Magnetic-nanoparticle-supported 2,2′-bis[3-(triethoxysilyl)propyl] imidazolium-substituted diethyl ether bis(tribromide): A convenient recyclable reagent for bromination

Article abstract of DOI:10.1002/ejic.201300755

A new magnetic-nanoparticle-supported bromination reagent was synthesized by anchoring a 2,2′-bis[3-(triethoxysilyl)propyl]imidazolium-substituted diethyl ether bis(tribromide) onto the surface of γ-Fe₂O ₃ nanoparticles and subsequently treating this new ionic liquid with bromine. The nanoparticle reagent was obtained with good loading levels and has been successfully used for the efficient bromination of a wide range of alkenes, alkynes, ketones, and aromatic substrates. More importantly, the reagent could be easily recovered by an external magnet and reused six times without significant loss of activity. A new maghemite nanoparticle bromination reagent has been prepared. The nanoparticle reagent was obtained with good loading levels and has been successfully used for the efficient bromination of a wide range of alkenes, alkynes, ketones, and aromatic substrates. Copyright

Full text of DOI:10.1002/ejic.201300755

FULL PAPER
DOI:10.1002/ejic.201300755
Magnetic-Nanoparticle-Supported 2,2Ј-Bis[3-
(triethoxysilyl)propyl]imidazolium-Substituted Diethyl
Ether Bis(tribromide): A Convenient Recyclable Reagent
for Bromination
Liqiang Wu*[a] and Zhikui Yin[a]
Keywords: Nanoparticles / Bromination / Alkenes / Alkynes / Ketones / Aromatic substitution
A new magnetic-nanoparticle-supported bromination rea-
gent was synthesized by anchoring a 2,2Ј-bis[3-(triethoxy-
silyl)propyl]imidazolium-substituted diethyl ether bis(tri-
bromide) onto the surface of γ-Fe2O3 nanoparticles and sub-
sequently treating this new ionic liquid with bromine. The
nanoparticle reagent was obtained with good loading levels
and has been successfully used for the efficient bromination
of a wide range of alkenes, alkynes, ketones, and aromatic
substrates. More importantly, the reagent could be easily re-
covered by an external magnet and reused six times without
significant loss of activity.
Introduction
Brominated compounds are a useful class of intermedi-
ates in organic synthesis because they are amenable to a
vast number of organic reactions involving functional-
group transformations. These include carbon–carbon bond
formations, organometallic preparations, and metal-cata-
lyzed cross-coupling reactions.[1–3] The use of liquid
bromine for bromination is still very common in industry
as well as in academia. However, liquid bromine is difficult
to handle because of its toxicity, corrosiveness, and high
volatility. A possible solution would be the development of
a solid green reagent by utilizing the liquid bromine precur-
sor of bromine manufacture.[4,5] Another is the application
of recyclable reagents with byproducts that can be ef-
ficiently separated from reaction mixtures and reused. For
example, to dress the recovery issue, many highly efficient
strategies have been used to immobilize the reagent onto
various supports such as organic polymers (Figure 1, a–
d),[6–9] silica sol–gel (Figure 1, e),[10] and ionic liquids (Fig-
ure 1, f).[11] However, substantial decreases in the activities
of these immobilized reagents are frequently observed ow-
ing to the heterogeneous nature of these support materials
in the reaction media. Furthermore, in many instances, the
recovery of heterogenized reagents through filtration is
cumbersome, especially in the case of air-sensitive or high-
toxicity products.
Figure 1. Examples of supported bromination reagents.
In recent years, magnetite or maghemite nanoparticles
(MNP) have acquired the attention of organic chemists as a
new alternative to porous materials for supporting catalytic
transformations.[12] The magnetic nature of these particles
allows the easy recovery and recycling of the catalysts by
the application of an external magnetic field, which may
reduce the operational cost and enhance the purity of the
product. Moreover, magnetic nanoparticles can be func-
tionalized easily through appropriate surface modifications,
which are able to load various functionalities. The magneti-
cally functionalized reagents often show identical and
sometimes even higher activities than their corresponding
homogeneous analogues owing to their high accessible sur-
face area.[13]
Driven by the unique properties of magnetic nano-
particles, we would like to report here our exploration of
the design of magnetic-nanoparticle-supported 2,2Ј-bis[3-
(triethoxysilyl)propyl]imidazolium-substituted diethyl ether
bis(tribromide) (MNP-BETB) and its application in the
bromination of alkenes, alkynes, ketones, and aromatic sub-
strates (Scheme 1). To the best of our knowledge, this is the
[a] School of Pharmacy, Xinxiang Medical University,
East of JinSui Road of Xinxiang City, 453003 Henan Province,
P. R. China
E-mail: wliq870@163.com
http://www.xxmu.edu.cn/
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first report on the preparation and application of a mag-
netic-nanoparticle-supported bromination reagent. As a re-
sult of the combination of the MNP support features and
flexible bis-silylated imidazolium linkers, the bromination
reagent acts as an efficient “quasihomogeneous” bromin-
ation reagent, which can be highly dispersed in the reaction
system like a homogeneous one, and easily separated and
reused like a heterogeneous bromination reagent by mag-
netic force. This new bromination reagent may be a signifi-
cant bridge between homogeneous and heterogeneous
bromination reagents. Furthermore, the use of bis-silylated
species may link the iron oxide nanoparticles to produce
nanoparticle networks, which can increase the surface area
and be propitious to the reaction process.
Scheme 2. Synthesis of MNP-BETB.
brating sample magnetometry (VSM), thermogravimetric
analysis (TG), and elemental analysis. The specific surface
area of the powder was determined by the Brunauer–
Emmett–Teller (BET) method. Unfortunately, owing to the
magnetic properties of 4, it is impossible to further charac-
terize this material by solid-state NMR spectroscopy.
To prove the successful functionalization of γ-Fe2O3, we
employed IR to give detailed investigations of the obtained
MNP-BETB (Figure 2). Compared with the unfunction-
alized γ-Fe2O3 and 2,2Ј-bis[3-(triethoxysilyl)propyl]imid-
azolium-substituted diethyl ether bis(tribromide), the sig-
nificant features of the spectrum of MNP-BETB were the
appearances of the peaks at 3182 (sp2 C–H stretching vi-
bration of the imidazole moiety), 2822 (N–CH2 stretching
vibration), 1565 (C–N and C=C vibrations of the imidazole
ring), and 1127 cm–1 (C–O–C stretching vibration), which
indicated the definite graft of precursor 2. This analysis, in
combination with microanalysis data (Figure 3), indicated
the successful anchoring on the surface of the MNPs. In
Scheme 1. Synthesis of brominated compounds by using MNP-
BETB.
Results and Discussion
MNP-BETB was synthesized according to the procedure
shown in Scheme 2. The precursor 2 was prepared by quat-
ernization of 1-[3-(triethoxysilyl)propyl]-1H-imidazole (1)
with bis(2-bromoethyl) ether. Maghemite (γ-Fe2O3) nano-
particles, which are easily prepared by a chemical coprecipi-
tation technique of ferric and ferrous ions in alkali solution,
were chosen as the support. The obtained MNPs were soni-
cated for one hour before treatment with excess 2 in an-
hydrous toluene under reflux. The subsequent treatment of
this new ionic liquid with bromine afforded the correspond-
ing tribromide. The loading of 4 is 0.60 mmol of tribromide
per gram as determined by elemental analysis. The new
bromination reagent is stable for several months without
loss of activity.
The MNP-BETB was characterized by FTIR spec-
troscopy, energy-dispersive X-ray spectroscopy (EDS),
scanning electron microscopy (SEM), transmission electron
microscopy (TEM), powder X-ray diffraction (XRD), vi- Figure 2. FTIR spectra of precursor 2, γ-Fe2O3, and MNP-BETB.
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addition, from EDS analysis, the bromine peak clearly con-
–
firms the presence of the Br3 group from liquid bromine
(Figure 3).
Figure 5. TG analysis for MNP-BETB.
Figure 3. EDS spectrum of MNP-BETB.
shows small nanosized grains with spherical and quasi-
spherical morphologies with a narrow size distribution,
which indicates the nanocrystalline nature of the γ-Fe2O3
nanoparticles. The presence of some larger particles is at-
tributed to aggregation or overlapping of smaller particles.
The XRD pattern of MNP-BETB exhibits diffraction
peaks at 2θ = 30.30, 35.74, 43.40, 54.09, 57.46, and 62.90°,
which correspond to the (220), (311), (400), (422), (511),
and (440) faces. The observed diffraction peaks agree well
with the tetragonal structure of maghemite (Figure 4). It is
clear that no other phases except those of maghemite are
detectable. The average crystallite size was calculated to be
13.7 nm by using the Scherrer equation.
Figure 4. XRD pattern of MNP-BETB.
The thermal stability of MNP-BETB was determined by
thermogravimetric analysis (Figure 5). The TG curve indi-
cates an initial weight loss of 5.3% up to 150 °C, which is
attributed to the loss of adsorbed water from the support.
The complete loss of weight is seen in the temperature range
250–840 °C, and the amount of organic moieties was ca.
23.16% of the total solid. Therefore, MNP-BETB is stable
to ca. 220 °C.
The shape and surface morphology of γ-Fe2O3 and
MNP-BETB were investigated by SEM and TEM. As
shown in Figure 6, the low-magnification SEM images Figure 6. SEM images of γ-Fe2O3 (top) and MNP-BETB (bottom).
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The size of MNP-BETB was further analyzed by TEM, and
The magnetic properties of MNP-BETB were investi-
the results (Figure 7) showed the nanoparticles have dimen- gated at room temperature (Figure 8). The room-tempera-
sions of 10–20 nm; in the TEM images, the γ-Fe2O3 par- ture magnetization curve of MNP-BETB shows that the
ticles are relatively round, and those of treated MNP-BETB samples exhibited typical superparamagnetic behavior with
are rather rectangular, which is attributed to the presence no observed hysteresis. The saturation magnetization value
of 2,2Ј-bis[3-(triethoxysilyl)propyl]imidazolium-substituted is 49.48 emu/g. This value is slightly smaller than that of γ-
diethyl ether bis(tribromide) covalently attached to the γ- Fe2O3 (61.2 emu/g), probably because the increased amount
Fe2O3 surfaces.
of nonmagnetic material (organic ligands) on the particle
surface makes a larger percentage of their mass nonmag-
netic. However, this value is sufficiently high for magnetic
separation. The strong magnetization of the nanoparticle
was also revealed by simple attraction with an external
magnet.
Figure 8. Magnetic curves of MNP-BETB.
The N2 adsorption–desorption isotherm provided a valu-
able tool to study the textural and structure properties. The
specific surface area of the powders was determined by the
Brunauer–Emmett–Teller (BET) method. The BET results
showed that the average surface area of γ-Fe2O3 was
73.79 m2 g–1 and that of MNP-BETB was 51.89 m2 g–1 (Fig-
ure 9). Therefore, γ-Fe2O3 has a much higher surface area
than MNP-BETB. This seems logical as the successful an-
choring of the tribromide on the surface of MNP decreases
the surface area.
MNP-BETB is a versatile bromination reagent and it can
be used instead of free bromine for the bromination of alk-
enes, alkyne, ketones, and aromatic groups (Table 1). The
bromination reagent transforms the alkene or alkyne into
dibromides in a completely stereoselective manner. Cyclic
olefins produced exclusively trans-dibromides, cis open
chain alkenes produced threo (or d,l) isomers, and trans
open chain alkenes led to erythro (or meso) dibromides
(Table 1, Entries 1–8). The reactions with alkynes yielded
dibromo E isomers (Table 1, Entries 11–13). The stereo-
chemical assignment was made by comparison of the cou-
Figure 7. TEM images of γ-Fe2O3 (top) and MNP-BETB (bottom). pling constants (J values) of the adjacent protons at the
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pear to affect the product compositions; no products from
ether cleavage were found (Table 1, Entry 22).
The separation of the product and recycling of the MNP-
BETB were indeed quite simple (Figure 10). After the reac-
tion, the organic layer was simply decanted, assisted by a
nearby magnet, to afford the desired products. The MNP-
BETB quickly concentrated to the side wall of the reaction
vial when a magnet was placed nearby. The separated
MNP-BETB was then washed and regenerated by treat-
ment with bromine. The reusability of the reagent was in-
vestigated for the bromination of cyclohexene. The pro-
cedure was repeated, and the results indicated that the rea-
gent could be recycled six times with no apparent loss of
activity (Figure 11).
Figure 10. Reaction mixture containing MNP-BETB (left), and
MNP-BETB collected by using an external magnet after the reac-
tion (right).
Figure 9. N2 adsorption–desorption isotherms of γ-Fe2O3 (top)
and MNP-BETB (bottom).
carbon atoms attached to the bromo groups with the re-
ported values. Activated alkenes were also smoothly
brominated by this procedure (Table 1, Entries 7–8). The
bromination reagent was very efficient for the α-mono-
bromination of ketones. We found that the reaction is appli-
cable to substituted acetophenone containing different sub-
stituents such as methoxy, nitro, and chloro (Table 1, En-
tries 14–18). It is concluded from these results that electron-
rich aryl groups activate the ketones in this chemoselective
electrophilic oxidative halogenation reaction at the α-car-
bon atom without further electrophilic halogenation at the
aromatic ring. Although electron-poor groups slightly in-
Figure 11. Recycling experiments for the bromination of cyclohex-
ene.
Conclusions
We have prepared MNP-BETB as a first maghemite nan-
creased the reaction times, no pronounced effect on the re- oparticle bromination reagent. The prepared MNP-BETB
action yield was observed. It is also notable that cyclic allowed the bromination of a wide range of alkenes, alk-
ketones and CH-active compounds can also participate in ynes, ketones, and aromatic substrates in excellent yields
this reaction with high yields (Table 1, Entries 19–21). The and high selectivities. Notably, the reagent could easily be
bromination reagent also effected efficient and selective recycled and reused without loss of activity. This new rea-
electrophilic substitutions of aromatic substrates (Table 1, gent can be regarded as a readily available alternative or as
Entries 22–24). In these reactions, the evolution of HBr was a complement to the known supported bromination rea-
expected and detected (qualitatively). The HBr did not ap- gents.
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Table 1. Bromination of organic substrates with MNP-BETB.
4000/TriStar II 3020 instrument at liquid nitrogen temperature
(77 K). The specific surface area was calculated by the BET equa-
tion. Thermogravimetric analysis was performed under nitrogen by
using a DT-40 thermoanalyzer. IR spectra were determined with
an FTS-40 infrared spectrometer. NMR spectra were determined
with a Bruker AV-400 spectrometer at room temperature with
tetramethylsilane (TMS) as an internal standard, and coupling con-
stants (J) were measured in Hz. Elemental analyses were performed
with a Vario-III elemental analyzer. Melting points were deter-
mined with an XT-4 binocular microscope. All solvents used were
strictly dried according to standard operations and stored over 4A
molecular sieves. All other chemicals (AR grade) were obtained
from commercial resources and used without further purification.
All products were characterized by comparison of their spectral
Experimental Section
General: X-ray powder diffraction (XRD) patterns were recorded
by using a Bruker D8 Advance Bruker powder diffractometer with
a Cu-Kα radiation source. Scanning electron microscopy (SEM)
studies were conducted with an Inspect F50 scanning electron
microscope. Transmission electron microscopy (TEM) studies were
performed by using an FEI Tecnai G2 20 transmission electron
microscope with an accelerating voltage of 150 kV. Elemental com-
positions were determined with a Hitachi S-4800 scanning electron
microscope equipped with an EDAX energy-dispersive spectrome-
ter (SEM-EDS). Magnetic measurements of particles were made
by using a vibrating sample magnetometer (MPMS-XL-7). N2 ad-
sorption–desorption isotherms were measured by using a NOVOE
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and physical data with those previously reported. The progress of
the reactions was monitored by TLC.
particles were then washed and regenerated by treatment with
bromine. The organics were concentrated in vacuo. The resulting
products were separated by column chromatography (silica gel, 9:1
hexanes/ethyl acetate as eluent) and their NMR spectra and ele-
mental analysis were compared with those of authentic samples.
5a: 1H NMR (400 MHz, CDCl3): δ = 4.23–4.21 (m, 2 H), 2.32–
2.08 (m, 2 H), 1.72–1.56 (m, 4 H), 1.31–1.21 (m, 2 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 55.9, 55.8, 32.3, 32.0, 22.7 ppm.
C6H10Br2 (241.95): calcd. C 29.78, H 4.17; found C 30.02, H 4.12.
5b: 1H NMR (400 MHz, CDCl3): δ = 4.52–4.50 (m, 2 H), 2.42–
2.38 (m, 2 H), 2.15–2.03 (m, 2 H), 1.82–1.46 (m, 8 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 61.5, 61.2, 33.2, 33.1, 25.7, 25.3,
25.1 ppm. C8H14Br2 (270.01): calcd. C 35.59, H 5.23; found C
35.62, H 5.18.
5c: 1H NMR (400 MHz, CDCl3): δ = 7.44–7.38 (m, 5 H), 5.20 (dd,
J = 5.7, 10.2 Hz, 1 H), 4.15–4.03 (m, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 138.5, 129.2, 128.9, 128.8, 127.6, 127.4,
51.1, 35.2 ppm. C8H8Br2 (263.96): calcd. C 36.40, H 3.05; found C
36.52, H 3.16.
1-[3-(Triethoxysilyl)propyl]-1H-imidazole (1): To a solution of imid-
azole (3.4 g, 50 mmol) in dry toluene (50 mL), 3-chloropropyltri-
ethoxysilane (12.0 mL, 50 mmol) was added, and the mixture was
heated to reflux overnight under a nitrogen atmosphere. The sol-
vent was removed by rotatory evaporation under reduced pressure,
and the intermediate 1 was obtained as a transparent liquid by
neutral Al2O3 column chromatography. 1H NMR (400 MHz,
CDCl3): δ = 7.51 (s, 1 H), 7.10 (s, 1 H), 6.89 (s, 1 H), 3.946 (t, J =
7.6 Hz, 2 H), 3.83 (q, J = 7.0 Hz, 6 H), 1.93–1.91 (m, 2 H), 1.20
(t, J = 7.0 Hz, 9 H), 0.587 (t, J = 8.0 Hz, 2 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 136.9, 129.2, 118.9, 58.0, 49.1, 24.9, 18.2,
7.3 ppm. C12H24N2O3Si (272.42): calcd. C 52.91, H 8.88, N 10.28;
found C 52.99, H 8.91, N 10.22.
3-[3-(Triethoxysilyl)propyl]-1-[2-(2-{1-[3-(triethoxysilyl)propyl]-1H-
imidazol-3-ium-3-yl}ethoxy)ethyl]-1H-imidazol-3-ium Bis(tribrom-
ide) (2): A mixture of 1 (8.16 g, 30 mmol) and bis(2-bromoethyl)
ether (1.91 mL, 15 mmol) was stirred in dimethylformamide
(DMF; 40 mL) at 120 °C for 4 h. The mixture was cooled, and the
solvent was removed under reduced pressure to give precursor 2 as
a viscous yellow liquid in 96% yield. 1H NMR (400 MHz, [D6]-
DMSO): δ = 8.73 (s, 2 H), 7.40 (m, 4 H), 4.38 (t, J = 4.8 Hz, 4 H),
3.99 (t, J = 7.6 Hz, 4 H), 3.83 (t, J = 4.8 Hz, 4 H), 3.79 (q, J =
7.2 Hz, 12 H), 1.90 (m, 4 H), 1.20 (t, J = 7.2 Hz, 18 H), 0.63 (t, J
= 7.6 Hz, 4 H) ppm. 13C NMR (100 MHz, [D6]DMSO): δ = 135.8,
132.1, 122.5, 66.2, 58.3, 56.5, 49.0, 25.1, 18.3, 7.3 ppm.
C28H56Br2N4O7Si2 (776.75): calcd. C 43.30, H 7.27, N 7.21; found
C 43.21, H 7.32, N 7.25.
5d: 1H NMR (400 MHz, CDCl3): δ = 3.97–3.89 (m, 1 H), 3.65–
3.60 (m, 1 H), 3.43–3.36 (m, 1 H), 1.93–1.85 (m, 2 H), 1.60–1.52
(m, 2 H), 1.40–1.08 (m, 6 H), 0.69 (d, J = 6.5 Hz, 3 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 53.5, 36.7, 36.5, 32.0, 28.9, 27.3,
23.0, 14.2 ppm. C8H16Br2 (272.02): calcd. C 35.32, H 5.93; found
C 35.26, H 6.02.
1
5e: H NMR (400 MHz, CDCl3): δ = 7.11–7.04 (m, 10 H), 5.49 (s,
2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 137.9, 128.7, 128.6,
128.3, 59.7 ppm. C14H12Br2 (340.06): calcd. C 49.45, H 3.56; found
C 49.38, H 3.60.
Synthesis of γ-Fe2O3: FeCl2·4H2O (9.25 mmol) and FeCl3·6H2O
(15.8 mmol) were dissolved in deionized water (150 mL) under an
Ar atmosphere at room temperature. An NH4OH solution (25%, (m, 6 H), 5.48 (s, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
5f: 1H NMR (400 MHz, CDCl3): δ = 7.58–7.56 (m, 4 H), 7.43–7.22
50 mL) was then added dropwise to the stirred mixture at room
temperature to reach a reaction pH of 11. The resulting black dis-
persion was continuously stirred for 1 h at room temperature and
then heated at reflux for 1 h to yield a brown dispersion. The as-
synthesized sample was heated to 200 °C at 2 °Cmin–1 and then
kept in a furnace for 3 h to give a red-brown powder.
129.3, 129.1, 128.6, 56.3 ppm. C14H12Br2 (340.06): calcd. C 49.45,
H 3.56; found C 49.42, H 3.58.
5g: 1H NMR (400 MHz, CDCl3): δ = 4.48–4.42 (m, 1 H), 4.24–
4.20 (m, 1 H), 2.05–1.99 (m, 1 H), 1.92–1.78 (m, 4 H), 1.67–1.61
(m, 1 H), 1.46–1.42 (m, 1 H), 0.99–0.95 (m, 3 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 59.8, 52.4, 35.9, 21.5, 21.1, 13.4 ppm.
C6H12Br2 (243.97): calcd. C 29.54, H 4.96; found C 29.85, H 5.03.
5h: 1H NMR (400 MHz, CDCl3): δ = 4.27–4.20 (m, 1 H), 4.15–
4.10 (m, 1 H), 2.04–2.00 (m, 1 H), 1.94–1.81 (m, 4 H), 1.66–1.61
(m, 1 H), 1.48–1.43 (m, 1 H), 0.97–0.95 (m, 3 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 61.4, 52.4, 39.1, 25.1, 20.3, 13.3 ppm.
C6H12Br2 (243.97): calcd. C 29.54, H 4.96; found C 29.63, H 4.99.
Magnetic Nanoparticle Compound 3: Magnetite nanoparticles
(2.0 g) were dispersed in dry toluene (50 mL) by sonication for 1 h.
Compound 2 (3.88 g, 5.0 mmol) was then added. The reaction mix-
ture was heated to reflux under nitrogen gas for 3 d. The reaction
mixture was cooled to room temperature, and the products were
sedimented on a magnet and washed successively with dry toluene
(50 mL) and dry acetone (50 mL) and then dried under vacuum.
The loading of 3 was 0.66 mmol of bromide per gram as deter-
mined by elemental analysis.
1
5i: H NMR (400 MHz, CDCl3): δ = 4.60 (s, 2 H), 4.37–4.22 (m,
4 H), 1.41–1.19 (m, 6 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
166.5, 62.7, 41.2, 13.8 ppm. C8H12Br2O4 (331.99): calcd. C 28.94,
H 3.64; found C 28.95, H 3.67.
MNP-BETB (4): Compound 3 (1 g, 0.33 mmol) was dispersed in
CH2Cl2 (10 mL) by sonication for 1 h, and then bromine (0.11 g,
0.7 mmol) dissolved in of CH2Cl2 (1 mL) was added dropwise. The
resulting mixture was stirred for 24 h at room temperature in a
sealed flask. MNP-BETB was collected with a permanent magnet
and washed three times with CH2Cl2 (20 mL). The loading of 4
is 0.60 mmol of tribromide per gram as determined by elemental
analysis.
1
5j: H NMR (400 MHz, CDCl3): δ = 7.44–7.38 (m, 5 H), 5.41 (d,
J = 11.2 Hz, 1 H), 4.68 (d, J = 11.2 Hz, 1 H), 4.42–4.35 (m, 2 H),
1.42–1.38 (M, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 167.7,
137.5, 129.3, 128.8, 128.0, 127.7, 62.5, 50.6, 46.9, 13.8 ppm.
C11H12Br2O2 (336.02): calcd. C 39.32, H 3.60; found C 39.42, H
3.62.
5k: 1H NMR (400 MHz, CDCl3): δ = 7.65–7.62 (m, 1 H), 7.37–
7.24 (m, 3 H), 6.87 (s, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
178.5, 133.2, 130.7, 130.4, 127.8, 122.2, 119.6, 107.1 ppm. C8H5Br3
(340.84): calcd. C 28.19, H 1.48; found C 28.21, H 1.52.
General Procedure for Bromination Reactions with MNP-BETB:
MNP-BETB (4, 0.75 mmol) was added to a solution of the sub-
strate (1 mmol) in CH2Cl2 (5 mL) and MeOH (2 mL), and the mix-
ture was heated to reflux for 3–10 h, After completion of the reac-
tion, MNP-BETB was collected at the side of the flask by using
a small magnet, and the supernatant was carefully decanted. The
1
5l: H NMR (400 MHz, CDCl3): δ = 6.39 (s, 1 H), 2.62–2.54 (m,
2 H), 1.62–1.51 (m, 2 H), 1.43–1.31 (m, 2 H), 1.10–0.91 (m, 3 H)
Eur. J. Inorg. Chem. 2013, 6156–6163
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ppm. 13C NMR (100 MHz, CDCl3): δ = 127.3, 102.6, 37.2, 29.6,
22.3, 14.2 ppm. C6H10Br2 (241.95): calcd. C 29.78, H 4.17; found
C 29.85, H 4.15.
CDCl3): δ = 158.7, 132.6, 115.9, 113.0, 55.8 ppm. C7H7BrO
(187.04): calcd. C 44.95, H 3.77; found C 45.03, H 3.69.
5w: 1H NMR (400 MHz, CDCl3): δ = 7.31 (d, J = 8.0 Hz, 2 H),
6.65 (d, J = 8.0 Hz, 2 H), 2.91 (s, 6 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 149.3, 133.2, 117.3, 112.4, 40.5 ppm. C8H10BrN
(200.08): calcd. C 48.02, H 5.04; found C 48.09, H 4.99.
5x: 1H NMR (400 MHz, CDCl3): δ = 7.34 (d, J = 8.0 Hz, 2 H),
6.72 (d, J = 8.0 Hz, 2 H), 4.75 (s, 1 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 157.6, 133.2, 118.3, 115.4 ppm. C6H5BrO (173.01):
calcd. C 41.65, H 2.91; found C 41.68, H 2.88.
5m: 1H NMR (400 MHz, CDCl3): δ = 2.70–2.65 (m, 4 H), 1.15–
1.10 (m, 6 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 122.4, 34.8,
12.2 ppm. C6H10Br2 (241.95): calcd. C 29.78, H 4.17; found C
29.80, H 4.22.
5n: 1H NMR (400 MHz, CDCl3): δ = 8.07–7.88 (m, 2 H), 7.62–
7.35 (m, 3 H), 4.45 (s, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ
= 191.2, 133.6, 129.8, 128.7, 128.6, 31.4 ppm. C8H7BrO (199.05):
calcd. C 48.27, H 3.54; found C 48.33, H 3.49.
Acknowledgments
5o: 1H NMR (400 MHz, CDCl3): δ = 7.98 (d, J = 7.8 Hz, 2 H),
6.95 (d, J = 7.8 Hz, 2 H), 4.43 (s, 2 H), 3.92 (s, 3 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 191.2, 164.5, 129.8, 128.6, 115.7,
31.5 ppm. C9H9BrO2 (229.07): calcd. C 47.19, H 3.96; found C
47.25, H 4.02.
The authors are pleased to acknowledge the financial support from
Xinxiang Medical University.
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5p: 1H NMR (400 MHz, CDCl3): δ = 7.82 (d, J = 7.6 Hz, 2 H),
7.41 (d, J = 7.6 Hz, 2 H), 4.50 (s, 2 H) ppm. 13C NMR (100 MHz,
CDCl3):
δ = 190.09, 138.8, 133.7, 129.9, 128.6, 31.3 ppm.
C8H6BrClO (233.49): calcd. C 41.15, H 2.59; found C 41.22, H
2.63.
5q: 1H NMR (400 MHz, CDCl3): δ = 8.79 (d, J = 2.0 Hz, 1 H),
8.52–8.30 (m, 2 H), 7.76 (t, J = 8.0 Hz, 1 H), 4.52 (s, 2 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 190.9, 150.4, 136.9, 131.8, 128.8,
125.6, 122.9, 31.4 ppm. C8H6BrNO3 (244.04): calcd. C 39.37, H
2.48, N 5.74; found C 39.42, H 2.43, N 5.69.
1
5r: H NMR (400 MHz, CDCl3): δ = 8.15–8.28 (m, 10 H), 6.42 (s,
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1 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 195.8, 136.7, 136.0,
132.9, 129.8, 129.5, 128.8, 128.7, 127.5, 56.9 ppm. C14H11BrO
(275.14): calcd. C 61.11, H 4.03; found C 61.21, H 4.00.
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5s: 1H NMR (400 MHz, CDCl3): δ = 4.77 (s, 1 H), 4.28 (q, J =
7.2 Hz, 2 H), 2.46 (s, 3 H), 1.32 (t, J = 7.2 Hz, 3 H) ppm. 13C
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NMR (100 MHz, CDCl3): δ = 196.2, 165.3, 63.5, 49.2, 26.4, 13.7 [12] a) A. H. Lu, E. L. Salabas, F. Schueth, Angew. Chem. 2007,
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ppm. C6H9BrO3 (209.04): calcd. C 34.47, H 4.34; found C 34.52,
H 4.29.
5t: 1H NMR (400 MHz, CDCl3): δ = 7.99–7.96 (m, 4 H), 7.61–7.57
(m, 2 H), 7.48–7.41 (m, 4 H), 6.58 (s, 1 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 188.6, 134.2, 133.7, 129.3, 128.7, 52.6 ppm.
C15H11BrO2 (303.15): calcd. C 59.43, H 3.66; found C 59.38, H
3.59.
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5u: 1H NMR (400 MHz, CDCl3): δ = 4.19–4.10 (m, 1 H), 2.43–2.33
(m, 4 H), 2.22–1.95 (m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ
= 211.3, 58.6, 35.3, 35.2, 33.8, 19.6 ppm. C5H7BrO (163.01): calcd.
C 36.84, H 4.33; found C 36.89, H 4.28.
5v: 1H NMR (400 MHz, CDCl3): δ = 7.37 (d, J = 8.0 Hz, 2 H),
6.77 (d, J = 8.0 Hz, 2 H), 3.82 (s, 3 H) ppm. 13C NMR (100 MHz,
Received: June 16, 2013
Published Online: November 12, 2013
Eur. J. Inorg. Chem. 2013, 6156–6163
6163
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim