Functional networks of organic and coordination polymers: Catalysis of fructose conversion

Article abstract of DOI:10.1021/cm503098p

The creation of functional porous nanoscale networks with enhanced reactive group accessibility provides rich promise for novel designs of composite materials. We present a straightforward strategy for the preparation of porous polymer/MOF hybrids via polymerization of organic monomers and cross-linkers impregnated within the pores of the MOFs followed by functionalization of the resulting composite. A poly(maleimide-co-dibinylbenzene) network was synthesized in the presence of MOF MIL-101(Cr), resulting in stable hybrid composites, which were then brominated to give porous hybrids of cross-linked poly(N-bromomaleimide), a polymeric analogue of N-bromosuccinimide, interconnected with crystalline nanoparticles of the MOF. Due to the large porosity and surface area, the active bromine (halamine) groups in the polymer network enabled high activity of the composites in heterogeneous catalysis of conversion of d-fructose into 5-hydroxymethylfurfural.

Full text of DOI:10.1021/cm503098p

Subscriber access provided by CARNEGIE MELLON UNIV
Article
FUNCTIONAL NETWORKS OF ORGANIC AND COORDINATION
POLYMERS: CATALYSIS OF FRUCTOSE CONVERSION
Lev Bromberg, Xiao Su, and T. Alan Hatton
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/cm503098p • Publication Date (Web): 23 Oct 2014
Downloaded from http://pubs.acs.org on October 29, 2014
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Chemistry of Materials is published by the American Chemical Society. 1155 Sixteenth
Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
FUNCTIONAL NETWORKS OF ORGANIC AND COORDINATION POLYMERS:
CATALYSIS OF FRUCTOSE CONVERSION
Lev Bromberg, Xiao Su, T. Alan Hatton*
Department of Chemical Engineering, Massachusetts Institute of Technology,
Cambridge, MA 02139. *Eꢀmail tahatton@mit.edu
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Abstract
The creation of functional porous nanoscale networks with enhanced reactive group accessibility
provides rich promise for novel designs of composite materials. We present a straightforward
strategy for the preparation of porous polymer/MOF hybrids via polymerization of organic
monomers and crosslinkers impregnated within the pores of the MOFs followed by
functionalization of the resulting composite. A poly(maleimideꢀcoꢀdibinylbenzene) network was
synthesized in the presence of MOF MILꢀ101(Cr), resulting in stable hybrid composites, which
were then brominated to give porous hybrids of crosslinked poly(Nꢀbromomaleimide), a
polymeric analogue of Nꢀbromosuccinimide, interconnected with crystalline nanoparticles of the
MOF. Due to the large porosity and surface area, the active bromine (halamine) groups in the
polymer network enabled high activity of the composites in heterogeneous catalysis of
conversion of Dꢀfructose into 5ꢀhydroxymethylfurfural.
Introduction
The environmental and energy challenges facing the global community today require creative
and innovative solutions that will most likely be based on new structured materials with
enhanced, tailored properties. For instance, diverse chemistries, high surface area and porosity
1
ACS Paragon Plus Environment

Chemistry of Materials
Page 2 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
of metalꢀorganic frameworks (MOFs) built into 3D crystalline structures from alternately
connecting metal ions and organic linkers make these materials exceptionally promising in
1
ꢀ7
applications ranging from gas storage and catalysis to proton conduction and lithium batteries.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Due to the highly ordered porous structures, MOFs can be used as sacrificial templates and/or
precursors to yield, via carbonization processes, porous carbon materials with nanostructured
6
,8
metal/metal oxide components. In addition to MOFs, porous organic polymers (POPs), a class
of amorphous polymers exhibiting permanent microporosity, appear to be resourceful materials
9
ꢀ11
for potential applications in gas storage, separation, and catalysis.
POPs are constructed from
rigid monomers that can crossꢀlink into networks with pores of uniform size. The chemical
stability of microporous organic networks makes them ideal for supporting chemical reactions
without framework destruction or loss of porosity. Polymerization in confined spaces of POPs or
MOFs affords hybrid nanocomposites with previously unknown architectures and
1
2ꢀ16
functionalities.
By radical polymerization of monomers such as styrene, methylmethacrylate,
vinyl acetate, etc. in microporous regular channels of MOFs, Kitagawa and coꢀauthors managed
15,16
to control dimensionality and stereoregularity of the resulting polymers.
The MOF structures
were used as sacrificial templates in the polymerizations resulting in polymers of wellꢀdefined
architecture, shape and size, which had been difficult to attain by conventional polymer synthesis
means. Similarly, a recent report described polymerization of vinylbenzyl trimethylammonium
hydroxide in MOF in zeolitic imidazolate framework (ZIFꢀ8) resulting in a composite capable of
17
ionꢀexchange.
Herein, we describe a straightforward strategy for the synthesis of novel, functional composite
materials that are hybrids of MOFs and polymer networks. These hybrids demonstrate potential
for the facile synthesis of highꢀvalue chemical intermediates from renewable resources,
2
ACS Paragon Plus Environment

Page 3 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
specifically by the dehydration of fructose. In our strategy (Fig.1), the MOF porous structure is
impregnated with organic monomers and crosslinkers, which are then polymerized inꢀsitu (P)
and functionalized (F) to form the resulting hybrid nanocomposite. Although the polymer
network fills some of the MOF pores, the surface area of the hybrid is still large, and the open
structure of the MOF enables ready access of the reactants to the functional groups on the
polymer chains situated on the pore surfaces. Chemical and structural stability of the hybrid
composite is enabled by the intertwined, interlocked structure wherein the polymer chains
threading through the pores of the MOF are locked in place by covalent crossꢀlinking. We chose
MILꢀ101(Cr) as the MOF component for a hybrid because of its excellent stability and open pore
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
8
structure with large, ~3.6 nm cavities accessible through 1.2ꢀ1.5 nm windows. Large cavities
of MILꢀ101(Cr) can be accessed by molecules of 13–14 Å in diameter through the impregnationꢀ
18,19
diffusion approach.
Maleimide was our monomer choice for the hybrid due to its small
molecular size (MW 97 g/mol), ease of freeꢀradical (co)polymerization via a very reactive
double bond, and presence of the ꢀC(O)NHC(O)ꢀ functional imide group that is susceptible to
halogenation and other reactions. We have shown previously that nonꢀporous poly(Nꢀ
bromomaleimideꢀcoꢀdivinylbenzene) networks are active solidꢀphase oxidants in reactions with
2
0
phosphorothioates, thioethers, and hydrazines due to the polymer’s active >NꢀBr groups. In this
work, we found the MOFꢀbrominated polymer hybrids to be potent heterogeneous catalysts for
the industrially important reaction of fructose conversion to 5ꢀhydroxymethylfurfural (HMF).
We envision that the simple and effective method of fabrication of hybrid, functional porous
3
ACS Paragon Plus Environment

Chemistry of Materials
Page 4 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
networks will promote the development of materials for a wide spectrum of applications.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Fig.1. Scheme of fabrication of functional hybrids of MOFs and polymer networks. MOF
impregnated by monomer and crosslinker is subjected to inꢀsitu polymerization (P) followed by
functionalization (F) by a reactive group.
Experimental
Materials
All chemicals and solvents used were obtained from SigmaꢀAldrich Chemical Co. and were of
the highest purity available.
Syntheses
2
0
Polymaleimide-based crosslinked networks (PMAi-co-DVB)
PMAiꢀcoꢀDVB networks were synthesized by freeꢀradical copolymerization of maleimide and
divinylbenzene. In a typical synthesis, a solution of maleimide (970 mg, 10 mmol),
divinylbenzene (390 mg, 3 mmol) and dicumyl peroxide (100 mg, 0.37 mmol) in 10 mL dioxane
o
was deoxygenated by freezeꢀthaw and nitrogen bubbling for 0.5 h and then kept at 80 C in a
sealed flask for 24 h. The resulting white solid was twice dispersed in excess diethyl ether,
4
ACS Paragon Plus Environment

Page 5 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
separated and then dispersed sequentially in acetone and methanol and then separated by filterꢀ
suction and dried under vacuum until constant mass. The yield of polymerization was measured
to be approximately 90 wt% relative to the initial maleimide loading. The effect of DVB
concentration on the solubility of the resulting networks by 24 h extraction in methanol and
acetonitrile was studied. At an initial DVB/maleimide concentration ratio below 0.15 mol/mol, a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
10ꢀ20 wt% fraction of the network appeared to be soluble, and thus the DVB/maleimide mol/mol
ratio of 0.15 to 0.3 was deemed to be suitable for the further network studies.
MOF MIL-101(Cr)
Particles of MOF MILꢀ101(Cr) were synthesized hydrothermally without the use of
1
9
hydrofluoric acid, utilizing an autoclave oven heat supply (Sꢀ1).
Hybrid MOF- PMAi-co-DVB composites
In a typical synthetic procedure, dry, powdered MOF MILꢀ101(Cr) was placed in a solution
containing 970 mg (10 mmol) maleimide, 284 ꢀL (2 mmol) divinylbenzene, 82 mg (0.3 mmol)
dicumyl peroxide and 10 mL dioxane. The mixture was sonicated for 30 s to disperse the MOF
o
particles, deaerated by freezeꢀthaw and nitrogen purge for 0.5 h, sealed and kept at 80 C for 24 h.
The resulting solids were crushed and washed sequentially with excess methanol, acetone, and
o
water. The particles were dried at 80 C for 8 h and then lyophilized under high vacuum to
dryness for 2 days. Separate synthetic procedures with varying initial MOF/maleimide ratios
were also conducted. Dry, ground composite materials with the initial divinylbenzene/imidazole
ratio of 0.2 mol/mol were subjected to stability studies. There was no visible separation of flaky
smaller particles after grinding. Likewise, when the polymerized material was suspended in
o
o
deionized water at 90 C or DMSO at 100 C overnight with occasional shaking, some solvent
uptake by the composite was observed, but the MOF particles could not be mechanically
5
ACS Paragon Plus Environment

Chemistry of Materials
Page 6 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
separated from the larger composite particles using flotation and centrifugation (5000 g, 15 min).
The chemical stability was accessed by elemental analysis of the washꢀouts in methanol after 8ꢀh
o
Soxhlet extraction of 10 mg/mL composite suspension at 70 C. Under harsh conditions, only ca.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
0.05 wt% of Cr and 0.9 wt% of carbon initially present in the composite particles were lost. After
o
equilibration of 10 mg/mL composite suspension in deionized water at 90 C for 3 h and particle
separation by centrifugation at 12,000 g, elemental analysis of the washꢀouts demonstrated below
1
wt% of the initial chromium and carbon were leached into water. The MOF component of the
o
composite was totally dissolved in 1 M aqueous NaOH at 90 C within 3 h. Polymerized in the
presence of MOF without any crosslinker, poly(Nꢀmaleimide) (PMAi) could be extracted readily
o
from the composite by equilibration in DMF at 70 C for 8 h. Weightꢀaverage molecular weight
of the extracted polymer was measured to be 60 kDa (polydispersity, 2.4). Exposure of the
o
composite particles to DMSO at 100 C followed by particle removal by centrifugation at 12,000
g and elemental analysis of the residual solvent for Cr yielded insignificant chromium
concentration (<10ꢀ20 ppb, or less than 0.1% of the initially present Cr), demonstrating stability
of the composites.
Composite functionalization
Finely powdered, dry PMAiꢀcoꢀDVB or MOFꢀPMAiꢀcoꢀDVB network (1 g) was
suspended in a glass flask with chilled, freshly prepared 20 wt% bromine solution in carbon
o
tetrachloride (15 mL) at 0 C under constant stirring. The suspension was sealed and brought up
to ambient temperature within 4 h under stirring, which continued for another 20 h. The
suspension was extractionꢀwashed by carbon tetrachloride, deionized water, and acetone and the
solids were carefully separated by suction filtration. The solids were again washed by acetone
and dried under vacuum. Bromine contents of the resulting brominated polymer network
6
ACS Paragon Plus Environment

Page 7 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
(
abbreviated PMAiꢀBr) and composite material (henceforth abbreviated MOFꢀPMAiꢀBr) were
2
0
measured by titration as described previously to be 3.9 and 1.8 meq/g, respectively. The yield
of the bromination reactions was at least 92 wt% relative to the initial polymer in the composite
material. For PMAiꢀBr, calc.: C, 33.5; H, 1.92; Br, 41.0; N, 7.19; found: C, 34.4; H, 1.66; Br,
41.9; N, 7.34. For MOFꢀPMAiꢀBr, calc.: C, 46.0; H, 2.65; Br, 13.8; Cr, 6.22; N, 2.61; found: C,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
4
6.3; H, 2.56; Br, 14.1; N, 2.48.
Monosaccharide conversion and HMF yield measurements
The progress of the fructose dehydration in DMSO with time was followed by NMR
21,22
measurements (S2).
Conversion of fructose and glucose into 5ꢀhydroxymethylfurfural (HMF) in DMSO was
TM
quantified using a PerkinElmer Flexar FXꢀ15 ultrahigh performance liquid chromatograph,
23ꢀ26
according to established protocols.
The HPLC system included PekinElmer UV/Vis and
refractive index (RI) detectors for measurement of HMF and fructose, respectively, and
PerkinElmer Brownlee Analytical columns: DB C18 (150 mm x 4.6 mm x 5 ꢀm) and Amino
(150 mm x 4.6 mm x 3 ꢀm, 110 Å). In experiments with glucose, only HMF yield was measured
o
at 2 and 6 h after the reaction commencement. The columns were maintained at 35 C, the mobile
phase was deionized water adjusted to pH 4.0 by HCl, with a flow rate of 0.7 mL/min and an
injection volume of 2 ꢀL. An assay was developed where calibration curves (absorbance at λ=
2
84 nm vs concentration for HMF, and refractive index units vs concentration for fructose) and
the retention times for HMF and fructose were determined using solutions of pure compounds in
o
the same mobile phase. The reaction experiments were performed at 100 C in stoppered glass
tubes immersed in a thermostatted oil bath and stirred using magnetic stirring bars. Prior to
equilibration at elevated temperatures, Dꢀfructose solutions in DMSO (concentrations, Cfo,
7
ACS Paragon Plus Environment

Chemistry of Materials
Page 8 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
o
ranging from 0.055 to 0.55 M) were deaerated by nitrogen flow and were stored frozen at 4 C to
prevent any premature reactions from occurring. Prior to the commencement of the reaction
measurements, the solutions (5 mL) were deaerated by nitrogen and briefly (10ꢀ30 s) sonicated at
ambient temperature with the added catalysts for the catalyst dispersal and immersed in the
heating bath while stirring vigorously. Samples (15ꢀ75 ꢀL) were withdrawn at predetermined
time intervals and immediately diluted 10ꢀfold by water (pH 4.0). After brief sonication, the
diluted samples were centrifuged for 30 s at 12,000 g to remove residual catalyst particles and
insoluble reaction products, if any, and the resulting clear solutions were subjected to the HPLC
analysis. The reaction progress was characterized by fructose fractional conversion (F) and HMF
yield (Y):
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
F = 1− C / C
(1)
(2)
f
f 0
Y = 100⋅ C
/ Cf 0 mol%
(
)
HMF
where C and C , are the concentrations of fructose in the sample initially and at time t,
f0
f
respectively, and CHMF is the concentration of HMF in the sample at time t. Based on eqns (1)
and (2), the selectivity of the fructose conversion to HMF, S, can be defined as S = (Y/F).
2
7ꢀ30
“
Hot filtration” experiments
were conducted to evaluate the effects of the MOFꢀPMAiꢀBr
removal from the reaction medium on the rate of Dꢀfructose conversion and HMF yield (Sꢀ3).
Catalyst recycling was accomplished by retrieval of the solid MOFꢀPMAiꢀBr catalyst
after 1 h of the fructose reaction by centrifugation of the entire reaction medium at 12000 g for 1
min, solids separation and repeated washing by deionized water, ethanol and acetone. The
washed catalyst was dried under vacuum and placed in a fresh fructose solution in DMSO at
o
1
00 C. Multiple fractions of the catalyst that underwent 4 cycles were combined and subjected to
powder XRD measurement to evaluate the effect of the catalyst reuse on its crystal structure. The
8
ACS Paragon Plus Environment

Page 9 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
catalyst that underwent 4 cycles was collected and subjected to regeneration via bromination
with bromine in CCl as described above.
4
General Methods
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scanning electron microscopy (SEM) images were taken with a Zeiss Merlin highꢀ
resolution SEM and FEI/Philips XL30 FEG ESEM microscope at 20 kV accelerating voltage, a
1
000ꢀ4000x magnification, and a working distance of 10.1 mm using low vacuum with H O
2
pressure of 0.5 Torr. The samples were mounted on a conductive copper tape. TEM was
performed on a JEOL 200ꢀCX transmission electron microscope. Energy dispersive Xꢀray
spectroscopy (EDS) data were obtained using an EDAX probe with a resolution of 512 x 400 at
1
200x magnification, 99 frames and 50 ꢁm dwell time. Surface area measurements were
conducted using an Accelerated Surface Area and Porosimetry Analyzer ASAP 2020
Micromeritics Corp.) at liquid nitrogen temperature (77 K). Prior to each adsorption
(
measurement, the sample was degassed at 323 K under vacuum for 16 h. The specific surface
areas were evaluated using the BrunauerꢀEmmettꢀTeller (BET) method in the P/P range of 0.06ꢀ
0
0.20. Pore size distribution curves were calculated using the BarrettꢀJoynerꢀHalenda (BJH)
method from the desorption branch of the isotherms and pore sizes were obtained from the peak
positions of the distribution curves. Thermogravimetric analysis (TGA) was conducted using a
Q600 thermogravimetric analyzer (TA Instruments, Inc.). Samples were subjected to heating
scans (20 °C/min) under a nitrogen atmosphere and in a temperature ramp mode. FTIR
spectroscopy was performed with a Nicolet 8700 FTIR spectrometer (Thermo Scientific Inc.)
using KBr pellets. Spectra were recorded over the wavenumber range between 4000 and 400
−
1
−1
1
13
cm at a resolution of 1 cm and are reported as the average of 64 spectral scans. H and C
NMR spectra were collected at 25 ± 0.5 °C using a Bruker Avanceꢀ400 spectrometer operating at
9
ACS Paragon Plus Environment

Chemistry of Materials
Page 10 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
4
00.01 and 100 MHz, respectively. Xꢀray powder diffraction (XRD) patterns were acquired for
4 h with a Panalytical X’Pert Pro multipurpose diffractometer equipped with an X’celerator
2
highꢀspeed detector coupled with a Ni βꢀfilter and using the Cu Kα radiation at room
temperature. Samples were packed in a ZBH placeholder. Programmable divergence slits were
used to illuminate a constant length of the samples (4 mm). The published XRD pattern for MILꢀ
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
01 was used as the reference pattern. Peak assignment and structure refinement were
accomplished with X’Pert Highscore Plus v3 software. XPS measurements were performed
using a PHI Versaprobe II Scanning XPS Microprobe (ULVAC, PHI). The survey scans were
performed with a 200 µm area scan with 50 W power and 15 kV, with a pass energy of 180 eV
with ion gun neutralization. The survey was performed from 0 to 1100 eV, with 10 cycles and
0.1 eV accuracy. The depth of measurement is between 4 to 10 nm. The high resolution scans
were performed on C1s, O1s, N1s, Cr2p and Br3d with 2 cycles and 10 scans each at 0.05 eV
steps and 11.5ꢀ24 eV pass energy.
Results and Discussion
The monomer and crosslinker were polymerized in MOF particle suspensions in dioxane, and
then dried to form a white solid powder. This solid product was washed, dried again, and crushed
to give 100ꢀ300 ꢀm particulates that contained ~20ꢀ50 nm octahedral MOF particles distributed
throughout the polymerized material (Fig.2 and S4).
1
0
ACS Paragon Plus Environment

Page 11 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig.2. Highꢀresolution SEM image of a MOFꢀPMAiꢀBr composite particle on the Zeiss Merlin
SEM under high vacuum and 5 kV (a) and EDS mapping analysis of the composite shown on the
same scale on the Philips XL 30 FEI SEM at 15 kV (b,c). In c, green and red dots show
chromium and bromine, respectively.
High chemical and compositional stability of composites with an initial
divinylbenzene/maleimide ratio of 0.2 mol/mol was observed in water and organic solvents (see
Experimental). The absence of a polymer/MOF phase separation or of leaching of the
components by water and organic solvents supports the notion of stable interlocked composite
structures (Fig.1). EDS chemical composition mapping demonstrated that both Cr and Br
elements were evenly distributed across the brominated composite particles, MOFꢀPMAiꢀBr
(Fig.2, b,c).
Hybrid, bromineꢀfunctionalized composites and their parent MOF and nonꢀfunctionalized MOFꢀ
PMAi materials and corresponding PMAiꢀBr polymer networks were characterized by nitrogen
1
1
ACS Paragon Plus Environment

Chemistry of Materials
Page 12 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
sorption isotherms (Fig.S5), thermogravimetric analysis (Fig.S6), FTIR (Fig.S7), XPS (Fig.S8)
and powder XRD spectroscopy (Fig.S9).
The PMAi and PMAiꢀBr polymer networks did not show any appreciable porosity, with BET
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
surface areas measured to be in the range of 10ꢀ20 m /g. In contrast, the MOFꢀPMAiꢀBr
composites appeared to be porous, with BET and Langmuir surface areas in the ranges of 1100ꢀ
2
1
600 and 1600ꢀ1800 m /g, respectively. The BJH desorption pore diameter was in the 2.0ꢀ2.9 nm
range. The surface areas of the MOFs depended strongly on their postꢀsynthesis treatment. The
2
as-prepared MOF possessed BET and Langmuir surface areas of 1350 and 1690 m /g,
2
respectively, whereas the MOF activation brought these parameters up to 3500 and 4300 m /g,
respectively. The surface area of the composites of MOF that underwent impregnation,
polymerization and bromination was also affected by whether or not the parent MOF was
activated prior to its impregnation. The MOF ꢀPMAiꢀBr composite resulting from the activated
a
MOF possessed a BET area that was ca. 10ꢀ15% higher than that of its counterpart based on the
nonꢀactivated MOF.
Bromine titration, FTIR, XPS and elemental analysis all indicated that the mass ratio of MOF to
the crosslinked polymer network in the MOFꢀPMAiꢀBr composite was approximately 50:50, the
presence of the bromosuccinimide groups was apparent and the active bromine content was 1.8ꢀ
1.9 mequiv/g. During TGA, MOFꢀPMAiꢀBr and PMAiꢀBr materials lost 20ꢀ35% of their initial
mass, attributable to bromine, in the temperature ranges 200−360 °C. Degradation of the MOF
o
organic linkers and PMAi network occurred at temperatures above 400 C, demonstrating high
thermal stability of these organic components. XRD patterns (Fig.S9) showed that the materials
possessed the crystalline MILꢀ101 topology, with or without the amorphous polymer, although
the intensities of the MILꢀ101 peak positions in the 2ꢀ8 degree range were diminished in the
1
2
ACS Paragon Plus Environment

Page 13 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
MOFꢀPMAi composite relative to those in the parent MILꢀ101(Cr) due to the presence of the Xꢀ
ray absorbing polymer in the path of the beam. Brominated MOFꢀPMAiꢀBr showed a distinct
MILꢀ101 XRD pattern, matching well the patterns of the MILꢀ101(Cr) computed using lattice
parameters obtained from the Cambridge Structural Database.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Catalysis of fructose dehydration
To elucidate the utility of the stable, porous and functional composite materials developed in this
work, we focused on the heterogeneous catalysis of the conversion of a bioꢀsourced substrate,
fructose, into 5ꢀhydroxymethylfurfural (HMF), one of the most important platform molecules
for, e.g., liquid biofuel and polyester production, (Fig.S10). The conversion was studied in
dimethylsulfoxide (DMSO), a common polar organic solvent for HMF synthesis. At a moderate
o
temperature of 100 C, the conversion of fructose to HMF was essentially complete after 1 h, as
demonstrated by the disappearance of the αꢀanomeric proton signals of fructose in the 4.3ꢀ5.8
ppm range and appearance of signals at 6.59 (d, J=3.6 Hz, 1 H), 7.47 (d, J=3.6 Hz, 1H), and 9.54
1
3
(s, 1 H) characteristic of HMF (Fig.S11). Production of HMF was further confirmed by the C
NMR spectra (Fig.S12), with the carbon signals at 56.4, 110.1, 124.8, 152.2, 162.6, and 178.3
o
ppm. After 1 h at 100 C, the HMF fraction gradually declined, indicating conversion of HMF
into other products. It is known that HMF is a transient product and can be decomposed to
levulinic acid, polymerized to humic acids and converted to dialdehyde in the presence of
3
0
oxidative species. Since we were interested in quantifying the fructoseꢀtoꢀHMF conversion, we
focused on the initial dehydration, and thus conducted the majority of measurements within the
first hour of the reaction. The quantification was conducted by HPLC. Kinetics of Dꢀfructose
o
dehydration in DMSO at 100 C and in the presence of MOF MILꢀ101(Cr), crosslinked and
1
3
ACS Paragon Plus Environment

Chemistry of Materials
Page 14 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
brominated polymer network (PMAiꢀBr), and the composite hybrid network (MOFꢀPMAiꢀBr),
are shown in Fig. 3.
0
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Control
-0.8
-1.6
-2.4
MIL-101(Cr)
PMAi-Br
MOF-PMAi-Br
(
a)
0
20
40
60
Time, t (min)
100
(b)
MOF-PMAi-Br
80
60
40
PMAi-Br
MIL-101(Cr)
Control
20
0
0
20
40
Time, t (min)
60
o
Fig. 3. Kinetics of Dꢀfructose conversion (a) and HMF percent yield (b) at 100 C. Initial
conditions: DMSO, 5 mL; Dꢀfructose concentration (C ), 0.555 M; catalyst loading, 50 mg/mL.
fo
Control: no catalysts added. Liquid samples were withdrawn every 10 min and fructose
concentration (C ) was measured by HPLC (RI detector) at each datum point, whereas HMF
ft
concentration (CHMF) was measured by UV detection. Fructose conversion was defined as
F = 1− C / C
.
f 0
ft
1
4
ACS Paragon Plus Environment

Page 15 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
Under the selected conditions, the initial kinetics of Dꢀfructose conversion (F) to 5ꢀ
hydroxymethylfurfural (HMF) could be described as pseudoꢀfirst order, with the assumptions
(verified by NMR) that HMF was initially the main product and that the conversion of HMF
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
24,26
itself to other products was a slow process.
Products other than HMF such as levulinic and
formic acids could be also observed, but they were in the minority within a 1ꢀhr reaction, not
exceeding 5ꢀ10% of the main product, HMF. Under the pseudoꢀfirst order approximation, the
fructose (C ) and HMF (CHMF) concentrations in the reaction medium are related by an observed
f
rate constant (k ) as follows:
obs
dCf
dt
dCHMF
=
−
= −k C ; i.e., ln(1ꢀ F) = −k t
obs
f
obs
dt
where F = ꢁC / C is the conversion degree; ꢁCf and Cf 0 are the change in the fructose
f
f 0
concentration and the initial fructose concentration, respectively.
As shown in Fig. 3a, the conversion kinetics were described well by the pseudoꢀfirst order
2
model, with excellent linear fits in the coordinates of eqn (1) (R > 0.98 in all cases). The
reaction was also pseudoꢀfirst order with respect to the initial MOFꢀPMAiꢀBr (catalyst)
(Fig.S13), so the final rate expression is
dCf
dt
= −k′′C Cf
cat
where k′′ is a second order rate constant, and Ccat is the catalyst concentration. We obtain an
ꢀ4
ꢀ1
ꢀ1
ꢀ4
estimated value of k′′to be 9.2 x10 min (mg/mL) , which compares favorably with 5.6 x 10
ꢀ1
ꢀ1
o
min (mg/mL) reported recently for the fructose conversion at 100 C in DMSO using MOF
3
2
MILꢀ101(Cr) modified with sulfonic groups as a catalyst (MILꢀ101(Cr)ꢀSO H). The activation
3
1
5
ACS Paragon Plus Environment

Chemistry of Materials
Page 16 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
o
energy (E ) for the fructose transformation over the 80ꢀ140 C range was 53 kJ/mol (Fig.S14).
a
Analogously, the Dꢀfructose conversion reactions have been found to be of the first order with
2
1
respect to the fructose concentration in DMSO without catalysts and with MOF MILꢀ101(Cr)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
32
modified with sulfonic groups as catalysts (MILꢀ101(Cr)ꢀSO H).
3
Comparison of the MOFꢀPMAiꢀBr material with other heterogeneous catalysts including solid
ꢀ1
acids is favorable. In our case, the values of kobs (2.97 h ) and activation energy (53 kJ/mol)
show a higher catalytic activity of MOFꢀPMAiꢀBr in the fructose conversion in DMSO than the
acidic MILꢀ101(Cr)ꢀSO H (15% sulfonic groups) catalyst (kobs and E , 2.01 and 55 kJ/mol,
3
a
respectively). An additional advantage of the MOFꢀPMAiꢀBr material over solid acid catalysts
such as MILꢀ101(Cr)ꢀSO H is its higher versatility due to the high content of halamine (>NꢀBr)
3
2
0
groups known for their mild oxidative and bromination action in a variety of reactions.
The HMF concentration increased gradually and plateaued at a yield of around 86ꢀ87% at high
degrees of the fructose conversion (F around 0.95ꢀ0.97) with MOFꢀPMAiꢀBr as a catalyst, but
did not decay over the course of the 1ꢀh reaction, thus supporting the hypothesis of the slow
conversion of the evolved HMF (Fig. 3b).
It is interesting to observe that some HMF formation was detected in DMSO without any acid or
solid catalyst added, in accordance with the notion that DMSO itself can facilitate, albeit less
2
1,33ꢀ35
efficiently, the fructose dehydration at elevated temperatures.
The presence of MILꢀ
1
01(Cr) at 50 mg/mL level increased both the rate of the fructose conversion (reaction halfꢀlife
o
1.1 h) and HMF production, with the HMF yield reaching 24% after 1 h at 100 C. MOF MILꢀ
1
01(Cr) is known to possess Lewis acid functionality due to the presence of unsaturated
chromium sites (CUS) formed upon removal of water or solvent molecules from the chromium
1
6
ACS Paragon Plus Environment

Page 17 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
35,36
clusters of the MOF.
This material has been tested previously (upon activation to free up
3
2,37
CUS) for its ability to catalyze carbohydrate dehydration.
In the presence of activated MILꢀ
3
2
o
1
01(Cr), at a temperature of 80ꢂ°C, the HMF yields were negligible and at 120 C the HMF
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
23
yield was observed to be low at 24%. We surmise that the Cr(III) centers in MILꢀ101(Cr) are
not sufficiently active in the dehydration of carbohydrates. MOF modification by incorporation
of strongly acidic polyoxometalate molecules into its pores or by attachment of sulfonic acid
groups through the terephthalic acid (MOF linker) sulfonation affords significant enhancement
3
2,37,38
of the MOF performance as a heterogeneous catalyst in the carbohydrate dehydration.
In the present work, we employed poly(Nꢀbromomaleimideꢀcoꢀdivinylbenzene) (PMAiꢀBr) as a
source of active bromine capable of monosaccharide oxidation. PMAiꢀBr is a polymeric, waterꢀ
and solventꢀinsoluble analogue of Nꢀbromosuccinimide (NBS). The latter has been proven to
mediate oxidation and dehydration of Dꢀfructose and some other monosaccharides in aqueous
3
9ꢀ44
acidic and polar organic solvent media.
NBS is a good source of electrophilic bromine in
polar solvents, which is why it has numerous applications in organic chemistry, and NBSꢀDMSO
in particular is a facile oxidation catalyst generating “activated DMSO” and nucleophilic
4
5ꢀ47
20
bromide species (Fig. S15).
As we have demonstrated, PMAiꢀBr is a versatile oxidant in
reactions with phosphorothioates, thioethers, and hydrazines due to the polymer’s active
bromine. In the current work, the presence of PMAiꢀBr accelerated the Dꢀfructose conversion
approximately 5ꢀfold (reaction halfꢀlife, 37 min) compared to the reaction in DMSO only
(
Fig.3a), and significantly enhanced the HMF yield, with Y reaching 50% after 1 h (Fig.3b).
However, when PMAiꢀBr was incorporated into the composite network with MILꢀ101(Cr), the
resulting material exceeded the activity of PMAiꢀBr significantly, despite the 2ꢀfold lower
effective bromine content, and exhibited synergism between the MOF and the brominated
1
7
ACS Paragon Plus Environment

Chemistry of Materials
Page 18 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
o
polymer as a promoter of the Dꢀfructose conversion, with the reaction halfꢀlife at 100 C less than
1
4 min and HMF yield reaching 85ꢀ87% after 1 h. The yield of HMF and the fructose conversion
rate with MOFꢀPMAiꢀBr compare favorably with most previously reported catalysts. For
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
example, in fructose conversion catalyzed in DMSO by Nꢀmethylꢀ2ꢀpyrrolidonium methyl
o
sulfonate in DMSO or by SnCl –tetrabutyl ammonium bromide, also in DMSO at 90ꢀ100 C, the
4
4
8,49
yield of HMF after 2ꢀh reaction was reported to be 69.1ꢀ69.4%.
An HMF yield of 83ꢂ% was
achieved in an ionic liquid such as 1ꢀethylꢀ3ꢀmethylimidazolium chloride, with CrCl as catalyst
2
5
0
at a temperature of 80ꢂ°C for a reaction time of 3 h. Analogously, an HMF yield of 96% was
observed at 100ꢂ°C after 6 h reaction time in 1ꢀbutylꢀ3ꢀmethyl imidazolium chloride, also using
5
1
CrCl as catalyst.
A disadvantage of such systems, however, is that the product cannot be
2
separated from the ionic liquid catalysts without significant input of energy; such a disadvantage
is not shared with solid, heterogeneous catalysts, which can be readily separated from the
reaction mixture and recycled in an environmentally friendly process for saccharide conversion
5
2
and biofuel production. Acids are wellꢀknown to induce saccharide dehydration when added to
a porous solid to form a heterogeneous catalyst, the activity of which is a function of the acidic
group content.
Good accessibility of the reactive sites by the reactants is crucial for the solid catalyst
52
efficiency. The MOFꢀPMAiꢀBr material possesses a surface area that is at least two orders of
magnitude higher than that of the PMAiꢀBr polymer network, and that explains the higher
catalytic activity of the composite (Fig.4). Mechanistically, the synergistic action of the
composite MOFꢀPMAiꢀBr material can be traced to the MILꢀ101(Cr) structure and the ability of
3
+
the Cr ions to coordinate with the carboxyls of the 1,4ꢀbenzene dicarboxylate, solvents and
water during the MOF synthesis and subsequent exchange of bromide formed at the PMAiꢀBr
1
8
ACS Paragon Plus Environment

Page 19 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
3+
chains in the immediate proximity to the Cr clusters. The MILꢀ101(Cr) framework consists of
terephthalate linkers and Cr Oꢀcarboxylate trimers with octahedrally coordinated metal ions
3
2
7,53
binding terminal water or other solvent molecules.
The terminal water molecules can be
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
removed readily by thermal treatment under vacuum, resulting in the appearance of CUS. Our
synthesis procedure, which involves copolymerization of maleimide (Mal) and divinylbenzene
within the porous structure of the activated MILꢀ101(Cr) followed by the workup and
bromination of the resultant hybrid material with Br , can promote formation of the bromide
2
anions from the Nꢀbromomaleimide units of the PMAiꢀBr, in a reaction where resultant
3+
succinimide units are complexed with the coordinated Cr cations (Fig.4)
H O
2
H O
2
L
L
Polymerization
Bromination
Workup
-
+
+
Br + H O
3
nMal, xBr2
O
L
O
H O
2
L: H
N Br PMAi-Br
O
N
O
O
H N
Mal:
O
Fig.4. Schematic representation of the MILꢀ101(Cr) trimeric building block sharing an oxygen
center and chelated by six carboxylates, with CUS sites coordinated with water molecules. Upon
polymerization of Nꢀmaleimide (Mal), workup of the resulting hybrid polymer/MOF network,
and subsequent bromination, the CUS sites become coordinated with Mal units of the PMAiꢀBr
network as ligands (L), while bromide evolves. Chromium, oxygen, and carbon atoms are in
3+ꢀ
green, red, and blue, respectively. Formation of mixed Cr carboxylateꢀsuccinimide complexes
1
9
ACS Paragon Plus Environment

Chemistry of Materials
Page 20 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
54ꢀ56
is known,
and substitution of coordinated water or solvent ligands in MILꢀ101(Cr) for other
terminal ligands such as pyridines, amines, and different solvent molecules is wellꢀdocumented.
The notion of MOF and brominated polymer coordination, coupled with the presence of the
bromide and bromine in the hybrid MOFꢀPMAiꢀBr network, can explain the facilitation of the
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ꢀ
fructose dehydration by the hybrid material via nucleophilic attack by the Br ion on the fructose
(Fig. 6).
Br
OH H
O OH
O
H
Br
O OH
-H O
HO
2
HO
HO
OH
HO
OH
OH
Br
HO
HO
HO
OH
H+
HBr
OH H
O
O
HO
-2H O
2
O
OH
HO
HMF
5
7,58
Fig.5. Putative mechanism of the fructose dehydration via nucleophilic attack by bromide.
The formation of the fructofuranosyl oxocarbenium ion at the beginning of the fructose
dehydration (Fig.5) with the spontaneous release of a proton at the Cꢀ1 position to form the enol
3
4,58ꢀ
furan intermediate is most often implied because it is energetically favored and more stable.
6
2
The oxocarbenium ion is attacked by a bromide ion with the formation of relatively stable 2ꢀ
58
deoxyꢀ2ꢀbromo intermediate that is less prone to revert back to fructose. The intermediate then
releases HBr to form the enol that loses two water molecules to yield 5ꢀHMF.
The role of chromium salts and complexes in the monosaccharide conversion catalysis is often
emphasized in the case of hexoses such as glucose, where the chromium compound enables
2
0
ACS Paragon Plus Environment

Page 21 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
conversion of the glucose to HMF by initially catalyzing the isomerization of glucose into
5
8
fructose, followed by dehydration. Chromium present in solution likely forms multicoordinate
complexes with the hydroxyl groups of glucose, catalyzing its isomerization. In our experiments
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
o
with MOFꢀPMAiꢀBr, the yield of HMF from glucose in DMSO at 100 C was only 7 and 16%
after 2 and 6ꢀh reaction, respectively (initial catalyst and glucose concentrations, 50 mg/mL and
0
.55M, respectively). The poor HMF yield from glucose can be explained by the absence of
chromium in solution, supporting the conclusion that chromium did not leach from the composite
into the solution, and by an overall low availability for the hexose of the CUS complexed with
the polymer. On the other hand, abundantly available halamine groups do not specifically
catalyze glucose isomerization.
Catalyst reuse
The implied participation of the bromine and bromide ions formed within the MOFꢀPMAiꢀBr
material in fructose dehydration suggests that some of the bromine initially present in the >NꢀBr
group of the Nꢀbromomaleimide units of the PMAiꢀBr component of the composite material can
be lost when the formed bromide is released into the reaction medium. We conducted “hot
filtration” tests to investigate whether catalyst components that might leach into DMSO from the
MOFꢀPMAiꢀBr composite would enable fructose conversion into HMF when the solid catalyst is
removed (Fig. 6).
2
1
ACS Paragon Plus Environment

Chemistry of Materials
Page 22 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
Control
Catalyst removed
-
-
-
-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
MOF-PMAi-Br
(a)
0
10 20 30 40 50 60 70
Time, t (min)
1
00
(b)
MOF-PMAi-Br
80
6
4
0
0
Catalyst removed
Control
20
0
0
10 20 30 40 50 60 70
Time, t (min)
Fig. 6. Effect of catalyst removal on kinetics of Dꢀfructose conversion (a) and HMF yield (b) in
o
DMSO at 100 C. Initial conditions: DMSO, 5 mL; Dꢀfructose concentration (C ), 0.555 M;
fo
catalyst MOFꢀPMAiꢀBr loading, 50 mg/mL. Control: no catalyst added. The reaction was
allowed to commence with the catalyst; at t=10 min a sample was withdrawn for fructose
measurement; at t=12 min, the catalyst was removed by centrifugation at 12,000 g for 1 min. The
o
supernatant separated from the catalyst was subjected to a further kinetic study at 100 C.
Catalyst removal event is shown by arrows.
Upon catalyst removal, the fructose conversion rate slowed down to become approximately
equal to that observed in DMSO in the control experiment without any catalyst. Analogously, the
HMF yield plateaued, increasing only 3ꢀ5% after the catalyst was removed, consistent with
2
2
ACS Paragon Plus Environment

Page 23 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
fructose dehydration conversion rates in DMSO only. Elemental analysis yielded bromine and
chromium concentrations in DMSO after catalyst removal to be 72 and < 2 mg/L (<detection
limit), respectively, showing that approximately 1% of the bromine and only insignificantly
small amounts of chromium initially present in the catalyst leached into the reaction medium.
The leached bromine failed to facilitate the fructose conversion rate beyond that observed in
DMSO without any bromine. These experiments demonstrate that, from a practical standpoint,
the MOFꢀPMAiꢀBr material acts as a heterogeneous catalyst in the fructose dehydration process.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
We were interested in exploring the recyclability of MOFꢀPMAiꢀBr (Fig.7). In each cycle, the
o
material was removed from the reaction medium after 1ꢀh reaction at 100 C, washed and worked
up as described in Experimental.
6
4
2
0
0
0
0
Y F
1
2
3
4
R
Cycle
Fig. 7. HMF yield (Y, filled columns) and fructose conversion (F, open columns) after 1ꢀh
o
reaction catalyzed by MOFꢀPMAiꢀBr at 100 C in DMSO in five consecutive cycles. Cycle R
refers to the catalyst regeneration by bromination after the 4ꢀth cycle. Initial conditions: DMSO,
5
mL; Dꢀfructose concentration (C ), 0.555 M; catalyst MOFꢀPMAiꢀBr loading, 25 mg/mL.
fo
Elemental analysis of the reaction medium in the recycling experiments yielded effective
bromine concentrations of 56ꢀ98 mg/L, which indicated that 1.3ꢀ2.8% bromine initially present
2
3
ACS Paragon Plus Environment

Chemistry of Materials
Page 24 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
on MOFꢀPMAiꢀBr was released into the reaction medium in each of the consecutive cycles.
Powder XRD of the catalyst recovered after the recycling (Fig. S16) demonstrated that the MOF
crystal structure remained intact, although there was some reduction in the peak intensity, which
probably indicated the presence of amorphous organic matter.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
By the fourth cycle, the yield of HMF and fructose conversion degree had declined by
approximately 6% compared to the first cycle. The accessibility of the bromine in the catalyst
might have been impacted by the sorption of the polymeric reaction products (humines) within
2
5,63ꢀ64
the catalyst pores.
After four cycles, only 3ꢀ4% of the catalyst mass was lost. The
selectivity for HMF production was high, ranging from 73 to 78%, and did not decline with
catalyst reuse. Notably, regeneration by bromination of the catalyst recovered after the fourth
cycle completely restored the MOFꢀPMAiꢀBr activity (Fig. 7). A small amount of the MOFꢀ
PMAiꢀBr material (25 mg containing 45 umol of bromine) converted over 1.9 g (11 mmol) of Dꢀ
fructose in four cycles, indicating a remarkable performance figure of merit for that catalyst.
Concluding remarks
A facile and straightforward method to fabricate novel composite organic and coordinate
polymeric networks with high surface area, mesoporous structure, and high content of functional
groups has been introduced. In this approach, vinyl monomers and crosslinkers impregnated
within MOF pores undergo freeꢀradical polymerization to form a crossꢀlinked polymer network
threading through the MOF porous structure; these polymers can be functionalized readily to
imbue them with catalytic properties. While in this work the functional groups are exemplified
by the Nꢀbromomaleimide units obtained via bromination, analogous postꢀsynthetic
functionalization of the composite by other groups is readily achievable. Stability of the
2
4
ACS Paragon Plus Environment

Page 25 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
composite material in solvents was enabled both by the chemical and structural stability of the
parent MOF and by the design of the crossꢀlinked polymeric network. We demonstrated that the
composite material is an effective, recyclable, heterogeneous catalyst for fructose dehydration
into 5ꢀhydroxymethylfurfural (HMF), which is a versatile intermediate in the production of high
value chemicals such as alternative fuels, diesel fuel additives, industrial solvents and bioꢀ
derived polymers.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Supporting Information
Detailed procedures of MOF synthesis, NMR experiments, detailed description of hot filtration
experiments, SEM and TEM images, BET adsorption isotherms, TGA curves, FTIR, XRD, XPS,
1
13
H and C NMR spectra, dependences of the observed rate constant of Dꢀfructose conversion on
the initial catalyst loading and temperature. This material is available free of charge via the
Internet at http://pubs.acs.org.
The authors declare no competing financial interest.
References
1
. Chae, H.K.; SiberioꢀPérez, D.Y.; Kim, J.; Go, Y.; Eddaoudi, M.; Matzger, A.J.; O'Keeffe,
M.; Yaghi, O.M. Nature, 2004, 427(6974), 523ꢀ527.
2
. Morozan, A.; Jaouen, F. Energy Environ. Sci., 2012, 5, 9269ꢀ9290.
3. Furukawa, H.; Cordova, K.E.; O'Keeffe, M.; Yaghi, O.M. Science. 2013, 341(6149),
230444.
. Horike, S.; Umeyama, D.; Kitagawa. S. Acc. Chem. Res. 2013, 46, 2376ꢀ2384.
5. Evans, J.D.; Sumby, C.J.; Doonan. C.J. Chem. Soc. Rev., 2014, 43, 5933ꢀ5951.
. Sun, J.ꢀK.; Xu, Q. Energy Environ. Sci., 2014, 7, 2071ꢀ2100.
1
4
6
2
5
ACS Paragon Plus Environment

Chemistry of Materials
Page 26 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
7
8
. Gándara, F.; Furukawa, H.; Lee, S.; Yaghi, O.M. J. Am. Chem. Soc. 2014, 136, 5271ꢀ
5
274.
. Zhang, L.; Su, Z.; Jiang, F.; Yang, L.; Qian, J.; Zhou, Y.; Li W.; Hong, M. Nanoscale,
014, 6, 6590ꢀ6602.
9. Holst, J. R.; Cooper, A. I. Adv. Mater., 2010, 22, 5212–5216.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
1
0. Ben, T.; Ren, H.; Ma, S.; Cao, D.; Lan, J.; Jing, X.; Wang, W.; Xu, J.; Deng, F.;
Simmons, J. M.; Qiu, S.; Zhu, G. Angew.Chem., 2009, 121, 9621–9624.
11. Comotti, A.; Bracco, S.; Mauri, M.; Mottadelli, S.; Ben, T.; Qiu, S.; Sozzani, P.
Angew.Chem.Int.Ed.; 2012, 51, 10136–10140.
1
2. Podsiadlo, P.; Kaushik, A. K.; Arruda, E. M.; Waas, A. M.; Shim, B. S.; Xu, J.;
Nandivada, H.; Pumplin, B. G.; Lahann, J.; Ramamoorthy, A.; Kotov, N. A. Science,
2
007, 318, 80ꢀ83.
1
3. Uemura, T.; Horike, S.; Kitagawa, K.; Mizuno, M.; Endo, K.; Bracco, S.; Comotti, A.;
Sozzani, P.; Nagaoka, M.; Kitagawa, S. J. Am. Chem. Soc. 2008, 130, 6781ꢀ6788.
4. Kageyama, K.; Tamazawa, J.; Aida, T. Science, 1999, 285, 2113ꢀ2115.
1
15. Uemura, T.; Yanai, N.; Kitagawa, S. Chem. Soc. Rev. 2009, 38, 1228ꢀ1236.
1
6. Distefano, G.; Suzuki, H.; Tsujimoto, M.; Isoda, S.; Bracco, S.; Comotti, A.; Sozzani, P.;
Uemura, T.; Kitagawa, S. Nature Chem. 2013, 5, 335ꢀ341.
17. Gao, L.; Li, C.ꢀY. V.; Chan, K.ꢀY.; Chen, Z.ꢀN. J. Am. Chem. Soc. 2014, 136,
209−7212.
8. JuanꢀAlcañiz, J.; RamosꢀFernandez, E. V.; Lafont, U.; Gascon, J.; Kapteijn, F. J. Catal.
010, 269, 229–241.
7
1
2
2
6
ACS Paragon Plus Environment

Page 27 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
1
9. Bromberg, L.; Diao, Y.; Wu, H.; Speakman, S. A.; Hatton, T. A. Chem. Mater. 2012, 24,
1
664−1675.
0. L. Bromberg, N. Pomerantz, H. SchreuderꢀGibson, T. A. Hatton, Ind.Eng.Chem.Res.,
014, DOI: 10.1021/ie501055g.
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
2
1. Amarasekara, A.S.; Williams L.D.; Ebede, C.C. Carbohydrate Res., 2008, 343, 3021ꢀ
024.
3
2
2. Kimura, H.; Nakahara, M.; Matubayasi, N. J. Phys. Chem. A, 2013, 117, 2102–2113.
3. Tian, G.; Tong, X.; Wang, Y.; Yan, Y.; Xue, S. Res. Chem. Intermed., 2013, 39, 3255ꢀ
2
3
263
2
4. Qi, X.; Watanabe, M.; Aida, T.M.; Smith, R.L. Green Chem., 2009, 11, 1327ꢀ1331.
25. RománꢀLeshkov, Y.; Chheda, J. N.; Dumesic, J. A. Science, 2006, 312, 1933ꢀ1937.
2
6. Lee, Y.ꢀY.; Wu, K. C.ꢀW. Phys. Chem. Chem. Phys., 2012, 14, 13914ꢀ13917.
7. Maksimchuk, N.V.; Zalomaeva, O. V., Skobelev, I. Y.; Kovalenko, K. A.; Fedin, V. P.;
Kholdeeva, O. A., Proc. R. Soc. A., 2012, 468, 2017ꢀ2034.
2
2
8. Valvekens, P.; Vermoortele, F.; De Vos, D. Catal. Sci.Technol., 2013; 3, 1435ꢀ1445.
9. Hwang, Y.K.; Fėrey, G.; Lee, U.ꢀH.; Chang, J.ꢀS. Chapter 8, In: Liquid Phase Oxidation
via Heterogeneous Catalysis: Organic Synthesis and Industrial Applications, Ed. by
Clerici, M. G.; Kholdeeva, O. A. John Wiley & Sons, 2013, 371ꢀ405.
2
30. Gascon, J.; Corma, A.; Kapteijn, F.; Llabrés i Xamena, F.X. ACS Catal., 2014, 4, 361–
78.
3
3
3
3
1. Lewkowski, J. Arkivos, 2001(i), 17ꢀ54.
2. Chen, J.; Li, K.; Chen, L.; Liu, R.; Huang, X.; Ye, D. Green Chem., 2014, 16, 2490ꢀ2499.
3. Musau, R.M.; Munavu, R.M. Biomass 1987, 13, 67ꢀ74.
2
7
ACS Paragon Plus Environment

Chemistry of Materials
Page 28 of 31
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
4. Akien, G. R.; Qi, L.; Horváth, I. T. Chem. Commun., 2012, 48, 5850ꢀ5852.
5. Vimont, A.; Goupil, J.M.; Lavalley, J.C.; Daturi, M.; Surblé, S.; Serre, C.; Millange, F.;
Férey, G.; Audebrand N. J. Am. Chem. Soc. 2006, 128, 3218ꢀ3227.
6. Wang, S.; Bromberg, L.; SchreuderꢀGibson, H.; Hatton, T.A. ACS Appl. Mater.
Interfaces. 2013, 5, 1269ꢀ1278.
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
3
7. Zhang, Y.; Degirmenci, V.; Li, C.; Hensen, E.J.M. ChemSusChem, 2011, 4, 59–64.
8. Akiyama, G.; Matsuda, R; Sato, H.; Takata, M.; Kitagawa, S.; Adv. Mater. 2011, 23,
3294ꢀ3297.
3
3
9. Singh, A. K.; Srivastava, R.; Srivastava, S.; Srivastava, J.; Rahmani, S.; Singh, B. J. Mol.
Catal. A: Chem. 2009, 310, 64ꢀ74.
40. Singh, A. K.; Rahmani, S.; Singh, V.; Gupta, V.; Singh, B. Oxid.Commun. 2000, 23, 55ꢀ
1.
6
4
4
4
1. Singh, A. K.; Rahmani, S.; Singh, V. K.; Gupta, V.; Kesarwani, D.; Singh, B. Ind. J.
Chem. 2001, 40A, 519ꢀ523.
2. Tian, G.; Tong, X.; Wang, Y.; Yan, Y.; Xue, S. Res. Chem. Intermed., 2013, 39, 3255ꢀ
3263.
3. Singh, A.K.; Singh, P.; Srivastava, J.; Jaya, Rahmani, S.; Singh, S.K. J.Energy Chem.
Eng., 2014, 2, 8ꢀ22.
44. Wolfe, S.; Pilgrim, W.R.; Garrard, T.F.; Chamberlain, P. Can J.Chem., 1971, 49, 1099ꢀ
105.
5. Uzagare, M.C.; Padiya, K.J.; Salunkhea, M.M.; Sanghvi, Y.S. Bioorg.Med. Chem. Lett.
003, 13, 3537–3540.
1
4
2
2
8
ACS Paragon Plus Environment

Page 29 of 31
Chemistry of Materials
1
2
3
4
5
6
7
8
9
4
6. Tojo, G.; Fernandez, M.I. In: Oxidation of Alcohols to Aldehydes and Ketones. A Guide
to Current Common Practice, Springer, 2006, Chapter 2, pp. 97ꢀ179.
7. Tong, X.; Li, Y. ChemSusChem, 2010, 3, 350–355.
4
4
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
8. Tian, G.; Tong, X.; Cheng, Y.; Xue, S.; Carbohydrate Res., 2013, 370, 33–37.
49. Zhao, H.; Holladay, J.E.; Brown, H.; Zhang, Z.C. Science, 2007, 316, 1597ꢀ1600.
5
0. Yong, G.; Zhang, Y.; Ying, J.Y. Angew. Chem., 2008, 120, 9485–9488.
1. Guo, F.; Fang, Z.; Xu, C.C.; Smith R.L.; Progr. Energy Combustion Sci. 2012, 38, 672ꢀ
690.
5
5
2. Asghari, F. S.; Yoshida, H. Ind. Eng. Chem. Res., 2006, 45, 2163–2173.
3. Férey, G.; MellotꢀDraznieks, C.; Serre, C.; Millange, F.; Dutour J.; Surblé S.; Margiolaki,
I. Science, 2005, 309, 2040ꢀ2042.
5
5
5
4. Islam, M. S.; Uddin, M.M. Synthesis and Reactivity in Inorganic and MetalꢀOrganic
Chemistry, 1992, 22, 1303ꢀ1315.
5. da Silva, A.G.M.; Rodrigues, T.S.; Gurgel, L.V.A.; Assis, P.A.; Gil, L.F.; Roblesꢀ
Dutenhefner, P.A. Industrial Crops and Products 2013, 50, 288– 296.
56. Llabrés i Xamena, F.X.; Luz, I.; Cirujano, F.C. In: Metal Organic Frameworks as
Heterogeneous Catalysts, Ed. by Llabrés i Xamena, F.X.; Gascon, J. RSC Catalysis
Series No. 12; RSC Publishing, Cambridge, UK, 2013 Chapter 7, pp.237ꢀ267.
57. Binder, J.B.; Raines, R.T. J. Am. Chem. Soc. 2009, 131, 1979–1985.
58. Ståhlberg, T.; Sørensen, M.G.; Riisager, A. Green Chem., 2010, 12, 321–325.
59. Antal, M.J.; Mok, W. S. L.; Richards, G. N. Carbohydrate Res. 1990, 199, 91ꢀ109.
60. Bing, L.; Zhang, Z.; Deng, K. Ind. Eng. Chem. Res., 2012, 51, 15331–15336.
61. Mittal, N.; Nisola, G.M.; Chung, W.ꢀJ. Tetrahedron Let.; 2012, 53, 3149ꢀ3155.
2
9
ACS Paragon Plus Environment