Construction of ZnII compounds with a chelating 2,2′-dipyridylamine (Hdpa) ligand: Anion effect and catalytic activities

Article abstract of DOI:10.1002/ejic.200700823

The structures of new compounds containing Zn^II ions and Hdpa (2,2′-dipyridylamine)-chelating ligands were determined. The Hdpa chelating ligands coordinate to Zn^II ions to form mononuclear units (1 and 5), and intermolecular non-classical hydrogen-bond (C-H...O or N/C-H...I) interactions generate polymeric compounds. The chelating ligands with a bipyridyl moiety form mostly mononuclear complexes of different types (I, II and III), and the combination of this ligand with a sulfate anion can produce polymeric species (Type IV). Interestingly, homogeneous catalyst 1 catalyzed efficiently the transesterification of a variety of esters with different alcohols, and hydrogen-bonded polymer 5 showed the heterogeneous catalytic activity for the transesterification reactions. Preliminary selectivity test of primary over secondary alcohol protection in the presence of 1 provided, exclusively, the primary acetate, which suggests the potential utility of this catalyst to be selective for primary alcohols. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200700823

FULL PAPER
DOI: 10.1002/ejic.200700823
II
Construction of Zn Compounds with a Chelating 2,2Ј-Dipyridylamine (Hdpa)
Ligand: Anion Effect and Catalytic Activities
[
a]
[a]
[a]
[a]
[a]
Han Kwak, Sun Hwa Lee, Soo Hyun Kim, Young Min Lee, Eun Yong Lee,
[a]
[a]
[a]
[b]
Byeong Kwon Park, Eun Young Kim, Cheal Kim,* Sung-Jin Kim, and
Youngmee Kim*[
b]
Keywords: Amines / Nitrogen heterocycles / Anion effects / Transesterification / Catalytic activities / Zinc
The structures of new compounds containing ZnII ions and
efficiently the transesterification of a variety of esters with
different alcohols, and hydrogen-bonded polymer 5 showed
the heterogeneous catalytic activity for the transesterification
reactions. Preliminary selectivity test of primary over second-
ary alcohol protection in the presence of 1 provided, exclu-
sively, the primary acetate, which suggests the potential util-
ity of this catalyst to be selective for primary alcohols.
Hdpa (2,2Ј-dipyridylamine)-chelating ligands were deter-
II
mined. The Hdpa chelating ligands coordinate to Zn ions to
form mononuclear units (1 and 5), and intermolecular non-
classical hydrogen-bond (C–H···O or N/C–H···I) interactions
generate polymeric compounds. The chelating ligands with
a bipyridyl moiety form mostly mononuclear complexes of
different types (I, II and III), and the combination of this li-
gand with a sulfate anion can produce polymeric species
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
(Type IV). Interestingly, homogeneous catalyst 1 catalyzed
Introduction
nomeric compounds. Moreover, the coordination polymer
[
[
Zn(Hdpa)(H O) (SO )] and hydrogen-bonded polymers
2 2 4
There has been much attention on the role played by
noncovalent interactions,[1] such as classical (N/O–H···N/O)
and nonclassical hydrogen bonding [C–H···X (X = halide)
or C–H···N/O/C], as well as anion effects[ in the construc-
tion of molecular packing and crystal structures, as they
can provide a good structural motif for the construction of
Zn(Hdpa)Br ] and [Zn(Hdpa)Cl ] have shown, surpris-
2
2
ingly, unusual heterogeneous catalytic activities in the trans-
[3d]
esterification reactions of esters.
2]
Transesterification reactions are important transforma-
tions in organic synthesis in industrial as well as in aca-
[4]
demic laboratories. There are many catalysts available for
[
1,2]
a polymeric compound from a simple building block.
We and others have previously shown that 2,2Ј-dipyridyl-
transesterification, and the most common procedure is to
heat the ester with a catalytic amount of Ti(OiPr) in an
4
amine (Hdpa) as a chelating ligand mostly formed mono-
[5]
alcohol solvent at reflux. Other Lewis acid catalysts such
II
nuclear Zn
complexes [zinc salts used: Zn(CN)2,
as BuSn(OH) and Al(OR) also catalyze this conversion.
3
3
Zn(O CCH ) , Zn(O C H ) , Zn(ClO ) , Zn(BF ) , ZnCl ,
2
3 2
2
6
5 2
3]
4 2
4 2
2
Transesterifications catalyzed by Ti(OiPr) and BuSn(OH)3
4
[
II
ZnBr , and Zn(CF SO ) ], and then these Zn complexes
2
3
3 2
require higher reaction temperatures and acidic condi-
can be used as building blocks for the construction of poly-
meric compounds through weak hydrogen bonds and π–π
interactions. However, the chelating ligand 2,2Ј-dipyr-
idylamine (Hdpa) unexpectedly forms a polymeric com-
[6]
tions. Such drawbacks experienced with these catalysts
drove us to develop new catalysts that operate under milder
conditions.
As a part of our continued interests in the syntheses,
structures, and reactivities of coordination complexes of
[3d]
pound with ZnSO4.
These results demonstrated that
both anion effect and intermolecular hydrogen bonds are
very important roles for the formation of polymeric or mo-
II
Zn with chelating Hdpa ligands, and with the aim to fully
understand the anion effect of our earlier work in order to
find efficient catalysts to mediate various catalytic reactions
that could be carried out under mild reaction conditions, we
employed two more zinc salts with different counteranions
(NO3– and I ) to develop new complexes. Herein we report
the syntheses, crystal structures, and reactivities of two new
Zn-containing compounds formed by the reaction of the
chelating Hdpa ligand and two different zinc salts. With the
[
a] Department of Fine Chemistry, and Eco-Product and Materials
Education Center, Seoul National University of Technology,
Seoul 139-743, Korea
–
Fax: +82-2-973-9149
E-mail: chealkim@snut.ac.kr
[b] Division of Nano Sciences, Ewha Womans University
Seoul 120-750, Korea
Fax: +82-2-3277-2384
E-mail: ymeekim@ewha.ac.kr
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
II
iodide anion, Zn produces a Type I mononuclear complex,
and with the NO3– anion, Zn produces a Type III mono-
II
408
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 408–415

ZnII Compounds with a Chelating Hdpa Ligand
nuclear complex. In both cases, intermolecular hydrogen Table 1. Selected bond lengths [Å] and angles [°] for compound 1.
bonds generate polymeric compounds. We also reported
that homogeneous catalyst 1 catalyzed efficiently the trans-
esterification of a variety of esters with different alcohols Zn1–N23
and that hydrogen-bonded polymer 5 showed hetero-
geneous catalytic activity for the transesterification reac-
tions. Importantly, the transesterification reaction catalyzed
by catalyst 1 is best among the catalytic systems reported N11–Zn1–O2 100.89(6)
previously in Zn-containing coordination and polymeric
compounds, to the best of our knowledge, and hetero-
geneous hydrogen-bonded polymer 5 is only the third exam-
ple of a catalyst used in heterogeneous transesterification
reactions of various p-substituted phenyl acetates and ben-
zoates under mild conditions.
Zn1–N11
Zn1–N21
2.0654(17)
2.0675(18)
2.1093(19)
Zn1–N13
Zn1–O2
Zn1–O1
2.1242(18)
2.2085(16)
2.3183(17)
N11–Zn1–N21 107.09(7)
N21–Zn1–N23 87.97(7)
N21–Zn1–N23 87.97(7)
N21–Zn1–N13 98.96(7)
N11–Zn1–N23 97.69(7)
N21–Zn1–N23 87.97(7)
N11–Zn1–N13 87.65(7)
N23–Zn1–N13 169.66(7)
N21–Zn1–O2 151.97(6)
N13–Zn1–O2 83.61(6)
N21–Zn1–O1 95.05(7)
N13–Zn1–O1 87.42(6)
N23–Zn1–O2 86.67(6)
N11–Zn1–O1 157.81(7)
N23–Zn1–O1 84.32(6)
O2–Zn1–O1
57.04(6)
Table 2. Selected bond lengths [Å] and angles [°] for compound 5.
Zn1–N1[
a]
2.013(4)
2.5669(8)
Zn1–N1
Zn1–I1
2.013(4)
[
a]
Zn1–I1
2.5669(8)
112.46(13)
112.47(13)
111.91(4)
[a]
[a]
[a]
N1 –Zn1–N1 93.9(3)
N1 –Zn1–I1
N1–Zn1–I1[
N1–Zn1–I1
a]
112.47(13)
112.46(13)
N1 –Zn1–I1
[a]
[
a]
Results and Discussion
I1 –Zn1–I1
[
–
a] Symmetry transformations used to generate equivalent atoms:
x + 1, y, –z + 1/2.
The structures of compounds 1 and 5 were determined
by X-ray crystallography. The Hdpa chelating ligands coor-
II
dinate to the Zn ions to form mononuclear units, and
intermolecular hydrogen-bond interactions such as
Crystal Structure of [Zn(Hdpa) (NO )](NO ) (1)
2
3
3
classical (N/O–H···N/O) and nonclassical hydrogen bond-
The asymmetric unit consists of a whole molecule con-
ing [C–H···X (X = halide) or C–H···N/O/C] generate poly- taining a zinc(II) ion, two Hdpa ligands, a nitrate ligand,
meric compounds. Tables 1 and 2 list the selected bond and a nitrate counteranion. Two Hdpa ligands and a nitrate
II
lengths and angles for these structures.
ligand coordinate to a Zn ion to form a six-coordinate
Figure 1. (a) Structure of [Zn(Hdpa)
structure derived by hydrogen bonds. Hydrogen bond lengths (angles): H12N···O32 (x, 1.5 – y, –0.5 + z) 2.022(3) Å [N12–H12N–O32
2
(NO
3
)](NO
3
) 1 with 50% ellipsoids. All hydrogen atoms are omitted for clarity; (b) 2D polymeric
1
1
71.02(2)°], H22N···O33 (1 + x, y, z) 1.932(4) Å [N22–H22N–O33 170.86(2)°], H12···O3 (x, 1.5 – y, –0.5 + z) 2.472(2) Å [C12–H12–O3
57.09(1)°].
Eur. J. Inorg. Chem. 2008, 408–415
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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409

C. Kim, Y. Kim et al.
FULL PAPER
ZnII complex with a N23–Zn1–N13 angle of 169.66° (Fig- for ZnII compounds with Hdpa,[3] and the Zn–I bond
ure 1a). The Zn–Npyridyl bond lengths range from length is 2.5669(8) Å (Table 2). There are nonclassical hy-
II
2
.0654(17) to 2.1242(18) Å, which are typical for Zn com- drogen bonds between the I atoms and the pyridyl hydrogen
[3]
pounds with Hdpa, and the Zn–Onitrate bond lengths are atoms (Zn–I···H–N) and between the I atoms and the amine
.2085(16) and 2.3183(17) Å (Table 1). Two pyridyl rings hydrogen atoms (Zn–I···H–C). These interactions further
2
are bent with torsion angles C24–C25–N22–C26 and C14– extend this mononuclear complex into a 2D architecture
C15–N12–C16 of 169.29(1) and 150.22(1)°, respectively. (Figure 2b). The H···I distance of 3.162(2) Å and the N–
There are hydrogen bonds between an amine hydrogen H···I angle of 137.73(1)° indicate the formation of N–H···I
atom and a nitrate oxygen atom (N–H···O–Nnitrate) and be- hydrogen bonds, and the H···I distance of 3.249(3) Å and
tween a coordinated nitrate oxygen atom and a neighboring the C–H···I angle of 145.86(1)° indicate the formation of
[
7]
pyridyl hydrogen atom (Cpyridyl–H···O–Nnitrate), and these C–H···I hydrogen bonds. The importance of such C–H···I
hydrogen bonds generate a 2D polymeric compound (Fig- hydrogen bonds in the supramolecular self-assembly was
[
7c,8]
ure 1b). The H···Onitrate distances of 1.932(4) and also reported recently.
2
Self-assembly of discrete metal
.022(3) Å and the N–H···O angles of 170.86(2) and complexes by weak C–H···I–Zn interactions was reported,[
9]
1
71.02(2)° indicate the formation of N–H···O hydrogen although intermolecular C–H···I interactions do exist in a
[
7c,8]
bonds, and the H···Onitrate distance of 2.471(2) Å and the few compounds.
This is only the second example of self-
Cpyridyl–H···O angle of 157.09(1)° indicate the formation of assembly of Zn–I···H–C nonclassical H-bonding interac-
[1]
[9]
C–H···O hydrogen bonds. In the 2D structure, the Zn···Zn tions. Moreover, Zn–I···H–N hydrogen bonding is a rare
[
7d]
II
distance is 8.195(1) Å.
case.
The Zn ion has a distorted tetrahedral geometry
with a I–Zn–I angle of 111.91(4)°. Two pyridyl rings are
nearly coplanar with the torsion angle C1–N1–Zn1–N1 (1 –
x, y, 0.5 – z) of –179.8(1)°.
Crystal Structure of [Zn(Hdpa)(I )] (5)
2
Hdpa has been used as a chelating ligand to mostly form
The asymmetric unit consists of half of a molecule, and
a mirror plane is located in the middle of the molecule. The
complete compound structure is generated by the symmetry
operation (–x + 1, y, –z + 1/2) as shown in Figure 2a. The
Zn–Npyridyl bond length is 2.013(4) Å, which is also typical
II
mononuclear Zn complexes. Previously, we showed the
II
anion effects on construction of Zn polymeric compounds
[
3]
containing chelating Hdpa ligands. Structure variation ac-
cording to anions is shown in Scheme 1.
Figure 2. (a) Structure of [Zn(Hdpa)I
I atoms and pyridyl hydrogen atoms and amine hydrogen atoms. Hydrogen bond lengths (angles): N2–H2N···I1(x, –1 + y, z) 3.162(2) Å
N2–H2N–I1 137.73(1)°], C3–H3···I1 (0.5 – x, 1.5 – y,–z) 3.249(3) Å [C3–H3–I1 145.86(1)°].
2
] 5 with 50% ellipsoids; (b) 2D polymeric structure derived by nonclassical hydrogen bonds between
[
410
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 408–415

ZnII Compounds with a Chelating Hdpa Ligand
torted tetrahedral (Td) (Type II), flattened tetrahedral (Td)
(
Type II), and six-coordinate geometries (Type III), respec-
[
3b,3c]
2–
II
tively.
For bridging SO4 anions, surprisingly, Zn
[
3d]
produced a polymeric compound (Type IV).
understand anion effects for Zn complexes containing
Hdpa, two more Zn salts containing iodide and nitrate
anions were used. With the iodide ligand, Zn produces a
To fully
II
II
II
Type I structure, and with the NO3– anion, Zn produces
a Type III structure. Importantly, these results suggest that
the chelating ligands with a bipyridyl moiety form mostly
mononuclear complexes of different types (I, II and III),
and the combination of this ligand with a sulfate anion can
produce polymeric species (Type IV); thus, intermolecular
hydrogen bonds as well as anion effects play very important
roles in the construction of polymeric crystal structures.
II
Homogeneous Catalytic Activity of Compound 1
As part of our efforts to develop transesterification cata-
lysts based on metal ions that are not redox active, we pre-
viously reported that Zn-containing coordination polymer
2
and hydrogen-bonded polymers 3 and 4 could carry out
the heterogeneous catalytic transesterification of a range of
esters with methanol at room temperature under mild con-
ditions (see Scheme 2 for structures of six compounds as
transesterification catalysts), whereas compound 6 [(Hdpa)-
Scheme 1. Structure types according to anions.
Zn(benzoate) ] did catalyze the homogeneous transesterifi-
2
With coordinating halide, cyanide, acetate, and benzoate cation reactions.[3d] In addition, heterogeneous catalyst 2
II
anions, Zn produced distorted tetrahedral mononuclear has shown even better catalytic activity than homogeneous
complexes (Type I) with two nitrogen donor atoms of Hdpa catalyst 6.
[
3a]
and two coordinating anions.
With noncoordinating
This catalyst system constitutes a promising class of
–
–
–
II
OTf , BF , and ClO anions, Zn also produced mononu- heterogeneous catalysts that allowed reuse without any loss
4
4
clear complexes but containing two Hdpa ligands with dis- of activity through 10 runs with ester and appears to be an
Scheme 2. Structures of six compounds containing chelating Hdpa ligands as transesterification catalysts.
Eur. J. Inorg. Chem. 2008, 408–415
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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411

C. Kim, Y. Kim et al.
FULL PAPER
efficient, mild, and easily recyclable method for the
In a certain case, transesterification of esters with alcohol
alcoholysis of esters. On the basis of previous results, com- cannot achieve high conversions because of the reversibility
pound 1 has also been employed as a homogeneous catalyst of the reaction. However, this problem can be solved by
in transesterification owing to its high solubility in meth- using enol esters as acylating agents, as the resultant enolate
anol. The ester, phenyl acetate, was initially used as a sub- is converted into an aldehyde or ketone that is unable to
[
12]
strate [Equation (1)].
participate in the reverse reaction.
Therefore, vinyl ace-
tate was used as an example and, expectedly, converted ef-
ficiently into the product methyl acetate within 0.17 d by 1
(Table 3, Entry 9), which suggests that this catalytic system
can be useful for the preparation of various esters by trans-
esterification.
On the basis of this promising result, transesterification
with the more challenging nucleophiles ethanol, 2-propa-
(
1)
We observed that 1 catalyzed the reaction of methanol nol, and propanol was tested with phenyl acetate. Whereas
with phenyl acetate, with quantitative conversion to methyl the reaction of phenyl acetate with either ethanol (60 d;
acetate in 0.25 d (Table 3, Entry 3) at room temperature un- data not shown) or 2-propanol (60 d; data not shown) was
der the neutral conditions. Because there is the possibility very slow, propanol drove the reaction to completion within
that the zinc salt [Zn(NO ) ] leached from compound 1 can 5 d (Table 3). Various esters were also examined with pro-
3
2
promote transesterification, we carried out the control ex- panol as a nucleophile. The substrates with electron-with-
periment of some esters with Zn(NO ) as shown in the drawing substituents underwent fast conversion into the
3
2
[
2e]
previous study. The transesterification reaction of phenyl corresponding products, whereas those with the electron-
acetate in the presence of Zn(NO ) was very slow (50 d donating ones underwent slow transesterification.
3
2
compared to 0.25 d for complex 1), which indicates that the
Protection of a primary alcohol in the presence of a sec-
zinc salt does not have any influence in our catalytic sys- ondary alcohol is useful in natural product synthesis.[4a,13]
tems. Importantly, this result is the best among the catalytic Therefore, selectivity of primary over secondary alcohol
systems reported previously in Zn-containing coordination protection was tested. In a mixture of propanol and 2-pro-
and polymeric compounds,[
2e,2f,3d,10]
to our best knowledge. panol (1/1) in the presence of 1 and phenyl acetate, only
Once having established that 1 represents an excellent cata- the reaction of propanol proceeded and propyl acetate was
lyst for the transesterification reaction of phenyl acetate obtained in 99.9% yield, whereas the secondary acetate was
with methanol, we investigated the transesterification of formed in Ͻ0.1% yield. This reaction suggests the potential
various p-substituted phenyl acetates and benzoates. The utility of our catalyst for the selective protection of primary
substrates with electron-withdrawing substituents under- alcohols.
went fast transesterification (Table 3, Entries 1, 5, and 6),
It was proposed that the mechanism of metal-ion-cata-
whereas those with electron-donating groups underwent lyzed transesterification probably involves electrophilic acti-
slow transesterification (Table 3, Entries 4 and 8). p-Ni- vation of the carbon center of the carbonyl moiety by bind-
trophenyl acetate and p-nitrophenyl benzoate with nitro ing of the metal to the carbonyl oxygen; hence, Lewis acid-
substituents in the para position, which are known to be ity of the metal center may be important in catalytic trans-
[
14]
problematic substrates for the transesterification reaction esterification. On the basis of this idea, a possible trans-
due to undesirable side reactions such as isomerization or esterification mechanism in this catalyst system can be pro-
[
11]
polymerization,
were also converted quantitatively into posed (Scheme 3). The phenyl acetate substrate substitutes
–
the corresponding products.
an anion (NO ) to give the adduct (Hdpa) Zn(NO )(Sub).
3
2
3
Table 3. Transesterfication of esters by alcohol in the presence of the compounds 1 and 5 at room temperature.[a]
Entry
Substrate
1 (Homo in methanol)[b]
1 (Homo in propanol)[b]
5 (Hetero in methanol)[c]
Time [d]
Time [d]
Time [d]
1
2
3
4
5
6
7
8
9
4-Nitrophenyl acetate
4-Fluorophenyl acetate
Phenyl acetate
0.17
4
0.25
3.9
1.3
0.38
1
5
–
9
4
–
8
–
33
9
12
12
5
4-Methylphenyl acetate
–
4-Nitrophenyl benzoate[
d]
36
13
12
13
8
4-Chlorophenyl benzoate
Phenyl benzoate
4-Methylphenyl benzoate
Vinyl acetate
0.88
0.17
[
0
a] All esters were completely converted into the corresponding products, methyl acetate and methyl benzoate. Reaction conditions: esters
.05 mmol, catalyst 2ϫ10–3 mmol, solvent methanol or propanol (1 mL). See the Experimental Section for detailed reaction conditions.
[
b] Homo means homogeneous catalytic reaction conditions. [c] Hetero means heterogeneous catalytic reaction conditions. [d] The solvent
was CH OH/CH CN (1:1) because of the low solubility of the substrate in CH OH.
3
3
3
412
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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ZnII Compounds with a Chelating Hdpa Ligand
Then, the methanol nucleophile would attack the carbon that the transesterification reaction with the filtered catalyst
atom of carbonyl moiety of the adduct to produce the prod- proceeded at the original rate, whereas the filtrate showed
uct methyl acetate. Detailed mechanistic studies are cur- about 10% conversion within the same time interval. This
rently under investigation.
result strongly suggests that the dominant reactive species
is heterogeneous catalyst 1 and not other species such as
the leached-out metal. On the other hand, the powder X-
ray diffraction (XRD) pattern of filtered catalyst 5 after the
reaction revealed the same pattern as that of original cata-
lyst 5, which suggests that the original structure of the fil-
tered catalyst was maintained during the reaction (see Fig-
ure S1 in the Supporting Information). On the basis of
these results, we concluded that heterogeneous hydrogen-
bonded polymer 5 could be recycled multiple times without
a significant loss in activity.
The transesterification of other esters including benzo-
ates by catalyst 5 was also carried out efficiently and the
results are given in Table 3. Catalyst 5 showed a similar
trend to that of catalyst 1. The substrates with electron-
withdrawing substituents underwent fast transesterification,
whereas those with electron-donating underwent slow reac-
tions. Benzoates underwent slower transesterification than
acetates. The problematic substrates for the transesterifica-
tion reaction, p-nitrophenyl acetate and p-nitrophenyl ben-
zoate with nitro substituents in the para position, were also
converted quantitatively into the corresponding products.
Moreover, an efficient acylating agent, vinyl acetate, was
converted efficiently into the product methyl acetate within
Scheme 3. Plausible transesterification mechanism.
Heterogeneous Catalytic Activity of Compound 5
We also examined the catalytic activity of heterogeneous 5 d by 5 (Table 3, Entry 9), as the resultant enolate was con-
hydrogen-bonded polymer 5 as a heterogeneous catalyst for verted into an aldehyde or ketone that was unable to par-
the transesterification of phenyl acetate [Equation (1)], be- ticipate in the reverse reaction.
cause it was insoluble in alcohol solvents. Treatment of
At this moment, we do not know the exact reactive spe-
phenyl acetate and methanol in the presence of 5, which cies or the reaction mechanism for the transesterification
was ground well into appropriate sizes for high surface area reaction by catalyst 5. A detailed study on these topics is
but not too small for a convenient filtration,[ produced ongoing.
15]
quantitatively methyl acetate in 8 d at room temperature
(Table 3, Entry 3). No or little transesterification occurs
without polymeric compound 5.
Conclusions
Because the potential benefits of the heterogeneous cata-
lyst include easy separation of the catalyst from reagents
and reaction products and recyclability for repeated use,
We showed two new structures of ZnII complexes con-
taining Hdpa ligands to complete the study of anion effects.
[
15]
we examined the recovery and reuse of catalyst 5 at room ZnI and Zn(NO ) produce mononuclear complexes with
2
3 2
[
16]
II
temperature on the basis of our previous experience. Af- different types of structures. Zn produces four types of
ter the reaction with phenyl acetate was complete, the cata- structures: with coordinating anions, Type I; with nonco-
lyst was recovered by filtration and thoroughly washed with ordinating anions, Type II; with ClO4– and NO , Type III;
–
3
methanol for the consecutive runs. The recovered catalyst with bridging sulfate anion, polymeric structure Type IV.
was used for a new reaction batch of phenyl acetate. Cata- These results indicate that an anion effect is very important
II
lyst 5 showed excellent recyclability for 10 times without for the construction of Zn complexes containing chelating
showing any significant deterioration of catalytic activity Hdpa ligands, and intermolecular hydrogen bonds also play
(
see Table S1 in the Supporting Information).
With the usefulness of the recyclability of catalyst 5 for tal structures.
efficient transesterification, we then checked for hetero- We also showed that homogeneous catalyst 1 catalyzed
very important roles for the construction of polymeric crys-
geneity, because in the process of catalysis, the metal species efficiently the transesterification of a variety of esters with
leached from the catalysts might catalyze efficiently the different alcohols, and hydrogen-bonded polymer 5 showed
transesterification reaction instead of the heterogeneous heterogeneous catalytic activity for the transesterification
[
15,16]
catalysts.
We filtered catalyst 1 after the transesterifica- reactions. Importantly, the transesterification reaction cata-
tion reaction of phenyl acetate and allowed the filtered cata- lyzed by catalyst 1 is the best among the catalytic systems
lyst and the filtrate to react with another aliquot of phenyl reported previously in Zn-containing coordination and
acetate, as shown in the previous study.[
15,16]
We observed polymeric compounds, to our best knowledge, and hetero-
Eur. J. Inorg. Chem. 2008, 408–415
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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413

C. Kim, Y. Kim et al.
(NO
)]+. IR (KBr): ν˜ =
FULL PAPER
geneous hydrogen-bonded polymer 5 is only the third exam- matic-H). MS (ESI): m/z = 468 [Zn(Hdpa)
2
3
3
(
1
313 (m), 3201 (m), 3074 (m), 3020 (br. s), 1650 (s), 1596 (s), 1582
ple of a catalyst used in the heterogeneous transesterifica-
tion of various p-substituted phenyl acetates and benzoates
under mild conditions. Moreover, the scope of the applica-
tion of 1 as a transesterification catalyst was expanded to
now include ethanol and propanol. Furthermore, prelimi-
s), 1535 (s), 1480 (s), 1396 (s), 1315 (s), 1285 (s), 1236 (s), 1162 (s),
–
1
052 (w), 1010 (s), 872 (m), 771 (s), 645 (m), 531 (m), 419 (m) cm .
Zn (531.79): calcd. C 45.17, H 3.42, N 21.07; found C
5.34, H 3.39, N 20.89.
20 18 8 6
C H N O
4
nary selectivity tests of primary over secondary alcohol pro- [Zn(Hdpa)(I
2
)] (5): ZnI
4 mL) and carefully layered with a solution of the 2,2Ј-dipyr-
idylamine ligand (34.2 mg, 0.2 mmol) in acetone (2 mL), ethanol
1 mL), and methanol (1 mL). Suitable crystals of compound 5 for
2 2
(31.9 mg, 0.1 mmol) was dissolved in H O
(
tection in the presence of 1 and phenyl acetate has provided,
exclusively, the primary acetate propyl acetate, which sug-
gests the potential utility of our catalyst to be used in the
selective protection of primary alcohols. Further explora-
tions into the uses of this catalyst family in organic trans-
formations as well as mechanistic investigations are ongo-
ing.
(
X-ray analysis were obtained in a few days. Yield: 32.8 mg (66.9%).
IR (KBr): ν˜ = 3335 (s), 1636 (s), 1585 (s), 1523 (s), 1479 (s), 1434
(
m), 1415 (w), 1231 (s), 1159 (s), 1021 (s), 909 (w), 772 (s), 653 (w),
–1
5
2
64 (w), 519 (w), 418 (w) cm . C10
4.49, H 1.85, N 8.57; found C 24.40, H 1.61, N 8.77.
9 2 3
H I N Zn (490.37): calcd. C
Catalytic Transesterification Reaction Conditions: To a solution of
Experimental Section
the esters (0.05 mmol) dissolved in methanol (1 mL) was added the
–
3
catalyst (2ϫ10 mmol), and the mixture was shaken at room tem-
perature (450 rpm). Reaction conversion was monitored by GC–
MS of 20-µL aliquots withdrawn periodically from the reaction
mixture. All reactions were run at least three times and the average
conversion yields are presented. Yield was based on the formation
of the products, methyl acetate, or methyl benzoate.
Materials: 2,2Ј-Dipyridylamine (Hdpa), methanol, ethanol, propa-
nol, para-substituted phenyl acetate, para-substituted phenyl ben-
zoate, methyl acetate, methyl benzoate, and zinc salts were pur-
chased from Aldrich and were used as received. 4-Fluorophenyl
acetate and 4-nitrophenyl benzoate were obtained from Lancaster.
Instrumentation: Elemental analysis for carbon, nitrogen, and hy-
drogen was carried out by using an EA1108 (Carlo Erba Instru-
ment, Italy) in the Organic Chemistry Research Center of Sogang
University, Korea. Product analysis for the transesterification reac-
tion was performed with either a Hewlett–Packard 5890 II Plus gas
chromatograph interfaced with a Hewlett–Packard Model 5989B
mass spectrometer or a Donam Systems 6200 gas chromatograph
equipped with a FID detector with a 30-m capillary column (Hew-
lett–Packard, HP-1, HP-5, and Ultra 2). XRD data were obtained
Crystallography: The diffraction data for compounds 1 and 5 were
collected with a Bruker SMART AXS diffractometer equipped
with a monochromator in the Mo-K (λ = 0.71073 Å) incident
α
beam. The crystal was mounted on a glass fiber. The CCD data
were integrated and scaled by using the Bruker-SAINT software
package, and the structure was solved and refined by using
SHEXTL V6.12.[ Hydrogen atoms were located in the calculated
positions. The crystallographic data for compounds 1 and 5 are
listed in Table 4. CCDC-655108 and -655109 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
17]
α
with a Rigaku X-ray diffractometer with Cu-K radiation (λ =
1.5418 Å).
[
Zn(Hdpa)
2
(NO
3
)](NO
3
)
(1):
Zn(NO
3
)
2
·6H
2
O
(37.2 mg,
0.125 mmol) was dissolved in methanol (4 mL) and carefully lay-
ered by a solution of the 2,2Ј-dipyridylamine ligand (42.8 mg,
.25 mmol) in acetone (4 mL). Suitable crystals of compound 1 for
X-ray analysis were obtained in a few weeks. Yield: 43.1 mg
Supporting Information (see footnote on the first page of this arti-
cle): Recycle experiments for the transesterification reactions of
phenyl acetate by heterogeneous catalyst 5 and PXRD data for
0
1
2
(65.4%). H NMR (300 MHz, D O): δ = 6.79–7.25 (m, 8 H, aro- before and after reaction of 5.
Table 4. Crystallographic data for compounds 1 and 5.
1
5
Empirical formula
Formula weight
Temp. [K]
Crystal system
Space group
a [Å]
C
531.79
293(2)
monoclinic
P2 /c (no. 14)
14.897(3)
9.7402(16)
16.259(3)
115.121(3)
2444.5(8)
4
20
H
18
N
8
O
6
Zn
10 9 2 3
C H I N Zn
490.37
293(2)
monoclinic
C2/c (no. 15)
16.393(3)
7.9432(16)
12.865(3)
128.296(3)
1314.7(5)
4
1
b [Å]
c [Å]
β [°]
Volume [Å ]
3
Z
–1
Absorption coefficient [mm ]
No. of data collected
1.208
11581
6.541
3424
No. of unique data
4166
0.0470
0.903
1261
0.0599
0.949
R
int.
Goodness-of-fit
Final R indices [IϾ2σ(I)]
Final R indices (all data)
R
R
1
= 0.0305, wR
= 0.0422, wR
2
= 0.0640
= 0.0654
R
R
1
= 0.0365, wR
= 0.0427, wR
2
= 0.0911
= 0.0926
1
2
1
2
414
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 408–415

ZnII Compounds with a Chelating Hdpa Ligand
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Published Online: November 21, 2007
[
Eur. J. Inorg. Chem. 2008, 408–415
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
415