DOI: 10.1002/chem.201404104
Communication
&
Metal–Organic Frameworks
MIL-101-SO H: A Highly Efficient Brønsted Acid Catalyst for
3
Heterogeneous Alcoholysis of Epoxides under Ambient
Conditions
[
a]
Yu-Xiao Zhou, Yu-Zhen Chen, Yingli Hu, Gang Huang, Shu-Hong Yu, and Hai-Long Jiang*
[4]
structures as well as very high surface area and exhibit po-
[5–7]
Abstract: For the first time, a ~100% sulfonic acid func-
tential applications in various fields.
In addition, MOFs usu-
tionalized metal–organic framework (MOF), MIL-101-SO H,
ally contain coordinatively unsaturated metal centers as Lewis
acids and also catalytically active sites suspended on the or-
ganic linkers, endowing MOFs powerful functionality in hetero-
3
with giant pores has been prepared by a hydrothermal
process followed by a facile postsynthetic HCl treatment
strategy. The replete readily accessible Lewis acidic and es-
pecially Brønsted acidic sites distributed throughout the
framework as well as high stability endow the resultant
MOF exceptionally high efficiency and recyclability, which
surpass all other MOF-based catalysts, for the ring open-
ing of epoxides with alcohols (especially, methanol) as nu-
cleophiles under ambient conditions.
[8]
geneous catalysis. Particularly, the active sites are uniformly
spatially distributed throughout the MOF and well accessible,
and the pore structure greatly facilitates the transfer of sub-
strates and products. Therefore, MOFs with high-density acid
sites may outperform the supported metal complexes for het-
erogeneous alcoholysis of epoxides. To date, only a couple of
Cu-, Zn- and Fe-based MOFs and an recent Eu-MOF have been
investigated for the alcoholysis of epoxides and all of them are
[9a–f]
Lewis acid type catalysts.
Most recently, MIL-101(HPW),
a Keggin phosphotungstic acid as active nanomaterial incorpo-
rated into a MOF, has been demonstrated to be an active het-
erogeneous catalyst for the ring-opening reaction of styrene
Epoxides are highly important and versatile synthetic inter-
mediates in organic synthesis and they undergo ring-opening
reactions with different nucleophiles such as alcohols to afford
b-alkoxyalcohols, which are precursors for a broad range of
[9g]
oxide. Herein, a sulfonic acid group functionalized MOF, MIL-
III
101-SO H, featuring giant cages replete with Lewis acidic Cr
3
[
1]
pharmaceuticals. Alcohols have relatively poor nucleophilicity
and thus strong acids or bases are required to promote such
kind of alcoholysis of epoxides. Quite a few conventional acids
or metal complexes were reported, while these homogeneous
systems have inherent limitations in terms of the separation of
and Brønsted acidic ÀSO H sites, has shown exceptionally high
3
activity, excellent selectivity and recyclability for alcoholysis of
epoxides under ambient conditions. Moreover, the catalytic ac-
tivity from Lewis acid sites is negligible compared to that from
Brønsted acid sites in MIL-101-SO H. To the best of our knowl-
3
[
2]
the product and catalyst recycling. Recently, a few heteroge-
neous catalysts, such as amberlyst-15, clays, aluminosilicate,
silica, or polymer stabilized metal complexes, etc., have been
edge, this is the first work on the ring opening of epoxides
over a MOF with Brønsted acid sites.
The reaction of 2-sulfoterephthalic acid monosodium salt
[
3]
[10a]
developed for the transformation. However, these reactions
have still witnessed more or less drawbacks like tedious cata-
lyst preparation or workup procedures, harsh reaction condi-
tions, unsatisfactory selectivity, etc. Therefore, it is of great im-
portance to develop highly efficient heterogeneous catalysts
for nucleophilic ring-opening of epoxides under mild condi-
tions.
and CrO in aqueous HCl solution yielded MIL-101-SO Na(H),
3
3
which contains 1.02% Na based on ICP and gave a pH value of
2.94 in the solution (Table 1). To eliminate the Na species and
Table 1. ICP-AES results for the contents of Na and Cr involved in MIL-
1
01-SO
ICP-AES
found [%]
3
3
Na(H) and MIL-101-SO H.
Metal-organic frameworks (MOFs) as a relatively new class of
crystalline porous materials feature versatile and tailorable
Element
Cr
MIL-101-SO
3
Na(H)
3
MIL-101-SO H
14.88
1.02
14.8
0.0028
Na
[a] Y.-X. Zhou, Y.-Z. Chen, Y. Hu, G. Huang, Prof. Dr. S.-H. Yu,
Prof. Dr. H.-L. Jiang
Hefei National Laboratory for Physical Sciences at the Microscale
Department of Chemistry
maximize the strength of Brønsted acidity, a postsynthetic HCl
University of Science and Technology of China
Hefei, Anhui 230026 (P.R. China)
Fax: (+86)551-63607861
treatment afforded MIL-101-SO H with <0.003% Na and
3
a lower pH value of 1.72 in solution, revealing a successful ion
+
exchange of all residual Na with proton (Table 1) and such an
E-mail: jianglab@ustc.edu.cn
approach is different from previous reports for the preparation
Supporting information for this article is available on the WWW under
[10b–d]
of MIL-101-SO H.
The MIL-101-SO H ideally formulated Cr -
3 3
3
Chem. Eur. J. 2014, 20, 14976 – 14980
14976
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim