A base-resistant metalloporphyrin metal-organic framework for C-H bond halogenation

Article abstract of DOI:10.1021/jacs.6b09463

A base-resistant porphyrin metal-organic framework (MOF), namely PCN-602 has been constructed with 12-connected LNi₈(OH)₄(H₂O)2Pz₁₂] (Pz = pyrazolate) cluster and a newly designed Pyrazolate-based porphyrin ligand, 5, 10, 15, 20-tetrakis(4-(pyrazolate-4-yl)-phenyl)porphyrin under the guidance of the reticular synthesis strategy. Besides its robustness in hydroxide solution, PCN-602 also shows excellent stability in aqueous solutions of F^-, CO,^2-, and PO₄^3- ions. Interestingly, the Mn³⁺-porphyrinic PCN-602, as a recyclable MOF catalyst, presents high catalytic activity for the C-H bond halogenation reaction in a basic system, significantly outperforming its homogeneous counterpart. For the first time, a porphyrinic MOF was thus used as an efficient catalyst in a basic solution with coordinating anions, to the best of our knowledge.

Full text of DOI:10.1021/jacs.6b09463

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Article
A Base-Resistant Metalloporphyrin MOF for C–H Bond Halogenation
Xiu-Liang Lv, Kecheng Wang, Bin Wang, Jie Su, Xiaodong Zou, Yabo Xie, Jian-Rong Li, and Hong-Cai Zhou
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 11 Dec 2016
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A Base-Resistant Metalloporphyrin MOF for C–H Bond Halo-
genation
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†,#
‡,#
†
§
§
†
,†
XiuꢀLiang Lv, Kecheng Wang, Bin Wang, Jie Su, Xiaodong Zou, Yabo Xie, JianꢀRong Li,*
,‡
and HongꢀCai Zhou*
†
Beijing Key Laboratory for Green Catalysis and Separation and Department of Chemistry and Chemical Engineering, Colꢀ
lege of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, P. R. China
‡
Department of Chemistry, Texas A&M University, College Station, Texas 77842ꢀ3012, USA
§
Berzelii Centre EXSELENT on Porous Materials and Inorganic and Structural Chemistry, Department of Materials and Enꢀ
vironmental Chemistry Stockholm University, Stockholm SEꢀ10691, Sweden
Supporting Information Placeholder
ABSTRACT: A baseꢀresistant porphyrin MOF, namely PCNꢀ602 has been constructed with 12ꢀconnected [Ni (OH) (H O) Pz ]
8
4
2
2
12
(Pz = pyrazolate) cluster and a newly designed pyrazolateꢀbased porphyrin ligand, 5,10,15,20ꢀtetrakis(4ꢀ(pyrazolateꢀ4ꢀ
yl)phenyl)porphyrin under the guidance of the reticular synthesis strategy. Besides its robustness in hydroxide solution, PCNꢀ602
–
2–
3–
3+
also shows excellent stability in aqueous solutions of F , CO3 , and PO4 ions. Interestingly, the Mn ꢀporphyrinic PCNꢀ602, as a
recyclable MOF catalyst, presents high catalytic activity for the C–H bond halogenation reaction in a basic system, significantly
outperforming its homogeneous counterpart. For the first time, a porphyrinic MOF was thus used as an efficient catalyst in a basic
solution with coordinating anions, to the best of our knowledge.
6
frequently involved in kinds of reactions. They are usually
essential reactants or work as compositions of buffer solutions
INTRODUCTION
Metalꢀorganic frameworks (MOFs), emerging as a new
class of porous materials, developed at an extraordinary pace
over the past two decades. They extended the field of porous
to control the pH in some reactions catalyzed by porphyrin
derivatives. Therefore, strong resistance of porphyrinic MOFs
towards these coordinating anions is also of significance to
extend their application scopes.
1
materials and showed excellent potential in numerous
applications, including catalysis, gas storage/separation,
It was found that many reported stable porphyrinic MOFs
2
sensing, luminescence, drug delivery and so forth.
4+
3+
are constructed with carboxylateꢀbased ligands and Zr , Fe ,
Porphyrinic MOFs, as a special group of MOFs, have been
tremendously studied because of not only the importance of
porphyrinic species in many applications, but also the inherent
advantages of MOFs as the platforms to immobilize porphyrin
3+
5dꢀf
or Al ꢀbased inorganic clusters. In the hardꢀsoftꢀacidꢀbase
HSAB) theory, the carboxylate groups and these high valent
(
metal ions are categorized as hard Lewis bases and acids, and
can form strong coordination bonds with each other, which
endows the frameworks with strong robustness. On the other
3,4
groups. The rigid structures, large surface area and high
porosity of MOFs can not only improve the catalytic activity
of porphyrin by preventing the aggregation of reaction centers,
but also increase the density of approachable active sites
without suffering from low solubility of porphyrin
–
2–
3–
hand, many coordinating anions, like F , CO3 , and PO4
,
have either small diameters or high charges. They are also
classified as Lewis base with great hardness. It leads to their
strong affinity towards the high valent metal ions, which is
confirmed by the high binding constants of these anions and
4
derivatives.
4+
3+
3+ 7
However, to exploit these desirable features of porphyrinic
MOFs, the materials should be stable under the harsh chemical
conditions involved in real applications. So far, the
explorations of the robustness of MOFs are mainly focused on
their chemical stability in water and acid aqueous solutions,
but the chemical resistance of MOFs towards other species has
Zr , Fe , and Al . As we proposed in our previous work,
the decomposition of MOFs in solutions can be considered as
the competition between coordination groups of ligands and
other molecules (or anions) for metal ions of the inorganic
clusters insides the frameworks. For the MOFs constructed
by high valent metal ions, when other hard Lewis bases
existing as competing species with high concentration in
solution, the carboxylate groups of ligands coordinated to
5g
5
not been extensively studied. Many coordinating anions
–
2–
3–
(
Lewis bases), such as F , CO , and PO4 , are also
3
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metal ions will be easily replaced, which leads to the MOF
decomposition. To overcome the vulnerability of these
materials in the solutions of coordinating anions with great
hardness, one method is to construct MOFs with metal ions
and ligands that have higher softness. With this strategy, the
strong coordination interaction between the metal ions and
ligands can be kept, while the affinity between coordinating
anions in the solutions and metal ions inside the frameworks is
weakened. This will endow MOFs with strong resistance to
the attack of coordinating anions with great hardness.
has been demonstrated by its extraordinary performance as a
regenerable heterogeneous catalyst in the halogenation of
hydrocarbons in basic condition. Compared to previous
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method with homogeneous Mnꢀporphyrin catalysts, much
higher yields were achieved under more environmentꢀfriendly
condition with PCNꢀ602(Mn).
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Recently, our group reported a MOF, namely PCNꢀ601, that
fulfill all the requirements mentioned above. It is constructed
2
+
8
by Ni
pyrazolate)
yl)porphyrin(TPP ) ligand, which are soft Lewis acid and
(as [Ni ] cluster [Ni (OH) (H O) Pz ], Pz =
8 8 4 2 2 12
and
5,10,15,20ꢀtetra(pyrazolateꢀ4ꢀ
4
–
5
g
base, respectively (Figure 1dꢀf). However, the window size
of the cages in PCNꢀ601 is too small (~2.1 × 8.0 Å after
deducting van der Waals Radii). When PCNꢀ601 is applied as
a catalyst, the small window size would slow down the
diffusion of reactants or even limit the approachability of
active sites for substrates. A direct method to augment the
window size and improve catalytic performance is to construct
an isoreticular MOF with the rationally designed elongated
ligand under the guidance of the reticular synthesis strategy
9
(Figure 1).
Figure 1. Reticular design and construction of PCNꢀ602: (a) ftwꢀa
We finally chosed 5,10,15,20ꢀtetrakis(4ꢀ(1Hꢀpyrazolꢀ4ꢀ
topological net; (b) 12ꢀconnected node with O symmetry; (c) 4ꢀ
h
4
–
yl)phenyl)porphyrin (H TPPP) as the ligand acid, based on
4
connected node with D4h symmetry; (d) TPP ligand; (e and h)
4–
two major considerations. First, in TPPP , each phenyl ring is
[Ni ] cluster; (f) structure of PCNꢀ601 (Ni atoms in the porphyrin
8
vertical to porphyrin center owing to the steric hindrance of
pyrazolate groups, while the pyrazolate groups prefer to be
parallel to the connected phenyl rings to enlarge the
conjugated system and lower the energy of molecule. As a
center are omitted for clarity); (g) proposed structure of PCNꢀ602;
4–
and (i) TPPP ligand.
EXPERIMENTAL SECTION
4
–
result, in its desired conformation, TPPP is a 4ꢀconnected D4h
symmetric ligand with 4 pyrazolate groups vertical to the
porphyrin center, which is symmetrically and geometrically
General information. The commercial chemicals are used as
purchased unless mentioned otherwise. Detailed chemical
sources are listed in the Supporting Information section 1.
4
–
equilivent to TPP . Therefore, the construction of an
4–
Instrumentation. Synchrotron powder Xꢀray diffraction
isoreticular framework of PCNꢀ601 with [Ni ] and TPPP
8
(PXRD) was carried out with Bruker D8ꢀDiscover diffractomꢀ
would be possible. Second, given the fact that the pore size
and stability of a MOF are usually inversely correlated,
extensive elongation of the ligand could undermine the
eter equipped with a Mo sealed tube (λ = 0.45336 Å) on the
beamline 17ꢀBM at the Advanced Photon Source, Argonne
National Laboratory. Other PXRD experiments were carried
out on a BRUKER D8ꢀFocus BraggꢀBrentano Xꢀray powder
Diffractometer equipped with a Cu sealed tube (λ = 1.54178
4–
robustness of resulting framework. Comparing with TPP ,
only one phenyl ring is inserted between the porphyrin center
4
–
and pyrazolate groups in TPPP , which makes it one of the
4
–
Å) at 40 kV and 40 mA. N
were measured using a Micrometritics ASAP 2420 system at
7 K. The UVꢀvis absorption spectra were recorded on a Shiꢀ
2
adsorptionꢀdesorption isotherms
shortest elongated versions of TPP . Furthermore, the
strcutural simulation suggests that the window size in the
resulting MOF is about 6.0 × 14.0 Å, which is large enough
for some substrates to diffuse inside its framwork. The MOF
7
madzu UVꢀ2450 spectrophotometer. The morphologies of the
MOF sample were observed by using a SU8020 Scanning
Electron Microscope (SEM) (Hitachi, Japan). Elemental analꢀ
ysis (EA) was performed by vario EL cube Elementar. Inducꢀ
tively Coupled PlasmaꢀOptical Emission spectroscopic (ICPꢀ
OES) data were collected on a Thermo iCAPꢀ6300 Spectromeꢀ
ter. The conversions of the reactants and the yields of products
were measure by Bruker Scion TQ GCꢀMS equipped with BRꢀ
4
–
constrcuted by TPPP may thus strike the balance between
cavity and robustness of the material.
Here, we report this rationally designed pyrazolateꢀbased
MOF, [Ni (OH) (H O) (TPPPꢀNi) ], namely PCNꢀ602(Ni).
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2
3
The experimental results of its stability tests show this
material has excellent robustness in aqueous solutions with
–
–
2–
3–
OH , F , CO , and PO4 ions. An isostructural MOF with
3
3
+
4–
5
MS capillary column.
Mn ꢀporphyrin ligand (TPPPꢀMnCl) was then prepared,
assigned as PCNꢀ602(Mn). Catalytic activity of PCNꢀ602(Mn)
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Synthesis of H TPPP and H TPPP-MnCl. The synthesis
profile function, followed by refinement of unit cells and zeroꢀ
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procedure is shown in Scheme 1 and details are in the supportꢀ
ing information section 2.
shift. Soft distance restraints were placed on the bonds beꢀ
tween the nickel and oxygen atoms (2.20 Å), and the nickel
and nitrogen atoms (2.10 Å). The rigid bodies were applied on
ligands. The ligand was not fully occupied. The occupancy
was refined to be 0.76. The additional oxygen atom (O2) with
the occupancy of 0.24 was located near nickel atom (Ni1) with
the Ni–O bond distance of 2.21 Å. The guest species in the
cages of the structure could not be located owing to their parꢀ
tial occupancies and low symmetry. Instead, three oxygen
atoms were added at random positions inside the cages to
compensate for the contributions of the guest species, and
refined subsequently. Crystallographic data and structural
refinement are provided in Table 1.
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Table 1. Crystallographic data and the Rietveld refinement result
of PCNꢀ602(Ni).
Chemical formula
Formula weight
Crystal system
Space group
C127.92H73.12N27.44Ni10.24O21.98
2948.80
cubic
Pm–3m
21.559(2)
1
a /Å
Scheme 1. Synthesis of H TPPP and H TPPPꢀMnCl.
4
4
Z
Synthesis of PCN-602(Ni). Ni(AcO) ·4H O (8 mg, 32.3
Temperature / K
Wavelength / Å
2θ range / °
298(2)
0.45336
0.8~21.39
686
2
2
mmol), H TPPP (10 mg, 17.4 mmol), and deionized (DI) waꢀ
4
ter (1.2 mL) in 2 mL of N,Nꢀdimethylformamide (DMF) were
mixed and ultrasonically dissolved in a 5 mL highꢀpressure
vessel. The resulting mixture was sealed and heated at 120 °C
for 24 h. After the vial cooled down to room temperature, redꢀ
dish crystalline powder of PCNꢀ602(Ni) was collected by filꢀ
tration (8 mg). FTꢀIR spectrum of asꢀsynthesized PCNꢀ
Number of reflections
Number of structural variables
49
Rp
0.03849
0.04896
0.00938
5.219
Rwp
6
02(Ni) is shown in Figure S1. The SEM image indicates that
Rexp
the crystal size of obtained powder is around 100 nm (Figure
S3 in the supporting information). Thermogravimetry analysis
reveals that the thermal stability of PCNꢀ602(Ni) can be held
up to 280 °C, from which it begins to decompose (Figure S4 in
the supporting information).
GOF
Gas adsorption of PCN-602(Ni) and -602(Mn). The redꢀ
dish/dark green powders obtained through the solvothermal
reaction were washed with DMF and DI water for several
times. Then the samples were washed with acetone for 3 times.
After being soaked in acetone for 12 h, the samples were actiꢀ
Synthesis of PCN-602(Mn). Ni(AcO) ·4H O (6 mg, 24.2
2
2
mmol), H TPPPꢀMnCl (10 mg, 15.0 mmol), DI water (2.5
4
mL), and DMF (1.5 mL) were mixed in a 5 mL highꢀpressure
vessel. The mixture was sealed and heated at 120 °C for 24 h.
After the vial cooled down to room temperature, dark green
crystalline powder of PCNꢀ602(Mn) was collected by filtraꢀ
tion (8 mg). FTꢀIR spectrum of asꢀsynthesized PCNꢀ602(Mn)
is shown in Figure S2. Thermogravimetry analysis reveals that
the thermal stability of PCNꢀ602(Mn) can be held up to 280
vated at 100 °C under vacuum for 10 h. Then, their N uptakes
2
were measured at 77 K, respectively.
PXRD measurements for stability test of PCN-602(Ni).
After being washed with DMF and DI water, asꢀobtained
PCNꢀ602(Ni) samples (10 mg for each batch) were immersed
in about 3.5 mL aqueous solutions of 0.1 mM HCl (pH = 4), 1
M NaOH (pH = 14), 1 M KF, 1 M Na CO , and 1 M K PO at
°
C, from which it begins to decompose (Figure S5 in the supꢀ
2
3
3
4
porting information).
room temperature for 24 h. The treated samples were collected
and washed successively with DI water (3 times) and acetone
Rietveld Refinement and Crystallographic Data of PCN-
(3 times). The obtained powders were dried in oven at 100 °C
6
02(Ni). The structure model of PCNꢀ602(Ni) was refined by
before PXRD measurements.
Rietveld refinement using Topas Academic version 4.1. Backꢀ
ground was fitted with a 15th order Chebychev polynomial.
The refinement was conducted using a Pearson VII type peak
N uptakes for stability test of PCN-602(Ni). Five batches
2
of samples (about 100 mg for each) were immersed in 35 mL
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of 0.1 mM HCl (pH = 4), 1 M NaOH (pH = 14), 1 M KF, 1 M
Na CO , and 1 M K PO aqueous solutions at room temperaꢀ
ture (RT) for 24 h, respectively. After being collected and
washed with DI water (3 times) and acetone (3 times), the
samples were activated under vacuum at 100 °C for 10 h on
ASAP 2420 system . These activated samples were then
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3
4
measured for N sorption at 77 K.
2
Catalysis. The C–H bond halogenations reactions were
conducted under two conditions. Condition 1: catalyst (13
mmol), NaClO (2 mL, 0.33 M in water), tetrabutylammonium
chloride (TBACl, 8 mg, as the phase transfer catalyst (PTC)),
substrate (2 mmol), and dichlormethane (2 mL) were mixed
and stirred under nitrogen at RT for 5 h. Condition 2: catalyst
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(13 mmol), NaClO (2 mL, 0.33 M in water), substrate (2
mmol), and acetone (2 mL) were mixed and stirred under niꢀ
trogen at RT for 2 h. After the completion of the reaction, the
heterogeneous catalyst was collected by filtration. The homoꢀ
geneous catalyst, inorganic salt and PTC in the filtrate were
removed by a short silica gel column eluted by CH Cl . Then,
2
2
the identities and the yields of the products were determined
by GCꢀMS. (detailed information is in section 13 of supportꢀ
ing information)
RESULTS AND DISCUSSION
The structural model of PCNꢀ602 with a space group of
Pm–3m was derived from PCNꢀ601 and constructed by Mateꢀ
rial Studio 6.0 (Figure 1g). The unit cell parameter of a =
2
1.559 Å was obtained through indexing experimental highꢀ
resolution PXRD data of PCNꢀ602(Ni). The predicted strucꢀ
ture was further refined by Rietveld refinement against the
synchrotron PXRD data with Topas Academic version 4.1
(
Figure 2a). The resulting structure of PCNꢀ602(Ni) has a
larger window size of 6.3 × 14.2 Å than that of PCNꢀ601 (2.1
8.0 Å). The N isotherm of activated PCNꢀ602(Ni) at 77 K
Figure 2. (a) Rietveld refinement of powder Xꢀray diffraction
data for PCNꢀ602(Ni) (the curves from top to bottom are simulatꢀ
ed (red), observed (blue), and difference profiles (gray), respecꢀ
tively; the bars below curves indicate peak positions; and (b) N2
adsorption/desorption isotherms of activated PCNꢀ602(Ni) at 77
K (inset shows DFT pore size distribution evaluated from the N2
adsorption data at 77 K).
×
2
reveals a BrunauerꢀEmmettꢀTeller (BET) surface area of 2219
2
–1
3
−1
m g and total pore volume of 1.36 cm g (Figure 2b), beꢀ
5
g
ing significantly larger than those of PCNꢀ601.
Chemical stability of PCNꢀ602(Ni) was firstly tested by
treating its samples with the aqueous solutions of HCl and
NaOH with pH = 4 and 14 for 24 h at RT, respectively. The
PXRD patterns of the treated samples remained intact, indicatꢀ
ing there was no phase transition or entire framework collapse
all the conjugate bases of weak acids, the hydrolysis of these
anions in aqueous solution will produce hydroxide anions,
which are also destructive to the MOFs. To assess the effect of
hydroxide anions in the decomposition of PCNꢀ224(Co), ꢀ222(Fe)
and ꢀ600(Mn), the pH values of 1 M KF, 1 M Na CO and 1 M
2
3
of PCNꢀ602(Ni) after the treatments (Figure 3a). N isotherms
2
K PO solutions were measured (Table S1). For instance, the pH
3
4
at 77 K of these treated samples further confirmed the robustꢀ
ness of PCNꢀ602(Ni) in the acid and base solutions (Figure
value of 1 M KF solution was 7.79, while PCNꢀ224(Co) ꢀ222(Fe)
and ꢀ600(Mn) were claimed to be stable in NaOH aqueous soluꢀ
3
b). Moreover, we also explored the stability of PCNꢀ602(Ni)
4b,4i,5e
tion with the pH value of 9.
The complete dissolution of
in 1 M KF, 1 M Na CO and 1 M K PO aqueous solutions,
2
3
3
4
these three MOFs in 1 M KF aqueous solution should be attributꢀ
respectively. After soaking PCNꢀ602(Ni) in these solutions for
4 h at RT, PXRD patterns and N isotherms of treated samꢀ
–
ed to attack of F anions. As revealed by the results above, when
2
2
we evaluate the robustness of porphyrinic MOFs for the real apꢀ
plications, not only their stability in hydroxide solutions but also
their resistance towards the attack of other coordinating anions
should be carefully considered. However, the later requirement
has been neglected for a long time, and can hardly been met by
the previously reported on porphyrinic MOFs.
ples remained unchanged, demonstrating its excellent stability
in these solutions. For comparison, when PCNꢀ224(Co), ꢀ
2
22(Fe) and ꢀ600(Mn) were treated under the same conditions,
the deep color of the solutions and the dissolution of the solid
phases clearly indicated the severe decomposition of these
–
2–
3–
MOFs (Figure 3b, inset). Considering F , CO and PO4 are
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in solutions of hydroxide and other coordinating anions makes
PCNꢀ602 a great candidate for the heterogeneous catalyst of
this reaction.
3+
The PCNꢀ602 with Mn ꢀporphyrin centers (assigned as
PCNꢀ602(Mn)) was synthesized. Its chemical stability in acidꢀ
ic, basic and coordinating anion containing aqueous solutions
was also tested (supporting information section 9). The results
demonstrated its stability is as high as that of PCNꢀ602(Ni).
Then, we applied PCNꢀ602(Mn) as the catalyst in the halogenꢀ
ation reaction (Scheme 2). By following the reaction condition
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described in Grove’s paper, PCNꢀ602(Mn) (5 mg), NaClO (2
mL, 0.33 M in water), TBACl (8 mg), cyclohexane (0.22 mL,
2
mmol), and dichlormethane (2 mL) were mixed and stirred
under nitrogen at RT for 5 h. A 92% yield of chlorocyclohexꢀ
ane was achieved. It is much higher than that reported in
Grove’s paper (57%) when homogeneous catalyst, Mn(TPP)Cl
1
0
(herein, H TPP = mesoꢀtetraphenylporphyrin) was applied.
2
The higher catalytic activity of PCNꢀ602(Mn) could be exꢀ
plained by its rigid framework structure. When porphyrin cataꢀ
lysts are dissolved, the formation of catalytically inactive diꢀ
mers is almost inevitable. As comparison, the porphyrinic
ligands are separated and anchored at the fixed positions in
PCNꢀ602(Mn), which makes every porphyrin center highly
active.
Scheme 2. C–H bond halogenation catalyzed by PCNꢀ
6
02(Mn)
Figure 3. (a) PXRD patterns simulated from the PCNꢀ602 strucꢀ
tural model, of pristine PCNꢀ602(Ni) sample, and of those treated
Table 2. Cataytic perfromance of PCNꢀ602(Mn) and other
in different aqueous solutions and (b) N adsorption/desorption
2
selected catalysts in the C–H bond chlorination/bromination of
isotherms of pristine PCNꢀ602(Ni) sample and of those treated in
different aqueous solutions (inset: photographs of PCNꢀ602(Ni), ꢀ
a
cyclohexane/cyclopentane.
2
2
24(Co), ꢀ222(Fe), and ꢀ600(Mn) soaked in different solutions for
4 h: DI water, 1 M KF, 1 M Na CO , and 1 M K PO aqueous
Entry Substrate
1
Catalyst
Product
Yield(%)
2
3
3
4
solutions, from left to right).
a
PCNꢀ602(Mn)
93
As we known, alkyl halides are widely applied in chemical
industry and afford important components of a variety of bioꢀ
a
2
3
4
5
Mn(TPP)Cl
PCNꢀ601(Mn)
PCNꢀ602(Mn)
PCNꢀ602(Mn)
8
1
1
logically and pharmacologically active molecules. Accordꢀ
ingly, the development of new synthesis approaches for alkyl
halides is quite interesting but challenging, especially for the
direct halogenation of inert C–H bonds. In 2010, Groves and
his coꢀworkers reported a method to directly halogenate alkylꢀ
ates with manganese porphyrin as the catalyst and hypohalite
b
15
a
95
c
89
1
0
as the halogen source. However, this method still suffered
from the moderate yields and the usage of homogeneous cataꢀ
lyst, which makes the recovery of the catalyst difficult. As we
mentioned above, immobilizing porphyrin into MOFs could be
an efficient method to improve the activity and recyclability of
catalysts. Unfortunately, most of the reported porphyrinic
MOFs cannot resist the attack of hydroxide and other coordiꢀ
nating anions in this reaction condition. As expected, the inꢀ
tergeneration of large porosity, high concentration of potenꢀ
tially catalytically active sites, and extreme chemical stability
c
6
PCNꢀ602(Mn)
85
a
Standard conditions: substrate/NaClO/catalyst = 2 : 0.66 : 0.013
mmol; in acetoneꢀwater (2 : 2 mL); and the suspension was stirred
at RT for 2 h.
b
The reaction time is extended to 10 h.
c
NaBrO was used instead of NaClO.
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Moreover, with PCNꢀ602(Mn) as the catalyst, further optiꢀ
structed. It shows extraordinary robustness in basic solutions
of several coordinating anions that are widely used in catalytic
mization could be achieved for this reaction. In the above
mentioned condition, two toxic species, dichloromethane and
PTC, are applied to dissolve catalyst better and/or facilitate the
3+
reactions. PCNꢀ602(Mn), with Mn ꢀporphyrin centers was
confirmed to be a highly effective heterogeneous catalyst for
the C–H halogenation of inert hydrocarbons under a basic
condition. The base resistance of PCNꢀ602 greatly broadens
the application scope of MOFs as catalysts.
–
immigration of ClO from aqueous phase to organic phase to
react with catalyst. However, the rigid structure and high poꢀ
rosity of PCNꢀ602(Mn) can provide high density of active
sites that are approachable to the substrates, which makes the
–
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solubility of the catalyst and the phase transfer rate of ClO not
the limiting factors any more. This encouraged us to develop a
reaction procedure with more environmentꢀfriendly solvent
and no PTC (Table S3). After systematic exploration, acetone
was finally chosen as the best organic solvent. The yield of the
chlorocyclohexane reached 93% at RT in an even shorter time
2 h) under this condition. As a comparison, when Mn(TPP)Cl
was used as the catalyst under this condition, the product yield
was only 8% (Figure 4a and Table 2).
(
In addition, to evaluate the effect of poreꢀwindow size of
the MOFs on the catalytic performance, PCNꢀ601(Mn) was
also prepared and applied as catalyst in the cyclohexane chloꢀ
rination under the same optimized condition. After an even
longer reaction time of 10 h, the yield was only up to 15%.
Clearly, the small window sizes of the cages in PCNꢀ601(Mn)
blocks the accesses of substrates to the active sites inside the
framework, and thereby reduces its catalytic activity.
It should also be pointed out that the recyclability is another
significant advantage of solid heterogeneous catalysts. To
assess the performance of PCNꢀ602(Mn) as a reꢀgenerable
catalyst, the cycling experiment was conducted. After one run
of reaction in acetoneꢀwater, the catalyst was collected
through centrifugation and reused in the next run of reaction
under the same condition. It was found that after three consecꢀ
utive cycles, PCNꢀ602(Mn) was still highly active with the
reaction yield maintaining up to 92% (Figure 4b). Moreover,
the unchanged PXRD pattern and the N adsorption isotherm
2
of PCNꢀ602(Mn) in Figure 4c and 4d further confirmed its
structural intactness after the cycling experiment.
The application scope of this MOF catalyst was also exꢀ
tended to the chlorination of cyclopentane and the bromiantion
of alkylane substrates. The high yields were achieved under
similar reaction conditions, with the chlorination of cyclopenꢀ
tane up to 95% and the bromination of cyclohexane and cyꢀ
clopentane up to 85 and 89%, respectively.
Figure 4. (a) Catalytic efficiencies of PCNꢀ602(Mn) and
Mn(TPP)Cl in the cyclohexane chlorination in the presence of
PTC and CH Cl (black) and under the optimal conditions in this
2
2
work without PTC (red); (b) catalytic efficiencies of PCNꢀ
02(Mn) in three consecutive cyclic runs; and (c) PXRD patterns
6
and (d) N adsorption/desorption isotherms (at 77 K) of pristine
2
PCNꢀ602(Mn) and that after 3 catalytic cycles, respectively.
Overall, the above results demonstrate that highꢀyield aliꢀ
phatic halogenations can be achieved with PCNꢀ602(Mn) as a
reꢀgenerable heterogeneous catalyst under a more environꢀ
mentꢀfriendly condition. This MOF catalyst significantly outꢀ
performed its homogeneous counterparts. To the best of our
knowledge, this is the first example for the application of porꢀ
phyrinic MOFs as highly efficient catalyst in a harsh basic
reaction condition.
ASSOCIATED CONTENT
Supporting Information.
Full details for the synthesis and characterizations of the ligands
and MOFs, SEM, FTꢀIR, crystallographic data of the refined
structure (CIF), N isotherms, BET calculation, pore size distribuꢀ
2
tion, thermal and chemical stability tests, and catalysis activity
test in the supporting information (PDF). This material is availaꢀ
ble free of charge via the Internet at http://pubs.acs.org.
In conclusion, guided by the reticular synthesis strategy, a
baseꢀresistant pyrazolateꢀbased porphyrinic MOF with high
porosity and large window size, namely PCNꢀ602, was conꢀ
AUTHOR INFORMATION
#
X.ꢀL.L. and K.W. contributed equally to this work.
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34, 928; (e) Johnson, J. A.; Zhang, X.; Reeson, T. C.; Chen, Y.ꢀS.;
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Corresponding Author
Zhang, J. J. Am. Chem. Soc. 2014, 136, 15881; (f) Lu, K.; He, C.; Lin, W.
J. Am. Chem. Soc. 2014, 136, 16712; (g) Anderson, J. S.; Gallagher, A. T.;
Mason, J. A.; Harris, T. D. J. Am. Chem. Soc. 2014, 136, 16489; (h) Liu,
Y.; Howarth, A. J.; Hupp, J. T.; Farha, O. K. Angew. Chem. Int. Ed. 2015,
54, 9001. (i) Feng, D.; Chung, W.ꢀC.; Wei, Z.; Gu, Z.ꢀY, Jiang, H.ꢀL.;
Chen, Y.ꢀP.; Darensbourg, D. J.; Zhou, H.ꢀC. J. Am. Chem. Soc. 2013,
J.ꢀR. Li: jrli@bjut.edu.cn
H.ꢀC. Zhou: zhou@chem.tamu.edu
Notes
The authors declare no competing financial interest.
1
35, 17105.
(5) (a) Deria, P.; GómezꢀGualdrón, D. A.; Bury, W.; Schaef, H. T.;
Wang, T. C.; Thallapally, P. K.; Sarjeant, A. A.; Snurr, R. Q.; Hupp, J. T.;
Farha, O. K. J. Am. Chem. Soc. 2015, 137, 13183; (b) Lin, Q.; Bu, X.;
Kong, A.; Mao, C.; Zhao, X.; Bu, F.; Feng, P. J. Am. Chem. Soc. 2015,
1
2
Khimyak, Y. Z.; Wiper, P. V.; Darwent, J. R.; Rosseinsky, M. J. Angew.
Chem. Int. Ed. 2012, 51, 7440; (e) Wang, K.; Feng, D.; Liu, T.ꢀF.; Su, J.;
Yuan, S.; Chen, Y.ꢀP.; Bosch, M.; Zou, X.; Zhou, H.ꢀC. J. Am. Chem. Soc.
2014, 136, 13983; (f) Liu, T.ꢀF.; Feng, D.; Chen, Y.ꢀP.; Zou, L.; Bosch,
M.; Yuan, S.; Wei, Z.; Fordham, S.; Wang, K.; Zhou, H.ꢀC. J. Am. Chem.
Soc. 2015, 137, 413; (g) Wang, K.; Lv, X.ꢀL.; Feng, D.; Li, J.; Chen, S.;
Sun, J.; Song, L.; Xie, Y.; Li, J.ꢀR.; Zhou, H.ꢀC. J. Am. Chem. Soc. 2016,
ACKNOWLEDGMENTS
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This work was financially supported by the Natural Science
Foundation of China (21576006); the Center for Gas Separations
Relevant to Clean Energy Technologies, an Energy Frontier Reꢀ
search Center funded by the U.S. Department of Energy, Office of
Science, Basic Energy Sciences (DEꢀSC00010150); and the Sweꢀ
dish Research Council (VR) for the MATsynCELL project, and
the Knut & Alice Wallenberg Foundation for the 3DEMꢀNATUR
project.
37, 2235; (c) Zheng, J.; Wu, M.; Jiang, F.; Su, W.; Hong, M. Chem. Sci.
015, 6, 3466; (d) Fateeva, A.; Chater, P. A.; Ireland, C. P.; Tahir, A. A.;
1
38, 914; (h) Mouchaham, G.; Cooper, L.; Guillou, N.; Martineau, C.;
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Graphic Abstract
A Base-Resistant Metalloporphyrin MOF for C–H Bond Halogenation
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