650
Y.-H. Niu et al. / Chinese Chemical Letters 27 (2016) 649–654
linear bis(phenolate) ligands, which displays selective catalytic
activity for the epoxidation of olefins [26]. Inspired by these
work, we tried to introduce transition metal ions into the title
tetravanadate cores to obtain hybrid vanadates, which might be
reduced to 0.2 mL. After the mixture was cooled to room
temperature, yellow crystals were isolated from the mixture.
Yield: 68% (based on NH4VO3); Anal. Calcd. for C36H64ÁZn2N12O14V4
(%): C, 35.3; H, 5.23; N, 13.73. Found: C, 35.36; H, 5.26; N, 13.61.
a
feasible way to improve the catalytic property in the
epoxidation of olefins.
2.4. Synthesis of [Zn(ipIM)3]2V4O12 (3)
Herein, using similar hydrothermal synthetic approach, we
successfully grafted different transition metal ions into POVs to
Compound 3 was synthesized by almost the same procedure as
compound 1 except the amount of eIM was reduced from 0.3 mL to
0.2 mL. After the mixture was cooled to room temperature, yellow
crystals were isolated from the mixture. Yield: 70% (based on
NH4VO3); Anal. Calcd. for C36H60Zn2N12O12V4 (%): C, 36.38; H, 5.05;
N, 14.14. Found: C, 36.52; H, 5.07; N, 14.19.
synthesize
a series of organic-inorganic hybrid vanadates
[Zn(eIM)3]2V4O12 (1), [Zn(pIM)3]2V4O12ÁH2O (2), [Zn(ipIM)3]2V4O12
(3), [Co(eIM)3]2V4O12ÁH2O (4), [Cu(eIM)2(H2O)]2V4O12 (5),
(eIM = 1-ethylimidazole, pIM = 1-propylimidazole, ipIM = isopro-
pylimidazole). By introducing Co2+, Cu2+ and Zn2+ as structural
connection nodes, the polyhedral fragments of tetravanadate
4À
[V4O12
]
units were linked together to create 2D network
2.5. Synthesis of [Co(eIM)3]2V4O12ÁH2O (4)
architectures and 1D chain structures, respectively. All compounds
were fully characterized by single-crystal X-ray diffraction (SXRD),
powder X-ray diffraction (PXRD), elemental analyses, TGA and FT-
IR spectroscopy. Further, not only the catalytic activity of these
compounds in the olefin epoxidation proved to be improved
greatly, but also the catalysts can be reused without losing their
activity after three circles and can function as heterogeneous
catalysts, which may have potential applications in the industry. To
our knowledge, this is the first time that inorganic–organic hybrid
vanadates were used as catalysts in the olefin epoxidation.
A
mixture of CoCl2Á6H2O (0.1705 g, 0.8 mmol), NH4VO3
(0.1404 g, 0.8 mmol), eIM (0.8 mL), and H2O (8 mL) was heated
at about 120 8C for 72 h. After the mixture was cooled to room
temperature, dark purple crystals were isolated from the mixture.
Yield: 62% (based on NH4VO3); Anal. Calcd. for C30H52Co2N12O14V4
(%): C, 31.96; H, 4.61; N, 14.91. Found: C, 31.71; H, 4.42; N, 14.58.
2.6. Synthesis of [Cu(eIM)2(H2O)]2V4O12 (5)
A
mixture of CuCl2Á2H2O (0.1705 g, 0.8 mmol), NH4VO3
2. Experimental
(0.1404 g, 0.8 mmol), eIM (0.7 mL), and H2O (8 mL) was heated
at about 120 8C for 72 h. After the mixture was cooled to room
temperature, green crystals were isolated from the mixture. Yield:
68% (based on NH4VO3); Anal. Calcd. for C20H36Cu2N8O14V4 (%): C,
25.44; H, 3.82; N, 11.87. Found: C, 25.65; H, 3.74; N, 11.75.
2.1. Materials and general methods
All chemicals and reagents were commercially obtained and
used without further purification. All syntheses were carried out in
20 mL Teflon-lined stainless steel containers under autogenous
pressure. The mixed reactants were stirred at room temperature
for 120 min before heating. The FT-IR spectra were recorded using
KBr pellets in the range of 4000–400 cmÀ1 on a Nicolet 170 SXFT/IR
spectrometer. The X-ray powder diffraction (XPRD) of samples was
2.7. Catalyzed epoxidation of olefin
Compound 1 (0.01 mmol, 5.0 mg), olefin (1 mmol), TBHP (tert-
butyl hydroperoxide, 2 mmol), acetonitrile (2 mL) were added to a
glass tube, then the catalytic reaction was performed on a Wattecs
Parallel Reactor at 75 8C for 24 h. After the reaction was completed,
the resulting mixture was analyzed by GC–MS and GC.
collected on a Bruker D8 X-ray diffractometer equipped with a
˚
graphite monochromatized Cu K
a radiator (l = 0.15418 A). The
TGA was performed on a DTG-60 AH instrument under a N2
atmosphere with a heating rate of 10 8C/min. Elemental (C, H and
N) analyses were performed on a PerkinElmer 2400 II analyzer. The
metal contents of the compounds 1–5 were measured by
inductively coupled plasma (ICP) on a JY-ULTIMA2 analyzer. After
the catalytic reaction was completed, the resulting mixture was
analyzed by GC–MS and GC using naphthalene as an internal
2.8. X-ray crystallography
The single-crystal XRD data of all compounds were collected on
a Bruker APEX-II CCD detector with graphite mobochromatic Mo
˚
K
a radiation (l = 0.71073 A) at room temperature. Crystals were
mounted on a glass fiber and coated with oil. All absorption
corrections were performed using a multiscan technique. The
reflections collected were integrated and scaled using the APEX
2 software package [27,28]. All crystal structures were solved by
the direct method and refined by full-matrix least-squares on F2
using the SHELXTL program package (Bruker) [27,28]. All of the
non-hydrogen atoms were located by the direct methods and were
refined anisotropically. All hydrogen atoms were fixed at
calculated position and refined as riding models. The crystallo-
graphic data have been deposited with the Cambridge Crystallo-
graphic Data Centre (CCDC), CCDC-1058623 (1), CCDC-1058590
(2), CCDC-1058657 (3), CCDC-1404876 (4), CCDC-1404877 (5). The
crystallographic details of 1–5 are summarized in Table S1
(Supporting information).
standard substrate. The GC analyses were performed on
a
Shimadzu GC-2014C with an FID detector equipped with an
Rtx-1701 Sil capillary column. The GC–MS spectra were recorded
on an Agilent 7890A-5975C at an ionization voltage of 1200 V.
Atomic absorption analysis were measured by an inductively
coupled plasma spectrometer (ICP) on an ICP-6000 analyzer.
2.2. Synthesis of [Zn(eIM)3]2V4O12 (1)
A mixture of Zn(CH3COO)2Á2H2O (0.1705 g, 0.8 mmol), NH4VO3
(0.1404 g, 0.8 mmol), eIM (0.3 mL), and H2O (8 mL) was heated at
about 120 8C for 72 h. After the mixture was cooled to room
temperature, yellow crystals were isolated from the mixture.
Yield: 76% (based on NH4VO3); Anal. Calcd. for C30H48Zn2N12V4O12
(%): C, 32.63; H, 4.35; N, 15.23. Found: C, 32.76; H, 4.41; N, 15.21.
3. Results and discussion
2.3. Synthesis of [Zn(pIM)3]2V4O12ÁH2O (2)
3.1. Synthesis
Compound 2 was synthesized by almost the same procedure as
compound 1 except eIM was replaced by ipIM, and the amount was
At present, many inorganic–organic hybrid vanadates with a
variety of structures have been synthesized using the hydrother-