Straightforward installation of carbon-halogen, carbon-oxygen and carbon-carbon bonds within metal-organic frameworks (MOF) via palladium-catalysed direct C-H functionalization

Article abstract of DOI:10.1039/c4cc05222f

The straightforward C-H functionalization of UiO-67-dcppy materials was realized by a Pd-catalysed PSM. This novel protocol provides an efficient method for the synthesis of various functionalized MOFs, which have shown promising adsorbent ability in removing phenolic contaminates from water. This journal is

Full text of DOI:10.1039/c4cc05222f

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Straightforward installation of carbon–halogen,
carbon–oxygen and carbon–carbon bonds
within metal–organic frameworks (MOF) via
palladium-catalysed direct C–H functionalization†
Cite this:DOI: 10.1039/c4cc05222f
Received 7th July 2014,
Accepted 8th September 2014
a
a
a
a
a
Tao Liu,‡ Da-Qiang Li,‡ Si-Yu Wang, Yong-Zhou Hu, Xiao-Wu Dong,*
DOI: 10.1039/c4cc05222f
b
cd
Xin-Yuan Liu* and Chi-Ming Che
www.rsc.org/chemcomm
The straightforward C–H functionalization of UiO-67-dcppy materials
was realized by a Pd-catalysed PSM. This novel protocol provides an
efficient method for the synthesis of various functionalized MOFs,
which have shown promising adsorbent ability in removing phenolic
contaminates from water.
Fig. 1 (A) The post-synthetic cyclometalation in previous work; (B) the
proposed cyclopalladation intermediate within UiO-67-dcppy.
Crystalline metal–organic frameworks (MOFs) have become
particularly attractive for a wide range of applications such as gas
1a,b
1c
1d
1e
storage,
separation, biomedicine, heterogeneous catalysis,
1f,g
7
and other technologies. The development of efficient methods heterogeneous catalysts (Fig. 1A). In particular, the usage of
0
for the construction of various types of functionalized MOFs is 2-phenylpyridine-5,4 -dicarboxylic acid (H
2
dcppy) as a building block
2
highly important. Recently, post-synthetic modifications (PSM) of is much more preferable for the preparation of efficient single-site
known MOFs have emerged as important tools for broader intro- MOF catalysts through the organometallic cyclometalation (i.e.
3
8
duction of functional groups into MOFs, in particular, which have iridium and ruthenium). However, to our knowledge, the C–H
also been achieved to produce functional materials with improved functionalization of MOFs assisted by a directing group with
4
5
catalytic and gas sorption properties. Despite these advancements transition metal catalysis has not been disclosed so far.
in PSM approaches, a large proportion of these methods depends on
Although Glorius and co-workers have recently reported
6a,b
6c
the interconversions of functional groups (e.g. amine, hydroxyl,
pioneering work on the direct palladium-catalysed C–H phenylation
6d
6e
9
azide, and aldehyde ), which are greatly limited by the require- of an indole-derived UMCM-1-type MOF, there are still some
ment of pre-formed functionality of MOFs, thereby promoting us to challenges needed to be addressed, such as the limited scope in
develop novel PSM methods for the straightforward functionaliza- terms of MOFs (only one example) and the long reaction time (seven
tion of MOFs.
days). Therefore, based on the mode of cyclometalation within MOFs
Recently, MOFs with open coordination sites have been shown to and owing to the use of 2-phenylpyridine as an effective directing
1
0
efficiently bind to various metal ions via PSM protocols, providing a group in Pd-catalysed C–H activation in homogenous systems,
useful platform for the development of coordination chemistry and we envisioned that MOFs bearing 2-phenylpyridine as a building
linkage would be the potential precursors for C–H functionalization
a
via a cyclopalladation intermediate (Fig. 1B). Herein, we reported
the first example of a convenient PSM protocol of UiO-67-dcppy
materials via a facile palladium-catalysed carbon–halogen, carbon–
oxygen and carbon–carbon bond-forming functionalization,
affording chemically stable, highly porous and functionally
diverse collection of MOFs (Scheme 1).
ZJU-ENS Joint Laboratory of Medicinal Chemistry, College of Pharmaceutical
Sciences, Zhejiang University, Hangzhou, 310058, P. R. China.
E-mail: dongxw@zju.edu.cn
b
c
Department of Chemistry, South University of Science and Technology of China,
Shenzhen, 518055, P. R. China. E-mail: liuxy3@sustc.edu.cn
Department of Chemistry, State Key Laboratory of Synthetic Chemistry,
The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China.
E-mail: cmche@hku.hk
To validate the feasibility of the proposed PSM process, three
Zr-cluster-based MOFs bearing the 2-phenylpyridine moiety (i.e.
UiO-67-dcppy, 2-Me-UiO-67-dcppy and 3-Me-UiO-67-dcppy) were
d
HKU Shenzhen Institute of Research and Innovation, Shenzhen, 518053,
P. R. China
†
Electronic supplementary information (ESI) available: Experimental procedures,
1
1
synthesized via solvothermal reaction, since this class of MOFs
characterization of synthesized compounds and MOFs, Tables S1–S4 and Fig. S1–S6.
See DOI: 10.1039/c4cc05222f
have exhibited particularly attractive features including chemical
1
2
‡
T. Liu and D.-Q. Li contributed equally to this work.
and thermal stability and large apparent surface areas. Powder
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UiO-67-dcppy was provided by the presence of typical C–Br
ꢀ
1
stretching vibrations (783 cm ) in IR spectra (Fig. S2†) and
ꢀ
ꢀ
molecular ion peaks of [Hdcppy-Br] (m/z 320) and [Hdcppy-diBr]
m/z 400) in negative mass spectra of digested solution.
(
Most importantly, the superior catalytic C–H bromination
performance and reactivity of UiO-67-dcppy derivatives were
observed as compared with that of H
under the homogeneous reaction conditions (42% yield of
-Br-H dcppy without 2,6-diBr-H dcppy) (Fig. S3†). It should
be noted that no brominated product was obtained by using a
2
dcppy as the substrate
2
2
2
14
non-porous amorphous Zr-based powder (Fig. S1† and Table S2†)
as the substrate under the standard conditions (Fig. S3†). Such
drastic difference could be attributed to their intrinsic topology and
porosity for efficiently substrate and catalysis binding and inter-
Scheme 1 PSM of UiO-67-dcppy materials via Pd-catalysed C–H activation.
15
action in the porous cage.
X-Ray Diffraction (PXRD) and Brunauer–Emmett–Teller (BET)
surface analyses clearly demonstrate that the resultant UiO-67-
type materials are highly porous crystalline which are isostructural
To further investigate the scope of application, we set out to
explore the scope of this protocol with respect to chlorinated
agent (N-chlorosuccinimide, NCS) and other UiO-67-dcppys.
To our delight, a good yield of desired chlorinated products
12
with UiO-67 materials (Fig. S1† and Table S2†). Then, these
UiO-67-dcppy materials were used as substrates for Pd-catalysed
C–H activation/C–X halogenation according to reported procedures
2-Cl-UiO-67-dcppy (26%) and 2,6-diCl-UiO-67-dcppy (70%) on a
13
proximal C–H site of 2-phenylpyridine were obtained with NCS
as the chlorinated agent at 60 1C (Table 1, entry 2 and Fig. 2).
for homogenous C–H activation reactions. The reaction of
UiO-67-dcppy and N-bromosuccinimide (NBS) using 20 mol% of
Pd(OAc)2 as the catalyst with acetic acid as the additive was
conducted in acetonitrile at room temperature for 24 hours
3
Moreover, mono-halogenated products 2-CH -UiO-67-dcppy and
3
-CH -UiO-67-dcppy with up to almost complete regioselectivity
3
were afforded with 2-Me-6-Br-UiO-67-dcppy, 3-Me-6-Br-UiO-67-
dcppy and 2-Me-6-Cl-UiO-67-dcppy in good yields of 46%, 85%
and 68%, respectively (Table 1, entries 3–5 and Fig. 2). The highly
regioselective features of C–H halogenation would be possibly
attributed to the steric hindrance originating from the substituent
side of the 2-phenylpyridine linker during the formation of a
cyclometalated intermediate within MOF lattices, thereby avoiding
the generation of the di-halogenated products.
(
Table S3,† entry 1) and afforded the desired brominated product
(2-Br-UiO-67-dcppy) on a proximal C–H site of 2-phenylpyridine,
albeit with low conversion (16%), which was quantified and
characterized using H NMR analysis of digested solution. Next,
the screening of solvents (i.e. 1,4-dioxane, DCE, DMF, Table S3†) for
the reaction reveals that DMF was the optimal one, affording a
good yield of 2-Br-UiO-67-dcppy (21%) and 2,6-diBr-UiO-67-dcppy
1
(75%) (Table S3,† entry 6 and Fig. 2). In contrast, no desired
Owing to the excellent reactive nature of UiO-67-dcppy in C–H
halogenation, we then tested the C–H oxidative functionalization
product was observed in the absence of Pd catalysis, indicating
that palladium is essential for this reaction (Table S3,† entry 4). The
of UiO-67-dcppy. Initially, UiO-67-dcppy was treated with Pd(OAc)2
2
different loadings of Pd(OAc) were examined, and it was found
(
20 mol%) and PhI(OAc) (5 equiv.) in DMF. It was found that
that 20 mol% of Pd(OAc) gave the best result. In addition to
2
2
the reaction could proceed, and a small amount of the desired
NMR analysis, other evidence for successful bromination on
Table 1 The Pd-catalysed C–X (i.e. Cl and Br), C–O and C–C bond-
forming functionalization of UiO-67-dcppy materials
e
Yield (%)
Entry
UiO-67-dcppy materials
Substrate
mono-
di-
a
1
UiO-67-dcppy
UiO-67-dcppy
2-Me-UiO-67-dcppy
3-Me-UiO-67-dcppy
2-Me-UiO-67-dcppy
UiO-67-dcppy
NBS
NCS
NBS
NBS
NCS
PhI(OAc)
PhB(OH)
2
21
26
46
85
68
—
20
75
70
—
—
—
75
—
b
2
a
3
a
4
b
5
c
6
2
d
7
UiO-67-dcppy
a
2
UiO-67 materials (0.1 mmol), Pd(OAc) (20 mol%), NBS (0.5 mmol)
and HOAc (0.5 mmol) in DMF (1.0 mL) at r.t. (B25 1C) for 24 hours.
b
UiO-67 materials (0.1 mmol), Pd(OAc)
HOAc (0.5 mmol) in DMF (1.0 mL) at 60 1C for 24 hours. UiO-67-dcppy
0.1 mmol), Pd(OAc) (20 mol%), PhI(OAc) (0.5 mmol) in DCE (1.0 mL) at
0 1C for 12 hours. UiO-67-dcppy (0.1 mmol), Pd(OAc) (30 mol%), BQ
2
(20 mol%), NCS (0.5 mmol) and
c
(
8
2
2
1
Fig. 2 H-NMR data of the organic linker of the digested post-modified
d
2
UiO-67-dcppy materials; di-substituted product (+), mono-substituted (0.3 mmol), PhB(OH) (0.3 mmol), DMF (1.0 mL) at 100 1C for 24 hours.
2
e
1
product (*) and the remaining starting material (#).
The conversion was determined by H NMR analysis of digested solution.
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di-acetoxylated product was obtained (15%). After optimizing 2,6-diOAc-Uio-67-dcppy than that of 2,6-diCl-Uio-67-dcppy
2
ꢀ1
the reaction conditions, the yield of the desired product via the (Table S4;† BET surface areas of 380 vs. 930 m g ). However,
C–H oxidative PSM protocol could be improved by using DCE in inductively coupled plasma-mass spectrometry (ICP-MS) analysis
place of DMF as solvent, affording 2,6-diOAc-UiO-67-dcppy in a of the obtained UiO-67-dcppy-Br showed the presence of a small
good yield (75%, Table 1, entry 6 and Fig. 2). Additionally, the IR amount of palladium residue (2.8 wt%), which will further
spectra of 2,6-diOAc-UiO-67-dcppy with C–H stretching vibrations require much efforts to overcome this problem. Overall, all of
ꢀ
1
(
(
2800–3000 cm ) and the characteristic CQO stretching vibrations the functionalized MOFs are still highly porous and crystalline even
ꢀ
1
B1770 cm ) clearly demonstrated the efficient introduction of an after post-synthetic modification, indicating that all of them would
acetoxyl group (CH CO) via the current PSM approach (Fig. S2†). provide a useful platform for the further development of their
The negative ion mass spectrum of digested 2,6-diOAc-UiO-67- potential applications in the field of materials.
3
dcppy gave a value of m/z 358, which is consistent with the presence
of a molecular ion peak of [Hdcppy-diOAc] . Furthermore, it is of as good adsorbents for phenolic compounds, which are
interest to note that chelation-directed C–H activation could be considered as one of the most important sets of organic
extended to C–C bond-forming PSM of UiO-67-dcppy with slight contaminants, the obtained functionalized UiO-67 materials
modification of the reaction conditions. Our preliminary results were also evaluated for their adsorbent ability in removing
showed that the reaction of UiO-67-dcppy with phenylboronic phenolic compounds from water (Fig. S6A†). Owing to the
Considering the fact that pyridine-based polymers can serve
ꢀ
16
1
7
acid (3 equiv.) in the presence of Pd(OAc)
,4-benzoquinone (3 equiv.) in DMF gave desired coupling incorporated onto the wall of UiO-67-dcppy, these MOFs showed
product 2-Ph-UiO-67-dcppy with relatively low yield (20%, different adsorbent capacity of phenol, and UiO-67-dcppy-Br was the
2
(30 mol%) and electronically distinct effect of different functionalized groups
1
ꢀ
1
Table 1, entry 7 and Fig. 2), which is currently under further best one with an adsorption capacity of 45 mg g . More signifi-
optimization in our laboratory. cantly, the adsorption capacities of UiO-67-dcppy-Br for phenol
The resultant functionalized MOFs after PSM were shown to derivatives bearing electron-withdrawing groups dramatically
ꢀ1
possess the same structure and comparable thermal stability to increased to 112, 205 and 361 mg g (Fig. S6B†) for 4-Cl-phenol,
that of parent UiO-67-dcppy as evidenced by PXRD (Fig. 3), 4-nitro-phenol and 2-nitro-phenol, respectively, possibly owing to the
Brunauer–Emmett–Teller (BET) surface area analysis (Table enhanced acidity of hydroxyl groups of phenols. Furthermore,
ꢀ
1
S4†), thermogravimetric analysis (TGA, Fig. S4†), scanning the treatment of 2-nitro-phenol solution (50 mg L , 10 mL) with
electron microscopy (SEM) images (Fig. S5†). It is demonstrated UiO-67-dcppy-Br (100 mg) for 3 hours resulted in excellent removal
that the crystallinity of the functionalized UiO-67-dcppy materials efficiency (96.2%) (Fig. S6C†), demonstrating the potential practical
remains reserved, although the decreased crystallinity of UiO-67- application of UiO-67-dcppy-Br for cleaning hazardous materials
dcppy-OAc was observed, which was confirmed by drastic BET from contaminated water.
2
ꢀ1
surface decrease from 2281 to 380 cm g (Table S4†) possibly
We have presented here the first example of a convenient
owing to slightly harsh conditions using acetic acid and higher PSM protocol for Pd-catalysed C–H functionalization within
temperature (80 1C). The chemical stability of these functionalized MOF lattices via a cyclopalladation strategy, leading to direct
UiO-67-dcppy derivatives was also found to be quite similar to installation of C–X (i.e. chloro and bromo), C–O and C–C bonds
UiO-67-dcppy, with good tolerance to polar solvents including onto the linker of MOFs. The superior catalytic C–H bromination
methanol, ethanol, acetone and DMF. Compared with that of performance and reactivity of UiO-67-dcppy were observed,
parent Uio-67-dcppy materials, the C–H functionalized Uio-67- suggesting that C–H functionalization of MOFs would be an
dcppys showed a significant decrease of the BET surface area. intriguing late-stage functionalization approach as advantageous
The larger molecular volume of the acetoxy group as compared alternative to traditional interconversions of functional groups in
with the chloro group led to more decreased BET surface area of PSM of MOFs. More significantly, the resulting UiO-67-dcppy-Br
has shown remarkable adsorbent ability of the phenol derivatives
bearing electron-withdrawing groups from contaminated water.
Further studies on a wider range of applications of these functiona-
lized MOFs are currently in progress in our laboratory.
Financial support from NSFC (No. 21302088), the National
Key Basic Research Program of China (973 Program
2
013CB834802), Shenzhen special funds for the development
of biomedicine, internet, new energy, and new material industries
JCYJ20130401144532131), as well as from South University of
(
Science and Technology of China is greatly appreciated.
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