Robust Metal-Organic Framework Containing Benzoselenadiazole for Highly Efficient Aerobic Cross-dehydrogenative Coupling Reactions under Visible Light

Article abstract of DOI:10.1021/acs.inorgchem.5b02626

A zirconium(IV)-based UiO-topological metal-organic framework (UiO-68Se) containing benzoselenadiazole was synthesized by an approach of the mixed dicarboxylate struts, which show highly efficient and recycalable photocatalytic activity for aerobic cross-dehydrogenative coupling reactions between tertiary amines and various carbon nucleophiles under visible-light irradiation.

Full text of DOI:10.1021/acs.inorgchem.5b02626

Communication
pubs.acs.org/IC
Robust Metal−Organic Framework Containing Benzoselenadiazole
for Highly Efficient Aerobic Cross-dehydrogenative Coupling
Reactions under Visible Light
Wen-Qiang Zhang,†,‡ Qiu-Yan Li,†,‡ Quan Zhang,§ Yingqiao Lu,† Han Lu,† Wenguang Wang,⊥
Xinsheng Zhao,∥ and Xiao-Jun Wang*,†
†Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, School of Chemistry and Chemical Engineering,
Jiangsu Normal University, Xuzhou 221116, P. R. China
§Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan
University, Wuxi 214122, P. R. China
⊥School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, P. R. China
∥School of Physics and Electronic Engineering, Jiangsu Normal University, Xuzhou 221116, P. R. China
S
* Supporting Information
incorporated noble-metal complexes, such as ruthenium(II),
ABSTRACT: A zirconium(IV)-based UiO-topological
metal−organic framework (UiO-68Se) containing benzo-
selenadiazole was synthesized by an approach of the mixed
dicarboxylate struts, which show highly efficient and
recycalable photocatalytic activity for aerobic cross-
dehydrogenative coupling reactions between tertiary
amines and various carbon nucleophiles under visible-
light irradiation.
into UiO-67 MOFs for efficient aza-Henry reactions, oxidation of
sulfides, and oxidative coupling of amines.13a The polypyridylru-
thenium complex was also introduced into UiO-67 MOFs via
postsynthetic methods toward the aerobic oxidation of
arylboronic acids.13b Duan et al. have utilized zinc-based MOFs
consisting of triphenylamine for asymmetric α-alkylation of
aldehydes with good enantioselectivity.13c Very recently, MOFs
based on porphyrins and metalloporphyrins were developed as
photoredox catalysts.13d,e
Although large progress has been made in MOF-based
photocatalysts for organic reactions, there are still some
challenges to be tackled, such as the complicated synthesis of
porphyrins and the possible leaching of toxic elements caused by
the decomposition of noble-metal complexes. Herein, we
reported a straightforward construction of benzoselenadiazole
containing the MOF UiO-68Se by an approach of mixed
dicarboxylate struts (H21 and H22; Figure 1), which has the
robust parent UiO-68 Zr6O4(OH)4(TPDC)6 framework
(TPDC = terphenyl-4,4″-dicarboxylic acid)14 and exhibits a
highly efficient and recycalable photocatalytic activity for aerobic
CDC reactions of tertiary amines and various carbon
nucleophiles under visible light.
he cross-dehydrogenative coupling (CDC) reactions from
Ttwo different C−H bonds under oxidative conditions
provide a simple and atom-economic method for the
construction of C−C bonds,1 because it could avoid the tedious
pre- and defunctionalization of substrates. The past 10 years have
witnessed huge progress in this field.1,2 In particular, the recent
development of visible-light-driven CDC reactions in the
presence of photoredox catalysts via single-electron transfer
(SET) has gained significant interest because of the mild and
environmentally benign characteristics.3 Various metal4 and
metal-free5 photocatalysts have been employed to efficiently
promote the cross-coupling reactions. However, most of these
reactions were conducted homogeneously. There are only a few
heterogeneous photocatalysts for CDC reactions.6
Metal−organic frameworks (MOFs)7 are built by the
coordination self-assembly of metal ions or clusters and
multidentate organic linkers, which have exhibited highly
promising applications in a wide variety of areas.8 In contrast
to pure inorganic materials such as metal oxide based
heterogeneous photocatalysts,6c,d the hybrid and modular nature
of MOFs allows a quite higher level of tailorability through ligand
design,9 postsynthetic modification,10 and postsynthetic ex-
change,11 thus resulting in the superior properties of MOFs.
Indeed, many photoactive MOFs have recently been prepared
for the degradation of organic pollutants, water splitting, and
CO2 reduction toward solar energy utilization.12 On the other
hand, less effort has been devoted to visible-light-induced
sophisticated organic transformations.13 Lin’s group first
Figure 1. Schematic representation of the preparation for the MOF
UiO-68Se.
Received: November 16, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.5b02626
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Communication
The new simple ligand H21, a benzoselenadiazole-function-
alized TPDC, was conveniently synthesized in high yield, as
described in Scheme S1 in the Supporting Information (SI).
Dimethyl-substituted TPDC H22 (Scheme S2 in the SI), owing
to much better solubility, was synthesized to replace the original
TPDC for preparation of the UiO-68 framework. Because of the
same length of the two ligands, we utilized the mix-and-match
synthetic strategy13a,15 to construct a benzoselenadiazole-doped
UiO-68 MOF (UiO-68Se). Specifically, UiO-68Se was synthe-
sized by heating the mixture of ZrCl4 and a combination of
ligands H21 and H22 in N,N′-dimethylformamide using HAc as
an additive at 100 °C for 2 days (for details, see the SI). Powder
X-ray diffraction (XRD) confirmed its highly crystalline nature
and the fact that it is isostructural with the parent UiO-68
framework (Figure S2 in the SI). Nitrogen sorption measure-
ment at 77 K revealed a typical type I reversible isotherm with
Brunauer−Emmett−Teller surface area of up to ∼3500 m2 g−1
(Figure S9 in the SI), indicating its high porosity.
The heterogeneity of the MOF UiO-68Se was confirmed by
removal of the catalyst after 1 h (yield: 32%), which resulted in
almost no further production of 3a after another 4 h of
irradiation. This indicates that UiO-68Se acts as a purely
heterogeneous catalyst with no leaching of catalytically active
species into solution. The reusability of the UiO-68Se catalyst
was also investigated. The same batch of UiO-68Se for the
reaction of 1a and nitromethane was performed over five
successive catalytic cycles (Figure S10 in the SI). The results
indicate that no obvious loss of activity of the catalyst occurs even
after five cycles (yield: 78%). Besides, powder XRD measure-
ments of the recycled photocatalyst revealed maintenance of its
crystalline structure and framework (Figure 2), confirming the
high stability of robust UiO frameworks.
Because of the presence of large open channels that will
facilitate the diffusion of substrates and products, UiO-68Se was
used as the heterogeneous photocatalyst for an aerobic CDC
model reaction of N-phenyl-1,2,3,4-tetrahydroisoquinoline (1a)
with nitromethane. As shown in Table 1, for a mixture of 1a and
a
Table 1. Screening of the Reaction Conditions
Figure 2. Powder XRD patterns for UiO-68Se.
It has been demonstrated that oxygen played an important role
in the photoinduced aerobic CDC reactions.4,5 To understand
the MOF UiO-68Se photocatalysed process clearly, electron spin
resonance (ESR) measurements were conducted in which
2,2,6,6-tetramethylpiperidine (TEMP) and 5,5-dimethyl-1-
pyrroline-N-oxide (DMPO) were used to capture singlet oxygen
1O2 and superoxide radical anion O2•−, respectively. As shown in
Figure 3, upon irradiation of the CH3CN mixture of UiO-68Se
b
b
entry
conditions
T (h)
conv (%)
yield (%)
1
2
3
4
UiO-68Se, 2 mg
UiO-68Se, 2 mg
UiO-68Se, 4 mg
UiO-68Se, 4 mg
UiO-68M, 4 mg
no catalyst
2
4
2
4
4
4
76
68
89
84
86
82
100
trace
trace
0
90
c
5
trace
trace
n.r.
n.r.
d
6
e
7
no light
f
8
no oxygen
4
0
a
Reaction conditions: 1a (0.1 mmol) and CH3NO2 (1.0 mL), blue
LEDs (λmax = 450 nm, 3 W). The reaction with stirring was conducted
b
in an air atmosphere at room temperature. Yield and conversion
determined by 1H NMR using methyl 3,5-dinitrobenzoate as an
c
internal standard. n.r. = no reaction. The reaction in the presence of
d
UiO-68M was irradiated for 4 h. The reaction without any catalyst
e
was irradiated for 4 h. The reaction in the presence of UiO-68Se was
f
stirred in the dark for 6 h. The reaction mixture was strictly degassed
by nitrogen for 6 h and then irradiated under a nitrogen atmosphere
for 4 h.
nitromethane containing a catalytic amount of UiO-68Se under
irradiation of blue LEDs at ambient conditions for several hours,
we observed formation of the desired cross-coupling product 3a
in good-to-excellent yield (entries 1−4). As expected, increasing
the amount of catalyst and irradiation time gives high
conversation and yield (entry 4). The inactivity of the parent
MOF UiO-68M in this reaction confirmed that the benzosele-
nadiazole-functionalized TPDC ligand in UiO-68Se acts as a
photocatalytically active center for this process (entry 5). Other
control experiments demonstrated that each component of the
reaction, including light, oxygen, and the MOF photocatalyst, is
essential for the progress of the aerobic CDC reaction (entries
6−8).
Figure 3. ESR spectra of a solution in CH3CN of UiO-68Se without 1a
(a) and with 1a (b) in the presence of DMPO under irradiation of blue
LEDs for 30 s and a solution in CH3CN of UiO-68Se without 1a (c) and
with 1a (d) in the presence of TEMP under irradiation of blue LEDs for
30 s.
1
and TEMP in air, a typically characteristic signal of O2 was
clearly observed. However, the signal disappeared upon the
addition of 1a to the mixture. By contrast, a clear characteristic
signal of O2•− was detected when DMPO was used as the radical
•−
scavenger. These findings indicate that O2 is the active
intermediate species in the reaction rather than 1O2.
B
DOI: 10.1021/acs.inorgchem.5b02626
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Communication
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We proposed a plausible reaction mechanism based on the
above results (Scheme S3 in the SI). Upon excitation of UiO-
68Se (PS), SET from 1a to PS* occurs with generation of the
radical cation 1a•+ and the radical anion PS•−, which transfer an
electron to O2 with the formation of O2•− and the simultaneous
regeneration of the ground-state PS. Meanwhile, O2•− abstracts a
proton from 1a•+, generating a hydroperoxide free radical and
intermediate 1a•. The latter lose one electron to afford the imine
cation, followed by nucleophile addition to give the product 3a.
With a well understanding of the reaction mechanism, we further
extended the scope of this aerobic CDC reaction photocatalyzed
by the MOF UiO-68Se shown in Table S1 (SI). It can be
observed that various substituted tetrahydroisoquinoline de-
rivatives can undergo aerobic CDC reactions with different
nitroalkanes catalyzed by UiO-68Se under visible light, giving the
coupling products in good-to-excellent yields. Moreover, the
MOF-photocatalyzed CDC reaction can also be expanded to the
direct construction of C−C bonds between N-aryltetrahydroi-
soquinolines with dialkyl malonates and ketones, with
satisfactory yields (Table S2 in the SI).
In summary, we designed and synthesized a simple
benzoselenadiazole-functionalized TPDC ligand. Subsequently,
a noble-metal-free Zr-MOF with a UiO-68 framework was
constructed by the straightforward reaction of ZrCl4 with the
mixed dicarboxylate struts. The robust MOF can act as a highly
efficient and heterogeneous photoredox catalyst for aerobic
CDC reactions between tertiary amines with various carbon
nucleophiles under visible light. It is envisioned that the MOF
can act as an ideal platform, allowing for the incorporation of
more photoredox catalysts.
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.5b02626.
■
S
Experimental details, thermogravimetric analysis and
nitrogen sorption of UiO-68Se, and other details (PDF)
(10) (a) Cohen, S. M. Chem. Rev. 2012, 112, 970−1000. (b) Wang, Z.;
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AUTHOR INFORMATION
Corresponding Author
*E-mail: xjwang@jsnu.edu.cn.
■
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Author Contributions
‡These authors contributed equally.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
We are grateful for financial support from NSFC (Grants
21302072, 51403081, and 21376113), NSF of Jiangsu Province
(Grants BK20130226 and BK20140137), and PAPD of Jiangsu
Higher Education Institutions.
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DOI: 10.1021/acs.inorgchem.5b02626
Inorg. Chem. XXXX, XXX, XXX−XXX