Synthesis of novel polyazacryptands for recognition of tetrahedral oxoanions and their X-ray structures

Article abstract of DOI:10.1021/ic400319b

The Mannich reaction of tris(pyrrolyl-α-methyl)amine (H ₃tpa) with a mixture of formaldehyde and primary amine hydrochloride (methyl or ethyl) gave two novel macrobicyclic molecules: a hexapyrrolic pentaazacryptand and an unusual pentapyrrolic tetraazacryptand, which were separated by column chromatography and their structures were determined by X-ray diffraction method. The analogous reaction using benzylamine hydrochloride yielded the encapsulated chloride anion complex in 16% yield even after neutralization with aqueous K₂CO₃, which was also characterized by X-ray diffraction. In addition, the anion binding properties of these macrobicycles were investigated by NMR titration methods, and the binding constants for halides and oxoanions were determined with the EQNMR program. The cavity of the hexapyrrolic pentaazacryptand is flexible and large enough enabling it to form inclusion complexes with the smaller size fluoride ion as well as with the bulkier oxoanions. This was demonstrated by ¹⁹F NMR spectroscopy and by the X-ray structures of the encapsulated sulfate, phosphate, and arsenate ion complexes. Upon complexation the distance between the bridgehead nitrogen atoms changes. Further, anion induced conformational changes were observed in the structures of the oxoanion complexes, particularly in the arsenate structure which represents the first azacryptand encapsulated structure of an arsenate ion. Furthermore, the competition crystallization experiment showed that the phosphate ion complex of the hexapyrrolic pentaazacryptand is the sole crystallization product from an aqueous-organic medium, as confirmed by IR and powder X-ray diffraction studies.

Full text of DOI:10.1021/ic400319b

Article
pubs.acs.org/IC
Synthesis of Novel Polyazacryptands for Recognition of Tetrahedral
Oxoanions and Their X‑ray Structures
Debasish Jana,† Ganesan Mani,*,† and Carola Schulzke‡
†Department of Chemistry, Indian Institute of Technology-Kharagpur, Kharagpur, West Bengal 721 302, India
‡Ernst-Moritz-Arndt-Universitat Greifswald, Institut fur Biochemie, Felix-Hausdorff-Strasse 4, Greifswald 17487, Germany
̈
̈
S
* Supporting Information
ABSTRACT: The Mannich reaction of tris(pyrrolyl-α-
methyl)amine (H3tpa) with a mixture of formaldehyde and
primary amine hydrochloride (methyl or ethyl) gave two novel
macrobicyclic molecules: a hexapyrrolic pentaazacryptand and
an unusual pentapyrrolic tetraazacryptand, which were
separated by column chromatography and their structures
were determined by X-ray diffraction method. The analogous
reaction using benzylamine hydrochloride yielded the
encapsulated chloride anion complex in 16% yield even after
neutralization with aqueous K2CO3, which was also charac-
terized by X-ray diffraction. In addition, the anion binding
properties of these macrobicycles were investigated by NMR
titration methods, and the binding constants for halides and
oxoanions were determined with the EQNMR program. The cavity of the hexapyrrolic pentaazacryptand is flexible and large
enough enabling it to form inclusion complexes with the smaller size fluoride ion as well as with the bulkier oxoanions. This was
demonstrated by 19F NMR spectroscopy and by the X-ray structures of the encapsulated sulfate, phosphate, and arsenate ion
complexes. Upon complexation the distance between the bridgehead nitrogen atoms changes. Further, anion induced
conformational changes were observed in the structures of the oxoanion complexes, particularly in the arsenate structure which
represents the first azacryptand encapsulated structure of an arsenate ion. Furthermore, the competition crystallization
experiment showed that the phosphate ion complex of the hexapyrrolic pentaazacryptand is the sole crystallization product from
an aqueous−organic medium, as confirmed by IR and powder X-ray diffraction studies.
remain an active area of research in supramolecular chemistry.8
INTRODUCTION
■
A variety of synthetic receptors have been designed to
recognize specific anions with great affinity and selectivity
effected by means of interactions such as hydrogen bonding,
electrostatic force, or covalent bonding. It is known that the
energy of interaction exerted by a synthetic receptor should be
large enough to overcome the Gibbs energy of hydration of the
anions of interest when seeking selective recognition in an
aqueous medium.9 Typically neutral hydrogen bonding
receptors have been shown to be selective in organic solvents,
but not in an aqueous medium. Nevertheless, Kubik and co-
workers have demonstrated selective binding of the sulfate
anion in an aqueous medium by the neutral cyclopeptide
receptors.10 Moyer, Sessler, Bowman-James, and co-workers
have reported the selective extraction of sulfate anions from an
aqueous medium by neutral macrocyclic calixpyrrole recep-
tors.11 Gabbai and co-workers have synthesized cationic borane
compounds, which very efficiently sense fluoride ions in
water.12
Oxoanions such as sulfate and phosphate are abundantly
present in biological and environmental systems and cause both
beneficial and deleterious effects to human beings.1 In nature,
the selective recognition and transport of these anions takes
place by hydrogen bonding alone as well as in combination
with charged peptide units. For example, the sulfate anion is
recognized and transported by the sulfate-binding protein
merely by means of hydrogen bonding.2 Sulfate ions are also
present in nuclear fuel waste along with other oxoanions, which
eventually end up in the environment.3 On the other hand, the
phosphate anion is being recognized and transported by both
hydrogen bonds and charged peptide residues. The large
quantity of phosphate ions stemming from factories and
fertilizers is responsible for causing eutrophication of rivers and
ponds, which poses a serious environmental problem.4 Another
deleterious anion is arsenate, which causes critical and chronic
diseases including cancer.5 Arsenic is present in soil as arsenite
[As(III)] or arsenate [As(V)] contaminating groundwater in
many parts of the world, and many people worldwide are
exposed to these ions.6,7
In view of this, recognition of anions by synthetic receptors
and their coordination chemistry have attracted attention and
Received: February 6, 2013
Published: May 10, 2013
© 2013 American Chemical Society
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Under these circumstances, bicyclic receptors are of great
importance and have attracted considerable attention as they
have optimum suitable size, which can be fine-tuned. With their
potentially interacting preorganized groups in the right places,
they are consequently potent receptors for the selective
recognition of various anions. Indeed, several bicyclic receptors
have been shown to possess size selective anion binding
properties.13 In particular, the tren-based bicyclic receptors
bearing bridgehead nitrogen atoms remain a well explored class
of bicyclic receptor systems for recognizing anions.14 For
example, some time ago Lehn and co-workers demonstrated
the size selective anion binding properties of multiprotonated
tris(2-aminoethyl)amine (tren)-based cryptands toward fluo-
ride and azide ions in aqueous media.15,16
In contrast to macrocyclic receptors, reports of macrobicyclic
receptor systems based on pyrrole building blocks are so far
rather limited.17As a continuation of our interests in developing
pyrrole-based synthetic receptors for anions, we have been
using the Mannich reaction approach for synthesizing novel
macrocycles and macrobicycles.18,13f,g Recently, we reported
macrobicyclic receptors A and B (Chart 1) containing both
because it requires not only a size-cavity match between the
anion and the receptor with preorganized binding groups, but
also the “windows” of the cryptand should be large enough to
allow these large anions to get in.4 Herein, we report a new
class of macrobicyclic pentaaza- and an unusual tetraazacryp-
tand/s synthesized by the Mannich reaction of tris(pyrrolyl-α-
methyl)amine and their anion binding properties. The X-ray
structures of both the azacryptands and their anion inclusion
complexes such as chloride, sulfate, phosphate, and arsenate are
discussed in detail. We also report the competition crystal-
lization experiment for selective crystallization of the phosphate
ion complex of the pentaazacryptand from an aqueous-organic
medium.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of the Azacryptands.
The cavity size of the macrobicyclic molecule A or B can be
enlarged by the Mannich reaction approach with a precursor
molecule containing additional spacer units such as the
methylene group between the binding sites. By this the
macromolecule should become suitable for the selective
recognition and encapsulation of larger oxoanions inside its
cavity. This hypothesis was investigated using tris(pyrrolyl-α-
methyl)amine. Thus, the Mannich reactions of tris(pyrrolyl-α-
methyl)amine (H3tpa) 1 with a mixture of formaldehyde and
primary amine hydrochloride (methyl or ethyl) were carried
out to give two novel macrobicyclic molecules, 2 and 3, which
were isolated in analytically pure form by basic alumina column
chromatography (Scheme 1). The yields for the hexapyrrolic
pentaazacryptands 2 are better (22%, Me and 15%, Et) than
those (2%, Me and 3%, Et) for the unusual pentapyrrolic
tetraazacryptands 3. While the symmetrical macrobicycle 2 is
the expected target molecule in this reaction, 3 is a rather
unexpected macrobicyclic product, which could have formed by
the cleavage of one of the −CH2(C4H4N) groups in 1.
Conversely, an analogous reaction using benzylamine hydro-
chloride gave the chloride ion inclusion complex 4 in 16% yield
even after neutralization with an aqueous K2CO3 solution
instead of the neutral compound that is analogous to 2; the
analogous pentapyrrolic macrobicycle was not isolated (Scheme
2). The structures of both types of azacryptands 2a and 3a and
the chloride cryptate 4 were confirmed by single crystal X-ray
diffraction and were further supported by solution state
spectroscopic data.
Chart 1. Bicyclic Pyrrole-Based Receptors Having Relatively
Small Cavities and Being Suitable Only for Encapsulating
the Comparably Small, Fluoride Ion, Inside Their Cavities
hydrogen bond acceptors and donors with bridgehead nitrogen
or carbon atoms which effectively recognize only fluoride ions
in the presence of other competing anions in a competitive
solvent, while larger ions or oxoanions bind to the clefts of the
macrobicycle.13f,g These results have encouraged us to further
explore the Mannich reaction with pyrrole systems to obtain
novel macrobicycles possessing suitable cavity sizes for the
selective recognition of different oxoanions. Although several
synthetic receptors have been reported for the selective
recognition of oxoanions,19 the encapsulation of oxoanions
inside the cavity of cryptand-like receptors is more challenging
1
The H NMR spectra of 2a and 2b in CDCl3 show broad
singlets at δ = 9.50 and 9.40 ppm for their pyrrolic NH
resonances, respectively, suggesting that all NHs are equivalent
because of their symmetrical structure. Although 2a bears two
Scheme 1. Synthesis of Macrobicyclic Receptors by the Mannich Reaction of H3tpa 1: Hexapyrrolic Pentaazacryptand 2 and
Pentapyrrolic Tetraazacryptand 3
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Scheme 2. Synthesis of the Chloride Cryptate 4 Using the
Mannich Reaction of H3tpa 1 with Benzylamine
Hydrochloride
types of methylene groups [N(CH2)3- and MeNCH2-], only
one broad singlet is observed, which is in contrast to 2b
displaying two separate singlets for its methylene groups. This
contrasting feature was settled by the 13C NMR spectra, which
showed one signal for each type of methylene group in 2 in
CDCl3. The pyrrolic NH resonance of 3a or 3b appears as two
separate broad singlets in the 1H NMR spectrum because of its
unsymmetrical structure. For example, the NH resonances at δ
= 9.21 and 10.10 ppm with the integrated intensity ratio of 1:4
are observed for 3a, just as expected. The presence of three
types of CH2 groups in 3a and four types in 3b are supported
by the respective H and 13C NMR spectra. The H NMR
spectrum of 4 shows three broad resonances with the
integrated intensity ratio of 1:3:3 for its three types of NH
protons: one ammonium N+H and two types of three pyrrolic
NH groups as expected for this structure. All methylene
protons, however, appear as broad signals probably indicating a
dynamic process in solution which may render all methylene
resonances to be broad signals for the chloride cryptate 4.
The three-dimensional shape of molecule 2a was confirmed
by X-ray diffraction (Figure 1), and the refinement data are
summarized in Table 1. The molecule adopts an eclipsed
conformation along the bridgehead nitrogen atoms that
resembles the shape of a three-bladed turbine having C3
symmetry with the lone pairs of the bridgehead nitrogen
atoms pointed inside the cavity of the macrobicycle, thus
exhibiting an in-in configuration. The distance between the
bridgehead nitrogen atoms (N1···N5) is 8.274 Å and the cavity
size is sufficiently large enough to accommodate inside two
water molecules, which are H-bonded to five of the six pyrrolic
NH groups and the amine nitrogen atoms.
The molecular structure of 3a is shown in Figure 2. This
relatively smaller sized bicyclic molecule can be viewed as the
macrocyclic molecule, octahomotetraazacalix[4]pyrrole, strap-
ped by a 2,5-dimethylenepyrrole unit. When viewed along the
bridgehead nitrogen atoms, the molecule adopts a tub shape
conformation in which one water molecule is bound by
hydrogen bonding interactions to four of its five pyrrolic NH
groups and two of its four amine groups. This is in contrast to
2a with two water molecules inside and indicates the presence
of a smaller cavity size in 3a which is supported by the distance
between the bridgehead nitrogen atoms (N1···N5 = 5.590 Å)
with an in/in configuration similar to 2a.
1
1
Figure 1. ORTEP diagram of hexapyrrolic pentaazacryptand 2a (30%
thermal ellipsoids): (a) top view and (b) side view. Most hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and bond
angles (deg): N2···O1, 3.162(6); H2n···O1, 2.36(3); N2−H2n···O1,
162(5); N8···O2, 3.236(8); H8n···O2, 2.61(5); N8−H8n···O2,
133(5); N6···O2, 3.227(8); H6n···O2, 2.51(4); N6−H6n···O2,
146(4).
and there is no defined cleft exhibited, probably because of the
presence of three sterically hindering benzyl groups at the
amine nitrogen atoms; the plane of each benzyl group intersects
the bridgehead N1···N5 vector. The bridgehead nitrogen atom
N5 is protonated and the resultant ammonium cation
neutralizes the chloride anion which is hydrogen bonded to
all the pyrrolic NH and the ammonium N+H groups; thus in
total there are seven hydrogen bonds involving NH groups to
the chloride anion. The chloride anion lies almost in the middle
of the vector line connecting the bridgehead nitrogen atoms.
The pyrrolic NH···Cl distances range from 2.52 to 2.90 Å and
the ammonium N+H···Cl distance is 2.059 Å with an N+−
H···Cl angle of 177° suggesting that the chloride anion is
bound by rather strong interactions. This hydrogen bonding
strength together with the steric protection rendered by the
benzyl groups, which “cover up” the three “windows” of the
macrobicycle, could enable the molecule to resist an easy
removal of the chloride ion from the cavity (K2CO3 was used as
a base in the synthesis of 4). On the contrary, in the case of
methyl and ethyl derivative reactions (Scheme 1), probably
steric protection of these groups to the initially formed chloride
ion complex is not sufficient which readily leads to the
formation of the neutral macrobicycles 2. The bridgehead
N1···N5 distance is 6.819 Å which is shorter than those found
for 2a, and its anion complexes (see below), but it is larger than
that reported (6.096 Å) for the chloride cryptate formed by the
thiophene-based azacryptand.20
In the structure of 4, the presence of one chloride anion
inside the cavity of the macrobicycle molecule bearing benzyl
groups, which is analogous to 2, was confirmed by X-ray
diffraction (Figure 3). In contrast to the structure of 2a, in this
sphere-shaped molecule 4, when viewed along the bridgehead
nitrogen atoms, only the bridgehead N−C bonds are eclipsed
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Table 1. Crystallographic Data for 2a·2H2O, 3a·H2O, 4·CH2Cl2, [2aH2]2+[SO4]2− (5), 6, and 7·17.5H2O
2a·2H2O
3a·H2O
4·CH2Cl2
5
6
7·17.5H2O
empirical formula
formula weight
wavelength (Å)
temperature (K)
crystal system
space group
a/Å
C39H55N11O2
709.94
C32H43N9O
569.75
C58H66Cl3N11
1023.57
0.71073
293(2)
C39H53N11O4S
771.98
C39H54N11O4P
771.90
C39H88AsN11O21
1122.12
0.71073
293(2)
0.71073
293(2)
0.71073
293(2)
0.71073
293(2)
0.71073
293(2)
monoclinic
P21/c
triclinic
monoclinic
P21/n
monoclinic
P21/n
monoclinic
Cc
triclinic
P1
̅
P1
̅
13.2379(16)
19.726(2)
15.9349(19)
90.0
10.7107(8)
11.4969(9)
14.4633(11)
99.001(2)
101.778(2)
111.484(2)
1569.2(2)
2
16.024(3)
15.833(3)
23.489(5)
90.0
13.810(4)
15.403(5)
18.966(6)
90.0
22.635(5)
15.677(3)
11.689(3)
90.0
13.0215(12)
16.1623(15)
16.6439(15)
66.874(3)
67.727(3)
67.019(3)
2858.4(5)
2
b/Å
c/Å
α/deg
β/deg
103.309(4)
90.0
109.111(6)
90.0
91.868(10)
90.0
104.148(10)
90.0
γ/deg
volume (Å3)
4049.3(8)
4
5631(2)
4
4032(2)
4
4022.1(16)
4
Z
D
calcd, mg m−3
1.165
1.206
1.207
1.272
1.275
1.304
μ/mm−1
0.075
0.077
0.210
0.135
0.123
0.673
F(000)
1528
612
2168
1648
1648
1200
θ range (degree)
total/unique no. of reflns.
Rint
1.58 to 25.00
47512/7099
0.1456
1.97 to 25.00
18659/5499
0.0228
1.58 to 24.62
63822/9466
0.0807
1.70 to 25.00
47523/7106
0.1114
1.60 to 26.39
25110/7527
0.1090
1.38 to 26.26
36590/11296
0.0723
data/restr/params.
GOF (F2)
7099/19/500
1.028
5499/11/401
1.026
9466/0/643
0.911
7106/21/531
0.980
7527/23/546
0.957
11296/24/593
0.906
R1, wR2
0.0842,
0.0365,
0.0580,
0.0527,
0.0957,
0.0697,
0.2080
0.0971
0.1435
0.1007
0.2184
0.1778
R indices (all data) R1, wR2
0.2077,
0.0479,
0.1135,
0.1217,
0.1555,
0.1210,
0.2701
0.1069
0.1676
0.1254
0.2458
0.1936
largest different peak and hole (e Å−3
)
0.420 and −0.196 0.181 and −0.147 0.168 and −0.148 0.196 and −0.221 0.673 and −0.307 0.647 and −0.391
Anion Binding Studies. The binding properties of 2a and
3a with anions were studied by 1H NMR titration methods and
their binding constants (Ka) were determined with the
EQNMR program.21 The NMR titration involves addition of
an incremental amount of anions in form of their n-Bu4N+ salts
to the receptor solution in DMSO-d6 or CDCl3 in an NMR
tube and monitoring the change in the NH resonance for
calculating apparent binding constants. In the case of the F−
ion, the titration spectra showed two NH resonances; one of
them appears as a doublet because of the coupling of fluorine
with all six NH hydrogen atoms yielding J(HF) = 29 Hz in the
deshielded region and corresponds to the fluoride ion complex;
the other appears in the shielded region and is due to the free
receptor 2a; all this indicates a slow complexation equilibrium
process in DMSO-d6 (see Supporting Information, Figure S30).
This suggests that the F− ion interacts strongly with the
hexapyrrolic macrobicycle 2a by being drawn inside the cavity
of the macrobicycle. To confirm that the F− ion is encapsulated,
proton coupled 19F NMR spectra were recorded for 2a in the
presence of different mole ratios of F− ions in DMSO-d6. The
19F NMR spectrum of 2a (Figure 4) with 1 equiv of F− ion
showed a septet at δ = −91.3 ppm because of the coupling of
the fluoride ion with all six equivalent NH protons yielding the
coupling constant J(HF) = 29.4 Hz, which is the same as
obtained from 1H NMR titration spectra, and thus supports the
formation of the F− ion inclusion complex in solution. In
addition, the spectrum showed multiplets in the shielded region
for the formation of F− ion complexes containing deuterium
atoms which occur because of the F− ion mediated H/D
exchange of the pyrrolic NH hydrogen atoms with DMSO-d6.22
When the mole ratio of F− ion is increased to 2 or 3 equiv, the
19F NMR spectra showed broad signals corresponding to the
F− ion complexes containing one, two, three, four and five
deuterium atoms formed sequentially; the fully deuterium
substituted F− ion complex is not observed probably because of
the slowness of the H/D exchange (see Supporting
Information, Figure S47). The observed broad nature of
these signals can be attributed to the formation of a mixture of
randomly deuterium substituted F− ion complexes for a given
number of deuterium atoms. Further, the 19F NMR spectrum
showed resonances at δ = −142.5(d) with J(HF) = 122 Hz and
at δ = −143.0(t) with J(DF) = 19 Hz corresponding to the
−
−
formation of HF2 and DF2 species in the solution,
respectively, because of H/D exchanges (see Supporting
Information, Figure S48). The binding property of 2a with
F− ion in a less polar solvent CDCl3 was also studied by the
NMR titration method. In contrast to DMSO, upon addition of
F− ions to a CDCl3 solution of 2a, the NH resonance gradually
shifted to the deshielded region, which indicates that all NH
groups are cooperatively involved in interacting with this small
guest species. However, the titration curve did not achieve a
saturation point even after the addition of an excess amount of
F− ions (4 equiv) (see Supporting Information, Figure S31).
The titration curve is best fitted for a 2:1 rather than 1:1
receptor:anion complex yielding an apparent binding constant
Ka of >104 M−2 (see Supporting Information, Figure S41). This
is in contrast to the titration spectra in DMSO-d6 and suggests
that the solvent polarity affects the binding stoichiometry.
Further, this 2:1 binding stoichiometry is supported by the
Job’s plot which shows a maximum around 0.7 mol fraction of
receptor, which is close to the expected value of 0.66 mol
fraction (see Supporting Information, Figure S45).
The analogous 1H NMR titration experiment using the
smaller macrobicycle 3a with the F− ion was carried out in
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Figure 2. ORTEP diagram of the pentapyrrolic tetraazacryptand 3a
(30% thermal ellipsoids): (a) top view and (b) side view. Most
hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and
bond angles (deg): N2···O1, 3.0812(16); H2···O1, 2.341(15); N2−
H2···O1, 143.1(14); N6···O1, 3.0435(17); H6···O1, 2.193(14); N6−
H6···O1, 163.7(15); N3···O1, 2.8458(16); N3···H2w, 1.969(15); O1−
H2w···N3, 168.1(16); N7···O1, 2.8478(16); N7···H1w, 1.977(15);
O1−H1w···N7, 166.2(16).
Figure 3. ORTEP diagram of the chloride cryptate 4 (30% thermal
ellipsoids): (a) top view and (b) side view. Most hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and bond angles (deg):
N2···Cl1, 3.425(3); H2···Cl1, 2.60(3); N2−H2···Cl1, 164(3);
N9···Cl1, 3.413(3); H9···Cl1, 2.60(3); N9−H9···Cl1, 169(3);
N4···Cl1, 3.477(3); H4···Cl1, 2.79(3); N4−H4···Cl1, 137(3);
N5···Cl1, 3.044(2); H5···Cl1, 2.09(3); N5−H5···Cl1, 176(2); N6−
Cl1, 3.506(3); H6···Cl1, 2.89(3); N6−H6···Cl1, 133(3); N8−Cl1,
3.404(3); H8···Cl1, 2.52(3); N8−H8···Cl1, 168(3); N11···Cl1,
3.500(3); H11···Cl1, 2.90(3); N11−H11···Cl1, 136(3); C47···N2,
3.659(5); H47···N2, 2.98; C47−H47···N2, 131.5; C32···N9, 3.614(4);
H32···N9, 2.84; C32−H32···N9, 141.9.
CDCl3, and showed a gradual change and broadening of both
of the NH resonances of 3a. Here again, the titration curve did
not reach a saturation point even after addition of 5 equiv of the
F− ion and was best fitted for the 2:1 stoichiometry (see
Supporting Information, Figures S37 and S43) yielding an
apparent binding constant Ka of 5029 M−2 (<5% error); the 2:1
binding could not be supported by the Job’s plot because of the
very broad NH resonances. The 19F NMR spectrum of 3a with
2 equiv of F− ions in DMSO-d6 showed a broad resonance at δ
−86.3 ppm for a F− ion complex. However, other F− ion
complexes containing deuterium atoms formed by H/D
exchange are not observed although the signals corresponding
−
−
to HF2 and DF2 species in solution were found (see
Supporting Information, Figure S51). The change in the NH
resonance upon addition of the larger spherical anions such as
Cl− and Br− to a solution of 2a or 3a in CDCl3 is negligible
probably because of comparably weak H-bonding abilities of
these anions relative to F− and the large cavity size of the
receptor which is too voluminous to bind these spherical anions
tightly; the determined Ka for 2a with Cl− is <10 M−1.
Figure 4. Partial proton coupled 19F NMR (470.6 MHz) spectrum of
the hexapyrrolic pentaazacryptand 2a (0.008M) with 1 equiv of F−
ions in the form of the n-Bu4N+ salt in DMSO-d6 at 298 K.
−
The added HSO4 ion could potentially protonate two of the
We then investigated the binding properties of these
receptors with bulkier tetrahedral oxoanions. The titration
spectra of 2a with the HSO4 anion in DMSO-d6 appeared to
be very complex and showed resonances corresponding to the
free receptor and its complex, suggesting a slow complexation
equilibrium process (see Supporting Information, Figure S34).
three NMe groups, but not the bridgehead nitrogen atoms as
shown by the X-ray structure of the sulfate complex (see below,
Figure 5). In the titration spectra, the three resonances
appeared as broad overlapped signals in the deshielded region
correspond to the pyrrolic NH groups of two types and the
ammonium hydrogen atoms (HN+Me) of one type. Hence, the
−
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nation with little or no change in the chemical shift position of
the NH hydrogens of 3a, indicating that this pentapyrrole
−
receptor interacts weakly with the H2PO4 ion probably
because of a size mismatch. Both receptors showed almost no
−
change in the pyrrolic NH resonance upon addition of NO3
ions in the form of its n-Bu4N+ salt in CDCl3. This indicates
that the NO3− ion is not able to form an inclusion complex via
hydrogen bonds alone, probably requiring a positively charged
receptor as is the case for the SO4 and H2PO4 ion
complexes.
2−
−
Crystal Structures of the Oxoanion Complexes. To
understand the anion coordination chemistry, binding modes,
and conformational changes of the new bicyclic receptor 2a, the
sulfate, phosphate and arsenate anion complexes were
synthesized. The sulfate anion complex 5 was obtained in
71% yield as a crystalline solid by the reaction of 2 equiv of [(n-
Bu)4N][HSO4] with 2a in an ethyl acetate/methanol mixture
(Scheme 3). The X-ray structure of the sulfate complex is
shown in Figure 5 along with selected bond lengths and angles.
The sulfate dianion is encapsulated inside the cavity of the
macrobicycle which adopts an eclipsed conformation with an
in-in configuration at the bridgehead nitrogen atoms, as in the
structure of 2a. However, the sulfate ion inclusion induces a
change in the bridgehead nitrogen distance: N1···N5 = 8.950 Å,
which is longer than that found in the structure of 2a. The
−
acidic HSO4 ion protonates sterically less encumbered NMe
groups rather than the sterically crowded bridgehead nitrogen
atoms, and the resultant two ammonium cations MeN+H
neutralize the sulfate dianion. Thus the protonated receptor
possesses eight potential acidic NH groups (six pyrrolic NH
and two ammonium hydrogen atoms) for hydrogen bonding.
While each oxygen atom of a sulfate ion can form at least two
hydrogen bonds, the sulfate ion in 5 is held tightly in place
primarily via bifurcated and trifurcated NH···O and NH···S
hydrogen bond types formed with all of the eight NH groups.
However, the oxygen atoms O1, O2, and O4 of the sulfate ion
are disordered over two positions indicating that the cavity size
of the macrobicycle is voluminous enough for the sulfate ion to
roll around.
Figure 5. ORTEP diagram of the sulfate anion encapsulated complex
5 (30% thermal ellipsoids): (a) top view and (b) side view. Most
hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and
bond angles (deg): N2···O4, 2.882(4); H2···O4, 2.00(3); N2−
H2···O4, 165(3); N2···S1, 3.702(3); H2···S1, 2.88(3); N2−H2···S1,
152(2); N9···S1, 3.715(3); H9···S1, 2.90(3), N9−H9···S1, 160(3);
N4···O2, 2.833(4); H5···O2, 1.97(3); N4−H5···O2, 178(3); N3···S1,
3.549(3); H13···S1, 2.69(3); N3−H13···S1, 161(2); N8···O4,
2.936(4); H8···O4, 2.11(3); N8−H8···O4, 161(3); N6···O2,
2.820(4); H6···O2, 1.87(3); N6−H6···O2, 174(3); N3···O3,
2.765(3); H13···O3, 1.88(3); N3−H13···O3, 167(3); N10···O1,
2.733(4); H14···O1, 1.76(3); N10−H14···O1, 169(3); N11···O2,
3.050(6); H12···O2, 2.25(3); N11−H12···O2 176(3).
The reaction between 2a and 2 equiv of KH2PO4 in THF/
water afforded the phosphate cryptate 6 in 77% yield as a
crystalline solid (Scheme 3). The X-ray structure (Figure 6)
revealed one encapsulated phosphate anion inside the cavity of
the pentaazacryptand, and its oxygen atoms are disordered over
two positions with several hydrogen bonding interactions. All
the pyrrolic NH hydrogen atoms are pointed inside the cavity,
and form bifurcated and trifurcated hydrogen bonds with the
oxygen atoms of the phosphate anion. The host molecule
adopts an eclipsed conformation with an in-in configuration, as
in the structures of 2a and 5, and the distance between the
bridgehead nitrogen atoms (N1 and N5) is 9.117 Å, which is
longer than those found in the structures of 2a and 5.
Considering the major component oxygen atoms, the two P−O
bond distances (P1−O2 = 1.523(6) Å and P1−O4 = 1.523(6)
Å) are shorter than the other two distances, P1−O1 = 1.539(5)
Å and P1−O3 = 1.559(6) Å; it may indicate the presence of the
binding constant could not be calculated. On the other hand,
−
the titration spectra of 2a with the HSO4 anion in CDCl3
showed the disappearance of the pyrrolic NH protons before
−
the addition of 1 equiv of HSO4 ion, which is probably
because of deprotonation of the acidic NH hydrogen atoms
(see Supporting Information, Figure S33). The analogous
titration spectra of 3a with HSO4− also showed a slow exchange
process in CDCl3 indicating the formation of the sulfate ion
complex containing the positively charged receptor in solution.
−
monobasic dihydrogenphosphate (H2PO4 ) as two of the
longer P−O distances could correspond to the protonated
−
−
oxygen atoms in H2PO4 . These values are longer, though, than
The titration spectra of 2a with H2PO4 in DMSO-d6 also
the corresponding values reported for the protonated cryptand
showed a slow exchange process indicating that the phosphate
anion binds as strongly as the sulfate anion. The analogous
titration spectra of 3a with H2PO4− in CDCl3 showed a gradual
disappearance of the NH resonance because of the deproto-
complex containing an encapsulated H2PO4 anion.23 How-
−
ever, the positions of hydrogen atoms bound to the bridgehead,
the NMe nitrogens or the oxygen atoms of the phosphate anion
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Scheme 3. Synthesis of the Oxoanion Encapsulated Complexes of the Hexapyrrolic Pentaazacryptand 2a: Sulfate 5, Phosphate
6, and Arsenate 7 Anion Complexes
could not be located exactly as expected. Whether the
3−
phosphate species is a neutral H3PO4 or trianionic PO4 or
an intermediate species, to balance the charge, three hydrogen
atoms need to be located in the structure. They were found in
five positions with an occupancy of roughly 60% each. This
occupancy was fixed to the value of 0.6 based on four
refinement cycles in which the occupancy was set to refine
freely and it is in agreement with three hydrogen atoms
distributed equally among five positions. In all of the five
“cationic” hydrogen atom positions, the hydrogen atoms are
located closer to a nitrogen atom rather than to an oxygen atom
along hydrogen bonds between the respective N and O atoms.
The coordinates of these hydrogen atoms were refined freely,
but their displacement factors were set to be dependent on
their parent atoms (1.2 times). It needs to be stressed, though,
that the data for these five hydrogen atom positions should be
taken with caution, since their positions lie along O−N vectors
in shallow potential wells. They were refined because electron
density was actually observed in suitable positions and because
it gives a more comprehensive picture of the hydrogen bonding
in the molecule than fixing them in randomly chosen positions
or not at all.
The observed two different types of P−O bond lengths may
be attributed to partly rather strong hydrogen bonding, as
shown by the N···O contacts including strong interactions/
short distances such as N10···O2 = 2.589(9) Å and N···O =
2.628(8) Å. Similar strong hydrogen bonding and ambiguity in
hydrogen-locations have been observed in the structures of
phosphate anion complexes formed by synthetic receptors
before.24 Such strong hydrogen bonding may influence P−O
bond lengths significantly. Analogous observations have been
made previously.25 Given the disorder and the distribution of
hydrogen atoms among the hydrogen bonding atoms within
the cavity, it is difficult to assign exactly what type of phosphate
anion is present; theoretically it may be any type of phosphate
anion structurally lying in between the two extremes, the fully
protonated H3PO4 and the deprotonated PO43−. Overall the
actually refined hydrogen atoms represent most likely the
average of a mixture of distinct cocrystallized species, reflecting
a dynamic proton ping-ponging situation in solution. In any
case, this structure represents, to the best of our knowledge,
only the second example of a structurally characterized
Figure 6. ORTEP diagram of the phosphate anion encapsulated
complex 6 (30% thermal ellipsoids): (a) top view and (b) side view.
Most hydrogen atoms are omitted for clarity. Selected bond lengths
(Å) and bond angles (deg): N1···O1, 3.066(7); H1n···O1, 1.65(12);
N1−H1n···O1, 166(8); N2···O1, 2.730(8); H2n···O1, 1.74(5); N2−
H2n···O1, 148(5); N6···O3, 2.888(10); H6n···O3, 1.85(5); N6−
H6n···O3, 156(7); N7···O3, 2.628(8); H7n···O3, 1.39(12); N7−
H7n···O3, 149(10); N8···O1, 2.770(8); H8n···O1, 1.73(4); N8−
H8n···O1, 157(6); N9···O1, 2.761(8); H9n···O1, 1.69(4); N9−
H9n···O1, 167(7); N10···O2, 2.589(9); H10n···O2, 1.41(13); N10−
H10n···O2, 164(11); N11···O2, 2.758(8); H11n···O2, 1.86(6); N11−
H11n···O2, 137(6).
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phosphate anion inclusion complex with a bicyclic azacryptand
molecule.23
We then set to synthesize encapsulation complexes of still
larger oxoanions with 2a for investigating anion induced
conformational changes in the macrobicycle. The reaction of 2
equiv of Na2HAsO4·7H2O with a mixture of 2a and 5 equiv of
HCl in tetrahydrofuran (THF)/water gave the novel inclusion
complex 7 containing an arsenate ion in 54% yield as a
crystalline solid (Scheme 3). 7 is not formed in the absence of
HCl suggesting that a cationic receptor is required for the
arsenate ion complex formation. The excess acid used in the
synthesis could give a cationic macrobicyclic complex
containing a chloride anion which is then replaced by the
mono- or dibasic arsenate ion to give 7. This process is
probably driven by the presence of both the hydrogen bond
−
donor and acceptor properties available with the H2AsO4 or
HAsO42−anion and favored by the suitable cavity size of the
macrobicycle 2a.
The structure of 7 was determined by X-ray diffraction
(Figure 7) and confirmed by the HRMS spectrum which shows
a peak m/z at 816.3549 corresponding to its [M+H+] ion. The
X-ray structure revealed the presence of an arsenate(V) species
inside the cavity of macrobicycle 2a along with 17.5 water
molecules as cocrystallized solvent in the lattice. The arsenic
atom and two of its oxygen atoms (O2 and O4) are disordered
over two positions with occupancy factors of 76% and 24%
within the cavity of the macrobicycle. Of overall 3.5 water
molecules per formula which could be refined (out of 17.5 in
total), half a water molecule (O8) is disordered in correlation
with both the disordered methyl group (C33) and the arsenate
ion. It appears as if the methyl group can occur as flipped into
the macrobicycle in case the arsenate oxygen atom is not
pointing into the same direction (O1 present not O1A). The
water (O8) is then hydrogen bonded to the parent nitrogen of
this methyl group from outside the cavity. With the minor
component of the arsenate disorder present, the methyl group
has to be flipped out of the macrocycle for steric reasons. In this
case the respective water molecule is apparently hydrogen
bonded to the arsenate oxygen and present in the vicinity of the
cavity. A third possibility is the presence of the water in this
location without the methyl group rotated in and with the
arsenate oxygen pointing into the other direction. It appears as
if all three possible isomeric structures are cocrystallized. Based
on an overall occupancy of only 50% for this water molecule
and the additional disorder, the respective water hydrogen
atoms could not be located.
Figure 7. ORTEP diagram of the arsenate anion encapsulated complex
7 (30% thermal ellipsoids): (a) top view and (b) side view. Most
hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and
bond angles (deg): As1−O1, 1.671(3); As1−O2, 1.700(4); As1−O3,
1.702(3); As1−O4, 1.664(3); O4−As1−O1, 113.40(17); O4−As1−
O2, 107.32(18); O1−As1−O2, 109.03(18); O4−As1−O3,
107.41(14); O1−As1−O3, 110.10(17); O2−As1−O3, 109.49(16);
C1−N1−C27, 111.1(3); C1−N1−C26, 110.2(3); C27−N1−C26,
110.0(3); C13−N5−C39, 111.5(3); C13−N5−C14, 111.1(3); C39−
N5−C14, 109.7(3); C39−N5−N1−C1 = 45.94; C13−N5−N1−C26
= 46.69; C14−N5−N1−C27 = 47.66.
1.679 Å, and 1.689 Å).27 Given these values, even if either
3−
In the major component arsenate ion, there are roughly two
types of As−O bond distances, as observed in the phosphate
complex 6; As1−O1 (1.671(3) Å) and As1−O4 (1.664(3) Å)
are one type, while As1−O2 (1.700(4) Å) and As1−O3
(1.702(3) Å) are the other type. If the former and the latter
distances correspond to the nonprotonated and protonated
AsO4 or H3AsO4 is present which are the two extremes,
location of the hydrogen atoms becomes essential for
confirming what type of arsenate ion is present. The counter
cationic moiety can be formed by protonation of any of the
amine nitrogen atoms of the receptor (HN+) or by protonation
of water to form H3O+, since the arsenate species moves inside
the cavity as shown by its disorder. However, the position of
any of the neutralizing “protons” (H+) attached to the arsenate
or water oxygen or amine nitrogen atoms could not be precisely
located. Residual electron density was found, though, in
positions in between the water molecules and the oxygen
atoms of arsenate (O1; O1A) pointing toward these water
molecules and in suitable distances to the NMe nitrogen atoms
of the macrobicycle (in particular N3 and N10). These
hydrogens appear to be distributed between different Lewis
basic atoms. Though it is weakly supported by the crystallo-
graphic data, that they are in specific locations (NMe,
−
oxygen atoms bound to the arsenic atom in H2AsO4 ,
respectively, then the difference between the average values
of this double and single bond is 0.034 Å. This is not
overwhelmingly supporting the presence of the monobasic
−
H2AsO4 anion because this difference is smaller than that
found for LiH2AsO4 (0.066 Å)26 or NH4H2AsO4 (0.05 Å)27
though it roughly falls into this range. On the other hand, if the
3−
encapsulated arsenate ion is AsO4 with the tripositively
charged receptor, then all four As−O bond distances should be
almost equal, as found for (NH4)3AsO4 (1.671 Å, 1.683 Å,
1.686 Å and 1.700 Å)28 or for Cs3AsO4 (1.670 Å, 1.670 Å,
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bridgehead N, As−O− and water O functions in particular), in
contrast to the structure of 6, a refinement in these positions
even with fractional occupancy did not lead to reasonable
results. These three hydrogen atoms have therefore not been
refined. This type of disordered hydrogen atoms suggests a
strong hydrogen bonding network which includes the
cocrystallized waters around the arsenate ion. In support of
this, the two of the arsenate oxygen atoms O3 and O4 are
almost collinear with the bridgehead nitrogens (N1 and N5)
and their distances, N1···O4 = 2.631 Å and N5···O3 = 2.619 Å,
indicate strong H-bonds with which the arsenate species is held
inside. Besides, the other two oxygen atoms (O1 and O2) of
the arsenate species also form strong H-bonds with the NMe
and the water molecules as shown by their contacts such as
N3···O2 = 2.614 Å, N10···O1 = 2.794 Å, O1···O7(water) =
2.648 Å, and O2···O8(water) = 2.560 Å. Further, it suggests
that in solution these hydrogen atoms are moving between the
donors and acceptors, or in other words, the positive charge or
H+ required for neutralizing any arsenate anion is delocalized
among the Lewis basic atoms involved in hydrogen bonds.
Aside from the more severe disorder, this is overall quite similar
to the situation found in the structure of phosphate complex 6.
Furthermore, this situation suggests that the encapsulated
arsenate anion can be neither H3AsO4 with a neutral receptor
AsO4 is larger than that of the PO4 ion,29 indicating a
certain flexibility of the macrobicycle’s 2a conformation. A
similar distinct property has been observed in the case of the
hexaprotonated azacryptand which exhibits a smaller bridge-
head N···N distance for the chloride inclusion complex than
does its fluoride analogue.30 This structure represents the first
arsenate anion inclusion complex with an azacryptand.
3−
3−
It is noteworthy that receptor 2a is involved in slow exchange
−
processes with anions such as F−, SO42−, and H2PO4 in
DMSO-d6. This led us to investigate which anion binds
selectively with 2a by a competition crystallization meth-
od.19f,i,18b,31 Thus, when a solution of 2a in THF/water (1:1 v/
−
−
v) containing anions such as H2PO4 , HSO4 , HAsO42−, F−,
Cl−, Br−, NO3− (2 equiv each) was allowed to evaporate slowly,
only the phosphate complex 6 was formed in 83% yield as a
solid. The IR spectrum (see Supporting Information, Figure
S53) and the powder XRD pattern (Figure 9) of the precipitate
3−
nor AsO4 with a tripositively charged receptor, but it may
very well be a system in between these two extremes or the
structure reflects cocrystallization of all potential species. The
As−O bond value can be in between the double and single
bond values when the O−H bonds are polarized followed by
conjugation, as found in the Cu(II) cryptate reported by
McKee, Nelson, and co-workers.25 Polarization of the O−H
bond of the arsenate species probably takes place because of the
conformational constraints of the receptor with which the
arsenate is sitting inside the cavity which offer rather close
contacts between the hydrogen donors and the acceptors.
Consequently, the observed As−O bond distances can reflect
the degree of polarization which can lead to As−O bond
lengths lying in between the AsO and As−OH distances, that
is, exhibiting partial double bond character, which can be
depicted as shown in Figure 8.
Figure 9. (a) Powder XRD pattern of the phosphate anion complex 6
obtained from its explicit synthesis; (b) the powder XRD pattern of
the precipitate obtained from the competition crystallization experi-
ment. The spectrum (a) matches with the spectrum (b), confirming
that the phosphate complex is the sole product of crystallization from
an aqueous−organic solvent in the presence of other oxoanions.
obtained from the competition experiment are the same as
those of 6 obtained from its explicit synthesis. Although it is
difficult to confirm the selectivity from this experiment alone
because crystallization is a kinetic process and it has to be
confirmed from the free energy difference (ΔΔG) among other
anion complexes,32 it is interesting to note that only the
phosphate is crystallized out in the presence of other competing
tetrahedral oxoanions; hence, it remains useful for separation of
phosphate anions from an aqueous−organic medium. This
selective crystallization of the phosphate species is attributed to
its hydrogen bond donor and acceptor abilities which
complement those present in receptor 2a. Other competing
Figure 8. Resonance structures illustrating the delocalization of
positive charges between the acceptor and the donor, explaining the
distribution of protons among the Lewis basic atoms such as amine,
and arsenate or water O atoms in the structure 7 and consequent
intermediate As−O distances.
2−
anions such as SO4 or halide anions apparently lack such
complementarity.
CONCLUSION
■
In conclusion, the Mannich reaction approach proved to be an
excellent method for synthesizing novel macrobicyclic
pentaaza- and tetraazacryptand molecules, which were structur-
ally characterized; the pentaazacryptand 2 is formed by
assembling 15 reactive sites in a single step. Interestingly,
when bulky benzylamine was used, in contrast to the syntheses
of 2 and 3, a structurally different sphere-like chloride cryptate
was isolated. The pentaazacryptand 2a is a flexible macrobicycle
and forms stable inclusion complexes that include the smaller
size fluoride ion and the larger size oxoanions, and possesses
both hydrogen bonding donors and acceptors with a rather
large cavity, as shown by NMR binding and X-ray crystal
The arsenate ion is held in place via both strong hydrogen
bonding as well as electrostatic interactions. The pyrrolic NH
groups are H-bonded to the arsenate oxygen atoms and also to
the water molecules present in the cleft of the macrobicycle.
Importantly, the arsenate anion induces a conformational
change from eclipsed, as found in the arsenate free macrobi-
cycle 2a, to a staggered conformation about the bridgehead N−
C bonds with an average torsion angle of 46.76° and an in/in
configuration at the bridgehead nitrogens. Interestingly, the
bridgehead N1···N5 distance of 7.832 Å is considerably shorter
than those found in 2a, 5, or 6, although the ionic size of
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1438(s), 1362(w), 1333(w), 1263(w), 1226(w), 1187(w), 1117(w),
1034(w),1018(w), 971(w), 861(w), 777(vs), 669(w), 650(w),
579(w), 546(w). HRMS(+ESI): m/z calcd for [M+H+] C39H52N11
674.4402, found 674.4403.
structure studies. Further, the competition crystallization
experiment in an aqueous−organic medium gave only the
phosphate cryptate of 2a. It is interesting to compare this with
the anion binding property of the macrobicycles A and B in
Chart 1 which have been shown to be selective receptors for
the smaller fluoride ion in the presence of larger anions which
rather bind in their clefts. In contrast to this, this work
demonstrated that the cavity size of the macrobicycle can be
enlarged using tris(pyrrolyl-α-methyl)amine and the resultant
azacryptand possesses additional methylene group spacers so
that it becomes suitable for encapsulating larger size oxoanions
such as sulfate, phosphate, and arsenate inside the cavity rather
than binding in clefts. The inclusion of the arsenate anion
inside the cavity of the macrobicycle induces a drastic
conformational change to the macrobicycle which is not
observed with other anions studied here. The structure of the
arsenate complex represents the first structure of an
encapsulated arsenate ion inside the cavity of an azacryptand.
For 3a: m.p: >200 °C. 1H NMR (400 MHz, CDCl3, 25 °C, ppm): δ
= 10.10 (br s, 4H, pyrrole NH), 9.21 (br s, 1H, pyrrole NH), 5.95−
5.87 (m, 10H, pyrrole β-CH), 3.65 (t, 16H, J(H,H) = 12.0 Hz, CH2),
3.42 (d, 4H, J(H,H) = 12.0 Hz, CH2), 2.40 (s, 6H, CH3). 13C NMR
(102.6 MHz, CDCl3, 25 °C): δ = 131.0, 130.0, 126.4 (pyrrole α-C),
108.5, 108.0, 105.3 (pyrrole β-C), 54.3, 51.6, 51.2 (CH2N), 42.7 ppm
(NCH3). FT-IR (KBr, cm−1): ν = 3412(vs), 3376(vs), 3104(w),
2928(w), 2873(w), 2803(vs), 2697(w), 1655(w), 1583(w), 1544(w),
1509(w), 1438(s), 1362(vs), 1278(w), 1259(w), 1226(s), 1178(w),
1116(w), 1035(w), 1013(s), 970(s), 869(w), 785(vs), 697(w),
647(w), 614(w), 573(w). HRMS(+ESI): m/z calcd for [M+H+]
C32H42N9 552.3558, found 552.3558.
Synthesis of 2b and 3b. 2b and 3b were synthesized by following
the above procedure for the synthesis of 2a and 3a. H3tpa (0.5 g, 1.96
mmol) was added to the mixture of EtNH2·HCl (0.24 g, 2.94 mmol)
and HCHO (0.46 mL, 39% aqueous solution, 5.88 mmol) in methanol
and stirred for 30 h. 2b and 3b were obtained as a colorless solid in
15% (0.105 g) and 3% (0.022 g) yields, respectively, after basic
alumina column chromatographic separation which involves elution
with ethyl acetate/petroleum ether (1:15 v/v) for 3b and then with
ethyl acetate/petroleum ether (1:3 v/v) for 2b.
EXPERIMENTAL SECTION
■
Tris(pyrrolyl-α-methyl)amine (H3tpa) was prepared according to the
literature procedure.33 Pyrrole, methylamine hydrochloride, benzyl-
amine hydrochloride, n-tetrabutylammonium fluoride solution (1.0 M
in THF), n-tetrabutylammonium chloride, n-tetrabutylammonium
bromide, n-tetrabutylammonium nitrate, DMSO-d6 and CDCl3 were
purchased from Aldrich and were used without further purification
except pyrrole, which was distilled, and methylamine hydrochloride,
which was dried under vacuum with warm water. Formaldehyde, n-
tetrabutylammonium hydrogensulfate, n-tetrabutylammonium dihy-
drogenphosphate, disodium hydrogenarsenate heptahydrate, ethyl-
amine hydrochloride and other reagents were purchased from local
For 2b: m.p: >200 °C. 1H NMR (200 MHz, CDCl3, ppm, 25 °C): δ
= 9.38 (br s, 6H, NH), 5.88 (d, J(H,H) = 2.0 Hz, 12H, pyrrole β-CH),
3.56, (s, 12H, CH2), 3.49 (s, 12H, CH2) 2.45 (q, J(H,H) = 7.1 Hz, 6H,
NCH2CH3), 0.87 (t, J(H,H) = 7.1 Hz, 9H, NCH2CH3). 13C NMR
(102.6 MHz, CDCl3, ppm): δ = 130.0, 127.9 (pyrrole α-C), 108.9,
107.5 (pyrrole β-C), 51.9, 51.7 (CH2N), 46.3 (NCH2CH3), 10.0
(NCH2CH3). FT-IR (KBr, cm−1): ν = 3388(vs), 3305(s), 3098(w),
2963(w), 2927(w), 2874(w), 2816(s), 2700(w), 1654(w), 1589(w),
1508(w), 1457(w), 1435(w), 1428(w), 1361(s), 1272(s), 1223(w),
1182(w), 1119(w), 1095(w), 1033(s), 971(w), 945(w), 861(w),
775(vs), 665(w), 551(w). HRMS(+ESI): m/z calcd for [M+H+]
C42H58N11 716.4871, found 716.4853.
1
commercial sources. H NMR (200 and 400 MHz) and 13C NMR
(102.6 and 51.3 MHz) spectra were recorded on Bruker
spectrometers. Chemical shifts are referenced with respect to the
chemical shift of the residual protons present in the deuterated
solvents. 19F NMR spectra were recorded on a 500 MHz spectrometer
operating at 470.6 MHz for which 0.05% trifluorotoluene in CDCl3
was used as an external reference resonating at −62.72 ppm. FTIR
spectra were recorded using Perkin-Elmer Spectrum Rx. High
Resolution Mass Spectra (ESI) were recorded using the Xevo G2
Tof mass spectrometer (Waters). Melting points were determined in
open capillaries and are corrected using benzophenone as a reference.
Synthesis of 2a and 3a. An aqueous formaldehyde solution (39%,
0.90 mL, 11.7 mmol) was added slowly to a solution of MeNH2·HCl
(0.40 g, 5.9 mmol) in methanol (700 mL) at 0 °C, and the solution
was stirred for 20 min. To this solution at 0 °C, a solution of
tris(pyrrolyl-α-methyl)amine (1.0 g, 3.93 mmol) in methanol (50 mL)
was added dropwise, and the resultant solution was stirred for 36 h at
room temperature. The solvent was removed under vacuum to give an
oily residue. Water (80 mL) was added to the residue to give a
colorless precipitate. To this reaction mixture, an aqueous solution of
K2CO3 (0.49 g in 10 mL of water, 3.54 mmol) was added slowly and
stirred for about 2 h. The reaction mixture was extracted with
dichloromethane (3 × 25 mL), and the combined organic portion was
dried over anhydrous Na2SO4 for 4 h. The solvent was removed under
vacuum, and the residue was loaded onto a column filled with basic
alumina. Elution using a mixture of ethyl acetate/petroleum ether
(1:10 v/v) afforded compound 3a (0.035 g, 2%) as a colorless solid
after removal of the solvents. Further elution using ethyl acetate/
petroleum ether (1:1 v/v) gave compound 2a (0.309 g, 22%) as a
colorless solid after removal of the solvents.
For 3b: m.p: >200 °C. 1H NMR (400 MHz, CDCl3, 25 °C, ppm): δ
= 9.94 (br s, 4H, NH), 9.04 (br s, 1H, NH), 5.92−5.86 (m, 10H,
pyrrole β-CH), 3.62−3.51 (m, 20H, CH2), 2.73 (q, J(H,H) = 6.9 Hz,
4H, NCH2CH3), 1.10 (t, J(H,H) = 7.2 Hz, 6H, NCH2CH3). 13C NMR
(102.6 MHz, CDCl3, 25 °C, ppm): δ = 131.1, 130.1, 127.0 (pyrrole α-
C), 108.5, 107.9, 105.6 (pyrrole β-C), 51.5, 51.2, 51.2, 48.8 (CH2N),
10.6 (NCH2CH3). FT-IR (KBr, cm−1): ν = 3410(vs), 3367(vs),
3098(w), 2969(w), 2924(w), 2868(w), 2816(s), 2700(w), 1654(w),
1636(w), 1586(w), 1507(w), 1437(w), 1360(s), 1264(s), 1225(w),
1175(w), 1116(s), 1030(s), 968(w), 869(w), 784(s), 763(s). HRMS-
(+ESI): m/z calcd for [M+H+] C32H42N9 580.3871, found 580.3870.
Synthesis of 4. The chloride cryptate 4 was synthesized by
following the synthetic procedure of 2a and 3a. H3tpa (2 g, 7.86
mmol) was added to the mixture of PhCH2NH2·HCl (1.69 g, 11.79
mmol) and HCHO (1.81 mL, 39% aqueous solution, 23.6 mmol) in
methanol and stirred for 12 h. 4 was isolated in 16% (0.63 g) yield as a
colorless solid by using silica gel column chromatography with ethyl
acetate/petroleum ether (2:1 v/v) as an eluting solvent. m.p: >200 °C.
1H NMR (200 MHz, CDCl3, 25 °C, ppm): δ = 11.85(br s, 1H, N+H),
10.82, (br s, 3H, pyrrole NH), 9.49 (br s, 3H, pyrrole NH), 7.03−6.81
(m, 15H, aromatic CH), 6.11 (br s, 6H, pyrrole β-CH), 5.84 (br d, 6H,
pyrrole β-CH), 5.30 (CH2Cl2), 4.13−2.76 (br m, 30H, NCH2 and
PhCH2). 13C NMR (102.6 MHz, CDCl3, 25 °C, ppm): δ = 139.9,
134.8, 131.0, 129.2, 128.4, 126.7 (aromatic C), 116.9, 114.0, 110.7,
106.3 (pyrrole C), 57.4 (CH2Cl2), 53.0, 52.5, 52.3, 50.3 (NCH2). FT-
IR (KBr, cm−1): ν = 3372(w), 3323(vs), 3103(w), 3025(w), 2916(w),
2798(w), 2672(w), 2574(w), 1732(w), 1654(w), 1508(w), 1449(w),
1428(w), 1364(s), 1267(w), 1247(w), 1222(w), 1180(w), 1116(w),
1068(w), 1039(w), 1012(w), 973(w), 899(w), 864(w), 776(vs),
742(w), 698(w), 643(w), 579(w), 506(w). HRMS(+ESI): m/z calcd
for [M+H+] C57H65ClN11 938.5113, found 938.5118.
For 2a: m.p: >200 °C. 1H NMR (400 MHz, CDCl3, 25 °C, ppm): δ
= 9.50 (br s, 6H, NH), 5.93 (s, 6H, pyrrole β-CH), 5.88 (s, 6H, pyrrole
β-CH), 3.51 (s, 24H, CH2), 1.96 (s, 9H, CH3). 13C NMR (102.6 MHz,
CDCl3, 25 °C): δ=130.7, 127.1, (pyrrole α-C), 109.2, 107.1, (pyrrole
β-C), 55.9, 51.8, (CH2N), 40.5 ppm (NCH3). FT-IR (KBr, cm−1): ν =
3372(vs), 3104(w), 2924(w), 2801(s), 1657(w), 1637(w), 1581(w),
Synthesis of [2aH2]2+[SO4]2−, 5. To a solution of 2a (0.025 g,
0.035 mmol) in ethyl acetate (6 mL) was added methanol solution (3
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Inorganic Chemistry
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mL) of n-Bu4NHSO4 (0.024 g, 0.070 mmol) and stirred for 5 min.
The resultant solution was allowed to evaporate slowly for 3 days at
room temperature to give colorless crystals of 5 which was filtered and
dried under vacuum. Yield: 0.019 g, 71%. These crystals are not
soluble in organic solvents and hence NMR data could not be
obtained. FT-IR (KBr, cm−1): ν = 3227 (vs), 3148(s), 2934(w),
2873(w), 2822(w), 2797(w), 1655(w), 1580(w), 1561(w), 1545(w),
1457(w), 1445(s), 1364(w), 1347(w), 1276(w), 1226(w), 1188(w),
1120(vs), 1092(vs), 1072(vs), 1037(w), 1001(s), 968(w), 868(w),
796(w), 774(s), 617(w). HRMS(+ESI): m/z calcd for [M+H+]
C39H54N11O4S 772.4075, found 772.4075.
Synthesis of Phosphate Cryptate, 6. To a THF (6 mL) solution
of 2a (0.025 g, 0.035 mmol) was added an aqueous solution (3 mL) of
KH2PO4 (0.010 g, 0.070 mmol) and stirred for 5 min. The resultant
solution was allowed to evaporate slowly for a week at room
temperature to give colorless crystals of 6 which was filtered and dried
under vacuum. Yield: 0.021 g, 77%. These crystals are not soluble in
organic solvents and hence NMR data could not be obtained. FT-IR
(KBr, cm−1): ν = 3373(s), 3188(s), 3091(s), 2969(s), 2812(vs),
2797(vs), 2723(s), 2689(s), 1748(w), 1650(w), 1634(w), 1586(w),
1502(w), 1450(s), 1360(s), 1343(s), 1280(s), 1240(s), 1187(s),
1155(w), 1110(s), 1085(s), 1027(s), 994(vs), 859(s), 785(s), 766(s),
750(s), 690(w), 551(w), 431(w). HRMS(+ESI): m/z calcd for [M
+H+] C39H55N11O4P 772.4171, found 772.4172.
Synthesis of Arsenate Cryptate, 7·17.5H2O. To a THF (10
mL) solution of 2a (0.025 g, 0.035 mmol) was added an aqueous
solution of HCl (0.044 mL, 0.175 mmol, 4M) with stirring, resulting in
a colorless precipitate. To this solution was added 3 mL of distilled
water to dissolve the precipitate to give a clear solution. Then an
aqueous solution (2 mL) of disodium hydrogenarsenate heptahydrate
(Na2HAsO4·7H2O) (0.021 g, 0.071 mmol) was added and stirred for 5
min. The solution was allowed to evaporate slowly at room
temperature over two weeks to give colorless crystals of 7. Yield:
0.021 g, 0.019, 54%. These crystals are not soluble in organic solvents
and hence NMR data could not be obtained. FT-IR (KBr, cm−1): ν =
3424(vs), 3154(s), 3011(s), 2868(w), 2818(w), 2725(w), 2643(w),
2533(w), 1655(w), 1624(w), 1578(w), 1561(w), 1459(s), 1443(w),
1404(w), 1364(w), 1281(w), 1224(w), 1193(s) 1114(w), 1023(w),
999(w), 903(w), 794(vs), 672(w), 611(w). HRMS (+ESI): calcd m/z
for [M+H+] C39H55AsN11O4 816.3649, found 816.3549.
Competition Crystallization. To a THF (14 mL) solution of 2a
(0.025 g, 0.035 mmol) at room temperature was added dropwise 6 mL
of aqueous solution containing KH2PO4 (0.010 g, 0.070 mmol),
Na2HAsO4·7H2O (0.022 g, 0.070 mmol), n-Bu4NHSO4 (0.024 g,
0.070 mmol), n-Bu4N(NO3) (0.020 g, 0.070 mmol), n-Bu4NF·3H2O
(0.022 g, 0.070 mmol), n-Bu4NCl (0.019 g, 0.070 mmol), and n-
Bu4NBr (0.023 g, 0.070 mmol) with stirring for 10 min and then the
solution (pH = 7.60) was allowed to evaporate slowly at room
temperature. After 3 days colorless precipitate was formed. The
mother liquor was decanted, and the precipitate was washed with
water followed by acetone (10 mL) two times and then dried under
vacuum. The IR spectrum and the powder XRD diffraction spectrum
of this precipitate exactly match with those obtained for the phosphate
complex 6. Yield: 0.022 g, 83%.
Single crystal X-ray diffraction data collections for all the
compounds were performed at room temperature using Bruker-
APEX-II CCD diffractometer with graphite monochromated MoKα
radiation (λ = 0.71073 Å). The structures were solved by SIR-9234 or
SHELXS-97 available in WinGX, which successfully located most of
the non-hydrogen atoms. Subsequently, least-squares refinements were
carried out on F2 using SHELXL-97 (WinGX version)35 to locate the
remaining non-hydrogen atoms.
Typically for all the structures, hydrogen atoms attached to carbons
were fixed in calculated positions. The NH and water hydrogen atoms
were located, refined isotropically with their thermal parameters set as
equivalent to 1.2 times that of their parent atoms and restrained with
SADI or DFIX. In case of the structure of 4, the unit cell contains
roughly one molecule of dichloromethane which has been treated as a
diffuse contribution to the overall scattering without specific atom
positions by SQUEEZE/PLATON.36 The presence of dichloro-
1
methane is supported by the H NMR spectrum recorded for crystals
of 4 in CDCl3 showing a singlet at δ 5.30 ppm. In case of the structure
of 5, the oxygen atoms (O1, O2, and O4) of the sulfate anion are
found to be disordered over two positions with occupancy factors of
88% and 12% which are handled successfully with EADP and SADI
options. In case of the structure of 6, the phosphate ion is found to be
disordered over two positions with occupancy factors of 79% and 21%.
The minor component was refined isotropically. The three counter
charge hydrogen atoms in total were found to be distributed among
five NMe nitrogen atoms. They were located and refined isotropically
with 0.6 occupancy factors each. In case of the structure of 7, the unit
cell contains 17.5 water molecules per formula; 14 of them were
treated as a diffuse contribution to the overall scattering without
specific atom positions by SQUEEZE/PLATON. The remaining 3.5
water molecules were refined. For those with hydrogen atoms that
could be located, the hydrogen atoms were located and refined
isotropically with their thermal parameters set to being equivalent to
1.5 times that of the parent, and restrained with DFIX to become
stable. Half a water molecule is disordered over two positions in
correlation with the arsenate disorder. The minor component oxygen
atom was refined isotropically. The respective hydrogen atoms could
not be found. The arsenic atom and two of its oxygen atoms (O1 and
O4) are disordered over two positions with occupancy factors of 76%
and 24%. Similarly, the methyl group attached to N7 atom was found
to be disordered with occupancy factors of 44% and 56%. The counter
charge hydrogen atoms could not be refined with a reasonable result
but are part of the calculated sum formula. Use of SQUEEZE/
PLATON necessarily contributes to the discrepancy between
calculated and reported formulas in the cif-files for the structure of
arsenate 7 and chloride complex 4. The refinement data for all the
structures are summarized in Table 1.
ASSOCIATED CONTENT
■
S
* Supporting Information
NMR, IR, binding constant calculations and graphs, crystallo-
graphic data (CIF). This material is available free of charge via
the Internet at http://pubs.acs.org.
NMR Titrations. Using a 10 μL Hamilton Gastight syringe, all the
titrations were carried out by adding an incremental amount of anions
as their n-tetrabutylammonium salts to the receptor solution in either
CDCl3 or DMSO-d6 (0.008 M, 0.5 mL) in NMR tube. For F−, Cl−,
and Br− anions, the incremental amount is 1 μL (1 × 10−4 mmol, 0.1
AUTHOR INFORMATION
■
Corresponding Author
−
−
−
*E-mail: gmani@chem.iitkgp.ernet.in. Fax: +91 3222 282252.
equiv) from the 0.4 M stock solution. For HSO4 , H2PO4 , and NO3
anions, the incremental amount is 2 μL (4 × 10−4 mmol, 0.1 equiv)
from the 0.2 M stock solution. After each addition, the spectrum was
recorded and the NH resonance was monitored for calculating the
association constants Ka by the EQNMR program and other methods.
X-ray Crystallography. Suitable single crystals of 2a were grown
from a solution of 2a in dichloromethane/petroleum ether (v/v = 1:1)
upon slow evaporation at room temperature. Suitable single crystals of
3a and 4 were obtained by layering petroleum ether with a solution of
3a or 4 in dichloromethane. Suitable single crystals of 5, 6, and 7 were
obtained from their syntheses.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the CSIR and DST (New Delhi, India) for financial
support and for the X-ray and NMR facilities. We thank Dr.
Swadhin Mandal, Indian Institute of Science Education and
Research, Kolkata, for 19F NMR spectra.
6437
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(15) (a) Dietrich, B.; Lehn, J. -M.; Guilhem, J.; Pascard, C.
Tetrahedron Lett. 1989, 30, 4125−4128. (b) Reilly, S. D.; Khalsa, G. R.
K.; Ford, D. K.; Brainard, J. R.; Hay, B. P.; Smith, P. H. Inorg. Chem.
1995, 34, 569−575. (c) Dietrich, B.; Dilworth, B.; Lehn, J. -M.;
Souchez, J. -P.; Cesario, M.; Guilhem, J.; Pascard, C. Helv. Chim. Acta
1996, 79, 569−587.
REFERENCES
■
(1) (a) Sessler, J. L.; Gale, P. A.; Cho, W.-S. Anion Receptor
Chemistry; Royal Society of Chemistry: Cambridge, U.K., 2006.
(b) Bianchi, A.; Bowman-James, K.; García-Espana, E. Supramolecular
Chemistry of Anions; Wiley-VCH: New York, 1997. (c) Katayev, E. A.;
Ustynyuk, Y. A.; Sessler, J. L. Coord. Chem. Rev. 2006, 250, 3004−
3037.
̃
(16) (a) Lehn, J. -M.; Sonveaux, E.; Willard, A. K. J. Am. Chem. Soc.
1978, 100, 4914−4916. (b) Dietrich, B.; Guilhem, J.; Lehn, J.-M.;
Pascard, C.; Sonveaux, E. Helv. Chim. Acta 1984, 67, 91−104.
(17) (a) Bucher, C.; Zimmerman, R. S.; Lynch, V.; Sessler, J. L. J. Am.
Chem. Soc. 2001, 123, 9716−9717. (b) Bucher, C.; Zimmerman, R. S.;
Lynch, V.; Sessler, J. L. Chem. Commun. 2003, 1646−1647. (c) Cafeo,
G.; Colquhoun, H. M.; Cuzzola, A.; Gattuso, M.; Kohnke, F. H.;
Valenti, L.; White, A. J. P. J. Org. Chem. 2010, 75, 6263−6266.
(d) Setsune, J.; Watanabe, K. J. Am. Chem. Soc. 2008, 130, 2404−2405.
(e) Fox, O. D.; Rolls, T. D.; Drew, M. G. B.; Beer, P. D. Chem.
Commun. 2001, 1632−1633. (f) Francesconi, O.; Ienco, A.; Moneti,
G.; Nativi, C.; Roelens, S. Angew. Chem., Int. Ed. 2006, 45, 6693−6696.
(18) (a) Mani, G.; Jana, D.; Kumar, R.; Ghorai, D. Org. Lett. 2010,
12, 3212−3215. (b) Mani, G.; Guchhait, T.; Kumar, R.; Kumar, S. Org.
Lett. 2010, 12, 3910−3913. (c) Kumar, R.; Guchhait, T.; Mani, G.
Inorg. Chem. 2012, 51, 9029−9038.
(2) (a) Pflugrath, J. W.; Quiocho, F. A. Nature 1985, 314, 257−260.
(b) Pflugrath, J. W.; Quiocho, F. A. J. Mol. Biol. 1988, 200, 163−180.
(3) (a) Moyer, B. A.; Custelcean, R.; Hay, B. P.; Sessler, J. L.;
Bowman-James, K.; Day, V. W.; Kang, S.-O. Inorg. Chem. 2013, 52,
3473−3490. (b) Moyer, B. A.; Delmau, L. H.; Fowler, C. J.; Ruas, A.;
Bostick, D. A.; Sessler, J. L.; Katayev, E.; Pantos, G. D.; Llinares, J. M.;
Hossain, M. A.; Kang, S. O.; Bowman-James, K. Advances in Inorganic
Chemistry; Academic Press: New York, 2006; Vol 59, pp 175−204.
(4) Bazzicalupi, C.; Bencini, A.; Lippolis, V. Chem. Soc. Rev. 2010, 39,
3709−3728.
(5) Hughes, M. F. Toxicol. Lett. 2002, 133, 1−16.
(6) (a) Nordstrom, D. K. Water Sci. 2002, 296, 2143−2144.
(b) Greven, M.; Green, S.; Robinson, B.; Clothier, B.; Vogeler, I.;
Agnew, R.; Neal, S.; Sivakumaran, S. Water Sci. Technol. 2007, 56,
161−168.
́
(19) (a) Mateus, P.; Delgado, R.; Brandao, P.; Carvalcho, S.; Felix, V.
̃
(7) Yusof, A. M.; Malek, N. A. N. N. J. Hazard. Mater. 2009, 162,
1019−1024.
Org. Biomol.Chem. 2009, 7, 4661−4673. (b) Bazzicalupi, C.; Bencini,
A.; Puccioni, S.; Valtancoli, B.; Gratteri, P.; Garau, A.; Lippolis, V.
Chem. Commun. 2012, 48, 139−141. (c) Tobey, S. L.; Jones, B, D.;
Anslyn, E. V. J. Am. Chem. Soc. 2003, 125, 4026−4027. (d) Mendy, J.
S.; Pilate, M. L.; Horne, T.; Day, V. W.; Hossain, M. A. Chem.
(8) (a) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486−
516. (b) Wenzel, M.; Hiscock, J. R.; Gale, P. A. Chem. Soc. Rev. 2012,
41, 480−520. (c) Bowman-James, K. Acc. Chem. Res. 2005, 38, 671−
678. (d) McKee, V.; Nelson, J.; Town, R. M. Chem. Soc. Rev. 2003, 32,
309−325. (e) Choi, K.; Hamilton, A. D. Coord. Chem. Rev. 2003, 240,
101−110. (f) Filby, M. H.; Steed, J. W. Coord. Chem. Rev. 2006, 250,
3200−3218. (g) Joyce, L. A.; Shabbir, S. H.; Anslyn, E. V. Chem. Soc.
Rev. 2010, 39, 3621−3632. (h) Dydio, P.; Lichosyt, D.; Jurczak, J.
Chem. Soc. Rev. 2011, 40, 2971−2985. (i) Hargrove, A. E.; Nieto, S.;
Zhang, T.; Sessler, J. L.; Anslyn, E. V. Chem. Rev. 2011, 111, 6603−
6782. (j) Gale, P. A. Chem. Commun. 2011, 47, 82−86.
Commun. 2010, 46, 6084−6086. (e) Mateus, P.; Delgado, R.; Brandao,
̃
́
P.; Felix, V. J. Org. Chem. 2009, 74, 8638−8646. (f) Yin, Z.; Zhang, Y.;
He, J.; Cheng, J.-P. Tetrahedron 2006, 62, 765−770. (g) Bazzicalupi,
C.; Bencini, A.; Giorgi, C.; Valtancoli, B.; Lippolis, V.; Perra, A. Inorg.
Chem. 2011, 50, 7202−7216. (h) Custelcean, R.; Bock, A.; Moyer, B.
A. J. Am. Chem. Soc. 2010, 132, 7177−7185. (i) Dey, S. K.; Das, G.
Dalton Trans. 2012, 41, 8960−8972.
(20) Saeed, M. A.; Fronczek, F. R.; Hossain, M. A. Chem. Commun.
2009, 6409−6411.
(9) (a) Schmidtchen, F. P.; Berger, M. Chem. Rev. 1997, 97, 1609−
1646. (b) Schmidtchen, F. P. Chem. Soc. Rev. 2010, 39, 3916−3935.
(c) Kubik, S. Chem. Soc. Rev. 2010, 39, 3648−3663.
(21) Hynes, M. J. J. Chem. Soc., Dalton Trans. 1993, 311−312.
(22) (a) Kang, S. O.; VanderVelde, D.; Powell, D.; Bowman-James,
K. J. Am. Chem. Soc. 2004, 126, 12272−12273. (b) Wang, Q.-Q.; Day,
V. W.; Bowman-James, K. J. Am. Chem. Soc. 2013, 135, 392−399.
(c) Chmielewski, M. J.; Jurczak, J. Chem.Eur. J. 2005, 11, 6080−
6094.
(10) (a) Kubik, S.; Kirchner, R.; Nolting, D.; Seidel, J. J. Am. Chem.
Soc. 2002, 124, 12752−12760. (b) Kubik, S.; Goddard, R.; Kirchner,
R.; Nolting, D.; Seidel, J. Angew. Chem., Int. Ed. 2001, 40, 2648−2651.
(11) (a) Fowler, C. J.; Haverlock, T. J.; Moyer, B. A.; Shriver, J. A.;
Gross, D. E.; Marquez, M.; Sessler, J. L.; Hossain, M. A.; Bowman-
James, K. J. Am. Chem. Soc. 2008, 130, 14386−14387. (b) Moyer, B.
A.; Sloop, F. V., Jr.; Fowler, C. J.; Haverlock, T. J.; Kanga, H.-A.;
Delmau, L. H.; Bau, D. M.; Hossain, M. A.; Bowman-James, K.;
Shriver, J. A.; Bill, N. L.; Gross, D. E.; Marquez, M.; Lynch, V. M.;
Sessler, J. L. Supramol. Chem. 2010, 22, 653−671.
(23) Yang, L.-Z.; Li, Y.; Jiang, L.; Feng, X.-L.; Lu, T.-B.
CrystEngComm 2009, 11, 2375−2380.
(24) (a) Nation, D. A.; Reibenspies, J. H.; Martell, A. E. Inorg. Chem.
1996, 35, 4597−4603. (b) Kral, V.; Furuta, H.; Shreder, K.; Lynch, V.;
Sessler, J. L. J. Am. Chem. Soc. 1996, 118, 1595−1607. (c) Bianchi, A.;
Escuder, B.; Fusi, V.; Garcia-Espana, E.; Giorgi, G.; Marcelino, V.;
̃
(12) Kim, Y.; Gabbaï, F. P. J. Am. Chem. Soc. 2009, 131, 3363−3369.
(13) (a) Dietrich, B.; Viout, P.; Lehn, J. -M. Macrocyclic Chemistry;
VCH: Weinheim, Germany, 1993. (b) Amendola, V.; Fabbrizzi, L.;
Mangano, C.; Pallavicini, P.; Poggi, A.; Taglietti, A. Coord. Chem. Rev.
2001, 219−221, 821−837. (c) Ballester, P. Chem. Soc. Rev. 2010, 39,
3810−3830. (d) Kang, S. O.; Llinares, J. M.; Day, V. W.; Bowman-
James, K. Chem. Soc. Rev. 2010, 39, 3980−4003. (e) Fabbrizzi, L. Top.
Curr. Chem. 2012, 323, 127−166. (f) Guchhait, T.; Mani, G. J. Org.
Chem. 2011, 76, 10114−10121. (g) Guchhait, T.; Mani, G.; Schulzke,
C.; Anoop, A. Inorg. Chem. 2012, 51, 11635−11644.
(14) (a) Amendola, V.; Bonizzoni, M.; Esteban-Gomez, D.; Fabbrizzi,
L.; Licchelli, M.; Sancenon, F.; Taglietti, A. Coord. Chem. Rev. 2006,
250, 1451−1470. (b) Kang, S. O.; Hossain, M. A.; Powell, D.;
Bowman-James, K. Chem. Commun. 2005, 328−330. (c) Das, M. C.;
Ghosh, S. K.; Bharadwaj, P. K. Dalton Trans. 2009, 6496−6506.
(d) Mateus, P.; Delgado, R.; Groves, P.; Campos, S. R. R.; Baptista, A.
Paoletti, P.; Valtancoli, B. J. Am. Chem. Soc. 1999, 121, 6807−6815.
(d) Gerasimchuk, O. A.; Mason, S.; Llinares, J. M.; Song, M. P.;
Alcock, N. W.; Bowman-James, K. Inorg. Chem. 2000, 39, 1371−1375.
(e) Saeed, M. A.; Pramanik, A.; Hossain, M. A. Inorg. Chem. Commun.
2012, 21, 32−34.
(25) Farrell, D.; Harding, C. J.; McKee, V.; Nelson, J. Dalton Trans.
2006, 3204−3211.
(26) Fanchon, E.; Vicat, J.; Qui, D. T.; Boudjada, A. Acta Crystallogr.,
Sect. C 1987, 43, 1022−1025.
(27) Mahler, J.; Persson, I.; Herbert, R. B. Dalton Trans. 2013, 42,
̈
1364−1377.
(28) Hseu, T. H.; Lu, T. H. Acta Crystallogr., Sect. B 1977, 33, 3947−
3949.
(29) Tawfik, D. S.; Viola, R. E. Biochemistry 2011, 50, 1128−1134.
(30) Hossain, M. A.; Llinares, J. M.; Miller, C. A.; Seib, L.; Bowman-
James, K. Chem. Commun. 2000, 2269−2270.
(31) Custelcean, R.; Sellin, V.; Moyer, B. A. Chem. Commun. 2007,
1541−1543.
(32) Ursu, A.; Schmidtchen, F. P. Angew. Chem., Int. Ed. 2012, 51,
242−246.
M.; Brandao, P.; Fel
́
ix, V. J. Org. Chem. 2012, 77, 6816−6824.
(e) Arunachalam, M.; Suresh, E.; Ghosh, P. Tetrahedron 2007, 63,
ix, V. J.
̃
11371−11376. (f) Mateus, P.; Delgado, R.; Brandao, P.; Fel
́
̃
Org. Chem. 2012, 77, 4611−4621. (g) Chen, D.; Martell, A. E.
Tetrahedron 1991, 47, 6895−6902.
6438
dx.doi.org/10.1021/ic400319b | Inorg. Chem. 2013, 52, 6427−6439

Inorganic Chemistry
Article
(33) Shi, Y.; Cao, C.; Odom, A. L. Inorg. Chem. 2004, 43, 275−281.
(34) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. J.
Appl. Crystallogr. 1993, 26, 343−350.
(35) (a) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.
(b) Farrugia, L. J. Appl. Crystallogr. 1999, 32, 837−838.
(36) van der Sluis, P.; Spek, A. L. Acta Crystallogr., Sect. A 1990, 46,
194−201.
6439
dx.doi.org/10.1021/ic400319b | Inorg. Chem. 2013, 52, 6427−6439