Reaction Environment Modification in Covalent Organic Frameworks for Catalytic Performance Enhancement

Article abstract of DOI:10.1002/anie.201900029

Herein, we show how the spatial environment in the functional pores of covalent organic frameworks (COFs) can be manipulated in order to exert control in catalysis. The underlying mechanism of this strategy relies on the placement of linear polymers in the pore channels that are anchored with catalytic species, analogous to outer-sphere residue cooperativity within the active sites of enzymes. This approach benefits from the flexibility and enriched concentration of the functional moieties on the linear polymers, enabling the desired reaction environment in close proximity to the active sites, thereby impacting the reaction outcomes. Specifically, in the representative dehydration of fructose to produce 5-hydroxymethylfurfural, dramatic activity and selectivity improvements have been achieved for the active center of sulfonic acid groups in COFs after encapsulation of polymeric solvent analogues 1-methyl-2-pyrrolidinone and ionic liquid.

Full text of DOI:10.1002/anie.201900029

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
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Accepted Article
Title: Reaction Environment Modification in Covalent Organic
Frameworks for Catalytic Performance Enhancement
Authors: Qi Sun, Yongquan Tang, Briana Aguila, Sai Wang, Feng-
Shou Xiao, Praveen K. Thallapally, Abdullah M. Alenizi,
Ayman Nafady, and Shengqian Ma
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201900029
Angew. Chem. 10.1002/ange.201900029
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10.1002/anie.201900029
Angewandte Chemie International Edition
COMMUNICATION
Reaction Environment Modification in Covalent Organic
Frameworks for Catalytic Performance Enhancement
Qi Sun,†[a,c] Yongquan Tang,†[b] Briana Aguila,[a] Sai Wang,[b] Feng-Shou Xiao,*[b] Praveen K.
Thallapally,[d] Abdullah M. Al-Enizi,[e] Ayman Nafady,[e] and Shengqian Ma*[a,e]
Abstract: The application of noncovalent interactions is a potentially
powerful strategy to exert control in catalysis. However, there is a
significant perceived challenge in manipulating the spatial
environment around the active sites in a heterogeneous catalyst.
Herein, we show how this can be accomplished in the functional pores
of covalent organic frameworks (COFs). The underlying mechanism
of this strategy relies on the placement of linear polymers in the pore
channels that are anchored with catalytic species, analogous to outer-
sphere residue cooperativity within the active sites of enzymes. This
approach benefits from the flexibility and enriched concentration of
the functional moieties on the linear polymers, enabling the desired
reaction environment in close proximity to the active sites, thereby
impacting the reaction outcomes. Specifically, in the representative
dehydration of fructose to produce 5-hydroxymethylfurfural, dramatic
activity and selectivity improvements have been achieved for the
active center of sulfonic acid groups on COFs after encapsulation of
polymeric solvent analogues 1-methyl-2-pyrrolidinone and ionic liquid.
materials science due to the unprecedented combination of ready
chemical tunability, high crystallinity, tunable pore structure, large
surface area, and stability.[4,5] COFs enable control over the
nature of a catalytic center and its spatial organization as well as
the identity and placement of surrounding surface functionalities,
forming structurally well-defined active sites.[6] The ordered pore
channels and large pore volumes of COFs make them very
attractive as host materials for guest encapsulation.[7] The
functional space within the pores of COFs thus provides an
auspicious platform for integrating multiple components, allowing
synergistic catalytic activation pathways to be triggered. Indeed,
multifunctional heterogeneous catalysts based on host-guest
cooperation have recently emerged as state-of-the-art hybrid
materials to tailor and enhance properties far beyond that of the
combined soluble parent species.[8] In that scenario, the catalytic
moieties on the flexible linear polymer, which are enriched in the
pore spaces, promote them to cooperate with the active sites
anchored on the pore walls of the host materials, lending to
exceptional performances, while providing the additional benefit
of recycling. Given these, it was hypothesized that this strategy
could be used to emulate some of the design principles of
enzymes, for which the improved performances are reliant on
both the highly potent catalytic center and the surrounding
polypeptide chains, and thereby would allow access to new types
of catalysts. In view of the high sensitivity of chemical reactions
towards changes in the solvation environment, we encapsulated
polymeric solvent analogues as a proof of principle study.[9] It is
shown that the partnership with the catalytic elements on the
COFs and the linear polymers hosted in the pore channels gives
great promise to optimize the reaction outcomes (Figure 1).
Specifically, the performance of sulfonic acid groups on COFs can
be greatly amplified after the introduction of polymeric solvent
analogues, which creates the desired solvation environments by
exerting hydrogen bonding interactions to achieve activity and
selectivity, as exemplified by the fructose to 5-
hydroxymethylfurfural (HMF) transformation.
The functions of active sites are directly linked to the local
environment where they are housed.[1] There is a growing body of
evidence that the strategic placement of noncovalent interactions
around a catalytic center can lead to remarkable increases in
selectivity and activity by stabilizing the transition state and having
favorable conformations of the active site and the products, in a
way reminiscent of enzymatic catalysis.[2] While profitable, precise
control over the periphery of an active site remains synthetically
challenging, particularly in heterogeneous catalytic systems.[3]
Unlike in biological/molecular systems, difficulties arise in solid
systems because their structures are often rigid, impeding the
cooperation between different catalytic elements and thereby
underscoring the need for new innovative technologies.
Covalent organic frameworks (COFs), a class of porous,
crystalline materials, have quickly moved to the forefront of
[*]
Dr. Q. Sun,[ †] B. Aguila, Prof. S. Ma
To implement this strategy, we first selected a COF prototype
for the potential installation of catalytic elements as well as
providing room for guest encapsulation. Earlier work has
established that the COF, TPB-DMTP-COF, synthesized by the
condensation of 1,3,5-tris(4-aminophenyl)-benzene (TPB) and
2,5-dimethoxyterephthalaldehyde (DMTA), can be used as an
excellent material platform for structural design and functional
development, as well as for guest encapsulation due to its high
crystallinity, large mesoporous channels, in conjugation with
ultrastability towards a wide range of conditions including strong
acids and strong bases.[10] By a multivariate (MTV) approach,
followed by post-synthetic modification, a family of COF-based
catalysts can be achieved, whereby the catalytic groups are
appended in a predefined way. A diverse range of catalytic
moieties is amenable to this role, for example organocatalysts,
and here, we opted for the sulfonic acid group given its versatility
Department of Chemistry, University of South Florida
4202 E Fowler Ave., Tampa, FL 33620 (USA)
E-mail: sqma@usf.edu
Y. Tang,[ †] S. Wang, Prof. F.-S. Xiao
Key Lab of Applied Chemistry of Zhejiang Province, Zhejiang
University, Hangzhou 310007 (China)
E-mail: fsxiao@zju.edu.cn
Dr. Q. Sun[ †]
College of Chemical and Biological Engineering, Zhejiang
University, Hangzhou, 310027 (China)
Prof. P. K. Thallapally
Physical and Computational Science Directorate, Pacific Northwest
National Laboratory, Richland, WA 99352 (USA)
Prof. A. M. Al-Enizi, Prof. A. Nafady, Prof. S. Ma
Chemistry Department, College of Science, King Saud University,
Riyadh, 11451 (Saudi Arabia)
[†]
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of
the document.
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10.1002/anie.201900029
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Figure 1. The concept of modification of the local reaction environment of the active sites on the porous materials by inserting highly flexible linear polymers and
scheme of PVP@[SO3H]x-COF synthesis and structures of [OH]x-COF (x = 0.17, 0.33, 0.5).
for a variety of industrially-relevant reactions.[11] The second
aspect of our design strategy is the insertion of functional linear
polymers into the pore channels. We anticipated that, via
noncovalent interactions with the reaction participants, the hosted
linear polymers may be able to influence the reaction rate or alter
the activity and selectivity of product formation.
Our initial step was to introduce catalytically active
perfluorinated sulfonic acid groups onto the pore walls of COFs.
We employed a three-component condensation system with 2,5-
informative tool for identifying the acidity of an acid site. A higher
31P chemical shift corresponds to a stronger acid site due to the
more polarized phosphorus–oxygen bond.[13] 31P MAS NMR
spectrum of TMPO after interaction with [SO3H]0.17-COF gave a
singlet peak at 76.0 ppm, appearing to possess a moderate to
high strength (Figure S4). The narrow NMR signal suggests the
homogeneity of the acid sites in these samples. The powder X-
ray diffraction (PXRD) showed that the diffraction pattern of
[SO3H]0.17-COF was in good agreement with that of [OH]0.17-COF
(Figure 2a). N2 sorption isotherms collected at 77 K revealed that
[SO3H]0.17-COF and [OH]0.17-COF exhibited similar adsorption
behavior, giving type IV isotherms. The BET surface area of
[SO3H]0.17-COF was calculated to be 1510 m2 g-1, with a slight
drop compared to [OH]0.17-COF (1898 m2 g-1, Figure 2b). Derived
from nonlocal density functional theory modeling, both samples
gave pore size distributions centered at 3.3 nm (Figure S5). These
results confirmed that the post-synthetic modification process had
little effect on the crystallinity and pore structure of the pristine
material, therefore still accessible for the accommodation of guest
species.
We subsequently incorporated linear polymers into the
perfluorinated sulfonic acid-containing frameworks, aiming to alter
the local environment of the acid sites on the COFs. Given that
the reaction medium is an important variable to control the
reactivity and selectivity for the catalytic processes, which affects
reaction kinetics, product selectivity, the stability of the desired
products, together with the economics of downstream separations,
1-vinyl-2-pyrrolidone was therefore chosen as a representative
monomer to show a proof of principle study. This is also based on
the following considerations: (i) the corresponding polymer,
polyvinylpyrrolidone (PVP), is the polymeric analogue of 1-
methyl-2-pyrrolidinone (NMP), which is a ubiquitous solvent in
organic transformations; (ii) due to the high boiling point, isolating
products from this solvent is cumbersome and even worse, side
reactions are often accompanied with the separation process. We
envisioned that the unbound PVP chains could provide a similar
solvation environment as NMP in the reaction, thereby regulating
the catalytic performance, while the heterogeneous nature of the
composites enables ready product isolation. To accommodate the
PVP polymers into the COF pore channels, in situ polymerization
of 1-vinyl-2-pyrrolidone monomer in [SO3H]x-COFs was
performed at 80 °C for 3 days. The resulting product was washed
thoroughly with DMF to remove unincorporated polymers and
unreacted monomers, affording the material denoted as
PVP@[SO3H]x-COFs. The appearance of C=O stretching
vibrations (1670 cm−1) in the FTIR spectrum corresponding to the
dihydroxyterephthalaldehyde
(DHTA)
and
2,5-
dimethoxyterephthalaldehyde (DMTA) as edge units to
synthesize the intermediate [OH]x-TPB-DMTP-COFs (hereafter
abbreviated as [OH]x-COF), where x is the percentage of
functional groups as a fraction of the groups lining the pore walls.
After
treatment
with
1,2,2-trifluoro-2-hydroxy-1-
trifluoromethylethane sulfonic acid sultone, the perfluoroalkyl
chain with terminal sulfonic acid functional groups were anchored
onto the channel walls by the reaction between the sultone ring
and OH group on the COFs, yielding [SO3H]x-COFs (Figure 1). As
representative samples, [OH]0.17-COF and the corresponding
post-modified sample, [SO3H]0.17-COF, were illustrated
thoroughly here, whereas the detailed characterization results of
other samples were placed in the Supporting Information. To
examine the post-synthetic modification, we performed X-ray
photoelectron spectroscopy (XPS), Fourier-transform infrared
spectroscopy (FTIR), transmission electron microscopy energy
dispersive X-ray spectroscopy (TEM-EDX), and elemental
analysis. The presence of the elements F (F1s at 689.1 eV) and
S (S2p at 170.7 eV) signals in the XPS spectra of [SO3H]0.17-COF,
verified the occurrence of post-synthetic modification (Figure S1).
Furthermore, additional peaks appeared at 1232 and 1445 cm−1
in the IR spectrum of [SO3H]0.17-COF, corresponding to the C-F
and S=O stretching vibrations, respectively, confirming the
successful incorporation of perfluorinated sulfonic acid groups
onto the COF (Figure S2).[12] The EDX mapping indicated the
homogeneously distributed F, N, O, and S elements throughout
the COF (Figure S3). To quantify the degree of post-synthetic
modification, the content of S species in [SO3H]0.17-COF was
evaluated by infrared absorption carbon-sulfur analysis, revealing
that the content of sulfonic acid groups in the COF is 0.39 mmol
g-1 (Tables S1 and S2). To evaluate the acid strength of the
resulting samples, we adsorbed trimethylphosphine oxide
(TMPO) into [SO3H]0.17-COF and performed solid-state 31P NMR
spectroscopy. Given a linear relationship between the 31P
chemical shift values of adsorbed TMPO and the strength of a
Brønsted acid site, this technology has proven to be an
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10.1002/anie.201900029
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against other acid catalysts (Nafion® NR50, Amberlyst-15, and 4-
methylbenzenesulfonic acid (TsOH)) for HMF selectivity and
output efficiency using THF as a reaction medium. The
advantages of using THF as the solvent is that it allows for ready
product isolation and negates the need to purify HMF from
unreacted fructose due to its negligible solubility at room
temperature. Our benchmark materials were chosen based on
their well proven efficiency for this transformation in the presence
of NMP (Table S3), and their catalytic activities were evaluated
with respect to the number of active sites of the catalyst.
PVP@[SO3H]0.17-COF was found to be very efficient in a wide
range of temperatures. The HMF selectivity of this composite was
99.1% at 100 °C and lower, yet remained at 92.8% at 140 °C
(Table S4). A full fructose conversion and a HMF yield of 99.1%
were achieved for PVP@[SO3H]0.17-COF within 30 min, which
compares far more favorably to the corresponding values of
[SO3H]0.17-COF, as well as Nafion® NR50, Amberlyst-15, and
TsOH, affording fructose conversions of 23.2%, 9.7%, 15.3%, and
28.5% as well as HMF yields of 17.9%, 5.3%, 10.3%, and 20.9%,
respectively, under otherwise identical conditions, and prolonging
the reaction time did not afford satisfied results, demonstrating the
importance of the PVP polymer (Table 1). Given the undetected
HMF rehydration products, levulinic acid and formic acid, we
reason that the decreased HMF selectivity along with the reaction
is a result of cross-polymerization between HMF and fructose
(see details in Figure S11).
Figure 2. (a) PXRD patterns, (b) N2 sorption isotherms, and (c) SEM images.
Scale bar: 500 nm.
amide bond in the pyrrolidinone moiety provided evidence for the
incorporation of PVP (Figure S6). The emergence of peaks at
175.9 ppm as well as in the range of 17.4-45.6 ppm in the 13C
MAS NMR attributable to the polymerized 1-vinyl-2-pyrrolidone
moieties confirmed the polymers encapsulation (Figure S7). To
provide additional chemical characterization, the PVP polymers
within PVP@[SO3H]0.17-COF were isolated from its host for 1H
NMR spectroscopy. The spectrum mirror that of the commercial
PVP, specifically lacking peaks in the 1H NMR between 5.5-7.0
ppm corresponding to the vinylic hydrogen peaks of the monomer
(Figure S8). Gel permeation chromatography (GPC) analyses
gave an average molecular weight (Mw) of 5833 g mol-1, showing
proof of the isolated PVP consisting up to 53 monomeric units
(Figure S9). To gain a better understanding of the entrapment of
the polymer within [SO3H]0.17-COF, scanning electron microscopy
(SEM) images were collected, with indistinguishable changes in
morphology, indicating that the polymer is included within the
pores of the COF and not on the surface (Figure 2c). To quantify
how much of the PVP polymer is present within the composite,
elemental analysis was performed, and its content was
determined to be 33 wt.% (Table S1). We then examined the
structural integrity of the composite. The crystallinity of the COF
was maintained as evidenced by PXRD. The decrease in relative
diffraction intensity can be explained by the change in electron
density of [SO3H]0.17-COF after filling with PVP (Figure 2a). As
expected, a decrease in BET surface area from 1510 m2 g-1 for
[SO3H]0.17-COF to 644 m2 g-1 for PVP@[SO3H]0.17-COF was
observed, yet it still enables the reactants to reach the active sites
situated on the pore surfaces (Figure 2b). The 31P MAS NMR
spectrum of TMPO after association with PVP@[SO3H]0.17-COF
showed a singlet peak at 75.6 ppm, a comparable value to that of
TMPO interacted with [SO3H]0.17-COF (76.0 ppm), indicative of
the maintenance of acid strength after the incorporation of PVP
(Figure S4).
Table 1. Catalytic data in the dehydration of fructose to HMF over various
catalysts using THF as the solvent. a
Entry
Catalyst
Time
(min)
30
Conv.
(%)
Select.
(%) b
99.1
Yield
(%) b
99.1
17.9
(33.3)
5.3
1 c
2
PVP@[SO3H]0.17-COF
[SO3H]0.17-COF
>99.5
30
23.2
(94.6)
9.7
77.1
(120)
30
(35.2)
54.6
3
4
5
Nafion® NR50
Amberlyst-15
TsOH
(360)
30
(89.3)
15.3
(19.4)
67.1
(17.3)
10.3
(28.1)
20.9
(37.8)
54.9
86.1
68.9
97.1
98.2
(180)
30
(95.2)
28.5
(29.5)
73.5
(120)
30
(>99.5)
86.7
(37.8)
62.7
6
7
PVP&DVB@[SO3H]0.17-COF
PVP@[SO3H]0.33-COF
PVP@[SO3H]0.50-COF
PVP@[SO3H]0.17-COF
PVP@[SO3H]0.17-COF
30
96.4
89.3
8
30
91.2
75.6
9 d
10 e
30
>99.5
97.1
30
>99.5
98.2
a Reaction conditions: fructose (100 mg, 0.56 mmol), catalyst (based on the
amount of sulfonic acid 2.0 mol%), 100 °C, THF (3.0 mL), and the reaction time
has been optimized; b the HMF selectivity and yield were determined by the
combination of liquid chromatography and gas chromatography. c isolated HMF
To demonstrate the possibility of the incorporated PVP as an
alternative to NMP in regulating the performance of the acid sites,
we set out to evaluate its performance in the selective dehydration
of fructose to produce HMF, a platform bridging biomass
chemistry and petrochemistry.[14] An important factor in the
synthesis of HMF through sugar dehydration is the occurrence of
side reactions, including organic acids and humins (Figure S10).
Although, the formation of those disfavored products can be
suppressed by performing the reaction using solvents like NMP,
it remains a substantial challenge to isolate HMF in an energy-
friendly manner from this high boiling point solvent.[15] To give a
better illustration, PVP@[SO3H]0.17-COF was benchmarked
d
e
yield 94.5% (Figure S12).
recycle for
5
times.
fructose (1.0 g),
PVP@[SO3H]0.17-COF (2.0 mol%), 100 °C, and THF (20 mL) for 30 min; The
values in parentheses refer to the time used, as well as the conversion of
fructose and selectivity and yield of HMF at that point.
To confirm the role of pyrrolidone moieties, we carried out a
series of control experiments. Adding free NMP to those catalytic
systems allowed catalytic activity to be restored, yet not
comparable to that of PVP@[SO3H]0.17-COF, even with more
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10.1002/anie.201900029
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pyrrolidone moieties compared with that in PVP@[SO3H]0.17-COF.
This is probably because the complementary catalytic partner is
diluted in the liquid phase, which does not permit the full pairing
of all the active components (Table S5). Adding PVP did not yield
appreciable improvement in activity of the solid catalysts,
however, significantly accelerated activity could be measured with
TsOH, which can be imparted to the fact that the PVP polymer
chains coiled, preventing it from fully approaching the active sites,
thereby leading to ineffectual cooperation (Table S5). Whereas,
the molecular catalyst TsOH is easily diffused to the nearby
pyrrolidone moieties in PVP, allowing for cooperation. This also
indicates the superiority of in situ polymerization, which renders
the polymers trapped within the pores for maximum utilization.
The results above imply that the local concentration of the
pyrrolidone moieties has a great effect on the performance of the
acid sites. To prove this, we synthesized PVP@[SO3H]0.33-COF
and PVP@[SO3H]0.5-COF with similar PVP amounts to that in
PVP@[SO3H]0.17-COF (Figures S13-S20). Catalytic data revealed
that upon increasing the density of sulfonic acid groups in the
COFs, diminished productivity as well as selectivity to HMF was
by PXRD and IR (Figures S22 and S23). According to these and
the previous research, a tentative mechanism is proposed for the
dehydration of fructose to HMF catalyzed by PVP@[SO3H]0.17
SO3H (Figure S24).[16]
-
To examine the stability as well as recyclability of the catalytic
material, PVP@[SO3H]0.17-COF was repeatedly used as a
catalyst up to 5 times. As depicted in Figure S25, HMF was
obtained in a 97.1% yield even after 5 runs and no significant loss
of activity was observed. A hot filtration test revealed that the
obtained activity is not related to any leaching of the catalytically
active acid sites (no remaining activity in the supernatant). The
neutrality of the isolated product further confirmed no undesired
leaching processes of acid species occurred during the course of
the catalytic transformation. The catalytic system was also
applicable for scaled-up conditions, where 1.0 g of fructose was
successfully converted into HMF, which can be readily isolated
after simple filtration of the catalyst and evaporation of THF (see
1H NMR spectrum in Figure S26). The structural integrity of
PVP@[SO3H]0.17-COF was also retained after the reactions as
confirmed by PXRD analysis of the spent catalyst (Figure S27).
Advantageously, our strategy of inserting linear polymers to
promote reaction performance is also easily extended to other
functional materials. To showcase, we incorporated an ionic
polymer (PIL, see details in the experimental section) within the
COFs and subjected them to identical reaction procedures.
PIL@[SO3H]0.17-COF also demonstrated a remarkably improved
efficiency of 97.6% HMF yield within 30 min at 100 ºC in the
presence of THF.
observed from 99.1% to 86.1% and 68.9% for PVP@[SO3H]0.17
-
COF, PVP@[SO3H]0.33-COF, and PVP@[SO3H]0.5-COF, with
initial reaction rates of 0.024, 0.018, and 0.013 mM min-1,
respectively (Table 1, entries 1,
7 and 8, with detailed
experimental procedures in the Supporting Information). It was
thus deduced that the ratio of pyrrolidone to the –SO3H group
content is vital to the performance. In line with the highest average
pyrrolidone moiety density per –SO3H group, among the samples
tested, PVP@[SO3H]0.17-COF exhibited the highest HMF yield,
ranking it among the best catalytic systems reported thus far as
well as surpassing those using NMP as a solvent (Table S6). To
gain insight about how the cooperation occurs between the
threaded PVP and the acid sites appended on the COFs, we
reasoned that the flexibility of the linear polymer should play an
important role. To give experimental evidences, a composite with
less flexibility was synthesized. In that case, the PVP chains
threaded through the channels of the COF are locked in place by
introduction of a covalent cross-linker (divinylbenzene, DVB)
during the polymerization process. The resulting catalyst
(PVP&DVB@[SO3H]0.17-COF, BET: 599 m2 g-1, Figure S21)
afforded the HMF yield at 64.9%, around 60% as much achieved
by employing PVP@[SO3H]0.17-COF, suggesting that the
restricted flexibility of cross-linked PVP significantly reduces the
catalytic components cooperation. Previous studies reveal that in
numerous carbohydrate involved reactions, some favorable
intermediates identified are complexes that incorporate with the
solvent moieties as a result of the strong solvation effect between
these solvents and the carbohydrates by hydrogen bonding
interactions, which favor the subsequent desired transformation
starting from such form.[15] Therefore, we infer that the flexible
PVP chains act as a pseudo-solvent, encapsulating reactants in
a local microenvironment by the hydrogen bonding interactions
between C=O and the hydroxyl protons of fructose, as evidenced
Our synthetic approach overcomes the challenges of spatial
isolation of catalytic elements, providing the rigorous
experimental demonstration of multiple non-covalent substrate–
catalyst interactions integrated to regulate the reaction outcomes
of heterogeneous catalysts. By leveraging the benefits of both
molecular and solid materials, the flexible linear polymer chains
confined in the pore channels enable them to cooperate with the
active sites anchored on the COF pore walls, hence the full
exploitation of the catalytic potential, while providing additional
recyclability. This approach should be relevant for parallel and
more complex reaction schemes, ultimately facilitating the
development of new catalytic processes. Together with its high
versatility to integrate with other functional materials, we envisage
our strategy presented herein as a cornerstone to realize a new
paradigm in the design of multifunctional molecular assemblies to
control functions at a level approaching biological systems.
Acknowledgements ((optional))
The authors acknowledge the National Science Foundation of
China (21720102001 and 91634201) as well as the National
Science Foundation (DMR-1352065) and the University of South
Florida for financial support of this work. The authors also extend
their appreciation to the Distinguished Scientist Fellowship
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Chem. Int. Ed. 2014, 53, 2878-2882; g) Y. Peng, Z. Hu, Y. Gao, D. Yuan,
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S. Xiao, S. Ma, J. Am. Chem. Soc. 2018, 140, 984-992; b) Ma, H.; Liu,
B.; Li, B.; Zhang, L.; Li, Y.-G.; Tan, H.-Q.; Zang, H.-Y.; Zhu, G. J. Am.
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Program (DSFP) at King Saud University for funding this work
partially.
[7]
Keywords: covalent organic framework • host-guest cooperation
• biomass conversion • acid catalysis • solvation environment
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10.1002/anie.201900029
Angewandte Chemie International Edition
COMMUNICATION
COMMUNICATION
Creation of a solvation
Qi Sun, Yongquan Tang, Briana
environment: The performance of
sulfonic acid groups on COFs can be
greatly amplified after the introduction
of polymeric solvent analogues,
which creates desired solvation
environments by exerting hydrogen
bonding interactions to achieve
activity and selectivity, as exemplified
by the fructose to 5-
Aguila, Sai Wang, Feng-Shou Xiao*,
Praveen K. Thallapally, Abdullah M. Al-
Enizi] Ayman Nafady, and Shengqian
Ma*
Page No. – Page No.
Reaction Environment Modification
in Covalent Organic Frameworks for
Catalytic Performance Enhancement
hydroxymethylfurfural transformation.
This article is protected by copyright. All rights reserved.