A porous metal-organic framework containing multiple active Cu2+ sites for highly efficient cross dehydrogenative coupling reaction

Article abstract of DOI:10.1039/c4dt03371j

A novel 3D porous metal-organic framework was constructed from imidazole carboxylate linkers and copper(ii) nodes, which in situ generates multiple active Cu^II sites in the nanosized channel walls for highly efficient cross dehydrogenative coup

Full text of DOI:10.1039/c4dt03371j

Dalton
Transactions
View Article Online
View Journal
COMMUNICATION
A porous metal–organic framework containing
multiple active Cu2+ sites for highly efficient
cross dehydrogenative coupling reaction†
Cite this: DOI: 10.1039/c4dt03371j
Received 3rd November 2014,
Accepted 1st December 2014
Shu-Lan Zhu, Sha Ou, Min Zhao, Hong Shen* and Chuan-De Wu*
DOI: 10.1039/c4dt03371j
www.rsc.org/dalton
A novel 3D porous metal–organic framework was constructed majorly controlled by the coordination environments of metal
from imidazole carboxylate linkers and copper(II) nodes, which sites, the most simple and straightforward strategy is to syn-
in situ generates multiple active CuII sites in the nanosized channel thesize MOF catalysts that contain substrate accessible and
walls for highly efficient cross dehydrogenative coupling reaction unsaturated metal coordination sites either vacant or occupied
between 1,2,3,4-tetrahydroisoquinoline derivatives and nitro- by volatile molecules, whereas the later ones can be easily acti-
alkanes that are superior to the simple copper salts.
vated by heating and/or vacuuming to remove the volatile
solvent molecules.6 Considering that the organic ligands con-
taining mixed N,O donors can give rise to multiple coordi-
nation environments of metal ions in a framework, which has
the opportunity to generate catalytically active metal sites with
unsaturated coordination sites,7 we have synthesized a ligand
containing mixed donors of imidazole and carboxylate groups
(5-(1H-imidazol-1-yl)isophthalic acid = H2L; Scheme 1). The
connection between CuII ions and L results in an interesting
MOF material [Cu2L(H2O)]·2Cl·2DMF·4H2O (1), containing
two kinds of coordinatively unsaturated copper sites on the
surfaces of channel walls, which is highly effective on CDC
reaction by direct activation of sp3 C–H bonds in hetero-
geneous catalysis.
Blue crystals of compound 1 were synthesized by heating a
mixture of CuCl2·2H2O and H2L in acidified DMF solvent at
80 °C for 2 days.‡ Single crystal X-ray diffraction analysis has
revealed that compound 1 crystallizes in the monoclinic C2/m
space group.§ Besides guest molecules, there are two copper(II)
ions, one L ligand and one water molecule in the asymmetric
unit. As shown in Fig. 1a, two symmetrically independent
copper ions comprise distinct coordination environments. The
first square-pyramid-coordinated copper ion and its symmetry-
operated one are coupled by four carboxylate groups to form a
Cu2(COO)4(H2O)2 paddle-wheel secondary building unit (SBU).
Selective C–C bond formation is one of the most important
catalytic reactions in organic chemistry, which can build more
complex molecules from simple precursors. Because sp3 C–H
bonds are ubiquitous in organic molecules, direct activation of
the inert sp3 C–H bonds is particularly attractive.1 Among the
vast C–H activation strategies, cross dehydrogenative coupling
(CDC) reaction offers an elegant pathway for the efficient and
atom-economical construction of new C–C and C–heteroatom
bonds, because it does not require tedious prior functionali-
zation of both coupling partners.2 From a practical point of
view, heterogenizing homogeneous catalysts has the advan-
tages of being atom-economical, environmental benignity, easy
separation and recyclability to meet the criteria of sustainable
chemistry.3 However, relatively long reaction time and high
temperature are the bottlenecks for the heterogenized CDC
catalysts. Therefore, to improve the efficiency of heterogeneous
CDC catalysts for sp3 C–H activation is a challenging subject.
Metal–organic frameworks (MOFs) are an emerging class of
porous materials, which are built from organic linkers con-
nected with metal nodes. The porosity and functionality of
MOFs are systematically tunable by judicious choice and modi-
fication of the constituent metal nodes and organic ligands,
which exhibit great potential for applications in sorption,
separation, recognition, sensing, drug delivery and catalysis.4,5
Since the catalytic properties of metal-containing catalysts are
Center for Chemistry of High Performance and Novel Materials, Department of
Chemistry, Zhejiang University, Hangzhou, 310027, P. R. China.
E-mail: cdwu@zju.edu.cn
†Electronic supplementary information (ESI) available: Additional experimental
procedures, figures, schemes, table and crystal data. CCDC 1032156. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
c4dt03371j
Scheme 1 5-(1H-imidazol-1-yl)isophthalic acid (H2L).
This journal is © The Royal Society of Chemistry 2014
Dalton Trans.

View Article Online
Communication
Dalton Transactions
Table 1 CDC reaction of 1,2,3,4-tetrahydroisoquinoline derivatives
with nitroalkanesa
Entry
1
R1
R2
H
Yieldb (%)
97
2
3
4
5
H
H
H
H
72c
75d
92
Fig. 1 (A) The coordination mode of L ligand and the coordination
environments of copper(II) ions in the channel wall of 1 as viewed along
the b-axis; (B) the 3D opening framework of 1 as viewed down the
a-axis; (C) a perspective view of two different active copper(II) sites
located in the channel wall; and (D) space-filling representation of the
3D structure of 1 viewed along the c-axis, showing the nanotubular
channels. Color scheme: Cu, purple balls and green square-pyramids;
O, red; N, blue; C, deep gray; H, light gray.
89
6
H
81
7
H
70
8
–CH3
–CH3
–CH3
H
75
The second copper ion is coordinating to two imidazoles and
two monodentate carboxylate groups in a square coordination
sphere. The L ligand acts as a tetradentate ligand to coordinate
with four copper ions, resulting in a 3D porous framework that
contains large 1D opening channels of 10.4 × 10.6 Å2 and 10.3 ×
15.0 Å2 as viewed along the a and c axes, respectively (Fig. 1).
In the crystal structure of 1, all copper ions are located in the
channel walls, which are accessible to solvent molecules
through the opening channels. Moreover, all copper(II) ions
are coordinating to labile water molecules or coordinatively
free, which can be simply activated for heterogeneous catalysis.
PLATON calculations suggest that 1 contains 72.8% void space
which is occupied by the solvent molecules and chloride ions.8
The TGA chart indicates that a weight loss of 23.3% occurred
between 30 and 275 °C as a result of the release of all solvent
molecules and aqua ligands (expected 24.3%).
9
91
10
11
12
13
14
65
76e
70e
62e
91f
H
H
H
a Tertiary amine (0.1 mmol), TBHP (0.15 mmol), catalyst (0.01 mmol)
and nitroalkane (1.0 mL) were stirred at room temperature for 6 h.
b Isolated yields. c Catalyzed by CuCl2. d Catalyzed by Cu(OAc)2.
e Catalyzed by HKUST-1. f The sixth cycle.
As demonstrated above, the prospect of using unfunctiona-
lized precursors to construct C–C bonds is one of the greatest
advantages of the CDC method over traditional strategies.
Since the homogeneous copper catalysts were proved to be the
efficient catalysts on the CDC reaction, the availability of the
copper sites in the channel walls of compound 1 prompted us vapor. These results indicate that the solvent guests play
to examine the catalytic efficiency in the CDC reaction. Com- crucial roles in maintaining the long range order of the frame-
pound 1 was activated by immersing in dry acetone to work structure. Solid 1 promoted CDC reaction was performed
exchange the solvent molecules included in the channels. under solvent free conditions in the presence of tert-butyl-
After a sample of 1 was treated with acetone at room tempera- hydroperoxide (TBHP) oxidant at room temperature for 6 h.¶
ture for 12 h, the positions of the sharp diffraction peaks of As shown in Table 1, compound 1 efficiently catalyzes the
PXRD are systematically shifted. It is interesting that the orig- CDC reaction of 1,2,3,4-tetrahydroisoquinoline derivatives
inal positions of the sharp PXRD peaks can be regenerated and nitroalkanes. The oxidation coupling reaction between
when the acetone activated sample was exposed to the DMF 2-phenyl-1,2,3,4-tetrahydroisoquinoline and nitromethane
Dalton Trans.
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Communication
proceeded smoothly with an excellent product yield of 97% derivatives with nitroalkanes, which is superior to the copper(II)
(Table 1, entry 1). For comparison, CuCl2 and Cu(OAc)2 were chloride and copper(II) acetate salts.
used as control catalysts to conduct the catalytic experiments.
This work was financially supported by the National NSF of
As shown in Table 1, their catalytic efficiency is inferior to that China (grant no. 21373180), the Fundamental Research Funds
of 1 under identical conditions (entries 2 and 3). These results for the Central Universities (2014FZA3006) and Zhejiang Provin-
demonstrate that the very high catalytic activity of 1 on CDC cial Natural Science Foundation of China (grant no. Z4100038).
reaction should be due to its porous structure that makes
the substrates have more chance to access the catalytic
metal centers in the pore surfaces. Compound 1 can promote
Notes and references
a range of oxidative coupling reactions. The CDC reaction
between 1,2,3,4-tetrahydroisoquinoline derivatives and
nitroalkanes proceeded smoothly with good to excellent
‡Synthesis of [Cu2L(H2O)]·2Cl·2DMF·4H2O (1). CuCl2·2H2O (10 mg, 0.06 mmol),
H2L (10 mg, 0.04 mmol) and 0.6 mL aqueous HCl (0.1 M) were dissolved in DMF
product yields (Table 1, entries 4–10). The slightly lowered
yields should be attributed to the steric hindrance and elec-
tronic effects. Moreover, the catalytic efficiency of 1 is superior
to that of the well-known HKUST-1 with Cu2(COO)4(H2O)2
paddle-wheel SBUs (Table 1, entries 11–13), which suggests
that the synergistic effect of multiple factors should also play
an important role.9
To prove that the catalysis chiefly occurs inside the pores of
1, we have monitored the accessibility of the open channels of
1 to both the reactant and product molecules by UV-Vis
absorption spectroscopy. The UV-Vis spectra clearly indicate
that the pores of 1 are accessible to both 2-phenyl-1,2,3,4-tetra-
hydroisoquinoline substrate and 1-(nitromethyl)-2-phenyl-
1,2,3,4-tetrahydroisoquinoline product molecules with the
uptakes of 9.6 and 10.7 wt%, respectively. Moreover, after the
reaction proceeded for 2 h, the catalytic reaction was intention-
(10 mL) at room temperature. The mixture was sealed in a screw cap vial and
heated at 80 °C for 2 days. Blue crystals of 1 were collected by filtration, washed
with DMF and acetone, and dried at room temperature. Yield: 18 mg (67% based
on Cu). Anal. Calcd for C28H36Cu2N6O15Cl2 (%): C, 37.59; H, 4.06; N 9.39. Found
(%): C, 37.05; H, 4.21; N, 9.47. FTIR (KBr pellet): ν/cm−1 = 1667(m), 1620(m),
1586(s), 1504(m), 1457(m), 1407(m), 1360(s), 1250(m), 1168(m), 1106(m),
1065(s), 949(m), 790(s), 730(s), 662(m).
§Crystal data for compound 1: C22H14Cu2N4O9, Mr = 605.45, monoclinic, space
group C2/m, a = 17.2044(9) Å, b = 25.9374(14) Å, c = 14.6116(8) Å, β = 100.672(6)°,
V
=
6407.5(6) Å3,
Z
=
4,
T = 293 K, Rint = 0.0553, Dc = 0.628 g ,
cm−3
μ = 1.021 mm−1, F(000) = 1216, R1 = 0.0881, wR2 = 0.2086, and S = 1.048.
¶A typical procedure for the CDC reaction. A mixture of 1 (0.01 mmol), 2-phenyl-
1,2,3,4-tetrahydroisoquinoline (21 mg, 0.1 mmol), TBHP (18 μL, 0.15 mmol),
and CH3NO2 (1 mL) was stirred at room temperature for 6 h. After the reaction
was complete, the solid catalyst was recovered by centrifugation and washed
with acetone. The combined plasma was evaporated under reduced pressure.
The residue was subjected to chromatography on silica gel with hexane–ethyl
acetate (10/1) as an eluent to isolate the product.
ally interrupted, and the solid catalyst was collected by 1 C. S. Yeung and V. M. Dong, Chem. Rev., 2011, 111, 1215.
1
centrifugation. The integration of the H NMR signals for the 2 (a) Z. Li and C.-J. Li, J. Am. Chem. Soc., 2005, 127, 3672;
digested sample has revealed that about 1.0 substrate and 1.1
product molecules per formula unit were embedded in the
pores of the used catalyst, which demonstrate that the catalytic
reaction does take place inside the pores.
(b) C.-J. Li, Acc. Chem. Res., 2009, 42, 335; (c) E. Boess,
C. Schmitz and M. Klussmann, J. Am. Chem. Soc., 2012, 134,
5317; (d) J. Xie, H. Li, J. Zhou, Y. Cheng and C. Zhu, Angew.
Chem., Int. Ed., 2012, 51, 1252; (e) Z. Li, D. S. Bohle and
C.-J. Li, Proc. Natl. Acad. Sci. U. S. A., 2006, 103, 8928.
After a mixture of 1 and TBHP in nitromethane was stirred
at room temperature for 6 h, the mixture was filtered. 3 (a) X.-Z. Shu, X.-F. Xia, Y.-F. Yang, K.-G. Ji, X.-Y. Liu and
2-Phenyl-1,2,3,4-tetrahydroisoquinoline and additional TBHP
were subsequently added to the supernatant, which was
further stirred at room temperature for another 6 h. The
Y.-M. Liang, J. Org. Chem., 2009, 74, 7464; (b) X.-L. Yang,
C. Zou, Y. He, M. Zhao, B. Chen, S. Xiang, M. O’Keeffe and
C.-D. Wu, Chem. – Eur. J., 2014, 20, 1447.
product yield is identical to that of the background reaction. 4 (a) M. P. Suh, H. J. Park, T. K. Prasad and D.-W. Lim, Chem.
Moreover, after the reaction proceeded for 2 h, the solid cata-
lyst was removed by centrifugation. The plasma together with
additional TBHP was stirred at room temperature for 4 h. The
product yield obviously did not increase under the same con-
ditions. The above results unambiguously proved that the CDC
catalysis by 1 is heterogeneous in nature. The PXRD pattern of
the recovered solid suggests that the structural integrity of the
catalyst was maintained during catalysis. Furthermore, catalyst 1
can be simply recovered by centrifugation, thoroughly washed
with acetone, and subsequently used in successive runs for six
cycles without loss of catalytic efficiency (Table 1, entry 14).
In summary, we have employed an imidazole carboxylate
ligand to connect with CuII nodes to construct a novel 3D
porous MOF 1 that contains coordinatively unsaturated copper
sites in the opening channel walls. Compound 1 efficiently
prompts the CDC reaction of 1,2,3,4-tetrahydroisoquinoline
Rev., 2012, 112, 782; (b) K. Sumida, D. L. Rogow, J. A. Mason,
T. M. McDonald, E. D. Bloch, Z. R. Herm, T.-H. Bae and
J. R. Long, Chem. Rev., 2012, 112, 724; (c) J.-R. Li, J. Sculley
and H.-C. Zhou, Chem. Rev., 2012, 112, 869; (d) E. Coronado
and G. Minguez Espallargas, Chem. Soc. Rev., 2013, 42, 1525;
(e) P. Horcajada, R. Gref, T. Baati, P. K. Allan, G. Maurin,
P. Couvreur, G. Férey, R. E. Morris and C. Serre, Chem. Rev.,
2012, 112, 1232; (f) Z. Hu, B. J. Deibert and J. Li, Chem. Soc.
Rev., 2014, 43, 5815; (g) Q.-L. Zhu and Q. Xu, Chem. Soc.
Rev., 2014, 43, 5468; (h) Y. Cui, Y. Yue, G. Qian and B. Chen,
Chem. Rev., 2012, 112, 1126; (i) L. E. Kreno, K. Leong,
O. K. Farha, M. Allendorf, R. P. Van Duyne and J. T. Hupp,
Chem. Rev., 2012, 112, 1105; ( j) M. Yoon, R. Srirambalaji
and K. Kim, Chem. Rev., 2012, 112, 1196; (k) H. R. Moon,
D.-W. Lim and M. P. Suh, Chem. Soc. Rev., 2013, 42, 1807;
(l) J. Liu, L. Chen, H. Cui, J. Zhang, L. Zhang and C.-Y. Su,
This journal is © The Royal Society of Chemistry 2014
Dalton Trans.

View Article Online
Communication
Dalton Transactions
Chem. Soc. Rev., 2014, 43, 6011; (m) T. Zhang and W. Lin,
Chem. Soc. Rev., 2014, 43, 5982; (n) M. Zhao, S. Ou and
C.-D. Wu, Acc. Chem. Res., 2014, 47, 1199.
5 (a) X. Zhao, B. Xiao, A. J. Thomas, K. Fletcher, D. Bradshaw
and M. J. Rosseinsky, Science, 2004, 306, 1012;
(b) R. E. Morris and X. Bu, Nat. Chem., 2010, 2, 353;
(c) H. Deng, C. J. Doonan, H. Furukawa, R. B. Ferreira,
J. Towne, C. B. Knobler, B. Wang and O. M. Yaghi, Science,
2010, 327, 846; (d) P. Nugent, Y. Belmabkhout, S. D. Burd,
A. J. Cairns, R. Luebke, K. Forrest, T. Pham, S. Ma, B. Space,
Chem., Int. Ed., 2014, 53, 1575; ( j) C. Zou, Z. Zhang, X. Xu,
Q. Gong, J. Li and C.-D. Wu, J. Am. Chem. Soc., 2012, 134, 87;
(k) X.-L. Yang, M.-H. Xie, C. Zou, Y. He, B. Chen, M. O’Keeffe
and C.-D. Wu, J. Am. Chem. Soc., 2012, 134, 10638;
(l) S.-L. Huang, Y.-J. Lin, T. S. Andy Hor and G.-X. Jin, J. Am.
Chem. Soc., 2013, 135, 8125; (m) S.-L. Huang, Y.-J. Lin,
Z.-H. Li and G.-X. Jin, Angew. Chem., Int. Ed., 2014, 53,
11218; (n) H. Li, Y.-F. Han, Y.-J. Lin, Z.-W. Guo and G.-X. Jin,
J. Am. Chem. Soc., 2014, 136, 2982; (o) S.-L. Huang, A.-Q. Jia
and G.-X. Jin, Chem. Commun., 2013, 49, 2403.
L. Wojtas, M. Eddaoudi and M. J. Zaworotko, Nature, 2013, 6 S. Ou and C.-D. Wu, Inorg. Chem. Front., 2014, 1, 721.
495, 80; (e) Z. Wang and S. M. Cohen, J. Am. Chem. Soc., 7 (a) H.-L. Jiang, Y. Tatsu, Z.-H. Lu and Q. Xu, J. Am. Chem.
2009, 131, 16675; (f) Y. Ikezoe, G. Washino, T. Uemura,
S. Kitagawa and H. Matsui, Nat. Mater., 2012, 11, 1081;
Soc., 2010, 132, 5586; (b) L.-X. Shi and C.-D. Wu, Chem.
Commun., 2011, 47, 2928.
(g) L. Ma, J. M. Falkowski, C. Abney and W. Lin, Nat. Chem., 8 A. L. Spek, PLATON, a multipurpose crystallographic tool,
2010, 2, 838; (h) W. Lu, D. Yuan, T. A. Makal, J.-R. Li and Utrecht University, Utrecht, The Netherlands, 2009.
H.-C. Zhou, Angew. Chem., Int. Ed., 2012, 51, 1580; 9 S. S.-Y. Chui, S. M.-F. Lo, J. P. H. Charmant, A. G. Orpen and
(i) M.-J. Dong, M. Zhao, S. Ou, C. Zou and C.-D. Wu, Angew.
I. D. Williams, Science, 1999, 283, 1148.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2014