Oxidation and reduction of various substrates over a Pd(II) containing post-synthesis metal organic framework

Article abstract of DOI:10.1007/s10562-012-0943-9

A palladium containing metal-organic framework (MOF) compound has been synthesized from MOF, (Zn₄O)₃(BDC-NH₂) ₃(BTB)₄ through Schiff base condensation reaction and complexation of Pd(II). Pd-MOF was found to be an effective heterogeneous catalyst for the oxidation and hydrogenation of various substrates under mild reaction conditions. This catalytic method is highly active and shape selective. Graphical Abstract: [InlineMediaObject not available: see fulltext.]

Full text of DOI:10.1007/s10562-012-0943-9

Catal Lett (2013) 143:122–125
DOI 10.1007/s10562-012-0943-9
Oxidation and Reduction of Various Substrates Over a Pd(II)
Containing Post-Synthesis Metal Organic Framework
•
Shahin Hossain Myung-Jong Jin Ji-hoon Park
•
•
•
Qian Yingjie Da-Ae Yang
Received: 28 October 2012 / Accepted: 15 November 2012 / Published online: 6 December 2012
Ó Springer Science+Business Media New York 2012
Abstract A palladium containing metal-organic frame-
work (MOF) compound has been synthesized from MOF,
(Zn4O)3(BDC–NH2)3(BTB)4 through Schiff base conden-
sation reaction and complexation of Pd(II). Pd–MOF was
found to be an effective heterogeneous catalyst for the
oxidation and hydrogenation of various substrates under
mild reaction conditions. This catalytic method is highly
active and shape selective.
both in industrial chemistry as well as in organic synthesis.
In particular, the controlled oxidation and reduction without
forming by-products is a challenging task for chemists.
Heterogeneously catalysed noble metals (Au, Pd, Pt) in the
aerobic oxidation of benzyl alcohol have been extensively
discussed by Hutching [22]. Among these noble metals, a
great number of studies have also been devoted to Pd-based
catalyst. Corma and coworkers [23] demonstrated shape-
selectivity in the hydrogenation of olefins, alcohol oxidation
and Suzuki C–C coupling reaction in Pd-containing MOFs.
They demonstrated that the active sites are located in the
framework metal centre for MOF catalyst. It was also
reported [18] that Pd-supported MOF-5 catalyst shows two
times higher activity than commercial Pd/C catalyst in the
hydrogenation of ethyl cinnamate using molecular hydro-
gen; the active Pd is located at the outer surface of the
MOF-5 and the catalyst was reusable without leaching of Pd
during the reaction.
Keywords Oxidation and reduction reactions ꢀ
Palladium acetate ꢀ Metal-organic framework ꢀ Selectivity
1 Introduction
Metal organic frameworks (MOFs) are porous and crystal-
line materials that are comprised of metal ions or metal ion
clusters and bridging organic multidentate ligands [1–6] that
have immersed increasing attention owing to their high
surface areas, uniform pores, and chemical tenability [7–9].
These porous crystalline materials are proving potential
applications in use such as separation, gas storage and
catalysis [10–15]. Past decade, several groups have shown
that MOFs can act as heterogeneous catalysts in a variety of
reactions such as alkene oxidation, aldol condensation,
hydrogenation, and epoxide ring opening [16–21]. The
selective oxidation and reduction is a highly desirable for
The aromatic polycarboxylate transition metal com-
plexes are interesting due to the variety of bridging abilities
of the polycarboxylate ligand in the formation of extended
porous frameworks. 4,40,40-benzene-1,3,5-triyl-tribenzoic
acid (BTB) presents interesting characteristics such as
three carboxylate groups which allows interesting struc-
tures with high porosity [9, 24]. A common representative
is UMCM-1-NH2, which consists of Zn4O6? clusters as
metal centers and NH2–BDC, BTB as linkers forming a
hexagonal crystal and a highly porous MOF reported by
Cohen and coworkers [25]. Various post-synthetic modi-
fication of this MOF has been reported for incorporating a
wide range of functional group [19, 20, 26]. Yaghi and
coworkers [26] reported the formation of imine through
2-pyridinecarboxaldehyde and UMCM-1-NH2 and metal-
lated with [PdCl2(CH3CN)2]. However, no any reactivity
was reported so far for the palladium-containing active site in
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-012-0943-9) contains supplementary
material, which is available to authorized users.
S. Hossain ꢀ M.-J. Jin (&) ꢀ J. Park ꢀ Q. Yingjie ꢀ D.-A. Yang
Department of Chemical Engineering, Inha University,
Incheon 402-751, Korea
e-mail: mjjin@inha.ac.kr
123

Oxidation and Reduction of Various Substrates
123
catalysis reaction. The BTB and H2N–BDC ligands may be
good choice for the preparation of highly porous structure
material. In this work, we describe the post-functionalization
of crystal (Zn4O)3(BDC–NH2)3(BTB)4 [26] which was
reacted a sequence of chemical reactions to make a cova-
lently bound chelating ligand and then used for the metalli-
zation with Pd(II) without loss of structural framework of
MOF. Here, we also report the detail catalytic activities of
Pd(II)-containing MOFs as a heterogeneous catalyst for
various oxidation and hydrogenation reactions under mild
reaction conditions. The modified MOF is shown to be an
active, stable and reusable MOF-based catalyst. To the best
of our knowledge, this is the first report on post-synthetically
modified MOF containing Pd(II) for heterogeneous catalyst
using oxidation and reduction reactions.
crystals were washed with toluene and acetone. To bind
metal ions, approximately 1.1 eq. Pd(OAc)2 was added in
acetone and kept for 12 h at room temperature. Prior to
drying, the solvated MOF samples were soaked in chlo-
roform for 3 days, during this time the solvent was changed
three times every 24 h.
2.3 General Procedures for Catalytic Reactions
with Catalyst MOF-3
2.3.1 Oxidation Reaction with Catalyst MOF-3
Chloroform containing MOF-3 was dried under vacuum at
room temperature for 2 h. Dried MOF samples (4 mg,
1.5 mol%) were placed in a vial and immersed in 1 mL of
anhydrous toluene, followed by alcohol (0.2 mmol). The
mixture was stirred under open air at 85 °C for appropriate
time. After completion of the reaction, the catalyst was
filtered off and the yield was measured using a GC (Agilent
Tecnologies, 7890A) fitted with a high performance HP-1
capillary column (60 m, 0.32 mm, 0.25 lm) and a FID.
The catalyst was recovered from the residue by centrifuge
and washed with toluene for next run.
2 Experimental
2.1 Equipment and Reagents
2-Aminoterephthalic acid (99 %, Aldrich), zinc nitrate
tetrahydrate (Merck), N,N-dimethylformamide (99.9 %,
Aldrich), toluene (99.5 %, Aldrich), 2-pyridinecarboxal-
dehyde (99 %, Aldrich), palladium acetate (99.9 %,
Aldrich) were purchased and other reagents and solvents
were also purchased from commercial suppliers and used
without any further purification.
2.3.2 Reduction Reaction with Catalyst MOF-3
MOF-3 samples (4 mg, 1.5 mol%) were placed in a small
vial and immersed in 1 mL methanol, followed by alkene
(0.2 mmol). In the case of lower solubility of trans-stilbene
in methanol, benzene was added in the reaction mixture. The
rubberic capped vial was then stirred at room temperature
with hydrogen at atmospheric pressure (using hydrogen-
filled balloons). On completion, the reaction mixture was
centrifuged and solution containing product was found by
GC analysis. Without any purification, in most cases, the
purity of the products was found to be[99 %.
X-ray powder diffraction patterns were recorded on a
˚
Rigaku diffractometer using Cu Ka (k = 1.54 A). Nitrogen
adsorption/desorption isotherms were measured on a Mi-
cromeritics ASAP 2020 surface analyzer at -196 °C. Prior
to the measurement, the sample was degassed at 50 °C under
vacuum for 12 h. Thermogravimetric analyses, in a range
25–600 °C, were carried out on a TGA (Scinco S-1000)
system under a N2 flow at a heating rate of 10.0 °C/min. The
FTIR spectra were obtained on a Nicolet iS10 FTIR spec-
1
trometer (Thermo Scientific) at ambient temperature. H
2.3.3 Catalyst Recycling
NMR was recorded on Varian Unity Inova. FT-NMR spec-
trometer (400 MHz) using a solution prepared by digesting
10 mg of sample in mixture of d6-DMSO (0.750 lL) and
dilute DCl (120 lL, 35 % DCl in D2O). Metal contents were
determined using inductively coupled plasma-MASS spec-
After the completion of a reaction, the mixture was cen-
trifuged and methanol solution was decanted. The solids
were washed with fresh methanol (2 9 2 mL), isolated by
centrifugation between washes and used for next run.
´
trometry (ICP-MS, Perkin-Elmer elan 6100). C, H and N
analyses were performed using a FLASH EA 1112 elemental
analyzer (Thermo Electron Corporation). The samples were
dried at 50 °C under vacuum for 12 h before elemental and
metal analyses.
3 Results and Discussion
The synthetic route of Pd-MOF-imine is shown in
Scheme 1. MOF-imine was synthesized according to the
literature [26]. Pd–MOF–imine was prepared by dissolving
palladium acetate in acetone at room temperature and
treating the resulting solution with MOF–imine at room
2.2 Synthesis of Catalyst
MOF-1 and MOF-2 were prepared using methods previ-
ously reported in the literature [26]. After that yellow
123

124
S. Hossain et al.
Table 1 Oxidation of different substrates using open air in the
presence of MOF-3
Entry
1
Substrate
Product
Time
(h)
GC yield
(%)
Benzyl alcohol
5.5
88 (55)a
O
R1
R2
5.5
5.5
80
74
Scheme 1 Synthetic route for MOF-3 catalyst
2
3
Cinnamyl alcohol
24
24
79
13
O
14000
12000
10000
8000
6000
4000
2000
0
O
O
sec-Phenethyl alcohol
3
4
4-Methoxybenzyl
alcohol
24
60
2
Reaction conditions: alcohol (0.2 mmol), catalyst MOF-3 (1.5 mol%),
solvent 1 mL toluene, 85 °C, R1-1st recycle, R2-2nd recycle
1
a
SiO2–schiff base–Pd(II) 3 mol% catalyst using O2, at 90 °C, 15 h [32]
5
10
15
20
2 Theta/deg.
sec-phenethyl alcohol and 4-methoxybenzyl alcohol, using
open air as oxidant at 85 °C. At 85 °C, benzyl alcohol was
converted into benzaldehyde with 88 % yield after 5.5 h.
However, cinnamyl alcohol, sec-phenethyl alcohol and
4-methoxybenzyl alcohol showed much lower yield than that
of benzyl alcohol under identical reaction conditions
(Table 1). The yield of corresponding aldehyde was
decreased in the following order: benzyl alcohol ꢁ cin-
namyl alcohol [4-methoxybenzyl alcohol ꢁ sec-phen-
ethyl alcohol (Table 1).
Fig. 1 X-ray powder diffraction patterns 1, 2, 3 represent MOF-1,
MOF-2 and MOF-3 respectively
temperature for 10 h. The material was washed with MC
and dried at 50 °C.
The characterization of MOFs was conducted by XRD,
BET surface area measurement, FT-IR, TGA and elemental
analysis. The micro-analytical results of MOF-3 suggested
its formula (Zn4O)3[(BDC–C6H5N2Pd(OAc)2]3(BTB)4
(see ESI). The X-ray powder diffraction pattern of MOF-1,
MOF-2 and MOF-3 are shown in Fig. 1. The X-ray powder
diffraction pattern of MOF-3 shows identical peak pattern as
those previously reported for MOF-1 [26] indicating that the
same structural framework is maintained during the post-
modification reaction (Fig. 1). N2 adsorption isotherms at
-196 °C MOF-3 are shown in Fig. S1 (see ESI). The BET
surface area of parent MOF-1 and post-synthesis MOF-3 are
3,900 [27] and 1,073 m2/g respectively. The decrease of the
surface area of MOF-3 with relative to parent MOF is due to
the addition of mass of Pd(Ac)2 to parent MOF. Similar
observations were found in other MOFs after post-modifi-
cation [28, 29]. The 1H NMR spectra of digested MOFs are
shown in Fig. S2 (see ESI). MOF-3 showed peaks at 1.8 and
8–9 ppm range for the methyl group of acetate and nitrogen
A comparison of silica supported Pd(II) with MOF-3 in the
oxidation of benzylalcohol are summarized in Table 1, which
may be helpful in suggesting the relationship between the
structure and performances ofthe catalytic centre. The present
MOF-3 showed much higher yield % of aldehyde than that
reported for silica supported palladium catalyst [32].
The modified MOF-3 was further tested for the hydro-
genation of various important alkenes. We chose the reac-
tants to explore the potential shape-selective properties of
the molecules. The results are shown in Table 2. It is found
that styrene showed highest activity than other alkenes.
On the other hand, the activities are decreased in the fol-
lowing odrer: trans-chalcone \ trans-stilbene ꢂ cinnamyl
acetate \ styrene, which indicated the shape selectivity of
the above said reaction.
1
containing ring respectively. H NMR of other digestion
The stability of the catalyst was studied by performing
repeated reaction using the same reaction conditions. At the
end of each reaction, the catalyst was recovered by filtration
and washed with solvent and then dried. The results are
shown in Tables 1 and 2. The yield of product was almost
identical irrespective of the number of cycles performed.
MOFs were found in similar value [30, 31].
The MOF-3 catalyst was tested in the oxidation and
hydrogenation reactions and the experimental results are
summarized in Tables 1 and 2.
The MOF-3 catalyst was tested in the oxidation of
various alcohols, viz., benzyl alcohol, cinnamyl alcohol,
123

Oxidation and Reduction of Various Substrates
125
Acknowledgments This work was supported by
Research Foundation of Korea Grant funded by the Korean Govern-
ment (2012-003212) and Inha University Research Grant.
a
National
Table 2 Reduction of different substrates using hydrogen in the
presence of MOF-3
Entry Substrate
Product
Time GC yield
(h)
(%)
OH
1
Benzaldehyde
12
91
References
1. Ferey G (2008) Chem Soc Rev 37:191–214
2. Rosi NL, Eckert J, Eddaoudi M, Vodak DT, Kim J, O’Keeffe M,
Yaghi OM (2003) Science 300:1127
3. Gardner GB, Venkataraman D, Moore JS, Lee S (1995) Nature
374:792–795
2
3
Styrene
0.5 100
Cinnamyl acetate
O
3
99
4. Yaghi OM, O’Keeffe M, Ockwig NW, Chae HK, Eddaoudi M,
Kim J (2003) Nature 423:705–714
O
5. Ockwig NW, Delgado-Friedrichs O, O’Keeffe M, Yaghi OM
(2005) Acc Chem Res 38:176–182
6. Kitagawa S, Kitaura R, Noro SI (2004) Angew Chem Int Ed
43:2334–2375
R1
R2
3
3
98
95
7. Eddaoudi M, Kim J, Rosi N, Vodak D, Wachter J, O’Keeffe M,
Yaghi OM (2002) Science 295:469–472
8. Chae HK, Siberio-Perez DY, Kim J, Go Y, Eddaoudi M, Matzger
AJ, O’Keeffe M, Yaghi OM (2004) Nature 427:523–527
9. Koh K, Wong-Foy AG, Matzger AJ (2008) Angew Chem Int Ed
47:677–680
10. Fujita M, Kwon YJ, Washizu S, Ogura KJ (1994) Am Chem Soc
116:1151
11. Evans OR, Ngo HL, Lin WJ (2001) Am Chem Soc 123:10395
4
5
trans-Stilbene
trans-Chalcone
3
25
2
O
3
12
15
´
12. Ferey G, Latroche M, Serre C, Millange F, Loiseau T, Percheron-
Guegan A (2003) Chem Commun 24:2976
13. Murray LJ, Dinca M, Long JR (2009) Chem Soc Rev
38:1294–1314
6
7
Cyclohexene
2
2
90
2-Cyclohexen-1-one
O
100
14. Alaerts L, Maes M, Giebeler L, Jacobs PA, Martens JA, Denayer
JFM, Kirschhock CEA, De Vos DE (2008) J Am Chem Soc
130:14170
15. Li JR, Kuppler RJ, Zhou HC (2009) Chem Soc Rev
38:1477–1504
8
4-Methoxybenzaldehyde
OH
12
97
16. Cho SI, Ma B, Nguyen ST, Hupp JT, Albrecht-Schmitt TE (2006)
Chem Commun 2563–2565
O
17. Gascon J, Aktay U, Hernandez-Alonso MD, van Klink GPM,
Kapteijn F (2009) J Catal 261:75–87
18. Opelt S, Tu¨rk S, Dietzsch E, Henschel A, Kaskel S, Klemm E
(2008) Catal Commun 9:1286–1290
Reaction conditions: substrates (0.2 mmol), catalyst MOF-3
(1.5 mol%), solvent 1 mL methanol, room temperature, R1-1st
recycle, R2-2nd recycle
19. Tanabe KK, Cohen SM (2010) Inorg Chem 49:6766–6774
20. Garibay SJ, Wang Z, Cohen SM (2010) Inorg Chem
49:8086–8091
21. Dhakshinamoorthy A, Alvaro M, Garcia H (2010) Chem Eur J
16:8530–8536
22. Hutchings GJ (2008) Chem Commun 1148
23. Llabres FX, Xamena I, Abad A, Corma A, Garcia H (2007) J
Catal 250:294
The 1H NMR spectrums (see ESI) of the solid catalyst after
reuse was indistinguishable from the fresh catalyst, sug-
gesting that no structural deterioration or any organic mol-
ecules decomposition occurred after catalytic reaction.
24. Li Y, Yang RT (2007) Langmuir 23:26
25. Wang Z, Tanabe KK, Cohen SM (2009) Inorg Chem 48:296–306
26. Doonan CJ, Morris W, Furukawa H, Yaghi OM (2009) J Am
Chem Soc 131:9492–9493
4 Conclusions
In this work, we describe the post-synthesis modification of
MOF, (Zn4O)3(BDC–NH2)3(BTB)4, containing Pd(II). The
Pd-containing MOF catalyst showed remarkable activity
for the oxidation of benzyl alcohol to benzaldehyde with
high substrate conversion and product selectivity. The
modified MOF-3 showed good activity and shape selec-
tivity in hydrogenation reactions of various industrially
important alkenes. The catalyst was sufficiently stable and
could be reused several times.
27. Tanabe KK, Cohen SM (2009) Angew Chem Int Ed
48:7424–7427
28. Ding SYD, Gao J, Wang Q, Zhang Y, Song WG, Su CY, Wang
W (2011) J Am Chem Soc 133:19816–19822
29. Bloch ED, Britt D, Lee C, Doonan CJ, Uribe-Romo FJ, Furukawa
H, Long JR, Yaghi OM (2010) J Am Chem Soc 132:14382–14384
30. Wang Z, Cohen SM (2008) Angew Chem 120:4777–4780
31. Oisaki K, Li Q, Furukawa H, Czaja AU, Yaghi OM (2010) J Am
Chem Soc 132:9262–9264
32. Choudhary D, Paul S, Gupta R, Clark JH (2006) Green Chem
8:479–482
123