Strong binding affinity of a zinc-porphyrin-based receptor for halides through the cooperative effects of quadruple C-H hydrogen bonds and axial ligation

Article abstract of DOI:10.1002/chem.201101884

A new type of host compound (1), tetraphenyl zinc-porphyrin (ZnTPP) that contains four triazole groups at the ortho-position of each phenyl group, has been synthesized and characterized by using ¹H, ¹³C NMR, and MALDI-TOF-MS analyses

Full text of DOI:10.1002/chem.201101884

DOI: 10.1002/chem.201101884
Strong Binding Affinity of a Zinc–Porphyrin-Based Receptor for Halides
À
through the Cooperative Effects of Quadruple C H Hydrogen Bonds and
Axial Ligation
Chi-Hwa Lee, Sangeun Lee, Hongsik Yoon, and Woo-Dong Jang*[a]
Abstract: A new type of host com-
pound (1), tetraphenyl zinc–porphyrin
(ZnTPP) that contains four triazole
groups at the ortho-position of each
phenyl group, has been synthesized and
characterized by using 1H, 13C NMR,
and MALDI-TOF-MS analyses. The
host–guest complex formation between
1 and halides was investigated by using
1H NMR spectroscopy in [D6]DMSO.
The triazole, benzyl, and phenylene
proton signals were shifted upfield by
the addition of halides in the form of
tetrabutylammonium salts, which im-
plies that the triazole protons in 1 are
allocated very closely to the porphyrin
ring and are directed toward the bind-
ing pocket over the porphyrin ring
during the formation of hydrogen
bonds. The UV/Vis absorption spectra
showed that both the Soret and Q band
absorptions of 1 underwent a strong
redshift due to the addition of halides.
Compound 1 exhibited surprisingly
strong binding affinities for the halides,
where the association constants for
ClÀ, BrÀ, and IÀ binding were estimat-
ed to be larger than 108, 1.79ꢀ107, and
1.84ꢀ105 mÀ1, respectively. The UV/Vis
absorption changes and the result of
competitive titration using 4-tert-butyl-
pyridine indicated that the cooperative
À
effects of axial coordination and C
H···X hydrogen bond interactions re-
sulted in the strong binding affinity of
1 to halides.
Keywords: cooperative binding
·
halides · host–guest systems · hy-
drogen bonds · porphyrins
À
Introduction
ized conformation of C H hydrogen bonding donors in the
shape-persistent host compound.[6d] However, flexible tria-
zole oligomers have shown relatively weak binding affinities
compared with those of the rigid triazolophane, indicating
the importance of preorganization.[6h] Herein, we demon-
strate the significantly strong anion binding affinity of a por-
phyrin-based receptor containing four triazole units despite
its acyclic structure.
There has been considerable interest in the design of artifi-
cial anion-binding receptors because anions play very impor-
tant roles in chemical and biological events.[1] Various types
of artificial anion binding receptors with multiple hydrogen-
binding donors have been designed and extensively explored
their anion binding phenomena.[2] For example, indole- or
pyrrole-based macrocyles and foldamers have exhibited
strong binding affinities to anionic guests through multiple
[3]
À
À
N H···X hydrogen-bonding events. In addition, C H···X
hydrogen bonding has been a highlighted topic in recent
studies because this type of bonding is also very important
in the recognition of biological anions.[4] However, only a
Results and Discussion
Synthesis: A new type of host compound (1), tetraphenyl
zinc–porphyrin (ZnTPP) containing four triazole groups at
the ortho-position of each phenyl group, has been prepared
and characterized by using 1H, 13C NMR, and MALDI-
TOF-MS analyses. The synthesis procedure of 1 is summar-
ized in Scheme 1. Briefly, a Sonogashira coupling reaction
between 2-bromobenzaldehyde and TMS–acetylene was
conducted to obtain 3. Subsequently, an acid-catalyzed con-
densation reaction of 3 with pyrrole and a successive oxida-
tion reaction were performed. The addition of zinc acetate
to the reaction mixture introduced a zinc ion to the center
of the porphyrin unit to obtain 4. This reaction was followed
by TMS deprotection to give 5, which was used to react
with methyl-4-(azidomethyl)benzoate (7) using a CuI-cata-
lyzed alkyne-azide click reaction.[7] The formation of four
different atropisomers was expected in the preparation of
porphyrins.[8] However, a successful separation method for
each atropisomer for 4 and 5 using conventional column
À
few examples of C H···X hydrogen bonding have been dem-
onstrated in artificial receptors.[5] In pioneering work, Flood
et al. recently reported that macrocyclic triazolophanes and
À
triazole-based foldamers exhibit C H···X hydrogen bonding
interactions that are strong enough to form a stable host–
guest complex.[6] In particular, macrocyclic triazolophane ex-
hibited unexpectedly large association constants to anionic
guests (1.1ꢀ107 mÀ1 for ClÀ in CH2Cl2) due to the preorgan-
[a] C.-H. Lee, S. Lee, H. Yoon, W.-D. Jang
Department of Chemistry
College of Science, Yonsei University
50 Yonsei-ro, Seodaemun-gu, Seoul 120-749 (Korea)
Fax : (+82)2-364-7050
E-mail: wdjang@yonsei.ac.kr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101884.
13898
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 13898 – 13903

FULL PAPER
For the mixture of 1 with ClÀ or BrÀ salt, the major intense
signals appeared at 1575.14 and 1619.12 Dalton, correspond-
ing to molecular weight of the [1+Cl]À and [1+Br]À, respec-
tively, indicating the high stability of ClÀ or BrÀ complex of
1.
1
1H NMR spectroscopy: H NMR studies have been carried
out in [D]6DMSO. The triazole proton signals in 1 appeared
at a quite strong upfield region (5.5 ppm) compared with
those of the general triazoles, indicating that the triazole
proton was located on the porphyrin ring and was influ-
enced by the porphyrin ring current effect. Figure 2 shows
Scheme 1. Synthesis of 1. Reagents and conditions: i) [Pd
CuI, TMS–acetylene, Et3N/THF, 508C, 16 h; ii) pyrrole, TFA, CH2Cl2,
258C, 12 h; iii) p-chloranil, 258C,4 h; iv) Zn(OAc)2, CH2Cl2/MeOH,
ACHTUGNERTN(NUNG PPh3)2Cl2],
Figure 2. Simplified chemical structures of amido- or urea-type picket
porphyrin and 1.
AHCTUNGTRENNUNG
258C, 1 h; v) tetrabutylammonium fluoride, CH2Cl2, 258C, 30 min; vi)
NaN3, acetone/H2O, 25 8C, 30 min; vii) 6, CuSO4·5H2O, sodium ascorbate,
THF/H2O, 50 8C, 12 h.
simplified chemical structures of amido- or urea-type picket
porphyrin and 1. It is noteworthy that 1 has an additional
À
À
C C bond between the hydrogen-bond donating triazole C
H group and phenyl ring in ZnTPP when it compared with
amido- or urea-type picket porphyrins. Considering the ad-
chromatography could not be established. After the click re-
action, the aaaa-atropisomer (1) was perfectly separated as
the major product from the reaction mixture using silica
column chromatography.
À
ditional C C bond, hydrogen-bonding donors in 1 are signif-
icantly closer to the porphyrin ring than other amido- or
À
urea-type picket porphyrins. Furthermore, the C H bonds
in the triazole group should be directed into the porphyrin
center due to the rigid chemical structure and bond angles.
Those distinct structural characteristics have a strong influ-
ence on the chemical shift changes of 1 by the anionic guest
bindings. As shown in Figure 3, the triazole, benzyl, and
phenylene proton signals were shifted upfield by the addi-
tion of halides in the form of TBA salts. In particular, the
MALDI-TOF-MS analysis: The host-guest complex forma-
tion between 1 and halides has been directly confirmed by
MALDI-TOF-MS analysis (Figure 1). In negative ionization
mode, the mass spectrum of 1 with tetrabutylammonium
(TBA) IÀ salt exhibited not only a molecular ion signal at
1538.04 Dalton but also a [1+I]À signal at 1665.05 Dalton.
triazole proton exhibited
a very strong upfield shift
(À0.94 ppm) due to the addition of ClÀ. To the best of our
knowledge, such a strong upfield shift has never been ob-
served in the process of hydrogen-bonding formation, even
in various picket-type porphyrin receptors.[9]
Figure 3. 1H NMR spectra (400 MHz, [D6]DMSO, 298 K) of 1 (1.6 mm)
Figure 1. MALDI-TOF-MS spectra of 1 with halides.
recorded upon addition of 10 equivalents of halides.
Chem. Eur. J. 2011, 17, 13898 – 13903
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13899

W.-D. Jang et al.
Two different effects can influence the triazole proton
upon host–guest complex formation. First, the electron den-
sity of protons eventually decreases when the protons partic-
ipate in hydrogen bonding; as such, a downfield shift can be
observed due to the deshielding effect. Second, porphyrin
ring current effects can lead to a shielding effect on triazole
protons if they are directed toward the center of the porphy-
rin; our results from NMR experiments indicate that this is
the predominant effect working in the triazole protons.
Therefore, the strong upfield shift implies that the triazole
protons in 1 are located very closely to the porphyrin ring
and are directed toward the binding pocket over the porphy-
rin ring when they form hydrogen bonds. According to the
increase in ionic radius, the upfield shift decreased because
the distance from the porphyrin center to the triazole
proton increased (Figure 3).
UV/Vis spectroscopy: The formation of a host–guest com-
plex between 1 and halides was again investigated using
UV/Vis spectroscopic analysis of the Soret and Q bands of
the porphyrin in CH2Cl2, acetone, and DMSO. The UV/Vis
absorption spectra showed that both the Soret and Q band
absorptions of 1 underwent a strong redshift with clear iso-
sbestic points due to the addition of halides (Figure 4a,
Figure 5, and Supporting Information). The spectral changes
of 1 took place in a symmetrical manner on the basis of iso-
sbestic points (Figure 4a and Supporting Information). The
continuous variation method (Jobꢂs plot) demonstrated that
1 and halides form 1:1 host–guest complexes.[10] The associa-
tion constant for halides to 1 was determined by nonlinear
curve-fitting analysis of the UV/Vis spectral changes using a
commercially available HypSpec software. Interestingly, 1
exhibited surprisingly strong halide binding affinities, in
which the association constants for ClÀ, BrÀ, and IÀ binding
were estimated to be larger than 108, 1.79ꢀ107, and 1.84ꢀ
105 mÀ1, respectively, in CH2Cl2 (Table 1). Notably, 1 has one
order of magnitude greater binding affinities for all halides
compared with the triazolophane values published by Flood
et al. under the same conditions.[6d] Because the binding af-
finity of 1 to halides was unexpectedly high, the estimated
association constant of 1 for ClÀ in CH2Cl2 is at the upper
limit for accurate calculation. Hence, we again carried out
the UV/Vis titration experiments in polar solvents, such as
acetone and DMSO, which showed that 1 still has strong
binding affinities for halides in polar solvents (results sum-
marized in Table 1). Although the binding affinities de-
creased, the relative binding strength in polar solvents was
still maintained. Considering the molecular structure of the
Figure 4. Spectroscopic titration of a) 1 (2.3 mm) with ClÀ and b) 1 con-
taining 300 equivalents of TBP with ClÀ. Inset: Spectroscopic titration
curves of ClÀ. Measured in CH2Cl2 at 298 K.
À
host compound, 1 can provide only four C H hydrogen-
Figure 5. Normalized absorption spectra of 1 and various host–guest com-
plexes.
bonding donors for the formation of a host–guest complex.
Also, 1 has a relatively flexible structure relative to the
cyclic triazolophane. Therefore, the strong binding affinities
for the anionic guests are clearly an abnormal aspect of 1
halides could take part in coordination to the zinc ion. As
mentioned above, the strong redshifts of the Soret and Q
band absorptions of 1 were observed due to the addition of
halide. Such strong absorption shifts cannot be achieved by
À
when only C H···X hydrogen bonding is considered.
On the other hand, zinc–porphyrin contains a Lewis
acidic site (Zn2+) for the binding of a lone pair of electrons.
Therefore, it is also possible that the lone pair electrons of
À
simple C H···X hydrogen-bond formation. It is known that
13900
www.chemeurj.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 13898 – 13903

Zinc–Porphyrin-Based Receptors
FULL PAPER
Table 1. Association constants K and DG for the complex formation of 1
À
the quadruple C H···X hydrogen bonding enables the
strong coordination interaction of halides onto Lewis acidic
Zn2+. However, 2 has a basic site at the center of the por-
phyrin, which may cause electronic repulsion to anionic spe-
cies; therefore, 2 cannot accommodate anionic guests. Ac-
cordingly, it was concluded that the cooperative effects of
with various anionic guests at 298 K.[a]
Solvent
CH2Cl2
Guest
K [mÀ1
>108
]
DG [kJmolÀ1
]
ClÀ
BrÀ
IÀ
>À45.6
À41.4
À30.0
À23.0
À37.4
À30.1
À20.0
À24.8
À14.9
À6.2
1.79ꢀ107
1.84ꢀ105
1.08ꢀ104
3.53ꢀ106
1.92ꢀ105
3.21ꢀ103
2.22ꢀ104
4.09ꢀ102
12
TBP[b]
ClÀ
BrÀ
IÀ
À
axial coordination and C H···X hydrogen bonding interac-
tions resulted in the strong binding affinity of 1 to halides.
acetone
DMSO
ClÀ
BrÀ
IÀ
Competitive binding experiments: To verify the strong bind-
ing affinity of 1 to ClÀ and BrÀ in CH2Cl2, we carried out
competitive binding experiments using 4-tert-butylpyridine
(TBP) and IÀ as competitive ligands (Table 2). The addition
[a]Estimated errors <5%. [b] TBP=tert-butylpyridine.
a very weak interaction exists between halides and ZnTPP
in CH2Cl2, where the association constants in CH2Cl2 were
about 290 and 17mÀ1 for ClÀ and BrÀ, respectively.[11] Nappa
and Valentine reported the relationship between the redshift
value and the axial ligation of various ligands and proposed
that the charge donation ability is related to the electro-
Table 2. Results of competitive binding experiments at 298 K in
[a]
CH2Cl2
.
[b]
[c]
[d]
[c]
Guest
Kapp [mÀ1
]
K [mÀ1
>108
]
Kapp [mÀ1
]
K [mÀ1
]
ClÀ
BrÀ
IÀ
1.00ꢀ108
1.90ꢀ106
4.72ꢀ104
8.71ꢀ105
6.46ꢀ104
–
1.35ꢀ108
1.03ꢀ107
–
1.51ꢀ107
4.43ꢀ105
ACHTUNGTRENNUNG
negativity and polarizability of the ligand.[11] Therefore, the
[a] Estimated errors <5%. [b] Apparent association constants of halides
to 1 in the presence of 300 equivalents of TBP. [c] Estimated association
constants of 1 to halides by nonlinear curve fitting. [d] Apparent associa-
tion constants of halides to 1 in the presence of 300 equivalents of IÀ.
order of redshifts due to halide ligation would be ClÀ <
BrÀ <IÀ. A large amount of halide was used to determine
the redshift values due to the very low binding affinity,
where the literature redshift values for ZnTPP were 770 and
850 cmÀ1 for ClÀ and BrÀ ligation, respectively. Moreover,
the ZnTPP redshift value due to IÀ ligation was not deter-
mined due to the lack of binding affinity. Throughout the
halide titration experiments with 1, all halides exhibited a
sufficiently strong affinity to successfully determine their
redshift values with minimum amounts of guest addition,
which were determined to be 750, 830, and 990 cmÀ1 for
ClÀ, BrÀ, and IÀ, respectively (Figure 5). The order of red-
shift and the values for ClÀ and BrÀ binding agree well with
the those from the experiments of Nappa and Valentine.[11]
Although the Lewis acidic zinc ion in the porphyrin center
had weak interactions with halides, such strong coordination
of IÀ to the porphyrin zinc ion has not been reported. There-
fore, to the best of our knowledge, this is the first examina-
of TBP to 1 resulted in a redshift of the Soret absorption
band to 540 cmÀ1, which also agrees with the redshift value
of ZnTPP (530 cmÀ1) by axial ligation of pyridine in CH2Cl2
(Figure 5), where the binding constant of 1 to TBP was esti-
mated to be 1.08ꢀ104 mÀ1. Halides were again titrated to 1
in the presence of 300 equivalents of TBP. As a result, the
Soret band of 1 was further redshifted due to the addition of
halides, even IÀ (Figure 4b and the Supporting Information).
On the other hand, the absorption bands of 1 exhibited
slight blue shift by addition of ClÀ and BrÀ when 300 equiva-
lent amounts of IÀ existed in the solution. All halides
showed a decreased binding affinity to 1, indicating that the
TBP and IÀ successfully worked as competitive ligands.
Using Hypspec software, nonlinear curve fitting analysis was
again carried out to estimate the binding affinities of ClÀ
and BrÀ. From the competitive binding experiments, we
could again confirm that the binding constants of 1 to ClÀ
and BrÀ are greater than 108 and 107, respectively.
À
tion of halide ligation to a zinc ion with the aid of C H···X
hydrogen bonds.
To confirm again the axial ligation interaction, halides
were titrated to 2, 1 without Zn2+. In these experiments
there was no evidence of halide bindings to 2 even in
1
CH2Cl2 using both UV/Vis and H NMR spectroscopy, indi-
cating that the axial ligation interaction is significantly im-
portant for the halide bindings. Considering the affinity of
oligotriACHTUNGTRENNUNGazoles to halides and extremely strong binding affini-
ty for halides to 1, it is unexpected result that 2 does not
have any affinity to anionic species. Such unusual behavior
by 2 can be explained by a repulsive interaction between
the electron-rich free-base porphyrin and anionic guests. As
mentioned above, when considering the chemical structure
Computer modeling: Structural optimization of host–guest
complexes was carried out using a CAChe 7.5 PM5 semi-
empirical calculation (Figure 6). The results indicate that all
protons in triazole units are directed to the center of the
porphyrin unit and create optimum cavity for the formation
À
of hydrogen bonding with halides. Because the triazole C H
is directed toward to the center of the porphyrin, all halides
become very close to the metal center. Interestingly, in the
energy-minimized structure of 1, all triazole groups have
tilted conformation with same direction for the formation of
À
of 1 it is important to note that the C H bonds in triazole
groups are directed into center of porphyrin. Therefore, if
anionic guests associate with 1 through hydrogen bonding,
anions should be located at the porphyrin center. Therefore,
À
C H···X hydrogen bonding. This observation may provide
another interesting aspect that 1 may create chiral space
Chem. Eur. J. 2011, 17, 13898 – 13903
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13901

W.-D. Jang et al.
Synthesis of 4: TFA (2.0 mL, 25.96 mmol) was added to a mixture solu-
tion of 3 (4.0 g, 19.77 mmol) and pyrrole (1.31 g, 19.77 mmol) in CH2Cl2
(1.0 L) and stirred for 12 h at 258C. Then, p-chloranil (7.29 g,
29.66 mmol) was added, and the reaction mixture was further stirred for
4 h. The reaction mixture was concentrated to a volume of 200 mL and
then chromatographed in silica gel with CH2Cl2. Without further purifica-
tion, the product was dissolved in 10% MeOH/CH2Cl2 containing Zn-
AHCTUNGRTEG(NNNU OAc)2 (4.34 g, 19.77 mmol) and then stirred for 1 h at 258C. The reac-
tion mixture was purified using column chromatography with 30%
CH2Cl2/hexane to produce a mixture of atropisomers of 4 as a reddish–
purple solid (0.79 g, 15%): MALDI-TOF-MS: m/z calcd for
C64H60N4Si4Zn: 1062.94 [M]+; found: 1063.08.
Synthesis of 5: Tetrabutylammonium fluoride (5.0 mL, 1m in THF) was
added to a solution of 4 (0.79 g, 0.74 mmol) in CH2Cl2 (100 mL) and
stirred for 30 min at 258C, then the solvent was removed under reduced
pressure. The residue was purified using column chromatography with
50% CH2Cl2/hexane as the eluent. Recrystallization from the CH2Cl2/
hexane gave a mixture of the atropisomers of 5 as a purple solid (0.55 g,
95%): MALDI-TOF-MS: m/z calcd for C52H28N4Zn: 774.22 [M]+; found
774.52.
Figure 6. The energy-minimized molecular structure of 1 with ClÀ and
omission of other functionalities except porphyrin and triazoles.
Synthesis of 6: NaN3 (1.14 g, 17.46 mmol) was added to a stirred solution
of methyl 4-(bromomethyl)benzoate (2.0 g, 8.73 mmol) in a 40.0 mL ace-
tone/H2O mixture (3:1). The resulting suspension was stirred for 30 min
at 258C, and the reaction mixture was evaporated. The residue was puri-
fied using column chromatography with 50% CH2Cl2/hexane to produce
6 as a white solid (1.6 g, 99%): 1H NMR (400 MHz, CDCl3, 258C): d=
8.05 (d, J=8 Hz, 2H), 7.49 (d, J=8 Hz, 2H), 4.41 (s, 2H), 3.92 ppm (s,
3H); 13C NMR (100 MHz, CDCl3, 258C): d=166.72, 140.49, 130.21,
128.02, 54.37, 52.30 ppm.
when it forms host–guest complexes with halides. Therefore,
we are going to investigate the control of chiral space using
chiral guest or introduction of chiral substituent in a further
study.
Conclusion
Synthesis of 1: CuSO4·5H2O (0.16 g, 0.65 mmol) and sodium ascorbate
(0.13 g, 0.65 mmol) were added to a mixture of 5 (0.1 g, 0.13 mmol) and 6
(0.13 g, 0.65 mmol) in 20 mL THF/H2O (1:1). The reaction mixture was
stirred for 12 h at 508C, and then the organic layer was separated, dried
over MgSO4, and filtered. After evaporation of the solvent under re-
duced pressure, the residue was purified using column chromatography
with 70% ethyl acetate/CH2Cl2, and the second fraction was collected
and evaporated to dryness. The residue was recrystallized from CH2Cl2/
hexane to produce 1 as a purple solid (0.1 g, 51%): 1H NMR (400 MHz,
[D6]DMSO, 258C): d=8.57 (s, J=8H), 8.37 (d, J=8 Hz, 4H), 7,93–7.86
(m, 8H), 7.78 (t, J=6 Hz, 4H), 6.89 (d, J=8 Hz, 8H), 5.74 (d, J=8 Hz,
8H), 5.62 (s, 4H), 4.36 (s, 8H), 3.72 ppm (s, 12H); 13C NMR (100 MHz,
[D6]DMSO, 258C): d=165.40, 149.30, 146.50, 140.12, 139.97, 134.76,
132.85, 131.40, 128.59, 128.43, 127.24, 126.16, 126.02, 123.03, 118.66, 52.12,
50.92 ppm; MALDI-TOF-MS: m/z calcd for C88H64N16O8Zn: 1538.96
[M]+; found: 1538.04.
We designed a new type of porphyrin-based host compound
containing four triazole groups. While this new host com-
pound does not have a shape-persistent macrocyclic struc-
ture of triazole groups, the cooperative effects of axial coor-
À
dination and quadruple C H···X hydrogen bonds resulted in
extremely high halide binding affinities. Moreover, we were
the first to examine halide ligation to zinc ions with the aid
À
of C H···X hydrogen bonds. Thus, the present work may
allow future investigation of new physicochemical aspects of
metalloporphyrins associated with axial ligation of halides.
In addition, new ideas for receptor design can be proposed
based on a combination of multiple binding motifs.
Synthesis of 2: Trifluoroacetic acid (1 mL) was added to a solution of 1
(50 mg, 0.03 mmol) in CH2Cl2 (10 mL), and stirred for 30 min. The reac-
tion mixture was poured into water, and then extracted with CH2Cl2.
After the evaporation of solvent, compound 2 was obtained as purple
solid with quantitative yield. 1H NMR (400 MHz, CDCl3, 258C): d=8.68
(s, 8H), 8.48 (d, J=8 Hz, 4H), 7.92 (t, J=7 Hz, 8H), 7.75 (d, J=7 Hz,
4H), 7.64 (t, J=8, 4H), 6.21 (d, J=8 Hz, 8H), 5.32 (s, 4H), 5.14 (d, J=8,
4H), 4.13 (s, 8H), 3.63 (s, 12H), À2.60 ppm (s, 2H); MALDI-TOF-MS:
m/z calcd for C88H66N16O8: 1476.58 [M+H]+; found: 1477.08.
Experimental Section
Measurements: Electronic-absorption spectra were recorded on
JASCO V-660 spectrometer. 1H and 13C NMR spectra were recorded on
Bruker Advance DPX 400 spectrometer at 258C in CDCl3 and
[D6]DMSO. MALDI-TOF-MS was performed on an Applied Biosystems
4700 proteomics analyzer with a-cyano-4-hydroxycinnamic acid as the
matrix.
a
a
Synthesis of 3: 2-Bromobenzaldehyde (10.22 g, 55.22 mmol), CuI
(0.526 g, 2.76 mmol), and [PdACHTNUGTRNEGNU(PPh3)2Cl2] (3.88 g, 5.52 mmol) were mixed
Acknowledgements
in a Schlenk flask. The flask was degassed three times under high
vacuum and back-filled with N2. Dried THF (70.0 mL), Et3N (30.0 mL),
and trimethylsilylacetylene (11.47 mL, 82.83 mmol) were added. The re-
action mixture was stirred for 16 h at 508C and then filtered through
Celite. The filtrate was concentrated and then purified using column
chromatography with 2% ethyl acetate/hexane to produce 3 as a color-
less oil (10.0 g, 90%): 1H NMR (400 MHz, CDCl3, 258C): d=10.55 (s,
1H), 7.90 (d, J=8 Hz, 1H), 7.58–7.51 (m, 2H), 7.43 (t, J=6 Hz, 1H),
0.27 ppm (s, 9H); 13C NMR (100 MHz, CDCl3, 258C): d=191.99, 136.30,
133.81, 133.63, 128.96, 127.00, 102.55, 100.19 ppm.
This work was supported by the Natianl Research Foundation of Korea
(NRF) grant funded by the Korea government (MEXT) (No. 2011–
0001126 and 2009-0073885). C.-H. Lee and H. Yoon acknowledge fellow-
ships from the BK21 program form the Ministry of Education, Science
and Technology, Korea.
13902
www.chemeurj.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 13898 – 13903

Zinc–Porphyrin-Based Receptors
FULL PAPER
H. Park, A. H. Flood, Org. Lett. 2010, 12, 2100; d) Y. Hua, A. H.
Flood, Chem. Soc. Rev. 2010, 39, 1262; e) I. Bandyopadhyay, K. Ra-
ghavachari, A. H. Flood, ChemPhysChem 2009, 10, 2535; f) J. L.
Sessler, J. Cai, H.-Y. Gong, X. Yang, J. F. Arambula, B. P. Hay, J.
Am. Chem. Soc. 2010, 132, 14058; g) Y. Li, A. H. Flood, J. Am.
Chem. Soc. 2008, 130, 12111; h) Y. Li, A. H. Flood, Angew. Chem.
2008, 120, 2689; Angew. Chem. Int. Ed. 2008, 47, 2649.
[1] a) C. Miller, Nature 2006, 440, 484; b) R. Dutzler, E. B. Campbell,
R. Mackinnon, Science 2003, 300, 108; c) R. Dutzler, E. B. Camp-
bell, M. Cadene, B. T. Chait, R. Mackinnon, Nature 2002, 415, 287.
[2] a) P. A. Gale, Chem. Commun. 2011, 47, 82; b) S.-O. Kang, J. M. Lli-
nares, V. W. Day, K. Bowman-James, Chem. Soc. Rev. 2010, 39,
3980; c) B. P. Hay, Chem. Soc. Rev. 2010, 39, 3700; d) V. Amendola,
L. Fabbrizzi, L. Mosca, Chem. Soc. Rev. 2010, 39, 3889; e) V. Amen-
dola, D. Esteban-Gomez, L. Fabbrizzi, M. Licchelli, Acc. Chem. Res.
2006, 39, 343; f) S. E. Matthews, P. D. Beer, Supramol. Chem. 2005,
17, 411.
[3] a) S. P. Mahanta, B. S. Kumar, P. K. Panda, Chem. Commun. 2011,
47, 4496; b) P. A. Gale, Acc. Chem. Res. 2011, 44, 216; Y. Haketa, H.
Maeda, Chem. Eur. J. 2011, 17, 1485; c) C.-H. Lee, H. Yoon, P. Kim,
S. Cho, D. Kim, W.-D. Jang, Chem. Commun. 2011, 47, 4246; d) C.-
H. Lee, H. Yoon, W.-D. Jang, Chem. Eur. J. 2009, 15, 9972; e) P. A.
Gale, Chem. Commun. 2008, 4525; f) J. M. Suk, K.-S. Jeong, J. Am.
Chem. Soc. 2008, 130, 11868; g) K. J. Chang, D. Moon, M. S. Lah,
K. S. Jeong, Angew. Chem. 2005, 117, 8140; Angew. Chem. Int. Ed.
2005, 44, 7926; h) K.-J. Chang, B.-N. Kang, M.-H. Lee, K.-S. Jeong,
J. Am. Chem. Soc. 2005, 127, 12214.
[7] V. V. Rostovtsev, L. G. Green, V. V. Fokin, K. B. Sharpless, Angew.
Chem. 2002, 114, 2708; Angew. Chem. Int. Ed. 2002, 41, 2596.
[8] a) E. Rose, A. Cardon-Pilotaz, M. Quelquejeu, N. Bernard, A. Kos-
sanyi, B. Desmazieres, J. Org. Chem. 1995, 60, 3919; b) P. Maillard,
S. Vilain, C. Huel, M. Momenteau, J. Org. Chem. 1994, 59, 2887;
c) J. S. Lindsey, J. Org. Chem. 1980, 45, 5215.
[9] a) J.-D. Lee, Y.-H. Kim, H.-I. Hong, J. Org. Chem. 2010, 75, 7588;
b) D. P. Cormode, M. G. B. Drew, R. Jagessar, P. D. Beer, Dalton
Trans. 2008, 6732; c) K. Calderon-Kawasaki, S. Kularatne, Y. H. Li,
B. C. Noll, W. R. Scheidt, D. H. Burns, J. Org. Chem. 2007, 72, 9081;
d) D. P. Cormode, S. S. Murray, A. R. Cowley, P. D. Beer, Dalton
Trans. 2006, 5135; e) D. H. Burns, K. Calderon-Kawasaki, S. Kular-
atne, J. Org. Chem. 2005, 70, 2803; f) Y.-H. Kim, J.-I. Hong, Angew.
Chem. 2002, 114, 3071; Angew. Chem. Int. Ed. 2002, 41, 2947; g) Y.-
H. Kim, J.-I. Hong, Tetrahedron Lett. 2000, 41, 4419.
[4] G. R. Desiraju, T. Steiner, The Weak Hydrogen Bond: In Structural
Chemistry and Biology, Oxford University Press, Oxford, 1999.
[5] a) M. L. Chabinyc, J. I. Brauman, J. Am. Chem. Soc. 2000, 122,
8739; b) B. P. Hay, V. S. Bryantsev, Chem. Commun. 2008, 2417;
c) G. Harakas, T. Vu, C. B. Knobler, M. F. Hawthorne, J. Am. Chem.
Soc. 1998, 120, 6405.
[10] K. A. Connors, Binding Constants: The Measurement of Molecular
Complex Stability, Wiley, New York, 1987, p. 24.
[11] M. Nappa, J. S. Valentine, J. Am. Chem. Soc. 1978, 100, 5075.
[6] a) Y. Hua, R. O. Ramabhadran, E. O. Uduehi, J. A. Karty, K. Ra-
ghavachari, A. H. Flood, Chem. Eur. J. 2011, 17, 312; b) Y. Hua,
A. H. Flood, J. Am. Chem. Soc. 2010, 132, 12838; c) S. Lee, Y. Hua,
Received: June 20, 2011
Revised: August 25, 2011
Published online: November 3, 2011
Chem. Eur. J. 2011, 17, 13898 – 13903
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13903