A SnIV-porphyrin-based metal-organic framework for the selective photo-oxygenation of phenol and sulfides

Article abstract of DOI:10.1021/ic200295h

A functional tin(IV)-porphyrin derivative was used as a building block to construct a novel 3D porous metal-organic framework (MOF). The MOF is built up from tin(IV)-porphyrin struts linking up Zn atoms and formates joining Sn ^IV centers. The i

Full text of DOI:10.1021/ic200295h

COMMUNICATION
pubs.acs.org/IC
IV
A Sn ÀPorphyrin-Based MetalÀOrganic Framework for the Selective
Photo-Oxygenation of Phenol and Sulfides
Ming-Hua Xie, Xiu-Li Yang, Chao Zou, and Chuan-De Wu*
Department of Chemistry, Zhejiang University, Hangzhou, 310027, P. R. China
S Supporting Information
b
IV
two pyridines of two Sn TPyP ligands and two water molecules
IV
ABSTRACT: A functional tin(IV)Àporphyrin derivative
was used as a building block to construct a novel 3D porous
metalÀorganic framework (MOF). The MOF is built up
from tin(IV)Àporphyrin struts linking up Zn atoms and
in a distorted tetrahedral geometry. Each Sn TPyP ligand acts as
a tetradentate ligand to bridge four Zn atoms, which further
propagates into a 2D framework structure lying in the ab plane
(
Figure 1). The porphyrin unit and tin atom adopt a coplanar
IV
formates joining Sn centers. The immobilization of the
conformation in 1. In the crystal structure, two porphyrin units
are coupled together by a formate strut to coordinate two tin
atoms. Consequently, the lamellae are linked by the formates to
extend into a 3D porous network (Figures 2 and 3). The solid-
photoactive SnÀporphyrins in the channel walls lets the
MOF present remarkable photocatalytic activities for the
oxygenation of phenol and sulfides, resulting in excellent
yields and remarkable selectivity in heterogeneous phases.
state framework contains two kinds channels with dimensions of
2
6
2
.32(1) Â 32.39(1) Å along the a and b axes and 5.97(1) Â
2
6.92(1) Å along the c axis. The channels are filled with DMF
and water solvent molecules and nitrate anions. PLATON
etalÀorganic frameworks (MOFs) have gained extensive
calculations indicate that 1 contains 54.8% void space, which is
M
attention in the past decade due to their interesting proper-
12
accessible to the guest molecules. TG showed that a weight loss
ties for potential applications in various fields such as nonlinear
of 15.2% occurred between 25 and 239 °C, corresponding to the
loss of DMF and water molecules (expected 15.3%).
1
2
3
4
optics, gas storage, catalysis, chemical sensoring, and biome-
5
dical imaging. Because of the remarkable functionalities of
Due to the widespread use of pesticides, herbicides, and
insecticides, pollution from phenolic compounds has increased
structural robustness, catalysis, charge ,and energy transforma-
6
tions derived from metalloporphyrin molecules, using metallo-
13
quickly. Most importantly, phenolic compounds are highly
porphyrins as building blocks for the construction of functional
toxic and are very difficult to degrade. To evaluate the photo-
catalytic activity, we have employed a system of the selective
photo-oxygenation of 1,5-dihydroxynaphthalene in the presence of 1.
When a mixture of 1,5-dihydroxynaphthalene and 1 in solvent
MeOH, THF, CH CN, H O, or CH Cl was subjected to a 350
7
MOFs has gained particular favor. Despite the fact that many
metalloporphyrins present distinct photocatalytic activity in the
8
homogeneous phase, an investigation of the photocatalytic
properties of metalloporphyrin-based MOFs has not been
initialized yet.
3
2
2
2
W Xe lamp irradiation in an oxygen atmosphere for 3.5 h, only a
small amount or no product was detected as monitored by GC-
MS (Supporting Information, Table S2). When the reaction was
performed in the optimized solvent of CH Cl /MeOH (4:1, v/v),
Sensitizers are conjugated organic molecules with good
photochemical characteristics for light activation. However, such
structural features allow the sensitizers to be easily deactivated by
reaction with the singlet oxygen in the homogeneous phase.
Therefore, an efficient way to overcome the quenching process
was developed involving immobilization of the sensitizers on
2
2
the substrate could be fully oxidized into 5-hydroxynaphthalene-
,4-dione (Table 1, entry 1). This should be attributed to
CH Cl being able to prolong the lifetime of the singlet oxygen
1
2
2
9
suitable solids. During our study of the synthesis of functional
1
(
O ), but it is not a good solvent for the substrate, while MeOH
2
MOFs for photochemical catalytic applications, we have synthe-
sized a series of metalloporphyrin-based porous MOFs. Herein,
14
is, on the contrary. Remarkably, the mixed solvents can merge
their merits to prompt photo-oxygenation smoothly. When the
reaction was performed in the dark, no product could be detected
IV
we report a 3D porous MOF of [Zn (H O) Sn (TPyP)(HC-
2
2
4
OO) ] 4NO DMF 4H O (1), which is constructed from
2
3
3
3
3
2
(
Table 1, entry 2). Detailed experiments showed that the
IV
5
,10,15,20-tetra(4-pyridyl)-tin(IV)-porphyrin (Sn TPyP) and
catalytic activity of 1 is very sensitive to various factors such as
the oxidant, light source, catalyst loading, and reaction time
formate linking up zinc atoms, and it presents excellent photo-
catalytic activities for phenol and sulfide oxygenations.
Dark purple crystals of 1 were synthesized by heating a
(
Supporting Information, Table S2).
To make a comparison, a series of control catalysts was used to
IV
mixture of Sn (OH) TPyP and Zn(NO ) 6H O in a mixed
IV
2
3 2
3
2
conduct the catalytic experiment. When Sn (OH) TPyP was
2
solvent of DMF and CH Cl at 50 °C for five days. Single crystal
2
2
used as a catalyst under identical conditions, the product yield
was 98%, while TPyP and Zn(NO ) 6H O only generated
X-ray diffraction analysis has revealed that compound 1 crystal-
lizes in the tetragonal P4/mbm space group with two zinc(II)
3
2
3
2
trace amounts of the product (Table 1, entries 3À5).
IV
atoms, one Sn TPyP ligand, four aqua ligands, and two formates
10
in the formular unit. The anionic formate should be a thermal
decomposition product of DMF. The Zn atom coordinates to
Received: February 11, 2011
Published: May 13, 2011
11
r 2011 American Chemical Society
5318
dx.doi.org/10.1021/ic200295h
|Inorg. Chem. 2011, 50, 5318–5320

Inorganic Chemistry
COMMUNICATION
Table 1. Photo-Oxygenation of 1,5-Dihydroxynaphthalene
a
Catalyzed by 1
b
entry
cat.
light source
yield%
1
2
3
4
5
6
7
1
1
Xe
dark
Xe
Xe
Xe
Xe
Xe
>99.9
0
IV
Sn (OH)
TPyP
2
TPyP
6H
98
<1
Zn(NO
3
)
2
2
O
<1
3
c
1
>99.9
IV
c
Sn (OH)
2
TPyP
17
a
Solid 1 (0.005 mmol) and 1,5-dihydroxynaphthalene (0.05 mmol) in a
mixed solvent of CH Cl /MeOH were stirred at room temperature
II
Figure 1. The lamellar network of Zn atoms linking up
2
2
IV
Sn Àporphyrins in 1 as viewed down the c axis.
under the irradiation of a 350 W Xe lamp for 3.5 h in the presence of O .
Based on GC-MS analysis. The fourth cycle.
2
b
c
IV
activity of the recovered Sn (OH) TPyP decreases gradually
2
to a minimum of 17% for the fourth run (Table 1, entry 7). These
results suggest that the homogeneous catalyst is easily deacti-
vated compared with solid 1.
Sulfoxides are important complexes which have been exten-
1
5
sively used as auxiliary ligands and synthetic intermediates. One
of the important methods for the synthesis of sulfoxides is via
16
photo-oxygenation of sulfides. To further evaluate the photo-
catalytic activity of 1, photo-oxygenation of methyl(phenyl)
thioether catalyzed by 1 was performed in various solvents at
room temperature under irradiation with a light source. Detailed
experiments showed that the catalytic activity is very sensitive to
various factors such as the oxidant, solvents, catalyst loading, and
reaction time (Supporting Information, Table S3). When the
reaction was performed in the optimized solvent CH Cl /MeOH,
Figure 2. A side view of the 3D network of the lamellae linked by the
formate struts in 1 down the b axis.
2
2
the substrate was completely converted into the corresponding
sulfoxide at room temperature under irradiation with a 350 W Xe
lamp using O as an oxidant (Table 2, entry 1). Under catalytic
2
conditions, compound 1 can also prompt the transformation of
various sulfides into sulfoxides (Table 2, entries 2À7). The
product yields of sulfoxides range from 93 to >99.9%. Catalyst 1
can be simply recovered by filtration, which was subsequently used
in the successive run without deterring the catalytic activity
(
Table 2, entry 8).
When Sn (OH) TPyP was used as a catalyst under iden-
IV
2
tical conditions, the sulfide could be fully oxidized into a
mixture of 94% sulfoxide and 6% sulphone (Table 2, entry 9),
while TPyP let the substrate be partially oxidized into a
mixture of 68% sulfoxide and 12% sulphone. Zn(NO3)2
3
Figure 3. A perspective view of the 3D framework of 1 down the c axis.
6
H O is less efficient at prompting the catalytic process
2
(
Table 2, entries 10 and 11). These results suggest that the
Catalyst 1 can be simply recovered by filtration, which was
subsequently used in the successive run without deterring the
catalytic activity (Table 1, entry 6). No trace product was detected
when the filtrate from a mixture of 1,5-dihydroxynaphthalene and
solid 1 in CH Cl /MeOH was used instead of 1 under otherwise
catalytic activity of 1 is superior to those of its corresponding
components.
In summary, we have synthesized a robust 3D porous MOF
IV
constructed from photoactive Sn TPyP building blocks. The
photo-oxygenation of 1,4-dihydroxybenzene and sulfides cata-
lyzed by 1 under Xe lamp irradiation gave excellent product
yields, which are superior to those of its corresponding
2
2
identical conditions, which proved that the present catalyst
platform is heterogeneous in nature. However, the catalytic
5
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dx.doi.org/10.1021/ic200295h |Inorg. Chem. 2011, 50, 5318–5320

Inorganic Chemistry
COMMUNICATION
a
Table 2. Photo-Oxygenation of Sulfides Catalyzed by 1
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AUTHOR INFORMATION
(
Corresponding Author
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*E-mail: cdwu@zju.edu.cn.
(
(
’
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No. 20090101110017).
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dx.doi.org/10.1021/ic200295h |Inorg. Chem. 2011, 50, 5318–5320