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ChemComm
DOI: 10.1039/C6CC00780E
macropores.15 The 3D Fe3O4@Cu2ꢀxSꢀMoS2F exhibits a large
portion of pores in the range of 5.2~120 nm (Figure 3B),
which originate from the pore formation between the MoS2
flakes after inserting Fe3O4@Cu2ꢀxS NPs, and a small portion
of pores in the range of 3.7~5.2 nm is associated with the
small mesoꢀ and micropores formed between MoS2 sheets
during their irreversible restacking, indicating that
Fe3O4@Cu2ꢀxS NPs do not insert into sheets of a small amount
of MoS2.16 So, the two types of pore size distribution should
be clearly attributed to different spatial structure of
frameworks. Brunauer Emmett Teller (BET) analysis
demonstrates a specific surface area of 66.85 m2 gꢀ1 for the 3D
Fe3O4@Cu2ꢀxSꢀMoS2F, which is 340 times as much as MoS2
nanosheets (0.19 m2 gꢀ1).
lower than that of the Fe3O4@Cu2ꢀxSꢀMoS2F sample, which
reveals that the 3D porous assembly structure plays an
important role for the enhancement of the photocatalytic
activity.
Subsequently, we investigated the substrate scope of the
Fe3O4@Cu2ꢀxSꢀMoS2F catalyst mediated direct CꢀH arylation
(Table 1). Gratifyingly, substrates bearing both electronꢀ
withdrawing as well as donating and neutral functional groups
could be activated. Thus, the corresponding products were
obtained in yields up to 72% (3aꢀ3h). Moreover, the
Fe3O4@Cu2ꢀxSꢀMoS2F photocatalyzed C−H arylation was also
effective for other heteroarenes, such as thiophene and
pyridine, and the corresponding products were obtained in
moderate to good yields (9aꢀ11c). Interestingly, our catalyst
could achieve moderate to good yields in very short time
(within 1h), which is better than that of other reported
photocatalysts.25
The UVꢀvis absorption spectroscopy of 3D Fe3O4@Cu2ꢀxSꢀ
MoS2F solutions showed an intense broad band in the range of
700ꢀ1800 nm (Figure 3C), which is similar with the
Fe3O4@Cu2ꢀxS NPs (Figure S8) due to the localized surface
plasmon resonances in vacancyꢀdoped semiconductors.17 In
contrast, 2D MoS2 nanosheets solutions did not exhibit any
appreciable absorption in that spectral range (Figure S9). The
above results indicated that the 3D Fe3O4@Cu2ꢀxSꢀMoS2F was
formed. In addition, the strong absorption in the NIR range
implicates the potential application of this nanohybrids in NIR
light photocatalysis. Furthermore, the formation of
Fe3O4@Cu2ꢀxSꢀMoS2F and their superparamagnetic property
were confirmed by FTꢀIR spectra and vibrating sample
magnetometer (VSM) (Figure S10 and S11 as well as related
discussions in the supporting information). Moreover, a
typical survey XPS spectrum in Figure S12A clearly shows
the presence of copper, sulfur, carbon, oxygen, nitrogen, iron,
and molybdenum in 3D Fe3O4@Cu2ꢀxSꢀMoS2F. The highꢀ
resolution N1s and O1s spectrum shows the presence of
amide (394.6 eV) and phenolic oxygen (531.7 eV),
respectively (Figure S12). As shown in Figure 3D, the upshift
of the phenolic O1s from 531.7 for Fe3O4@Cu2ꢀxSꢀMoS2F to
532.0 eV for DPAꢀMoS2 is attributed to the coordination of
oxygen atoms to copper.18 Figure S12E shows the binding
energies of Cu 2p3/2 and Cu 2p1/2 peaks at 932.2 and 952.3
eV, respectively, which can be attributed to the Cu+1 state.19
Arylated heteroarenes are widely used in materials science
due to their interesting optical and electronic properties20 as
well as biomedical applications as peptide mimetics21 or
drugs.22 Recently, direct utilization of visible sunlight in
combination with metal and metalꢀfree catalysts23 received
significant attention as a promising method for the C−H
arylation with diazonium salts.24 Based on the strong
absorption band of 3D Fe3O4@Cu2ꢀxSꢀMoS2F in the range of
700−1800 nm, we decided to investigate the direct arylation
of heteroarenes between diazonium salts with heteroarenes by
using this heterogeneous catalyst and irradiating with NIR
light (≥700 nm) at 25 0C for 1 h. Among the different solvents
tested (Table S1), ethanol was found to be a good solvent for
the photoreaction (Table S1 entry 6). Meanwhile, the
photocatalytic activities of MoS2, Fe3O4@Cu2ꢀxS, simply
mixed Fe3O4@Cu2ꢀxS and MoS2, and Fe3O4@Cu2ꢀxSꢀMoS2F
without light were also carried out. As shown in Figure S13,
the use of Fe3O4@Cu2ꢀxSꢀMoS2F catalyst resulted in > 98%
yield under NIR light. However, no traceable products were
detected for control experiments. Also, we found that the
photocatalytic activity of the Fe3O4@Cu2ꢀxS sample and
simply mixed Fe3O4@Cu2ꢀxS and MoS2 was significantly
Table 1. Substrate Scope of Furan with Aryldiazonium Salts.
Reaction conditions: 0.1 mmol 1aꢀh, 1 mL EtOH, 1 mL heteroarene, 2 mg 3D
Fe3O4@Cu2ꢀxSꢀMoS2F, irradiation with Xenon lamp equipped with 700nm
cutoff filter for 1 h under argon atmosphere. All the yields were determined by
GC.
Good recyclability is the main superiority of heterogeneous
catalysts. The reusability of Fe3O4@Cu2ꢀxSꢀMoS2F catalyst in
the direct arylation of heteroarenes between aryldiazonium
tetrafluoroborate with furan was also tested. The active
material was separated from the reaction mixture via magnet,
and reused directly for 6 times. To our delight, no obvious
deactivation was observed. The yield of the desired product
amounted to 93% at the sixth cycle (Figure 4A). Meanwhile,
the TEM and SEM results of the used catalyst show no
obvious change in morphology or aggregation of the
Fe3O4@Cu2ꢀxSꢀMoS2F and Fe3O4@Cu2ꢀx
S
nanoparticles
(Figure S14), showing a good recyclability in this type of
photocatalytic arylation of heteroarenes reactions.
A plausible mechanism for this photoreaction is depicted in
Figure 4B, similar to used TiO2 catalyst.25 Based on our
findings (Figure S15 as well as related discussions in the
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Zhi, Lihua
