Catalytic transesterification reactions of one-dimensional coordination polymers containing paddle-wheel-type units connected by various bridging ligands

Article abstract of DOI:10.1016/j.ica.2013.03.043

The paddle-wheel dinuclear unit consists of two Cu^II ions bridged by four benzoate ligands, and these paddle-wheel [Cu₂(O ₂CPh)₄] units are connected by various bridging ligands to form one-dimensional chained compounds formulated as [Cu₂(O ₂CPh)₄(μ-L)] (L = 2,4-bpe (1), 3,3'3′-dipicam (3), 2,5-Me₂pyz (4), pyz (5), 4,4'4′-bpy (6), and 4-pds (7)). The compound 2, formulated as [[Cu₂(O₂CPh) ₄][Cu(O₂CPh)₂](μ-bpp)₂], consists of alternating units of [Cu₂(O₂CPh)₄] and [Cu(O₂CPh)₂] connected by via bpp. Compounds 1-5 and 7 efficiently catalyzed the transesterification of a variety of esters, while it has been reported that Cu-containing complexes or coordination polymers do not usually show catalytic activities for the transesterification reactions. Among these compounds, 2 was most effective. It has been proposed that in the transesterification reaction, a mononuclear type of Cu complex might be the major species of compound 2 in solution, while for all other compounds, a paddle-wheel unit might be the major reactive species.

Full text of DOI:10.1016/j.ica.2013.03.043

Inorganica Chimica Acta 402 (2013) 39–45
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Catalytic transesterification reactions of one-dimensional coordination
polymers containing paddle-wheel-type units connected by various
bridging ligands
a
a
a
a
b
a,
⇑
In Hong Hwang , Young Dan Jo , Hyun Kim , Kyeong Beom Kim , Kwang-Deog Jung , Cheal Kim ,
Youngmee Kim , Sung-Jin Kim c
c,
⇑
a
Department of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743, Republic of Korea
Clean Energy Research Center, Korea Institute of Science & Technology, Seoul 130-650, Republic of Korea
Department of Chemistry and Nano Science and Institute of Nano-Bio Technology, Ewha Womans Univeristy, Seoul 120-750, Republic of Korea
b
c
a r t i c l e i n f o
a b s t r a c t
The paddle-wheel dinuclear unit consists of two CuII ions bridged by four benzoate ligands, and these
Article history:
Received 11 December 2012
Received in revised form 25 March 2013
Accepted 28 March 2013
Available online 6 April 2013
paddle-wheel [Cu
2
(O
2
CPh)
4
] units are connected by various bridging ligands to form one-dimensional
0
chained compounds formulated as [Cu
(O
2 2
4
CPh) (
l
-L)] (L = 2,4-bpe (1), 3,3 -dipicam (3), 2,5-Me
2
pyz
CPh)
] connected by via bpp. Com-
0
(
4), pyz (5), 4,4 -bpy (6), and 4-pds (7)). The compound 2, formulated as [[Cu
2
(O
2
CPh)
4
][Cu(O
2
2
]
(l
-bpp)
2
], consists of alternating units of [Cu
2 2
(O CPh)
4
] and [Cu(O
2
CPh)
2
pounds 1–5 and 7 efficiently catalyzed the transesterification of a variety of esters, while it has been
reported that Cu-containing complexes or coordination polymers do not usually show catalytic activities
for the transesterification reactions. Among these compounds, 2 was most effective. It has been proposed
that in the transesterification reaction, a mononuclear type of Cu complex might be the major species of
compound 2 in solution, while for all other compounds, a paddle-wheel unit might be the major reactive
species.
Keywords:
Cu complexes
Coordination polymers
Catalyst
Transesterification
II
Ó 2013 Elsevier B.V. All rights reserved.
1
. Introduction
The construction of coordination networks via self-assembly
We have recently shown that the assembly process of zinc ben-
zoates is highly influenced by the types of bridging ligands used
[50]. Assembly of zinc(II)–benzoate with different types of pyra-
zine gives different structures ranging from dinuclear, trinuclear,
and pentanuclear complexes to one-dimensional (1-D) and two-
dimensional (2-D) coordination polymers. Moreover, we have fur-
ther observed the various complex formations (0-D, 1-D, and 2-D)
of manganese(II)–benzoates with various bridging ligands, such as
processes has attracted considerable attention in the fields of
supramolecular chemistry and crystal engineering [1–5] because
such coordination networks have an intriguing variety of topolo-
gies, structural diversity, and potential applications as functional
materials [6–16]. Much effort has been devoted to the study of fun-
damental structural aspects to understand and control several fac-
tors that affect the self-assembly of coordination networks. These
factors are the coordination geometry of metal ions [17,18], the
structure of organic ligands [19–22], hydrogen bonding [23–32],
0
0
0
0
pyrazine (pyz), 4,4 -bipyridine (4,4 -bpy), 3,3 -dipicoylamine (3,3 -
0
0
dpicam), 3-methylisoquinoline, and 4,4 -dithiopyridine (4,4 -dtp)
[51]. These observations led us to perform a systematic investiga-
tion of the relationships between the Cu–benzoate unit and the
nature of the ligands because such a factor was seldom systemat-
p–p stacking [4], counter-anions [33–37], pH values [38,39], tem-
perature [40,41], the ligand-to-metal ratio [42,43], the solvent sys-
tem [44–48], and the template effect [49]. A subtle change in any of
these factors can lead to new complexes with different structural
topologies and different functions. Therefore, there is a need for
greater understanding of the factors because their rational controls
produce the desired topologies with specific properties.
ically considered in the assembly of Cu(benzoate)
coordination polymers.
We report herein the syntheses, structures, and reactivities of
the Cu–benzoate unit with various bridging ligands. The Cu–ben-
zoate system afforded predominantly 1-D coordination polymers
with a paddle-wheel building block unit. Importantly, compounds
2
-containing
1–5 and 7 efficiently catalyzed the transesterification reaction of a
variety of esters, while it has been reported that Cu-containing
complexes or coordination polymers do not usually show catalytic
activities for the transesterification reactions.
⇑
Corresponding authors. Tel.: +82 2 970 6693; fax: +82 2 973 9149 (C. Kim). Tel.:
82 2 3277 3589; fax: +82 2 3277 3419 (Y. Kim).
E-mail addresses: chealkim@seoultech.ac.kr (C. Kim), ymeekim@ewha.ac.kr
+
(
Y. Kim).
0
020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.03.043

4
0
I.H. Hwang et al. / Inorganica Chimica Acta 402 (2013) 39–45
2
. Experimental
.1. Materials
Cu(NO
ꢀH
(28.4 mg, 0.2 mmol). Blue block crystals of compound 3 suitable
for X-ray analysis were obtained in 2 weeks. The yield was
17.2 mg (21.2%) based on metal for compound 3. The purity of
the bulk sample was checked by powder XRD (Fig. S3). IR (KBr):
2
ꢁ
1
3
)
2
2
O,
C H
6 5
COONH
4
,
trans-1-(2-pyridyl)-2-(4-pyri-
m
(cm
1021(w), 969(w), 841(w), 814(w), 715(s), 683(s). Anal. Calc. for C40-
33Cu O (810.77), 3: C, 59.25; H, 4.11; N, 5.18. Found: C, 59.43;
H, 4.10; N, 5.37%.
) = 1610(m), 1567(m), 1479(w), 1398(s), 1063(w),
0
0
dyl)ethylene, pyrazine, 4,4 -trimethylene dipyridine, 3,3 -dipicoyl-
amine, 2,5-dimethylpyrazine, 4-nitrophenyl acetate, phenyl
acetate, 4-methylphenyl acetate, 4-nitrophenyl benzoate, phenyl
benzoate, 4-chlorophenyl benzoate, 4-methylphenyl benzoate, vi-
nyl acetate, methylacetate, methylbenzoate, methylene chloride,
tetrahydrofuran and methanol were purchased from Aldrich and
were used as received. 4-Fluorophenyl acetate and 4-nitrophenyl
benzoate were obtained from Lancaster.
H
2 3
N
2.6. Synthesis of [[Cu
2 2
(O CPh)
4
(l
2 2 n
-2,5-Me pyz)]ꢀ2(H O)] (4)
2
,5-Dimethylpyrazine (21.8 mg, 0.2 mmol) was dissolved in
4
mL methylene chloride and carefully layered with 4 mL of a
ꢀH O (23.7 mg, 0.1 mmol) and C
(28.4 mg, 0.2 mmol). Blue rod-type crystals of compound
suitable for X-ray analysis were obtained in 10 days. The yield
methanol solution of Cu(NO
COONH
4
3
)
2
2
6 5-
H
2.2. Instrumentation
4
Elemental analysis for carbon, nitrogen, and hydrogen was per-
was 31.7 mg (40.0%) based on metal for compound 4. The purity
formed using a vario MACRO (Elemental Analysensysteme, Ger-
many) in the Laboratory Center of Seoul National University of
Science and Technology, Korea. IR spectra were measured on a
BIO RAD FTS 135 spectrometer as KBr pellets. Thermogravimetric
analyses (TGA) were performed on a Shimadzu TA50 integration
thermal analyzer. Product analysis for the transesterification reac-
tion was performed on either a Hewlett–Packard 5890 II Plus gas
chromatograph interfaced with a Hewlett–Packard Model 5989B
mass spectrometer or on a Donam Systems 6200 gas chromato-
graph equipped with a FID detector using a 30-m capillary column
of the bulk sample was checked by powder XRD (Fig. S4). IR
ꢁ1
(
KBr):
m(cm ) = 1613(m), 1570(m), 1494(w), 1403(s), 1334(w),
1
064(w), 1026(w), 843(w), 715(s), 683(s). Anal. Calc. for C34
H36Cu2-
2
N O12 (791.74), 5: C, 51.58; H, 4.59; N, 3.54. Found: C, 51.85; H,
4
.01; N, 3.72%.
2.7. Synthesis of [[Cu
2 2
(O CPh)
4
(l
2 2 n
-pyz)]ꢀ2(CH Cl )] (5)
Pyrazine (16.2 mg, 0.2 mmol) was dissolved in 4 mL methylene
chloride and carefully layered with 4 mL of a methanol solution of
Cu(NO O (23.7 mg, 0.1 mmol) and C COONH (28.4 mg,
ꢀH
.2 mmol). Blue plate crystals of compound 5 suitable for X-ray
(
Hewlett–Packard, HP-1, HP-5, and Ultra 2). Electrospray ioniza-
tion mass spectra (ESI-MS) were collected by manually infusing
samples directly into the source. The spray voltage was set at
3
)
2
2
6
H
5
4
0
4
.2 kV and the capillary temperature at 80 °C.
.3. Synthesis of [[Cu (O CPh)
-2,4-bpe)]ꢀ(THF)]
trans-1-(2-Pyridyl)-2-(4-pyridyl)ethylene (37.6 mg, 0.2 mmol)
analysis were obtained in 2 weeks. The yield was 23.2 mg (26.9%)
based on metal for compound 5. The purity of the bulk sample
ꢁ
1
2
2
2
4
(l
n
(1)
was checked by powder XRD (Fig. S5). IR (KBr):
614(m), 1570(m), 1402(s), 1050(w), 1025(w), 844(w), 802(w),
716(m), 684(m). Anal. Calc. for C34 Cu (861.46), 5: C,
47.40; H, 3.28; N, 3.25. Found: C, 47.03; H, 3.44; N, 2.85%.
m(cm ) =
1
H28Cl
4
2 2 8
N O
was dissolved in 4 mL tetrahydrofuran and carefully layered with
mL of a methanol solution of Cu(NO O (23.7 mg, 0.1 mmol)
ꢀH
and C COONH (28.4 mg, 0.2 mmol). Blue block crystals of com-
4
3
)
2
2
H
6 5
4
2.8. Synthesis of [[Cu
2 2
(O CPh)
4
(l
3 n
-4pds)]ꢀ0.5(CH OH)] (7)
pound 1 suitable for X-ray analysis were obtained in 2 weeks. The
yield was 27.8 mg (32.1%) based on metal for compound 1. The
purity of the bulk sample was checked by powder XRD (Fig. S1).
0
Compound 7 was synthesized by a modified procedure [52]. 4,4 -
ꢁ1
Dithiopyridine (45.4 mg, 0.2 mmol) was dissolved in 4 mL of meth-
ylene chloride and carefully layered with 4 mL of a methanol solu-
IR (KBr):
101(w), 1068(w), 1025(w), 842(w), 711(s). Anal. Calc. for C44
Cu (865.84), 1: C, 60.98; H, 4.43; N, 3.24. Found: C, 60.58; H,
m(cm ) = 1619(m), 1570(m), 1484(w), 1396(s),
1
H
38-
tion of Cu(NO
28.4 mg, 0.2 mmol). Blue plate crystals of compound 7 suitable
for X-ray analysis were obtained in a week. The yield was 25.1 mg
3
)
2
2 6 5 4
ꢀH O (23.7 mg, 0.1 mmol) and C H COONH
2 2 9
N O
(
4
.63; N, 3.11%.
ꢁ
1) =
(
(
8
(
29.7%) based on metal for compound 7. IR (KBr):
m), 1571(m), 1481(w), 1397(s), 1220(w), 1066(w), 1024(w),
43(w), 708(s), 684(s). Anal. Calc. for
845.83), 7: C, 54.67; H, 3.34; N, 3.31. Found: C, 54.61; H, 2.97; N,
m
(cm
1615
2 2 4 2 2 2 n
2.4. Synthesis of [[Cu (O CPh) ][Cu(O CPh) ](l-bpp) ] (2)
38.5 2 2 8.5 2
C H28Cu N O S
0
4
,4 -Trimethylene dipyridine (40.5 mg, 0.2 mmol) was dissolved
in 4 mL tetrahydrofuran and carefully layered with 4 mL of a meth-
anol solution of Cu(NO O (23.7 mg, 0.1 mmol) and C
ꢀH
COONH (28.4 mg, 0.2 mmol). Blue block crystals of compound 2
3
.42%.
3
)
2
2
6 5-
H
4
suitable for X-ray analysis were obtained in a week. The yield
was 21.2 mg (16.14%) based on metal for compound 2. The purity
of the bulk sample was checked by powder XRD (Fig. S2). IR (KBr):
2
.9. Catalytic activity of compounds 1–5 and 7
Catalytic reaction conditions: The ester (0.05 mmol) was dis-
ꢁ1
m
1
(
(cm ) = 1614(m), 1569(m), 1499(w), 1398(s), 1351(m), 1221(w),
067(w), 822(w), 714(s), 683(s). Anal. Calc. for C68
1313.80), 2: C, 62.16; H, 4.46; N, 4.47. Found: C, 62.48; H, 4.52;
N, 4.12%.
solved in methanol (1 mL), one of the compounds 1–5 or 7
H58Cu
3
N
4
O
12
ꢁ3
ꢁ3
ꢁ3
ꢁ3
(
1
1
1.0 mg, 1.15 ꢂ 10 mmol for 1, 2.0 mg, 1.14 ꢂ 10 mmol for 2,
.0 mg, 1.23 ꢂ 10 mmol for 3, 1.0 mg, 1.26 ꢂ 10 mmol for 4,
ꢁ 3 ꢁ 3
.0 mg, 1.16 ꢂ 10 mmol for 5, and 1.0 mg, 1.20 ꢂ 10 mmol
for 7) was added, and the resulting solution was shaken at 50 °C
(450 rpm). The reaction conversion was monitored by GC/mass
0
2.5. Synthesis of [[Cu
2
(O
2
CPh)
4
](l
-3,3 -dipicam)]
n
(3)
analysis of 20 lL aliquots drawn periodically from the reaction
0
3
,3 -Dipicoylamine (36.7
l
L, 0.2 mmol) was dissolved in 4 mL
mixture. All reactions were run at least three times, and the aver-
age conversion yields are presented. Yields are based on the forma-
tion of the products, methylacetate or methylbenzoate.
methylene chloride and carefully layered with 4 mL of a methanol
solution of Cu(NO O (23.7 mg, 0.1 mmol) and C COONH
3
)
ꢀH
2 2
6
H
5
4

I.H. Hwang et al. / Inorganica Chimica Acta 402 (2013) 39–45
41
2.10. Crystallography
form one-dimensional chained compounds formulated as
[
(
Cu
2
(O
2
CPh)
4
(
l
-2,4-bpe)]ꢀ(THF) (1) (Fig. 1), [Cu
(O CPh) -2,5-Me
pyz)]ꢀ2(H
Cl ) (5), [Cu (O CPh)
-4-pds)]ꢀ0.5(CH OH) (7) [52] (2,4-bpe =
trans-2(2-pyridyl)2-(4-pyridyl)ethylene, 3,3 -dipicam = 3,3 -dipic-
2
(O
O) (4),
4
(l-4,4 -bpy)] (6)
2 4
CPh)
0
The diffraction data for all six compounds were collected on a
l-3,3 -dipicam)] (3), [Cu
2
2
4
(l
2
2
0
Bruker SMART AXS diffractometer equipped with a monochroma-
tor in the Mo K (k = 0.71073 Å) incident beam. The crystal was
[Cu
2
(O
2
CPh)
4
(l
-pyz)]ꢀ2(CH
2
2
2
2
a
[18], and [Cu
2
(O CPh)
2
4
(l
3
0
0
mounted on a glass fiber. The CCD data were integrated and scaled
using the BRUKER-SAINT software package, and the structure was
solved and refined using SHEXTL V6.12 [53]. All hydrogen atoms ex-
cept the hydrogen atoms of water molecules were located in the
calculated positions. The crystallographic data for compounds 1–
olylamine, 2,5-Me
4 -bpy = 4,4 -bipyridine, and 4pds = 4,4 -dithiobis(pyridine). Com-
2
pyz = 2,5-dimethylpyrazine, pyz = pyrazine, 4,
0
0
0
pound 2, formulated as [Cu
(bpp = 1,3-bis(pyridyl)propane), consists of alternating units of
[Cu (O CPh) ] and [Cu(O CPh) ] connected by bpp (Fig. 2). The
2 2 4 2 2 2
(O CPh) ][Cu(O CPh) ](l-bpp) ]
5
and the previously reported compounds 6 and 7 are listed in
2
2
4
2
2
Table 1. Structural information was deposited at the Cambridge Crys-
tallographic Data Center (CCDC reference numbers: CCDC 858917 for
elongation of the Cu–N bond distances of 2.1–2. 2 Å in all five
new compounds relative to the typical Cu–N distance (ca. 2.0 Å)
is due to a Jahn–Teller distortion of the copper(II) ion (Table 2);
similar elongations are observed in related chain compounds of
copper(II) carboxylates [54,55].
1, 858918 for 2, 858919 for 3, 858920 for 4, and 858921 for 5).
3
. Results and discussion
As we have previously reported, the construction of the crystal
structures of zinc-benzoate compounds was strongly affected by
the types of bridging pyrazine ligands used [50]. Simple pyrazine
and 2,5-dimethlpyrazine produced two-dimensional and one-
dimensional polymeric compounds, respectively. The other
quinoxaline and two dimethyl-substituted pyrazine ligands gave
dinuclear, trinuclear, and pentanuclear complexes. We have also
found that the bridging bipyridyl ligands play very important roles
in the construction of manganese(II)–benzoate coordination poly-
mers [51]. The bridging bipyridyl ligands produced 1-D or 2-D
polymeric manganese(II)–benzoate compounds. The pyz produced
2
The paddle-wheel-type Cu units were connected by various
bridging ligands to form one-dimensional chains. All five struc-
tures were determined by X-ray crystallography. The structures
of all five compounds containing paddle-wheel Cu
2
units are
shown in Scheme 1. The previously reported crystal structures of
compounds 6 [18] and 7 [52] are also shown in Scheme 1 for
comparison.
The paddle-wheel dinuclear unit consists of two CuII ions
bridged by four benzoate ligands, and these paddle-wheel
[
Cu
2
(O
2 4
CPh) ] units are connected by various bridging ligands to
6
a Mn cluster molecule, and 3-methylisoquinoline yielded a
Table 1
Crystallographic data for compounds 1–7.
1
2
3
4
5
6a
7b
Empirical
formula
Formula weight
T (K)
k (Å)
Space group
C
44
H
38Cu
2 2
N O
9
C
68
H
58Cu
3
N
4
O
12
C
40
H
33Cu
2
3
N O
8
C
34
H
28Cu
2 2
N O
12
C
34
H
28Cl
4
Cu
2
N
2
O
8
C
38
H
28Cu
2 2
N O
8
38.5 2 2 8.5 2
C H28Cu N O S
865.84
170(2)
0.71073
1313.80
293(2)
0.71073
810.77
170(2)
0.71073
783.66
293(2)
0.71073
861.46
293(2)
0.71073
767.72
170(2)
0.71073
C2/c
845.83
293(2)
0.71073
P2
1
/c
P1ꢀ
P1ꢀ
P2
1
/c
P1ꢀ
P1ꢀ
a (Å)
b (Å)
c (Å)
10.4155(16)
20.113(3)
19.323(3)
90.00
104.032(3)
90.00
3927.1(10)
4
1.464
9.8178(10)
10.299(6)
10.846(6)
16.531(9)
75.827(10)
86.068(10)
88.446(9)
1786.1(17)
2
11.104(2)
9.780(2)
18.453(4)
90.00
97.12(3)
90.00
1988.5(7)
2
1.309
9.7440(19)
10.039(2)
10.740(2)
89.94(3)
83.54(3)
62.30(3)
922.7(3)
1
20.3982(18)
18.9865(16)
21.4028(18)
90.00
118.152(2)
90.00
7308.5(11)
8
1.425
10.382(2)
10.868(2)
17.793(4)
107.27(3)
90.28(3)
91.67(3)
1916.1(7)
2
10.7740(11)
14.9306(15)
79.685(2)
81.615(2)
78.697(2)
1513.6(3)
1
a
(°)
b (°)
(°)
c
3
V (Å )
Z
D
calc (Mg/m3)
1.441
1.508
1.550
1.466
Absorption
coefficient
1.143
1.112
1.250
1.126
1.493
1.220
1.273
ꢁ
1
(
mm )
Crystal size (mm) 0.15 ꢂ 0.08 ꢂ 0.05 0.08 ꢂ 0.05 ꢂ 0.05 0.08 ꢂ 0.05 ꢂ 0.05 0.15 ꢂ 0.05 ꢂ 0.02 0.35 ꢂ 0.30 ꢂ 0.03 0.10 ꢂ 0.08 ꢂ 0.08 0.10 ꢂ 0.05 ꢂ 0.02
Reflections
collected
19,821
8547
8855
10017
5185
20023
10074
Independent
reflections
7470 (0.0618)
5820 (0.0272)
6124 (0.0784)
3751 (0.0667)
3541 (0.0257)
7123 (0.0589)
7137 (0.0811)
int
(R )
Data/restraints/
parameters
7470/0/511
0.900
5820/0/394
1.053
6124/1/482
0.759
3751/0/227
0.967
3541/0/226
0.943
7123/0/461
0.945
7137/1/405
0.796
Goodness-of-fit
(
GOF) on F2
Final R indices
I > 2 (I)]
R indices (all
data)
R
1
= 0.0420,
wR = 0.1141
= 0.0726,
wR = 0.1298
0.492 and ꢁ0.832 0.432 and ꢁ0.722 0.818 and ꢁ0.900 1.331 and ꢁ0.537 0.668 and ꢁ0.537 2.361 and ꢁ0.885 1.220 and ꢁ1.230
R
1
= 0.0560,
wR = 0.1298
= 0.1016,
wR = 0.1445
R
1
= 0.0609,
wR = 0.1221
= 0.1633,
wR = 0.1440
R
1
= 0.0733,
wR = 0.1722
= 0.1279,
wR = 0.2031
R
1
= 0.0499,
wR = 0.1208
= 0.0708,
wR = 0.1281
R
1
= 0.0570,
wR = 0.1517
= 0.0852,
wR = 0.1578
R
1
= 0.0961,
wR = 0.2393
= 0.2127,
wR = 0.2982
[
r
2
2
2
2
2
2
2
R
1
R
1
R
1
R
1
R
1
R
1
R
1
2
2
2
2
2
2
2
Largest
difference
peak and hole
ꢁ
3
(
e Å )
a
See Ref. [18].
See Ref. [52].
b

4
2
I.H. Hwang et al. / Inorganica Chimica Acta 402 (2013) 39–45
2
Scheme 1. Structures of compounds containing paddle-wheel-type Cu units.
2
Fig. 1. One-dimensional structure of 1 containing paddle-wheel-type Cu units. All hydrogen atoms and THF solvent molecules were omitted for clarity.
2 2 4 2 2
Fig. 2. One-dimensional structure of 2 containing alternating units of [Cu (O CPh) ] and [Cu(O CPh) ] connected by bpp. All hydrogen atoms were omitted for clarity.
benzoate-bridged 1-D Mn
6
compound. Unlike Zn–benzoate and
3.1. Catalytic transesterification reactions by compounds 1–5 and 7
Mn–benzoate systems, Cu–benzoate system afforded predomi-
nantly 1-D coordination polymers with a paddle-wheel building
block unit.
Although an enormous number of polymeric compounds con-
taining Cu ions have been reported over the last decade, their

I.H. Hwang et al. / Inorganica Chimica Acta 402 (2013) 39–45
43
Table 2
Selected bond distances and angles for compounds 1–7.
1
2
3
4
5
6a
7b
Cu–O (Å)
Cu–N (Å)
Cu. . .Cu
1.963(2)–1.993(2)
1.941(3)–1.975(3)
1.926(5)–1.987(5)
1.944(4)–1.964(4)
1.952(3)–1.978(3)
1.947(4)–1.998(3)
1.947(7)–
2
.000(8)
2.198(4),
.161(5)
2.191(3), 2.136(3)
2.6269(6)
2.153(3), 2.032(5)
2.6566(9)
2.135(6), 2.162(5)
2.217(4)
2.192(3)
2.150(4)
2
2.652(2),
2.6285(13)
2.6079(9)
2.6417(8)
2.640(2),
(
Å)
N–Cu–O
°)
2.6540(18)
88.67(19)–
103.94(19)
2.620(3)
92.3(3)–99.8(3)
89.65(11)–
103.32(10)
89.79(16)–
97.56(13)
90.17(15)–
101.34(15)
91.37(11)–
99.49(11)
87.43(16)–
102.80(15)
(
a
See Ref. [18].
See Ref. [52].
b
Table 3
Transesterification of esters with methanol in the presence of compounds 1–5 and 7 at 50 °C.
a
Entry
Substrate
1
(
2
3
4
5
7
time/day)b
(time/day)b
(time/day)b
(time/day)b
(time/day)b
(time/day)b
1
2
3
4
5
6
7
8
9
4-nitrophenyl acetate
4-fluorophenyl acetate
phenyl acetate
4-methylphenyl acetate
4-nitrophenyl benzoatec
4-chlorophenyl benzoate
phenyl benzoate
0.38
3
2
7
2
0.16
1
1
2
0.5
2
4
5
0.14
0.29
3
2
4
2
0.33
3
2
3
2
6
9
9
0.38
2
2
3
2
0.38
2
2
3
2
6
9
4
4
8
4
10
10
0.25
11
12
0.33
4-methylphenyl benzoate
vinyl acetate
10
0.29
12
0.21
0.21
a
All esters were completely converted to the corresponding products, methyl acetate and methyl benzoate. Reaction conditions: esters, 0.05 mmol; catalyst,
ꢁ
3
ꢁ3
ꢁ3
ꢁ3
ꢁ3
ꢁ3
1
.15 ꢂ 10 mmol for 1, 1.14 ꢂ 10 mmol for 2, 1.23 ꢂ 10 mmol for 3, 1.26 ꢂ 10 mmol for 4, 1.16 ꢂ 10 mmol for 5 and 1.20 ꢂ 10 mmol for 7; methanol (1 mL).
b
Time necessary for the complete conversion of substrate to product.
The solvent was a mixture of CH OH/CH Cl (1/1) because of the low solubility of the substrate in methanol.
3 2 2
c
application as catalysts is relatively rare [11,56–60]. We have re-
and benzoates, by compounds 1–5 and 7. The results are also given
in Table 3. These compounds demonstrated high reactivity, com-
pleting the transesterification of p-nitrophenyl acetate, which con-
tains an electron-withdrawing group, within 0.16–0.38 day (entry
1). 4-Fluorophenyl acetate and phenyl acetate displayed similar
reactivities with the catalysts (entries 2 and 3). 4-Methylphenyl
acetate showed somewhat decreased reactivity (entry 4). The
transesterification of other esters by the catalysts was also per-
formed efficiently (entries 5–9), although benzoates underwent
slower transesterification than acetates. The p-nitrophenyl benzo-
ate, with its electron-withdrawing substituent, underwent faster
transesterification (entry 5), whereas the p-methylphenyl benzo-
ate, with its electron-donating group, showed a slower reactivity
(entry 8). Notably, vinyl acetate, which is widely used as a precur-
sor for ester synthesis, was also converted efficiently to the product
methyl acetate by the catalysts within 0.14–0.33 day (entry 9),
suggesting that this catalytic system can be useful for preparing
various esters by transesterification. This result suggests the possi-
bility of using many of the Cu-containing polymeric compounds re-
ported to date as potential catalysts for transesterification
reactions.
It has been proposed that the mechanism of metal ion-cata-
lyzed transesterification most likely involves electrophilic activa-
tion of the carbon center of the carbonyl moiety by binding of
the metal to the carbonyl oxygen [35,50,51]. Therefore, the Lewis
acidity of the metal center may be important in catalytic transeste-
rification. Based on this idea, we used electrospray ionization mass
spectrometry (ESI-MS) to detect the possible reactive species for
the transesterification reaction in methanol. As shown in the ESI-
Mass data (Figs. 3 and 4, and Figs. S11–S14), all compounds except
for 2 might exist as paddle-wheel units in solution, while com-
pound 2 may exist as a mononuclear type of Cu complex. These re-
sults are consistent with the X-ray structures of these compounds.
Given these results, we propose a possible transesterification
mechanism for these catalytic systems (Scheme 2). The substrate
cently reported that the Cu-containing coordination polymer 6
0
formed from the reaction of Cu(O
2
CPh)
2
with linear ligand 4,4 -
0
bpy (4,4 -bipyridine) carried out the catalytic transesterification
of a range of esters [18]. While this catalyst system constitutes a
promising class of catalysts that appears to be an efficient, mild
method for the alcoholysis of esters, there is still a high demand
for the development of new types of highly efficient catalysts. To
systematically study their catalytic reactivities in transesterifica-
tion reactions, we explored the catalytic activity of new copper-
containing polymers 1–5 and 7 using a wide range of esters with
methanol [35,61]. The compounds 1–5 and 7 were found to per-
form the catalytic transesterification reaction efficiently. The treat-
ment of phenyl acetate and methanol in the presence of the
catalysts produced methyl acetate quantitatively under neutral
conditions within 1–2 days (Eq. (1); see entry 3 of Table 3), while
little transesterification occurred without the polymeric com-
pounds. Interestingly, compound 2 is twice as efficient as the other
compounds. To the best of our knowledge, the compound is the
most efficient of the previously reported Cu-containing polymeric
catalytic systems [56–58], and its efficiency is comparable to those
of Zn-containing coordination and polymeric compounds that are
well-known as efficient catalysts for these transesterification reac-
tions [35,57,58,61]. More importantly, these results are surprising,
because it has been reported that Cu-containing complexes or
coordination polymers do not generally catalyze the transesterifi-
cation reactions, whereas they has been known to be the good cat-
alysts for epoxide ring-opening [18].
These promising results led us to further examine the transeste-
rification of other esters, including p-substituted phenyl acetates

4
4
I.H. Hwang et al. / Inorganica Chimica Acta 402 (2013) 39–45
room for the substrate. In contrast, the mononuclear Cu complex
of 2 can bind to the substrate in all directions (Scheme 1). There-
fore, the steric effect of compound 1, 3–5, and 7 might slow down
the transesterification reaction.
4
. Conclusions
The paddle-wheel dinuclear unit consists of two CuII ions
bridged by four benzoate ligands, and these paddle-wheel [Cu
CPh)
2
(O2-
4
] units are connected via various bridging ligands to form
one-dimensional chained compounds formulated as [Cu
2
(O2-
0
CPh)
4
(
l
-L)] (L = 2,4-bpe (1), 3,3 -dipicam (3), 2,5-Me
2
pyz (4), pyz
0
(
(
[
5), 4,4 -bpy (6), and 4-pds (7)). Compound 2, formulated as [[Cu
2
O
2
CPh)
4
][Cu(O
2
CPh)
2
](
l
-bpp) ], consists of alternating units of
2
CPh) ] connected by bpp. Reactions of
2
Cu (O CPh)
2
2
4
] and [Cu(O
2
Cu-benzoate with various bipyridyl ligands predominantly pro-
duce 1-D coordination polymers containing paddle-wheel units,
whereas Zn–benzoate and Mn–benzoate units afforded various
structures depending on the bridging ligands. We have also shown
that compounds 1–5 and 7 catalyzed the transesterification of a
variety of esters. Notably, the transesterification by catalyst 2 with
a mononuclear unit is very efficient and is the most efficient of the
previously reported Cu-containing polymeric compounds. A mono-
nuclear type of Cu complex might be the major reactive species for
the transesterification reaction by compound 2, whereas a possible
reactive species of the other complexes might be a paddle-wheel
unit in solution. Therefore, it has been proposed that the paddle-
wheel dinuclear unit has a steric hindrance, resulting in a slow
transesterification reaction. This result also suggests the possibility
of using many of the Cu-containing polymeric compounds reported
to date as potential catalysts for transesterification reactions.
Fig. 3. Positive-ion electrospray ionization mass spectrum of complex 1 in MeOH.
Acknowledgements
Financial support from Converging Research Center Program
through the National Research Foundation of Korea (NRF) funded
by the Ministry of Education, Science and Technology
(
2012001725, 2011K000675, and 2012008875), Basic Science Re-
search Program through the National Research Foundation of Korea
Fig. 4. Positive-ion electrospray ionization mass spectrum of complex 2 in MeOH.
(
(
NRF) funded by the Ministry of Education, Science and Technology
20110008018), and the RP-Grant 2013 of Ewha Womans Univer-
sity are gratefully acknowledged.
Appendix A. Supplementary material
CCDC 858917–858921 contain the supplementary crystallo-
graphic data for compounds 1–5, respectively. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at http://dx.doi.org/10.1016/j.ica.2013.03.043.
Scheme 2. Proposed reaction mechanism for the transesterification reaction.
References
phenyl acetate binds to the Cu center of the paddle-wheel unit to
2
give the adduct (L)Cu (benzoate)2–4(Sub). Then, the nucleophile
[
[
1] S.R. Batten, R. Robson, Angew. Chem., Int. Ed. 37 (1998) 1460.
2] M. Eddaoudi, D.B. Moler, H. Li, B. Chen, T.M. Reineke, M. O’Keeffe, O.M. Yaghi,
Acc. Chem. Res. 34 (2001) 319.
3] K. Kim, Chem. Soc. Rev. 31 (2002) 96.
4] C. Janiak, J. Chem. Soc., Dalton Trans. (2003) 2781.
5] S. Noro, R. Kitaura, M. Komdo, S. Kitagawa, T. Ishii, H. Matsuzaka, M.
Yamashita, J. Am. Chem. Soc. 124 (2002) 2568.
6] H. Chun, H. Jung, Inorg. Chem. 48 (2009) 417.
7] A. Kuc, T. Heine, G. Seifert, H.A. Duarte, Chem. Eur. J. 14 (2008) 6597.
8] S.Y. Lee, S. Park, H.J. Kim, J.H. Jung, S.S. Lee, Inorg. Chem. 47 (2008) 1913.
methanol attacks the carbon atom of the carbonyl moiety of the
adduct to produce the methyl acetate product. In the case of com-
pound 2, a mononuclear Cu complex might be a possible reactive
species for the transesterification reaction, as interpreted from
Fig. 4. Moreover, based on the proposed mechanism (Scheme 2)
and the results of the transesterification reaction shown in Table 3,
we could infer of why 2 with the mononuclear Cu complex unit
shows the efficient transesterification reaction than 1, 3–5, and 7
with the dinuclear paddle-wheel complex units. As shown in
Scheme 2, the substrate phenyl acetate could bind only to one side
of the Cu paddle-wheel complex because the other side has no
[
[
[
[
[
[
[9] E. Shyu, R.M. Supkowski, R.L. LaDuca, Inorg. Chem. 48 (2009) 2723.
[10] S. Takizawa, H. Somei, D. Jayaprakash, H. Sasai, Angew. Chem., Int. Ed. 42
(
2003) 5711.
[
11] S.J. Hong, J.Y. Ryu, J.Y. Lee, C. Kim, S.-J. Kim, Y. Kim, J. Chem. Soc., Dalton Trans.
(2004) 2697.

I.H. Hwang et al. / Inorganica Chimica Acta 402 (2013) 39–45
45
[
[
[
[
[
12] S. Hasegawa, S. Horike, R. Matsuda, S. Furukawa, K. Mochizuki, Y. Kinoshita, S.
Kitagawa, J. Am. Chem. Soc. 129 (2007) 2607.
13] D.N. Dybtsev, A.L. Nuzhdin, H. Chun, K.P. Bryliakov, E.P. Talsi, V.P. Fedin, K.
Kim, Angew. Chem., Int. Ed. 45 (2006) 916.
[37] G.H. Eom, H.M. Park, M.Y. Hyun, S.P. Jang, C. Kim, J.H. Lee, S.J. Lee, S.-J. Kim, Y.
Kim, Polyhedron 30 (2011) 1555.
[38] Y.-B. Dong, Y.-Y. Jiang, J. Li, J.-P. Ma, F.-L. Liu, B. Tang, R.-Q. Huang, S.R. Batten, J.
Am. Chem. Soc. 129 (2007) 4520.
[39] L.-F. Ma, L.-Y. Wang, D.-H. Lu, S.R. Batten, J.-G. Wang, Cryst. Growth Des. 9
(2009) 1741.
[40] P. Mahata, M. Prabu, S. Natarajan, Inorg. Chem. 47 (2008) 8451.
[41] A.S.R. Chesman, D.R. Turner, D.J. Price, B. Moubaraki, K.S. Murray, G.B. Deacon,
S.R. Batten, Chem. Commun. (2007) 3541.
14] G.A. Mines, B.-C. Tzeng, K.J. Stevenson, J. Li, J.T. Hupp, Angew. Chem., Int. Ed. 41
(
2002) 154.
15] A. Lan, K. Li, H. Wu, D.H. Olson, T.J. Emge, W. Ki, M. Hong, J. Li, Angew. Chem.,
Int. Ed. 48 (2009) 2334.
16] L.-G. Qiu, Z.-Q. Li, Y. Wu, W. Wang, T. Xu, X. Jiang, Chem. Commun. (2008)
3
642.
[42] N.L. Toh, M. Nagarathinam, J.J. Vittal, Angew. Chem., Int. Ed. 44 (2005) 2237.
[43] R. Carballo, B. Covelo, M.S.E. Fallah, J. Ribas, E.M. Vazquez-Lopez, Cryst. Growth
Des. 7 (2007) 1069.
[44] M.V. Marinho, M.I. Yoshida, K.J. Guedes, K. Krambrock, A.J. Bortoluzzi, M.
Horner, F.C. Machado, W.M. Teles, Inorg. Chem. 43 (2004) 1539.
[45] H. Kwak, S.H. Lee, S.H. Kim, Y.M. Lee, B.K. Park, Y.J. Lee, J.Y. Jun, C. Kim, S.-J. Kim,
Y. Kim, Polyhedron 28 (2009) 553.
[
[
17] Z. Lin, M.-L. Tong, Coord. Chem. Rev. 255 (2010) 421.
18] Y.J. Song, H. Kwak, Y.M. Lee, S.H. Kim, S.H. Lee, B.K. Park, J.Y. Jun, S.M. Yu, C.
Kim, S.-J. Kim, Y. Kim, Polyhedron 28 (2009) 1241.
[
[
[
[
19] T. Gadzikwa, B.-S. Zeng, J.T. Hupp, S.T. Nguyen, Chem. Commun. (2008)
3
672.
20] M.A. Withersby, A.J. Blake, N.R. Champness, P.A. Cooke, P. Hubberstey, W.-S. Li,
M. Schroder, Inorg. Chem. 38 (1999) 2259.
21] J. Yang, J.-F. Ma, Y.-Y. Liu, J.-C. Ma, S.R. Batten, Cryst. Growth Des. 9 (2009)
[46] W.-X. Chen, S.-T. Wu, L.-S. Long, R.-B. Huang, L.-S. Zheng, Cryst. Growth Des. 7
(2007) 1171.
1
894.
[47] R.-Q. Fang, X.-M. Zhang, Inorg. Chem. 45 (2006) 4801.
[48] Y.B. Go, X. Wang, E.V. Anokhina, A.J. Jacobson, Inorg. Chem. 44 (2005) 8265.
[49] Q. Fang, G. Zhu, M. Xue, Z. Wang, J. Sun, S. Qiu, Cryst. Growth Des. 8 (2008) 319.
[50] H. Kwak, S.H. Lee, S.H. Kim, Y.M. Lee, B.K. Park, E.Y. Lee, Y.J. Lee, C. Kim, S.-J.
Kim, Y. Kim, Polyhedron 27 (2008) 3484.
[51] I.H. Hwang, Y.D. Jo, H.-Y. Kim, J. Kang, J.Y. Noh, M.Y. Hyun, C. Kim, Y. Kim, S.-J.
Kim, Polyhedron 42 (2012) 282.
[52] R. Horikoshi, M. Mikuriya, Bull. Chem. Soc. Jpn. 78 (2005) 827.
[53] Bruker, SHELXTL/PC, Version 6.12 for Windows XP, Bruker AXS Inc., Madison,
Wisconsin, USA, 2001.
22] Y.J. Lee, E.Y. Kim, S.H. Kim, S.P. Jang, T.G. Lee, C. Kim, S.-J. Kim, Y. Kim, New J.
Chem. 35 (2011) 833.
23] H.W. Roesky, M. Andruh, Coord. Chem. Rev. 236 (2003) 91.
24] X.J. Luan, Y.-Y. Wang, D.-S. Li, P. Liu, H.-M. Hu, Q.-Z. Shi, S.-M. Peng, Angew.
Chem., Int. Ed. 44 (2005) 3864.
[
[
[
[
25] B.-B. Ding, Y.-Q. Weng, Z.-W. Mao, C.-K. Lam, X.-M. Chen, B.-H. Ye, Inorg. Chem.
4
4 (2005) 8836.
26] A. Angeloni, P.C. Crawford, A.G. Orpen, T.J. Podesta, B.J. Shore, Chem. Eur. J. 10
2004) 3783.
(
[
[
[
[
[
[
[
27] V. Balamurugan, M.S. Hundal, R. Mukherjee, Chem. Eur. J. 10 (2004) 1683.
28] Y. Wang, J. Yu, Y. Li, Z. Shi, R. Xu, Chem. Eur. J. 9 (2003) 5048.
29] D. Braga, F. Grepioni, G.R. Desiraju, Chem. Rev. 98 (1998) 1375.
30] C. Janiak, T.G. Scharmann, Polyhedron 22 (2003) 1123.
31] L. Brammer, E.A. Bruton, P. Sherwood, Cryst. Growth Des. 1 (2001) 277.
32] G.R. Desiraju, Acc. Chem. Res. 35 (2002) 565.
33] A.J. Blake, N.R. Brooks, N.R. Champness, P.A. Cooke, A.M. Deveson, D. Fenske, P.
Hubberstey, M.J. Schroder, J. Chem. Soc., Dalton Trans. 111 (1999) 2103.
34] Y.-Q. Huang, X.-Q. Zhao, W. Shi, W.-Y. Liu, Z.-L. Chen, P. Cheng, D.-Z. Liao, S.-P.
Yan, Cryst. Growth Des. 8 (2008) 3652.
[54] M. Mikuriya, R. Nukada, H. Morishita, M. Handa, Chem. Lett. (1995) 617.
[55] R. Nukada, W. Mori, S. Takamizawa, M. Mikuriya, M. Handa, H. Naono, Chem.
Lett. (1999) 367.
[56] I.H. Hwang, J.M. Bae, W.S. Kim, Y.D. Jo, C. Kim, Y. Kim, S.-J. Kim, S. Huh, Dalton
Trans. 41 (2012) 12759.
[57] S.H. Kim, B.K. Park, Y.J. Song, S.M. Yu, H.G. Koo, E.Y. Kim, J.I. Poong, J.H. Lee, C.
Kim, S.-J. Kim, Y. Kim, Inorg. Chim. Acta 362 (2009) 4119.
[58] J.H. Kim, J.M. Bae, H.G. Lee, N.J. Kim, K.-D. Jung, C. Kim, S.-J. Kim, Y. Kim, Inorg.
Chem. Commun. 22 (2012) 1–5.
[59] M. Yoon, R. Srirambalaji, K. Kim, Chem. Rev. 112 (2012) 1196.
[60] L.E. Kreno, K. Leong, O.K. Farha, M. Allendorf, R.P. Van Duyne, J.T. Hupp, Chem.
Rev. 112 (2012) 1105.
[
[
[
35] H. Kwak, S.H. Lee, S.H. Kim, Y.M. Lee, E.Y. Lee, B.K. Park, E.Y. Kim, C. Kim, S.-J.
Kim, Y. Kim, Eur. J. Inorg. Chem. (2008) 408.
36] R. Mondal, T. Basu, D. Sadhukhan, T. Chattopadhyay, M. Bhunia, Cryst. Growth
Des. 9 (2009) 1095.
[61] S.P. Jang, J.I. Poong, S.H. Kim, T.G. Lee, J.Y. Noh, C. Kim, Y. Kim, S.-J. Kim,
Polyhedron 33 (2012) 194.