Zinc amidoisophthalate complexes and their catalytic application in the diastereoselective Henry reaction

Article abstract of DOI:10.1039/c4nj02371d

Reactions of 5-propionamidoisophthalic acid (H₂L1) and 5-benzamidoisophthalic acid (H₂L2) with Zn(NO₃)₂·6H₂O under different hydrothermal conditions lead to two pairs of Zn(ii) compounds, viz. the mon

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Zinc amidoisophthalate complexes and their
catalytic application in the diastereoselective
Cite this:DOI: 10.1039/c4nj02371d
Henry reaction†
Anirban Karmakar,* M. Fatima C. Guedes da Silva,* Susanta Hazra and
´
Armando J. L. Pombeiro*
Reactions of 5-propionamidoisophthalic acid (H2L1) and 5-benzamidoisophthalic acid (H2L2) with
Zn(NO3)2Á6H2O under different hydrothermal conditions lead to two pairs of Zn(II) compounds, viz. the
mononuclear [Zn(L1)(H2O)3]ÁH2O (1) and [Zn(L1)(H2O)3]Á3H2O (2), and the 1D polymers [Zn(L2)(H2O)2]n (3)
Received (in Victoria, Australia)
22nd December 2014,
Accepted 5th February 2015
%
and [{Zn(L2)(H2O)2}Á2H2O]n (4). They crystallize in orthorhombic [Pbca (1) and P212121 (3)] or triclinic (P1, 2
and 4) systems, and their formation depends on the particular reaction conditions. Compounds 1 and 2,
as well as 3 and 4, are solvatomorphs, the latter presenting different 1D metal–organic polymeric chains.
All of them act as heterogeneous catalysts for the diastereoselective nitroaldol (Henry) reaction of different
aldehydes with nitroalkanes and can be recycled without losing activity.
DOI: 10.1039/c4nj02371d
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The application of the formed coordination polymers in
catalysis is the main general objective. For such a purpose,
Introduction
Crystal engineering of coordination polymers is a matter of we have selected the Henry reaction, a base-catalyzed C–C coupling
current interest, namely in view of their unique and outstand- of a methylene-active nitroalkane and a carbonyl compound to
ing properties, such as gas storage and separation, magnetism afford nitroalkanols.7 It is widely used for the synthesis of organic
and catalysis.1 In particular, the solvent effects on coordination compounds of, e.g., pharmaceutical significance.8 Often this reac-
polymers are of inherent interest due to their complexity and tion is carried out in the presence of strong bases, leading to
difficulty in predicting the network connectivity.2 The solvent dehydration with concomitant formation of a nitroolefin.9 The
concurs to influence namely the crystal growth, crystalline development of new catalysts and procedures for the Henry
morphology and the lattice of the polymers. For such com- reaction is a matter of current interest, namely towards the
pounds, the occurrence of different crystal forms obtained from reduction of toxic by-products and the increase of yield and
the same building blocks concerns ‘‘polymorphism’’,3a–g but if diastereoselectivity. In the last two decades asymmetric cata-
the solvent acts as a component incorporated in the crystal lysts have been developed to convert aldehydes or a-keto esters
lattice that determines the final network of the coordination into the corresponding nitroalkanols with good enantio- and
polymer, the polymorphism can be more appropriately termed diastereoselectivities.10 Even though high yields were obtained
as ‘‘solvatomorphism’’ (also known as pseudopolymorphism).3h–m for reactions performed using homogeneous catalysts,11b–g,12a–f
Such different crystal forms often result from the variation of the achievement of a high stereoselectivity is still challenging
factors such as temperature, pH, the method of crystallisation or and moreover only scant examples are known11 using hetero-
the crystallization solvent.4 Polymorphism and solvatomorphism geneous catalysts.
are important in terms of the modulation of the physicochemical
Some iron, copper and zinc containing complexes have been
properties of materials, of significance, e.g., in the pharmaceutical reported by our group,12 which catalyze the nitroaldol reaction,
industry.5 Such systems have been well studied for organic but most of them are homogenous catalysts, and now we wish
compounds6a,b but only a few reports are available for coordina- to extend our study to heterogeneous systems. Recently, we
tion compounds or polymers.6c–e
have found that a few zinc amidoterephthalate coordination
polymers are active towards the nitroaldol reaction,13 and this
promising line of research is worthwhile to be continued.
The development of cheap, new, efficient and selective hetero-
geneous catalysts, with the expected advantages over the homo-
genous ones, namely in terms of easier separation and catalyst
recycling, would be a significant addition to this field.
´
´
Centro de Quımica Estrutural, Instituto Superior Tecnico, Universidade de Lisboa,
Av. Rovisco Pais, 1049-001, Lisbon, Portugal. E-mail: anirbanchem@gmail.com,
fatima.guedes@tecnico.ulisboa.pt, pombeiro@tecnico.ulisboa.pt
† Electronic supplementary information (ESI) available. CCDC 1040066–1040069.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c4nj02371d
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the symmetric one. The corresponding n(C–O) stretching is
observed in the 1278–1242 cmÀ1 range, whereas n(OH) of water
molecules is in the 3355–3316 cmÀ1 region. For complexes 1
and 2, a strong band at 1637–1625 cmÀ1 appears due to the
non-coordinated carboxylate groups.14 These complexes are
also characterized by X-ray diffraction, elemental and thermo-
gravimetric analyses.
Crystal structure analyses
Scheme 1
The solvent variant (DMF–MeOH/DMF–dioxane) hydrothermal reac-
tions of 5-propionamidoisophthalic acid (H2L1) or 5-benzamidoiso-
phthalic acid (H2L2) with the zinc(II) salt lead to the formation of the
zinc(II) complexes (1–4). According to the X-ray diffraction analysis,
compounds 1 and 2 are solvatomorphs, their crystal structures
presenting similar mononuclear metal complexes but different
numbers of crystallization water molecules. Compounds 3 and 4
are also solvatomorphs, presenting different 1D metal–organic
polymeric chains, but the latter has additional crystallization water
molecules. They crystallize in different space groups (1 in Pbca, 3 in
Thus, two main objectives of the current work are as follows:
(i) to synthesize Zn(II)-complexes by using amidoisophthalate
linkers; (ii) to apply the synthesized complexes as hetero-
geneous catalysts in the nitroaldol combination of nitroethane
with various aldehydes.
Hence, in this work we focus on the synthesis and char-
acterization of new ligands bearing different amide side func-
tional groups, 5-propionamidoisophthalic acid (H2L1) and
5-benzamidoisophthalic acid (H2L2) (Scheme 1), which are
then applied to the synthesis of Zn(II) coordination compounds,
[Zn(L1)(H2O)3]ÁH2O (1), [Zn(L1)(H2O)3]Á3H2O (2), [Zn(L2)(H2O)2]n
(3) and [{Zn(L2)(H2O)2}Á2H2O]n (4), whose structures are estab-
lished by single crystal X-ray diffraction analysis. These com-
plexes act as heterogeneous catalysts in the nitroaldol reaction of
nitroethane with various aldehydes.
%
P212121 and 2 and 4 in P1). The coordination polymers 3 and 4 have
helical and zig-zag type one dimensional structures, respectively.
The asymmetric units of 1 and 2 contain a tri-aqua zinc(II)
entity coordinated by an O-carboxylate from a L12À ligand, as
well as one (1) or three (2) crystallization water molecules
(Scheme 2 and Fig. S4, ESI†). Both the Zn(II) centres in 1 and
2 present tetrahedral geometries (t4 = 0.88 and 0.97, respec-
tively).15 The M–OL1 bond distances are 2.0008(19) Å in 1 and
1.9680(18) Å in 2, whereas the remaining M–O ones vary in the
2.008(3)–2.026(3) Å range. The C–O bond lengths in the non-
coordinated carboxylate groups differ by 0.038 Å in 1 but only
by 0.007 Å (a non-significant difference) in 2 (Table S3 in ESI†).
Results and discussion
Syntheses and characterization
The syntheses of complexes [Zn(L1)(H2O)3]ÁH2O (1), [Zn(L1)- The structures also differ in the twisting of the carboxylate
(H2O)3]Á3H2O (2), [Zn(L2)(H2O)2]n (3) and [{Zn(L2)(H2O)2}Á2H2O]n groups from the phenyl rings; although no great disparity was
(4) were carried out (see the ‘‘Experimental’’ section) under found for the free COO group (17.171 in 1 and 16.681 in 2), the
hydrothermal/solvothermal conditions, by reacting 5-propionamido- coordinated carboxylate deviates by 19.531 in 1 and only by
isophthalic acid (H2L1) or 5-benzamidoisophthalic acid (H2L2) 3.391 in 2. The minimum ZnÁ Á ÁZn distance reaches 6.1286(8) Å
with zinc(II) nitrate hexahydrate in the presence of a DMF and in 1 and 5.1906(4) Å in 2.
methanol (for 1 and 3) or DMF and 1,4-dioxane mixture (for 2
and 4) (Schemes 2 and 3, respectively).
Extensive H-bond interactions could be found in both com-
plexes (Fig. 1). The amide group in 1 donates to the free O-atom of
In the IR spectra, the characteristic strong bands of the the coordinated carboxylate moiety in a vicinal molecule and thus
coordinated carboxylate groups appear at 1584–1550 cmÀ1 for generates a 1D chain that spreads along the crystallographic b
the asymmetric n(CQO) stretching and at 1367–1338 cmÀ1 for direction. By means of the coordinated water molecules that donate
Scheme 2
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Scheme 3
Fig. 1 H-bond networks of 1 (A) and 2 (B) [hydrogen bonding interaction drawn using black dotted lines].
to the uncoordinated water (which also acts as a donor) and to water molecules, and the remaining ones which work as donors
neighbouring O-carboxylates or O-amide groups, the structure of 1 (and also as acceptors) to other free or coordinated water molecules.
expands into the third dimension. A 3D network could also be found
The asymmetric units of 3 and 4 include a deprotonated ligand
in 2 resulting from the amide group which donates to one of the free (L22À) linked to a di-aqua Zn(II) cluster together with, for 4, two
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uncoordinated water molecules (Scheme 3 and Fig. S5, ESI†).
Moreover, in 3 both the metal carboxylate bond dis-
Both carboxylate groups coordinate to a tetrahedral metal cation tances [1.969(2) and 1.958(2) Å] are shorter than the metal
(t4 = 0.92 for 3 and 0.89 for 4)15 in anti (3) or syn (4) fashion, this water bond lengths [2.006(3) and 2.018(3) Å] but in 4 such
fact being the driving force for the 1D (along the crystallographic a difference is lessened, with the Zn–Ocarboxylate distances
b axis), helical- or comb-type polymeric chain, respectively (Fig. 2). [1.9929(19) and 2.014(2) Å] closer to the Zn–Owater ones
This also disturbs the relative orientation of the phenyl groups of [2.008(3) and 2.016(3) Å] (Table S3, ESI†). Thus, the intra
L22À and consequently the least-square planes of adjacent ligands chain ZnÁ Á ÁZn distance reaches 9.5556(7)
Å in 3, but
in 3 make an angle of 52.551 while in 4 that angle is nil.
10.153(2) Å in 4.
Fig. 2 The 1D structures of 3 (A) and 4 (C) with partial atom labelling schemes and a representation of the helical structure of 3 (B). Symmetry operations
to generate equivalent atoms: (i) Àx, 1/2 + y, 1/2 À z; (ii) x, 1 + y, z; (iii) Àx, À1/2 + y, 1/2 À z (3). (i) x, 1 + y, z; (ii) x, À1 + y, z (4).
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As in 1 and 2, the extensive H-bond contacts that are found
Paper
Complex 1 shows a weight loss of 19.0% between 42 and
in 3 and 4, all of them involving the coordinated and the free (in 4) 318 1C, corresponding to the loss of three coordinated and one
water molecules, spread both structures into 3D (Fig. 3A and B). non-coordinated water molecules (calcd: 19.3%). Similarly,
Such interactions impact upon the interchain ZnÁÁÁZn distances complex 2 exhibits a weight loss of 25.8% in the 43–275 1C
which reach 6.785 Å in 3, but 4.289 Å in 4.
temperature range which accounts for the total removal of the
The topological analysis of 3 and 416 indicates that they can six water molecules (calcd: 26.4%). Both derived species are
be represented as 2-connected uninodal nets with topology of stable up to 355 1C, but above this temperature further decom-
type 2C1 (Fig. S2, ESI†).
position occurs towards the final product ZnO.
Complex 3 exhibits a weight loss of 9.5% in the 204–327 1C
temperature range, which accounts for the removal of the two
coordinated water molecules (calcd: 9.3%). The remaining
Thermogravimetric analyses
Thermogravimetric analyses were carried out under dinitrogen material is stable up to 371 1C beyond which it starts to
in the range from room temperature to ca. 750 1C at a heating decompose. Complex 4 shows a three-step decomposition
rate of 10 1C minÀ1. Features of the thermal stability of complexes process. In the first step it loses 8.3% of its weight within
1–4 are illustrated in Fig. 4.
65–124 1C, most likely due to the loss of two non-coordinated
Fig. 3 (A) Hydrogen bonding network of 3 (H-interaction drawn using black dotted lines). (B) Hydrogen bonded networks of 4 (hydrogen bonding
represented using black dotted lines and water molecules represented using a spacefill model).
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also did not take place by using compound H2L1 or H2L2 instead
of the metal catalyst (Table 1, entries 21 and 22, respectively).
We have also checked the reactivity of Zn(NO3)2Á6H2O in methanol
medium and the obtained reaction yield was much lower, i.e., 15%
(entry 20, Table 1), than in the presence of any of the catalysts 1–4.
When 3 mol% of 3 is used as a catalyst, a conversion of
87% (syn : anti = 85 : 15) of benzaldehyde into b-nitroalkanol is
reached (entry 7, Table 1). With 1, 2 and 4 conversions of 78%
(syn : anti = 84 : 16), 76% (syn : anti = 82 : 18) and 82% (syn : anti =
81 : 19) were obtained, respectively (entries 16–18, Table 1).
Extending the reaction time to 72 h did not increase the yield
of the reaction. The plot of yield versus time for the Henry
reaction of benzaldehyde and nitroethane with complex 3 is
presented in Fig. 5A.
We have also tested the effects of the catalyst amount,
solvents and temperature for the Henry reaction. An increase
of the catalyst amount from 1.0 to 3.0 mol% enhances the
product yield from 76 to 87%, respectively (entries 8 and 7,
Table 1), but a further increase decreases the reaction yield to
80% (entry 9, Table 1).
Fig. 4 Thermogravimetric curves of 1–4.
water molecules (calcd: 8.5%). In the second step, in the
temperature range of 125–210 1C, it loses the two coordinated
water molecules, corresponding to a weight loss of 8.8%
(calcd: 9.4%). In the final step, the remaining material starts
to decompose at 369 1C up to 541 1C.
To select the most suitable solvent, experiments using
various solvents (CH3CN, THF, MeOH and H2O) have been
carried out with catalyst 3 (entries 7 and 10–12, Table 1) and
the results indicate that MeOH (87% yield) is the best polar
solvent for this catalytic reaction, whereas CH3CN is the worst
(0% yield). In water and THF, the yields of 70% or 75%,
respectively, were obtained (entries 11 and 10, Table 1).
Varying the temperature from 20 to 70 1C improved the yield
of b-nitroalkanol from 12 to 87% (entries 7 and 13–14, Table 1)
but a further increase in the reaction temperature had a
negative effect (entry 15, Table 1). The systems exhibit diastereo-
selectivity towards the syn isomer, typically leading to syn : anti
molar ratios in the range of 88: 12 to 80: 20 using nitroethane as
a substrate. The size of the nitroalkane chain also affects the
yield and with nitropropane the lower yield of 66% was achieved
(entry 23, Table 1).
We have also compared the activities of catalyst 3 in the
reactions of a variety of ortho-, meta- or para-substituted aro-
matic and aliphatic aldehydes with nitroethane, producing the
corresponding b-nitroalkanols with yields ranging from 37 to
97% (Table 2). Aryl aldehydes bearing an electron-withdrawing
group exhibit higher reactivities (Table 2, entries 1 and 3) as
compared to those having electron-donating moieties, which
may be related to an increase of the electrophilicity of the
substrate in the former case.
Catalytic activity towards the Henry reaction
We have tested the catalytic activity of compounds 1–4 as solid
heterogeneous catalysts in the nitroaldol (or Henry) reaction of
nitroethane with various aldehydes. In a typical reaction, a
mixture of aldehyde (1.0 mmol), nitroethane (0.3 mL, 4.0 mmol)
and the Zn-catalyst (3.0 mol%) in 2.0 mL of MeOH, contained
in a capped glass vessel, was stirred at 70 1C for 48 h, where-
upon the solution was filtered to remove the catalyst. The
solvent was evaporated in a vacuum, giving the crude product
as a mixture of the b-nitroalkanol diastereoisomers (syn and
anti forms, with predominance of the former; Scheme 4) which
1
was analyzed by H NMR.
By using benzaldehyde as a test compound, we found that 3
showed a higher activity than the other complexes, for the same
reaction time and the same temperature. Consequently, the
optimization of the reaction conditions (temperature, reaction
time, the amount of catalyst and solvent) was carried out in
a model nitroethane–benzaldehyde system with catalyst 3
(Scheme 4 and Table 1).
A blank test was carried out with benzaldehyde in the absence
of any metal catalyst, at 70 1C in methanol. No b-nitroalkanol
was detected after a reaction time of 48 h. The nitroaldol reaction
In order to examine the stability of 3 in the Henry reaction,
this catalyst was recycled for six consecutive experiments and
it was observed that its activity remained almost the same
(Fig. 5B). We have also performed the six recycling experiments
for all the other catalysts (Fig. S6, ESI†) and observed only a
slight decrease in reaction yields over the 4th–6th cycles. There
were no significant changes in the FT-IR spectra of all the
catalysts (1–4) recorded before and after the reaction (Fig. S3A
and S7A–S9A, ESI†), suggesting the integrity of the polymeric
structure of the solid. This was confirmed by PXRD also performed
before and after the Henry reaction (Fig. S3B and S7B–S9B, ESI†).
Scheme 4 Nitroaldol (Henry) reaction.
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Table 1 Optimization of the parameters of the Henry nitroaldol reaction between benzaldehyde and nitroethane with 3 as the catalysta
Paper
Amount of
catalyst (mol%)
Selectivityc
(syn/anti)
Entry
Catalyst
Time (h)
T (1C)
Solvent
Yieldb (%)
TONd
1
2
3
4
5
6
7
8
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
1
2
4
6
3.0
3.0
3.0
3.0
3.0
3.0
3.0
1.0
5.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
—
70
70
70
70
70
70
70
70
70
70
70
70
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
THF
34
47
56
62
73
79
87
76
80
75
70
—
12
76
52
78
76
82
—
15
—
—
66
84 : 16
85 : 15
86 : 14
88 : 12
85 : 15
86 : 14
85 : 15
85 : 15
80 : 20
87 : 13
82 : 18
—
82 : 18
84 : 16
85 : 15
84 : 16
82 : 18
81 : 19
—
11.3
15.6
18.6
20.6
24.3
26.3
29.0
25.3
26.6
25.0
23.3
8
12
24
48
48
48
48
48
48
48
48
48
48
48
48
48
48
48
48
48
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23e
H2O
CH3CN
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
RT (20 1C)
50
100
70
70
70
70
70
70
70
4.0
25.3
17.3
26.0
25.3
27.3
—
5.0
—
—
22.0
2
4
Blank
Zn(NO3)2Á6H2O
3.0
3.0
3.0
3.0
88 : 12
—
—
H2L1
H2L2
3
70
90 : 10
a
b
Reaction conditions: 3.0 mol% of catalyst 3, benzaldehyde (1.0 mmol), nitroethane (0.3 mL, 4.0 mmol) and methanol (2.0 mL). Number of
moles of b-nitroalkanol per 100 moles of aldehyde. Calculated by 1H NMR. Number of moles of b-nitroalkanol per mole of the catalyst.
c
d
e
Nitropropane was used as a substrate.
Fig. 5 (A) Plot of b-nitroalkanol yield vs. time for the Henry reaction of benzaldehyde and nitroethane with 3 (’). (B) Kinetic profiles in six consecutive
reaction cycles employing 3 as a catalyst.
Additionally, the filtrate solution, after the separation of the 4-nitrobenzaldehyde and nitroethane, leads to an overall
catalysts by filtration, was evaporated to dryness and the amount yield of only 15% after 72 h of reaction time;17a with a
of zinc determined, being only between 0.012% and 0.022% of 1,4-diazabicyclo[2.2.2]octane (DABCO) functionalized 3D-Zn
the amount used in the reaction, thus ruling out any significant MOF a yield of 34% after 120 h was obtained.17b Moreover,
leaching of the catalyst.
our catalyst 3 exhibits a marked higher yield (98% after 48 h)
Although there are some reports on coordination polymers17 and selectivity towards the syn diastereoisomer (Table 2, syn :
which are catalytically active for this kind of reaction, the yields anti = 80 : 20) which was not reported for other cases. The
and selectivity are usually higher for our compounds as com- overall yield (87%) with benzaldehyde in the presence of
pared to other metal organic frameworks. The 3D zinc(II) frame- catalyst 3 is comparable with those obtained for other zinc
work with 1,3,5-tri(4-carboxyphenoxy)benzene, in the reaction of amidoterephthalate coordination polymers.13
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Table 2 Henry reaction of various aldehydes and nitroethane with catalyst 3a
The syn/anti ratio of the nitroaldol products depends on various
factors, such as the amount of catalyst, the electrophilicity of
the substrates and the reaction conditions.
Entry Aldehyde
Yieldb (%) Selectivityc (syn/anti) TONd
The above observations provide further evidence that simple
Zn(II) complexes can be utilized as effective heterogeneous
catalysts in the important type of reactions studied here.
Further explorations on the use of this catalyst family in other
organic transformations, as well as mechanistic investigations,
are ongoing.
1
2
3
4
97
37
82
63
80 : 20
85 : 15
81 : 19
85 : 15
32.3
12.3
27.3
21.0
Experimental
5
67
86 : 14
22.3
Materials and physical methods
The synthetic work was performed in open air atmosphere and
at room temperature. All the chemicals were obtained from
commercial sources and used as received. The infrared spectra
(4000–400 cmÀ1) were recorded on a Bruker Vertex 70 instru-
ment using KBr pellets; abbreviations: s = strong, m = medium,
w = weak, bs = broad and strong, mb = medium and broad. The
1H and 13C NMR spectra were recorded at ambient temperature
on a Bruker Avance II + 300 (UltraShieldtMagnet) spectrometer
operating at 300.130 and 75.468 MHz for proton and carbon-13,
respectively. The chemical shifts are reported in ppm using
tetramethylsilane as the internal reference; abbreviations: s =
singlet, d = doublet, t = triplet, q = quartet. Carbon, hydrogen
and nitrogen elemental analyses were carried out by the Micro-
6
81
81 : 19
27
7
8
CH3CHO
CH3CH2CHO
94
89
84 : 16
85 : 15
31.3
29.6
a
Reaction conditions: 3.0 mol% of catalyst 3, aldehyde (1.0 mmol),
nitroethane (0.3 mL, 4.0 mmol) and methanol (2.0 mL). b Number of moles
of b-nitroalkanol per 100 moles of aldehyde. Calculated by 1H NMR.
c
d Number of moles of b-nitroalkanol per mole of the catalyst.
A possible reaction mechanism for the Henry reaction
catalyzed by 3 involves the activation of both the aldehyde
and nitroethane by the metal centre (with deprotonation of the
latter) and is followed by the formation of a C–C bond upon
nucleophilic addition leading to the b-nitroalkanol.11a,12,13,18
The proton abstraction from the nitroalkane ligand and the
protonation of the C–C coupled species can be assisted by the
ligand (with a carboxylate and an amide group) and also by
methanol, thus possibly accounting for the good activity of our
catalyst in the presence of methanol.
´
analytical Service of the Instituto Superior Tecnico. Electrospray
mass spectra (ESI-MS) were obtained using an ion-trap instru-
ment (Varian 500-MS LC Ion Trap Mass Spectrometer)
equipped with an electrospray ion source. For electrospray
ionization, the drying gas and flow rate were optimized accord-
ing to the particular sample with 35 p.s.i. nebulizer pressure.
Scanning was performed from m/z 100 to 1200 in methanol
solution. The compounds were observed in the positive mode
(capillary voltage = 80–105 V). Thermal properties were analyzed
using a Perkin-Elmer Instrument system (STA6000) at a heating
rate of 10 1C minÀ1 under a dinitrogen atmosphere. Powder
X-ray diffraction (PXRD) was conducted in a D8 Advance Bruker
AXS (Bragg Brentano geometry) theta-2theta diffractometer, with
copper radiation (Cu Ka, l = 1.5406 Å) and a secondary mono-
chromator, operated at 40 kV and 40 mA. A flat plate configu-
ration was used and the typical data collection range was between
51 and 401.
Concluding remarks
We successfully isolated four zinc(II) coordination compounds
derived from the 5-propionamidoisophthalic (H2L1) and 5-benz-
amidoisophthalic (H2L2) acids under various synthetic condi-
tions. They exhibit 0D (1 and 2) and 1D (3 and 4) structures, due
to the various coordination modes of the ligands. Single-crystal
X-ray diffraction analyses reveal that the structures of 1 and 2
(also 3 and 4) are solvatomorphs with respect to the different
numbers of water molecules present in the lattices. Complexes 1
and 2 have similar types of mononuclear structures but contain
different numbers of non-coordinated water molecules. The
Syntheses of 5-propionamidoisophthalic acid (H2L1) and
5-benzamidoisophthalic acid (H2L2)
coordination polymers 3 and 4 have helical and zig-zag type 1D Both compounds were synthesized by similar two-step procedures.
polymeric structures, respectively. Their construction depends In the first step, dimethyl-5-aminoisophthalate (2.09 g,
on the particular reaction conditions, which lead to significant 10.0 mmol) and NEt3 (1.51 g, 15.0 mmol) were placed in a
differences in the coordination networks. round bottom flask and then dry dichloromethane (30 mL) was
These complexes effectively catalyze the Henry reaction added. After cooling in an ice bath followed by dropwise
of nitroethane with various aldehydes producing the corres- addition of acid chloride [propionyl chloride (1.10 g, 12.0 mmol)
ponding b-nitroalkanols in high yields. Among the four com- for H2L1 or benzoyl chloride (1.68 g, 12.0 mmol) for H2L2], the
plexes studied here, complex 3 is the most active one. We have reaction mixture was stirred overnight at room temperature.
also proved the stability and recyclability of the catalysts. Upon removal of the solvent under reduced pressure a white
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solid was obtained. 20 mL of water were then added to the 2976 (m), 2932 (w), 1681 (s), 1625 (s), 1567 (s), 1408 (s), 1362 (s), 1271
white solid which was then extracted with dichloromethane. (s), 1209 (m), 1128 (m), 1073 (m), 902 (m), 773 (s), 731 (s).
The organic extracts were collected over anhydrous sodium Synthesis of 3. A mixture of Zn(NO3)2Á6H2O (20.7 mg.
sulfate; subsequent removal of the solvent gave the methyl ester 0.07 mmol) and H2L2 (20.0 mg. 0.07 mmol) was dissolved in
of compound H2L1 or H2L2. DMF and MeOH (1 : 1). A white precipitate was obtained after
In the second step, the isolated ester (2.65 g, 10.0 mmol for adding 0.5 mL of 28% aqueous solution of NH4OH to this
the methyl ester of H2L1/3.13 g, 10.0 mmol for the methyl ester reaction mixture. The precipitate was dissolved upon addition
of H2L2) and NaOH (0.8 g, 20.0 mmol) were dissolved in 20 mL of additional 0.4 mL of 28% aqueous solution of NH4OH. The
of MeOH : water (4 : 1). The reaction mixture was refluxed for 4 h resulting mixture was sealed in a 8 mL glass vessel and heated
at 80 1C, after which the solvent was removed under reduced at 80 1C for 48 h. It was subsequently cooled to room tempera-
pressure. 10 mL of water were added and the solution was ture (0.2 1C minÀ1), affording plate-like colorless crystals. Yield:
acidified (pH = 2) with dilute HCl solution. The obtained white 74% (based on Zn). Anal. calcd for C15H13NO7Zn (M = 384.63):
solid product H2L1 or H2L2 was removed by filtration and C, 46.84; H, 3.41; N, 3.64; found: C, 46.23; H, 3.21; N, 3.42. FT-IR
washed with water until total removal of the acid. Yield: 62% (KBr, cmÀ1): 3421 (s), 3327 (bs), 3168 (s), 1643 (s), 1579 (s), 1494
(1.47 g) for H2L1 and 81% (2.31 g) for H2L2. (m), 1427 (s), 1338 (s), 1278 (s), 910 (m), 781 (s), 819 (m), 771 (s),
Characterization details for H2L1: anal. calcd for C11H11NO5 732 (s).
(M = 237.21): C, 55.70; H, 4.67; N, 5.90. Found: C, 55.11; H, 4.50;
Synthesis of 4. A mixture of Zn(NO3)2Á6H2O (25.0 mg,
N, 4.72. FT-IR (KBr, cmÀ1): 3387 (s), 3208 (s), 3101 (m), 2973 0.084 mmol) and H2L2 (24.0 mg, 0.084 mmol) was dissolved
(m), 2634 (w), 2511 (w), 1719 (s), 1693 (s), 1642 (m), 1563 (m), in 3 mL of DMF and 1,4-dioxane (1 : 1). A white precipitate
1389 (m), 1300 (m), 1255 (s), 1199 (s), 1079 (w), 940 (w), 918 (w), was obtained when the mixture was stirred at room tempera-
779 (m), 680 (m); 1H-NMR (CD3OD): 8.43–8.42 (2H, d, Ar–H), ture for 1 h. The precipitate was dissolved by adding 0.6 mL of
8.31 (1H, s, Ar–H), 2.40–2.37 (2H, q, –CH2), 1.20–1.15 (3H, t, –CH3); 28% aqueous ammonia solution, and the resulting mixture was
MS (ESI): m/z: 260.1 [M + Na]+.
Characterization details for H2L2: anal. calcd for C15H11NO5 Subsequent gradual cooling to room temperature (0.2 1C minÀ1
sealed in an 8 mL glass vessel and heated at 75 1C for 24 h.
)
(M = 285.25): C, 63.16; H, 3.89; N, 4.91. Found: C, 63.14; H, 3.60; afforded needle-like colorless crystals. Yield: 73% (based on Zn).
N, 4.82. FT-IR (KBr, cmÀ1): 3532 (mb), 2849 (w), 2571 (w), 1719 Anal. calcd for C15H17NO9Zn (M = 420.66): C, 42.83; H, 4.07; N,
(s), 1645 (m), 1566 (s), 1436 (s), 1385 (m), 1348 (w), 1254 (s), 913 3.33; found: C, 42.23; H, 4.21; N, 3.12. FT-IR (KBr, cmÀ1): 3332
(w), 757 (w), 710 (m), 694 (m), 665 (m), 602 (w), 544 (w); 1H-NMR (bs), 1643 (s), 1550 (s), 1491 (m), 1429 (s), 1367 (s), 1286 (m), 1259
(DMSO-d6): 10.612 (1H, s, ÀNH), 8.70 (2H, s, Ar–H), 8.24 (1H, d, (m), 1105 (w), 1029 (w), 777 (s), 733 (s).
Ar–H), 8.02–8.002 (2H, d, Ar–H), 7.51–7.62 (3H, m, Ar–H); 13C-
Procedure for the Henry reaction catalyzed by the Zn-complexes
NMR (DMSO-d6): 167.01, 166.3, 140.3, 134.7, 132.3, 132.09,
128.8, 128.2, 125.4, 125.2, MS (ESI): m/z: 308.1 [M + Na]+.
In a typical reaction, a mixture of aldehyde (1.0 mmol),
Synthesis of 1. A mixture of Zn(NO3)2Á6H2O (25.0 mg, nitroethane (0.3 mL, 4.0 mmol) and Zn-catalyst (3 mol%,
0.084 mmol) and H2L1 (20.0 mg, 0.084 mmol) was dissolved 11.2 mg for 1, 12.2 mg of 2, 11.5 mg of 3 and 12.6 mg of 4)
in 5 mL of DMF and methanol (1 : 1). A white precipitate was was placed in a capped glass vessel, and then 2 mL of MeOH
obtained when the mixture was stirred at room temperature for were added into it. The mixture was heated at 70 1C for 48 h,
30 min. The precipitate was dissolved by adding 0.5 mL of 28% and subsequently quenched by centrifugation and filtration at
aqueous ammonia solution, and the resulting mixture was room temperature. The filtrate was evaporated in vacuum to
sealed in an 8 mL glass vessel and heated at 75 1C for 48 h. give the crude product. The residue was dissolved in DMSO-d6
Subsequent gradual cooling to room temperature (0.2 1C minÀ1
)
and analyzed by 1H NMR. The yield of the b-nitroalkanol
afforded needle-like colorless crystals. Yield: 81% (based on Zn). product (relatively to the aldehyde) was established typically
Anal. calcd for C11H17NO9Zn (M = 372.62): C, 35.46; H, 4.60; N, by taking into consideration the relative amounts of these
1
3.76; found: C, 35.63; H, 4.21; N, 3.42. FT-IR (KBr, cmÀ1): 3447 compounds, as given by H NMR and previously reported.12,13,19
(bs), 3316 (bs), 2979 (m), 2941 (w), 1637 (s), 1584 (s), 1363 (s), The syn/anti selectivity was calculated on the basis of 1H-NMR
1242 (m), 1217 (m), 1104 (w), 1080 (m), 901 (m), 774 (s), 735 (s). spectra which is presented in Fig. S7 (ESI†). In the 1H NMR spectra,
Synthesis of 2. Zn(NO3)2Á6H2O (25.0 mg. 0.084 mmol) and the values of vicinal coupling constants (for the b-nitroalkanol
H2L1 (20.0 mg. 0.084 mmol) were dissolved in DMF : 1,4- products) between the a-N–C–H and the a-O–C–H protons identify
dioxane (1 : 1). A white precipitate was obtained after adding the isomers, being J = 7–9 or 3.2–4 Hz for the syn or anti isomers,
0.2 mL of 28% aqueous ammonia solution to this reaction respectively.19
mixture. The precipitate was dissolved upon addition of addi-
In order to perform the recycling experiment, first we washed
tional 0.5 mL of 28% aqueous ammonia solution. The resulting the used catalyst with methanol and dried it at room temperature.
mixture was sealed in a capped glass vessel and heated to 75 1C It was then used for the nitroaldol reaction as described above.
for 48 h. Subsequent gradual cooling to room temperature
(0.2 1C minÀ1) afforded colorless crystals. Yield: 65% (based on
Crystal structure determination
Zn). Anal. calcd for C11H21NO11Zn (M = 408.66): C, 32.33; H, 5.18; N, X-ray quality crystals of the compounds (1–4) were immersed in cryo-
3.43; found: C, 32.13; H, 5.21; N, 3.18. FT-IR (KBr, cmÀ1): 3355 (bs), oil, mounted in a nylon loop and measured at room temperature.
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Commun., 2014, 46, 113–117; ( j) Z. Zhang and M. J.
Zaworotko, Chem. Soc. Rev., 2014, 43, 5444–5455; (k) A. Karmakar,
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Intensity data were collected using a Bruker AXS-KAPPA APEX-II
PHOTON 100 diffractometer with graphite monochromated
Mo-Ka (l 0.71073) radiation. Data were collected using phi
and omega scans of 0.51 per frame and a full sphere of data was
obtained. Cell parameters were retrieved using Bruker SMART20
software and refined using Bruker SAINT20a on all the observed
reflections. Absorption corrections were applied using SADABS.20a
Structures were solved by direct methods by using the SHELXS-97
package20b and refined using SHELXL-97.20b Calculations were
performed using the WinGX System-Version 1.80.03.20c The
hydrogen atoms attached to carbon atoms and to the nitrogen
atoms were inserted at geometrically calculated positions and
included in the refinement using the riding-model approxi-
mation; Uiso(H) were defined as 1.2Ueq of the parent nitrogen
atoms or the carbon atoms for phenyl and methylene residues,
and 1.5Ueq of the parent carbon atoms for the methyl groups.
The hydrogen atoms of coordinated water molecules were
located from the final difference Fourier map and the isotropic
thermal parameters were set at 1.5 times the average thermal
parameters of the belonging oxygen atoms; their positions were
restrained by using DFIX and DANG. Least square refinements
using anisotropic thermal motion parameters for all the non-
hydrogen atoms and isotropic ones for the remaining atoms
were employed. In compound 2, the ethyl group was struc-
turally disordered over two orientations and were refined with
the use of PART instruction; the occupancy was refined to a
ratio of 0.66 and 0.34. Crystallographic data are summarized in
Table S1 (ESI†) and selected bond distances and angles are
presented in Table S3 (ESI†). CCDC 1040066–1040069 for 1–4.
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Acknowledgements
This work has been supported by the Foundation for Science
and Technology (FCT), Portugal (project UID/QUI/00100/2013).
Author A. Karmakar and S. Hazra express their gratitude to the
FCT for post-doctoral fellowships (Ref. No SFRH/BPD/76192/
2011 and SFRH/BPD/78264/2011). The authors acknowledge the
Portuguese NMR Network (IST-UL Centre) for access to the NMR
facility, and the IST Node of the Portuguese Network of mass-
˜
spectrometry (Dr Conceiçao Oliveira) for the ESI-MS measurements.
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