Immobilisation of a molecular epoxidation catalyst on UiO-66 and -67: the effect of pore size on catalyst activity and recycling

Article abstract of DOI:10.1039/c5dt01340b

Amino-functionalised metal-organic frameworks UiO-66 and -67 were post-synthetically modified with salicylaldehyde. A molybdenum complex was immobilised on the resulting materials. They were characterised by ¹³C-MAS-NMR, XPS and PXRD to confirm immobilisation and stability. The immobilised complex is an active and reusable catalyst for olefin epoxidation with tert-butyl hydroperoxide (TBHP) as an oxidant. It is shown that the effective pore size, probed with Brunauer-Emmett-Teller (BET) surface area analysis and the number of amino groups affect the diffusion of reactants and products, as well as catalyst recycling.

Full text of DOI:10.1039/c5dt01340b

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Kühn, Dalton Trans., 2015, DOI: 10.1039/C5DT01340B.
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Immobilisation of a molecular epoxidation catalyst on UiO-66 and
67: effect of pore size on catalyst activity and recycling
-
Received 09th April 2015,
Accepted 00th January 20xx
a
a,
a
a
b
Marlene Kaposi, Mirza Cokoja, * Christine H. Hutterer, Simone A. Hauser, Tobias Kaposi,
b
a
b
a
Florian Klappenberger, Alexander Pöthig, Johannes V. Barth, Wolfgang A. Herrmann and Fritz
DOI: 10.1039/x0xx00000x
a,
E. Kühn *
www.rsc.org/dt
Amino-functionalised metal-organic frameworks UiO-66 and -67 were post-synthetically modified with salicylaldehyde. A
1
3
molybdenum complex was immobilised on the resulting materials. They were characterised by C-MAS-NMR, XPS and
PXRD to confirm immobilisation and stability. The immobilised complex is an active and reusable catalyst for olefin
epoxidation with tert-butyl hydroperoxide (TBHP) as oxidant. It is shown that the effective pore size, probed with
Brunauer-Emmett-Teller (BET) surface areas, and the number of amino groups affect the diffusion of reactants and
product, as well as catalyst recycling.
and more specifically metal-organic frameworks (MOF) appear
to be interesting supports for molecular catalysts, since they
allow both a variation of pore size and introduction of
Introduction
The catalytic epoxidation of olefins is a very important reaction
in chemical industry since epoxides are starting materials for a
1
1
functional groups by design of the organic linkers. So far,
some epoxidation catalysts have been immobilised on IRMOF-
1
,2
plethora of chemicals. Although there are numerous highly
active molecular catalysts of titanium, vanadium, manganese,
3
rhenium, and more recently, iron, most of them have been
1
2
13
paddle-wheel MOFs, or MIL-101(Al) and MIL-47. To
14
15
3,
the best of our knowledge there are three reports of Mo(VI)
species immobilised on MOFs, but either the conversions are
neglected so far in industrial epoxidations since they are
usually too expensive and cannot be easily recycled for a large
number of runs.
1
6
lower compared to the homogeneous analogue,
the
materials decompose over time in presence of an excess of
1
oxidant or comparability is not possible, because no catalyst
7
Molybdenum complexes have been used as catalysts for the
industrial Halcon-ARCO, and more recently, the Sumitomo
2
processes. In the 1970s two mechanistic pathways for the
1
0
loading is reported. Hence, the molecular catalyst must be
strongly bound to the MOF, the pore size must allow for a
facile diffusion of both substrate and product, and the MOF
must be stable to air, water and oxidants. Zr-based UiO
frameworks 66 and -67 (UiO = Universitetet i Oslo) by Lillerud
Mo-catalysed epoxidation were proposed, both involving the
formation of a Mo-peroxo intermediate, which is transferring
4
,5,6,7
an oxygen atom to the olefin.
1
8,19
et al.
are exceptionally stable compounds, which have
Molecular molybdenum epoxidation catalysts have been
heterogenised to various supports over the last 15 years (silica,
including MCM materials, polymers, carbon, etc.) to facilitate
recently been used as support materials for epoxidation
1
reactions.
0,17
8
In this work, UiO-66 and -67 materials with varying contents of
amino groups were fabricated and postsynthetically
functionalised whereby the amino groups were employed for
the immobilisation of a molecular molybdenum catalyst. The
postsynthetic method used in this work has been applied in
catalyst recycling. However, in many cases the immobilisation
is associated either with a loss of activity compared with the
homogeneous congeners, or with a slow but significant
catalyst leaching into the reaction slurry. Particularly the
activity loss is a serious issue, originating from both
diminishing accessibility of the metal centres and diffusion
1
2b
20
21
the immobilization of metals such as V(V) , Au(III) , Ni(II)
2
2
9
,10
and Ir(I) , however, the incorporation of Mo(VI) into an
amino-containing MOF is reported for the first time. The
obtained entities have been applied for the epoxidation of
olefins, with special regard to material recycling and stability.
limitations.
For this reason, porous coordination polymers,
Results and Discussion
Synthesis and characterisation
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Fig. 2 Mo 3d XPS line with binding energies of 232.8 and 236.0 eV for the Mo 3d5/2 and
d3/2 levels, respectively.
3
experimental values. Furthermore the degree of
functionalisation of Mo@UiO MOFs can vary and therefore has
to be considered. The solvents most presumably interact with
either the SBU or the amino group (in the case of the
functionalised MOFs) via hydrogen bonds, and therefore a
complete removal of all solvent molecules is difficult. It also
has to be noted that for the functionalised Mo@UiO-67 and
Mo@UiO-67 mixed the content of residual solvents is
significantly lower than for the Mo@UiO-66 and Mo@UiO-66
mixed MOF composites (see the Experimental Section), which
have smaller quantities. Therefore, it can be concluded that in
dependence of the pore size solvent removal is hindered and
thus can also negatively affect the diffusion of substrates in
catalysis (see below).
2
Fig. 1 X-ray single crystal structure of UiO-67-NH (Amino groups are disordered due to
2
the statistical distribution of the NH -groups within the pores and are therefore
omitted for clarity, see the Supporting Information (SI) for details).
A set of four carrier materials was synthesised, including the
1
fully amino-functionalised UiOs, as well as mixed UiOs, where
8
23
only 1/6 of the linkers contain –NH
functionalisation – full or partial – reduces the effective pore
size. The structure of UiO-67-NH was confirmed by single
crystal X-ray diffraction (see Fig. 1) using a crystal obtained via
2
groups. Already the
2
2
4
modulated synthesis with benzoic acid. Despite all efforts,
single crystals of the Mo complex immobilised on UiO
materials could not be obtained due to the statistical
Fig. 2 shows the powder X-ray diffraction (PXRD) patterns of
UiO-67-mixed (4) before and after functionalisation (Fig. 3a-c),
1
3
C MAS-NMR spectra of the same structure are shown in Fig.
. The patterns are similar to previous reports, showing that
distribution of the NH
The amino groups in the functionalised MOFs UiO-66-NH
UiO-66 mixed ( ), UiO-67-NH ) and UiO-67 mixed ( ) were
transformed with salicylaldehyde to salicylidene (SI)
substituent via previously reported vapour diffusion
reaction. The washed and dried materials were then treated
with a solution of [MoO (acac) ] (acac = acetylacetonate) in
2
-groups within the pores.
4
2
(1),
1
8,24
the UiO-type structure is formed.
After modification with
2
2
(
3
4
13
the Mo compound C MAS-NMR show an additional peak at
4-25 ppm corresponding to the methyl groups of
a
2
a
9
acetylacetonate. In the Mo-NMR spectrum no signal was
5
2
5
9
5
observed due to both low natural abundance of the Mo
2
2
9
5
isotope (ca. 15 %), the quadrupolar moment of the Mo
nucleus (I = 5/2), leading to broad signals and the low
concentration of immobilised Mo.
methylene chloride, washed and dried again prior to
characterisation and catalysis tests (for details see the
Experimental Section). The steps of the modification are
shown in Scheme 1. The obtained MOFs are denoted as UiO-SI
and Mo@UiO respectively. Their molybdenum content after
modification was determined by elemental analysis. The values
for carbon, hydrogen and nitrogen deviate from the expected
ones and were different for every batch of MOF, because
different amounts of solvent remained in the pores. Even
extensive drying could not completely remove the solvents.
This is in particular the case for the UiO-66 materials, which
exhibit smaller pores than the UiO-67 type composites. In the
experimental part the values for the MOFs used in catalysis are
Additionally, XPS measurements were performed to confirm
the valence of the immobilised molybdenum. The Mo3d
given. Different amounts of H
the unmodified MOFs) and additionally CH
Mo@UiOs had to be added to the calculation to fit the
2
O and dimethylformamide (for
2
2
Cl for the
2
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-1
calculated to be 130 h (after 15 min). With the homogeneous
O
NH
2
OH
vapor
diffusion
O
O
O
O
O
Mo
O
2 2
CH Cl ,4d, RT
O
O
O
N
N
Mo
O
OH
O
Scheme 1 Post-functionalisation route of UiO-MOFs with salicylaldehyde and
MoO (acac) ].
[
2
2
Fig. 3 PXRD patterns of (a) UiO-67-mixed, (b) UiO-67-SI-mixed, (c) Mo@UiO-67-mixed
spectrum exhibits two clear peaks, one at 232.8 eV and one at
36.0 eV (see Fig. 2). Both the binding energy splitting (3.2 eV)
and (d) Mo@UiO-67-mixed after catalysis.
2
and the relative peak intensities (59:41) agree well with
expected values for the spin-orbit coupled Mo3d line (3.13 eV
2
6,16
and 3:2, respectively).
Accordingly, the XPS signature
evidences the presence of a single Mo species with an
oxidation state of 6+ as concluded from the measured binding
energies.
2
-1
For UiO-67-mixed a specific surface area of 2200 m g was
found using BET measurements (Fig. 5), while the surface of
2
-1 27
2
fully functionalised UiO-67-NH is reported as 1800 m g ,
which is clearly showing the effect of reducing the number of
amino groups in the porous material. Furthermore for
Mo@UiO-67-mixed BET measurements showed a specific
2
-1
surface area of 2000 m g . Therefore it can be stated that the
pores are not obstructed by the immobilised complex (Fig. 5).
13
Fig. 4 C-MAS-NMR spectra of (a) UiO-67-mixed and (b) Mo@UiO-67-mixed.
Catalytic tests and recycling
All four Mo@UiO composites (wt.% Mo: 8.48% for UiO-66,
5
.69% for UiO-66 mixed, 3.23% for UiO-67 and 2.43% for UiO-
7 mixed) were examined as catalysts for the epoxidation of
6
cyclooctene in neat TBHP (5.5 M in decane) at 50 °C.
After catalysis the Mo@UiO-67-mixed
material
remainsunchanged (see Fig. 3d), suggesting that the
framework is still intact and stable towards TBHP.
While in all cases the selectivity of cyclooctene oxide is very
high, the conversion shows a strong dependence on the
degree of functionalisation (Table 1). Note that the
epoxidation does not take place in the case of UiO-66 and -67
without immobilised Mo catalyst (not shown in Table 1).
Additionally, in all cases a reduction of the reaction
temperature has a detrimental effect on the conversion.
Kinetic studies have been performed (Figure 6) and TOF was
2
Fig. 5 Nitrogen adsorption isotherms of mixed UiO-67-NH and Mo@UiO-67 mixed.
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-
1
a
analogue a TOF of 870 h is reached. The reduced TOF for the Table 1. Epoxidation of cyclooctene with different catalysts at 50 °C
MOF catalyst can be attributed to the intrinsic diffusion
b
Catalyst
Substrate
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
1-Octene
Conv. (%)
63
Sel. (%)
limitation of heterogeneous systems. A leaching experiment
was performed with Mo@UiO-67 by separating the reaction
mixture from the solid catalyst after 50 % conversion (30 min).
The remaining solution showed an increase in conversion to 62
Mo@UiO-66
100
100
100
100
70
Mo@UiO-66 mixed
Mo@UiO-67
94
100
100
62
Mo@UiO-67 mixed
Mo@UiO-67 mixed
Mo@UiO-67 mixed
%
over the next 4 h. However, it has to be noted that substrate
and oxidant without catalyst yielded in a conversion of 8 %
after 4 h.Therefore it can be concluded that no leaching
occurred. The catalysts were used for ten cycles to investigate
the stability and recyclability of the materials. After each cycle
the MOFs were separated from the reaction products by
decantation, washed with dichloromethane and dried in
vacuum overnight either at room temperature (run 1-3) or at
Styrene
38
68
a Reaction conditions: 1 mol % catalyst, 150 mol % TBHP, 50 °C, 4h,
b Selectivity to cyclooctene oxide
150 °C (run 4-10). Powder X-ray diffraction (PXRD)
measurements after the reactions confirmed that the
frameworks stay intact during catalysis and recycling (Fig. 3 for
Mo@UiO-67 mixed, Fig. S1-S3 in the SI for the others). In a
parallel study by Valente et al. recycling was not possible since
1
7
the network decomposed.
Best recycling results were achieved with Mo@UiO-67 mixed
Fig. 7). This fact can be attributed to the larger pore size of
(
the mixed MOF compared to Mo@UiO-67 and the UiO-66
series. Therefore the pores are not as easily obstructed and
the remaining educts, products and by-products can be
removed in vacuum even at room temperature. However, for
an efficient recycling of the unmixed MOF it is necessary to
heat the system to 150 °C to remove all remaining substrate,
solvent and product molecules.
Fig. 6 Plot of yield versus time in the oxidation of cyclooctene with TBHP and 1 mol % of
Mo@UiO-67-mixed at 50 °C and [MoO (acac)(PhN=C-PhO)] at room temperature.
2
After several runs even heating could not clear the pores of
the unmixed Mo@UiO-67 and the UiO-66 MOFs completely,
leading to a drop in activity. This was most prominently
observed for Mo@UiO-66, which is exhibiting the smallest
pores. A comparison of the catalytic results with those
1
0
reported previously is not possible since in this work the Mo
content in the catalyst has not been given.
Furthermore, Mo@UiO-67 mixed was tested for epoxidation
of 1-octene and styrene (see Table 1, entries 5 and 6). In
contrast to cyclooctene, here the conversions are lower, which
can be attributed to the fact that additionally to its Lewis acid
character the MOF contains OH groups coordinated to the
zirconium clusters. Therefore diols are formed from less stable
epoxides. To eliminate the OH groups the MOF was heated in
2
8
vacuum to 300 °C for 48 h prior to modification and catalysis.
By using this method the selectivity is increased to 100 %,
whereas the conversion for 1-octene drops to 13 % after 24 h.
This effect is most presumably due to tert-butanol
coordinating to the free coordination sites at the zirconium
cluster, which blocks the pores and inhibits further reaction.
To prove this hypothesis, we added tert-butanol to the
dehydrated Mo@UiO-67-mixed material prior to addition of
cyclooctene and TBHP solution. Indeed, the conversion
Fig. 7 Recycling of the different modified MOF catalysts in epoxidation reaction with
cyclooctene.
t
drastically reduces, corroborating the hypothesis that the BuO
groups coordinate to Zr centres and decrease the pore size of
the material, thus limiting substrate diffusion and hence the
conversion.
Conclusions
4
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2
9
In summary, a series of chemically robust composite materials by using the APEXII software package. The measurements
containing molecular molybdenum complexes anchored to were performed on single crystals coated with perfluorinated
UiO-type MOFs has been synthesised. Both the catalyst anchor ether. The crystals were fixed on the top of a glass fiber and
and the porous host network are very stable towards oxidative transferred to the diffractometer. Crystals were frozen under a
conditions and leaching was not observed. It could be shown stream of cold nitrogen. A matrix scan was used to determine
that the catalytic activity depends strongly on the effective the initial lattice parameters. Reflections were merged and
pore size of the carrier material, owing to diffusion limitations corrected for Lorenz and polarisation effects, scan speed, and
3
0
of substrate, product and oxidant. This can be easily background using SAINT. Absorption corrections, including
modulated by changing the content of amino functionalities at odd and even ordered spherical harmonics were performed
3
0
the organic linker. The Mo@UiO catalyst with the highest using SADABS. Space group assignments were based upon
effective pore size can be reused for several times without a systematic absences, E statistics, and successful refinement of
notable loss of activity, rendering this material viable for two- the structures. Structures were solved by direct methods with
3
1
phase epoxidation of various olefins.
the aid of successive difference Fourier maps, and were
2
refined against all data using the APEX 2 software in
9
3
2
33
conjunction with SHELXL-97 and SHELXLE. Methyl hydrogen
atoms were refined as part of rigid rotating groups, with a C–H
Experimental
distance of 0.98 Å and Uiso(H) = 1.5·Ueq(C). Other H atoms were
General Remarks
placed in calculated positions and refined using a riding model,
with methylene and aromatic C–H distances of 0.99 and 0.95
All chemicals were obtained commercially (Aldrich, Acros) and
used without further purification.
Å, respectively, and Uiso(H) = 1.2·Ueq(C). Hydrogen atoms bond to
Liquid NMR spectra were recorded on a Bruker Avance DPX
nitrogen were not refined. Non-hydrogen atoms were refined
400 and a Bruker DRX 400. Chemical shifts are given in parts
with anisotropic displacement parameters. Full-matrix least-
2
per million (ppm) and the spectra were referenced by using
the residual solvent shifts as internal standards
squares refinements were carried out by minimizing Σw(F
2 2
c
o
-
32
F
) with SHELXL-97 weighting scheme.
Neutral atom
1
13
H NMR: 2.50 ppm, C NMR: 39.52
(
dimethylsulfoxide-d
6
,
scattering factors for all atoms and anomalous dispersion
corrections for the non-hydrogen atoms were taken from
34
1
3
ppm). Solid-state C NMR spectra were recorded on a Bruker
Avance 300 spectrometer equipped with a 4 mm BBMAS
probe head and referenced to adamantane as an external
standard at 298 K.
the International Tables for Crystallography. Images of the
35
UiO-67-NH
2
crystal structures were generated by Diamond,
36
for [MoO (acac)(PhN=C-PhO)] by PLATON.
2
Specific surface area, pore diameters and pore size
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
2
distributions were determined by physisorption of N .
Measurements were carried out using a PMI automatic BET-
Sorptometer operating at liquid nitrogen temperature (77 K),
after outgassing under vacuum. The results were calculated
using the weight after outgassing. Prior to analysis the samples
were outgassed to 20 microns vacuum at 250 °C.
publication No.’s CCDC-1026989 ([MoO
2
(acac)(PhN=C-PhO)])
and CCDC-1026990 (UiO-67-NH ). Copies of the data can be
2
obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: (+44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
XPS measurements were performed in a UHV chamber at a
-10
pressure of 5∙10 mbar and approximately 77 K sample
temperature with a non-monochromatic Mg anode source (
1253.6 eV) at magic angle incidence and normal emission.
ℏ
ω
Linker preparation
=
Dimethyl-2-nitrobiphenyl-4,4’-dicarboxylate (1). The compound
3
Data were obtained with a hemispherical electron energy
analyser (100 mm radius) set at a pass energy of 20 eV. To the
Mo3d raw data a Shirley-type background subtraction was
applied and the energy binding scale was calibrated against
7
was prepared similar to literature-known procedure.
A
mixture of nitric acid (56%, 1.3 mL, 74 mmol) and concentrated
sulfuric acid (1.6 mL) was added dropwise to a solution of
the C1s line at 284.8 eV. For peak fitting a Voigt line slope was dimethylbiphenyl-4,4’-dicarboxylate (5 g, 74 mmol) in 50 mL of
employed; no constraints were utilized for relative peak concentrated sulfuric acid at 0 °C under intense stirring. The
energies or intensities.
reaction mixture was maintained at 0-5 °C for 1 h and at 10-
Elemental analysis was obtained from the microanalytical 15 °C for 4 h before being poured on crushed ice. The
laboratory of the Technische Universität München.
precipitated solids were separated by filtration, washed with
X-ray powder diffraction was carried out using a Stoe Stadi P
water and recrystallised from isopropanol. Yield: 4.12 g (71 %)
1
1
diffractometer operated with CuKα radiation (λ = 1.5406 Å)
of colorless powder. H NMR (400 MHz, DMSO-d
6
, ppm) δ =
), 7.56 (d, 2H, J = 8.4 Hz,
’,5’/2’,6’-Ar), 7.76 (d, J = 8.0 Hz, 6-Ar(NO )), 8.06 (d, 2H, J =
.4 Hz, 3’,5’/2’,6’-Ar), 8.31 (dd, 1H, J = 1.65, 8.01 Hz, 5-
and a Ge(111) monochromator in transmission mode. X-ray
single crystal diffraction data were collected on an X-ray single
crystal diffractometer equipped with a CCD detector (APEX II,
κ-CCD), a rotating anode FR591 equipped with a Montel mirror
3
3
8
3 3
.89 (s, 3H, -CH ), 3.94 (s, 3H, -CH
2
13
Ar(NO
2
)), 8.51 (d, 1H, J = 1.55 Hz, 3-Ar(NO
2
)); C NMR (101
optic (UiO-67-NH
2
) or a fine focused sealed tube equipped
(acac)(PhN=C-PhO)])
MHz, DMSO-d
6
, ppm) δ = 52.8, 53.4, 125.4, 128.8, 130.0,
with a graphite monochromator ([MoO
2
1
30.3, 130.9, 133.2, 133.7, 138.9, 141.4, 148.9, 164.8, 166.2.
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Other data matched those previously reported for this for 24 h at 60 °C. The resulting powder was dried under
compound.
vacuum for 16 h.
Dimethyl-2-aminobiphenyl-4,4’-dicarboxylate (2). To a stirred UiO-66: C MAS-NMR: δ = 116.2, 132.5, 138.6, 152.4, 170.7,
solution of dimethyl-2-nitrobiphenyl-4,4’-dicarboxylate (2.9 g, 172.5; elemental analysis (%): calcd. for C48 ∙(9 DMF
O): C 36.53, H 4.21, N 8.52; found: C 32.40, H 4.53, N
3
8
13
34 6 6
H N O32Zr
9
.19 mmol) in 115 mL of methanol tin powder (6.45 g) and + 3 H
.16.
UiO-66 mixed: C MAS-NMR: δ = 118.0, 129.4, 138.1, 148.0,
70.9; elemental analysis (%): calcd. for C48 ∙(15
O): C 29.58, H 3.05, N 0.72; found: C 29.65, H 3.42, N 0.65.
2
8
40 mL of an aqueous 1 M HCl solution were added. The
1
3
suspension was heated to reflux for 2 h under intense stirring
before being poured on to crushed ice. The solution was then
basified with aq. 1 M NaOH solution and the precipitated
solids were separated by filtration. The crude product was
extracted with warm ethyl acetate. Any remaining insoluble
byproducts were removed by filtration over Celite. The solvent
was removed under vacuum and crude product was purified
1
H29NO32Zr
6
H
2
1
3
UiO-67: C MAS-NMR: δ = 119.6, 127.2, 128.6, 130.3, 136.2,
37.9, 142.8, 144.2, 171.9, 172.5; elemental analysis (%): calcd.
∙(8 H O): C 42.84, H 3.17, N 3.57; found: C
2.65, H 2.96, N 3.60.
1
for C84
H
58
N
6
O32Zr
6
2
4
13
UiO-67 mixed: C MAS-NMR: δ = 124.9, 130.1, 134.9, 143.4,
by flash chromatography (ethyl acetate/dichloromethane: 10
1
). Yield: 2.18 g (92 %) of light yellow powder. H NMR (400
1
7
72.3; elemental analysis (%):calcd. for C84
O): C 44.75, H 3.19, N 1.20; found: C 44.74, H 2.75, N 1.2.
were obtained when ZrCl (108
6
H53NO32Zr ∙(1 DMF +
%
H
2
MHz, DMSO-d
6
, ppm) δ = 3.83 (s, 3H, -CH
3
3
), 3.88 (s, 3H, -CH ),
Single-crystals of UiO-67-NH
2
4
5
.23 (s, 2H, -NH ), 7.14 (d, 1H, J = 8.0 Hz, 6-Ar(NH )), 7.22 (dd,
2
2
mg, 0.42 mmol), BPDC-NH (100 mg, 0.42 mmol) and benzoic
2
1H, J = 1.8, 7.8 Hz, 5-Ar(NH
2
)), 7.44 (d, 1H, J = 1.6 Hz, 3-
acid (1.54 g, 12.6 mmol) were dissolved in 12 mL DMF. The
Ar(NH
2
)), 7.61 (d, 2H, J = 8.4 Hz, 3’,5’/2’,6’-Ar), 8.04 (d, 2H, J =
1
resulting mixture was placed in a preheated oven at 35 °C and
3
8
5
1
.4 Hz, 3’,5’/2’,6’-Ar); C NMR (101 MHz, DMSO-d , ppm) δ = slowly heated to 120 °C over a time period of five days and left
6
2
4
2.0, 52.2, 116.0, 117.1, 128.3, 128.5, 128.9, 129.7, 129.9, at that temperature for 12 days.
30.4, 143.7, 145.6, 166.1, 166.5. Other data matched those Modification with salicylaldehyde
prepared using previously reported vapor diffusion
.
UiO-SI MOFs were
previously reported for this compound.
-Aminobiphenyl-4,4’-dicarboxylic acid (BPDC-NH
a
2
5
3
)
8
method. Salicylaldehyde (50 µL, 0.48 mmol, 2 equiv.) was
introduced into a Schlenk tube and the MOFs (1 equiv. of
2
2
.
A
mixture of dimethyl-2-aminobiphenyl-4,4’-dicarboxylate (0.68
g, 2.39 mmol, 1 equiv.) in 13 mL of THF and 13.2 mL of an
aqueous 1M KOH solution was heated to reflux for 16 h. After
cooling to room temperature in air, the THF was removed
under vacuum and the solution was acidified with aq. 1M HCl.
The resulting precipitate was separated by filtration, washed
amino groups; 70 mg, 0.04 mmol UiO-66-NH
mmol UiO-66 mixed; 88 mg, 0.04 mmol UiO-67-NH
.24 mmol UiO-67 mixed) were weight into a conical filter
2
; 400 mg, 0.24
2
; 508 mg,
0
paper and fixed in the Schlenk tube not touching the liquid.
The system was evacuated and heated overnight at 100 °C
under static vacuum. The products were washed with
dichloromethane three times for 24 h and dried under vacuum
with water, then methanol and air-dried. Yield: 0.585 g (95 %)
1
of yellow powder. H NMR (400 MHz, DMSO-d
6
, ppm) δ = 5.15
)), 7.21 (dd, 1H, J
)), 7.41 (d, 1H, J = 1.6 Hz, 3-Ar(NH )),
.58 (d, 2H, J = 8.4 Hz, 3’,5’/2’,6’-Ar), 8.02 (d, 2H, J = 8.4Hz,
1
3
for 16 h. UiO-66-SI: C MAS-NMR: δ = 116.8, 132.3, 138.8,
(
s, 2H, -NH
2
), 7.12 (d, 1H, J = 8.0 Hz, 6-Ar(NH
2
1
3
51.9, 171.5, 172.9; UiO-66-SI mixed: C MAS-NMR: δ = 115.9,
1
1
1
=
7
3
1.4, 7.8 Hz, 5-Ar(NH
2
2
1
33.0, 138.3, 152.0, 170.4; UiO-67-SI: C MAS-NMR: δ = 117.0,
3
1
3
19.8, 127.7, 128.8, 129.6, 134.3, 135.9, 143.3, 173.1, 173.7;
’,5’/2’,6’-Ar), 12.83 (bs, 2H, -CO
, ppm) δ = 116.7, 117.8, 128.8, 129.2, 129.9, 130.3,
30.7, 131.4, 143.8, 145.9, 167.6, 168.0. Other data matched
2
H); C NMR (101 MHz,
elemental analysis (%): C 53.37, H 2.92, N 2.96; found: C 45.78,
DMSO-d
6
1
H 2.74, N 2.69; UiO-67-SI mixed: C MAS-NMR: δ = 119.7,
3
1
1
30.4, 134.1, 143.3, 172.2; elemental analysis (%):C 48.80, H
.57, N 0.63; found: C 47.81, H 3.22, N 0.72.
those previously reported for this compound.
2
Modification with [MoO
imide groups; 61 mg, 0.03 mmol UiO-66-NH
mmol UiO-66-SI mixed; 72 mg, 0.03 mmol UiO-67-NH
2
(acac)
2
]. Dried MOFs (1 equiv. of
-SI; 182 mg, 0.1
-SI; 229
Catalyst preparation
1
8
2
Preparation of UiO-MOFs . All preparations were performed
in a 100 mL screw thread glass vials. ZrCl (650 mg,
.73 mmol,) and the linker (500 mg (2.73 mmol) 2-
2
4
mg, 0.1 mmol UiO-67-SI mixed) were reacted with
bis(acetylacetonato)dioxomolybdenum(VI) (100 g, 0.31 mmol)
in dichloromethane over four days under inert atmosphere.
The products were washed with dichloromethane three times
for 24h and dried under vacuum for 16 h.
2
2
aminotherephthalic acid for UiO-66-NH ; 83 mg (0.45 mmol) 2-
aminoterephthalic acid and 382 mg (2.28 mmol) terephthalic
acid for UiO-66 mixed; 703 mg (2.73 mmol) BPDC-NH for UiO-
7-NH ; 117 mg (0.45 mmol) BPDC-NH and 569 mg (2.28
2
6
2
2
13
Mo@UiO-66: C MAS-NMR: δ = 25.0, 118.5, 133.1, 138.8,
mmol) biphenyl-4,4’-dicarboxylic acid for UiO-67 mixed) were
dissolved in 64 mL DMF and water (0.2 mL, 11.1 mmol). The
resulting mixture was placed in a preheated oven at 80 °C for
1
50.9, 171.8; elemental analysis (%): calcd. for
∙(9 DMF + 20 H O + 15 CH Cl ): C 31.62, H
.84, N 3.69, Mo 8.42; found: C 32.06, H 3.93, N 3.78, Mo 8.48.
C
108
H84Mo
5
N
6
O57Zr
6
2
2
2
3
12 h and then held at 100 °C for 24 h. After cooling to room
13
Mo@UiO-66 mixed: C MAS-NMR: δ = 25.9, 118.2, 129.6,
temperature in air, the liquid was decanted and the resulting
solid was washed with 30 mL of absolute ethanol three times
1
37.4, 163.3, 171.6; elemental analysis (%): calcd. for
∙(2 DMF + 30 H O + 8 CH Cl ): C 27.73, H
C
72
H54Mo
2
N
2
O42Zr
6
2
2
2
3.90, N 1.50, Mo 5.15; found: C 26.74, H 3.10, N 1.38, Mo 5.69.
6
| Dalton Trans., 2015, 44, 1-7
This journal is © The Royal Society of Chemistry 2015
Please do not adjust margins

Ple Da sae l tdo onn To rt aa nd sj ua sct t mi o an r sg ins
Page 8 of 9
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DOI: 10.1039/C5DT01340B
Dalton Transactions
ARTICLE
1
3
Mo@UiO-67: C MAS-NMR: δ = 24.4, 116.8, 119.4, 128.7,
29.8, 134.3, 137.9, 143.1, 172.2; elemental analysis (%): calcd.
∙(1 DMF + 2 H O): C 46.23, H 3.04, N
.56, Mo 3.48; found: 46.27, H 2.85, N 3.02, Mo 3.23.
Acknowledgements
1
MK thanks the TUM Graduate School for support. The authors
thank Xaver Hecht and Monica Markovits for BET
measurements, as well as Dr. Gabriele Raudaschl-Sieber for
MAS-NMR measurements, and Karl Eberle for XPS
measurements. Parts of this work were funded by the
European Union via ERC Advanced Grant MolArt (No. 247299).
for C103
H72MoN
6
O
38Zr
6
2
3
1
3
Mo@UiO-67 mixed: C MAS-NMR: δ = 24.6, 125.0, 130.3,
35.0, 143.4, 172.2; elemental analysis (%):calcd. for
∙(2 CH Cl ): C 44.70, H 2.54, N 0.55, Mo
.53; found: C 44.20, H 2.59, N 0.58, Mo 2.43.
1
C
92
H
59.7Mo0.7NO35.3Zr
6
2
2
2
3
9
2 2 2
Preparation of [MoO (acac)(PhN=C-PhO)] (4). A CH Cl (5
0
mL) solution of previously prepared PhN=C-PhOH (292 mg,
4
Notes and references
1.48 mmol) was added to a solution of [MoO
2 2
(acac) ] (483 mg,
1
2
F. Cavani and J. H. Teles, ChemSusChem, 2009, 2, 508.
1
.48 mmol) in CH Cl (15 mL). The reaction mixture was stirred
2
2
Catalysts for fine chemical synthesis regio- and
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at room temperature overnight, and the resulting yellow
mixture was filtered via a cannula. The solvent was removed
under vacuum and the yellow oily residue suspended in Et
2
O
3
Technol., 2013, 3, 552; (b) S. Huber, M. Cokoja and F. E.
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(
10 mL). The solution was filtered and left overnight to give
1
yellow crystals. H NMR (400 MHz, CD
2 2
Cl , ppm) δ = 8.25 (1H,
4
5
6
s, N=CH), 7.58 (1H, m, 5-Ar), 7.47 (1H, m, 3-Ar), 7.35 (2H, m,
3
,5-Ar(-N)), 7.27 (1H, m, 4-Ar(-N)), 7.16 (2H, m, 2,6-Ar(-N)),
.10 (1H, m, 9-Ar), 7.07 (1H, m, 11-Ar), 5.46 (1H, s, acac), 2.00
7
1
3H, s, Me), 1.47 (3H, s, Me). C NMR (101 MHz, CD
3
(
2 2
Cl , ppm)
3
4
6
4, 1737; (b) W. R. Thiel, J. Mol. Catal. A: Chem., 1997, 117
49; (c) W. R. Thiel and J. Eppinger, Chem. Eur. J., 2006,
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,
,
δ = 196.5, 186.5, 166.4, 161.6, 151.9, 136.1, 135.2, 129.1,
3
9
5
27.2, 123.7, 122.3, 121.7, 120.2, 104.5, 28.0, 25.4. Mo NMR
1
(26 MHz, CD Cl , ppm): -25.2.
2
2
7
8
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Catalytic tests
5
All catalytic tests were performed under argon using Schlenk
techniques.
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2
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decane) at 50 °C. Samples were taken after 4 h and analysed
3
by NMR spectroscopy in CDCl .
Kinetic study for Mo@UiO-67 mixed. The reaction for the
kinetic study was performed as described above. The resulting
graph is displayed in Figure 5. TOF was determined for the
sample taken after 15 min.
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of
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homogeneous
catalyst
3
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2
4
(0.012 mmol, 5 mg)
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was examined as catalyst for the epoxidation of cyclooctene
1.18 mmol, 154 µL) in neat tert-butyl hydroperoxide (2.36
9
(
mmol, 430 µL, 5.5 M solution in decane) at room temperature.
The resulting graph is displayed in Figure 5. TOF was
determined for the sample taken after 5 min.
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examined for leaching by performing a catalytic reaction with
cyclooctene (1 mmol; 130 µL) in neat tert-butyl hydroperoxide
1
1
1
(1.5 mmol; 273 µL, 5.5 M solution in decane) at 50 °C. Samples
were taken after 5 and 30 min. After that the solid catalyst was
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four more hours, a last sample was taken and analysed by
3
NMR spectroscopy in CDCl .
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 1-7 | 7
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DOI: 10.1039/C5DT01340B
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| Dalton Trans., 2015, 44, 1-7
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