Synthesis, structures, and heterogeneous catalytic applications of {Co 3+-Eu3+} and {Co3+-Tb3+} heterodimetallic coordination polymers

Article abstract of DOI:10.1002/ejic.201000651

Two {Co³⁺-Eu³⁺} and {Co³⁺-Tb³⁺} heterodimetallic coordination polymers have been synthesized by using a Co ³⁺-based coordination complex as the building block. Structural studies show that the lanthanide atoms are coordinated to the cobalt complex through O_amide groups. This results in the generation of a one-dimensional zigzag coordination polymer. These coordination polymers have been shown to catalyze the ring-opening reactions of the epoxides with anilines and alcohols under heterogeneous and solvent-free conditions. Interestingly, a perfect regioselectivity was observed in the aminolysis and alcoholysis reaction of styrene oxide. Two {Co³⁺-Eu³⁺} and {Co ³⁺-Tb³⁺} zigzag coordination polymers have been synthesized by using a Co³⁺-based coordination complex. These coordination polymers have been shown to catalyze the ring-opening reactions of epoxides with anilines and alcohols under heterogeneous and solvent-free conditions.

Full text of DOI:10.1002/ejic.201000651

FULL PAPER
DOI: 10.1002/ejic.201000651
Synthesis, Structures, and Heterogeneous Catalytic Applications of
3+
3+
3+
3+
{
Co –Eu } and {Co –Tb } Heterodimetallic Coordination Polymers
[a]
[a]
[a]
Girijesh Kumar, Amit Pratap Singh, and Rajeev Gupta*
Keywords: Cobalt / Europium / Terbium / Polymers / Heterogeneous catalysis
Two {Co3+–Eu3+} and {Co3+–Tb3+} heterodimetallic coordina-
mer. These coordination polymers have been shown to cata-
lyze the ring-opening reactions of the epoxides with anilines
and alcohols under heterogeneous and solvent-free condi-
tions. Interestingly, a perfect regioselectivity was observed in
the aminolysis and alcoholysis reaction of styrene oxide.
3+
tion polymers have been synthesized by using a Co -based
coordination complex as the building block. Structural stud-
ies show that the lanthanide atoms are coordinated to the
cobalt complex through Oamide groups. This results in the
generation of a one-dimensional zigzag coordination poly-
Introduction
however, several drawbacks with the routine lanthanide
salts, such as recovery after the catalytic reactions and reus-
ability. Thus, the traditional approach to Lewis acid based
catalysis demands rapid change to reusable and hetero-
geneous catalysts. In this context, porous metal–organic
frameworks and coordination polymers offer an excellent
In recent years, the quest for materials with useful prop-
erties has led to intense studies on the development of inor-
ganic–organic hybrid compounds, because they offer ad-
vantages that emerge from both metal and ligand compo-
nents. Metal–organic frameworks and coordination poly-
mers belong to this new class of materials with potential
applications in gas storage, separation, sensing, and cataly-
sis.[ An important characteristic of these materials is the
single-site active species, in which every active site has an
identical chemical environment due to the highly crystalline
nature of the material. Such special features emulate en-
zymes with the inherent advantages of the heterogeneous
[
1,2]
alternative to heterogeneous catalysis,
that contain lanthanide metals.
especially those
[
1i]
Our group has been working on developing coordination
complexes as the building blocks for the construction of
ordered structures in which two different metal ions could
1]
[
7–11]
be placed in close proximity.
A coordination complex
as the building block offer many benefits such as spectro-
scopic and magnetic properties as well as structural rigidity.
Such an induced rigidity has the ability to place the auxil-
iary functional groups in a preorganized conformation with
an option to control the geometrical placement of such
groups. These auxiliary functional groups could then be uti-
lized to coordinate a secondary metal ion. This synthetic
strategy leads to the generation of heterodimetallic com-
[
2]
catalysis.
Lewis acid catalyzed organic transformation reactions
are of great importance because of their unique reactivities
[
3,4]
and selectivities.
Furthermore, such catalytic reactions
often require mild reaction conditions.[
3,4]
A wide variety
of organic transformations by using Lewis acids have been
developed, and they have been applied to the synthesis of
an assorted variety of compounds. Traditionally, strong
Lewis acids based on Al , B , Ti , and Sn metal ions
have been utilized;[ however, more than stoichiometric
amounts of such Lewis acids are required in several cases.
Moreover, most of these Lewis acids are moisture-sensitive
and tend to decompose or deactivate in the presence of even
a small amount of water.[ In this context, lanthanide salts,
[
8–10]
[11]
plexes
lizing this strategy, we have recently demonstrated the Co
and networks of a highly ordered nature. Uti-
3+
3
+
3+
4+
4+
[
7]
coordination complex 1 as the building block for the
preparation of {Zn –Co –Zn }, {Cd –Co –Cd },
and {Hg –Co –Hg }
5]
2+
3+
2+ [8]
2+
3+
2+ [9]
2+
3+
2+ [9]
heterodimetallic complexes
(Scheme 1). The selection of the peripheral metal ion was
based on the possible application of the exposed Lewis-
acidic metal ion in organic transformations. Indeed, the
Lewis-acidic property of the peripheral metal ion was dem-
onstrated by catalytic organic transformation reactions
such as the Beckmann rearrangement of aldoximes and
ketoximes, cyanation of imines, and ring-opening reactions
5]
in particular, lanthanide triflates [Ln(OTf) ], are compara-
3
tively moisture-tolerable Lewis acids and have been widely
applied to a variety of organic transformations.[ There are,
6]
[
a] Department of Chemistry, University of Delhi,
[
8,9,12]
Delhi 110007, India
of oxiranes and thiiranes.
Interestingly, these organic
Fax: +91-11-2766-6605
E-mail: rgupta@chemistry.du.ac.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000651.
transformation reactions were found to be secondary-
metal-specific. Very recently, we have also synthesized
+
3+
+
{Cu –M –Cu } (M = Co or Fe) heterodimetallic com-
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G. Kumar, A. P. Singh, R. Gupta
FULL PAPER
Scheme 1. Structurally characterized heterodimetallic complexes reported from our laboratory.
3
+
–1
plexes utilizing Co -containing building block 1 and its (νC–O at ca. 1175 cm ). The presence of the triflate ion was
3
+
[10]
I
Fe analogue.
The peripheral Cu ions were shown to established by the observation of the ν
stretches at
S=O
–1
participate in the aerial oxidation of hindered phenols to around 1243–1247, 1030, and 639 cm . The IR spectra of
yield carbon–carbon-coupled products as well as dealkyl- both 2 and 3 also show a strong band in the 1590–
ated products. To further understand the coordination abili- 1595 cm–1 region due to the νamide stretches. A negative shift
ties of such molecular clefts and their ability to accommo- of 25–30 cm–1 for the νamide stretch (with respect to complex
date assorted cations with variable coordination require- 1) indicates the involvement of Oamide in the bonding. Con-
ments, we were encouraged to look to the lanthanide metal ductivity measurements[13b] indicate a 1:2 electrolytic nature
ions. The present work explores the coordinating ability of of complexes 2 and 3 and clearly suggest that the triflate
3
+
3+
the building block 1 towards Eu and Tb ions. This ions are not involved in coordination. The absorption spec-
3
+
move was driven by the notion that the ionic radii of Eu
tra of complexes 2 and 3 show λmax in the range of 645–
3
+
(
Hg
{
1.09 Å) and Tb (1.06 Å) are comparable to that of the 650 nm that has been assigned to the d–d transition based
2
+
2
3+
[8]
ion (1.16 Å), and the structurally characterized on the Co building block 1 (Figure S1 in the Supporting
+
3+
2+
2+
Hg –Co –Hg } complex has revealed that the Hg
Information). Both complexes 2 and 3 were also charac-
1
13
ions can be placed within the clefts after coordination to terized by H and C NMR spectra (Figures S2 and S3
[
14]
the Npyridine donors (Scheme 1). Interestingly, despite the in the Supporting Information). The NMR spectra were
3
+
3+
2+
[7,8]
comparable size of the Eu and Tb ions to that of Hg , interpreted by comparison with that of building block 1.
the lanthanide atoms opted to interact with the Oamide The coordination of the Eu3 and Tb ions to 1 does not
+
3+
atoms rather than be placed within the clefts. This results significantly alter the chemical environment of the proton
3
+
3+
3+
3+
1
in the generation of {Co –Eu } and {Co –Tb } hetero- or carbon atoms of the pyridyl rings. In the H NMR spec-
dimetallic coordination polymers. Herein, we show the syn- tra, for both complexes, the pyridyl protons were found to
thesis, structures, and catalytic applications of such coordi- resonate between δ = 6.8 and 8.1 ppm. For both complexes,
nation polymers in ring-opening reactions of epoxides with the signal of the CH group of the coordinated CH OH
3
3
1
anilines and alcohols under solvent-free conditions.
molecule was observed at δ ≈ 3.2 and 48.7 ppm in the H
and 13C NMR spectra, respectively.
The thermal gravimetric analysis (TGA) for complexes 2
and 3 supports the structural analysis (cf. crystal struc-
tures). For complex 2 (Figure S4 in the Supporting Infor-
mation), the observed weight loss of 14.67% fits nicely with
Results and Discussion
Synthesis and Characterization of 2 and 3
The heterodimetallic complexes 2 and 3 were synthesized the calculated value of 14.90% in the temperature range
by treating the building block 1 with the appropriate of 50–188 °C. This corresponds to the loss of three water
Ln(OTf) salt in CH OH (Scheme 2). Both complexes were molecules and a triflate ion. The second step between 330
3
3
isolated as pale green crystalline materials in good yields and 540 °C corresponds to the observed weight loss of
after recrystallization from CH OH/Et O. They are iso- 43.94% (calcd. 43.14%), which is ascribed as the loss of one
3
2
structural in nature as revealed by their superimposable IR MeOH molecule, one triflate ion, and a ligand molecule. In
and NMR spectra and crystal structures. The FTIR spec- a similar manner, complex 3 (Figure S6 in the Supporting
tra[
3
13a]
of both complexes indicate the νO–H stretch at 3370– Information) also showed a weight loss due to three water
400 cm–1 due to the presence of coordinated water mole- molecules and one triflate ion (found 13.21%; calcd.
cules. In addition, the spectra also show the stretches for 14.82%) as the first step and a loss of one MeOH molecule,
the coordinated as well as solvated CH OH molecules one triflate ion, and a ligand molecule (found 42.78%;
3
5104
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Eur. J. Inorg. Chem. 2010, 5103–5112

Heterodimetallic Coordination Polymers
Scheme 2. Synthesis of coordination polymers 2 and 3. Arrows indicate further coordination to/from the building blocks.
calcd. 42.88%) as the second step. In the differential scan- and 4). In both complexes, Eu3+ and Tb3+ ions have eight-
ning calorimetric (DSC) analysis (Figures S5 and S7 in the coordinate geometry in which five coordinations come from
Supporting Information), both complexes show a combined the water molecules and one comes from the coordinated
broad feature for the loss of water molecules and triflate CH OH molecule, whereas the remaining two sites are oc-
3
ions in the exothermic region of 60–165 °C. Both complexes cupied by the Oamide atoms (O1 and O3) from the building
display thermal stability up to approximately 350 °C with blocks. The Eu···O1amide and Eu···O3amide bond lengths are
the observation of crystallization temperature at 352 and 2.340 and 2.305Å, respectively, whereas the Tb···O1amide
3
58 °C for 2 and 3, respectively.
and Tb···O3amide bond lengths were found to be 2.291 and
.320Å, respectively. Both Oamide atoms make an angle of
around 146° with the lanthanide metal ion. The
2
Crystal Structures
Both heterodimetallic complexes 2 and 3 were crystallo- Eu···OMeOH and Tb···OMeOH distances are 2.470 and
graphically characterized and found to be isostructural. The 2.445 Å for complexes 2 and 3, respectively. The Eu···Owater
molecular structures of complexes 2 and 3 are shown in and Tb···Owater bond lengths fall in the range of 2.366–
Figures 1, 2, 3, and 4, whereas selected bonding parameters 2.466 Å. Interestingly, out of four Oamide atoms (O1, O2,
are contained in Tables 1 and 2. The unit cell in both cases O3, and O4) only two Oamide atoms, O1 and O3, were found
3
+
consists of one building block (Co complex), one lantha- to coordinate the lanthanide metal ion. Initially, this obser-
nide metal ion (coordinated with one methanol and five vation was puzzling; however, a closer look at the crystal
water molecules), two triflate ions, and three molecules of structure revealed that the remaining Oamide atoms (O2 and
methanol as the solvent of crystallization. Two deproton-
ated tridentate ligands are arranged in a meridional fashion
3
+
3+
around the central Co metal ion. The central Co metal
ion is coordinated by four deprotonated Namide atoms in
the equatorial basal plane, whereas two N
atoms oc-
pyridine
cupy the axial positions. The geometry around the Co3 ion
can best be described as compressed octahedral as also
noted for the precursor complex 1[ and other structurally
+
8]
[
15]
characterized complexes with closely similar ligands. The
average Co···Namide and Co···Npyridine bond lengths are
1.952 and 1.854 Å, and 1.955 and 1.862Å for 2 and 3,
respectively. These distances are a little shorter than those
of building block 1.[ Moreover, the crystal structures of
the heterodimetallic complexes 2 and 3 revealed that the
8]
3
+
geometry around the central Co ion is unaffected by the
coordination to the secondary metal ions. The lanthanide
3
+
3+
Figure 1. Partial crystal structure of 2 showing the coordination
3+
metal ions (Eu for 2 and Tb for 3) are coordinated
through the amide oxygen atoms O1 and O3 diagonally
from two building blocks. This arrangement has resulted in
environment around the Eu center and its bonding with the
building block molecule. Thermal ellipsoids are drawn at 50%
probability level; hydrogen atoms, anions, and solvent molecules
the formation of a one-dimensional zigzag chain (Figures 3 have been omitted for clarity.
Eur. J. Inorg. Chem. 2010, 5103–5112
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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G. Kumar, A. P. Singh, R. Gupta
FULL PAPER
O4) are involved in intermolecular hydrogen bonding with
the water molecules (O4W and O5W) coordinated to the
lanthanide ion from the adjacent chain. Thus, two Oamide
Table 1. Comparative bond lengths [Å] and bond angles [°] around
3
+
the central Co ion for complexes 1, 2, and 3.
Bond
Complex 1[a]
Complex 2
Complex 3
Co–N1
Co–N2
Co–N3
Co–N4
Co–N5
Co–N6
N1–Co–N2
N3–Co–N4
N2–Co–N4
N1–Co–N3
N5–Co–N6
1.998(7)
1.962(8)
2.048(7)
1.935(8)
1.872(7)
1.870(7)
162.8(3)
162.4(3)
91.5(3)
1.959(4)
1.955(4)
1.959(4)
1.936(4)
1.853(4)
1.856(4)
163.15(15)
163.43(15)
92.67(15)
94.23(15)
176.84(16)
1.961(3)
1.937(3)
1.966(3)
1.956(4)
1.863(3)
1.859(3)
163.44(14)
163.31(14)
92.81(15)
94.24(15)
176.85(15)
Figure 2. Partial crystal structure of 3 showing the coordination
environment around the Tb3 center and its bonding with the
building block molecule. Thermal ellipsoids are drawn at 50%
probability level; hydrogen atoms, anions, and solvent molecules
have been omitted for clarity.
+
92.3(3)
175.2(3)
[a] See ref.[8]
Figure 3. Weak interactions and packing diagram of coordination polymer 2. Hydrogen atoms, anions, and solvent molecules have been
omitted for clarity. See text for details.
Figure 4. Weak interactions and packing diagram of coordination polymer 3. Hydrogen atoms, anions, and solvent molecules have been
omitted for clarity. See text for details.
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Eur. J. Inorg. Chem. 2010, 5103–5112

Heterodimetallic Coordination Polymers
atoms are coordinated to the lanthanide atom to generate interacts weakly with the C–H bonds of an adjacent pyr-
a zigzag chain, and the remaining two Oamide atoms are idine ring. It is important to mention that such
stabilizing the secondary structure (see below).
Npyridine···H–Owater and Npyridine···H–Cpyridine hydrogen
bonds lock the uncoordinated pyridine rings, thus not al-
lowing them to interact/coordinate to the lanthanide metal
ion.
Table 2. Comparative bond lengths [Å] and bond angles [°] around
the lanthanide metal ion for complexes 2 and 3.
Bond[a]
Complex 2
Complex 3
A similar type of packing behavior was observed in case
3+
3+
M–O1
M–O3
2.340(3)
2.305(3)
2.291(3)
2.320(3)
of the {Co –Tb } complex 3. Two zigzag strands are con-
nected through hydrogen bonds between the amide oxygen
atom O2 and water molecules O2W and O4W with O···O
distances of 2.691 and 2.702 Å, respectively (Figure 4). The
other amide atom O4 interacts with the O4S atom of the
methanol present as the solvent of crystallization by means
of a hydrogen bond (O4amide···O4Smethanol: 2.678 Å). The
M–O1S
M–O1W
2.470(3)
2.385(3)
2.445(4)
2.371(4)
M–O2W
M–O3W
2.395(4)
2.466(4)
2.423(3)
2.452(4)
M–O4W
M–O5W
2.403(4)
2.450(3)
2.377(3)
2.366(3)
O1–M–O3
O1–M–O1W
O1–M–O2W
O1–M–O3W
O1–M–O4W
O1–M–O5W
O1–M–O1S
O3–M–O1S
O3–M–O1W
O3–M–O2W
O3–M–O3W
O3–M–O4W
O3–M–O5W
O1W–M–O1S
O2W–M–O1S
O3W–M–O1S
O4W–M–O1S
O5W–M–O1S
145.89(11)
76.14(11)
86.32(15)
140.67(12)
105.86(13)
74.38(11)
79.08(11)
78.15(11)
73.87(12)
99.83(14)
71.92(12)
89.62(12)
139.66(11)
75.80(12)
147.67(13)
134.45(13)
69.81(12)
127.53(11)
145.68(11)
99.96(14)
140.02(12)
72.33(13)
89.67(12)
73.81(12)
77.91(12)
78.93(12)
86.46(13)
74.23(11)
140.45(12)
105.67(12)
76.20(11)
147.50(12)
127.64(12)
135.02(14)
69.95(12)
75.81(12)
atom
O4S
further
interacts
with
O5W
water
3+
(O4Smethanol···O5W: 2.690 Å) coordinated to the Tb cen-
ter. Within a zigzag strand, hanging pyridine nitrogen atom
N7 forms an intramolecular hydrogen bond with the water
molecule O5Wwater (N···O separation: 2.813 Å), whereas N8
is connected to the O2W (N···O separation: 2.798Å). The
pyridine atom N9 interacts much more weakly with hydro-
gen atoms of the water molecules O2W and O4W, with an
N···O separation of around 3.391 Å. As noted for complex
2
, such interactions lock the pyridine rings in this case as
well.
Based on our earlier heterodimetallic complexes
[8–10]
3+
3+
(Scheme 1),
we postulated that the Eu and Tb ions
may also be accommodated within the molecular clefts cre-
ated by the hanging pyridine rings. However, the structural
observation of the coordination of the Eu and Tb ions
to Oamide instead of Npyridine suggests the preference of lan-
thanide metal ions to coordinate hard donors such as
[
a] M = Eu for 2 and Tb for 3.
3+
3+
Weak Interactions
Both complexes 2 and 3 show various kinds of weak in- Oamide instead of soft Npyridine donors. It may be noted that
teractions that result in a two-dimensional (2D) network the building block 1 was able to accommodate three-coordi-
+
2+
(
Figures 3 and 4). In complex 2, one zigzag strand is con- nate Cu ion (0.72Å), four-coordinate Zn (0.74 Å), six-
nected to the adjacent zigzag strand through hydrogen coordinate Cd2 (1.09 Å), and six-coordinate Hg (1.16 Å)
+
2+
bonding between the amide oxygen atom O4 and water mo- ions within the clefts created by the hanging pyridine rings
[
8–10]
lecules O4W and O5W coordinated to the europium center. as evidenced by the structural characterization.
We be-
The O···O heteroatom separations were found to be 2.690 lieve there are two reasons for such an observation. First,
[
16]
and 2.683 Å, respectively. Similarly, the amide oxygen atom the hard/soft acid–base concept that usurped the size fac-
[
17]
3+
3+
O4 of the second strand (symmetry-related) also forms re- tor,
because the ionic radii of Eu (1.09 Å) and Tb
2+
ciprocal hydrogen bonds with the water molecules O4W (1.06 Å) are comparable to that of the Hg ion (1.16 Å).
and O5W of the first strand (Figure 3). The other amide Second, the pyridine nitrogen atoms are locked due to the
atom O2 forms a hydrogen bond with the O2S atom formation of strong Npyridine···H–Owater hydrogen bonds
(
O2amide···O2Smethanol: 2.678 Å) of the methanol present as and thus are not available to coordinate/accommodate the
the solvent of crystallization. The atom O2S further inter- lanthanide ion.
acts with O1W (O2Smethanol···O1W: 2.679 Å) coordi- X-ray powder diffraction (XRPD) was used to check the
water
3
+
nated to the Eu center. Additional intramolecular hydro- crystalline homogeneity and purity of the bulk product.
gen bonds form within the strand between the hanging pyr- The measured XRPD pattern closely matches the one simu-
idine nitrogen atoms and the water molecules coordinated lated from the single-crystal diffraction data for both coor-
to the europium ion. For example, N9pyridine forms a strong dination polymers 2 and 3 (Figures S8 and S9 in the Sup-
hydrogen bond with O1Wwater, with a heteroatom distance porting Information), thereby indicating that a single phase
of 2.827 Å. Similarly, N10pyridine forms an equally strong has resulted during the bulk synthesis of the polymers.
hydrogen bond with O5Wwater, with an N···O separation of
2
.797Å. The pyridine nitrogen atom N8 forms weak hydro-
Solvent-Free Catalytic Applications of Networks 2 and 3
gen bonds, with the hydrogen atoms attached to the O4W
and O5W water molecules (N···O separation: ca. 3.395 Å).
Ring-opening reactions of epoxides with various nucleo-
On the other hand, the fourth pyridine nitrogen atom N7 philes are attractive due to applications in the synthesis of
Eur. J. Inorg. Chem. 2010, 5103–5112
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5107

G. Kumar, A. P. Singh, R. Gupta
FULL PAPER
pharmaceutically and industrially important compounds.[18] identical results. A comparison of XRPD patterns of cata-
A variety of nucleophiles have been employed for such reac- lysts 2 and 3 before and after the catalytic reaction did not
tions successfully, with the majority of nucleophiles being reveal significant differences (Figures S10 and S11 in the
heteroatom-based. These methodologies have provided Supporting Information) and thus strongly suggests that
[
19]
[20]
practical access to 1,2-azido alcohols, 1,2-halohydrins,
the structural integrity of the material is preserved after the
[21]
[22]
1
,2-hydroxy sulfides, 1,2-benzoyloxy alcohols, 1,2-aryl- catalytic reaction. The effect of electronic substituents on
[
23]
[24]
oxy alcohols, 1,2-alkoxy alcohols, and 1,2-hydroxyan- the product yield was evaluated by the placement of elec-
[
25]
ilines. Generally, the activation of the epoxide is a prereq- tron-donating and -withdrawing groups at the para position
uisite for such reactions, and such an activation has been of the aniline ring. As anticipated, the yields were higher
achieved by using a protonic acid or a metal-based Lewis with electron-rich anilines (Table 3, Entries 2 and 3) due to
acid. Several Lewis acids have been reported for the ring- the better nucleophilicity than with electron-poor anilines
[26]
opening reaction of epoxides such as metal amides, metal (Entries 4–6). A similar observation has been noticed in the
[
27]
[28]
[29]
[9,33,34]
alkoxides,
metal triflates,
metal halides,
Compared to the well-studied ring-opening ine, for both catalysts 2 and 3, the yield dropped to less
reactions of epoxides with amines, similar reactions that in- than 10% (Entry 6) even when the reaction was carried out
and other literature.
For example, in the case of para-nitroanil-
[
30]
metal salts.
[
31]
volve alcohols as the nucleophiles are less studied.
The for 24 h as compared to 4 h in other cases.
poor nucleophilic nature of alcoholic substrates has been
suggested as the potential reason and led to the use of
strong acidic or basic media for carrying out such reac-
Table 3. Ring-opening reactions of cyclohexene oxide with aniline
and para-substituted anilines by using catalysts 2 and 3.
[
32]
tions.
Thus, there is a need for a widely applicable ap-
proach whereby a common catalyst could perform ring-
opening reactions by using both amines and alcohols as the
3
+
3+
nucleophile under ambient conditions. The {Co –Eu }
3
+
3+
and {Co –Tb } heterodimetallic coordination polymers
are shown here to act as heterogeneous catalysts for the
aminolysis and alcoholysis reactions under solvent-free
conditions.
For the aminolysis reaction, an equimolar mixture of cy-
clohexene oxide and aniline was stirred under solvent-free
conditions at room temperature in the presence of catalyst
Entry
R
H
Time [h][b]
Yield [%][a]
Catalyst 2
Catalyst 3
98, 96,[b] 94[c]
98, 95,[b] 94[c]
1
2
3
4
5
6
4
4
4
4
4
C
2
H
5
O
90
72
63
46
8
99
66
58
32
6
CH
3
Cl
F
NO
(5 mol-% 2 or 3). Under these conditions, a smooth reac-
tion took place and, after workup, the respective product,
β-amino alcohol, was isolated in high yield. As shown in
the Table 3, the coordination polymers 2 and 3 could pro-
mote the reaction between the cyclohexene oxide with ani-
2
24
[
a] Isolated yield. [b] Third run with reused catalyst. [c] Sixth run
with reused catalyst.
line (Entry 1) and para-substituted anilines that contain
various functional groups (Entries 2–6). Without catalysts as a representative unsymmetrical epoxide
To determine the regioselectivity, styrene oxide was used
[
33,34]
and was
2
or 3, the reaction did not proceed at all, thereby support- treated with aniline or para-substituted anilines in the pres-
ing the possible Lewis-acidic metal-catalyzed activity of the ence of catalyst 2 or 3 (5 mol-%; Table 4). Interestingly, a
coordination polymers. Further, when the catalyst was fil- perfect regioselectivity was observed that resulted in only a
tered off, the reaction was no longer promoted. A control single product in all cases with both catalysts 2 and 3. Out
experiment of using the building block 1 also did not result of two possible products due to the nucleophilic attack
in any product formation. However, a reaction by using Eu- either at the benzylic carbon atom or at the less hindered
[6a]
(
OTf) or Tb(OTf) as a catalyst
under homogeneous carbon atom of the epoxide ring, in all cases, nucleophilic
2
2
conditions (with THF as the solvent) did result in Ͻ20% attack took place at the benzylic carbon atom of the epox-
conversion, thus demonstrating the enhanced catalytic ac- ide. The regioisomer formed by the reaction of the amine
tivity of coordination polymers 2 and 3 under hetero- at the benzylic carbon atom of the epoxide ring showed the
+
geneous and solvent-free conditions. These experiments characteristic molecular ion peak [M – 31] due to the loss
[
33]
clearly show that the soluble and catalytically active species of the CH OH fragment in the GC–MS studies.
This
2
are not eluted at all from coordination polymers 2 and 3 conclusively proves a single product, as the other re-
+
under the reaction conditions. Thus, the reaction does pro- gioisomer is expected to show the molecular ion peak [M –
ceed by heterogeneous catalysis of the coordination poly- 107] due to the loss of the C H CHOH fragment for the
6
5
mers. In addition, the catalysts can be recovered after the product formed by the reaction at the terminal carbon atom
[
33]
reaction and reused several times (tested six times; Table 3, of the epoxide ring. These results indicate that the epox-
Entry 1) without significant loss of activity (Ͻ5% drop in ide ring has interacted with the lanthanide ion through the
isolated yield in the sixth run). The recovered coordination less-hindered side, possibly due to steric reasons caused by
polymers 2 and 3 were characterized by XRPD and FTIR the attached pyridine rings and solvent molecules. As noted
spectra before and after the catalytic reaction and showed for the cyclohexene oxide, here also the yields were found
5108
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5103–5112

Heterodimetallic Coordination Polymers
to be higher with electron-rich anilines (Table 4, Entries 2 istry.[35] The styrene oxide always led to the formation of
and 3) than with electron-poor ones (Entries 4–6). In ad- one regioisomer, through incorporation of the alcohol at
dition, the reused catalysts were able to catalyze the reac- the phenyl-substituted carbon atom, irrespective of the na-
tion efficiently several times without any further purifica- ture of the alcohol, as expected for a charge-controlled ring-
[
36]
tion or regeneration (tested six times; Table 4, Entry 1).
opening process. A similar observation was made for the
aminolysis reactions that used styrene oxide as an unsym-
metrical epoxide. All control experiments showed no con-
version, even after prolonged reaction time (up to 72 h).
Table 4. Ring-opening reactions of styrene oxide with aniline and
para-substituted anilines by using catalysts 2 and 3.
Conclusion
3+
3+
3+
3+
Two new {Co –Eu } and {Co –Tb } coordination
polymers 2 and 3, respectively, have been synthesized and
characterized. The crystallographic investigations show that
the lanthanide ions are connected to the building-block co-
balt complex through Oamide groups. This results in the gen-
eration of a one-dimensional zigzag coordination polymer.
Furthermore, the individual chains were found to connect
to each other through several hydrogen bonds that result in
the generation of a two-dimensional network. These coordi-
nation polymers have been shown to catalyze the ring-open-
ing reactions of epoxides with anilines and alcohols under
heterogeneous and solvent-free conditions. Interestingly, a
perfect regioselectivity was observed in the aminolysis and
alcoholysis ring-opening reaction of styrene oxide. Future
studies will target harnessing the presence of both the Lewis
acidity of the lanthanide ion and the Brønsted basicity of
the uncoordinated pyridine rings in a multifunctional cata-
lytic endeavor.
Entry
R
H
Time [h][b]
Yield [%][a]
Catalyst 2
Catalyst 3
1
2
3
4
5
6
4
4
4
4
4
83, 80,[b] 76[c]
98, 96,[b] 94[c]
C
2
H
5
O
85
65
55
12
4
99
68
52
85
7
CH
3
Cl
F
NO
2
24
[
a] Isolated yield. [b] Third run with reused catalyst. [c] Sixth run
with reused catalyst.
The heterogeneous catalytic reactions were then extended
to alcoholysis by using alcohols as the nucleophile.
Both cyclohexene oxide and styrene oxide were opened with
few alcoholic substrates carrying various steric groups (iso-
propyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and
benzyl alcohol) in the presence of catalyst 2 or 3 (5 mol-
[
31,32,35]
%). In general, the alcoholysis reactions were found to take
longer (24 h), and the results indicate poorer transforma-
tions than the corresponding aminolysis reactions (Table 5).
Out of several alcohols tested, tert-butyl alcohol was found
Experimental Section
Materials and Reagents: The solvents were purified as reported be-
to be the best (Table 5, Entries 1 and 5), whereas benzyl fore.[37–41] The ligand H2L
1
1
and complex Na[Co(L )2] (1) were syn-
alcohol poorly promoted the ring-opening reaction (En- thesized according to our earlier reports.[
tries 4 and 8). This could be explained by the electron-do-
nating character of the tert-butyl group in the former and
7,8]
Synthesis of [{Co(L1)
2
2 5 3 3 3 2 3 n
–Eu(OH ) (CH OH)}(CF SO ) ·3CH OH]
(
2): Complex 2 was synthesized by treating a solution of
the electron-withdrawing effect of the benzene ring in the
Eu(CF SO (669 mg, 1.116 mmol) in CH OH (2 mL) with a solu-
3
3
)
3
3
latter. In the case of cyclohexene oxide, products were ob- tion of complex 1 (400 mg, 0.558 mmol) in CH OH (4 mL). The
3
tained as the single diastereoisomer with trans stereochem- reaction mixture was stirred at room temperature for 2 h. The solu-
Table 5. Ring-opening reactions of cyclohexene oxide and styrene oxide with alcohols by using catalysts 2 and 3.[a]
Entry
Epoxide[b]
Alcohol
Product
R–
Yield [%][c]
Catalyst 2
Catalyst 3
1
2
3
4
5
6
7
8
C.O.
C.O.
C.O.
C.O.
S.O.
S.O.
S.O.
S.O.
(CH
CH CH(CH
(CH CHOH
CH OH
COH
CH(CH
CHOH
CH OH
3
)
3
COH
(CH
CH CH(CH
(CH CH–
CH
C–
CH(CH
CH–
CH
3
)
3
C–
65
60
55
30
74
56
56
25
58
55
50
24
54
55
55
24
CH
3
2
3
)OH
CH
CH
3
2
3
3
)–
)–
3
H
)
5
2
3 2
)
C
6
2
C
6
H
5
2
–
(CH
CH
(CH
3
)
3
(CH
CH
(CH
3 3
)
CH
3
2
3
)OH
3
2
3
H
)
2
3
H
)
5
2
C
6
5
2
C
6
2
–
[a] Reaction time: 24 h. [b] C.O. and S.O. stand for cyclohexene oxide and styrene oxide, respectively. [c] Isolated yield.
Eur. J. Inorg. Chem. 2010, 5103–5112
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5109

G. Kumar, A. P. Singh, R. Gupta
FULL PAPER
tion was filtered through a pad of Celite in a medium-porosity frit,
and the solvent was evaporated under reduced pressure. The crude
product thus obtained was redissolved in methanol and vapors of
diethyl ether were diffused at room temperature. After a period of
madzu and TA-DSC Q200 instruments, respectively, at 5 °Cmin–1
heating rate under nitrogen. The X-ray powder diffraction studies
were performed either with an X’Pert Pro from Panalytical or a
α
Bruker AXS D8 Discover instrument (Cu-K radiation, λ =
3
–4 d, pale green crystalline material was obtained that was filtered
and dried under vacuum. Yield: 360 mg (65%). C40 48CoEu-
(1361.88): calcd. C 33.00, H 3.19, N 10.45; found C
3.84, H 3.34, N 10.89. FTIR (KBr, selected peaks): ν˜ = 3400
OH), 1593, 1556 (C=O), 1247, 1030, 639 (S–O), 1175 (O–CH
1.54184 Å). The samples were ground and subjected to the range
of θ = 2–50° with a scan rate of 1° per minute at room temperature.
H
6 10 19 2
F N O S
3
(
Crystallography: Single crystals suitable for the X-ray diffraction
studies were grown by vapor diffusion of diethyl ether to a solution
3
)
of the complex in CH
complexes 2 and 3 were obtained with a Bruker Kappa Apex-CCD
diffractometer by using graphite-monochromated Mo-K radiation
Intensity data were corrected for
3
OH in both cases. The intensity data for
–1
cm . Conductivity (ca. 1 m solution, 298 K): Λ
CH OH), 115 (in DMF), 175 (in CH CN), 60 (in DMSO)
cm mol . Absorption (DMSO): λmax (ε) = 645 (165), 470 (sh,
M
= 130 (in
3
3
–
1
2
–1
–1
α
Ω
42,43]
(
λ = 0.71073 Å) at 293K.[
10 –1 cm ) nm. FAB-MS: calcd. for {[Co(L )
O)
1
-Eu(CH
] + K } 1396.98; found 1397. H NMR ([D ]DMSO,
00 MHz, 25 °C, TMS): δ = 8.04 (t, J = 7.2 Hz, 2 H, 10-H), 7.67
2
2
3 4
OH) -
Lorentz polarization effects, and an empirical absorption correc-
tion (SADABS) was applied.[ The structures were solved by di-
rect methods and refined by full-matrix least-squares refinement
+
1
(H
2
5
(OTf)
2
6
44]
3
(
(
4 H, 2-H), 7.58 (d, J = 9 Hz, 4 H, 5-H), 7.28 (m, 4 H, 4-H), 7.03
br. d, J = 6 Hz, 4 H, 9-H), 6.70, (br. m, 4 H, 3-H), 3.2 (s, 3 H,
2
techniques on F by using the programs SHELXL-97 in the
WinGX module.[ All hydrogen atoms were fixed at calculated
positions with isotropic thermal parameters, whereas all non-hy-
drogen atoms were refined anisotropically. Details of the crystallo-
graphic data collection and structural solution parameter are given
in Table 6. CCDC-780429 (2) and -780430 (3) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Data Center via
www.ccdc.cam.ac.uk/data_request/cif.
45]
3 3 6
of CH ]DMSO, 300 MHz, 25 °C,
OH) ppm. 13C NMR ([D
CH
TMS): δ = 147.37 (C-2), 122.30 (C-3), 122.95 (C-4), 117.97 (C-5),
1
1
57.25 (C-6), 167.25 (C-7), 159.76 (C-8), 135.46 (C-9), 138.66 (C-
0), 48.72 (CH of CH OH) ppm.
3
3
Table 6. Crystallographic data collection and structural refinement
parameters for complexes 2 and 3.
2
3
Empirical formula
Formula mass
T [K]
C
40
H
48CoEuF
6
N
10
O
19
S
2
40 6 10 19 2
C H48CoF N O S Tb
1368.85
293(2)
1361.89
293(2)
Crystal system
Space group
a [Å]
b [Å]
c [Å]
monoclinic
monoclinic
P2 /n
1
Synthesis of [{Co(L1)
3): This compound was synthesized in a similar manner as com-
plex 2 by using Tb(CF SO . Yield: 400 mg (62%). C40
Tb (1368.84): calcd. C 32.55, H 3.18, N 10.72; found C
2.05, H 3.15, N 10.34. FTIR (KBr, selected peaks): ν˜ = 3370
OH), 1594, 1558 (C=O), 1243, 1030, 639 (S–O), 1174 (O–CH
2
2 5 3 3 3 2 3 n
–Tb(OH ) (CH OH)}(CF SO ) ·3CH OH]
1
P2 /n
(
15.225(5)
18.546(5)
19.479(5)
90
105.944(5)
90
5289(3)
4
1.710
1.670
2744
0.0576
R1 = 0.0429
wR2 = 0.1188
R1 = 0.0694
wR2 = 0.1475
1.112
15.235(5)
18.531(5)
19.469(5)
90
105.849(5)
90
5288(3)
4
1.720
1.822
2752
0.0565
R1 = 0.0455
3
3
)
3
H48CoF6-
N
3
(
10
O
19
S
2
α [°]
β [°]
3
)
–1
γ [°]
V [Å ]
M
cm . Conductivity (ca. 1 m solution, 298 K): Λ = 135 (in
3
CH OH), 145 (in DMF), 165 (in CH CN), 62 (in DMSO)
3
3
Z
–1
2
–1
Ω
2
cm mol . Absorption (DMSO): λmax (ε) = 646 (170), 472 (sh,
–
3
d [g cm ]
µ [mm ]
05 –1 cm )
Tb(CH OH)
[D
.65 (br., 4 H, 2-H), 7.44 (br., 4 H, 5-H), 7.22 (br., 4 H, 4-H), 6.98
br., 4 H, 9-H), 6.64, (br., 4 H, 3-H), 3.2 (s, 3 H, CH of CH OH)
]DMSO, 300 MHz, 25 °C, TMS): δ = 147.31
C-2), 122.19 (C-3), 122.87 (C-4), 117.85 (C-5), 157.31 (C-6), 167.06
C-7), 159.76 (C-8), 135.32 (C-9), 138.50 (C-10) ppm.
–1
nm.
O) (OTf)
FAB-MS:
calcd.
for
{[Co(L )
1
-
2
–1
+
1
3
4
(H
2
5
2
]+K } 1403.94; found 1404. H NMR
F(000)
R(int.)
(
7
(
6
]DMSO, 300 MHz, 25 °C, TMS): δ = 7.86 (br., 2 H, 10-H),
Final R indices
[
a]
[IϾ2σ(I)]
R indices
all data)
wR2 = 0.1277
R1 = 0.0590
wR2 = 0.1522
1.091
3
3
13
ppm. C NMR ([D
6
(
(
(
2
GOF on F
|; wR = {Σ[w(F2
– F
2 2
) ]/Σ[wF4
]}1/2
.
[
a] R = Σ||F
1
o
| – |F
c
||/Σ|F
o
o
c
o
Physical Measurements: The conductivity measurements were car-
ried out in organic solvents with a digital conductivity bridge from
the Popular Traders, India (model number: PT 825). The elemental
analysis data were obtained with an Elementar Analysen Systeme
GmbH Vario EL-III instrument. The NMR spectroscopic mea-
surements were carried out with a Bruker Avance (300 MHz) in-
strument. The IR spectra (either as KBr pellet or as a mull in min-
eral oil) were recorded with a Perkin–Elmer FTIR 2000 spectrome-
ter. The absorption spectra were recorded with a Perkin–Elmer
Lambda 25 spectrophotometer. GC–MS studies were performed
with a Shimadzu instrument (QP 2010) with an RTX-5SIL-MS col-
umn. The FAB mass spectra were recorded with a Jeol SX 102/Da-
General Procedure for the Catalytic Reactions: The ring-opening
reactions of the epoxides were carried out in oven-dried glassware
under an inert gas. In a typical aminolysis reaction, cyclohexene
oxide (0.98 mmol) was treated with aniline (1.18 mmol) in the pres-
ence of catalyst 2 or 3 (0.0495 mmol). However, in case of styrene
oxide, the epoxide (0.875 mmol) was treated with aniline
(1.05 mmol) in the presence of catalyst 2 or 3 (0.0438 mmol). For
the alcoholysis reactions, epoxide (0.98 mmol) and catalyst 2 or 3
(0.0495 mmol) were stirred in alcohol (2 mL) at room temperature
for 24 h. The reactions were monitored by thin-layer chromatog-
raphy (TLC). After 4 h, the catalyst was filtered off, and the filtrate
was concentrated under reduced pressure. The crude product was
600 instrument. Thermal gravimetric analysis (TGA) and differen-
tial scanning calorimetry (DSC) were performed with DTG 60 Shi-
5110
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5103–5112

Heterodimetallic Coordination Polymers
purified by flash column chromatography on silica gel using a hex-
ane/ethyl acetate mixture (5:1) as the eluent. The products were
isolated and analyzed by GC/GC–MS techniques. The recovered
catalyst was washed with diethyl ether, dried, and reused without
further purification or regeneration. Moreover, the recovered cata-
lysts were characterized by X-ray powder diffraction and FTIR
spectra and showed identical results to those of the fresh samples.
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ray powder diffraction (Figures S8–S11).
[
14] It is important to mention that, although the coordination
1
13
polymers 2 and 3 dissolve in [D
6
]DMSO and their H and
C
NMR spectra were recorded, the exact identity of the species
present during the spectral analysis is not clear. It is likely that
these coordination polymers are fragmented to their molecular
components or some oligomers.
Acknowledgments
R. G. gratefully acknowledges the generous financial support of the
Department of Science and Technology (DST), New Delhi. Crys-
tallographic data collection was provided by IIT-Roorkee (Pro-
fessor U. P. Singh). The AIRF center of JNU, New Delhi served
as the GC–MS and XRPD facility. FAB-MS spectra were provided
by SAIF-CDRI, Lucknow. A. P. S thanks the Council of Scientific
and Industrial Research (CSIR) for the award of an SRF fellow-
ship.
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