A Sustainable Heterogeneous Iron Catalyst Fe/SBA-15 towards Direct Arylation of Unactivated C(sp3)?H and C(sp2)?H Bonds with Arenes

Article abstract of DOI:10.1002/cctc.201601562

Iron grafted over mesoporous silica (8 wt %Fe/SBA-15) is a sustainable, efficient heterogeneous iron catalyst for direct arylation of biphenyl methane C(sp³)?H and benzene C(sp²)?H bonds. The selective extraction deposition (SED) technique was adopted to graft iron easily over the mesoporous support SBA-15 by using LaFeO₃ as an iron precursor. The synthesized catalyst has been characterized by EPR spectroscopy, diffuse reflectance UV/Vis spectroscopy, and temperature programmed reduction (TPR) analysis to understand the coordination environment and state of oxidic iron species grafted over the mesoporous SBA-15. TPR results confirm the presence of isolated, clustered, oligomeric oxidic iron species in the catalyst. The adopted SED technique is highly successful for grafting 8 wt % iron into the mesopores of SBA-15 without forming iron oxide particles. Unlike homogeneous iron, the 8 wt %Fe/SBA-15 catalyst does not need support from an electron-withdrawing group and additives to carry out arylation of benzene and could be successfully recycled five times.

Full text of DOI:10.1002/cctc.201601562

Accepted Article
Title: Sustainable Heterogeneous Iron catalyst Fe/SBA-15 towards
direct arylation of unactivated C(sp3)-H and C(sp2)-H with arenes
Authors: Chandran Rajendran and Govindaswamy Satishkumar
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Sustainable Heterogeneous Iron catalyst Fe/SBA-15 towards
direct arylation of unactivated C(sp3)-H and C(sp2)-H with arenes
C. Rajendran and G. Satishkumar*
Abstract: Iron grafted SBA-15, 8wt%Fe/SBA-15, has proven as
sustainable, efficient heterogeneous iron catalyst for direct arylation
of biphenyl methane C(sp3)-H and benzene C(sp2)-H. Selective
extraction deposition (SED) technique was adopted to graft iron
easily over the mesoporous support SBA-15 using LaFeO3 as iron
precursor. The synthesized catalyst has been characterized by EPR,
DRS-UV and TPR to understand the coordination environment and
state of oxidic iron species grafted in the mesoporous SBA-15. TPR
results confirm the presence of isolated, cluster, oligomeric oxidic
iron species in the catalyst. The adopted SED technique is highly
successful to graft 8wt% iron without forming iron oxide particle into
the mesopores of SBA-15. Unlike homogeneous iron, 8wt%Fe/SBA-
15 catalyst does not need the support from the electron withdrawing
group and additives to carry out arylation of benzene and could be
successfully recycled for 5 cycles.
strategy to acquire an active heterogeneous catalyst, although it
is challenging due to fast hydrolysis and condensation of iron
ions in solutions of Fe-precursors (salts, alkoxides, etc.,). Tilley
et al. have successfully grafted iron on mesoporous silica SBA-
15 using Fe(OSi(O-tBu)3]3 as iron precursor followed by
thermolytic cleavage of organic ligands.[5] Notestein et al. have
found iron ethylene(diamine)tetraacetic acid (EDTA) as a better
iron precursor to immobilize iron in highly dispersed state over
silica and EDTA was removed by calcination. These catalysts
exhibited good catalytic activity in oxidation of alkanes, alkene
and arenes with good selectivity.[6] Recently, Hock et al. found
that isolated FeII/SiO2 prepared using bis(2,4-dimethyl-1,3-
pentadienide)Iron(II) and hydrogen treatment at 650°C able to
catalyze non-oxidative propane dehydrogenation reaction with
high selectivity of propene.[7] Nevertheless, silica support can
accommodate more isolated iron, loading achieved in the above
studies are lower due to steric hindrance by the bulk ligands or
required essential calcination would result iron agglomeration
to form iron oxide particles.
Introduction
We have developed a technical solution for easy grafting of
more isolated iron ion over the silica support through a new
technique called selective extraction deposition (SED) using
LaFeO3 as an iron precursor in acidic solution. [8] The controlled
decomposition of LaFeO3 by acidic protons minimizes the
residence time and concentration of released iron ions in the
solution avoiding self-condensation of Fe-ions and facilitates
In the past few decade, the significant contribution of late
and first row transition metal catalysts in Carbon-Carbon (C-C)
coupling reactions has great impact in organic chemistry and
offers unlimited opportunities to get
a variety of organic
compounds. However, high cost, less abundance and toxicity of
late transition metals strongly hamper their further
advancement
in
organic
synthesis.[1]
Consequently,
grafting of iron with silica gel. It was demonstrated that
mixing
development of first row transition metals, particularly iron
catalyzed reactions in C-C coupling reaction has been
intensively investigated in the last ten years on account of its low
price, high abundance, environmental benign and exhibiting
variety of oxidation states.[2] Conversely, its homogeneous
nature creates problems such as recovery, high consumption,
use of additives and product selectivity which are downsides of
this catalyst to employ it in large scale industrial use. Only a few
attempts have been made with heterogeneous iron catalysts
(iron oxide, bimetallic iron oxide and iron-nickel alloy) in C-C
coupling due to its limited scope.[3] Therefore, an effective
heterogeneous iron catalyst for C-C coupling reaction besides
possessing its own advantages must have well-defined active
sites like its homogeneous counterpart.[4] Therefore,
immobilization of more iron ions without iron oxide particles at
the surface of suitable support would be good
of LaFeO3 with silica-gel gives an advanced catalytic material
with high activity towards phenol degradation (TOC removal of
90%) and stability without iron leaching in continuous reactor.[8a]
In this proposed work we grafted 8wt% iron over SBA-
15(mesoporous silica) using SED technique. It is anticipated that
in SED procedure controlled release of active Ferric hydroxide
from the LaFeO3 precursor would eliminate iron oxide particle
formation and permit high percent of iron grafting over SBA-15
as isolated, cluster and oligomeric species through oxolation.[9]
Herein, we report the performance of 8wt% iron grafted SBA-15
(8wt%Fe/SBA-15) catalyst prepared using SED technique
towards cross-dehydrogenative arylation of biphenyl methane
C(sp3)-H and arylation of benzene C(sp2)-H using
[a]
C. Rajendran, Dr. G. Satishkumar
Department of chemistry
School of Advanced Sciences
VIT University
Vellore-632 014
Tamil Nadu, India
E-mail: satishkumar.g@vit.ac.in,satishgsamy@gmail.com
Supporting information for this article is given via a link at the end of
the document. ((Please delete this text if not appropriate))
Scheme 1. 8wt%Fe/SBA-15 catalyzed arylation of biphenylmethane and
benzene.
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various arylboronic acid which already has been reported by Z.J.
Shi et al.[10] and T.Hayashi et al.[11] respectively, with
homogeneous iron catalyst (Scheme 1). The objective for
choosing these reactions are direct functionalization of C(sp3)-H
carbon is challenging in the former case, while in the latter case
simple FeCl2 and FeCl3 catalysts were failed, whereas, Fe(OTf)3
coordinated with substituted phenanthroline was able to
accomplish the coupling reaction with good yield through the
establishment of Fe(IV). In addition, few new substrates were also
experimented in both the reactions along with catalyst recycle
study. To the best of our knowledge, no heterogeneous iron
catalyst has been employed for the above challenging reactions.
centered at g value of 2.14 assigned to polynuclear oxy-hydroxy
Fe(III) arrays (Figure S4).[12a] Upon decreasing the temperature
to -196°C, the resonance line appears at g = 4.28 and 1.984.
The extra framework iron present in zeolite structure, similar to
grafted isolated FeIII, in octahedral and distorted octahedral
environment signals at g value slightly lesser than 2 and for fully
rhombic environment at 4.3. However, the signal slightly lesser
than
2
may also indicate the presence of iron oxide
2.2-2.5
clusters.[12b,13a] The absence of signals at
g
=
evidences devoid of iron oxide in the mesoporous of silica.[13c]
DRS-UV spectrum of 8wt%Fe/SBA-15 (Figure S5) showed a
weak signal at 220 nm and a peak at 250 nm due to oxygen to
Fe(III) charge transfer involving isolated FeIII in octahedral
environment.[6a,13,14] In addition, an intense band at
Results and Discussion
The low-angle XRD pattern of 8wt%Fe/SBA-15 (Figure S1)
displayed a high intensity peak (100) with two less intensive
reflections consistent with the hexagonal arrangement of the
mesopores in SBA-15. The amorphous wide angle XRD patterns
of 8wt%Fe/SBA-15 (Figure S2) not only confirm the complete
decomposition of LaFeO3 in acidic solution, but also the
existence of 8wt% iron (confirmed by ICP-OES) not in form of
crystalline oxide. By complementing the XRD result
8wt%Fe/SBA-15 exhibit high surface area 640 m2/g, pore
volume 1.28 cc/g and typical type IV isotherm of ordered
mesopore indicate successful grafting of iron ions without
blocking the mesopore through SED technique (Figure S3 and
Table S1). In order to gain more insight about the coordination
environment, i.e., the presence of different types of oxidic iron
species of grafted Fe(III) in the mesopores, catalyst has been
characterized by EPR, DRS-UV and TPR. The EPR spectrum
recorded at room temperature consists of a broad absorption
Figure 1. TPR profile of 8wt%Fe/SBA-15.
Figure 2. TEM images of 8wt%Fe/SBA-15 particles with different iron loading (A) 7wt% and (B) 1.5wt%.
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330 nm and a shoulder at 470 nm at higher wavelength can be
assigned to Fe(III)-clusters and amorphous FeOx oligomers
respectively, due to increase in the nuclearity of Fe(III)-
oxide.[13a,b,14b,c] The absence of peak beyond 500 nm
undoubtedly indicates the absence of bulk iron oxide phase
formation in the mesopores during the grafting process.[6b]
high iron loading (8wt%). Unlike the iron oxide particle where
most of iron sites are concealed, the cluster and oligomeric form
of iron oxide species possess more exposed iron sites. Hence, it
is expected that all available oxidic iron catalytic sites (single,
cluster, oligomer) would demonstrate good catalytic activity
towards the proposed challenging C-C coupling.
TPR profile of 8wt%Fe/SBA-15 displayed four reduction
events based on the nuclearity of the Fe (III)-oxide species
(Figure 1). Generally, low nuclearity species reduces at high
temperature due to strong interaction with the support, while the
reverse is likely for the high nuclearity species. The first
reduction peak centered at 410°C is attributed to two-
dimensional oligomeric FeOx species as there is no evidence for
In the initial attempt experiments were conducted with various
reactant’s equivalent ratio and different oxidants to attain
maximum yield for the arylation of biphenylmethane with 2-
chloroanisole. Increasing the amount of biphenylmethane from
1.5 to 6 equivalents and 2,3-dichloro-5,6-dicyanobenzoquinone
(DDQ) from 0.5 to 2.5 showed a better yield of 85% (Table 1,
entry 3). The use of other oxidants di-tert-butyl peroxide (DTBP)
three dimensional Fe2O3 crystallites in DRS-UV and EPR results. and benzoquinone were found to be less effective than DDQ
[14b]
It has been reported in the literature that reduction of single
site iron takes place between 600°C to 700°C. Hence, reduction
event occurred around 675°C is owing to the isolated FeIII
ions.[15] Based on the evidence from DRS-UV and EPR about the
existence of Fe(III)-cluster, reduction peak centered at 570°C can
be attributed to the Fe(III)-clusters, tetramers, trimers and dimers
species. The emergence of reduction peak at high temperature
centered at 815°C ascribed to the Fe3+ site in the micropores of
SBA-15.[15b] Figure 2 (A and B) shows the TEM images of
8wt%Fe/SBA-15 grains oriented parallel to the electron beam
with its corresponding EDAX data. In one of the SBA-15
particles mesoporous channels (Figure 2(A)) are appear dark
due to presence of more iron content (7wt%) while in the other
SBA-15 particle (Figure 2(B)) mesoporous channels are free
with 1.5 wt% of iron. These TEM pictures strongly suggest the
existence of various oxidic forms of iron, confirmed through
earlier characterization results is disproportionately distributed in
the mesopores of SBA-15. Based on the above characterization
results it is understood that grafted iron in SBA-15 mesopore
channels exists as isolated, cluster and oligomer species as
illustrated in the Figure 3. Thus, SED technique successfully
eliminated the formation of iron oxide particles during the
grafting process inside the mesopore of SBA-15 with
(Table 1, entry 8,9). As anticipated, iron oxide particles
containing 8wt%Fe/SBA-15(500) at the best reaction condition
showed very less catalytic activity with 22% yield of 3a (Table1,
entry 10). Interestingly, 8wt%Fe/SBA-15 at the optimized
condition demonstrated excellent regio control with high yield
towards orthoester, acetoxy, carbonyl, methyl and halide
substituted anisole 3a–3i[10] (Figure 4). In particular, methyl 4-
methoxyphenylacetate also produced single product with good
yield 3j and its mass (346.1868) has been confirmed by HRMS.
It is interesting to note that cross coupling did not occur at the
methylene group in 4-methoxyphenylacetate as no electron rich
center is available in biphenylmethane. Coupling reaction did not
Table 1: Optimization Study on coupling reaction between 2-chloroanisole and
biphenylmethane
Entry
Catalyst
Biphenyl
methane
(equiv.)
1.5
Oxidant
(equiv.)
Yield (%)[a]
1
2
3
4
5
6
7
8
9
DDQ (2.5)
DDQ (2.5)
DDQ (2.5)
DDQ (0.5)
DDQ (1)
20%
8wt%Fe/SBA-15
8wt%Fe/SBA-15
8wt%Fe/SBA-15
8wt%Fe/SBA-15
8wt%Fe/SBA-15
8wt%Fe/SBA-15
8wt%Fe/SBA-15
8wt%Fe/SBA-15
8wt%Fe/SBA-15
3
6
6
6
6
6
6
6
25%
85% (65%)[b]
Small clusters Iron
61%
64%
DDQ (1.5)
DDQ (2)
69 %
82%
Micropore
DTBP(2.5)
15%
Benzoquinon
e (2.5)
No product
10
6
DDQ (2.5)
22%
8wt%Fe/SBA-
15(500)
11
12
6
6
TEMPO (2.5)
DDQ (2.5)
No product
No product[c]
8wt%Fe/SBA-15
-
Mesopore
13
6
DDQ (2.5)
No product[d]
AlCl3
Figure 3. Schematic illustration of various oxide forms of iron present in
[a] Yield determined by GC-MS methods using n-decane as the internal
standard. [b] Yield of isolated product. [c] Without catalyst, [d] AlCl3 catalyst
(15 mole %)
8wt%Fe/SBA-15
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Figure 4. 8wt%Fe/SBA-15 catalyzed arylation of biphenylmethane with
various anisole. [a]GC Yield determined using n-decane as the internal
standard. [b] Isolated Yield
Scheme 2. Proposed mechanism for 8wt%Fe/SBA-15 catalyzed arylation of
biphenylmethane and 4-methoxyphenylacetate.
proceed when 2.5 equivalent of TEMPO was added to the
reaction mixture (Table 1, entry 11) suggesting the involvement
of radical species in the coupling process. In the absence of
8wt%Fe/SBA-15 and in presence of AlCl3 (15 mole %) (Table 1,
entry 12, 13) coupling was not witnessed indicating the
participation of grafted iron in the reaction as redox catalyst.
Therefore, based on the above occurrences, it is anticipated that
reaction may proceed through iron assisted single electron
transfer (SET), similar to earlier report with homogeneous iron[10]
except change of oxidation state of iron from III to IV in case of
8wt%Fe/SBA-15. Based on the experimental results plausible
mechanism is proposed in scheme 2 for above reaction. Initially,
Fe(III) is oxidized to Fe(IV) by the oxidant DDQ through SET to
generate the radical species (Ph)2CH˙. (Ph)2CH˙ is further
oxidized by Fe(IV) to (Ph)2CH+, followed by Friedel-Crafts type
coupling with methyl 4-methoxyphenylacetate. Finally, proton
abstraction by reduced hydroquinone regenerates the catalyst
and delivers the product 4A.
To further confirm the establishment of Fe(IV) in
8wt%Fe/SBA-15 during the coupling process it is intended to
experiment Fe(IV) involved coupling reaction like arylation of
benzene with substituted phenylboronic acid.[11] From the
optimization study (Table 2) it is evident that DTBP is better
oxidant than DDQ for the arylation of benzene with 4-
bromophenylboronic acid. It is fascinating to note that under
identical reaction condition, 8wt%Fe/SBA-15 exhibited 45% yield
of 6a without additives whereas homogeneous iron yielded the
same in the presence of triflate and 2,2’-bipyridine.[11] Due to
steric hindrance, DTBP cannot access the iron sites available in
the micropores of SBA-15.
Table 2: Optimization of coupling reaction between 4-bromophenylboronic
acid and benzene
,
Entry
Catalyst
Time(h)
Oxidant
Yield
(%)[a]
Trace
(100mg)
8wt%Fe/SBA-15
1
2
3
24
24
48
DDQ (2 equiv)
DTBP (2 equiv)
DTBP (2 equiv)
8wt%Fe/SBA-15
8wt%Fe/SBA-15
40%
45%
8wt%Fe/SBA-15
4
72
DTBP (2 equiv)
47%
8wt%Fe/SBA-15
8wt%Fe/SBA-15
5
6
24
48
DTBP (3 equiv)
DTBP (3 equiv)
50%
59%
8wt%Fe/SBA-15
7
8
72
DTBP (3 equiv)
70%
DTBP (3 equiv)
8wt%Fe/SBA-
24
Trace
15(500)
-
9
72
DTBP (3 equiv)
Trace[b]
[a] Isolated yield, [b] without catalyst
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Further, chemisorbed DTBP oxidant in the mesopores of SBA-
15 prevents accessibility of neighboring iron sites to the free
oxidants. Hence, increment in DTBP equivalent, and reaction
time was essential to achieve the best yield of 70% (Table 2,
entry 7). When 8wt% Iron oxide loaded SBA-15, 8wt%Fe/SBA-
15(500), was employed for the above reaction at the optimized
condition results only trace amount of 6a (Table 2, entry 8). This
implies that the establishment Fe(IV) in iron oxide was not
possible. After optimization, scope of the reaction was further
explored with phenyl boronic acid bearing electron withdrawing
and electron donating group, and the results are compiled in
figure 5.
radical 7B which is further coupled with benzene to form
cyclohexadienyl radical. It is then oxidized by the Fe(IV) to give
the coupled product 4B and regenerate the catalyst. From the
catalytic activity study, it is understood that various types of iron
sites exist in the mesopores of SBA-15 are capable of catalyzing
the challenging coupling reactions. Contrary to homogeneous
iron use of electron withdrawing group and additives were not
required for 8wt%Fe/SBA-15 towards arylation of benzene.
Under the optimized condition, biphenyl compounds containing
various functional groups were obtained in moderate to good
yield 6a-6l (Figure 5). Interestingly homo coupling products were
not observed in the above reactions, when substituted boronic
acid were used (confirmed by GC-MS). The reaction of 4-
bromophenyl boronic acid with DTBP in CDCl3 gave 4-bromo-
benzene-d, confirm the formation of t-BuO˙ through
establishment of Fe(IV) in the 8wt%Fe/SBA-15 as observed in the
literature with homogeneous Fe(III) complex (Supporting
information, page No. S11).[11] Existence of iron in higher
coordination number in solid system has already been reported
in literature.[16] Based on the experimental results plausible
mechanism is proposed in scheme 3 for the arylation of
benzene reaction catalyzed by 8wt%Fe/SBA-15. Initially, Fe(III) is
oxidized to Fe(IV) by the oxidants DTBP through SET to generate
the radical species t-BuO˙. t-BuO˙ generates bromine
substituted aryl
Scheme 3. Proposed mechanism for 8wt%Fe/SBA-15 catalyzed arylation of 4-
bromophenylboronic acid and benzene
The benefit of using heterogeneous catalyst is appreciated
through its recyclability. Hence, the recyclable study of
8wt%Fe/SBA-15 was conducted for arylation of benzene with 4-
bromophenylboronic acid and the results are shown in the
(Figure 6). Catalyst could be successfully recycled for 5 times
without significant loss in its activity. ICP-OES analysis of the
spent 8wt%Fe/SBA-15 showed 7.8wt% iron after 5 cycles.
Amorphous pattern of wide angle XRD and retaining of
characteristic peak of
isolated, cluster and oligomer iron
species in DRS-UV spectrum (Figure S2, S5) confirms that
grafted active iron sites are intact with the SBA-15 after 5 cycles.
Figure 5. 8wt%Fe/SBA-15 catalyzed arylation of benzene with various
arylboronic acids. Yield obtained of isolated product. (a) Reaction condition:
48h, 110℃ and the ratio of the regioisomers was determined by 1H NMR and
GC-MS spectroscopy.
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Characterization information:
100
90
80
70
60
50
40
30
20
10
XRD: Powder X-ray diffraction (XRD) patterns were obtained
with a D8 Advance (BRUKER), diffractometer with a Cu Ka (k =
1.5418 Å) radiation source 2.2 KW Cu anode, Ceramic X-ray
tube Detector, Lynx Eye detector (Silicon strip detector
technology) apparatus using Cu Kα,1 radiation. XRD profiles
Scans were recorded at 2θ = 0.75–5° with a step size of 0.05
and step time = 1s for low angle and at 2θ = 10–90° for wide
angle analysis. BET: N2 adsorption-desorption isotherms were
performed at liquid nitrogen temperature (-195°C) using an
ASAP 2020 analyser from Micromeritics. Before each measure-
ment, samples were out-gassed 12h at 200°C under vacuum.
Surface area, pore volume and pore size distribution were
obtained from N2 adsorption–desorption isotherms, by using the
conventional BET and BJH methods. TPR: Temperature-
programmed reduction (TPR) (CHEMISORB 2750) analysis was
0
1
2
3
4
5
Cycle time
Figure 6. Recycle study of 8wt%Fe/SBA-15 catalyst towards arylation of
arylboronic acids with arenes under optimized condition.
performed with
a
ChemiSoft TPx V1.02 linear quartz
Conclusions
microreactor (i.d. 4 mm) fed with a sample pretreated at 120°C
in High pure Helium Gas (25cc/min) for 1 hour and cooled to
room temp in Helium . Gas changed to 5%H2/Ar (25cc/min) at
RT and waited till baseline is stable. Then TPR started from RT
to 815 °C at 10°C/min and hold for 15min. Calibration:
(CHM_0022) 10/7/14 TCD-TPR hydrogen calibration, Measured
Flow Rate: 25.00 mL STP/min. Hydrogen consumption was
registered using a TCD detector. EPR: EPR spectroscopy was
performed under nitrogen at ambient and Liquid Nitrogen
temperature using JEOL Model JES FA200 instrument, X- Band
frequency: 8.75 - 9.65 GHz, Sensitivity: 7x109 spins /0.1m T.
Resolution: 2.35 μT or better. The measurements were
performed on a typically, a fixed amount of sample after a
certain pre-treatment was transferred into a quartz tube instantly,
and the quartz tube was set in a quartz Dewar vessel in the EPR
cavity. The temperature was typically set at 100 K (-170°C)
unless otherwise stated. DRS-UV: Diffuse reflectance UV–vis
In conclusion, we have established 8wt%Fe/SBA-15 as efficient,
sustainable heterogeneous iron catalyst for direct arylation of
biphenyl methane and benzene. SED technique successfully
eliminated the formation of iron oxide particles during the
grafting procedure inside the mesopores of SBA-15. The
participation of different type of oxidic iron sites (single,
oligomer, cluster) in the above challenging coupling reactions is
confirmed in this study. Contrary to homogeneous iron use of
electron withdrawing group and additives were not required in
8wt%Fe/SBA-15 for arylation of benzene. Recyclability of our
catalyst proves its robustness and opens a new avenue to
employ this catalyst in academic research and industries for
challenging C-C coupling reaction. Further investigations on
scope and mechanism of this catalyst are currently underway.
spectra were recorded on
a Perkin-Elmer Lambda 900
UV/VIS/NIR spectrometer. The powder samples were loaded in
a quartz cell and the spectra were collected with BaSO4 as a
reference. HR-TEM: High Resolution Transmission electron
microscopy (HR-TEM) images were taken using a Model FEI-
TECNAI G2-20 TWIN 200kV instrument, filament LaB6. To get
the TEM images, the powdered samples were dispersed in
isopropyl alcohol and then loaded on Cu grids, EDS detector.
Prior to the experiment, each sample was first suspended in
absolute ethanol for 10 min by ultrasonication. Then, the
suspension was deposited on a lacey carbon film supported on
a copper grid. NMR: NMR spectra were recorded on Bruker FT-
Experimental Section
Materials:
All chemicals were purchased from commercial suppliers and
used without further purification. TEOS, HCl and P123 were
purchased
from
Sigma
Aldrich.
Lanthanum
nitrate
(La(NO3)3·6H2O), ferric nitrate (Fe(NO3)3·9H2O), citric acid
(C6H8O7 ·H2O) and ammonia (NH3 ·H2O, 25~28 wt%) bought
from Alfa Aesar. Di-tert-butyl peroxide (DTBP) procured form
Merck. 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), TLC
plates (60 F254, 0.2 mm) and all other reagent grade chemicals,
solvents were used as received from Avra synthesis pvt. Ltd.
1
NMR-400 MHz instrument for H and 13C NMR, respectively. All
1H NMR spectra were reported in units ppm (parts per million),
and were measured relative to residual chloroform signal (7.26
ppm or 7.18 ppm) in the deuterated solvent. 13C NMR spectra
were reported in ppm relative to deuterated chloroform (77.23
ppm). Coupling constants (J) are reported in Hz; splitting
patterns are assigned s = singlet, d = doublet, t = triplet, q =
quartet, quin = quintet; br = broad signal.GC-MS: GC-MS Perkin
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General procedure for 8wt% Fe/SBA-15 catalysed arylation
of benzylic C-H bonds with arenes.
Elmer, GC model: Clarus 680, Mass Spectrometer: Clarus 600
(EI). Acquisition parameters, Oven: Initial temp 60°C for 2 min,
ramp 10°C/min to 300°C, hold 6 min, Total Run Time: 32.00 mint,
Inj A auto=250°C, Volume=1 μL, Split=10:1, Flow Rate: 1
mL/min., Carrier Gas=He, Column=Elite-5MS (30.0m, 0.25mmID,
250μm df). mass condition (EI) : Solvent Delay=2.00 min,
Transfer Temp=230°C, Source Temp=230°C, Scan: 50 to
The reaction was carried out by adding the 100mg 8wt %
Fe/SBA-15 catalyst to the mixture of
6
equiv. of
diphenylmethane (3mmol), 1 equiv of 2-chloro anisole (0.5mmol),
2.5 equiv of DDQ (274mg, 1.25 mmol) and 2-3ml of
dichloroethane solvent. The reaction mixture was stirred for 36 h
under N2 atmosphere at 100°C. After cooling, the reaction
mixture was stirred with 10ml of ethylacetaete/methanol (8:2)
and the catalyst was separated from the reaction mixture by
filtration. The filtrate was further concentrated to remove the
solvent and used for GC-MS analysis. For column
chromatography, 1.4 g of silica gel (100-200 mesh) was added
to the residue and purified by eluting with Chloroform and
Hexane (3:7) to get the desired product 3a.
600Da, GC-FID detector.HR-MS:
A high resolution mass
spectrum (HR-MS) was recorded using Electron ionization (EI)
method using JEOL HR Mass spectrometer, operating at an
accelerating voltage of 1.5 kV. Electron ionization (EI) mass
spectra (mass range 50-1000 amu) were recorded using a direct
probe with evaporation of the samples into the ion source kept at
ca. 200 °C and an electron beam energy of 70 eV. ICP-OES:
The ICP-OES analysis was done using Perkin Elmer Optima
5300 DV. Sample preparation: 0.100 g of catalyst mixed with 10
ml of hydrochloric acid and 5ml of Con. H2SO4. The mixture was
stirred thoroughly at RT for 24h. Catalyst was filtered and
transferred to the 100ml standard flask remaining volume was
adjusted with distilled water.
General procedure for 8wt% Fe/SBA-15 catalysed arylation
of arylboronic acids with arenes.
100mg of 8wt% Fe/SBA-15 catalyst was added to the
reaction mixture of 0.5mmol of arylboronic acid (1 equiv), 50
mmol of benzene (100 equiv) and 1.5 mmol of DTBP oxidant (3
equiv). The reaction mixture was stirred for 72h under N2
atmosphere at 80°C. After cooling, reaction mixture was stirred
for 1h with 10ml of ethylacetaete and the catalyst was separated
from the reaction mixture by filtration. Further, organic solution
was concentrated to remove the solvent. 1g of silica gel (100-
200mesh) was added to the residue and separated by column
chromatography using hexane/chloroform (9:1) to afford the
desired white solid product 6a. After completion of reaction 10ml
Ethylacetaete/Methanol (7:3) mixture was added to the reaction
mixture and stirred for 1h. The catalyst was separated by
filtration and dried overnight then it was used for the next cycle.
Synthesis of 8wt%Fe/SBA-15
Mesoporous silica SBA-15 was synthesized through
hydrothermal technique using P123 triblock copolymer template
as reported in the literature.[17] The LaFeO3 perovskite iron
precursor was prepared by the citrate-based sol–gel method.[18]
Required amount of Iron (8wt%) was grafted over SBA-15 using
LaFeO3
as
precursor
in
acidic
medium
through
selective extraction deposition technique (SED).[8] Briefly, 0.5g of
calcined SBA-15 and 0.190g of LaFeO3 are mixed together and
transferred to 250ml of 3 neck round bottom flask contains
Acknowledgements
⁰
150ml distilled water. The mixture was heated up to 80 C and
pH of the solution was found to be 5.8. Required amount of
dilute H2SO4 (0.005M) was introduced in to the reaction mixture
till the solution pH attains 3. After consumption of the dilute
H2SO4 by LaFeO3, the solution pH rises to 5 and released iron
ion is grafted into the mesopores of SBA-15. Addition of dilute
H2SO4 was continued till entire LaFeO3 decomposes and the
solution pH remain constant at pH 3. The solid material was
washed, filtered and dried at 100°C overnight.
This study was supported by DST-SERB Fast Track (Sanction
No. SR/FT/CS-138/2011) and DST-INDO-ISRAEL Bilateral
project (Sanction No. DST/INT/ISR/P-09/2014), Government of
India, New Delhi. One of the authors (C. Rajendran) is thankful
to DST for the research fellowship. NMR and TEM facility
provided by VIT-SIF and VIT university is gratefully
acknowledged.
Keywords: C-H activation • cross-coupling • Fe/SBA-15 •
Synthesis of 8wt%Fe/SBA-15(500)
heterogeneous iron • mesoporous materials
8wt%Fe/SBA-15(500) catalyst was prepared following the
procedure reported in the literature [19] using ferric nitrate as iron
precursor. Briefly, 0.585g of Fe(NO3)3.9H2O in 10 ml of ethanol
was stirred with 1g of calcined SBA-15. This suspension was
stirred at 60℃ overnight until dried and the sample was treated
to 500℃ for 5h at the heating rate 3℃ per minute in the furnace.
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Iron grafted SBA-15,
C. Rajendran , G.Satishkumar*
8wt%Fe/SBA-15,
has
Page No. – Page No.
proven as sustainable,
efficient heterogeneous
iron catalyst for direct
arylation of biphenyl
methane C(sp3)-H and
Sustainable Heterogeneous Iron
catalyst Fe/SBA-15 towards direct
arylation of unactivated C(sp3)-H and
C(sp2)-H with arenes
benzene
Unlike
C(sp2)-H.
homogeneous
iron,
8wt%Fe/SBA-15
catalyst does not need
the support from the
electron
withdrawing
group and additives to
carry out arylation of
benzene and could be
successfully recycled for
5 cycles.
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