S.-C. Chen et al.
Molecular Catalysis 450 (2018) 104–111
II
II
II
II
metal ions (soft Lewis acids, such as Co , Ni , Cu , or Zn ), being co-
ordinated with N-heterocyclic aromatic ligands (soft Lewis bases, such
as pyridine-, imidazole-, or triazole-based ligands), can favor the for-
mation of stable complexes. Recently, Garcia and co-workers have il-
lustrated that acid-base mixed-ligand MOFs possess superior robust and
catalytic activity over those with only single ligand [32]. Previously, we
synthesized a new stable Cu-MOF based on mixed ligands of Fbtx and
phthalic acid and found that this MOF could be used as a highly effi-
cient heterogeneous catalyst for selective aerobic oxidation of alcohols
to aldehydes [33]. To further demonstrate the utility of mixed-ligand
strategy, herein we wish to report the synthesis and characterization of
SHELXS program of SHELXTL packages and refined anisotropically for
2
all non-hydrogen atoms by full-matrix least squares on F with SHELXL
[36]. C-bound hydrogen atoms were placed in geometrically calculated
positions by using a riding model. O-bound hydrogen atoms were firstly
localized by difference Fourier maps and then fixed geometrically with
isotropic temperature factors. Further crystal data and structural re-
finement parameters are summarized in Table S1.
CCDC-1814834 (Co-MOF) contains the supplementary crystal-
2 2 2 n
a new Co(II)-based MOF {[Co(tcpa)(Fbtx)(H O) ] 0.5H O} , denoted as
Co-MOF, constructed from mixed ligands of 1,4-bis(1,2,4-triazole-1-
ylmethyl)-2,3,5,6-tetrafluorobenzene (Fbtx) and 3,4,5,6-tetrachloro-
2.4. Characterization of Co-MOF catalyst
2
phthalic acid (H tcpa). The crystalline Co-MOF with a rare two-fold
interpenetrating cds-type framework indicated good chemical stability
toward dilute acidic and basic aqueous solutions as well as various
boiling solvent systems, and was shown to a highly active, readily re-
cyclable and reusable catalyst for oxidative CDC amination of benzox-
azoles through CeH bond activation under mild conditions. The Co-
Powder X-ray diffraction (PXRD) patterns were recorded on a
Rigaku D/max-2000 diffractometer at 40 kV and 100 mA for a Cu-target
tube (λ = 1.5418 Å), and the calculated PXRD patterns were obtained
from the single-crystal diffraction data using the PLATON software
[37]. Thermogravimetric analysis (TGA) experiment was carried out in
MOF also exhibited higher catalytic activity than that of Co-containing
the temperature range of 25–800 °C on a Dupont thermal analyzer
under N atmosphere at a heating rate of 10 °C min . BET surface area
2
2
−1
hydrotalcite CO
3
-Co
4
Al-LDH and Co-doped zeolites including Co-Ets-
1
0, Co-ZSM-5 and Co-Beta.
analysis was performed by nitrogen sorption isotherms in a Micro-
meritics ASAP2460 surface area analyzer at 77 K. Scanning electron
microscopy (SEM) images were obtained on a field scanning emission
Gemini Zeiss SUPRA55 at an accelerating voltage of 5 kev. X-ray pho-
toelectron spectroscopy (XPS) measurements were performed on a PHI
2
. Experimental
2.1. Preparation of Co-MOF catalyst
5
000 Versa Probe II XPS system with a monochromatic Al Kα X-ray
In a typical preparation, a mixture of Co(OAc)
2
·4H
2
O (24.9 mg,
source (hv = 1486.7 eV) and a charger neutralizer. The Fourier trans-
0
.1 mmol), H
2
tcpa (30.4 mg, 0.1 mmol), Fbtx (31.2 mg, 0.1 mmol) and
form (FT) IR spectra (KBr pellet) were taken on a Nicolet ESP 460 FT-IR
−
1
water (6 mL) was stirred for 60 min at room temperature and then
sealed in a 15-mL Teflon-lined stainless steel autoclave, which was
heated to 140 °C for 2 days. After it was cooled down to room tem-
perature at a rate of 5 °C h , pink block-shaped crystals suitable for X-
ray diffraction analysis were obtained in ca. 65% yield (46.5 mg, based
spectrometer in the range of 4000–400 cm . Elemental analyses were
performed on a PE–2400II (Perkin-Elmer) analyzer. Gas chromato-
graphic analyses were carried out using an Agilent 7890 B GC system
equipped with fused silica capillary HP-5 column (30 m × 0.32 mm)
and a flame ionization detector (FID).
−1
on H
1.75%; found: 33.68; H, 1.38; N, 11.72%. IR (cm , KBr pellet): 3433
br, 3124 m, 3118 m, 2976 m, 1587 s, 1536 m, 1491 s, 1414 m, 1382 s,
2 4 4 6
tcpa). Anal. calcd for C20H10Cl CoF N O6.5: C, 33.59; H, 1.39; N,
−
1
1
3. Results and discussion
1
6
336 m, 1285 s, 1208 w, 1124 s, 1034 s, 898 m, 854 w, 784 m, 661 s,
10 m.
3.1. Synthesis and characterization of catalyst
During the acid-base mixed-ligand self-assembly process, the nature
of organic ligands plays a crucial role in determining the final MOF
structures and properties [38]. Recently, our group has utilized a series
of halogen-substituted dicarboxylate acids and N-heterocyclic bridging
ligands as the functional and structural units to develop families of
halogen-modified metal-organic hybrid materials [39–45]. Meanwhile,
a new stable copper(II) MOF based on the mixed ligands of Fbtx and
phthalic acid has been reported by us [33]. Considering the unique
coordination geometry of cobalt(II) ion and its potential catalytic
properties, we hoped to build more robust cobalt(II) complexes based
on mixed halogen-substituted ligands of acid- and base-type. Although
many attempts have been devoted to the combination of Fbtx with
several analogues dicarboxylate ligands, such as phthalic acid, 3,4,5,6-
tetrafluoro-phthalic acid, 3,4,5,6-tetrabromo-phthalic acid, it was a pity
that pink precipitates but not crystals which are unsuitable for X-ray
single-crystal analyses were always obtained. Therefore, it should be
pointed out that the choice of carboxylate ligands plays an important
role in the self-assembly. In addition, when cobalt(II) sources including
2
.2. Catalytic studies
Co-MOF-catalyzed CDC amination of benzoxazoles: in a typical
procedure, 5-methylbenzoxazole (0.5 mmol, 1.0 equiv), morpholine
(
(
0.6 mmol, 1.2 equiv), Co-MOF (0.015 mmol, 3 mol%), acetic acid
1 mmol, 2 equiv), TBHP (70% in H O) (1 mmol, 2 equiv) and acet-
2
onitrile (2 mL) were taken in a 10-mL Schlenk flask. The reaction
mixture was stirred for 12 h at room temperature under air atmosphere.
The progress of the reaction was monitored via gas chromatography
(
Shimadzu GC-2010AF) equipped with fused silica capillary HP-5
column (30 m × 0.32 mm) and a flame ionization detector. The pro-
1
13
ducts were further confirmed by using GC–MS, H NMR and C NMR.
The concentration of 5-methylbenzoxazole and 5-methyl-2-(4-mor-
pholinyl)benzoxazole was calibrated by external standard method with
standard samples. The reaction solution containing Co-MOF catalyst
was easily separated by filtration, and the catalyst was washed with
DMF and ethanol and dried under vacuum before reutilization.
Co(NO
tained under the similar reaction conditions. Moreover, the introduc-
tion of NaOH, KOH or Et N to adjust the pH value was also examined,
3 2 2
) and CoCl were used, only amorphous powders were ob-
2.3. Single crystal X-ray diffraction
3
The crystal data of Co-MOF were collected on a Bruker Apex II CCD
where such bases were ineffective during the assembly processes.
As shown in Fig. 1a, photo of single crystals of Co-MOF shows high
quantity. Single-crystal X-ray diffraction analysis reveals that Co-MOF
crystallizes in the monoclinic system with the C2/c space group, and
shows a three-dimensional two-fold interpenetrating framework with
diffractometer at 293 K with Mo Kα radiation (λ = 0.71073 Å). A
semiempirical absorption correction was applied using SADABS [34],
and the program SAINT was used for integration of the diffraction
profiles [35]. The structure was solved by the direct methods using
105