A urea-containing metal-organic framework as a multifunctional heterogeneous hydrogen bond-donating catalyst

Article abstract of DOI:10.1016/j.catcom.2019.105837

A urea-containing metal-organic framework (MOF) was synthesized from a V-shaped dicarboxylate ligand and Cu(II) ions. As the undesirable self-aggregation of the urea moiety has been prohibited in the framework, this MOF can act as a heterogeneous hydrogen

Full text of DOI:10.1016/j.catcom.2019.105837

Journal Pre-proof
A urea-containing metal-organic framework as a multifunctional
heterogeneous hydrogen bond-donating catalyst
Chengfeng Zhu, Haitong Tang, Keke Yang, Xiang Wu, Yunfei
Luo, Jin Wang, Yougui Li
PII:
S1566-7367(19)30298-5
DOI:
https://doi.org/10.1016/j.catcom.2019.105837
CATCOM 105837
Reference:
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
6 August 2019
28 September 2019
30 September 2019
Please cite this article as: C. Zhu, H. Tang, K. Yang, et al., A urea-containing metal-organic
framework as a multifunctional heterogeneous hydrogen bond-donating catalyst, Catalysis
Communications (2019), https://doi.org/10.1016/j.catcom.2019.105837
This is a PDF file of an article that has undergone enhancements after acceptance, such
as the addition of a cover page and metadata, and formatting for readability, but it is
not yet the definitive version of record. This version will undergo additional copyediting,
typesetting and review before it is published in its final form, but we are providing this
version to give early visibility of the article. Please note that, during the production
process, errors may be discovered which could affect the content, and all legal disclaimers
that apply to the journal pertain.
© 2019 Published by Elsevier.

Journal Pre-proof
A Urea-containing Metal-Organic Framework as a
Multifunctional Heterogeneous Hydrogen Bond-Donating
Catalyst
Chengfeng Zhu* ZhuCF@hfut.edu.cn, Haitong Tang, Keke Yang, Xiang Wu, Yunfei Luo, Jin Wang,
and Yougui Li* liyg@hfut.edu.cn
Anhui Province Key Laboratory of Advanced Catalytic Materials and Reaction Engineering, School of
Chemistry and Chemical Engineering, Hefei University of Technology, Hefei, 230009, P. R. China
*Corresponding author. Chengfeng Zhu, ; Yougui Li,
Abstract
A urea-containing metal-organic framework (MOF) was synthesized from a V-shaped dicarboxylate
ligand and Cu(II) ions. As the undesirable self-aggregation of the urea moiety has been prohibited in the
framework, this MOF can act as a heterogeneous hydrogen bond-donating (HBD) catalyst, which
accelerates the cyanosilylation reaction of aldehydes, the Henry reaction of aldehydes, and the
methanolysis reaction of epoxides. It also displays a significantly enhanced catalytic activity when
compared with its homogeneous urea counterpart and analogous MOF structures.
Keywords: Hydrogen bond-donating catalyst, Heterogeneous catalysis, Metal-organic frameworks, Urea
1. Introduction
Hydrogen bond-donating (HBD) catalysis has been recognized as an effective approach for the
synthesis of various highly valuable intermediates for pharmaceutical and agricultural industries
because HBD catalysts are capable of binding selectively and activating reactive substrates during the
reaction process through hydrogen bonding or other noncovalent interactions [1-4]. In the past decades,

Journal Pre-proof
numerous HBD catalysts with different structures and functionalities have been designed for specific
reactions including Friedel–Crafts (F–C) reactions, Mannich reaction, Strecker reaction, etc. [5-8].
Among these catalysts, urea has been widely utilized as a catalytic moiety owing to its chelating
hydrogen bonding through acidic N-H sites [9,10]. However, the intrinsic self-assembly of urea
molecules caused by the intermolecular interactions of hydrogen bonding always leads to a potential
deterioration in catalytic reactivity [11,12]. Thus, it is necessary to introduce enhanced catalyst loading
or elongated reaction time or external toxic additives to achieve high yield in a certain homogeneous
catalytic system [13,14]. In contrast to the conventional approach of enhancing the reactivity of
urea-based catalysts, various supports have been exploited to break the self-association of urea moieties
in catalysis. For instance, the Lin group demonstrated that mesoporous silica nanosphere materials could
serve as support for a urea-based catalyst to achieve superior catalytic behavior in some important
chemical transformations compared with their corresponding precursors [15,16]. The Portnoy group has
developed a urea-based organocatalyst supported by a porous organic polymer. This organocatalyst has
been established as an efficient catalyst for promoting nitro-Michael addition [17]. Additionally,
metal-organic frameworks (MOFs), emerging as new support materials for heterogeneous catalysis, are
gaining increasing interest owing to their unique features of high porosity, structural tunability, excellent
stability, and well-defined catalytic sites [18-22]. For example, Roberts and co-workers first synthesized
one MOF-based catalyst bearing a urea moiety, which is highly active in the F–C reactions between
pyrroles and nitroalkenes. Subsequently, a few MOF-based HBD catalysts derived from urea-, thiourea-,
or squaramide-functionalized molecules were prepared through direct synthesis or post-synthetic
modification. These MOF catalysts also displayed high efficiency in catalyzing F–C reactions [23-30].
In spite of a growing interest in such solid catalysts, studies on multifunctional MOF-based HBD
catalysts remain limited. In this work, a urea-containing MOF was synthesized and utilized as a highly
efficient HBD catalyst to promote the cyanosilylation reaction of aldehydes, the Henry reaction of
aldehydes, and the methanolysis reaction of epoxides. Additionally, this urea-based MOF catalyst
exhibits a broad substrate scope and excellent recyclability.

Journal Pre-proof
2. Experimental section
2.1 Synthetic chemistry
In this work, the urea-containing MOF (1) was synthesized from a V-shaped dicarboxylate ligand
(L1-H2) with urea moiety according to a previously reported procedure (Scheme 1) [31]. For the
comparison of catalytic activity, MOF 2 was readily obtained from a solvothermal reaction of copper
nitrate and ligand L2-H2. MOF 1 and 2 both possessed a similar two-dimensional framework. The
structures of both MOFs were confirmed by the results of single-crystal X-ray diffraction analysis
(Scheme 1 and Figs. S1-2).
2.2 Catalytic procedure
As shown in the structure of MOF 1 (Scheme 1 and Fig. S1), the guest DMF molecules remained in
the framework through hydrogen bonding to urea moieties. Therefore, the active urea N-H sites in the
channels of 1 were blocked. To remove the guest DMF molecules within the cavities, 1 was treated with
anhydrous MeOH and CH2Cl2, followed by placing in vacuum for two hours at 100 °C. The activated
MOF 1 was named as 1a. General procedure for cyanosilylation reaction: 1.5 mol% 1a (catalyst loading
based on aldehydes) was added to a solution of indicated aldehyde (0.10 mmol), TMSCN (0.12 mmol),
and dry MeOH (0.5 mL). The resulting mixture was stirred at 60 °C. For Henry reaction: a reaction
mixture consisting of 1.5 mol% 1a (based on aldehydes), indicated aldehyde (0.10 mmol), and MeNO2
(1.0 mmol) was stirred at 60 °C. For methanolysis reaction of epoxides: a reaction mixture consisting of
1.5 mol% 1a (based on epoxides), indicated epoxide (0.10 mmol), and dry MeOH (0.5 mL) was stirred
at 60 °C. The three reactions were carried out for 24 hours, and the yields were determined by 1H NMR.
3. Results and discussion
To the best of our knowledge, the intrinsic unwanted self-association behavior of the urea moieties is
quite common in homogeneous catalysis. This phenomenon usually hampers their catalytic
performance. It can be clearly seen that the self-association of the urea-containing ligand L1-H2
(Scheme 2a) was successfully restricted when it was immobilized on the MOF structure. Therefore,
MOF 1 can serve as a potential HBD catalyst. Cyanosilylation of various aldehydes using trimethylsilyl

Journal Pre-proof
cyanide is one of the important C-C bond formation methods. It could provide vital intermediates for
numerous biologically active products. As such, we would like to examine the effectiveness of the
urea-containing MOF 1 in the cyanide reaction.
It is found that 1.5 mol% activated 1 (1a) can effectively catalyze the cyanosilylation reaction of
benzaldehyde under optimized conditions to afford a corresponding product with 97% NMR yield
(entry 1 in Table 1). To confirm that the main reactivity was contributed by the catalytic sites coming
from the isolated urea moieties on the MOF structure, three control experiments were carried out. (i)
The free ligand L1-H2 was first utilized as a homogeneous catalyst to run the same reaction, and only
24% yield was obtained (entry 2 in Table 1) even at 3.0 mol% catalyst loading (twice the urea units in
1a). The obviously low catalytic activity can be ascribed to the unwanted dimerization of L1-H2 through
intermolecular hydrogen-bonding interactions, resulting in the loss of active free ligand (Scheme 2a).
(ii) Considering the presence of coordination-saturated copper sites in MOF 1 that may play some role
in the catalysis, MOF 2, sharing a similar structure with 1 but without urea moiety on its framework,
was synthesized and used as a catalyst to catalyze the same reaction (Scheme 1 and Fig S2). This
control experiment showed that MOF 2 gave only a 34% yield (the equal loading of copper as that in 1a,
entry 3 in Table 1), which implied that dicopper units in MOF 1 made some contribution to the
cyanosilylation reaction of benzaldehyde. (iii) It is noted that a significant decrease in catalytic
performance occurred when the pristine crystals of 1 were used as a catalyst (entry 4 in Table 1). This
result presumably could be explained by the fact that the dual N-H sites in the MOF structure were
blocked by guest DMF molecules through strong hydrogen-bonding interactions (Scheme 1 and Fig S1).
On the basis of the above discussions, enhancement of the catalytic activity of 1a should be mainly
attributed to the isolated and unblocked urea functional groups immobilized on the MOF structure, in
which the carbonyl group of aldehydes could be activated by the acidic dual N-H group of the urea units
(Scheme 2b) [1].
The substrate tolerance of catalyst 1a was further examined with various aromatic aldehydes. In the
presence of 1a, a wide range of aromatic benzaldehyde derivatives bearing both electron-donating and

Journal Pre-proof
electron-withdrawing substituents were found to react efficiently with trimethylsilyl cyanide and
generate corresponding products in excellent yields ranging from 84% to 97% (entries 5-9 in table 1).
Taken together, the above results suggest that 1a could be used as a highly efficient HBD catalyst in the
cyanosilylation reaction of multiple aldehydes. To the best of our knowledge, this is the first example of
a urea-based MOF catalyst with high performance in cyanosilylation reaction. This excellent result
encourages us to extend the applications of 1a to other catalytic reactions.
We then attempted to apply this MOF catalyst to the Henry reaction. The reaction was
performed between aldehydes and nitromethane by using 1.5 mol% catalyst 1a. An optimum
result was that benzaldehyde and its derivatives bearing electron-poor groups reacted with
nitromethane efficiently to give β-nitro alcohols in 80-95% yields (entries 1-2, 6-9 of Table 2).
Three control experiments were additionally carried out to determine the role of the open and
isolated urea sites in this catalysis. Free ligand L1-H2, 2, and pristine 1 afforded only 36%, 9%,
and 10% yields (entries 3-5 in Table 2), respectively, when they were used as catalysts in the
Henry reaction of 4-nitrobenzaldehyde with nitromethane. The significant catalytic performance
of 1a in catalyzing the Henry reaction of aldehydes again implied that it is a highly efficient
HBD catalyst.
To further investigate the versatility of this HBD MOF catalyst, the alcoholysis of epoxides to various
alkoxy alcohols, an important reaction for pharmaceutical and agrochemical industries, was also tested
with this MOF catalyst. As far as we know, studies of this reaction catalyzed by urea-containing MOFs
to date are scarce [32]. In this work, the alcoholysis of epoxides was performed at 60°C for 24 h, in
which methanol was used as both a nucleophile and a solvent. To our delight, 1a can effectively
catalyze the methanolysis of phenyl glycidyl ether to afford the product of
1-methoxy-3-phenoxypropan-2-ol with an excellent yield of 96% (entry 1 in Table 3). When the
reaction was performed using L1-H2, 2, and pristine 1 as the catalysts, significantly lower yields were
observed (entries 2-4 in Table 3). From the control experiments, we expected that the MOF-containing
urea moieties can activate the oxygen atom of the epoxide to achieve higher catalytic activity (Scheme

Journal Pre-proof
2d). The reaction could be extended to other epoxides such as 4-Me, 4-Br, 4-OMe-substituted phenyl
glycidyl ether, and 2-naphthyl glycidyl ether. In these reactions, 1a could give the corresponding
products a yield of 80-90%. Again, these results demonstrated the high utility of 1a as an HBD catalyst.
Moreover, the heterogeneity and the recyclability of this HBD MOF catalyst were investigated. Upon
completion of the methanolysis of phenyl glycidyl ether under the typical condition, solid catalyst 1a
can be easily recovered with quantitative mass from the reaction mixture through centrifugation and
washed with excessive MeOH. Subsequently, the recovered catalyst 1a could be reused for another four
runs without any obvious loss of catalytic activity (ca. 96%, 93%, 92%, 91%, and 92% yields for runs
1-5, respectively). In addition, a comparison of the PXRD patterns of the recovered solid catalysts 1a
and the pristine crystal of 1 clearly showed that no significant changes occurred (Fig S3). These results
suggest that this urea-containing MOF is a versatile HBD heterogeneous catalyst with high catalytic
performance.
4. Conclusions
In summary, a urea-containing MOF was synthesized from a V-shaped urea-functionalized
ligand. The MOF possesses catalytically active dual N-H groups that allow for the activation of
the carbonyl compound. This HBD MOF catalyst demonstrated excellent activity in the
cyanosilylation reaction, the Henry reaction of aldehydes, and the methanolysis of epoxides.
Further, the HBD MOF catalyst can be easily recovered and reused without any apparent loss of
catalytic activity. Our study, therefore, provides a highly efficient heterogeneous HBD catalyst
functionalized with urea moieties in the MOF structure. This approach can be further extended
for a variety of important organic transformations.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (No. 21401037 and
21672049), Anhui Provincial Natural Science Foundation (No. 1508085QB26), and Fundamental
Research Funds for the Central Universities of China (No. PA2019GDPK0058 and

Journal Pre-proof
PA2019GDPK0084). We also thank the staff from BL17B beamline of National Facility for Protein
Science in Shanghai (NFPS) at Shanghai Synchrotron Radiation Facility for assistance during crystal
data collection.
Declaration of interest: None.
Appendix A. Supplementary data
Supplementary data associated with this article can be found in the online version at
https://doi.org/ xx.xxxx /j. catcom. xxxx.xx.xxx.
References
[1]. P. R. Schreiner, Chem. Soc. Rev., 2003, 32 (5), 289-296.
[2]. M. S. Taylor; Jacobsen, E. N., Angew. Chem., Int. Ed., 2006, 45 (10), 1520-1543.
[3]. A. G. Doyle; Jacobsen, E. N., Chem. Rev., 2007, 107 (12), 5713-5743.
[4]. W. Zheng; Fu, Y.; Liu, L.; Guo, Q., Acta Phys.-Chim. Sin., 2007, 23 (7), 1018-1024.
[5]. Y. Nishikawa, Tetrahedron Lett., 2018, 59 (3), 216-223.
[6]. T. J. Auvil; Schafer, A. G.; Mattson, A. E., Eur. J. Org. Chem., 2014, 2014 (13), 2633-2646.
[7]. D. Roca-Lopez; Marques-Lopez, E.; Alcaine, A.; Merino, P.; Herrera, R. P., Org.Biomol. Chem.,
2014, 12 (25), 4503-4510.
[8]. S. Xu; Zhu, H.; Li, Z.; Wei, F.; Gao, Y.; Xu, J.; Wang, H.; Liu, J.; Guo, T.; Guo, K., Eur. Polym. J.,
2019, 112, 799-808.
[9]. Y. Takemoto, Org.Biomol. Chem., 2005, 3 (24), 4299-4306.
[10]. M. S. Taylor; Jacobsen, E. N., Angew. Chem., Int. Ed., 2006, 45 (10), 1520-1543.
[11]. R. Custelcean, Chem. Commun., 2008, (3), 295-307.

Journal Pre-proof
[12]. P. Howlader; Das, P.; Zangrando, E.; Mukherjee, P. S., J. Am. Chem. Soc., 2016, 138 (5),
1668-1676.
[13]. Z. G. Zhang; Bao, Z. B.; Xing, H. B., Org.Biomol. Chem., 2014, 12 (20), 3151-3162.
[14]. R. P. Herrera; Sgarzani, V.; Bernardi, L.; Ricci, A., Angew. Chem., Int. Ed., 2005, 44 (40), 6576-9.
[15]. S. Huh; Chen, H.-T.; Wiench, J. W.; Pruski, M.; Lin, V. S. Y., Angew. Chem., Int. Ed., 2005, 44
(12), 1826-1830.
[16]. H.-T. Chen; Trewyn, B. G.; Wiench, J. W.; Pruski, M.; Lin, V. S. Y., Top Catal., 2010, 53 (3-4),
187-191.
[17]. L. Tuchman-Shukron; Portnoy, M., Adv.Synth. Catal., 2009, 351 (4), 541-546.
[18]. J. Liu; Chen, L.; Cui, H.; Zhang, J.; Zhang, L.; Su, C. Y., Chem. Soc. Rev., 2014, 43 (16), 6011-61.
[19]. L. Jiao; Wang, Y.; Jiang, H.-L.; Xu, Q., Adv. Mater., 2018, 30 (37), 1703663.
[20]. A. H. Chughtai; Ahmad, N.; Younus, H. A.; Laypkov, A.; Verpoort, F., Chem. Soc. Rev., 2015, 44
(19), 6804-6849.
[21]. Y.-B. Huang; Liang, J.; Wang, X.-S.; Cao, R., Chem. Soc. Rev., 2017, 46 (1), 126-157.
[22]. G. Yuan; Jiang, H.; Zhang, L.; Liu, Y.; Cui, Y., Coordin. Chem. Rev., 2019, 378, 483-499.
[23]. X.-W. Dong; Liu, T.; Hu, Y.-Z.; Liu, X.-Y.; Che, C.-M., Chem. Commun., 2013, 49 (70),
7681-7683.
[24]. Y. Luan; Zheng, N.; Qi, Y.; Tang, J.; Wang, G., Catal. Sci. Technol., 2014, 4 (4), 925-929.
[25]. C. M. McGuirk; Katz, M. J.; Stern, C. L.; Sarjeant, A. A.; Hupp, J. T.; Farha, O. K.; Mirkin, C. A.,
J. Am. Chem. Soc., 2015, 137 (2), 919-925.
[26]. X.-J. Wang; Li, J.; Li, Q.-Y.; Li, P.-Z.; Lu, H.; Lao, Q.; Ni, R.; Shi, Y.; Zhao, Y., CrystEngComm.,
2015, 17 (25), 4632-4636.

Journal Pre-proof
[27]. E. A. Hall; Redfern, L. R.; Wang, M. H.; Scheidt, K. A., ACS Catal., 2016, 6 (5), 3248-3252.
[28]. Z. Ju; Yan, S.; Yuan, D., Chem.Mater., 2016, 28 (7), 2000-2010.
[29]. X. Zhang; Zhang, Z.; Boissonnault, J.; Cohen, S. M., Chem. Commun., 2016, 52 (55), 8585-8.
[30]. P. C. Rao; Mandal, S., Chemcatchem., 2017, 9 (7), 1172-1176.
[31]. C. Zhu; Mao, Q.; Li, D.; Li, C.; Zhou, Y.; Wu, X.; Luo, Y.; Li, Y., Catal. Commun., 2018, 104,
123-127.
[32] A. A. Tehrani; Abedi, S.; Morsali, A.; Wang, J.; Junk, P. C., J. Mater. Chem. A, 2015, 3 (40),
20408-20415.
Figure Captions:
Scheme 1. Synthesis and structures of 1 and 2.

Journal Pre-proof
Scheme 2. Self-association of urea-containing ligand, L1-H2, in homogeneous catalysis (a) and
substrate activation by the urea unit through hydrogen bonding for cyanosilylation reaction (b), Henry
reaction (c), and methanolysis reaction (d), when urea has been immobilized in MOF.
Table 1 Results of cyanosilylation reaction catalyzed by different catalysts a
Enty
R
Ph
Ph
Ph
Ph
Cat.
1a
L1-H2
2
1
1a
1a
1a
1a
1a
Cat. Load. (mol%) b
Conversion (%) e
1
2
3
4
5
6
7
8
9
1.5
3.0c
1.5d
1.5
1.5
1.5
1.5
1.5
1.5
97
24
34
36
94
97
84
93
97
4-Me-Ph
4-Cl-Ph
4-OMe-Ph
4-CN-Ph
2-naphtyl
a For reaction details, see Experimental Section. b Catalyst loading based on aldehyde. c Twice the urea
units in 1a. d The same loading of copper as that of 1a. e Calculated by 1H NMR.
Table 2 Results of the Henry reaction catalyzed by different catalysts a
Enty
R
Ph
Cat.
1a
1a
L1-H2
2
1
1a
1a
1a
Cat. Load. (mol%) b
Conversion (%) e
1
2
3
4
5
6
7
8
9
1.5
1.5
3.0c
1.5d
1.5
1.5
1.5
1.5
1.5
83
95
36
9
10
91
93
90
80
4-NO2-Ph
4-NO2-Ph
4-NO2-Ph
4-NO2-Ph
3-NO2-Ph
2-NO2-Ph
4-CN-Ph
4-Br-Ph
1a
a For reaction details, see Experimental Section; the reaction time is 24 h. b Catalyst loading is based

on aldehyde. c Twice the urea units in 1a. d The sJamoeulorandiangl oPfrceop-pperroasothfat of 1a. e Calculated by 1H
NMR.
Table 3 Ring-opening reactions of various epoxides with MeOH a
Enty
R
Cat.
1a
L1-H2
2
1
1a
1a
Cat. Load. (mol%) b
Conversion (%) e
1
2
3
4
5
6
7
8
CH2OPh
CH2OPh
CH2OPh
CH2OPh
1.5
3.0c
1.5d
1.5
1.5
1.5
1.5
1.5
96
22
6
12
80
84
90
88
CH2O(p-BrC6H4)
CH2O(p-MeC6H4)
CH2O(p-OMeC6H4)
CH2O(2-naphtyl)
1a
1a
a For reaction details, see Experimental Section. b Catalyst loading based on epoxide. c Twice the urea
units in 1a. d The same loading of copper as that of 1a. e Calculated by 1H NMR.

Journal Pre-proof
Highlights




Two 2D metal-organic frameworks (MOFs) were readily synthesized and characterized.
This urea-containing MOF is a superb hydrogen-bond-donating (HBD) catalyst.
Three types of important reactions could be efficiently catalyzed.
This HBD catalyst showed a superb catalytic activity and excellent recyclability.
Graphical abstract