Azacalix[7]arene heptamethyl ether: Preparation, nanochannel crystal structure, and selective adsorption of carbon dioxide

Article abstract of DOI:10.1021/jo801543z

(Figure Presented) To investigate the solid-state complexation of nitrogen-bridged calixarene analogues, azacalix[7]arene heptamethyl ether 1 has been prepared by applying a 5 + 2 -fragment coupling approach using Buchwald-Hartwig aryl amination reaction aided by our previously devised temporal N-silylation protocol. X-ray crystallographic analysis revealed that azacalix[7]arene 1 adopted a highly distorted 1,2-alternate conformation in the solid state as a result of intramolecular NH/O hydrogen bonding interactions and steric repulsion between the methoxy groups. In the crystal, molecules of 1 are mutually interacted by intermolecular NH/O and CH/π interactions to establish one-dimensional (1D) hexane-filled nanochannel crystal architecture. Similarly to our recently reported azacalix[6]arene 2, the desolvated crystalline powder material of 1 was capable of selectively and rapidly adsorbing CO₂ among the four main components of the atmosphere. The adsorption capacity of 1 for CO₂ nearly doubled as compared to that of 2 because of the formation of the 1D nanochannel with almost twice the volume of the latter.

Full text of DOI:10.1021/jo801543z

Azacalix[7]arene Heptamethyl Ether: Preparation, Nanochannel
Crystal Structure, and Selective Adsorption of Carbon Dioxide†
Hirohito Tsue,* Kazuhiro Matsui, Koichi Ishibashi, Hiroki Takahashi, Satoshi Tokita,
Kohei Ono, and Rui Tamura
Graduate School of Human and EnVironmental Studies, Kyoto UniVersity,
Sakyo-ku, Kyoto 606-8501, Japan
tsue@ger.mbox.media.kyoto-u.ac.jp
ReceiVed July 14, 2008
To investigate the solid-state complexation of nitrogen-bridged calixarene analogues, azacalix[7]arene
heptamethyl ether 1 has been prepared by applying a “5 + 2”-fragment coupling approach using
Buchwald-Hartwig aryl amination reaction aided by our previously devised temporal N-silylation protocol.
X-ray crystallographic analysis revealed that azacalix[7]arene 1 adopted a highly distorted 1,2-alternate
conformation in the solid state as a result of intramolecular NH/O hydrogen bonding interactions and
steric repulsion between the methoxy groups. In the crystal, molecules of 1 are mutually interacted by
intermolecular NH/O and CH/π interactions to establish one-dimensional (1D) hexane-filled nanochannel
crystal architecture. Similarly to our recently reported azacalix[6]arene 2, the desolvated crystalline powder
material of 1 was capable of selectively and rapidly adsorbing CO2 among the four main components of
the atmosphere. The adsorption capacity of 1 for CO2 nearly doubled as compared to that of 2 because
of the formation of the 1D nanochannel with almost twice the volume of the latter.
Introduction
chemistry, in that solid-gas adsorption phenomenon has entered
as a new research area in the host-guest study of calixarenes
with the intention of achieving selective gas recognition, storage,
and separation. Indeed, Atwood and Barbour demonstrated that
p-tert-butylcalix[n]arenes (n ) 4 and 5) were capable of
efficiently adsorbing gaseous molecules on the apparently
nonporous crystals under ambient conditions,5 where the calix-
arenes exhibited greater adsorption ability as compared to those
of metal-organic frameworks (MOFs) and carbon nanotubes.5i
Similar gas adsorption behavior was observed for other
calix[4]arene derivatives in which tert-pentyl and tert-octyl
groups were introduced onto the upper rim.5e
Over the past decades calixarenes have been playing an
important role as a molecular receptor in host-guest chemistry
because of their versatile ability to form inclusion complexes
with a variety of organic and inorganic guests species.1-4 An
accumulated diverse knowledge on the host-guest chemistry
of calixarenes in solution phase renders them further intriguing,
coupled with their ease of synthesis and derivatization. Recently,
there has been a marked development in the calixarene
† This paper is dedicated to Professor Yoshiteru Sakata on the occasion of
his 70th birthday.
(1) (a) Gutsche, C. D. Calixarenes; Stoddart, J. F., Ed.; The Royal Society
of Chemistry: Cambridge, U.K., 1989. (b) Gutsche, C. D. Calixarenes ReVisited;
Stoddart, J. F., Ed.; The Royal Society of Chemistry: Cambridge, U.K., 1998.
(2) Calixarenes: A Versatile Class of Macrocyclic Compounds; Vicens, J.,
Bo¨hmer, V., Eds.; Kluwer: Dordrecht, The Netherlands, 1991.
(3) Calixarenes 2001; Asfari, Z., Bo¨hmer, V., Harrowfield, J., Vicens, J.,
Saadioui, M., Eds.; Kluwer: Dordrecht, The Netherlands, 2001.
(4) For a review on calix 7arene derivatives, see: Martino, M.; Neri, P. Mini-
ReV. Org. Chem. 2004, 1, 219.
7748 J. Org. Chem. 2008, 73, 7748–7755
10.1021/jo801543z CCC: $40.75 2008 American Chemical Society
Published on Web 08/23/2008

Azacalix[7]arene Heptamethyl Ether
Very recently, we found that solid-gas adsorption was also
feasible by a calixarene analogue involving nitrogen atoms as
the bridging units.6,7 After desolvation of the hexane clathrate
of azacalix[6]arene 2, the resultant crystalline powder material
exhibited selective and rapid uptake of CO2 among the four
main gaseous components of the atmosphere. The adsorption
capacity of 2 for CO2 was comparable to or somewhat poorer
than those of MOFs8 and zeolites,9 which similarly exhibited
the selective adsorption of CO2. In contrast, smaller azacalix[4]-
arene 310,11 gave rise to no uptake of CO2 in the solid state.
These foregoing experimental findings naturally compelled us
to prepare a larger homologue. In the present study, to gain a
deeper insight into the solid-gas adsorption behavior of this
molecular system, we have synthesized azacalix[7]arene hep-
tamethyl ether 1 with a larger ring size than in 2 and 3. As in
the case of 2, selective and rapid adsorption of CO2 was
observed on the desolvated crystalline powder material of 1,
which was obtained from the single crystals of the hexane
clathrate with a 1:2 host-guest ratio. To our knowledge, the
present X-ray crystallographic analysis of 1 has provided the
second instance12 of solid-state structure in nitrogen-bridged
calix[7]arene analogues reported to date.12,13 More interestingly,
it was also found that adsorption capacity of 1 for CO2 was
almost twice as much as that of 2. In this paper, we report the
synthesis, crystal structure, and solid-gas adsorption behavior
of azacalix[7]arene 1.
Results and Discussion
Synthesis. Preparation of azacalix[7]arene 1 was accom-
plished by using a convergent “5 + 2”-fragment coupling
approach shown in Scheme 1. The “5”-fragment 10 was
prepared according to our described procedure,14 whereas the
“2”-fragment 9 was newly synthesized via the following six
reaction steps. Starting from hydrazine reduction of nitroanisole
4
15 in 94% yield, the resultant aniline 5 was treated with Boc2O
to give monoprotected aniline 6 in 99% yield. Buchwald-Hartwig
aryl amination reaction16 of 6 and monoprotected m-phenylene-
diamine 710 smoothly proceeded to furnish dimer 8 in 92% yield.
The 2-fragment 9 was finally prepared by the additional
protection of the terminal amino groups of 8 with Boc2O in the
presence of DMAP, followed by the N-benzylation of the
bridging nitrogen atom and by the removal of all Boc groups
with TFA. Buchwald-Hartwig aryl amination reaction using a
temporal N-silylation protocol17 was applied to the ring-closing
reaction of 5-fragment 10 with 2-fragment 9. From this
macrocyclization reaction, regioselectively pentabenzylated
azacalix[7]arene 11 was obtained in 33% yield through the in
situ N,N′-bissilylation of 2-fragment 9 with dimethylphenylsilyl
chloride (DMPSCl) in the presence of t-BuONa, followed by
the one-pot Pd(0)-catalyzed aryl amination reaction with 5-frag-
ment 10 and by the subsequent cleavage of N-Si bond in the
workup process. As a final step, all the N-benzyl groups of 11
were deprotected by hydrogenolysis using 10% Pd(OH)2/C as
a catalyst to afford azacalix[7]arene 1 in 89% yield. HRMS,
1H NMR, 13C NMR, FT IR, elemental analysis, and X-ray
crystallographic analysis fully characterized the structure of this
new azacalix[7]arene 1.
Crystal Structure. A single crystal of 1 was obtained by
slow crystallization from hexane involving a few drops of
CH2Cl2. Azacalix[7]arene 1 crystallizes with two molecules of
hexane and adopts a highly distorted 1,2-alternate conformation
in the solid state, as shown in Figure 1. As a result of
intramolecular NH· · ·OMe hydrogen bonding interactions, the
aromatic rings A, B, C, D, and E are directed upward with
respect to the mean plane defined by all of the bridging nitrogen
atoms, whereas the remaining aromatic rings F and G are
directed downward. The observed nonsymmetry of 1 is much
different from our previously reported azacalix[6]arene 2 with
S2 symmetry in the solid state,6 though both compounds involve
essentially the same type of intramolecular NH/O hydrogen
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J. Org. Chem. Vol. 73, No. 19, 2008 7749

Tsue et al.
SCHEME 1. Preparation of Azacalix[7]arene 1a
a DPEphos ) bis[2-(diphenylphosphino)phenyl] ether.18
symmetry of 1. As a result, the molecular structure of 1 in the
solid state is controlled not only by intramolecular NH/O
hydrogen bonding interactions but also by the inevitable collapse
of the favorable alternate arrangement of the methoxy groups.
Of seven NH hydrogens of 1, six are involved in the formation
of intramolecular NH/O hydrogen bonds, whereas the remaining
one at N(2) atom takes part in the formation of intermolecular
hydrogen bonds mentioned below.
Also interesting is the crystal packing characterized by
hexane-filled one-dimensional (1D) nanochannel crystal archi-
tecture shown in Figure 2. In the crystal, each azacalix[7]arene
1 is mutually interacted with adjacent molecules by intermo-
lecular NH · · ·OMe hydrogen bonds formed between the bridg-
ing nitrogen atoms N(2) and the methoxy groups of the aromatic
ring E belonging to the neighboring molecule (type R, N· · ·O,
3.05 Å; NH · · ·O, 2.29 Å and 148.1°), as depicted in Figure 3a.
By virtue of the intermolecular NH/O hydrogen bonds, a 1D
chain structure is formed along the crystallographic b axis in
an antiparallel direction. Besides, the 1D chains interact with
each other by intermolecular CH/π interactions formed between
the methoxy groups located on the rings C and the centroid of
the rings F belonging to the nearest molecules (type ꢀ,
C · · · centroid 3.47 Å, CH · · · centroid 2.73 Å and 133.1°), as
shown in Figure 3b. As a consequence of the intermolecular
NH/O and CH/π interactions, a two-dimensional (2D) sheet
structure of 1 is eventually formed on the bc plane, as
schematically illustrated in Figure 3c. In the 2D sheet structure,
each molecular assembly comprising six molecules of 1 creates
an interstitial pore (465 Å3), in which four molecules of hexane
are embedded. As a result, the hexane-filled 2D sheet structure
is stacked along the a axis to form the 1D nanochannel crystal
architecture of the hexane clathrate of 1 with a 1:2 host-guest
FIGURE 1. ORTEP drawing19 of azacalix[7]arene 1. The displacement
ellipsoids are drawn at the 50% probability level. Solvent molecules
and all hydrogen atoms but for the bridging NH groups are omitted
for clarity. Numbers indicate O· · ·H distances (Å) of intramolecular
NH· · ·OMe hydrogen bonds.
bonds. A conclusive difference between 1 and 2 is the spatial
arrangements of the methoxy groups. In azacalix[6]arene 2, each
methoxy group is always oriented to the opposite direction from
the neighboring ones to avoid steric hindrance between them.
This is also the case for azacalix[4]arene 3 with apparent D2d
symmetry in the crystal.10 In contrast, such regularly alternating
arrangement of the methoxy groups is fundamentally unfeasible
in azacalix[7]arene 1 because of the presence of an odd number
of methoxy groups. In fact, the aromatic ring E of 1 is fluctuated
to avoid the close proximity of the methoxy groups attached to
the aromatic rings D and E, thereby lowering the molecular
(19) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
7750 J. Org. Chem. Vol. 73, No. 19, 2008

Azacalix[7]arene Heptamethyl Ether
FIGURE 2. Crystal structure of the hexane clathrate of azacalix[7]arene
1 viewed along the crystallographic a axis. Molecules of azacalix[7]arene
1 and hexane are represented by stick and space-filling models,
respectively. Hydrogen atoms except for those of nondisordered hexane
are omitted for clarity. Hydrogen atoms of disordered hexane are not
included in the crystallographic calculation.
ratio, as shown in Figure 2. Azacalix[6]arene 2 also forms a
similar hexane-filled 1D nanochannel crystal structure,6 but the
interstitial void space of 1 is almost twice as large as that of
2 (208 Å3) because the highly distorted conformation of 1
(Figure 1) probably leads to the less efficient packing in the
crystal than 2.
Solid-Gas Adsorption Behavior. For the sake of desolva-
tion, single crystals of the hexane clathrate of 1 were heated at
30 °C for 24 h under reduced pressure. As shown in Figure 4b,
no 1H NMR signal of hexane was observed after the desolvation
procedure, indicating the complete escape of the molecules of
hexane from the single crystals of 1. After desolvation, however,
the hexane clathrate of 1 lost the single crystallinity and turned
to crystalline powder 1P. The letter “P” is used below to
represent the solvent-free powder material obtained from the
single crystals of the hexane clathrate of 1.
To gain an insight into the crystallographic aspect of 1P, the
synchrotron powder X-ray diffraction (XRD) data was collected
at the BL02B2 beamline of the Super Photon Ring (SPring-8,
Hyogo, Japan).20 The crystal structure of 1P could not be solved
from the XRD pattern at this moment, but the lattice parameters
of 1P were found to be almost identical to those of the hexane
clathrate of 1, as summarized in Table 1. This essential
agreement is clearly reflected in the XRD pattern of 1P (Figures
5a and S13 in Supporting Information), which displays a
dissimilarity to that simulated from the X-ray crystallographic
data of the hexane clathrate of 1 (Figure 5b) but a similarity to
that simulated from the imaginary crystal structure simply
created by deleting the atomic coordinates of hexane from the
crystallographic data of the hexane clathrate (Figure 5c).
Furthermore, FT IR measurement of 1P revealed no appreciable
changes in the NH-stretching, NH-bending, and CN-stretching
bands even after the loss of single crystallinity (Figure 6),
FIGURE 3. Crystal structure of the hexane clathrate of azacalix[7]arene
1 viewed along (a) the c axis and (b) the b axis. The carbon, nitrogen,
and oxygen atoms are represented by open, shaded, and closed circles,
respectively. The two-dimensional structure on the bc plane is
schematically illustrated in panel (c), where the aromatic rings from A
to G are represented by closed circles with lettering. For clarity, only
the functional groups are depicted that are involved in the formation
of intermolecular NH/O and CH/π interactions. Panel c schematically
illustrates the arrangement of the molecules in the unit cell shown in
Figure 2.
suggesting that the 1D nanochannel structure shown in Figure
2 remained almost unchanged in 1P. From these experimental
facts, it is conceivable that, upon heating the single crystals of
the hexane clathrate of 1, molecules of hexane escape through
the 1D nanochannel almost keeping the intra- and intermolecular
(20) Nishibori, E.; Takata, M.; Kato, K.; Sakata, M.; Kubota, Y.; Aoyagi,
S.; Kuroiwa, Y.; Yamakata, M.; Ikeda, N. J. Phys. Chem. Solids 2001, 62, 2095.
J. Org. Chem. Vol. 73, No. 19, 2008 7751

Tsue et al.
FIGURE 4. 1H NMR spectra taken in CDCl3 (a) before and (b) after
heating the single crystals of the hexane clathrate of azacalix[7]arene
1 at 30 °C for 24 h under reduced pressure.
TABLE 1. Crystallographic Data of Desolvated Crystalline
Powder 1P and the Single Crystal of the Hexane Clathrate of 1
1P
1 ·2hexane
crystal system
space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c
monoclinic
P21/c
17.879
24.487
19.198
103.030
8189
18.458(1)
24.536(2)
19.523(1)
101.494(2)
8664(1)
ꢀ (deg)
V (Å3)
FIGURE 5. (a) Synchrotron powder X-ray diffraction (XRD) pattern
of desolvated crystalline powder 1P. (b) XRD pattern simulated from
the X-ray crystallographic data of the hexane clathrates of 1. (c) XRD
pattern simulated from the imaginary crystal structure simply created
by deleting the atomic coordinates of hexane from the crystallographic
data of the hexane clathrate of 1.
NH/O hydrogen bonding interactions as well as the intermo-
lecular CH/π-interactions.
To examine the ability of 1P as a nanoporous material,
adsorption experiments for gaseous molecules were carried out.
According to the described procedure,5c adsorption isotherms
for the four main atmospheric components such as N2, O2, Ar,
and CO2 were recorded at room temperature and 195 K on the
desolvated powder 1P. The initial pressure was set to ca. 100
kPa in all adsorption experiments. As shown in Figure 7a, almost
no uptake was observed for all of the examined gases at room
temperature. In contrast, CO2 was rapidly and selectively
adsorbed on 1P at 195 K (Figure 7b), and the initial pressure
of ca. 100 kPa was decreased within 20 min to reach equilibrium
at 34 kPa, corresponding to the uptake of 3.0 mol of CO2 per
mol of 1 (i.e., 55 cm3 g-1 at standard temperature and pressure).
It is interesting to note that the observed adsorption capacity of
1P for CO2 is almost comparable to those of MOFs8 and
zeolites9 capable of selectively adsorbing CO2, though the
adsorption of CO2 on 1P only takes place at 195 K. It is also
noteworthy that the adsorption capacity of 1P for CO2 is nearly
twice as much as that of our recently reported azacalix[6]arene
2 (1.8 mol of CO2 per mole of 2)6 because the former creates
the 1D nanochannel with almost twice the volume of the latter.
Because the observed gas adsorption behavior of 1P at 195
K is essentially the same as that of 2 except for the adsorption
capacity, the selective and rapid uptake of CO2 by 1P at 195 K
can be interpreted by considering the following three factors,
as in the case of 2.6 The first is the molecular sieve effect based
on the difference in the kinetic diameters of the examined gases
such as N2 (3.64 Å), O2 (3.46 Å), Ar (3.40 Å), and CO2 (3.3
Å),21 the last of which is the smallest to ensure the easy diffusion
into the 1D nanochannel of 1P. The second is hydrogen bonding
interactions between the NH hydrogen atoms and CO2 molecules
diffused into the 1D nanochannel of 1P. This is parallel to our
previous experimental facts that both azacalix[4]arene 3 and
p-tert-butylcalix[6]arene hexamethyl ether give rise to almost
no uptake of CO2 even at 195 K because of the lack of hydrogen
bonding sites, together with their densely packed crystal
structures.6,10 The third is the quadrupole/induced-dipole inter-
actions between CO2 and the surrounding aromatic “walls” built
along the 1D nanochannel of 1P, judging from the greater
quadrupole moment (absolute value)22 of CO2 (13.4 × 1040
C
(21) Breck, D. W. Zeolite Molecular SieVes; John Wiley & Sons: New York,
1974; pp 633-645.
(22) Steele, W. Chem. ReV. 1993, 93, 2355.
7752 J. Org. Chem. Vol. 73, No. 19, 2008

Azacalix[7]arene Heptamethyl Ether
Conclusions
We have demonstrated that azacalix[7]arene 1 can be prepared
by using a Pd(0)-catalyzed aryl amination reaction, together with
our previously devised temporal N-silylation protocol. X-ray
crystallographic analysis clearly revealed that conformation of
1 in the solid state was controlled by intramolecular NH/O
hydrogen bonding interactions and the inevitable collapse of
the favorable alternating arrangement of the methoxy groups.
In the crystal, molecules of 1 are mutually interacted by
intermolecular NH/O hydrogen bonding interactions as well as
the intermolecular CH/π-interactions to establish the infinite 1D
nanochannel crystal architecture of the hexane clathrate of 1
with a 1:2 host-guest ratio. As in the case of azacalix[6]arene
2, the desolvated powder 1P was capable of selectively and
rapidly adsorbing CO2 among the four main components of the
atmosphere. Because both azacalix[7]arene 1 and azacalix[6]arene
2 can selectively adsorb CO2 in the solid state, we anticipate
that their homologues with larger and/or smaller ring sizes may
do so similarly to 1 and 2. Investigations along this line are
under progress to gain a more profound insight into the dynamic
solid-state complexation of this molecular system.
Experimental Section
Palladium bis(benzylideneacetone) [Pd(dba)2],23 bis[2-(diphe-
nylphosphino)phenyl] ether (DPEphos),18 and compounds 4,14 7,10
and 1014 were prepared according to the described procedures.
3-Bromo-5-tert-butyl-2-methoxyaniline (5). A solution of 4
(11.5 g, 39.9 mmol), FeCl3 ·6H2O (569 mg, 2.11 mmol), and active
carbon (1.20 g) in MeOH (120 mL) was refluxed for 30 min. After
H2NNH2 ·H2O (10.3 g, 206 mmol) was added dropwise to the flask,
the mixture was heated under reflux for 1 h. The reaction mixture
was cooled to room temperature, passed through Celite, evaporated,
and extracted with CH2Cl2. The organic layer was washed with
saturated NaHCO3, dried over anhydrous K2CO3, filtered, and
evaporated. Flash column chromatography on silica gel (hexane/
CH2Cl2 ) 1:1, v/v) afforded 5 (9.71 g, 94%) as colorless solid, mp
FIGURE 6. FT IR spectra of (a) desolvated crystalline powder 1P and
(b) single crystals of the hexane clathrate of 1.
1
48-49 °C; H NMR (CDCl3, 500 MHz) δ 6.91 (d, J ) 2.1 Hz,
1H, Ar-H), 6.69 (d, J ) 2.1 Hz, 1H, Ar-H), 3.87 (br s, 2H, NH2),
3.82 (s, 3H, OMe), 1.26 (s, 9H, t-Bu); 13C NMR (125 MHz, CDCl3)
δ 149.1, 141.9, 140.5, 119.6, 116.5, 112.5, 59.5, 34.4, 31.2; IR
(KBr) 3480, 3368 (νN-H) cm-1. Anal. Calcd for C11H16BrNO: C,
51.18; H, 6.25; N, 5.43. Found: C, 51.14; H, 6.05; N, 5.47.
tert-Butyl (3-Bromo-5-tert-butyl-2-methoxyphenyl) Carbam-
ate (6). To a solution of 5 (2.58 g, 10.0 mmol) in t-BuOH (10 mL)
was added Boc2O (2.40 g, 11.0 mmol) in t-BuOH (5 mL). After
stirring for 3 h at room temperature, the reaction mixture was
evaporated and extracted with EtOAc. The organic layer was
washed with saturated NaHCO3, dried over anhydrous Na2SO4,
filtered, and evaporated. Flash column chromatography on silica
gel (hexane/CH2Cl2 ) 1:1, v/v) yielded 6 (3.55 g, 99%) as colorless
solid, mp 132-134 °C; 1H NMR (500 MHz, CDCl3) δ 8.10 (br s,
1H, NHBoc), 7.17 (d, 2H, J ) 1.8 Hz, Ar-H), 7.00 (br s, 2H,
Ar-H), 3.83 (s, 3H, OMe), 1.54 (s, 9H, t-Bu), 1.30 (s, 9H, t-Bu);
13C NMR (125 MHz, CDCl3) δ 152.8, 148.2, 138.3, 133.5, 131.4,
107.7, 106.5, 80.3, 59.3, 34.6, 31.4, 28.4; IR (KBr) 3428 (νN-H),
1730 (νCdO) cm-1. Anal. Calcd for C16H24BrNO3: C, 53.64; H, 6.75;
N, 3.91. Found: C, 53.38; H, 6.72; N, 3.86.
FIGURE 7. Gas adsorption isotherms recorded at (a) room temperature
and (b) 195 K for N2, O2, Ar, and CO2 using desolvated crystalline
powder 1P as adsorbent. Isotherms for N2, O2, Ar, and CO2 are shown
by green, black, blue, and red lines, respectively.
Di-tert-butyl [3,3′-Iminobis(5-tert-butyl-2-methoxyphenyl)] Di-
carbamate (8). A solution of 6 (2.16 g, 6.03 mmol), 7 (1.77 g,
6.00 mmol), Pd(OAc)2 (67.5 mg, 301 µmol), DPEphos (242.5 mg,
450 µmol), and t-BuONa (693 mg, 7.21 mmol) in anhydrous toluene
(12 mL) was stirred at 80 °C for 23 h under Ar. After cooling to
m2) than the other examined gases such as N2 (4.7 × 1040), O2
(1.3 × 1040), and Ar (0). As a result, it is conceivable that a
synergetic effect of these three factors is responsible for the
observed selective and rapid uptake of CO2 by 1P.
(23) Ukai, T.; Kawazura, H.; Ishii, Y.; Bonnet, J. J.; Ibers, J. A. J. Organomet.
Chem. 1974, 65, 253.
J. Org. Chem. Vol. 73, No. 19, 2008 7753

Tsue et al.
room temperature, the reaction mixture was passed through Celite,
evaporated, and dried in vacuo. Flash column chromatography on
silica gel (hexane/CH2Cl2 ) 1:2, v/v) gave 8 (3.14 g, 92%) as
3404 (νN-H) cm-1. Anal. Calcd for C112H135N7O7: C, 79.54; H, 8.05;
N, 5.80. Found: C, 79.24; H, 8.05; N, 5.71.
5,11,17,23,29,35,41-Hepta-tert-butyl-43,44,45,46,47,48,49-hep-
tamethoxy-2,8,14,20,26,32,38-heptaazacalix[7]arene (1). A solu-
tion of 11 (198 mg, 117 µmol) and 10% Pd(OH)2/C (220 mg) in
cyclohexane (25 mL) was stirred at room temperature for 2 days
under H2 (3.9 atm). The reaction mixture was passed through Celite
and evaporated. Flash column chromatography on silica gel (hexane/
EtOAc ) 4:1, v/v) furnished 1 (130 mg, 89%) as pale pink solid,
1
colorless solid, mp 124-125 °C; H NMR (500 MHz, CDCl3) δ
7.70 (br s, 2H, NHBoc), 7.05 (d, J ) 2.3 Hz, 2H, Ar-H), 6.96
(br s, 2H, Ar-H), 6.09 (br s, 1H, NH), 3.75 (s, 6H, OMe), 1.55 (s,
18H, t-Bu), 1.30 (s, 18H, t-Bu); 13C NMR (125 MHz, CDCl3) δ
152.8, 147.8, 135.8, 134.8, 131.7, 108.8, 108.6, 80.4, 60.1, 34.9,
31.4, 28.4; IR (KBr) 3431, 3387, 3358 (νN-H), 1728 (νCdO) cm-1
.
1
Anal. Calcd for C32H49N3O6 ·0.2H2O: C, 66.80; H, 8.65; N, 7.30.
mp 184-186 °C; H NMR (500 MHz, CDCl3) δ 6.90 (s, 14H,
Found: C, 66.67; H, 8.43; N, 7.30.
Ar-H), 6.40 (s, 7H, NH), 3.44 (s, 21H, OMe), 1.22 (s, 63H, t-Bu);
13C NMR (125 MHz, CDCl3) δ 147.0, 139.0, 138.0, 110.3, 60.0,
34.6, 31.4; IR (KBr) 3379 (νN-H) cm-1; MS (FD) m/z 1240 [M+];
HRMS (FD) m/z calcd for C77H105N7O7 1239.8075 [M+], found
1239.8047. Anal. Calcd for C77H105N7O7 ·hexane: C, 75.13; H, 9.09;
N, 7.39. Found: C, 74.95; H, 9.04; N, 7.09.
Bis(3-amino-5-tert-butyl-2-methoxyphenyl)-N-benzylamine (9).
To a solution of 8 (2.74 g, 4.80 mmol) and DMAP (120 mg 985
µmol) in anhydrous THF (50 mL) was added Boc2O (3.14 g, 14.4
mmol) in anhydrous THF (10 mL). The mixture was heated under
reflux for 15 h. After cooling to room temperature, the reaction
mixture was extracted with Et2O. The organic layer was washed
with saturated NaHCO3, dried over anhydrous K2CO3, filtered, and
evaporated. Flash column chromatography on silica gel (hexane/
EtOAc ) 4:1, v/v) afforded colorless solid. The solid was dissolved
in anhydrous DMF (15 mL), and 60% NaH (301 mg, 7.53 mmol)
was added at 0 °C under Ar. After stirring for 15 min, BnBr (884
mg, 5.63 mmol) was added. Stirring was continued at room
temperature for 5 h, and then CH2Cl2 was added to the reaction
mixture. The organic layer was washed with brine, dried over
anhydrous Na2SO4, filtered, and evaporated. To the resultant residue
CH2Cl2 (10 mL) and TFA (8 mL) were added, and the solution
was stirred at room temperature for 1.5 h. After cooling to 0 °C,
the reaction mixture was made basic to pH 11 with 5% aqueous
NaOH and extracted with CH2Cl2. The organic layer was dried over
anhydrous K2CO3, filtered, and evaporated. Flash column chroma-
tography on silica gel (hexane/EtOAc ) 4:1, v/v) afforded 9 (922
mg, 42%) as colorless solid, mp 158-159 °C; 1H NMR (500 MHz,
CDCl3) δ 7.38 (d, J ) 7.4 Hz, 2H, Ar-H), 7.24 (t, J ) 7.4 Hz,
2H, Ar-H), 7.15 (d, J ) 7.4 Hz, 1H, Ar-H), 6.51 (d, J ) 2.3 Hz,
2H, Ar-H), 6.45 (d, J ) 2.3 Hz, 2H, Ar-H), 4.86 (s, 2H, CH2Ph),
3.66 (br s, 4H, NH2), 3.54 (s, 6H, OMe), 1.17 (s, 18H, t-Bu); 13C
NMR (125 MHz, CDCl3) δ 146.7, 142.1, 139.9, 139.7, 139.1,
128.04, 128.01, 126.5, 112.1, 108.0, 59.0, 57.6, 34.3, 31.3; IR (KBr)
3449, 3428, 3327 (νN-H) cm-1. Anal. Calcd for C29H39N3O2 ·
0.3H2O: C, 74.56; H, 8.55; N, 8.99. Found: C, 74.45; H, 8.41; N,
8.89.
2,8,14,26,38-Pentabenzyl-5,11,17,23,29,35,41-hepta-tert-butyl-
43,44,45,46,47,48,49-heptamethoxy-2,8,14,20,26,32,38-heptaaz-
acalix[7]arene (11). A solution of 9 (46.5 mg, 101 µmol), 10 (141
mg, 101 µmol), t-BuONa (48.1 mg, 500 µmol), and dimethylphe-
nylsilyl chloride (DMPSCl) (38.1 mg, 223 µmol) in anhydrous
toluene (20 mL) was stirred at 80 °C under Ar. After stirring for
30 min, Pd(dba)2 (12.0 mg, 20.9 µmol) and 10 wt% t-Bu3P in
hexane (50 µL, 16.7 µmol) were added. A solution was refluxed
for 17 h and then cooled to room temperature. The reaction mixture
was passed through Celite and evaporated. Flash column chroma-
tography on silica gel (hexane/CH2Cl2 ) 1:1, v/v) gave 11 (56.9
mg, 33%) as colorless solid, mp 162-164 °C; 1H NMR (500 MHz,
CDCl3, 55 °C) δ 7.44 (d, J ) 7.3 Hz, 2H, Ar-H), 7.34 (d, J ) 7.3
Hz, 4H, Ar-H), 7.28s7.04 (m, 19H, Ar-H), 6.83 (d, J ) 2.1 Hz,
2H, Ar-H), 6.81 (d, J ) 1.8 Hz, 2H, Ar-H), 6.73 (d, J ) 2.1 Hz,
2H, Ar-H), 6.69 (d, J ) 2.1 Hz, 2H, Ar-H), 6.61 (br s, 2H,
Ar-H), 6.59 (br s, 2H, Ar-H), 6.58 (d, J ) 2.1 Hz, 2H, Ar-H),
5.95 (s, 2H, NH), 4.90 (s, 2H, CH2Ph), 4.87 (s, 4H, CH2Ph), 4.78
(s, 4H, CH2Ph), 3.41 (br s, 6H, OMe), 3.25 (br s, 6H, OMe), 3.15
(s, 6H, OMe), 3.13 (s, 3H, OMe), 1.16 (s, 18H, t-Bu), 1.11 (s,
18H, t-Bu), 1.01 (s, 18H, t-Bu), 0.98 (s, 9H, t-Bu); 13C NMR (125
MHz, CDCl3, 55 °C) δ 146.1, 145.9, 145.5, 145.1, 145.0, 143.5,
143.1, 142.4, 141.6, 140.2, 140.0, 139.9, 137.2, 136.9, 128.3,
128.12, 128.10, 128.0, 127.9, 127.8, 126.6, 126.5, 126.1, 116.93,
116.86, 115.9, 113.3, 113.0, 109.8, 59.3, 59.0, 58.7, 58.6, 57.8,
57.7, 56.6, 34.55, 34.49, 34.4, 34.4, 31.4, 31.3, 31.2, 31.1; IR (KBr)
Gas Adsorption Experiments. By reference to the literature of
Atwood and Barbour,5c essentially the same devise was constructed
to record solid-gas absorption isotherms of 1P at room temperature
and 195 K. The powder material 1P (25.45 mg) was placed in a
sample chamber, and then both sample and reference chambers
(each volume ) 2.0 cm3) were evacuated at 1 kPa for 1 h. After
the chambers were pressurized to ca. 100 kPa by the desired gas,
their internal pressures were monitored by using two pressure
transducers attached to each chamber. Adsorption equilibrium was
reached within 30 min, and the gas adsorption capacity was
estimated from the changes in pressure.
Synchrotron Powder Diffraction Experiment. Powder diffrac-
tion experiments were carried out at 93 ( 1 K on a large
Debye-Scherrer camera with synchrotron X-ray radiation (12.4 keV,
λ ) 0.99889 Å) at the BL02B2 beamline of the Super Photon Ring
(SPring-8, Hyogo, Japan).20 All calculations were performed by using
a software module Reflex Plus implemented in MS Modeling version
3.2.24 The XRD pattern of 1P was indexed by a software X-cell25
using 35 reflections (3.2° < 2θ < 12.9°). The resultant lattice
parameters were refined over the range of 2.5° < 2θ < 40° by the
Pawley method26 (Rp ) 0.012, Rwp ) 0.019); the observed and
simulated XRD patterns are shown in Figure S13. The space group
and cell parameters of 1P are summarized in Table 1.
X-ray Crystallographic Analysis. Measurement was made by
using graphite-monochromated Mo KR radiation (λ ) 0.71075 Å).
All the crystallographic calculations were performed by using a
crystallographic software package, CrystalStructure version 3.8.2.27
The crystal structure was solved by direct methods and refined by
full-matrix least-squares. All non-hydrogen atoms were refined
anisotropically, and hydrogen atoms were refined using the riding
model except for the bridging NH hydrogen atoms whose
positions were determined by D-Fourier synthesis. Crystal data
for 1 · 2hexane: Mr ) 1413.07, monoclinic, space group P21/c
(No. 14), a ) 18.458(1), b ) 24.536(2), c ) 19.523(1) Å, ꢀ )
101.494(2)°, V ) 8664(1) Å3, Z ) 4, Fcalc ) 1.083 g cm-3, µ )
0.679 cm-1, T ) 113(1) K, 18904 independent reflections, 975
refined parameters, R1 ) 0.1167 (I > 2σ(I)), wR2 ) 0.3759,
S ) 0.935. CCDC-692763 contains the supplementary crystal-
lographic data for this paper. The data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research (No. 19550037 to H.T.) from
the Ministry of Education, Culture, Sports, Science and
Technology, Japan. The synchrotron radiation experiment was
performed at the BL02B2 beamline of the SPring-8 with the
(24) MS Modeling, Version 3.2; Accelrys Inc.: San Diego, CA, 2004.
(25) Neumann, M. A. J. Appl. Crystallogr. 2003, 36, 356.
(26) Pawley, G. S. J. Appl. Crystallogr. 1981, 14, 357.
(27) CrystalStructure, Version 3.8.2; Rigaku and Rigaku Americas: The
Woodlands, TX, 2000-2007.
7754 J. Org. Chem. Vol. 73, No. 19, 2008

Azacalix[7]arene Heptamethyl Ether
approval of the Japan Synchrotron Radiation Research
Institute (JASRI) (Proposal No. 2008A1157). We are grateful
to the GC-MS and NMR Laboratory, Faculty of Agriculture,
Hokkaido University for FD MS measurements.
pattern of desolvated crystalline powder of azacalix[7]arene 1,
and a CIF file containing crystallographic data for the hexane
clathrate of 1. This material is available free of charge via the
Internet at http://pubs.acs.org.
Supporting Information Available: 1H and 13C NMR
spectra for all new compounds, synchrotron X-ray diffraction
JO801543Z
J. Org. Chem. Vol. 73, No. 19, 2008 7755