi-
neered over the magnetic nanoparticles to encompass the captivating features of homogeneous iridium
photocatalyst with the magnetically recyclable core. A household photoreactor was designed and fabri-
cated to achieve highly selective visible light driven oxidative C-H arylation and C-H cyanation under sus-
tainable and ambient reaction conditions utilizing the Ir@PyBz@ASMNPs photoredox nanocatalyst. The
environment friendly Ir@PyBz@ASMNPs shows excellent photocatalytic activity, broad substrate adapt-
ability and outstanding recyclability compared to the analogous homogeneous catalysts. Indeed, the
Ir@PyBz@ASMNPs possess some key features including high surface area, high iridium metal loading
and excellent stability. This work is expected to enlighten and provide new insights in the rational design
of high performance and recoverable photoredox nanocatalyst through surface engineering strategy.
Ó 2021 Elsevier Inc. All rights reserved.
Received 8 April 2021
Revised 10 July 2021
Accepted 2 August 2021
Available online 9 August 2021
Keywords:
Photoredox
Nanocatalyst
Magnetically retrievable
Visible light
Heterogeneous catalyst
1. Introduction
and UV light catalyzed reactions, the visible light catalyzed reac-
tions reduce the possibility of side reactions due to lack of visible
Photoredox catalysis has gained colossal attention for engineer-
ing environmentally sustainable processes due to its ability to
exploit inexpensive, clean and endless renewable solar energy to
engage single electron transfer (SET) for synthetic manipulation
or catalytic activation of organic molecules [1]. Over the past few
years, numerous research groups have widely employed the power
of light for various applications such as photocatalysis, pho-
todegradation, singlet oxygen generation, water splitting, reduc-
tion of carbon dioxide, etc. [2–5]. In fact, several transition
metals based homogeneous catalysts (such as ruthenium, iridium
and copper polypyridyl complexes) and organic moieties (like
eosin Y, rose bengal etc.) have garnered particular appreciation in
the field of photocatalysis [3,6–9]. These photocatalysts possess
various attention grabbing properties such as energy efficiency,
stability, absorbance in visible range, long-lived photoexcited
states, versatile nature and readily tunable photophysical proper-
ties by modification of the ligand scaffold [6]. Unlike the thermal
light absorbance by organic compounds [9,10].
Over the years, the chemistry of tris-cyclometalated coordina-
tively saturated, 18-electron d6 complexes of iridium, such as Ir
(ppy)3, has been the focus of great attention due to the ease of syn-
thesis and diversification, stability at room temperature, and excel-
lent photoredox properties [11,12]. Additionally, the iridium
complexes unveil a wide variety of applications in the field of solar
cells, light-emitting diodes (LEDs), sensing, biology and as initia-
tors in free radical polymerization [12]. Despite these above-
mentioned advantages, progress must be made toward ease of sep-
aration, recyclability, stability, and environmental neutrality of
these photoredox catalysts in order to move the field toward prac-
tical utility in academia and industry [13,14]. Consequently, the
development of a heterogeneously immobilized photosensitizer
system that maintains photoredox capability upon immobilization
is a significant step toward this goal. Henceforth, coordination
chemistry delivers a new pathway for engineering heterogeneous
supports through immobilizing photocatalytically active sites hav-
ing high activity and selectivity. To date, a limited number of cova-
lently or physically immobilized photoredox catalyst over cores
(such as graphene, TiO2, silica, polymer, ZnO, NPs etc.) have been
⇑
Corresponding authors.
E-mail addresses: mb.gawande@marj.ictmumbai.edu.in (M.B. Gawande), rkshar-
magreenchem@hotmail.com (R.K. Sharma).
https://doi.org/10.1016/j.jcat.2021.08.014
0021-9517/Ó 2021 Elsevier Inc. All rights reserved.

P. Rana, R. Gaur, B. Kaushik et al.
Journal of Catalysis 401 (2021) 297–308
developed and utilized for catalytic applications [15–19]. Apart
from their countless advantages and tremendous efforts in the
field, certain drawbacks such as difficult surface modification to
introduce chelating sites, durability, reduced recyclability and seri-
ous economic and environmental issues need to be resolved.
Hence, a versatile heterogeneous system is required which can
overcome these aforementioned challenges and can be further
explored for efficient organic transformation of pharmaceutically
metals remain the center of attraction among the scientific com-
munity [23–25]. However, the previously reported methodologies
have several limitations such as utilization of highly toxic and
unrecoverable catalysts, harsh reaction conditions like bulk
amount (more than 3 equiv.) of strong base, longer reaction time,
and elevated temperatures [26–28]. On a different note, research-
ers have also explored straightforward approaches for the C-C
bond formation by utilizing AgF based and nickel superstructure
heterogeneous photocatalysts for the synthesis of biaryls (see com-
parison table S1a). Unfortunately, the involvement of high power
consuming white light sources (such as Xenon lamps with power
more than 100 W) as well as destructive nature of UV radiation,
rigorously dry conditions, and low recyclability limits the large-
scale efficacy (see comparison table S1a). Recently, our group
devised a magnetically retrievable ruthenium based photocatalytic
system, Ru@DAFO@ASMNPs, which exhibited outstanding cat-
alytic performance [29]. In extension to our ongoing research work,
[30–33] our efforts are to design and develop a heterogeneous pho-
viable motifs (such as biaryls,
of visible light.
a-aminonitriles etc.) in the presence
Biaryl moieties are ubiquitous and are utilized extensively in a
variety of materials, catalytic systems, biological and pharmaceuti-
cal fields. The biaryl motifs also show high utility in various molec-
ular switches, motors and medicines such as antibiotic, angiotensin
receptor blockers (ARBs), antifungal, anticancer, anti-inflamma
tory/antiarthritic, analgesic, antiemetic as well as antihypertensive
drugs (Fig. 1) [20–22]. Despite various achievements in the field,
the C-C bond formation reaction by availing various transition
Fig. 1. Utilization of biaryl precursors in diverse fields.
298

P. Rana, R. Gaur, B. Kaushik et al.
Journal of Catalysis 401 (2021) 297–308
toredox nanocatalyst by adopting the coordination chemistry for
stably anchoring the iridium metal complex over the magnetic
support to achieve a highly efficient, robust, cost-effective, mag-
netically retrievable and reusable system.
triethoxysilane and iridium chloride were acquired from Alfa
Aesar.
4-(2-Pyridyl)benzaldehyde
and
1,2,3,4-
tetrahydroisoqinoline were commercially obtained from TCI. The
commercially unavailable substrates, including tetrahydroiso-
quinolines derivatives were prepared in the lab by utilizing previ-
ously reported methods. All the photochemical reactions were
under air atmosphere, unless otherwise indicated. The solvents/-
substrate, like benzene and p-xylene were of analytical grade and
purified by distillation prior to use. HPLC grade DMSO was dried
using activated molecular sieves. Double distilled water was used
for the synthetic procedure of material.
Henceforth, Scheme 1 was employed to acquire the iridium
based magnetically retrievable photoredox nanocatalyst. Initially,
the magnetic nanoparticles of Fe3O4 (MNPs) were synthesized by
availing the co-precipitation technique [34]. Afterwards, the silica
coated MNPs (SMNPs) were prepared simply by sol–gel approach
by suspending the Fe3O4 NPs with tetra-ethyl orthosilicate (TEOS)
under vigorous stirring [29]. These SMNPs were modified with (3-
aminopropyl)triethoxysilane (APTES) to form amine functionalized
SMNPs (ASMNPs) with subsequent immobilization of 4-(2-pyridyl)
benzaldehyde (PyBz) ligand via Schiff base condensation [35].
Afterwards, homogeneous dimer complex of [Ir(PyBz)2Cl]2 was
separately synthesized by modification of previously reported pro-
tocol [36] and was utilized along with PyBz immobilized nanopar-
ticles (PyBz@ASMNPs) for the synthesis of the final photoredox
nanocatalyst of iridium (Ir@PyBz@ASMNPs) [36]. The obtained
Ir@PyBz@ASMNPs photoredox nanocatalyst was characterized by
Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction
(XRD), transmission electron microscopy (TEM), energy dispersive
spectrometry (EDS) and various other physico-chemical tech-
niques. The photocatalytic performance of Ir@PyBz@ASMNPs pho-
toredox nanocatalyst was also studied in detail for C-H arylation of
arenes with aryl iodide and oxidative cyanation of tertiary amines.
The aforementioned method has potential to fabricate various high
performance heterogeneous photoredox nanocatalysts. These pho-
toredox nanocatalysts can be further utilized as a reliable and pow-
erful tool to carry out light promoted organic synthesis under mild
conditions in environmentally benign way.
2.2. Synthesis of photoredox nanocatalyst
2.2.1. Preparation of magnetically retrievable nanoparticles of Fe3O4
Magnetically retrievable nanoparticles of Fe3O4 were synthe-
sized by adopting co-precipitation methodology. Initially, FeSO4·7-
H2O (4.2 g) and Fe2(SO4)3 (6.0 g) were dissolved in a 500 mL round
bottom flask using double distilled water (250 mL) and stirred to
obtain a clear orange solution. Afterwards, 15 mL of ammonium
hydroxide (25%) was added dropwise to the respected solution to
maintain pH 10. The reaction mixture was continuously stirred
for a period of 1 h at 60ꢀC to obtain black precipitate of Fe3O4 which
were separated via an external magnet, washed with water and
ethanol and further, dried under a vacuum oven at 50ꢀC [29].
Amount obtained: 2.8 g
2.2.2. Preparation of silica coated magnetically retrievable
nanoparticles, SMNPs.
Silica coated MNPs were fabricated by utilizing sol–gel
approach using TEOS. In a normal procedure, 0.5 g of Fe3O4
nanoparticles were activated by employing 0.1 M HCl solution
(2.2 mL). Subsequently, 4:1 v/v ethanol–water (250 mL) mixture
was added to the activated Fe3O4 and put through sonication for
a period of 30 min for the consistent dispersion of the nanoparti-
cles in the solution. Thereafter, 25% NH4OH solution (5 mL) and
TEOS (1 mL) were introduced in the dispersed solution and stirred
at 60ꢀC for 6 h. Lastly, the SMNPs were collected by applying exter-
nal magnetic force, washed with water and ethanol and dried at 50
ꢀC [29]. Amount obtained: 0.75 g.
2. Experimental
2.1. Chemicals and reagents
Unless otherwise indicated, all the chemicals were obtained
from commercial source and were used without further purifica-
tions. Ferric sulphate hydrate and ferrous sulphate heptahydrate
were obtained from Central Drug house and Thomas Bakers,
respectively.
Tetraethyl
orthosilicate,
(3-aminopropyl)
Scheme 1. Scheme for the synthesis of Ir@PyBz@ASMNPs based magnetic photoredox nanocatalyst.
299

P. Rana, R. Gaur, B. Kaushik et al.
Journal of Catalysis 401 (2021) 297–308
2.2.3. Preparation of amine functionalized silica coated magnetically
retrievable nanoparticles, ASMNPs.
of Ir@PyBz@ASMNPs (0.42 mol%) catalyst in 1 mL of acetonitrile
(MeCN) and sealed with rubber cap. Afterwards, 30% acetic acid
(0.3 mL) was added to the mixture via syringe to avoid the acciden-
tal exposure to the cyanide. Afterwards, the vial was properly
sealed with parafilm tape and irradiated with 2 ꢀ 12 W white LEDs
by keeping at a distance of 10 cm. The completion of the reaction
was monitored by TLC (hexane/ethyl acetate). After completion
of the reaction, the catalyst was separated via external magnet
and the synthesized product was purified by column chromatogra-
phy using ethyl acetate and hexane (1:9).
Amine functionalized silica coated magnetically retrievable
nanoparticles, ASMNPs were fabricated by taking 0.2 g of SMNPs
in 200 mL of ethanol and sonicated for 30 min. Afterwards, 1 mL
of APTES was added dropwise to the resultant solution and sub-
jected to stirring at 60ꢀC for 6 h to form amine functionalized
SMNPs. Subsequently, the synthesized ASMNPs were separated
via an external magnet, washed with ethanol and kept for drying
under a vacuum oven at 50ꢀC [29]. Amount obtained: 0.19 g.
Note: The researchers are requested to wear lab coat, safety
glasses, mask and nitrile gloves and perform all the reactions in a
well-ventilated fume hood to avoid inhalation exposure. Exposure
of cyanide poisoning from ingestion and inhalation can be treated
by using cyanide antidote kit (amyl nitrite, sodium nitrite and
sodium thiosulfate).
2.2.4. Preparation of [Ir(PyBz)2Cl]2.
A 50 mL round bottom flask equipped with magnetic stir bar
was charged with IrCl3 (0.2470 g, 0.8273 mmol), 4-(2-pyridyl)
benzaldehyde (0.579 g) and
a solution of 2-ethoxy ethanol
(19 mL) and water (6.4 mL) was added to dissolve the reactants.
The reaction mixture was kept at 125ꢀC for 16 h under nitrogen
atmosphere. After the completion of the reaction, the reaction mix-
ture was cooled to room temperature, filtered and washed with
H2O, ethanol and hexane. The obtained desired bright orange col-
ored compound was dried under vacuum oven and afterwards uti-
lized for next step without further purification [36]. Yield: 75%.
Disposal of KCN: Treat the waste with alkaline sodium
hypochlorite (household bleach, <1g/L) in excess.
2.4. Analysis
The infrared spectra were analyzed by employing PerkinElmer
Spectrum 2000 using KBr pellet method in the range of 4000 to
400 cmꢁ1. UV–Vis spectra have been recorded on a Thermo Scien-
tific absorption spectrophotometer within the wavelength range of
250–800 nm. The photoluminescence (PL) spectroscopy measure-
ments were performed on a FLS980 fluorescence spectrometer
(Edinburgh Instruments) with double monochromators on both
excitation and emission sides, equipped with a R928P photomulti-
plier in a thermoelectrically cooled housing (Hamamatsu Photon-
ics), with a 450 W xenon arc lamp as the excitation source for
steady-state spectra. Spectral correction curves were provided by
Edinburgh Instruments.
2.2.5. Preparation of PyBz@ASMNPs
4-(2-Pyridyl)benzaldehyde grafted ASMNPs (PyBz@ASMNPs)
were synthesized via Schiff base condensation. A 250 mL round
bottom flask was charged with 100 mg of ASMNPs and 200 mg
of 4-(2-pyridyl)benzaldehyde in 150 mL of anhydrous ethanol.
The resulting mixture was sonicated for 30 min and afterwards
subjected to vigorous stirring at 80ꢀC for 3 h under nitrogen atmo-
sphere. After completion of the reaction, PyBz@ASMNPs were col-
lected via an external magnet, washed with crude ethanol and
dried under a vacuum oven for 12 h. Amount obtained: 0.11 g.
Powder sample was mounted on a front face sample holder
using a dedicated quartz cell holder.
For time-resolved measurements an EPL-375 ps pulsed diode
laser (kem = 372 nm with a pulse width of 66.5 ps, a repetition rate
2.2.6. Preparation of Ir@PyBz@ASMNPs
The final iridium based photoredox catalyst was synthesized by
utilizing PyBz@ASMNPs and [Ir(PyBz)2Cl]2. In a 100 mL round bot-
tom flask, PyBz@ASMNPs (110 mg) and [Ir(PyBz)2Cl]2 (50 mg) were
dissolved in 30 mL of ethylene glycol and subjected to sonication
for 30 min. Afterwards, the sonicated solution was heated to 150
ꢀC for 16 h under nitrogen atmosphere. After the completion of
the reaction, the desired synthesized catalyst was collected by
applying external magnet, washed with ethanol and dried in a vac-
uum oven for 12 h [36,37]. Amount obtained: 0.11 g.
of 20 MHz, and an average power of 75
lW; Edinburgh Instru-
ments) in conjunction with a time-correlated single photon count-
ing (TCSPC) system were used.
The obtained PL decay curves were fitted using a three-
exponential function:
ꢀ
ꢁ
X
X
3
t
si
3
IðtÞ ¼
i¼1Bi exp
ꢁ
;
i¼1Bi ¼ 1;
2.3. Procedure for photocatalytic organic transformations
In this expression,
s
i represent the decay time constants, and Bi
represents the normalized amplitudes of each components. The
amplitude weighted average decay lifetime savg of the entire fluo-
rescence decay process was calculated in the form:
2.3.1. C-H arylation of arenes with aryl iodide by utilizing photoredox
nanocatalyst
A 15 mL glass vial equipped with magnetic stir bar was charged
with 1 mmol of aryl iodide substrate, arene (3 mL, 67 equiv), tert-
potassium butoxide (2 equiv), 35 mg of Ir@PyBz@ASMNPs
(0.42 mol%) catalyst in 1 mL DMSO, purged with nitrogen and
sealed with rubber cap. Afterwards, the system was sonicated for
15 min and irradiated with the 2 ꢀ 12 W white LEDs by keeping
at a distance of 10 cm for 18 h under constant stirring. After com-
pletion of the reaction, the catalyst was separated via external
magnet and the supernatant was extracted with (3 ꢀ 30 mL) ethyl
acetate and water. Subsequently, the organic layer was collected,
rotary evaporated and further purified by silica gel column chro-
matography using hexane.
s
iBi
P
sav
¼
g
s
iBi
PXRD patterns were investigated on a Rigaku Cu (K ) diffrac-
a
togram at a scan rate of 4 degree per min and 2h range of 10–
80ꢀto determine the phase, purity and crystalline nature. FEI TECH-
NAI G2 T20 transmission electron microscope operated at 200 KV
was retained to capture the TEM images of the nanoparticles.
The TEM samples were prepared by drop casting a sonicated etha-
nol suspension of the desired nanoparticles over a carbon coated
copper grid. SEM images were recorded on a Tescan MIRA3 FE-
SEM microscope. SEM grids were prepared using gold sputtered
nanoparticles over a carbon tape placed on a SEM stub. Elemental
analysis of the catalyst was investigated using an Ametek EDAX
system. Brunauer-Emmett-Teller (BET) method was acquired using
an ASI-CT-11 Quantachrome instrument at a degassing tempera-
2.3.2. Oxidative cyanation of tertiary amines by utilizing photoredox
nanocatalyst.
A 15 mL glass vial equipped with magnetic stir bar was charged
with 1 mmol of tertiary amine substrate, 1.2 equiv of KCN, 35 mg
300

P. Rana, R. Gaur, B. Kaushik et al.
Journal of Catalysis 401 (2021) 297–308
ture of 150ꢀC to determine the specific surface area, pore volume
and pore size distribution. Metal content of the catalyst was mea-
sured on Perkin Elmer Avio 200 ICP-OES System. Magnetization of
the nanoparticles were confirmed by using a vibrating sample
magnetometer (EV-9, Microsense, ADE) in the range of ꢁ10000
Oe to 10,000 Oe. The cyclic voltammetry (CV) curve was recorded
on an Autolab Potentiostat Galvanostat (AUT204 Netherlands). The
measurement was performed utilizing a three-electrode system
with ITO coated glass electrode as the working electrode, platinum
(Pt) as the counter electrode, and silver-silver chloride (Ag/AgCl) as
the reference electrode in PBS solution of pH 7.0 containing 5 mM
of [Fe(CN)6]3-/4-. The optimization studies and control experiments
were carried out using an Agilent gas chromatograph (6850 GC)
having a HP-5MS capillary column (stationary phase: 5% phenyl
methyl siloxane; column length: 30 m; internal diameter:
(TRPL) spectroscopy; which showed the steady-state emission
spectra excited at 355 nm, the Ir@PyBz@ASMNPs showed strong
emission peaks at 430 nm (Fig. 2a). Such observed emission of
Ir@PyBz@ASMNPs is due to effective electron transfer process
and inhibited recombination of electrons and holes. Such observed
phenomenon; eventually promotes electron transfer and reduces
the photogenerated electron–hole recombination rate via inhibi-
tion of charge carrier recombination [39,42,43]. In addition; Time
resolved photoluminescence (TRPL) spectroscopy carried out for
Ir@PyBz@ASMNPs photocatalyst; confirms ligand–metal charge
transfer lifetimes which showed an average fluorescence decay
lifetimes (save) of 13.6 ns. Observed fluorescence decay lifetimes
(save) could be well attributed to the emergence of a non-
radiative pathway from Ir(ppy)3 organometallic complexes well
supported over heterogeneous system (Fig. 2b) [44] suggesting
that photo generated charge carriers survived longer on its surface.
The generated sites might be working as a bridge to facilitate the
faster electron transfer and enhancing the charge density on Ir cen-
tre thus reducing the photocarrier transfer barrier and enabling the
photocatalytic activity. On another note; since Ir(ppy)3 based
organometallic complexes, are good organic phosphorescent mate-
rials system and well known for absorbance due to the large
amount of spin–orbit coupling induced by the heavy metal ion
0.25 mm; film thickness: 0.25
lm) and a quadrupole mass filter
equipped 5975C mass selective detector (MSD) using helium as a
carrier gas. 1H NMR (400 MHz) and 13C NMR (100 MHz) spectra
were recorded on a JEOL JNM-EXCP 400 unless otherwise noted
and data are reported in terms of chemical shift related to CDCl3
(7.26 ppm) or with tetramethylsilane (TMS, d 0.00 ppm) as the
internal standard, abbreviation used to indicate the multiplicity
(s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet,
dd = doublet of doublet, dt = doublet of triplet, ddd = doublet of
doublet of doublet), coupling constant (Hz), integration. Thin-
layer chromatography (TLC) was performed by utilizing Merck sil-
ica gel plates 60 F254 to check the course of reactions and visual-
ized under UV light. Light Source. 12 W Philips white LEDs, Quantity
of Light Source: Two
[44–46]. The PL excitation
ꢁ
emission map of the Ir@PyB-
z@ASMNPs is presented in Fig. 2c where Ir based photocatalyst
exhibited an excitation-dependent emission since the position of
the emission peak widely shifts over a wide range of excitation
wavelengths [44–46]. The crystallographic properties and struc-
tures of the MNPs and Ir@PyBz@ASMNPs photoredox nanocatalyst
were also characterized by X-ray diffraction (XRD). The XRD pat-
tern of the fabricated Ir@PyBz@ASMPs photoredox nanocatalyst
exhibited consistency with the peaks of Fe3O4 (Fig. S4a) along with
the emergence of a new strong diffraction peak at 12.9ꢀcorrespond-
ing to the IrPC moiety (Fig. S4b) [44,47]. X-ray photoelectron spec-
troscopy (XPS) was carried out to investigate the surface chemical
nature of Ir in Ir@PyBz@ASMNPs. As shown in Fig. 3a, the Ir binding
energy spectra displayed two emission peaks at 60.2 eV (Ir 4f7/2
level) and 63.3 eV (Ir 4f5/2 level) respectively, which is in agree-
ment with the XPS spectra of Ir 4f region reported in literature
and can be attributed to Ir (+3) [15–17,48]. Survey scan and
detailed XPS spectra of the elements manifest the presence of Fe
2p, Si 2p, C 1 s, N 1 s and O 1 s in the final Ir@PyBz@ASMNPs
(Fig. S5). The transmission electron microscopy (TEM) analysis
was carried out to record images of MNPs, SMNPs and Ir@PyB-
z@ASMNPs (Fig. 3b-d). From the TEM image of MNPs (Fig. 3b), it
is evident that MNPs have an average diameter of 13 nm. The inset
of Fig. 3b spectacles the selected area electron diffraction pattern
(SAED) of MNPs. The bright diffraction rings and white spots points
towards the highly crystalline nature of the synthesized magnetic
nanoparticles. TEM image of SMNPs reveals a silica coating of
about 6 nm in thickness over the MNPs (Fig. 3c). Furthermore,
TEM images of MNPs and SMNPs nanoparticles show the spherical
morphology of the nanoparticles. In addition, the TEM image in
Fig. 3d indicates that Ir@PyBz@ASMNPs have some irregular spher-
ical nanoparticles in the range of 23–26 nm.
3. Results and discussion
3.1. Characterization of the photoredox nanocatalyst
Characterization of the structure of iridium photoredox
nanocatalyst, Ir@PyBz@ASMNPs was verified by employing various
physico-chemical techniques. Fourier transform infrared (FT-IR)
was carried out to identify the functional groups present at each
stage during the synthesis of the catalyst (Fig. S2, see SI for details).
The observed photocatalytic result can be correlated with the opti-
cal properties of Ir@PyBz@ASMNP photocatalyst; such as UV–Vis
diffuse reflectance spectrum, photoluminescence, time resolved
photoluminescence (TRPL) analysis and Excitation-emission color
map are plotted in Fig. S3 and Fig. 2 a, b, c respectively. Primarily;
UV–Vis spectrum of homogeneous iridium photocatalyst displays
an intense absorption peak at 280 nm in the range of 250 nm to
350 nm in MeOH, shows intense absorption from ligand
p – p*
and MLCT transitions Fig. S3. The * absorption (singlet–singlet
p– p
ligand-centered) band for both (homo and hetero) Ir organometal-
lic complex falls in the range 250–320 nm which is an intense
ultraviolet band, and closely resembles the spectrum of the free
ppy ligand associated with Ir metal center [38,39]. Clear evidence
for significant mixing of the singlet and triplet excited states is
seen in both the absorption and emission spectra of Ir@PyB-
z@ASMNPs photo-catalysts. On another note, the weaker absorp-
tion band 375 nm that extend to the visible region of low energy
is conventionally assigned to metal-to-ligand charge-transfer tran-
sitions (3MLCT) (Fig. S3). Both 1MLCT and 3MLCT bands are typi-
cally well observed in both homogeneous and heterogeneous Ir-
organometallic based complex system. Such absorption spectrum
of Ir@PyBz@ASMNPs were well matched and nearly the same as
that for Ir(ppy)3 complexes as reported previously [37,40–42].
Furthermore; the separation of photogenerated electrons and
holes in Ir@PyBz@ASMNPs generated system was investigated
through photoluminescence and time resolved photoluminescence
Likewise, the SEM images of Ir@PyBz@ASMNPs also reveal that
the iridium based photoredox nanocatalyst retains the spherical
shape (Fig. S6). The qualitative analysis of elements (Fe, Si, C, N,
O and Ir) was performed by energy-dispersive X-ray Spectroscopy
(EDS) and energy dispersive X-ray Fluorescence (ED-XRF) (Fig. S7)
while quantitative determination of iridium metal content in the
Ir@PyBz@ASMNPs was accomplished by ICP-OES and was found
to be 0.1207 mmol gꢁ1. The magnetization properties of the MNPs,
SMNPs and Ir@PyBz@ASMNPs were recorded by using vibrating-
sample magnetometer (VSM) at room temperature (300 K)
(Fig. S8). The saturation magnetization, Ms value of the Ir@PyB-
301

P. Rana, R. Gaur, B. Kaushik et al.
Journal of Catalysis 401 (2021) 297–308
Fig. 2. a) PL excitation (kex = 355 nm, black line) and PL emission (kem = 430 nm, red line) spectra, b) PL decay collected at the emission maximum. Experimental data are
represented by symbols, whereas a solid line is a three-exponential fit (see the Experimental section for details) and c) Excitation-emission color map. (For interpretation of
the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 3. a) XPS spectra of Ir@PyBz@ASMNPs photoredox nanocatalyst, TEM images of b) MNPs; inset: SAED pattern of MNPs, c) SMNPs and d) Ir@PyBz@ASMNPs photoredox
nanocatalyst.
z@ASMNPs photoredox nanocatalyst is found to be 27.6 emu/g
which is sufficient enough for the magnetic separation of the pho-
toredox nanocatalyst from the dispersed reaction mixture with a
simple external magnet within the time period of 40 sec.
To investigate the redox potential of the Ir@PyBz@ASMNPs, cyc-
lic voltammetry experiment (CV) was performed in the presence of
5 mM [Fe(CN)6]3ꢁ/4ꢁ containing PBS (Phosphate buffer saline) at
pH 7 at a scan rate of 0.1 V/s in potential range from ꢁ 1.0 V to
1.0 V. As seen from curve in Fig. 4, the Ir@PyBz@ASMNPs exhibited
well defined characteristic redox peaks at ꢁ0.16266 and 0.40863 V
[49,50]. TGA curve illustrates that the weight loss of Ir@PyB-
z@ASMNPs (13 %) mainly occurs in the temperature range of 23–
150 °C due to the volatilization of adsorbed water. It is evident
from the results that our fabricated photoredox Ir@PyBz@ASMNPs
nanocatalyst is thermally stable and only 29 % weight loss occurs
up to the temperature of 600 °C (Fig. S9). The Brunauer–Emmet
302

P. Rana, R. Gaur, B. Kaushik et al.
Journal of Catalysis 401 (2021) 297–308
methodologies exhibit various challenges such as high cost, time
consuming separation, transition metal impurity in the final pro-
duct, formation of undesired, toxic and stoichiometric side prod-
ucts, involvement of high power consuming white light sources
(Xenon lamp with power more than 100 W) as well as destructive
nature of UV radiation and harsh reaction conditions. Herein, we
employed the heterogeneous Ir@PyBz@ASMNPs photoredox
nanocatalyst for the C-H arylation, appealing to the principles of
sustainable chemistry. Initially, we commenced our studies by
probing the C-H arylation of unactivated benzene using iodoben-
zene as the model reaction for optimizing the reaction conditions.
Notably, a control experiment was initially performed with various
solvent systems. Unfortunately, unsatisfactory results were
obtained with acetonitrile (ACN) and methanol (MeOH) (Table 1,
entries 1 and 2). Nevertheless, superior results were observed
when the reaction was performed in dimethyl sulfoxide (DMSO)
(Table 1, entry 3). Additionally, presence of water in DMSO drasti-
cally hampered the catalytic progress of the reaction and no
desired product was obtained. (Table 1, entry 4). Further, effect
of various inorganic and organic bases, such as K2CO3 (Table 1,
entry 5), Cs2CO3 (entry 6) and triethylamine (Table 1, entry 7)
was also examined and the best performance was attained with
t-KOBu (Table 1, entry 3). The unique catalytic performance is par-
ticularly noticeable when Ir@PyBz@ASMNPs is excluded, as only
38% yield of the desired biphenyl was afforded (Table 1, entry 8).
Almost no product was formed on carrying out the reaction under
the dark conditions (Table 1, entry 9).
Fig. 4. Cyclic voltammetry curve of Ir@PyBz@ASMNPs at a scan rate of 0.1 V/s.
t–Teller (BET) analysis reveal that Ir@PyBz@ASMNPs photoredox
catalyst has specific surface area of 5.298 ꢀ 10 m2gꢁ1 and average
pore diameter of 7.201E + 01 Å.
3.2. Catalytic activity
Therefore, control reactions disclosed that the heterogeneous
photoredox nanocatalyst (Ir@PyBz@ASMNPs), white light
To date, many groups have reported the C-C bond formation
using various photoredox catalysts (Table S1a). However, these
Table 1
Optimization of C-H arylation of arene with aryl iodide.a.
Entry
Catalyst
(mg)
Base
(2 equiv)
Solvent
(1 mL)
Time
(h)
Yieldb
(%)
Ir@PyBz@ASMNPs
(0.42 mol%, 35 mg)
Ir@PyBz@ASMNPs
(0.42 mol%, 35 mg)
Ir@PyBz@ASMNPs
(0.42 mol%, 35 mg)
Ir@PyBz@ASMNPs
(0.42 mol%, 35 mg)
Ir@PyBz@ASMNPs
(0.42 mol%, 35 mg)
Ir@PyBz@ASMNPs
(0.42 mol%, 35 mg)
Ir@PyBz@ASMNPs
(0.42 mol%, 35 mg)
–
t-KOBu
t-KOBu
t-KOBu
t-KOBu
K2CO3
ACN
24
24
24
24
24
24
24
24
24
24
24
24
24
18
12
18
–
2.
MeOH
DMSO
DMSO:H2O (1:1)
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
34
>99
0
3.
4.
5.
0
6.
Cs2CO3
Triethylamine
t-KOBu
t-KOBu
t-KOBu
t-KOBu
t-KOBu
t-KOBu
t-KOBu
t-KOBu
t-KOBu
–
7.
0
8.
38
Tracec
72d
91
95
0e
9.
Ir@PyBz@ASMNPs
(0.42 mol%, 35 mg)
Ir@PyBz@ASMNPs
(0.42 mol%, 35 mg)
Ir@PyBz@ASMNPs
(0.3 mol%, 25 mg)
Ir@PyBz@ASMNPs
(0.6 mol%, 70 mg)
Ir@PyBz@ASMNPs
(0.3 mol%, 35 mg)
Ir@PyBz@ASMNPs
(0.42 mol%, 35 mg)
Ir@PyBz@ASMNPs
(0.42 mol%, 35 mg)
Homogeneous IrPC
(0.5 mol%)
10.
11.
12.
13.
14.
15.
16
97
83
>99
a
Reaction conditions: iodo-benzene (1 mmol), benzene (67 equiv, 3 mL), solvent (1 mL), 25ꢀC, two 12 W white LEDs, N2 atm. bGC-MS yield. cDark. d12 W white LEDs. eAir.
303

P. Rana, R. Gaur, B. Kaushik et al.
Journal of Catalysis 401 (2021) 297–308
(2 ꢀ 12 W), and t-KOBu were all necessary individually to execute
the reaction. However, over irradiation using 12 W white LED light
instead of 2 ꢀ 12 W for 24 h led to the reduction in the yield (72%)
of the desired biphenyl (Table 1, entry 10). Afterwards, decreasing
the amount of catalyst from 35 mg to 25 mg led to decline in the
product yield (Table 1, entry 11). Further, on increasing the
amount of catalyst from 35 mg to 70 mg, slight decrease in the
yield was observed which could be accredited to the interference
of the mass transfer between the active sites and reagent caused
by the low dispersity of the excess catalyst in the reaction media
or low dispersity of light due to fouling of vial (Table 1, entry
12). Moreover, reaction in the absence of inert atmosphere did
not proceed at all (Table 1, entry 13). Furthermore, running the
reaction for 18 h instead of 24 h provides comparable yield (Table 1,
entry 14). Although, significant decrease in yield was observed on
further decreasing the reaction time to 12 h (Table 1, entry 15).
Additionally, we have also utilized homogeneous iridium photore-
dox catalyst (IrPC) which disclosed that upon immobilization of
the photocatalyst over heterogeneous support, no significant
change in the efficiency of the catalyst was observed (Table 1,
entry 16). In view of the above findings, a series of aryl halides
were also scrutinized under continuous visible light excitation
which indicates the decrease in yield of the desired product in
the order of iodide, bromide and chlorides that could be probably
due to the different bond dissociation energies (Table S2, see SI
for details).
3.3. Substrate scope
Following the establishment of the optimized standard condi-
tions (Table 1, entry 14), substrate scope of the photocatalytic C-
H arylation of various aryl iodide substrates was explored to
demonstrate the applicability of the reaction with the fabricated
Ir@PyBz@ASMNPs photoredox nanocatalyst. Initially, we focused
on various para substituted electron donating aryl iodides which
exhibited good to excellent yields (Scheme 2, 3a-c). Moreover,
the meta substituted electron donating aryl iodides were well
tolerated for the reaction and furnished the desired product in
good yield (Scheme 2, 3d, 3e). The ortho substituted electron
donating aryl iodides delivered the desired product in low yield
and revealed the impact of steric hinderance over the reaction
(Scheme 2, 3f-h). The results conclude that the yield of the cou-
pling products increases progressively in the order of o- to m- to
p- substituted aryl iodides. Likewise, the electron withdrawing
groups positioned at para position such as –NO2, -F and -CF3
are also withstand well and provided good yields (Scheme 2, 3-
i-k).
Further analysis was carried out to deduce a plausible mecha-
nism for the SET initiated C-H arylation reaction. The mechanistic
experiment suggests that in the presence of radical scavenger
(TEMPO (1.5 equiv)) (Scheme 3), the C-H arylation transformation
is completely inhibited, consistent with a mechanism in which ion
radicals initiate the reaction.
Scheme 2. Substrate scope for C-H arylation of arenes with aryl iodide using Ir@PyBz@ASMNPs based photoredox nanocatalyst.a. aReaction conditions: aryl halide (1 mmol),
aryl (67 equiv, 3 mL), t-KOBu (2 equiv), DMSO (1 mL), Ir@PyBz@ASMNPs (0.42 mol%, 35 mg), 25ꢀC, two 12 W white LEDs, 18 h, N2 atm., isolated yield. bGC-MS yield; TOF = TON
per hour (TON is the number of moles of the product per mole of the catalyst).
304

P. Rana, R. Gaur, B. Kaushik et al.
Journal of Catalysis 401 (2021) 297–308
Scheme 3. Mechanistic control experiment.
3.4. Plausible mechanism
reaction cannot be extended to heteroatomic amines which
afforded unpredictable compounds (Scheme 5, 5d).
Previously reported kinetic isotope effect (KIE) studies in vari-
ous literatures suggest that the C-H cleavage of benzene is not
the rate determining step [51–53]. On the basis of above men-
tioned experiments and previous literature precedents, a tentative
mechanism is proposed for the activation of aryl halide by SET
from visible-light excited photoredox catalyst, Ir(III)*@PyB-
z@ASMNPs (Scheme 4). The generated aryl halide radical anion
(Ar-Xꢂ-) further undergoes mesolytic fragmentation to form aryl
radical by the fragmentation of halogen anion. Afterwards, the rad-
ical (Ar·) undergo coupling reaction with another aryl molecule to
form the key transition state of biaryl radical anion. Subsequently,
the intermediate is further deprotonated by the base to afford the
biaryl radical anion. Finally, the highly reductive biaryl radical
anion undergoes oxidation via donating an electron to the oxidized
Ir(IV)@PyBz@ASMNPs photoredox nanocatalyst to provide the tar-
geted biaryl product and to complete the catalytic cycle [54].
To our delight, the versatile Ir@PyBz@ASMNPs photoredox
nanocatalyst was not limited to the C-H arylation of aryl iodides.
We further probed the photoredox nanocatalyst to carry out the
oxidative Strecker reaction via C-H activation to construct biologi-
3.5. Catalytic reusability test
The long lifetime, recyclability and reusability of heterogeneous
catalyst are some of the significant milestones towards achieving
the goal of green and sustainable chemistry. Henceforth, we turn
our attention towards the reusability of the photoredox nanocata-
lyst and investigated the catalytic durability of Ir@PyBz@ASMNPs
with the model C–H arylation reaction under optimized reaction
conditions. After completion of the reaction, the Ir@PyBz@ASMNPs
catalyst was separated, washed with absolute ethanol, dried in
vacuo overnight prior to use and it was subjected to the subse-
quent recycle runs under the same reaction conditions (Fig. 5a).
The catalytic reusability test of the fabricated magnetic Ir@PyB-
z@ASMNPs photoredox nanocatalyst suggests that the catalyst
can be reused with high selectivity, although the rate of reaction
decreases. The TEM analysis (Fig. 5c), FT-IR (Fig. S11), VSM analysis
(Fig. S12), SEM (Fig. S13b) and ED-XRF (Fig. S14) unveiled no note-
worthy physical and chemical change in the structure and mor-
phology of the Ir@PyBz@ASMNPs and the photoredox
nanocatalyst was preserved even after five consecutive runs.
ICP analysis of the mother liquor after the first cycle revealed
only negligible leaching of the Ir species (<0.1%). However, the
decrease in catalyst efficiency from third run onwards upon reuse
could be attributed to the partial conversion of Ir (III) to Ir (IV)
which was further confirmed by XPS analysis of the reused cata-
lyst. The XPS analysis of recovered catalyst after five cycles
(Fig. S15f) suggested that during the catalytic cycle, Ir (III) got par-
cally important
a-amino nitriles which are the key intermediates
of -amino carbonyl compounds and 1,2-diamines. Notably, the
a
cyano functionalized tertiary amines can further be utilized as
starting materials for the synthesis of vitally important hetero-
cyclic and carbocyclic molecules used in pharmacological and bio-
logical compounds [55]. The valuable
a-amino nitriles were
synthesized by employing the previously reported optimized con-
ditions by Rueping and co-workers [56]. Primarily, we carried out
the regioselective reaction with a set of cyclic tertiary amines
which illustrated excellent functional group compatibility and
afforded the resulting products in good to excellent yield
(Scheme 5, 5a-c). The results point toward the wider utility and
generality of our synthesized iridium catalyst. Conversely, this
tially converted to Ir (IV). The doublet component at 61.30 (4f7/2
and 64.28 (4f5/2) was attributed to Ir (III), while the doublet at
62.65 and 65.64 eV to Ir (IV) oxidized state [57].
Our group further envisions to work towards regenerating the
catalyst [58–60] completely to fully explore its potential by
employing various reducing species such as triethylamine [61] as
an electron donor, non-heme iron (IV) oxo complex via a photon
coupled electron transfer [62] etc. responsible for the restoration
of photoactive state.
)
3.6. Leaching test
In order to examine the heterogeneous nature of the fabricated
Ir@PyBz@ASMNPs catalyst, leaching test was carried out for the C-
H arylation of arenes with aryl iodide under the optimized reaction
conditions. After 9 h, catalyst was magnetically separated from the
reaction mixture and the reaction mixture was evaluated using
GCMS which revealed that only 52% conversion was achieved. Fur-
ther exposing the reaction mixture with light in absence of catalyst
and continuous stirring showed only 63% conversion of the desired
product which indicates that there is negligible leaching of the
active species in the supernatant. Moreover, the leaching of the
iridium species from the heterogeneous catalyst was also analyzed
via ICP-OES analysis which revealed that<0.07 % of iridium of the
initially added catalyst was leached from the surface during the
course of the reaction.
Scheme 4. Proposed mechanism of the photoredox homolytic aromatic
substitution.
305

P. Rana, R. Gaur, B. Kaushik et al.
Journal of Catalysis 401 (2021) 297–308
Scheme 5. Substrate scope for Ir@PyBz@ASMNPs based photoredox nanocatalyst mediated
a
-cyanation of tertiary amines.a. aReaction conditions: tertiary amine (1 mmol),
KCN (1.2 equiv), 30% acetic acid (AcOH) (0.3 mL), Ir@PyBz@ASMNPs (0.42 mol%, 35 mg), MeCN (1 mL), 25ꢀC, two 12 W white LEDs, air, isolated yield, 12 h. bTMSCN as
cyanation source. cTOF = TON per hour (TON is the number of moles of the product per mole of the catalyst).
Recyclability
a)
92
100
85
80
90
80
70
60
50
40
30
20
10
0
77
65
1
2
3
4
5
Number of runs
b)
c)
20 nm
20 nm
Fig. 5. a) Reusability test of Ir@PyBz@ASMNPs for the C-H arylation of arenes with aryl iodide; TEM images of b) fresh and c) reused Ir@PyBz@ASMNPs catalyst.
any significant decrease in the catalytic activity for visible light
mediated organic reactions at room temperature and atmospheric
pressure. The proposed radical mechanism is reinforced by the
intensely reduced reaction rate in the presence of TEMPO scav-
enger (as radical trapping agent). The catalyst embraces great
potential as substitute of the homogeneous catalysts and provides
a green and sustainable chemical route. We envisioned that the
surface engineering protocol over nano sized magnetic core
4. Conclusions
In this study, we have fabricated a magnetically retrievable irid-
ium complex surface engineered over the silica coated Fe3O4 and
demonstrated its effectiveness as an effective visible light photo-
catalyst for C-H arylation as well as C-H cyanation. The Ir@PyB-
z@ASMNPs shows high surface area, thermal and chemical
stability and can be recovered and reused up to five runs without
306

P. Rana, R. Gaur, B. Kaushik et al.
Journal of Catalysis 401 (2021) 297–308
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CRediT authorship contribution statement
Pooja Rana: Investigation, Data curation, Writing – original
draft, Methodology. Rashmi Gaur: Conceptualization, Visualiza-
tion. Bhawna Kaushik: Validation, Data curation, Writing – origi-
nal draft, Visualization. Pooja Rana: Formal analysis, Writing –
review & editing. Sneha Yadav: Validation, Writing – review &
editing. Priya Yadav: Validation, Writing – review & editing. Priti
Sharma: study of photophysical characterization. Manoj B.
Gawande: Supervision, Project administration. Rakesh K. Sharma:
Supervision, Project administration.
[18] B. An, L. Zeng, M. Jia, Z. Li, Z. Lin, Y. Song, Y. Zhou, J. Cheng, C. Wang, W. Lin,
Molecular Iridium Complexes in Metal-Organic Frameworks Catalyze CO2
Hydrogenation via Concerted Proton and Hydride Transfer, J. Am. Chem. Soc.
139 (49) (2017) 17747–17750.
[19] J. Ma, F. Strieth-Kalthoff, T. Dalton, M. Freitag, J.L. Schwarz, K. Bergander, C.
Daniliuc, F. Glorius, Direct Dearomatization of Pyridines via an Energy-
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2854–2864.
[20] M. Simonetti, D.M. Cannas, I. Larrosa, Biaryl Synthesis via C-H Bond Activation:
Strategies and Methods, in Advances in Organometallic Chemistry, Elsevier
(2017) 299–399.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
[21] F. Kloss, T. Neuwirth, V.G. Haensch, C. Hertweck, Metal-free synthesis of
pharmaceutically important biaryls by photosplicing, Angew. Chem. Int. Ed.
130 (44) (2018) 14684–14689.
[22] S. Yuan, J. Chang, B. Yu, Construction of biologically important biaryl scaffolds
through direct C-H bond activation: advances and prospects, Top. Curr. Chem.
378 (2020) 1–70.
[23] K.M. Saini, R.K. Saunthwal, A.K. Verma, Pd-Catalyzed One-Pot Sequential
Cross-coupling reactions of Tetrabromothiophene, Org. Biomol. Chem. 15 (48)
(2017) 10289–10298.
[24] F.X. Felpin, S. Sengupta, Biaryl synthesis with arenediazonium salts: cross-
coupling, CH-arylation and annulation reactions, Chem. Soc. Rev. 48 (2019)
1150–1193.
Acknowledgments
The work was supported by the Department of Science and
Technology (DST) (Grant ID: DST/TMD-EWO/WTI2K19/EWF
H/2019/290(G)) to design a commercial scale photoreactor. Pooja
Rana, Bhawna Kaushik, Pooja Rana, Sneha Yadav and Priya Yadav
gratefully acknowledge CSIR and UGC, Delhi, India for awarding
research fellowships. Moreover, the authors also thank USIC-CLF,
DU for FT-IR, XRD, VSM analysis, PerkinElmer (Mumbai) for ICP-
OES analysis and TERI (Gurugram, India) for TEM analysis.
[25] A.K. Rathi, M.B. Gawande, J. Pechousek, J. Tucek, C. Aparicio, M. Petr, O.
Tomanec, R. Krikavova, Z. Travnicek, R.S. Varma, Maghemite Decorated with
Ultra-Small Palladium Nanoparticles (c-Fe2O3-Pd): Applications in the Heck-
Mizoroki Olefination, Suzuki Reaction and Allylic Oxidation of alkenes, Green
Chem. 18 (2016) 2363–2373.
Appendix A. Supplementary material
[26] I. Hussain, T. Singh, Synthesis of Biaryls through Aromatic C-H Bond
Activation: A Review of Recent Developments, Adv. Synth. Catal. 356 (8)
(2014) 1661–1696.
Supporting Information contains UV-Vis analysis, TEM image,
SEM image, ED-XRF analysis, XPS, VSM curves and TGA of fresh
and recovered catalyst, Reusability test of catalyst, Literature
precedence table. NMR data and spectra. GC-MS Spectra. Supple-
mentary data to this article can be found online at https://doi.
org/10.1016/j.jcat.2021.08.014.
[27] S.E. Hooshmand, B. Heidari, R. Sedghi, R.S. Varma, Recent advances in the
suzuki-miyaura cross-coupling reaction using efficient catalysts in eco-
friendly media, Green Chem. 21 (3) (2019) 381–405.
[28] I. Ghosh, L. Marzo, A. Das, R. Shaikh, B. König, visible light mediated
photoredox catalytic arylation reactions, Acc. Chem. Res. 49 (8) (2016)
1566–1577.
[29] P. Rana, R. Gaur, R. Gupta, G. Arora, A. Jayashree, R.K. Sharma, Cross-
Dehydrogenative C(sp3)–C(sp3) coupling via C-H Activation using
Magnetically Retrievable Ruthenium-based Photoredox Nanocatalyst under
Aerobic Conditions, Chem. Commun. 55 (51) (2019) 7402–7405.
[30] R. Gupta, M. Yadav, R. Gaur, G. Arora, P. Rana, P. Yadav, A. Adholeya, R.K.
Sharma, Silica-Coated Magnetic-Nanoparticle-Supported DABCO-Derived
Acidic Ionic Liquid for the Efficient Synthesis of Bioactive 3, 3-Di (indolyl)
indolin-2-ones, ACS Omega 4 (25) (2019) 21529–21539.
[31] P. Yadav, M. Yadav, R. Gaur, R. Gupta, G. Arora, P. Rana, A. Srivastava, R.K.
Sharma, Fabrication of copper-based silica-coated magnetic nanocatalyst for
efficient one-pot synthesis of chalcones via A3 coupling of aldehydes-alkynes-
amines, ChemCatChem 12 (9) (2020) 2488–2496.
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