Ullmann Coupling Reaction of Nitro-Substituted Aryl Halides with Phenols under Mild Conditions: Micro-/Mesoporous Hierarchical LaAlPO-5 Zeolite Catalyst

Article abstract of DOI:10.1002/cctc.201501426

Heterogeneous catalytic reactions of aromatic organic molecules over zeolite catalysts present many challenges because of the shape selectivity of the micropores of conventional zeolites that limits the diffusion of aromatic molecules. Herein, Ullmann coupling reactions of phenols with nitro-substituted aryl halides were catalyzed by rare-earth-doped mesoporous AlPO-5 zeolites in the absence of ligands. The AlPO-5-MAlPO-5-M zeolites had a pure AFI structure and consisted of spherical particles assembled by nanofibers. The rare-earth elements were highly dispersed in the AlPO-5-MAlPO-5-M samples. The LaAlPO-5-MAlPO-5-M zeolite is an excellent catalyst for Ullmann coupling reactions of phenols and nitro-substituted aryl halides. Mesoporous LaAlPO-5 has an excellent stability and recyclability in the Ullmann coupling of p-X-nitrobenzene (X=Cl, Br, and I) with 2-naphthol. These results are important in the exploration of attractive Ullmann coupling reactions and in the development of mesoporous zeolite catalysts for other organic reactions.

Full text of DOI:10.1002/cctc.201501426

DOI: 10.1002/cctc.201501426
Full Papers
Ullmann Coupling Reaction of Nitro-Substituted Aryl
Halides with Phenols under Mild Conditions: Micro-/
Mesoporous Hierarchical LaAlPO-5 Zeolite Catalyst
[
a]
Qingping Ke, Mingzhou Wu, Chao Wang, and Guanzhong Lu*
Heterogeneous catalytic reactions of aromatic organic mole-
cules over zeolite catalysts present many challenges because
of the shape selectivity of the micropores of conventional zeo-
lites that limits the diffusion of aromatic molecules. Herein, Ull-
mann coupling reactions of phenols with nitro-substituted aryl
halides were catalyzed by rare-earth-doped mesoporous AlPO-
were highly dispersed in the AlPO-5-MAlPO-5-M samples. The
LaAlPO-5-MAlPO-5-M zeolite is an excellent catalyst for Ull-
mann coupling reactions of phenols and nitro-substituted aryl
halides. Mesoporous LaAlPO-5 has an excellent stability and re-
cyclability in the Ullmann coupling of p-X-nitrobenzene (X=Cl,
Br, and I) with 2-naphthol. These results are important in the
exploration of attractive Ullmann coupling reactions and in the
development of mesoporous zeolite catalysts for other organic
reactions.
5
zeolites in the absence of ligands. The AlPO-5-MAlPO-5-M
zeolites had a pure AFI structure and consisted of spherical
particles assembled by nanofibers. The rare-earth elements
Introduction
Diaryl ether compounds often exist in medicines, natural prod-
ucts, and fine chemicals. The Cu-assisted Ullmann coupling of
phenols with aryl halides is a valuable and important chemical
reaction for the synthesis of diaryl ethers. However, harsh reac-
tion conditions, such as a high reaction temperature (>1508C),
the requirement for stoichiometric equivalents of Cu, and low
unique pores make the MeAlPO-n molecular sieves important
materials in the design of new catalysts. Relative to other mi-
croporous zeolites, the large microporous channels (0.73 nm)
of AlPO-5 facilitate the diffusion of aryl compounds with
a large size. However, the diffusion of some bulky aryl mole-
cules in the micropores of AlPO-5 is still difficult, which is an
important challenge for the application of MeAlPO-5 catalysts
in organic syntheses. Therefore, only mesoporous zeolites can
catalyze the reactions of bulky molecules efficiently.
[
1–3]
to moderate yields have limited its commercial utilization.
Ullmann coupling reactions can be catalyzed efficiently by
II [4–6]
I [7–15]
II[16]
Pd ,
Cu ,
and Ni
compounds with ligands, such as N-
[
13]
[14]
dimethylglycine, salicylaldimine, and atropisomeric dipyr-
Catalytic materials based on rare earths (RE) are used widely
[
16]
[34,35]
[36–38]
idyl diphosphine, in the presence of organic additives under
mild conditions (90–1208C). Simple and ligand-free catalytic
systems that are recoverable and reusable have received in-
in the water gas shift,
oxidative dehydrogenation,
[
39]
[40]
aldol condensation, and other reactions because of their
[
41–43]
specific chemical properties.
We reported that Ce-doped
[17]
creasing attention, for example, copper fluorapatite, copper
AlPO-5 materials exhibit a high catalytic performance for the
[
18,19]
[20]
[44,45]
oxide on alumina,
copper ferrite nanoparticles,
nano-
oxidation of cyclohexane
and the oxidation of styrene
[
21,22]
[23]
[24]
[46]
[47]
CuO,
Au-Pd alloy nanoclusters, and Cu-USY.
over La-MCM-48 and Ln-MCM-41 (Ln=La, Ce, Sm, Yb) cat-
alysts. Herein, RE-doped mesoporous AlPO-5 (LnAlPO-5-MAlPO-
5-M) catalysts were prepared and used to catalyze Ullmann
coupling reactions of phenols with nitro-substituted aryl hal-
ides in the absence of ligands for the first time. The prepared
micro-/mesoporous LaAlPO-5-MAlPO-5-M zeolites exhibit an
excellent catalytic performance for the Ullmann coupling reac-
tions of p-X-nitrobenzene (X=Cl, Br, and I) with 2-naphthol
under mild conditions (808C) with good operational stability.
Zeolite molecular sieves are solid porous materials with
a high stability that are used widely as adsorbents and cata-
[
25–27]
lysts.
Compared with microporous aluminosilicate zeolites,
aluminophosphate zeolites (AlPO-n) exhibit more attractive
properties, and its Al and/or P atoms can be replaced by Si to
form SAPO-n materials, and by other metals to form metal-
[28–33]
doped aluminophosphate (MeAlPO-n) materials.
The inter-
action between these metal species, framework acid sites, and
[
a] Q. Ke, M. Wu, C. Wang, Prof. Dr. G. Lu
Key Laboratory for Advanced Materials and
Research Institute of Industrial Catalysis
East China University of Science and Technology
Shanghai 200237 (P.R. China)
Results and Discussion
As shown in the XRD pattern (Figure 1a), the AlPO-5-MAlPO-5-
[
41–43]
M sample has an AFI structure and high crystallinity.
In the
N sorption isotherm of AlPO-5-MAlPO-5-M (Figure 1b), there is
2
Fax: (+86)21-6425-3703
E-mail: gzhlu@ecust.edu.cn
a step at P/P =0.4–0.9, which is typical of mesostructures. Its
0
mesopore size is 2–10 nm, and the most probable pore size is
3.97 nm (Figure 1b, inset). The SEM image (Figure 1c) shows
Supporting Information for this article can be found under http://
dx.doi.org/10.1002/cctc.201501426.
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2
Figure 1. a) XRD pattern, b) N sorption isotherm, c) SEM image, and d) TEM image of AlPO-5-M.
that its morphology is spherical with a particle size of 20–
0 mm, which is composed of bread-shaped fibers (inset). The
shows that the LnAlPO-5-MAlPO-5-M (Al/Ln=50) samples pos-
sess the typical AFI structure with a high crystallinity. The dif-
fraction peaks of lanthanide oxides are not observed in the
XRD patterns, which shows that the Ln elements are highly
dispersed in the AlPO-5-MAlPO-5-M samples and that some Ln
species are trapped inside zeolite cavities.
5
TEM image (Figure 1d) shows that the AlPO-5-MAlPO-5-M
sample has hierarchical mesopores of 2–10 nm, some of which
are interconnected, which can be corroborated by the TEM
image of a thin-section of AlPO-5-MAlPO-5-M sample (Fig-
ure S1 of the Supporting Information).
UV/Vis spectra of LaAlPO-5-M samples with different ratios
of Al/La are shown in Figure 2. The absorption peak at l=
256–300 nm (Figure 2a) for LaAlPO-5-M (Al/La=50) is assigned
AlPO-5-MAlPO-5-M and LnAlPO-5-MAlPO-5-M (Al/Ln=50,
Ln=La, Ce, Sm, and Yb) were synthesized, and their textural
parameters are presented in Table 1. Notably, the LnAlPO-5-
III
to four-coordinate La in the sample framework and six-coordi-
[
45]
nated extra-framework La species. The peak at l~220 nm
assigned to La O ) can hardly be observed, which is in agree-
(
2
3
Table 1. BET surface areas (SBET), micropore and mesopore volumes (Vmicro
and Vmeso), and mesopore diameters (dmeso) of LnAlPO-5-M samples (Ln=
La, Ce, Sm, and Yb, Al/Ln=50).
ment with the XRD results. For LaAlPO-5-M (Al/La=25), a peak
at l~220 nm from La O can be seen clearly (Figure 2b). This
2
3
Ln
Ln loading
wt%]
S
BET
2
V
micro
3
V
meso
3
d
meso
[nm]
À1
À1
À1
[
[m g
]
[cm g
]
[cm g
]
Solution
Solid
La
Ce
Sm
Yb
–
2.5
2.5
2.5
2.5
0
2.1
2.4
1.5
<0.001
0
281
301
262
270
354
0.08
0.11
0.07
0.08
0.10
0.22
0.23
0.18
0.19
0.24
4.43
4.42
4.53
3.71
5.02
MAlPO-5-M samples have similar BET surface areas (262–
2
À1
3
À1
3
01 m g ) and mesopore volumes (0.18–0.23 cm g ). Induc-
tively coupled plasma atomic emission spectroscopy (ICP-AES)
showed that the Ln doping amounts in LaAlPO-5-MAlPO-5-M,
CeAlPO-5-MAlPO-5-M, and SmAlPO-5-MAlPO-5-M are ~2.1, 2.4,
and 1.5 wt%, respectively. However, the amount of Yb in
YbAlPO-5-MAlPO-5-M is less than the limit of detection
Figure 2. UV/Vis spectra of LaAlPO-5-M with Al/La of a) 50 and b) 25 (in the
(
<0.001 wt%). Analysis of the XRD patterns shown in Figure S2
synthesis solution).
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indicates the formation of La O in the LaAlPO-5-M sample if
promoted by ligands or noble metals, which increases costs.
Therefore, the development of simple catalyst systems for the
Ullmann reaction without ligands and noble metals is a chal-
2
3
the La amount is high.
27
31
Solid-state Al and P magic-angle spinning (MAS) NMR
spectra of the LnAlPO-5-M (Al/Ln=50) samples are shown in
Figures S3 and S4. The signal at d=39–40 ppm in the
[
17,18]
lenge.
Herein, the Ullmann coupling of p-bromonitroben-
zene and p-cresol was used as a model reaction, and the cata-
lytic performances of the LnAlPO-5-M (Al/La=50) catalysts are
shown in Table 2.
27
Al MAS NMR spectra of the LnAlPO-5-M samples is assigned
to tetrahedral Al in the crystalline aluminophosphate frame-
work; this chemical shift is d=2–3 ppm higher than that of
The results show that the CeAlPO-5-M catalyst with K CO as
2
3
[42,43]
the AlPO-5 sample (d=37 ppm).
This is convincing evi-
the base additive and DMSO as the solvent led to 32% prod-
uct yield at 408C for 12 h (Table 2, entry 1); if the temperature
was increased to 1308C, the yield increased to >99% (Table 2,
entry 3). If we used the LaAlPO-5-M catalyst, the most efficient
catalyst among the Ln-doped AlPO-5 catalysts, the yield
reached >99% at 808C (Table 2, entry 4). As the Yb amount in
the YbAlPO-5 catalyst was very low, the product yield over this
catalyst was the lowest (17%; Table 2, entry 6). Notably, 24%
yield was obtained over the AlPO-5 catalyst (Table 2, entry 7),
and the blank run without LnAlPO-5-M or AlPO-5 catalysts
yielded no desired products as detected by GC (Table 2,
entry 8). These results show that the Ln species are the effi-
cient catalytically active components for the coupling reac-
tions. The nature of the base is crucial in the Ullmann coupling
reaction, and the effect of the base additive (K PO , KOH, and
3+
dence for the doping of Ln in the framework (Figure S3). In
31
the P MAS NMR spectra of the LnAlPO-5-M samples, the
signal at d=À5 to À13 ppm, ascribed to P(3Al, 1Ln) can be
3+
observed clearly, which further proves the presence of Ln
species in the framework (Figure S4). No lanthanide oxide was
detected in the XRD patterns, which confirms that some Ln
species were trapped inside zeolite cavities (Figure S2). The
atomic ratios of P/Ln were estimated from the simulation of
31
the P MAS NMR spectrum of LnAlPO-5-M as the NMR spectra
reflect the amount of Ln that occupies framework Al sites (Fig-
ure S4). The XPS spectra of LaAlPO-5-M are shown in Figure 3.
The surface atom concentrations of LnAlPO-5-M (Al/Ln=50)
were obtained based on the XPS data and are shown in
Table S1. For the LaAlPO-5-M sample, P/La was 63.8:1, higher
than the theoretical value of 59:1 in the gel; for CeAlPO-5-M,
P/Ce was 55.8:1, and P/Sm was 127.3/1 for SmAlPO-5-M.
3
4
NaOtBu) on the yield of the coupling reaction of p-bromonitro-
benzene with p-cresol was investigated (Table 2). Compared
with that of K CO (>99%; Table 2, entry 4), the use of K PO ,
Although many highly efficient catalytic systems have been
2
3
3
4
[9,10,14]
developed for the Ullmann reaction,
many catalysts are
Table 2. Ullmann coupling reaction of p-bromonitrobenzene with p-
cresol over the LnAlPO-5-M catalysts.
[a]
Entry
Catalyst
Base
T/t
Yield
[%]
TOF
À1
[
8C/h]
[h
]
1
2
3
4
5
6
7
8
9
CeAlPO-5-M
CeAlPO-5-M
CeAlPO-5-M
LaAlPO-5-M
SmPO-5M
YbPO-5M
AlPO-5-M
–
K
K
K
K
K
K
K
K
K
2
2
2
2
2
2
2
2
3
CO
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
3
3
40/12
32 (26)
77 (71)
>99
–
–
–
8.75
–
–
–
–
–
–
–
–
12
100/12
130/12
80/12
80/12
80/12
80/12
80/12
80/12
80/12
80/12
80/12
110/2
100/12
130/16
110/21
80/12
140/10
80/12
[e]
>99 (91)
83 (78)
17 (10)
24 (20)
n.d.
49 (44)
71 (65)
55 (50)
56 (51)
72
>99 (87)
88
88
>99 (89)
95
>99 (92)
LaAlPO-5-M
LaAlPO-5-M
LaAlPO-5-M
PO
4
1
0
KOH
NaOtBu
1
1
1
1
1
1
1
1
1
1
2
3
4
5
6
7
8
9
La/AlPO-5-M
K
2
CO
KOH
CO
KF
Cs
3
[
48]
[b]
Nano-CeO
2
[
b]
LaAlPO-5-M
K
2
3
–
[
49]
50]
II
Cu /silica
1.1
0.4
–
–
–
[
[c]
CuI/ligand
2
CO
3
[
c]
LaAlPO-5-M
K
–
K
2
CO
3
[
51]
[d]
Cu-Fe-HT
[
d]
LaAlPO-5-M
2
CO
3
Reaction conditions: LnAlPO-5-M (100 mg), p-bromonitrobenzene
0.1 mmol), p-cresol (0.15 mmol), base additive (2.5 equiv.), DMSO (2 mL),
0–1308C, GC yield. [a] The value in the parentheses is the isolated yield.
b] Coupling of p-cresol with p-chloronitrobenzene. [c] Coupling of
(
4
[
phenol with p-iodonitrobenzene. [d] Coupling of phenol with p-bromoni-
trobenzene. [e] TOF calculated based on 1 mmol reaction, reaction time
1
h (yield of 17.5%).
Figure 3. a) Whole and b) La3d XPS spectra of the LaAlPO-5-M sample.
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KOH, and NaOtBu resulted in lower yields (49–71%; Table 2,
entries 9–11).
In comparison with reported results (72–95% yield; Table 2,
[48–51]
entries 13, 15, 16, and 18),
the catalytic performance of
LaAlPO-5-M (>99% yield; Table 2, entries 4, 14, 17, and 19) is
superior. The excellent catalytic performance of LaAlPO-5-M for
the Ullmann coupling reaction is attributed to the high and
uniform dispersion of La species because of the large surface
area and the abundant mesopores, which facilitate the diffu-
sion of the reactant and product molecules.
The catalytic performances of LaAlPO-5-M for the Ullmann
coupling reaction of bulky 2-naphthol with p-X-nitrobenzene
(
X=Cl, Br, and I) are listed in Table 3, and the results for the re-
Figure 4. Possible mechanism of the synthesis of diaryl ether.
action with other halide substituents are listed in Table S2. If
Br- (or I-)para-substituted nitrobenzenes were used, high yields
of 91% (88%) were obtained at 808C (Table 3, entries 1 and 3).
For the reaction of 2-naphthol with p-nitrochlorobenzene at
only traces of diaryl ether were obtained in the reaction of p-
bromo- and p-iodonitrobenzene with 2-naphthol at 808C with-
out LnAlPO-5 (Table 3, entries 9 and 10). These results indicate
8
08C, only a trace of product was obtained (Table 3, entry 4); if
the reaction temperature was increased to 1008C, a high yield
89%) was obtained (Table 3, entry 5). Meanwhile, good to ex-
(
that the pathway of Ullmann coupling is different from an S Ar
N
cellent isolated yields were obtained for the Ullmann coupling
pathway. A possible synthesis mechanism of diaryl ether cata-
lyzed by LnAlPO-5-M is shown in Figure 4.
reaction of 2-naphthol with COH- (or OCH -)para-substituted
3
bromobenzenes over LaAlPO-5-M (Table S2, entries 1–2).
As it is different from the LaAlPO-5-M mesoporous catalyst,
the yield over the LaAlPO-5 microporous catalyst was only
2
5% (Table 3, entry 2) if p-bromonitrobenzene was used at
08C. The significant differences of the catalytic performance
Table 3. Catalytic performance of LaAlPO-5-M for a series of Ullmann
coupling reactions of p-X-nitrobenzenes (X=Cl, Br, and I) with 2-naph-
thol.
8
of the microporous and mesoporous LaAlPO-5 catalysts sug-
gest that the highly efficient Ullmann coupling reaction of
bulky molecules should be attributed mainly to the mesopo-
rous structure.
To verify the real heterogeneity of the LaAlPO-5-M zeolite,
a Sheldon test was performed to evaluate possible metal
Entry
1
X
T [8C]
Yield in repeated run [%]
2nd 3rd 4th 5th 6th 7th
1
st
[
53]
leaching. Thus, after 2 h at 808C, the reaction mixture was
filtered, and the filtrate was heated at 808C for an additional
2 h. The catalytic performance of the reused LaAlPO-5-M cata-
lyst for Ullmann coupling reactions of p-bromonitrobenzene
with 2-naphthol was also conducted at 808C for 4 h. These re-
sults are listed in Table 4. The obtained results indicated clearly
that there is no appreciable leaching of La ions under the
given reaction conditions (Table 4). Furthermore, La species
were not detected in the liquid mixture (less than the ICP-AES
detection limit of 10 ppm), which indicates negligible La leach-
ing from the LaAlPO-5-M catalyst in this coupling reaction.
To investigate the stability of the LaAlPO-5-M catalyst, Ull-
mann coupling was performed on the recycled catalyst
Br
Br
I
Cl
Cl
Br
80
80
80
80
100
80
91
25
88
trace
89
91
100
63
trace
trace
89
–
87 82 81 80 80
[a]
2
3
4
5
6
7
8
9
1
–
–
–
–
–
88
–
85 85 83 83 82
–
–
–
–
–
87
92
96
86 84 81 81 79
92 90 89 87 87
94 88 85 83 80
[
b]
Recycled catalyst [mg]
[
c]
c]
[
Cl
Br
I
100
80
80
[
c]
0
Reaction conditions: LaAlPO-5-M catalyst (100 mg), aryl halide (0.1 mmol),
-naphthol (0.15 mmol), K CO (2.5 equiv.), and DMSO (2 mL), 808C, 12 h,
isolated yield. [a] LaAlPO-5 catalyst (100 mg); mesopore volume=
2
2
3
3
À1
0
.09 cm g . [b] The reaction conditions were the same as for entry 1,
and the used catalyst was calcined at 5508C for 3 h after each cycle.
[
c] The reaction was performed in the absence of zeolite catalyst.
Table 4. Sheldon test on the LaAlPO-5-M-catalyzed Ullmann coupling of
p-bromonitrobenzene with 2-naphthol.
The lower reactivity of p-nitrochlorobenzene than that of p-
nitrobromobenzene should be ascribed to the different CÀX
À1
bond energies, such as the CÀCl energy of ~81 kcalmol and
À1
[52]
CÀBr energy of ~70.2 kcalmol . Interestingly, Taillefer et al.
Entry
1
X
T [8C]
GC Yield [%]
2+2 h Reused catalyst
reported a 68% yield of diaryl ether from the reaction of p-io-
donitrobenzene with 3,5-dimethylphenol at 908C for 18 h over
a base catalyst instead of a metal catalyst. Although there is an
approximately 63% yield of diaryl ether from the reaction of p-
chloronitrobenzene with 2-naphthol at 1008C (Table 3, entry 8),
2
h
Br
80
67
68 82
Reaction conditions: LaAlPO-5-M catalyst (100 mg), p-bromonitrobenzene
0.1 mmol), 2-naphthol (0.15 mmol), K CO (2.5 equiv.), and DMSO (2 mL).
(
2
3
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(
Table 3). After the catalyst was recycled seven times, the yield
of 2-(4-nitrophenoxy)naphthalene was still maintained at 80%
Table 3, entry 1). The slight decrease in product yield is attrib-
Table 5. Ullmann coupling of aryl halides with phenols over LaAlPO-5-M.
(
uted to the loss of catalyst during recovery (separation by cen-
trifugation and washing with ethanol three times) and/or deac-
tivation. After it was used repeatedly seven times, the catalyst
mass was reduced to 0.08 g (Table 3, entry 7).
1
2
Entry
R
X
R
T
Conversion Selectivity Isolated yield
[8C] [%]
[%]
[%]
1
2
3
4
5
6
7
8
9
4-NO
4-NO
4-NO
4-NO
4-NO
4-NO
4-NO
4-NO
4-NO
4-NO
4-NO
4-NO
4-NO
2-NO
2-NO
2-NO
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
Br 4-Me
Br 4-Cl
Br 3-Me 100 100
80 100
80 100
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
91
91
90
92
89
89
92
63
91
87
86
88
90
30
85
67
To clarify whether the LaAlPO-5-M catalyst had changed
during the reaction, the fresh and used catalysts (LaAlPO-5-M-R
after recycling seven times) were analyzed by thermogravimet-
ric analysis (TGA; Figure 5). The fresh catalyst underwent a mini-
Br
H
H
4-Me
4-Cl
100 100
80 100
80 100
80 100
I
I
I
Cl 4-Cl
Cl 4-Cl
Cl 4-Me 100 100
Cl 3-Me 100 100
Cl 2-Me 100 100
80
65
100 100
10
1
1
1
1
1
1
1
2
3
4
5
6
Cl
Br
Br
H
H
H
120 100
80 34
120 100
75
Br 4-Me 120
Reaction conditions: LaAlPO-5-M (100 mg), aryl halide (0.1 mmol), phenol
0.15 mmol), K CO (2.5 equiv.), and DMSO (2 mL). For the isolated yield,
(
2
3
the conversion and selectivity were calculated from GC–MS data.
zene exhibited a low reactivity, and only if the reaction temper-
ature was increased to 1208C did the yield reach 90% (Table 5,
entry 13).
Figure 5. TGA curves of fresh LaAlPO-5-M and LaAlPO-5-M-R used seven
times.
Conclusions
mal weight loss (~3% at 6008C), and the used catalyst exhibit-
ed ~10% weight loss in the same temperature range, which
indicates that the LaAlPO-5-M-R catalyst suffered a degree of
coke formation. After the used catalyst was calcined at 5508C
for 3 h, its catalytic activity could be recovered to the initial ac-
tivity (Table 3, entry 6), which indicates that coke formation is
a key factor that results in catalyst deactivation.
Mesoporous AlPO-5 zeolites doped with rare earths (LnAlPO-5-
M, Ln=La, Ce, Sm, Yb) were prepared successfully. These
LnAlPO-5-M zeolites have high BET surface areas (262–
2
À1
3
À1
301 m g ) and mesoporous volumes (0.18–0.23 cm g ). The
results show that the mesoporous AlPO-5 zeolite is an effective
catalyst for Ullmann coupling reactions, and modification with
rare earths can improve the catalytic performances of mesopo-
rous AlPO-5 zeolites significantly. Among the LnAlPO-5-M sam-
ples, the LaAlPO-5-M catalyst exhibited the best catalytic per-
formance for the Ullmann coupling reaction of p-bromonitro-
benzene with p-cresol. In the Ullmann coupling reactions of
halonitrobenzenes with 2-naphthol and aryl halides with phe-
nols, the LaAlPO-5-M zeolite catalyst possessed excellent cata-
lytic performances: the yields reached >99% at 80–1008C
after 12 h. After the LaAlPO-5-M catalyst was recycled seven
times in the reaction of 2-naphthol and 4-nitrobromobenzene,
the product yield decreased slightly from 91 to 80%, which
should be attributed to the catalyst loss during the catalyst re-
covery and surface coke formation. After the used catalyst was
calcined at 5508C for 3 h, its catalytic activity could be recov-
ered. The LaAlPO-5-M catalyst, which possesses a hierarchical
micro-/mesoporous structure, exhibits an excellent catalytic
performance in terms of a high catalytic activity, excellent recy-
clability, and negligible metal leaching, and therefore, presents
a promising alternative for Ullmann coupling. The hierarchical
micro-/mesoporous zeolite catalyst was used here to catalyze
the reactions of bulky molecules, which provides valuable
Ullmann coupling reactions of aryl halides with phenols
were performed over the LaAlPO-5-M catalysts, and the results
are listed in Table 5. Phenol derivatives can react well with aryl
halides that have electron-rich or electron-poor substituents in
the benzene ring to form the desired products in excellent
yields (Table 5, entries 1–7). This indicates that the electronic
nature of the phenol substrate does not affect its reactivity re-
markably.
In addition, we investigated Ullmann reactions of nitroben-
zenes with Cl, Br, and I at the para position systematically with
a series of phenols. As p-nitrochlorobenzene is less reactive
than p-nitrobromo/iodobenzene, a lower yield (63%) of the
product was obtained at 808C (Table 5, entry 8); if the reaction
temperature was increased to 1008C, the isolated yield
reached 91% (Table 5, entry 9). For the reaction of 2-nitrobro-
mobenzene with phenol, only 34% conversion was obtained
at 808C (Table 5, entry 14), which implied the presence of
steric hindrance for the aryl halides in the Ullmann coupling. If
the reaction temperature was increased to 1208C, the isolated
yield was enhanced to 85% (Table 5, entry 15). Similar to the
Ullmann coupling reaction of iodobenzene, 2-nitrobromoben-
ChemCatChem 2016, 8, 1557 – 1563
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1561
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Full Papers
guidance for the future development of other organic transfor-
mations.
Catalyst recycling
LaAlPO-5-M (100mg), p-halonitrobenzene (0.15 mmol), 2-naphthol
(
0.1 mmol), DMSO (2 mL), and K CO3 (40 mg, 0.3 mmol) were
2
added to the reactor. The mixture was stirred at 808C for 12 h and
then cooled to RT. The LaAlPO-5-M catalyst was separated by cen-
trifugation, washed three times with ethanol, and dried at 1008C
for 12 h. The catalyst was reused directly.
Experimental Section
Materials
Orthophosphoric acid and Ln(NO ) ·6H O (Ln=La, Ce, Sm, Yb)
3
3
2
were obtained from the Sinopharm Chemical Reagent Co., Ltd.
China). Aluminum isopropoxide (98%) was purchased from the
Aladdin Reagent Database Inc. (China). Tetramethylguanidine
Catalyst characterization
(
N2 adsorption–desorption isotherms were measured at 77 K by
using a Micromeritics ASAP 2020 surface area and porosity ana-
lyzer. Before the measurements, the sample was degassed for 4 h
at 3508C. The BET method was used to calculate the specific sur-
face areas of the samples. The pore size distributions of the sam-
ples were calculated by Barrett–Joyner–Halenda method from the
desorption branches of the isotherms. The XRD patterns of the
samples were obtained by using a Rigaku Ultima IV diffractometer
(
(
TMG, 99.2%) was supplied by the Xinhua Wanbo Company
China). All reagents were used without further purification.
Synthesis of AlPO-5 and AlPO-5-M
AlPO-5-M samples were synthesized hydrothermally from an alumi-
nophosphate gel in the presence of TMG and
a
silane
using CuK radiation. TGA was performed by using a PerkinElmer
a
[
1
(C H O) SiC H N(CH ) C H ]Br (TPOAB); the composition was
Pyris Diamond instrument with a WCT-2 thermal analyzer at
108Cmin from RT to 8508C. TEM images of the samples were ob-
2
5
3
3
6
3 2 18 37
À1
P O :0.8Al O :0.6TMG:0.12TPOAB:33H O. Typically, aluminium
2
5
2
3
2
isopropoxide (9.155 g) was added to deionized water (15.8 mL), fol-
lowed by addition of TPOAB (2 mL) and H PO (3.6 mL) under stir-
tained by using a FEI Tecnai G2 F30 S-Twin microscope operated at
300 kV. SEM images were obtained by using a high-resolution
field-emission scanning electron microscope (JSM6700F, JEOL) op-
erated at 15 kV. The samples were coated with a thin layer of Pt to
prevent charging before scanning. The amounts of rare-earth ele-
ments in AlPO-5-M were determined by using ICP-AES (Varian 710-
ES). X-ray photoelectron spectroscopy (XPS) was performed by
3
4
ring. TMG (2.2 mL) was then introduced into the gel under stirring.
All operations were performed at RT. Finally, the gel was trans-
ferred to an autoclave to be crystallized hydrothermally at 1508C
for 6 h. The formed solid was collected by filtration, dried at 1008C
overnight, and calcined at 5508C for 5 h. AlPO-5 was prepared
using the same method above without the addition of TPOAB.
using a Thermo ESCALAB 250 with AlK
radiation (hn=1486.6 eV)
a
À9
operated at 150 W under 10 mbar in the analytical chamber. All
binding energies were determined with respect to the C1s line
(
284.7 eV) that originates from adventitious carbon. Solid-state Al
Synthesis of LaAlPO-5, LnAlPO-5-M, and La/AlPO-5-M
and P MAS NMR spectra were recorded by using an AVANCE 500
NMR spectrometer at 130.3 and 202.1 MHz, respectively. The prod-
LaAlPO-5
was
synthesized
from
a
gel
of
1
13
ucts were characterized by using H (500 MHz) and C NMR
125 MHz) spectroscopy. NMR spectra were recorded at 208C using
1
P O :0.8Al O :0.034La:0.6TMG:33H O and the LnAlPO-5-M sam-
2
5
2
3
2
(
ples (Ln=La, Ce, Sm, Yb) were synthesized from a gel of
P O :0.8Al O :0.034Ln:0.6TMG:0.12TPOAB:33H O. All experimen-
CDCl as the solvent. Chemical shifts are given in ppm relative to
tetramethylsilane as the internal standard.
1
3
2
5
2
3
2
tal procedures and conditions were the same as those used for the
synthesis of AlPO-5 and AlPO-5-M, apart from the addition of Ln to
the synthesis solution before TMG addition.
Acknowledgements
For comparison, La was supported on AlPO-5-M by impregnation
with an aqueous solution of lanthanum or cerium nitrate, followed
by drying at 1008C, and calcination in air at 5508C for 5 h. These
samples are denoted as La/AlPO-5-M. The loading amount of rare-
earth metal was ~2.5 wt%.
This work was supported financially by the National Basic Re-
search Program of China (2010CB732300, 2013CB933201) and
the National Natural Science Foundation of China (21306142).
Keywords: doping · heterogeneous catalysis · mesoporous
materials · rare earths · zeolites
Catalytic activity testing
A solution of aryl halide (0.15 mmol), phenol (0.1 mmol), catalyst
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