Immobilizing of oxo-molybdenum complex on cross-linked copolymer and its catalytic activity for epoxidation reactions

Article abstract of DOI:10.1016/j.catcom.2015.10.022

This work describes the immobilization of molybdenum acetylacetonate oxygen (MoO₂(acac)₂) on cross-linked porous copolymer support via covalent attachment under mild conditions. The obtained solid product DVB-AA-Mo was fully characterized by FT-IR, TG, CHN elemental analysis, nitrogen adsorption/desorption, and SEM, and was tested for the epoxidation of various alkenes with tert-butyl hydroperoxide (TBHP) as the oxidant. DVB-AA-Mo was proved to be a highly efficient catalyst for epoxidation reactions, it could easily be recovered by filtration and reused for five runs without significant loss in activity.

Full text of DOI:10.1016/j.catcom.2015.10.022

Catalysis Communications 74 (2016) 1–4
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Immobilizing of oxo-molybdenum complex on cross-linked copolymer
and its catalytic activity for epoxidation reactions
⁎
Weizheng Fan, Dongyang Shi, Bainian Feng
School of Pharmaceutical Science, Jiangnan University, Wuxi 214122, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
This work describes the immobilization of molybdenum acetylacetonate oxygen (MoO2(acac)2) on cross-linked
porous copolymer support via covalent attachment under mild conditions. The obtained solid product DVB–AA–Mo
was fully characterized by FT-IR, TG, CHN elemental analysis, nitrogen adsorption/desorption, and SEM, and was
tested for the epoxidation of various alkenes with tert-butyl hydroperoxide (TBHP) as the oxidant. DVB–AA–Mo
was proved to be a highly efficient catalyst for epoxidation reactions, it could easily be recovered by filtration and
reused for five runs without significant loss in activity.
Received 28 September 2015
Received in revised form 15 October 2015
Accepted 16 October 2015
Available online 20 October 2015
Keywords:
Epoxidation
© 2015 Elsevier B.V. All rights reserved.
Oxo-molybdenum complex
Supported catalyst
Copolymer support
Heterogeneous catalysis
1. Introduction
(MoO2(acac)2) on cross-linked porous copolymer support via covalent
attachment, and use it as the catalyst for epoxidation of alkenes with
Epoxidation of alkenes is an important reaction in laboratory as well
as in the chemical industry, because epoxides are widely used for
manufacturing epoxy resins, surfactants, and intermediates, etc. in
organic synthesis [1–4]. This reaction is catalyzed by a number of tran-
sition metal compounds, titanium silicalites, Cu oxide, W-containing
compounds, and titanium-containing molecular sieves [5–9]. Among
the most efficient catalysts suggested for alkene epoxidation are
Mo-containing compounds [9–13].
tert-butyl hydroperoxide (TBHP) as the oxidant. The catalytic activity
of this newly prepared catalyst was higher than that of the homoge-
neous MoO2(acac)2, and can be easily recovered and steadily reused.
2. Experimental
2.1. Reagents and analysis
As highly active oxidation species, organic metal molybdenum com-
plexes are known to be good epoxidation catalysts due to their high ac-
tivity and selectivity [14–16]. However, problems of catalyst separation
and recyclability should be addressed for these homogeneous catalysts.
To this end, several strategies involving immobilization of the active
catalytic moiety, viz. to zeolites [17,18], polymer [19,20], silica [21],
graphene nanosheets [22], layered double hydroxide [23], and amine
modified multi-wall carbon nanotubes [24], have been reported.
Though good activity was achieved in those cases, most of them still
bear some drawbacks like need for excess metal complex, the slow
reaction speed, leaching of active species, or limited accessibility to
the reactants. To circumvent the limitations associated with the
known methods, a new strategy for catalyst preparation to overcome
the above problems is therefore highly desirable.
Please see Supplementary material (SM).
2.2. Preparation of catalysts
2.2.1. Synthesis of copolymer support DVB–AA
DVB–AA was prepared according the previous literature [25]. To
prepare the cross-linked polymer DVB–AA, divinyl benzene (DVB)
(3.9 g, 30 mmol), AIBN (0.1 g), and alyl amine (AA) (0.6 g, 5 mmol)
were dissolved in ethyl acetate (100 ml) under nitrogen. The mixture
was refluxed at 90 °C with stirring. After 24 h, a white solid formed
was filtrated and was washed with ethanol for three times. The final
product was dried in vacuum at 60 °C for 12 h. Element analysis: C,
86.4%; H, 8.13%; N, 3.02%. Theoretical value: C, 89.71%; H, 7.32%; N, 3.2%.
In this work, we demonstrate an efficient, high-yielding approach
for the immobilization of molybdenum acetylacetonate oxygen
2.2.2. Synthesis of MoO2(acac)2
Molybdenyl acetylacetonate (MoO2(acac)2) was prepared according
to the previous literature [26].
⁎
Corresponding author.
E-mail address: fengbainian@jiangnan.edu.cn (B. Feng).
http://dx.doi.org/10.1016/j.catcom.2015.10.022
1566-7367/© 2015 Elsevier B.V. All rights reserved.

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W. Fan et al. / Catalysis Communications 74 (2016) 1–4
Scheme 1. Synthesis of the immobilized MoO2(acac)2 catalyst DVB–AA–Mo.
2.2.3. Synthesis of DVB–AA–Mo
methanol, ethyl alcohol, chloroform, ethyl acetate, THF, DMF, DMSO,
and H2O.
In detail, DVB–AA (2.68 g, 6 mmol) was dispersed in anhydrous
ethanol (10 mL), the ethanol (10 mL) solution of MoO2(acac)2 (0.65 g,
2 mmol) was added into the above mixture with vigorous stirring, the
resulting mixture was refluxed at 80 °C for 24 h under a nitrogen atmo-
sphere. The formed light-blue solid precipitate was filtered off and
washed thoroughly by H2O and ethanol, and dried under vacuum.
CHN elemental analysis for DVB–AA–Mo (by the mass percentage): C,
66.17%; N, 1.74%; H, 6.96%. Theoretical value: C, 69.16%; H, 6.4%; N,
1.87%.
DVB–AA–Mo was characterized by IR, CHN elemental analysis, TG,
nitrogen adsorption/desorption, and SEM. As shown in Fig. 1(A), the
IR spectrum of DVB–AA shows the bands at 2800–3100 cm−1 assigned
to symmetric and asymmetric vibration of –C–H, and the bands at 902,
837, and 794 cm−1 assigned to vibration of substituted aromatic rings.
The intense peaks appeared at 935 and 906 cm−1 in the spectrum of
MoO2(acac)2 is attributed to the symmetric and asymmetric stretching
mode of the cis-MoO2. For DVB–AA–Mo, these peaks appeared distinc-
tively with the slight shift of peak positions. Meanwhile, the intensity
of the band at 906 cm−1 corresponding to asymmetric stretching
mode of the cis-MoO2 increased, which reveals the covalent attachment
of MoO2(acac)2 with DVB–AA support.
2.3. Catalytic tests
Typically, cyclooctene (1 mmol), CHCl3 (5 mL), and catalyst DVB–
AA–Mo (0.05 mmol) were added into a 25 mL round bottom flask.
The reaction started after the addition of aqueous TBHP (3 mmol) at
70 °C under vigorous stirring. After the reaction, the catalyst was filtered
off, washed with ethanol and dried for the next run. The product
mixture was analyzed by gas chromatography (GC) (SP-6890A)
The TG spectra of DVB–AA–Mo in Fig. 1(B) illustrate a high thermal
stability up to ca. 450 °C, and the weight loss in the temperature 450–
500 °C is attributed to the decomposition of the organic groups.
Sublimation of the left-over residue (18%) at 800 °C suggested the for-
mation of MoO3 which revealed the percentage of Mo in the catalyst
to be 12%. This result is in accordance with that of the elemental
analysis. All these results suggest that DVB–AA–Mo has the structure
illustrated in Scheme 1. The ICP-AES for the catalyst DVB–AA–Mo
shows about 7.7 wt.% Mo in the catalyst, which is lower than the theo-
retical value 12.8% of Mo in DVB–AA–Mo. This is mostly due to that
the catalyst could not completely dissolve in the solvents during the
characterization.
equipped with
a FID detector and a capillary column (SE-54
30 m × 0.32 mm × 0.3 m). The conversion and selectivity was calculated
by calibration area normalization method, and each reaction mixture
sample was detected at least three times to take the average. The
epoxidation of other alkenes were carried out in the same way.
The surface area and pore structure are examined by nitrogen sorp-
tion measurements (Figure S1, SM), the isotherm of DVB–AA is type IV
with a clear H1-type hysteresis loop at partial pressure region of P/P0 =
0.8–1.0, reflecting the existence of mesopores. DVB–AA has a high BET
surface area of 866.4 cm2/g. After the combination of MoO2(acac)2,
DVB–AA–Mo also shows a IV type nitrogen sorption isotherm with
high specific surface area of 801.2 cm2/g.
Fig. 2 shows the SEM images of DVB–AA and DVB–AA–Mo. The DVB–
AA is collective spherical particles with a size in micrometers (diameter:
1–3 μm, Fig. 2A). After the attachment of MoO2(acac)2, the smooth outer
surface of DVB–AA changed to be rough with the appearance of small
3. Results and discussion
3.1. Catalyst preparation and characterization
The copolymer support DVB–AA was prepared by free radical poly-
merization of divinyl benzene and alyl amine [25], and the required
MoO2(acac)2 was prepared by the reaction of (NH4)6MoO24·4H2O
with acetylacetone. Reaction of the obtained MoO2(acac)2 with support
DVB–AA resulted in the covalently attached solid catalyst DVB–AA–Mo
(Scheme 1), which is insoluble in common used solvents, such as
Fig. 1. (A) FT-IR spectra of (a) DVB–AA, (b) MoO2(acac)2, (c) DVB–AA–Mo, and (d) reused DVB–AA–Mo, and (B) TG curves of DVB–AA and DVB–AA–Mo.

W. Fan et al. / Catalysis Communications 74 (2016) 1–4
3
Fig. 2. SEM images of (A) DVB–AA and (B) DVB–AA–Mo.
particles on the surface of DVB–AA–Mo. We thus proposed that the
MoO2(acac)2 have been successfully attached onto the DVB–AA support
(Fig. 2B).
3.2. Epoxidation of alkenes over DVB–AA–Mo and MoO2(acac)2
The catalytic activities of the prepared immobilized catalyst DVB–
AA–Mo and a comparison with the corresponding homogeneous
MoO2(acac)2 was studied for the epoxidation of alkenes using TBHP as
oxidation in CHCl3 solvent, the results are summarized in Table 1. For
the epoxidation of cyclooctene, there is no product that was detected
without the use of catalyst. With MoO2(acac)2 as the catalyst, it caused
a homogenous catalysis, and exhibit a 96% conversion and 95% selectiv-
ity (entry 1). When DVB–AA–Mo was used as the catalyst, it caused a
solid–liquid heterogeneous catalysis, giving 95% conversion with 100%
selectivity (entry 1). This implies that the featured cross-linked porous
framework of DVB–AA endows the catalyst with an insoluble nature
and high catalytic activity. Encouraged by this result, we assessed the
catalytic activity of DVB–AA–Mo and MoO2(acac)2 under the described
reaction conditions, using a series of various types of alkenes. As can be
seen in Table 1 entries 2–7, these alkenes were selectively and efficient-
ly oxidized to the corresponding oxides by using TBHP as oxidant in the
presence of the catalyst DVB–AA–Mo. Styrene and indene afforded rel-
ative low conversions and selectivity mostly due to the presence of
more electron withdrawing groups connected to the double bond.
Also noticeably, the immobilized catalyst DVB–AA–Mo showed higher
selectivity than the homogeneous MoO2(acac)2 did with comparable
conversion, and facile recovery as well as recycling ability of the DVB–
AA–Mo make it superior catalyst.
Fig. 3. Catalytic performance of DVB–AA–Mo in epoxidation of cyclooctene with TBHP in
different solvents. Reaction condition: solvent (5 mL), cyclooctene (1 mmol), catalyst
DVB–AA–Mo (0.05 mmol), TBHP (3 mmol), 70 °C, 4 h.
The catalyst DVB–AA–Mo exhibits different performances in the ep-
oxidation of cyclooctene with TBHP by using various solvents. As shown
in Fig. 3, in chlorinated solvents such as CCl4, CHCl3 and CH2Cl2 in the
presence of TBHP high conversions were observed, this can be related
to low dielectric constant of chlorinated solvents. The catalytic conver-
sion in solvent CH3COOC2H5 was found to relative low, presumably
due to the higher dielectric constants than those of chlorinated solvents.
In the solvents, such as CH3CN, CH3OH, and C2H6CO, very low conver-
sions were obtained, this is mostly attributed that hard coordinate do-
nating atoms (O and N as hard bases) in these solvents tend strongly
Table 1
Epoxidation of various substrates with TBHP over heterogeneous DVB–AA–Mo and homogeneous MoO2(acac)2 catalyst.a
Con (%)b
Sel (%)c
Con (%)b
Sel (%)c
Entry
Substrate
Product
t (h)
DVB–AA–Mo
MoO2(acac)2
1
2
3
4
4
6
95
94
55
100
98
96
93
60
95
90
66
76
4
5
4
6
93
79
90
88
77
83
99
100
6
8
6
35
28
80
87
25
31
45
79
7
a
Reaction conditions: solvent (CHCl3, 5 mL), alkene (1 mmol), catalyst (0.05 mmol), TBHP (3 mmol), 70 °C.
Conversion of the substrate.
Selectivity of the epoxidation product. Byproducts for entry 3: 1,2:8,9-diepoxy-p-menthane and 1,2-ene-p-menth-8,9-epoxy; entry 4: 1,2-ene-p-menth-8,9-epoxy; entry 6:
b
c
benzaldehyde; entry 7: 3,4-epoxyhexane-1-aldehyde.

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W. Fan et al. / Catalysis Communications 74 (2016) 1–4
covalent attachment. The key advantages such as simplicity in use,
high efficiency in terms of high catalyst loading onto polymer support
without using excess of metal species, make this strategy a facile
and improved approach for the preparation of immobilized metal
complexes. The obtained polymeric hybrids were found to be a highly
efficient catalyst for epoxidation of alkenes using TBHP as oxidant. The
catalyst was recovered and reused five times without significant loss
in catalytic activity and detectable leaching of metal. The porous catalyst
structure and high specific surface area may be responsible for the ex-
cellent catalytic performance of DVB–AA–Mo.
Acknowledgments
This work was supported financially by grants from the National
Natural Science Foundation of China (grants 21302066) and Young
Program, SCF of Jiangsu Province (BK20130129).
Fig. 4. Catalyst recycling in epoxidation of cyclooctene with TBHP over DVB–AA–Mo.
Reaction conditions are the same with that in Table 1.
Appendix A. Supplementary data
to link to the hard metal centers Mo(VI), which results in a low catalytic
activity.
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2015.10.022.
3.3. Catalyst reusability
References
The recyclability and reusability of the immobilized catalyst DVB–
AA–Mo were tested using cyclooctene as the model substrate under
the described reaction conditions in Fig. 4. At the end of the reaction,
the catalyst was recovered by filtration and washed with ethanol,
dried and reused for subsequent experiments (five runs) without
adding any fresh catalyst. The five-run test gave 98–99% selectivity
without significant loss of conversion, revealing a quite steady reusabil-
ity. In the fifth run, the conversion and selectivity were 89% and 98%,
respectively. With a less amount of catalyst, it can also be steadily
reused with a slight decrease in activity (Figure S2, SM). Additionally,
we have carried out controlled hot-filtration experiments to check the
possible catalysis of the slightly leached metal species in the reaction so-
lution from the catalyst. Initially, the mixture of catalyst DVB–AA–Mo
and TBHP in CHCl3 was stirred at 70 °C for 1.5 h. Then, the catalyst
was then removed and the reaction proceeded for another 3 h with
the homogeneous filtrate. The GC results demonstrate that no oxidation
occurred. Furthermore, the selected filtrate samples during the
recycling experiments were also analyzed by ICP-AES elemental analy-
sis and no solvated Mo species could be detected (0.1 ppm detection
limit), which strongly indicate the heterogeneous nature of the present
catalyst DVB–AA–Mo for the epoxidation reaction. The slight decrease
of the activity in the fourth run is mostly due to the weight loss in the
operation for recovering the catalyst. Furthermore, the IR spectrum in
Fig. 1A for the recovered catalyst DVB–AA–Mo was well consistent
with that of the fresh one, demonstrating a durable catalyst structure.
[1] K. Kamata, K. Yonehara, Y. Sumida, K. Hirata, S. Nojima, N. Mizuno, Angew. Chem.
Int. Ed. 50 (2011) 12062.
[2] M. Herbert, E. Alvarez, D.J. Cole-Hamilton, F. Montilla, A. Galindo, Chem. Commun.
46 (2010) 5933.
[3] S.P. Maradur, C. Jo, D. Choi, K. Kim, R. Ryoo, ChemCatChem 3 (2011) 1435.
[4] Y. Leng, J. Wang, D. Zhu, M. Zhang, P. Zhao, Z. Long, J. Huang, Green Chem. 13 (2011)
1636.
[5] N.E. Thornburg, A.B. Thompson, J.M. Notestein, ACS Catal. (2015) http://dx.doi.org/
10.1021/acscatal.5b01105.
[6] Q. Zhao, C. Bai, W. Zhang, Y. Li, G. Zhang, F. Zhang, X. Fan, Ind. Eng. Chem. Res. 53
(2014) 4232.
[7] Y. Leng, J. Zhao, P. Jiang, J. Wang, ACS Appl. Mater. Interfaces 6 (2014) 5947.
[8] X.T. Ma, X.H. Lu, C.C. Wei, Z.S. Zhao, H.J. Zhan, D. Zhou, Q.H. Xia, Catal. Commun. 67
(2015) 98.
[9] J.W. Brown, Q.T. Nguyen, T. Otto, N.N. Jarenwattananon, S. Glöggler, L.S. Bouchard,
Catal. Commun. 59 (2015) 50.
[10] R.K. Sharma, A. Pandey, S. Gulati, Polyhedron 45 (2012) 86.
[11] C.I. Fernandes, N.U. Silva, P.D. Vaz, T.G. Nunes, C.D. Nunes, Appl. Catal. A 384 (2010)
84.
[12] M. Fariasa, M. Martinelli, D.P. Bottega, Appl. Catal. A 384 (2010) 213.
[13] A.C. Coelho, S.S. Balula, S.M. Bruno, J.C. Alonso, N. Bion, P. Ferreira, M. Pillinger, A.A.
Valente, J. Rocha, I.S. GonÅalves, Adv. Synth. Catal. 352 (2010) 1759.
[14] K.C. Gupta, A.K. Sutar, Coord. Chem. Rev. 252 (2008) 1420.
[15] P.G. Cozzi, Chem. Soc. Rev. 33 (2004) 410.
[16] C. Che, J. Huang, Coord. Chem. Rev. 242 (2003) 97.
[17] P.K. Khatri, B. Singh, S.L. Jain, B. Sain, A.K. Sinha, Chem. Commun. 47 (2011) 1610.
[18] A. Lazar, P. Sharma, A.P. Singh, Microporous Mesoporous Mater. 170 (2013) 331.
[19] S.L. Jain, B. Sain, Adv. Synth. Catal. 350 (2008) 1479.
[20] M.R. Maurya, U. Kumar, P. Manikandan, Dalton Trans. (2006) 3561.
[21] S. Verma, M. Nandi, A. Modak, S.L. Jain, A. Bhaumik, Adv. Synth. Catal. 353 (2011)
1897.
[22] H.P. Mungse, S. Verma, N. Kumar, B. Sain, O.P. Khatri, J. Mater. Chem. 22 (2012)
5427.
[23] S. Xia, F. Liu, Z. Ni, W. Shi, J. Xue, P. Qian, Appl. Catal. B 144 (2014) 570.
[24] M. Moghadama, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork, N.S.
Mirbagheri, Appl. Organomet. Chem. 24 (2010) 708.
4. Conclusion
[25] F. Liu, L. Wang, Q. Sun, L. Zhu, X. Meng, F. Xiao, J. Am. Chem. Soc. 15 (2012) 16948.
[26] G.J.J. Chen, J.W. Mcdonald, W.E. Newton, Mechanistic Implications, Inorg. Chem. 15
(1976) 2612.
In conclusion, we have developed novel porous heterogeneous
organic metal molybdenum catalyst DVB–AA–Mo by immobilization
of MoO2(acac)2 on amino-containing cross-linked copolymer via