Efficient and recyclable copper-based MOF-catalyzed N-arylation of N-containing heterocycles with aryliodides

Article abstract of DOI:10.1039/C6OB02068B

Copper-based MOF-199 was used as an efficient heterogeneous catalyst to catalyze cross-coupling reactions between N-containing heterocycles and aryliodides with high yields. The catalyst can be easily separated from the reaction mixture, and can be reused at least 5 times without significantly decreasing the activity. The XRD results showed that the crystallinity and structure of MOF-199 can be maintained well during the coupling reaction.

Full text of DOI:10.1039/C6OB02068B

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Takeharu Haino et al.
Solvent-induced emission of organogels based on tris(phenylisoxazolyl)
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Efficient and recyclable copper‐based MOF‐catalyzed N‐arylation
of N‐containing heterocycles with aryliodides
Zihao Li,a Fei Meng,b Jie Zhang,a Jianwei Xiea,* and Bin Daia
Received 00th January 20xx,
Accepted 00th January 20xx
Copper‐based MOF‐199 was used as an efficient heterogeneous catalyst to catalyze the crossing‐coupling reactions
between N‐containing heterocycles and aryliodides with high yields. The catalyst can be easily separated from the reaction
mixture, and be reused at least 5 times without significantly decreasing activity. The XRD results showed that the
DOI: 10.1039/x0xx00000x
www.rsc.org/
crystallinity
and
structure
of
MOF‐199
can
be
kept
well
during
the
coupling
reaction.
Metal‐organic frameworks (MOFs) are a unique class of porous
and crystalline materials composed of metal cations (or metal
clusters) and organic linkers, and are receiving extensive
attention for their specific applications in the areas of gas
separation and storage, drug delivery and chemical sensor.20
Since several MOFs possess large surface areas, good thermal
stability and potentially metal active sites, their application in
heterogeneous catalytic reactions is another important field.21
Introduction
Copper‐catalyzed Ullmann‐type C‐N bond‐forming reactions
are widely used in industry and academic for the synthesis of
pharmaceuticals, materials, natural products and other
biologically active molecules.1 To date, the development, in
these field, continues to progress dramatically by the discovery
of various of efficient monodentate and bidentate ligands.2
Despite the extensive investigations on homogeneous
copper/ligand catalytic system for N‐arylation reactions, they
inherently suffer from non‐reusability, difficulty in separating
from the reaction media, as well as difficulty in the removal of
residual copper impurities from the final products. Thereafter,
several heterogeneous copper‐based catalysts have been
developed to overcome these drawbacks mentioned above.
For example, supported copper or copper nanoparticles (such
as CELL‐Cu(0)3, CuO nanoparticles (NPs)4, Cu2O coated Cu NPs5,
CuO NPs6, Cu0 or Cu2+/4Å7, RGO/Cu NPs8, electrospun CuO
NPs9, Cu NPs/Zeolite10, Cu@Cu2O NPs‐RGO11, CuO
Among
them,
MOF‐199
[copper(II))‐benzene‐1,3,5‐
tricarboxylate] is one of the well‐studied MOFs, which was
firstly reported in 1999 by Chui et al., who denominated the
structure as ‘‘HKUST‐1”.22 After then, MOF‐199 has been
employed widely as heterogeneous catalyst for various
transformations.23 However, to the best of our knowledge,
there is no example using MOF‐199 as catalyst for Ullmann‐
tpye C‐N coupling reactions. As part of our studies on the
homogeneous copper‐catalyzed coupling reactions,24 in this
paper, we wish to report the direct N‐arylation of heterocycles
with aryl iodides by using MOF‐199 as the efficient and
recyclable heterogeneous catalyst.
NPs/MWCNT12,
activated
Cu
powder13
and
Cu+‐
montmorillonite14) have been used successfully as the
heterogeneous catalyst for C‐N coupling reactions with the
advantages of simplified isolation of the product, easy
recovery and recyclability of the catalysts. Meanwhile,
Results and discussion
Initially, 4‐iodotoluene and 1H‐pyrrole were chosen as the
model substrates to optimize the reaction conditions,
including catalyst, bases and solvents. The results are listed in
Table 1. High value of yield toward the cross‐coupling product
(96%) was obtained, when the reaction was carried out in
DMSO using 10 mol% of MOF‐199 catalyst, in the presence of
NaOH (2 equiv.) as a base at 120 oC for 12 h (entry 1). Cu(NO3)2
or the mixture of Cu(NO3)2 and trimesic acid, which were used
as the catalyst under the same reaction conditions, both
results in obviously decrease yields (entries 2 and 3). Control
experiment was carried out in the absence of catalyst, and no
product was afforded (entry 4). The catalytic efficiency was
observed to be reduced when the catalyst loading was
decreased to 5 mol% or 2.5 mol% (entries 5 and 6). Several
bases, including KOH, K2CO3, Cs2CO3 and K3PO4, were assayed,
immobilized
copper‐ligand
complexes
such
as
[Cu(Im12)]2CuCl215, MCM‐41‐2N‐CuI16, polystyrene‐supported‐
N,N‐dimethylethylenediamine Cu(II)17 complex, polymer‐
supported‐β‐alanine Cu(I)18 and Fe3O4‐EDTA–Cu(II)19 were also
been applied for these reactions due to their thermal stability,
reusability and high catalytic activities.
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Table 1 Optimization of the reaction conditionsa
Table 2 Reaction of aryl iodides with nitrogen‐containing heterocyclesa
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DOI: 10.1039/C6OB02068B
Entry Catalyst (mol%)
Base
NaOH
NaOH
Solvent
DMSO
DMSO
Yieldb (%)
96
68
1
2
MOF‐199 (10)
Cu(NO3)3 (10) + trimesic
acid (20)
3a, 96% (10%b, tracec)
3b, 93%
3e, 95%
3c, 97%
3f, 72%
3
4
5
6
7
8
9
10
11
12
13
14
15
Cu(NO3)3 (10)
‐
NaOH
NaOH
NaOH
NaOH
KOH
K2CO3
Cs2CO3
K3PO4
NaOH
NaOH
NaOH
NaOH
NaOH
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
DMAC
Dioxane
DMSO
DMSO
50
0
MOF‐199 (5)
MOF‐199 (2.5)
MOF‐199 (10)
MOF‐199 (10)
MOF‐199 (10)
MOF‐199 (10)
MOF‐199 (10)
MOF‐199 (10)
MOF‐199 (10)
MOF‐199 (10)
MOF‐199 (10)
89
83
81
15
75
78
15
51
0
3d, 95%
3g, 80%
3h, 79% (15%b, tracec)
3i, 87%
72c
75d
a
Reaction conditions: 1a (0.5 mmol), 2a (0.75 mmol), catalyst, base (1.0 mmol),
solvent (1 mL), 120 °C, 12 h. b Isolated yield. c 100 °C. d 8 h.
3j, 84%
3k, 50%
3n, 66%
3l, 82%
3o, 92%
and NaOH provided the highest yield (entries 7‐10). The
reaction conducted in DMSO were found faster than those
conducted in DMF, dimethylacetamide (DMAC) or 1,4‐dioxane
(entries 11‐13). Moreover, lowering the reaction temperature
from 120 °C to 100 °C led to a dramatic decrease in the yield
(entry 14), and the same result also appeared in shorting
reaction time from 12 to 8 h (entry 15). In summary, the
combination of 10 mol% MOF‐199 and 2 equiv. NaOH in DMSO
at 120 oC for 12 h was the optimal condition.
Under the optimal conditions, the scope of the MOF‐199
catalyst system was explored between various aryl iodides and
N‐containing heterocycles. As shown in Table 2, the coupling
reactions were performed well for most of aryl iodides with
electron‐rich, electron‐neutral and electron‐deficient groups
with 1H‐pyrrole to afford corresponding 1‐aryl‐1H‐pyrrole in
3m, 92%
3p, 67% (13%b, tracec)
3q, 83%
3t, 56%
3r, 73%
N
N
N
Ph
3s, 90%
3u, 94%
good to excellent yields (3a‐3f). In general, the electron‐
deficient aryl iodides gave the coupling products in lower
3x, 88% (38%b, tracec)
yields. Indoles could also be reacted well with 50‐92% yields
(3g‐3n), and the electron‐rich indole exhibited a higher activity
3v, 50%
3y, 73%
3w, 85%
3z, 85%
than the electron‐deficient one (3m vs 3n). For 1H‐1,2,4‐
triazole, this catalyst system also applied to react, however,
the reactions of the 1‐iodo‐4‐nitrobenzene and the 1‐(4‐
iodophenyl)ethanone gave the N‐arylated products in 56% and
50% yields (3t and 3v) due to incomplete conversion of aryl
iodides and formation of dehalogenated by‐products.
Additionally, other reactions of aryl iodides with 1H‐1,2,4‐
a
Reaction conditions: 1 (0.5 mmol), 2 (0.75 mmol), MOF‐199 (10 mol%), NaOH
b
(1.0 mmol), DMSO (1 mL), 120 °C, 12 h; isolated yield. 4‐Bromotoluene as the
substrate. c Chlorobenzene as the substrate.
triazole provided 73%‐94% yields (3o‐3u). Furthermore, we
this process to 4‐bromotoluene gave lower yields.
were pleased to find that the crossing‐coupling reactions
proceeded well to give the respective products in good to
excellent yields, when the 1H‐imidazole was used as the
Unfortunately, the reaction did not occur when chlorobenzene
was used as the substrate under the standard reactions (3a, 3h,
3p and 3x). Table 3 provides a comparison of the results
obtained for our present MOF‐199 catalyst with other
reported copper heterogeneous catalytic systems3,7,27‐29 in
nucleophile (3w‐3z). Because of less reactivity, extension of
2 | J. Name., 2012, 00, 1‐3
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Ullmann‐type C‐N cross‐coupling reactions of aryl iodides with coupling reaction was carried out in DMSO at 120 oC for 12 h,
View Article Online
N‐containing heterocycles. And we can see that the present using 4‐iodotoluene (0.5 mmol), pyrrolDeO(I0: 1.70.510m39m/Co6Ol),B0in206th8Be
catalyst exhibited higher efficiency compared to other presence of 10 mol% MOF‐199 catalyst. After completion of
reported system, with higher yields, relatively milder the first run, the catalyst was separated from the reaction
conditions and broader functional groups tolerate.
mixture by simple centrifugation, washed with H2O, ethyl
On the basis of the optimal reaction conditions, we also acetate and ethyl alcohol, and dried 100 oC under vacuum in 6
carried out for each type of reaction in a large scale by taking h. The recovered MOF‐199 was then reused as catalyst in
10 mmol of 4‐iodotoluene in 10 mL DMSO at 120 C for 12 h. further transformation under the standard conditions.
As shown in the Scheme 1, the reactions proceeded without Experimental results indicated that the MOF‐199 catalyst could
any difficulty to obtain 93% yield of 3a (1.46 g), 94% yield of 3h be recovered and reused without a significant deactivation in
(1.95 g), 73% yield of 3p (1.16 g) and 92% yield of 3x (1.46 g), catalytic activity, and the yield of 3a always maintains above
respectively.
90% after 5 runs. By comparing the XRD of MOF‐199 before
As a solid catalyst in organic transformation, issues that should and after 5 runs’ reaction, we can find that there are no
be addressed are the ease of separation as well as the obvious differences, which indicate that the crystallinity and
deactivation and reusability of the catalyst. The MOF‐199 was structure of MOF‐199 can be kept well during the course of
therefore investigated for the recoverability and reusability, by the reaction. Furthermore, we have investigated the metal
repeatedly separating from the reaction mixture via leaching of catalyst MOF‐199 by atomic absorption
centrifugation, washing it and then reusing it (Scheme 2). The
spectroscopy (AAS) analysis. And low than 0.18% of the initial
copper content was detected in reaction solution, which
indicated that MOF‐199 was an excellent heterogeneous
catalyst for this type reaction.
Table 3 The comparison of efficiency of different heterogeneous copper catalyst in
Ullmann‐typle C‐N coupling reactions of aryl iodides with N‐containing heterocycles
Catalyst (Cu mol%)
MOF‐199 (10)
Condition and yield (%)
NaOH, DMSO, 120 °C; 50‐97%
K2CO3, DMSO, 130 °C; 40‐95%
Cs2CO3, pyrrole, 135 °C; 25-100%
KOtBu, DMF, 120 °C; 0-84%
KOH, DMSO, 125 °C; 88%
Ref.
This work
CELL‐Cu(0) (0.9)
3
7
27
28
29
Cu0/4Å (8.7)
Cu2(BDC)2(DABCO) (5)
CuI/meso‐N‐C‐1 (15)
CuO/AB (5)
KOtBu, toluene, 180 °C; 26-100%
I
N
MOF-199, NaOH
+
HN
DMSO, 120 °C,12h
Me
Me
1a, 10 mmol
2a-d , 15 mmol
3a, 3h, 3p, 3x
N
Scheme 2 X‐ray powder diffractogram of the fresh (a: black trace) and reused (b: red
trace) MOF‐199.
N
N
N
N
N
N
Me
Me
Me
Me
3a, 1.46 g, 93%
3h, 1.95 g, 94%
3p, 1.16 g, 73% 3x, 1.46 g, 92%
Ar-N-Het
Ar-X + NaOH
Scheme 1 Gram‐scale reactions of N‐arylation of heterocycles with 4‐iodotoluene.
MOF-199
Oxidative
addition
Reductive
elimination
N-Het
X
Ar
Ar
B
A
NaX + H2O
Het-NH + NaOH
Scheme 3 Plausible reaction mechanism.
Based on previous literature reports12,25,26, the reaction
mechanism for this transformation is proposed and shown in
Scheme 3. This reaction involves a heterogeneous process and
the catalysis may occur on the exposed copper site. In the
presence of KOH, oxidative addition of MOF‐199 with aryl
Scheme 2 The recyclability of MOF‐199 for N‐arylation of pyrrole with 4‐iodotoluene.
Reaction conditions: 4‐iodotoluene (0.5 mmol), pyrrole (0.75 mmol), MOF‐199 (10
mol%), NaOH (1.0 mmol), DMSO (1 mL), 120 °C, 12 h; isolated yield.
halides provided Cu‐complex
A. And then, the nucleophilic
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substitution of intermediate
A
with N‐containing heterocycles After completion of the reaction, the reaction mixture was hot
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DOI: 10.1039/C6OB02068B
gives B, followed by reductive elimination lead to desired N‐ filtrated under vacuum. The solid was washed with DMSO, and
arylated products and regenerate the active copper catalyst.
the liquid phase was analyzed by AAS.
Conclusions
Acknowledgements
In conclusion, we have established a simple and efficient We are grateful to the NSFC (no. 21606153) for the financial
copper‐based MOF‐catalyzed N‐arylation of N‐containing support for this work.
heterocycles with aryl iodides, the corresponding target
products were obtained in moderate to excellent yields. The
convenient approach, the stable and reusable catalyst, as well
Notes and references
as the option for efficient large scale preparation, are the
features of the catalytic process presented in the current
paper. Further investigation into other types copper‐based
MOFs‐catalyzed reactions are currently ongoing in our
laboratory and will be reported in due course.
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General methods
All the reactions were carried out under air using magnetic
1
stirring unless otherwise noted. H NMR and 13C NMR were
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aryl halides (0.50 mmol), N‐containing heterocycles (0.75
mmol), NaOH (1.0 mmol) and DMSO (1 mL). The reaction
mixture was reacted at 120 °C in a preheated oil bath for 12 h.
The reaction mixture was cooled to room temperature,
extracted with ethyl acetate (20 mL×3). The combined organic
phases was washed with water and brine, dried over
anhydrous Na2SO4, and concentrated in vacuo. The residue
was purified by flash column chromatograph on silica gel (ethyl
acetate/petroleum ether as the eluent) to afford the target
4
product 3a‐3z.
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separated from the reaction mixture by simple centrifugation,
washed with copious amounts of H2O, ethyl acetate and ethyl
alcohol, and dried 100 oC under vacuum in 6 h. The recovered
MOF‐199 catalyst was then reused as catalyst in further
transformation under identical conditions. This process was
then repeated.
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