Polyoxotungstates incorporated organophosphonate and nickel: Synthesis, characterization and efficient catalysis for epoxidation of allylic alcohols

Article abstract of DOI:10.1039/c8dt02590h

Three new sandwich-type organophosphonate-functionalized polyoxotungstate clusters, [{Ni(H₂O)₅}_x(AsW₆O₂₁)₂{Ni(OOCCH₂NCH₂PO₃)₂}₃] (x = 0 (Ni1), 1 (Ni2 and Ni3)), were successfully isolated via a "top-down" synthetic strategy. Compounds (Ni1-Ni3) were characterized by single crystal X-ray analysis, X-ray powder diffraction (XRPD), IR spectroscopy, UV-vis spectroscopy, and thermogravimetric analyses (TGA). Magnetic properties provide evidence for antiferromagnetic coupling in Ni2 and Ni3 and ferromagnetic interaction in Ni1. Catalytic studies of the three polyoxotungstates for the oxidation of allylic alcohols to epoxides have been investigated in water with H₂O₂ as the oxidant. All three polyoxotungstates exhibit efficient catalytic performance with excellent conversion and high selectivity at room temperature.

Full text of DOI:10.1039/c8dt02590h

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ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
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DOI: 10.1039/C8DT02590H
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ARTICL
Polyoxotungstates incorporated organophosphonate and nickel:
synthesis, characterization and efficient catalysis for epoxidation
of allylic alcohols
Received 00th January 20xx,
Accepted 00th January 20xx
Qiaofei Xu, Yingguang Li, Ran Ban, Zhao Li, Xiao Han, Pengtao Ma, Vikram Singh, Jingping Wang*
and Jingyang Niu*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Abstract:
Three
new
sandwich-type
organophosphonate-functionalized
polyoxotungstate
clusters,
[{Ni(H2O)5}x(AsW6O21)2{Ni(OOCCH2NCH2PO3)2}3] (x = 0 (Ni1); 1 (Ni2 and Ni3)), were successfully isolated via executing the
‘‘top-down’’ synthetic strategy. Compounds (Ni1-Ni3) were characterized by single crystal X-ray analysis, X-ray powder
diffraction (XRPD), IR spectroscopy, UV-vis spectroscopy, and thermogravimetric analyses (TGA). Magnetic properties
provide evidence for antiferromagnetic coupling in Ni2 and Ni3 whereas ferromagnetic interaction in Ni1. Catalytic studies
of three polyoxotungstates for the oxidation of allylic alcohols to epoxides have been investigated in water with H2O2 as
the oxidant, which exhibits efficient catalytic performance with excellent conversion and high selectivity at room
temperature.
(POTs), in contrast to the abundant derivatives of
polyoxomolybdates10 and polyoxovanadates.11 In fact, the first
example of organophosphonate-based POTs is Pope’s
[(O3PCH2PO3)4W12O36]16- reported in 1994,12 thereafter, only several
Introduction
Polyoxometalates (POMs), as the metal-oxide nanoclusters exhibit
controllable and diversiform structures, along with high thermal and
oxidative stability. Nowadays, the consistent use of POMs is mainly
manifested due to their remarkable electronic behavior, magnetism
and Brønsted acidity, thus expanding them in catalysis,1
magnetism,2 biology3 and in pharmacy.4 Moreover, the nucleophilic
surface-oxygen atoms facilitates POMs to be used as multidentate
inorganic ligands to coordinate metal centers5 (transition metals
(TMs) or lanthanide ions) but could also functionalized with organic
groups, which is an effective strategy in obtaining POM-based
multifunctional materials.6 Meanwhile, organophosphorus, a kind of
multifunctional ligands, possesses high thermostability and robust
resistivity against hydrolysis, which has exhibited wide applications
ranging from catalysis to medicine.7 Moreover, organophosphonate-
based POMs derivatives occupy an important place in POMs
chemistry due to their splendid properties.8 Thereby, inorganic (TMs)
and organic (phosphonates) functionalized POMs could be used in
improving the physicochemical phenomena in catalysis.9 It is worth
noting that there are still relatively limited studies have been
performed on organophosphonate-functionalized polyoxotungstates
literatures
contributed
towards
the
development
of
organophosphonate-decorated POTs.13 Until 2012, TMs was firstly
introduced into organophosphonate-based POTs by Mialane and co-
workers
for
the
preparation
of
.
[{(B-α-
Afterwards,
PW9O34)Co3(OH)(H2O)2(O3PC(O)(C3H6NH3)PO3)}2Co]14- 14
they synthesized organophosphonate-based POTs containing nickel
atoms in Later on, our group reported,
2013.15
[H4{(AsW9O33)Zn(H2O)W5O11(N(CH2PO3)3)}2(μ2-O)2]10- in the year
2014, which contains different geometry of
a
[{Zn(H2O)W5O19(N(CH2PO3)3)}]12− cluster in a chiral conformation
which was also used as an efficient catalyst for olefin epoxidation.16
Hence, it is significant to construct original organophosphates
functionalized POTs, which bear novel properties but also, can
contribute significantly to the development of POMs chemistry.
However,
organophosphonate-based polyoxomolybdates, there were few
reports which deals on POTs functionalized with
compared
to
the
rapid
development
of
organophosphonates which might be attributed to lower reactivity
amongst organophosphorus and POTs. In order to overcome this
obstacle, the following strategies were adopted: 1) contrary to the
traditional “bottom-up’’ condensation reactions, “top-down’’
approach was used to produce the active species in order to
improve the reactivity between POTs and organophosphorus.17 2)
Organophosphorus equipped nitrogen enhance the coordination
ability.
a.Henan Key Laboratory of Polyoxometalate Chemistry, Institute of Molecular and
Crystal Engineering, College of Chemistry and Chemical Engineering, Henan
University, Kaifeng, Henan 475004, P. R. China. E-mail: jyniu@henu.edu.cn,
jpwang@henu.edu.cn; Fax: (+86)371-23886876
Electronic Supplementary Information (ESI) available: The infrared spectrum of the
three POMs (Figure S1); The XRD of the three POMs (Figure S2); The structure of
the POMs (Figure S3); The plots for and χM-1 vs T between 1.8 K and 300 K for
three POMs (Figure S4); The TGA curves of Ni1, Ni2 and Ni3 (Figure S5); The Vis
Recently, considerable efforts have been aimed towards the
epoxidation of allylic alcohols as the products have been applied as
raw materials for epoxy resins, building blocks for biologically
spectra of Ni1, Ni2 and Ni3 (Figure S6); The comparison of solution 1H NMR
spectra of the three POMs and glyphosate (Figure S7). See
DOI: 10.1039/x0xx00000x
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important compounds and chiral molecules.18 Thus, substantial Materials and Methods
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DOI: 10.1039/C8DT02590H
researches in the design and construction of splendid catalytic
All the reagents were of analytical grade and obtained from
system for the rapid transformation from allylic alcohols to epoxides
have been gaining much attention, where POTs appears with good
catalytic performance in the aforementioned process.19
Furthermore, the combination of TMs and glyphosate into POTs may
possess wonderful catalysis for the epoxidation, which is also in
consistent with the synthetic target. Moreover, the development of
commercial
sources
without
further
purification.
K14[As2W19O67(H2O)] was prepared using literature methods21
and characterized by IR spectroscopy. All of the allylic alcohols
were purchased from J&K Chemical. Hydrogen peroxide was
obtained from Deen Reagent.
efficient and practical epoxidation technology mainly employs Synthesis of K14H10[(AsW6O21)2{Ni(OOCCH2NCH2PO3)2}3]·25H2O (Ni1)
aqueous H2O2 as the oxidant because of its high contents of active
K14[As2W19O67(H2O)] (0.66 g) and glyphosate were dissolved in
10 mL of deionized water and NiCl2·6H2O (0.24 g) was added
after 10 minutes stirred solution. Followed by the addition of
oxygen species and co-production of eco-friendly water.20
Herein, K14[As2W19O67(H2O)] (As2W19) as an active precursor was
chosen to be disassembled to generate peculiar and active building
KCl (0.1 g) into the above mixture, the pH was adjusted to 6 by
blocks. Meanwhile, glyphosate, as a kind of the organophosphorus
3M KOH. Afterwards, the green clear solution was stirred in 80
ligands in this synthetic system, have one phosphoryl and carboxyl
oC for 1.5 h and then the precipitate was removed by filtration.
group on two terminals along with one center nitrogen atom, which
The blue block shape crystals of Ni1 were collected after about
three weeks. Yield: 0.42g (23.9% based on NiCl2·6H2O).
Elemental analysis (%) calcd for Ni1: C, 4.15; H, 1.61; N, 1.61;
Ni, 3.38; P, 3.57; W, 42.41; As, 2.88; K, 10.52. Found: C, 3.98; H,
1.84; N, 1.73; Ni, 3.28; P, 3.82; W, 42.25; As, 2.23; K, 10.41.
Selected IR (KBr, cm–1; b, broad; s, strong; m, medium; w,
weak;): 3385 (b), 3256 (w), 2948 (w), 1595 (s), 1394 (m), 1260
(w), 1214 (w), 1110 (s), 998(w), 922 (s), 876 (s), 797 (m), 693
(s), 609 (w), 518 (w).
could be used to increase the possible combination of TMs and
POMs. As expected, three new sandwich-type TMs-containing POTs
functionalized
K14H10[(AsW6O21)2{Ni(OOCCH2NCH2PO3)2}3]·25H2O
glyphosate
were
obtained:
(Ni1),
K8H14[{Ni(H2O)5}(AsW6O21)2{Ni(OOCCH2NCH2PO3)2}3]·20H2O
(Ni2)
and Cs2K5H15[{Ni(H2O)5}(AsW6O21)2{Ni(OOCCH2NCH2PO3)2}3]·18H2O
(Ni3), where TMs and organophosphorus were incorporated into
POTs successfully. Beside this, the catalytic process was executed
with H2O2 as oxidant and water as solvent which limits the
expensive environmentally-unacceptable oxidants and hazardous Synthesis of
organic solvents. Notably, the synthetic POTs have shown superior K8H14[{Ni(H2O)5}(AsW6O21)2{Ni(OOCCH2NCH2PO3)2}3]·20H2O (Ni2)
catalytic performance for epoxidation of allylic alcohols at room
The preparation of Ni2 (light block shape crystals) is quite similar to
Ni1, but with RbCl (0.1 g) instead of KCl and the pH was adjusted
temperature in an economic and eco-friendly approach.
Results and discussion
Table 1 Crystallographic data and structure refinement parameters for Ni1, Ni2 and Ni3.
Ni1
As2Ni3O97P6W12C18H84N6K14
5202.06
Ni2
C18H88N6O97P6As2W12Ni4K8
5030.20
Ni3
C18H85N6O95P6Ni4As2W12K5Cs2
5143.69
Empirical formula
Formula weight
Space group
Crystal system
a [Å]
P321
trigonal
22.6407(11)
22.6407(11)
19.7106(10)
90
C2/c
Pbca
monoclinic
23.181(6)
18.465(5)
34.868(12)
90
orthorhombic
26.670(2)
29.464(3)
36.519(3)
90
b [Å]
c [Å]
α [°]
β [°]
γ [°]
V[Å3]
90
120
8750.0(10)
3
2.918
105.887(5)
90
14356(7)
4
2.284
10.927
90
90
28696(4)
8
2.355
Z
ρcalcd [g cm-3]
μ [mm-1]
Rint
13.507
0.0581
11.346
0.1077
0.1038
-27 ≤ h ≤ 25,
-27 ≤ k ≤ 23,
-23 ≤ l ≤ 23
45446
-27 ≤ h ≤ 27,
-18 ≤ k ≤ 22,
-31 ≤ l ≤ 41
35144
-31 ≤ h ≤ 31,
-35 ≤ k ≤ 29,
-43 ≤ l ≤ 43
145052
Limiting indices
Reflections collected
F (000)
7008
1.039
9040
1.033
18520
1.063
GOF on F2
R1, wR2 (I > 2σ (I))
R1, wR2 (all data)
0.0418, 0.1018
0.0505, 0.1067
0.0882, 0.2422
0.1275, 0.2776
0.0691, 0.1679
0.1242, 0.2110
2 | J. Name., 2012, 00, 1-3
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Fig. 1. (a) Schematic presentation of synthesis of the anion Ni1; (b) The polyhedral/ball-and-stick representation of the polyanionic skeleton of Ni1; (c) The ball-and-stick
representation of the building blocks; (d) The planform of the three Ni atoms incorporated with glyphosate ligands; (e) the coordination mode between one Ni atom and two
ligands. (WO6/W: cyan, P: yellow, Ni: green, C: black, N: blue, O: red.)
to 5.8. Yield: 0.39g (30.5% based on NiCl2·6H2O). Elemental spectrometer. IR spectra were recorded on a Bruker VERTEX
analysis (%) calcd for Ni2: C, 4.29; H, 1.75; N, 1.67; Ni, 4.67; P, 70 IR spectrometer (Nicolet, Madison, WI, USA) (using KBr
3.70; W, 43.86; As, 2.98; K, 6.22. Found: C, 4.15; H, 1.83; N, pellets) in the range of 4000–400 cm-1. X-ray powder
1.51; Ni, 4.52; P, 3.97; W, 44.68; As, 3.23; K, 6.28. Selected IR: diffraction (XRPD) data were recorded on a Bruker AXS D8
3410 (b), 3253 (w), 2945 (w), 1695 (s), 1391 (m), 1331 (w), Advance diffractometer (Bruker, Karlsruhe, Germany) with Cu
1257 (w), 1216 (w), 1110 (s), 998 (w), 926 (s), 876 (s), 793 (m), Kα radiation in the angular range 2θ = 5–45◦ at 293 K. TG
693(s), 605 (w), 513 (m).
analysis was measured on NETZSCH STA449F5/QMS403D
instrument (Mettler-Toledo, Schwerzenbach, Switzerland) with
a heating rate of 10 ◦C min-1 from 25 ◦C to 870 ◦C in N2 flow.
Synthesis of
Cs2K5H15[{Ni(H2O)5}(AsW6O21)2{Ni(OOCCH2NCH2PO3)2}3]·18H2O (Ni3)
The procedure of the catalysis for the epoxidation of allylic alcohols
The preparation of Ni3 (light block shape crystals) is similar to
Ni1, but with CsCl (0.1 g) instead of KCl and the pH was The allylic alcohols (5 mmol), H2O2 (5 mmol) catalyst (0.2 mol%)
adjusted to 6.5. Yield: 0.45g (34.5% based on NiCl2·6H2O). and water (1 ml) were added into a tube at room temperature.
Elemental analysis (%) calcd for Ni3: C, 4.20; H, 1.65; N, 1.63; Afterwards, the mixture was stirred at the prescribed
Ni, 4.56; P, 3.62; W, 42.89; As, 2.91; K, 3.80; Cs, 5.17. Found: C, conditions on the parallel reactor. The product carried on
4.02; H, 1.72; N, 1.89; Ni, 4.43; P, 3.85; W, 43.58; As, 2.96; K, qualitative detection by GC-MS and the yield was monitored
3.69; Cs, 5.22. Selected IR: 3400 (b), 3248 (w), 2951 (w), 1595 by GC with dodecane as internal standard.
(s), 1391 (m), 1333 (w), 1251 (w), 1214 (w), 1101 (m), 998 (m),
X-ray crystallographic determination
928 (s), 879 (s), 801 (m), 740(s), 693 (s), 604 (w), 517 (m).
Crystallographic study for Ni1
296(2) K on a Bruker Apex-II CCD diffractometer using
, Ni2, and Ni3 were performed at
Characterization
Elemental analyses of C, H, and N were performed with an graphite-monochromated Mo Kα radiation (λ = 0.71073 Å).
Elementar Vario Elcube CHNS analyzer (Perkin-Elmer, Waltham, Intensity data were corrected for Lorentz and polarization
MA, USA). Elemental analysis for W, Ni and P were performed effects as well as for multi-scan absorption by an applied
with a Perkin Eimer Optima 2100 DV (Perkin-Elmer, Waltham, multiscan absorption correction SADABS program. Direct
MA, USA) inductively coupled plasma optical emission methods (SHELXS97) were used to solve their structures, and
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the heavy atoms were located by full matrix least-squares disordered nickel atom in the {Ni(H2O)5} unit has existed in two
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refinements on F2 and Fourier syntheses using the SHELXS- locations which have been shown in Fig.DOS1I:b1.0.I1n0t3e9r/eCs8tiDnTg0ly2,59t0hHe
1997 program package. In the final refinement cycles, the W, disordered Ni atom bonded with the above nickel atoms in the
As, Ni, and P atoms were refined anisotropically; the O, C and triangle, which has made an obvious effect on their structures. As it
N
atoms were refined isotropically. The lattice water has been shown in Fig. S1e, the triangles in Ni2 have transformed to
molecules were determined by the TGA results. The hydrogen isosceles triangles, where the length of two same sides is 7.617 Å
atoms of organic groups were fixed in calculated positions and and the length of the longer side is 7.746 Å. As to Ni3, three sides in
then refined using a riding model. Collected crystal data and the triangle are not equivalent due to the different occupancy of
structure refinement parameters for Ni1
,
Ni2, and Ni3 are the nickel at two sites, which are in the length of 7.755 Å, 7.565 Å
given in Table 1.
and 7.768 Å (Fig. S1f).
Structure description
Magnetic Properties
X-ray analyses reveal that compounds Ni1, Ni2 and Ni3 crystallize in
the trigonal P321, monoclinic C2/c and orthorhombic space group
Pbca, respectively. The polyanions (Ni2 and Ni3) exhibit similar
framework to Ni1 except one extra disordered Ni atoms. Herein,
the crystal description of only Ni1 is described in detail. The
structural units of Ni1 contains 14 potassium cations, 10 hydrogen
Variable-temperature magnetic susceptibilities of the three
POTs have been investigated under an applied direct current
(dc) field of 1000 Oe from 300 to 1.8 K. As shown in Fig. 2, the χMT
value of 3.12 cm3 K mol-1 at 300 K for Ni1 is in good agreement with
Ⅱ
that expected for three non-interacting Ni ions of 3.00 cm3 K mol-1
(S = 1, g = 2). Upon cooling, the χMT value of Ni1 increases to a
maximum of 3.75 cm3 K mol-1 at 14 K, and then decreases to the
minimum of 2.26 cm3 K mol-1 at 1.8 K. Ni1 exhibits Curie–Weiss
behavior in the temperature range of 110–300 K, with a Curie
constant of C =3.23 cm3 K mol-1 and Weiss constant of Θ = 3.68 K
(Fig. S4a and S4d), which has shown that the ferromagnetic
interaction exists in Ni1. As to Ni2 and Ni3, the value of χMT at 300
K is 4.69 cm3 K mol-1 for Ni2 and 4.24 cm3 K mol-1 for Ni3, which is in
cations,
25
water
molecules
and
one
[(AsW6O21)2{Ni(OOCCH2NCH2PO3)2}3]24-. As shown in Fig. 1b, the
polyoxoanion in Ni1 consists of two {AsW6O21} building blocks,
three nickels and six glyphosates. To be specific, the same building
blocks {AsW6O21} in three polyoxoanions as shown in Fig. 1c, mainly
generated by the connection of one As atom with three {W2O10}
units which are in vertex-sharing, formed by the side-sharing of two
{WO6} octahedrons. Additionally, each nickel atom is octahedrally
coordinated by two nitrogen atoms and four oxygen atoms of two
glyphosate molecules, respectively, which constructs the
framework of {Ni(OOCCH2NCH2PO3)2} subunits (Fig. 1e). Afterwards,
there are three {Ni(OOCCH2NCH2PO3)2} subunits, sandwiched by
two {AsW6O21} building blocks via the six P—Ow linkers generating
polyoxoanions in Ni1. Notably, three nickel atoms in
{Ni(OOCCH2NCH2PO3)2} subunits are located at the three vertexes of
one equilateral triangle (Fig. 1d), respectively, where the same
distance among them is 7.553 Å. For Ni2 and Ni3, there is one
Ⅱ
good consistent with that for four non-interacting Ni ions of 4.00
cm3 K mol-1. However, the χMT value undergoes a gradual decrease
while the temperature is lowered, which is different from Ni1.
Afterwards, there is a sharp reduction in the temperature range of
16—2 K and the χMT value reaches a minimum of 2.24 cm3 K mol-1
at 1.8 K. Besides, the plots of 1/χM versus T for Ni2 and Ni3 conform
to the Curie-Weiss law (Ni2: C = 4.63 cm3Kmol-1，Θ = −2.27 K; Ni3:
C = 4.18 cm3Kmol-1，Θ = −2.39 K (Fig. S4b, S4c and S4e)), which
indicated that there are antiferromagnetic couplings in Ni2 and Ni3.
{Ni(H2O)5} unit (Fig. S1h and S1i, respectively) filled in the triangle Solution 31P NMR Studies
consisted of three nickel atoms in Fig. S1b. Moreover, the
The solution 31P NMR spectra (D2O) of Ni1
, Ni2, Ni3 and raw
materials have been investigated at room temperature. As
Fig 2. (a) the comparison of solution 31P NMR spectra of POMs, raw materials
and the mixture of NiCl2 and H2O2; (b) the solution 31P NMR spectra of Ni1
versus different time.
Fig. 2. χMT versus T plots of Ni1
4 | J. Name., 2012, 00, 1-3
, Ni2 and Ni3 in the 1.8-300 K range.
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shown in Fig. 3a, the 31P NMR spectra have shown that there is which is assigned to electronic transitions which could be assigned
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3
3
23
DOI: 10.1039/C8DT02590H
only one signal in each POMs with slight difference in chemical for either d−d ( T1 → T2) or LMCT in character.
shifts, which indicates that all P atoms are magnetically
equivalent phosphorus corresponding to the symmetrical
framework. Moreover, the comparison of the 31P NMR
Catalysis
Optimization of the catalyst
chemical shifts of glyphosate and the mixture (As2W19, NiCl2
Initially, the epoxidation of 3-Methyl-2-buten-1-ol as the
and glyphosate) shows an obvious difference from the
synthetic POMs, as the peaks appear wider and weaker
because of the paramagnetic centers (Ni2+). Besides, a small
model reaction was performed with different catalysts in order
to select the optimal catalyst to be employed in this system. As
shown in Table 2, the reaction hardly took place in the absence
of the catalyst (entry 1, Table 2). However, there is huge
promotion once adding the POMs into this reaction. Besides,
the precursors were also investigated in the same conditions
and the results have shown that no efficient catalysis for the
process could be detected. Obviously, Ni1 has exhibited the
best catalytic performance (98% conversion and 96%
selectivity, entry 2, Table 2) among three POMs, which could
induce itself to be used for the following studies.
1
skewing in the H NMR spectra between the synthetic POMs
and glyphosate has been observed in Fig. S7, which indicated
bonded glyphosates to the nickel centers in In order to detect
the stability of Ni1, the 1H NMR study for the mixture (Ni1 and
H2O2) and Ni1 in aqueous solution versus time have been
performed. The results showed that the chemical shift has
changed when H2O2 was added; however, it is different from
raw materials and glyphosate. As it has shown in Fig. 3b, the
31P NMR spectra of Ni1 was tested versus time and the results
have shown that there was no apparent change for Ni1 in
aqueous solution even after 11 hours.
Influence of different factors on the process
To our best knowledge, reaction temperature, dosage of
catalyst, loading of H2O2, temperature and solvents all play
critical roles in this transformation. On the basis of the above
results, Ni1 was employed for the transformation to
investigate the effect of different factors. As shown in Fig. 5a,
the influence of dosage of catalyst was studied from 0.1 to 0.3
mol%. And the results have shown that the conversion and
selectivity of the reaction have been significantly improved
when the dosage of catalyst was enhanced from 0.1 to 0.20
mol%. However, there was not obvious increase in conversion
and selectivity when the amount of catalyst was from 0.20 to
0.25 mol% but a little decrease in selectivity from 0.25 to 0.30
mol%. Hence, 0.20 mol% consider as optimal dosage of
catalyst in the reactions. For the effective H2O2 loading, the
ratio (H2O2: substrate) of 0.8, 1, 1.2 and 1.6 have been applied
(Fig. 5b), which have shown the enhancement from 0.8 to 1 in
their catalytic activity a reduction in selectivity were noticed
with the continued increase in H2O2 amount. Considering the
temperature effect on catalytic process, an obvious
UV/Vis spectra
In order to investigate the UV
solution, systematic studies of UV
–
vis spectra behaviors of the POMs in
–vis spectra for time-dependent
and the comparison between the obtained POMs and raw materials
were monitored. As shown in Fig. 4, the UV spectra of three POMs
are monitored in the range of 190-400 nm. The strong peak at 195
nm is assigned to the charge transfer transition of pπ–dπ from Ot to
W, while the peak at 265 nm corresponds to the charge transfer
transition of pπ–dπ from Ob and Oc to W. As the results of the
comparison showed in Fig. 4a, although the UV spectra of the
samples containing W also showed the peak at 265 nm, there were
obvious distinction between raw materials and synthetic POTs at the
range of 190–
220 nm.22 Additionally, Fig. 4b-d have exhibited that
the UV absorption peaks of three compounds are almost unchanged
in principle, which proves that they can exist stably in aqueous
solution for at least ten hours at room temperature. In the visible
region, a broad peak at around 630 nm is observable in Fig. S6,
Fig. 5. The influence of different factors for the epoxidation of 3-methyl-2-
buten-1-ol: (a) the amount of Ni1; (b) the ratio of H2O2 : substrate; (c) reaction
temperature; (d) solvents.
Fig. 4. (a) The compared UV spectra of different samples (L: glyphosate,
mixture: As2W19 + NiCl2 + glyphosate); The UV-vis spectra of Ni1 (b), Ni2 (c)
and Ni3 (d) for time-dependent.
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Table 2.
Journal Name
View Article Online
DOI: 10.1039/C8DT02590H
The epoxidation of methyl-2-buten-1-ol was performed with different catalysts.
Entry
Cat.
Conv. b (%)
2
97.5
94.5
94.8
4.3
3.3
53.4
67.6
Sel. (%)
1a
2
3
4
5
6
7
8
--
Ni1
Ni2
Ni3
glyphosate
NiCl2
As2W19
Mixture
80
96
89
90.5
77.8
86
53.6
82.7
a Reaction conditions: 3-methyl-2-buten-1-ol (5 mmol), H2O2 (5 mmol), catalyst (0.2 mol%) H2O (1 mL), 25 oC; b All of the products were identified by GC–MS spectra.
The results refer to GC spectra based on dodecane as internal standard.
melioration with the rise of temperature were observed till it catalytic system. As can be seen from Fig. 6, 3-Methyl-2-buten-1-ol
reaches to 25 oC (Fig. 5c). As the increase of temperature went afforded the best activity: 98% epoxide conversion and 96%
on, the conversion and selectivity of the reaction would selectivity in one hour, which may benefit from the higher
decline. Besides, solvents also have an important effect on this nucleophilicity of the C=C. While the trans-2-hexen-1-ol is less
reaction, consequently, several contrast experiments were reactive: only 63% conversion and 96% selectivity could be detected
performed in various solvents. As it has been shown in Fig. 5d, after 6 hours. In addition, 2-methyl-2-propen-1-ol and Crotyl
the reaction executed in acetone could obtain better catalysis alcohol have shown 100% selectivity at 99.2% conversion and
than in alcohol and acetonitrile, which may be influenced by 99.5% selectivity at 98% conversion, respectively, which were
the polarity of solvent. Besides, the reaction in eco-friendly obtained by prolonging the reaction time to 6 h. Therefore, the
water exhibited the best catalytic performance amongst the results suggested that Ni1 have shown splendid catalysis for the
other solvents. Unfortunately, the results of solution 31P NMR epoxidation of allylic alcohols.
spectra have shown that Ni1 will change when H2O2 is added
but the contrast experiments implied that the raw materials
Conclusion
presented little catalytic performance, which hinted that Ni1 In
summary,
a
plausible
route
to
introduce
may have been transformed into other active species in the organophosphonate into POTs have been accomplished via the
process to benefit this catalysis.
disassembly of the [As2W19O67]14- into active species and
glyphosate (containing N atom) as the ligand to improve the
reactivity among organophosphonate, TMs and POTs. As
Scope of substrate
expected,
three
sandwich-type
organophosphonate-
Encouraged by the above results, the epoxidation of various allylic
alcohols (2-methyl-2-propen-1-ol, trans-2-hexen-1-ol and crotyl
alcohol) with equivalence of aqueous H2O2 was carried out in this
functionalized POTs incorporated TMs were synthesized
successfully by self-assembly, which is of utmost importance in
POM chemistry. Interestingly, the magnetic properties of three
POMs
have
been
investigated
systematically:
antiferromagnetic coupling in Ni2 and Ni3 but the
ferromagnetic interaction in Ni1. Notably, the three POMs all
exhibited efficient catalysis for the transformation from allylic
alcohols to epoxides at room temperature. In addition, water
as solvent and H2O2 as oxidant have prevented environment
from the damage of nocuous organic solvents and oxidants,
which is advocated in the green process of chemical
production.
Conflicts of interest
There are no conflicts of interest to declare.
Fig. 6. The epoxidation of different allylic alcohols in the presence of Ni1
.
6 | J. Name., 2012, 00, 1-3
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ARTICLE
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1975, 97, 5735–5738; (b) Nakamura, I.; MiVriaews,Article Online
DOI: 10.1039/C8DTH0.259N0H.;
Acknowledgements
We gratefully acknowledge support from the NSFC (2117205)
and the Natural Science Foundation of Henan Province
(162300410015).
Fujiwara, A.; Fujibayashi, M.; Song, Y.-F.; Cronin, L.;
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N. Biboum, B. Keita, L. Nadjo, S. Nellutla, J. van Tol, N. S.
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DOI: 10.1039/C8DT02590H
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DOI: 10.1039/C8DT02590H
Polyoxotungstates incorporated organophosphonate and nickel:
synthesis, characterization and efficient catalysis for epoxidation of
allylic alcohols
Qiaofei Xu, Yingguang Li, Ran Ban, Zhao Li, Xiao Han, Pengtao Ma, Vikram Singh, Jingping Wang*
and Jingyang Niu*
Henan Key Laboratory of Polyoxometalate Chemistry, Institute of Molecule and Crystal Engineering,
College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan 475004, P. R. China
.
‘‘Top-down’’ synthetic strategy was performed via K14[As2W19O67(H2O)] as precursor to be
disassemble to obtain active building blocks which can incorporate nickle and glyphosate to
overcome the trouble in the synthesis of organophosate-based POTs. Moreover, the
synthetic POTs exhibited superior catalysis for the epoxidation of allylic alcohols in water
with H2O2 as oxidant under room temperature, which prevented environment from the
damage of nocuous organic solvents and oxidants.