Facile synthesis of oligophenylene-substituted calix[4]arenes and their enhanced binding properties

Article abstract of DOI:10.1021/jo048545p

(Chemical Equation Presented) A facile and efficient protocol for the synthesis of oligophenylene OPP(n)-substituted calix[4]arenes (with n up to 4) via iodo-substituted oligoarylcalix[4]arenes has been developed. The cooperation effect of the proximate fluoroionophores in hexylsulfanyl end-capped OPP(n)-substituted calix[4]arene assemblies leads to metal ion binding enhancement.

Full text of DOI:10.1021/jo048545p

properties of these π-conjugated molecules by means of
structural modifications.7 On the other hand, the use of
intramolecular interaction or cooperation effect of the
proximate chromo- or fluorophores in multi-π-conjugated
molecular assemblies, in which chromo- or fluorophores
are preorganized and preoriented within a molecular
framework, to modify and tune the functional properties
of a material is largely unexplored.8
We have previously shown that multifluorophoric
assemblies based on oligophenylene (OPP)-substituted
calix[4]arene assemblies exhibit a dramatic difference in
the fluorescence properties when compared to that of the
corresponding monomeric unit. Interestingly, the donor-
acceptor type calix[4]arene assemblies exhibit strong and
enhanced fluorescence as compared to those of the
donor-donor type assemblies.9 Continuing our effort in
investigating the structural factor(s) that can enhance a
functional property of an assembly, we report herein a
more efficient protocol for the synthesis of OPP(n)-
substituted calix[4]arene assemblies with n up to 4 via
tetraiodophenyl- or tetraiodobiphenylcalix[4]arenes and
an investigation of the cooperation effect of the proximate
fluoroionophores for soft metal ion binding in hexylsulf-
anyl end-capped OPP(n)-substituted calix[4]arene as-
semblies.
Although various aryl-substituted calix[4]arenes have
been synthesized in good yields by various metal-
catalyzed cross-coupling protocols,10 our early attempt to
synthesize higher homologous of OPP-substituted calix-
[4]arene assemblies using the palladium-catalyzed Su-
zuki cross-coupling of oligoarylboronic acid and tetra-
bromophenylcalix[4]arene as well as to improve the
efficiency of such a strategy was not so successful. It was
attributed to the increased steric crowdedness of the
multiple reaction sites and the low reactivity of tetra-
bromophenylcalix[4]arene employed. As the oxidative
addition step is often considered to be the rate-determin-
ing step in the Suzuki cross-coupling reaction, the use of
aryl iodide would certainly increase the efficiency and
reactivity of the coupling.11 However, there is no facile
method of synthesizing iodo-substituted oligoarylcalix-
[4]arenes reported so far. As a result, method to synthe-
Facile Synthesis of
Oligophenylene-Substituted Calix[4]arenes
and Their Enhanced Binding Properties
Man Shing Wong,*,† Ping Fang Xia,† Xiao Ling Zhang,†
Pik Kwan Lo,† Yuen-Kit Cheng,† Kai-Tai Yeung,†
Xiliang Guo,†,‡ and Shaomin Shuang‡
Department of Chemistry, Hong Kong Baptist University,
Kowloon Tong, Hong Kong SAR, China, and School of
Chemistry and Chemical Engineering, Institute of Advanced
Chemistry, Shanxi University, Taiyuan 030006, China
mswong@hkbu.edu.hk
Received August 19, 2004
A facile and efficient protocol for the synthesis of oligo-
phenylene OPP(n)-substituted calix[4]arenes (with n up to
4) via iodo-substituted oligoarylcalix[4]arenes has been
developed. The cooperation effect of the proximate fluoro-
ionophores in hexylsulfanyl end-capped OPP(n)-substituted
calix[4]arene assemblies leads to metal ion binding enhance-
ment.
There is considerable interest in developing novel
π-conjugated molecular systems, i.e., oligomers1 or den-
drimers2 or assemblies,3 into useful functional materials
for various technological applications such as sensors4
and optoelectronic devices, i.e., field effect transistors5
and light-emitting diodes.6 Much progress has been made
toward tuning/enhancing the various functional/material
† Hong Kong Baptist University.
‡ Shanxi University.
(1) (a) Tour, J. M. Chem. Rev. 1996, 96, 537-553. (b) Martin, R. E.;
Diederich, F. Angew. Chem., Int. Ed. 1999, 38, 1350-1377.
(c) Berresheim, A. J.; Mu¨ller, M.; Mu¨llen, K. Chem. Rev. 1999, 99,
1747-1785. (d) Sheats, J. R.; Barbara, P. F. Acc. Chem. Res. 1999, 32,
191-192. (e) Segura, J. L.; Martin, N. J. Mater. Chem. 2000, 10, 2403-
2453.
(5) (a) Garnier, F.; Hajlaoui, R.; Yassar, A. Sciences 1994, 265, 1684.
(b) Katz, H. E. J. Mater. Chem. 1997, 7, 369-376. (c) Horowitz, G.
Adv. Mater. 1998, 10, 365-377. (d) Garnier, F. Acc. Chem. Res. 1999,
32, 209-215.
(6) (a) Kraft, A.; Grimsadle, A. C.; Holmes, A. B. Angew. Chem., Int.
Ed. 1998, 37, 402-428. (b) Friend, R. H.; Gymer, R. W.; Holmes, A.
B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.;
Dos Santos, D. A.; Bre´das, J. L.; Lo¨gdlund, M.; Salaneck, W. R. Nature
1999, 397, 121-128. (c) Mitschke, U.; Ba¨uerle, P. J. Mater. Chem.
2000, 10, 1471-1507.
(7) Mu¨llen, K.; Wegner, G. Electronic Materials: The Oligomer
Approach; Wiley-VCH: Weinheim, 1998.
(8) Takahashi, K.; Grunji, A.; Guillaumont, D.; Pichierri, F.; Naka-
mura, S. Angew. Chem., Int. Ed. 2000, 39, 2925-2927.
(9) Wong, M. S.; Zhang, X. L.; Chen, D. Z.; Cheung, W. H. Chem.
Commun. 2003, 138-139.
(10) (a) Junejia, R. K.; Robinson, K. D.; Johnson, C. P.; Atwood, J.
L. J. Am. Chem. Soc. 1993, 115, 3818-3819. (b) Wong M. S.; Nicoud,
J.-F. Tetrahedron Lett., 1993, 34, 8237-8240. (c) Larsen M.; Jorgensen,
M. J. Org. Chem. 1997, 62, 4171-4173.
(11) Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M.
Chem. Rev. 2002, 102, 1359-1469.
(2) (a) Dendrimers and Other Dendritic Polymers; Fre´chet, J. M. J.,
Tomalia, D. A., Eds.; J. Wiley and Sons: New York, 2001. (b) Newkome,
G. R.; Moorefield, C. N.; Vo¨gtle, F. Dendritic Molecules: Concept,
Synthesis, Perspectives; VCH: Weinheim, 1996. (c) Matthews, O. A.;
Shipway, A. N.; Stoddart, J. F. Prog. Polym. Sci. 1998, 23, 1-56.
(d) Frey, H.; Lach, C.; Lorenz, K. Adv. Mater. 1998, 10, 279-293.
(e) Fischer, M.; Vo¨gtle, F. Angew. Chem., Intl. Ed. 1999, 38, 885-905.
(f) Majoral, J. P.; Caminade, A. M. Chem. Rev. 1999, 99, 845-880.
(3) (a) Kelderman, E.; Heesink, G.; Derhaeg, L.; Verbiest, T.; Klaase,
P. T. A.; Verboom, W.; Engbersen, J. F. J.; van Hulst, N. F.; Clays, K.;
Persoons, A.; Reinhoudt, D. N. Adv. Mater. 1993, 5, 925-930. (b) Wong,
M. S.; Li, Z. H.; Kwok, C. C. Tetrahedron Lett. 2000, 41, 5719-5723.
(c) Gu, T.; Accorsi, G.; Armaroli, N.; Guillon, D.; Nierengarten, J.-F.
Tetrahedron Lett. 2001, 42, 2309-2313. (d) Yonetake, K.; Nakayama,
T.; Ueda, M. J. Mater. Chem. 2001, 11, 761-767. (e) Szemes, F.; Drew,
M. G. B.; Beer, P. D. Chem. Commun. 2002, 1228-1229.
(4) de Silva, A. P.; Nimal Gunaratne, H. Q.; Gunnlaugsson, T.;
Huxley, A. J. M.; Mccoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem.
Rev. 1997, 97, 1515-1566.
10.1021/jo048545p CCC: $30.25 © 2005 American Chemical Society
Published on Web 03/08/2005
2816
J. Org. Chem. 2005, 70, 2816-2819

SCHEME 1. Syntheses of OPP(n)-Substituted Calix[4]arenes 4a,b and 5a-ca
a Reagents and conditions: (i) TMS-(C6H4)n-B(OH)2, 20 mol % Pd(OAc)2/2P(o-tol)3, K2CO3, toluene-CH3OH, 45-65 °C, overnight;
(ii) I2, CF3COO-Ag+, CHCl3, 75 °C, 2-4 h; (iii) C6H13S-(C6H4)m-n-B(OH)2, 20 mol % Pd(OAc)2/2P(o-tol)3, K2CO3, toluene-CH3OH, 50 °C,
6-40 h; (iv) m-CPBA, CHCl3, 0 °C, 1 h.
size tetraiodophenyl- and tetraiodobiphenylcalix[4]arenes
was first explored.
Classical iodination strategies such as direct iodination
of tetraphenylcalix[4]arene by means of iodine-silver
trifluoroacetate in refluxing chloroform, which is often
used to prepare tetraiodocalix[4]arene,12 as well as
bromide-lithium exchange of tetrabromophenylcalix[4]-
arene followed by subsequent quenching with iodine were
not useful. Taking advantage of the facile ipso substitu-
tion of arylsilane by electrophile, iododesilylation of tetra-
(trimethylsilyl)oligoarylcalix[4]arenes was investigated.
Following the same synthetic strategy used previously,
FIGURE 1. 1H NMR spectra of 5b and 5c.
tetra(trimethylsilyl)phenylcalix[4]arene, 2a, was synthe-
sized by cross-coupling of tetraiodocalix[4]arene with
trimethylsilylphenylboronic acid, which was obtained in
1). The 1H NMR spectrum of 5c is very similar to that of
5b except with more aromatic proton resonances, which
a one-pot synthesis by a sequence of lithiation-quenching
correspond to an increase in phenylene units (Figure 1).
reactions: mono-transmetalation of 1,4-dibromobenzene
The MALDI-TOF mass spectrum of 5c showed a base
with 1 equiv of n-butyllithium followed by treatment with
peak at m/z 2818.10, corresponding to [M + Na]+ ion.
The poor conversion was presumably due to the increased
steric hindrance between partially oligophenylene-sub-
chlorotrimethylsilane at low temperature and subsequent
addition of a second equivalent of n-butyllithium followed
by the reaction with trimethyl borate and then acid
stituted calix[4]arene and the highly extended terphenyl-
hydrolysis (see the Supporting Information), under modi-
boronic acid. To improve the synthesis further, tetraiodobi-
phenylcalix[4]arene, 3b was pursued and prepared
according to the newly developed protocol as shown in
fied Suzuki protocol. Treatment of 2a with ICl under
various reaction conditions afforded no desired product.
However, iododesilylation was achieved smoothly by
Scheme 1. Great improvement was indeed achieved by
reaction with iodine-silver trifluoroacetate in refluxing
cross-coupling of 3b and 4′-(hexylsulfanyl)biphenyl-
CHCl3, which afforded tetraiodophenylcalix[4]arene, 3a,
boronic acid followed by subsequent m-CPBA oxidation,
in good yields. It is important to note that in contrast to
affording 5c14 in 76-85% overall isolated yields.
other silylated heteroaromatic systems,13 this reaction
did not proceed in THF. Cross-coupling of 3a with
4-(hexylsulfanyl)phenylboronic acid and 4′-(hexylsulfa-
nyl)biphenylboronic acid afforded assembly of 4a and 4b,
respectively, in excellent yields (77-92%) as shown in
Scheme 1. This confirms that iodo-substituted phenylcalix-
[4]arene was more reactive and efficient for coupling.
Interestingly, cross-coupling of 3a and 4′′-(hexylsulfanyl)-
terphenylboronic acid gave an insoluble reaction mixture
that could not be characterized by any spectroscopic
techniques. Fortunately, m-CPBA oxidation of this reac-
tion mixture in CHCl3 at low temperature afforded the
desired hexylsulfonylquaterphenylcalix[4]arene 5c, ex-
cept in a relatively low yield (33%) for two steps (Scheme
The widely employed ligating groups in calixarene-
based receptors/ionophores are (crown) ether, keto, ester,
and amide.15 Some of these receptors show good affinity
for Ag+ and Hg2+ ions;16 on the other hand, the use of
alkylsulfanyl functionality is relatively less. According
to the soft-hard acid-base principle, the ionophore
containing sulfur atom(s) would have an affinity for soft
metal ions such as Ag+ and Hg2+. Upon addition of
CF3COOAg in a CDCl3/CD3COCD3 (v/v ) 10:1) solution
of hexylsulfanyl end-capped OPP-substituted calix[4]-
(14) The nonlinear optical properties of hexylsulfonyl-OPP(n)-
substituted calix[4]arene derivatives are currently under investigation
and will be reported elsewhere.
(15) For recent review, see: (a) Calixarenes 2001; Asfari, Z., Bohmer,
V., Harrowfield J., Vicens, J., Eds.; Kluwer: Dordrecht, 2001. (b) Ikeda,
A.; Shinkai, S. Chem. Rev. 1997, 97, 1713-1734. (c) Danil de Mamor,
A. F.; Cleverley, R. M.; Zapata-Ormachea, M. L. Chem. Rev. 1998, 98,
2495-2525.
(12) Timmerman, P.; Verboom, W.; Reinhoudt, D. N.; Arduini, A.;
Sicuri, A. R.; Pochini, A.; Ungaro, R. Synthesis 1994, 185-189.
(13) Liu, J. H.; Chan, H. W.; Wong, H. N. C. J. Org. Chem. 2000,
65, 3274-3283.
J. Org. Chem, Vol. 70, No. 7, 2005 2817

FIGURE 2. DFT-optimized geometries of an analogue of 4a‚Ag+ complex for the (a) pseudo-C4v binding mode and (b) near the
C2v binding mode. The drawings were performed by MOLDRAW.19
arene assemblies, there were substantial shifts of the
proton resonances and peak broadening in the H NMR
facilitating complexation. On the other hand, the binding
association of the OPP-substituted calix[4]arene de-
creases with an increase in a phenylene unit. This is
attributed to the increased degrees of freedom of extended
oligophenylene arms in the longer homologues hindering
the cooperation binding. The moderate increase in bind-
ing association of 4b·Ag+ may additionally be due to the
crowdedness around the sulfur binding sites imposed by
the solubilizing hexyl groups, which hinders the ef-
fectiveness of cooperation binding as compared to their
monomeric counterparts.
Attempt to grow single crystals of the complexes was
not so successful. To probe the binding behavior, ab inito
quantum chemical calculations using Gaussian0318
(B3LYP 6-31G(d) with ECP for the Ag atom from
LANL2DZ) were pursued. For the computational simplic-
ity, an analogue of 4a bearing propoxy cone-stabilizing
substituents and methylsulfanyl endcaps was used. It is
interesting to find that the pseudo-C4v binding mode, in
which the three sulfur atoms on the oligophenylene
scaffolds cooperatively bind to Ag+ ion with the fourth
arm being slightly swayed away, is 3.28 kcal/mol enthal-
pically more stable than the near C2v binding mode, in
which the Ag+ ion is cooperatively bound by the two
opposite methylsulfanyl groups conforming to a pinched
structure (Figure 2). These results further confirm the
importance of the cooperative effect in binding.
1
spectra indicating the presence of interaction between
the calix[4]arene assemblies and Ag+ ion. Such a change
in chemical shifts or peak broadening was not observed
for 4-methoxyphenyl-substituted calix[4]arene and the
hexylsulfonyl end-capped OPP-substituted series as well
as for phenyl-substituted calix[4]arene, which excludes
the involvement of π-cation interactions. Of a particular
large downfield shift of proton resonance comes from
the methylene adjacent to the sulfur atom (∆δ )
0.17-0.25 ppm), suggesting that the binding site is at
the sulfur atoms. The binding stoichiometry of 4b‚Ag+
complex determined by Job plot using the fluorescent
titrations of 4b with CF3COOAg in CHCl3/CH3OH
(v/v 1:1) supported a 1:1 binding mode. This was further
confirmed by high-resolution MALDI-TOF MS analyses
in which the spectra of the mixture of alkylsulfanyl end-
capped OPP-substituted calix[4]arenes and CF3COOAg
show a peak at m/z 2164.3030 and 2468.4402 with
expected isotopic distribution, which correspond to
[4a + Ag]+ and [4b + Ag]+ ions, respectively (see the
Supporting Information). The association constants, es-
timated by nonlinear curve fitting analysis using data
obtained from fluorescent titrations in CHCl3/CH3OH
(v/v 1:1), were 23.5 × 104 and 2.0 × 104 M-1 for 4a‚Ag+
and 4b‚Ag+, respectively (see the Supporting Informa-
tion). These binding associations are much stronger than
those of the corresponding monomeric counterparts17 in
which their association constants as determined by
On the other hand, the changes in chemical shifts of
hexylsulfanyl end-capped OPP-substituted calix[4]arene
1
assemblies in the H NMR spectra were apparent upon
fluorescent titrations are 1.2 × 103 and 1.9 × 103 M-1
,
respectively, indicating the advantage of cooperation
binding. In the monomeric system, an increase in a
phenylene unit leads to an enhancement of the Ag+ ion
binding indicating the contribution of π-conjugation in
(18) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P.
Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; and Pople, J. A. Gaussian 03, Revision C.02; Gaussian,
Inc.: Wallingford, CT, 2004.
(16) For recent references: (a) Kim, S. K.; Lee, J. K.; Lee, S. H.;
Lim, M. S. Lee, S. W.; Sim, W.; Kim, J. S. J. Org. Chem. 2004, 69,
2877-2880. (b) Kim, J. S.; Noh, K. H.; Lee, S. H.; Kim, S. K.; Kim, S.
K.; Yoon, J. J. Org. Chem. 2003, 68, 597-600. (c) Budka, J.; Lhota´k,
P.; Stibor, I.; Michlova´, V.; Sykroa, J.; Cisarova´, I. Tetrahedron Lett.
2002, 43, 2857-2861. (d) Metivier, R.; Leray, I. Valeur, B. Chem. Eur.
J. 2004, 10, 4480-4490. (e) Kim, J. H.; Hwang, A. R.; Chang, S. K.
Tetrahedron Lett. 2004, 45, 7557-7561. (f) Choi, M. J.; Kim, M. Y.;
Chang, S. K. Chem. Commun. 2001, 1664-1665.
(17) The monomer of 4a is 4-decyloxy-3,5-dimethyl-4′′-hexylsufanyl-
terphenyl and the monomer of 4b is 4-decyloxy-3,5-dimethyl-4′′′-
hexylsufanylquaterphenyl.
2818 J. Org. Chem., Vol. 70, No. 7, 2005

dryness. The crude product was purified by silica gel column
chromatography using petroleum ether and CH2Cl2 as eluent.
5,11,17,23-Tetrakis(4-trimethylsilylphenyl)-25,26,27,28-
tetradecyloxycalix[4]arene (2a): mp 86-88 °C; 1H NMR
(400 MHz, CDCl3, 25 °C, δ) 7.43 (d, J ) 8.0 Hz, 8H), 7.26
(d, J ) 8.0 Hz, 8H), 7.00 (s, 8H), 4.61 (d, J ) 12.8 Hz, 4H), 4.03
(t, J ) 7.4 Hz, 8H), 3.38 (d, J ) 12.8 Hz, 4H), 2.08 (bs, 8H),
1.34-1.46 (bs, 56H), 0.92 (bs, 12H), 0.27 (s, 36 H); 13C NMR (67.8
MHz, CDCl3, 25 °C, δ) 157.6, 141.8, 137.5, 135.3, 134.7, 133.3,
127.1, 126.3, 75.6, 32.1, 31.6, 30.5, 30.2, 29.9, 29.6, 26.5, 22.8,
14.2, -0.85; MS (FAB) m/z 1578.6 [M]+. Anal. Calcd for
C104H152O4Si: C, 79.13; H, 9.70. Found: C, 79.47; H, 10.01.
5,11,17,23-Tetrakis[4′-(trimethylsilyl)biphenyl]-25,26,-
27,28-tetradecyloxycalix[4]arene (2b): mp 195-197 °C;
1H NMR (400 MHz, CDCl3, 25 °C, δ) 7.48 (s, 16 H), 7.42
(d, J ) 8.0 Hz, 8H), 7.26 (d, J ) 7.6 Hz, 8H), 7.03 (s, 8H), 4.62
(d, J ) 13.2 Hz, 4H), 4.03 (t, J ) 7.4 Hz, 8H), 3.34 (d, J ) 13.2
Hz, 4H), 2.05 (bs, 8H), 1.27-1.44 (bs, 56H), 0.89 (t, J ) 6.6 Hz,
12H), 0.29 (s, 36 H); 13C NMR (67.8 MHz, CDCl3, 25 °C, δ) 157.3,
141.2, 140.3, 138.9, 138.7, 135.1, 134.8, 133.7, 127.2, 127.1, 127.0,
126.3, 75.6, 32.0, 31.8, 30.4, 30.1, 29.9, 29.7, 29.5, 26.5, 22.7,
14.2, -1.0; HRMS (MALDI-TOF) calcd for C128H168O4Si 1881.2020,
found 1881.2117 [M]+.
5,11,17,23-Tetrakis(4-iodophenyl)-25,26,27,28-
tetradecyloxycalix[4]arene (3a): mp 139-140 °C; 1H NMR
(400 MHz, CDCl3, 25°C, δ) 7.45 (d, J ) 8.0 Hz, 8H), 6.85 (s, 8H),
6.83 (d, J ) 8.0 Hz, 8H), 4.53 (d, J ) 13.2 Hz, 4H), 3.96
(t, J ) 7.2 Hz, 8H), 3.25 (d, J ) 13.2 Hz, 4H), 1.96-1.98
(m, 8H), 1.29-1.41 (m, 56H), 0.87 (t, J ) 6.8 Hz, 12H); 13C NMR
(100 MHz, CDCl3, 25°C, δ) 156.4, 140.3, 137.3, 135.1, 133.8,
128.3, 126.6, 92.0, 75.5, 32.1, 31.2, 30.4, 30.1, 30.1, 29.9, 29.5,
26.5, 22.8, 14.2; MS (FAB) m/z 1793.2 [M]+. Anal. Calcd for
C92H116O4I4: C, 61.61; H, 6.52. Found: C, 61.74; H, 6.82.
5,11,17,23-Tetrakis(4′-iodobiphenyl)-25,26,27,28-
tetradecyloxycalix[4]arene (3b): mp 130-131.5 °C; 1H NMR
(400 MHz, CDCl3, 25°C, δ) 7.59 (d, J ) 8.4 Hz, 8H), 7.27
(bs, 8H), 7.23 (bs, 8H), 7.10 (d, J ) 7.6 Hz, 8H), 6.99 (s, 8H),
4.60 (d, J ) 13.2 Hz, 4H), 4.00 (t, J ) 7.2 Hz, 8H), 3.32
(d, J ) 13.2 Hz, 4H), 1.96-2.04 (m, 8H), 1.29-1.44 (m, 56H),
0.90 (t, J ) 6.8 Hz, 12H); 13C NMR (100 MHz, CDCl3, 25°C, δ)
156.5, 140.5, 139.9, 137.7, 137.6, 135.2, 134.3, 128.4, 127.1, 126.9,
126.7, 92.8, 75.6, 32.0, 31.4, 30.4, 30.0, 29.8, 29.5, 26.4, 22.7,
14.1. Anal. Calcd for C116H132O4I4: C, 66.41; H, 6.34. Found: C,
66.35; H, 6.17.
5,11,17,23-Tetrakis[4′′′-(hexylsulfonyl)quaterphenyl]-
25,26,27,28-tetradecyloxycalix[4]arene (5c): mp 314 °C dec;
1H NMR (400 MHz, CDCl3, 25°C, δ) 7.91 (d, J ) 8.4 Hz, 8H),
7.70 (d, J ) 8.0 Hz, 8H), 7.62 (d, J ) 8.0 Hz, 8H), 7.54-7.58
(m, 24H), 7.45 (bs, 8H), 7.31 (bs, 8H), 7.06 (bs, 8H), 4.64
(d, J ) 13.2 Hz, 4H), 4.02 (bs, 8H), 3.37 (d, J ) 13.2 Hz, 4H),
3.16 (t, J ) 8.0 Hz, 8H), 2.05 (bs, 8 H), 1.72-1.80 (m, 8H), 1.25-
1.46 (m, 80H), 0.85-0.93 (m, 24H); 13C NMR (100 MHz, CDCl3,
25°C, δ) 156.4, 145.7, 140.8, 140.3, 140.0, 138.4, 138.0, 137.6,
135.2, 134.5, 128.6, 127.6, 127.4, 127.2, 127.1, 127.1, 126.9, 75.6,
56.2, 32.0, 31.6, 31.2, 30.4, 30.0, 29.8, 29.7, 29.5, 27.9, 26.4,
22.7, 22.5, 22.3, 14.1, 13.9; MS (MALDI-TOF) m/z calcd for
C188H215O12S4Na 2818.03, found 2818.10 [M + Na]+.
FIGURE 3. 1H NMR spectra of 4a in CDCl3 (below) and 4a
with an addition of solid sample of Hg(OAc)2 (top).
an addition of one equivalent of Hg2+ salt in contrast to
their corresponding monomeric counterparts, which show
no significant change in chemical shifts. These results
indicate that the Hg2+ binding is also enhanced in the
calix[4]arene assemblies. Interestingly, dependent on the
deuterated solvent(s) used (i.e., CDCl3), Hg2+ and 4a
binding could be kinetically slow compared to NMR time
scale. Under such a slow exchange condition, the proton
resonances of both OCH2 and SCH2 from 4a‚Hg2+ com-
plex split into two sets of two magnetically nonequivalent
peaks20 (Figure 3). This splitting pattern suggests that
Hg2+ ion was bound by two sulfur atoms leading to a
conformationally stable pinched cone structure, analo-
gous to the tert-butyl-1,3-dihydroxy-2,4-disulfanylcalix-
arene-Hg2+ complex.21 The association constants, esti-
mated based on fluorescent titrations in CHCl3/CH3OH
(v/v 1:1) were 4.0 × 102 and 1.2 × 102 M-1 for 4a‚Hg2+
and 4b‚Hg2+, respectively.
In summary, we have developed a facile and mild
protocol for iodination of oligoaryl-substituted calix[4]-
arenes for the improved synthesis of highly extended
OPP-substituted calixarenes. The first efficient synthesis
of highly extended quaterphenylcalix[4]arene assembly
was also reported. We have shown that the binding
affinities of hexylsulfanyl end-capped OPP(n)-substituted
calix[4]arene assemblies toward Ag+ and Hg2+ ions are
stronger than those of the corresponding monomeric units
because of the cooperation effect of the proximate fluoro-
ionophores. This result provides an alternatively useful
approach to design chromo- and fluoroionophores to
enhance metal ion binding.
Experimental Section
Improved Procedure for Pd-Catalyzed Suzuki Cross-
Coupling of Oligoarylboronic Acid and Tetraiodoarylcalix-
[4]arene. To a stirred solution of tetraiodoarylcalix[4]arene
(0.1-0.6 mmol) and about 20 mol % of Pd(OAc)2/2P(o-tol)3 in
15 mL of toluene were added 5 mL of 2 M K2CO3 under N2 and
6 equiv of arylboronic acid in 10 mL of methanol, respectively.
After being heated to 50-65 °C for overnight, the reaction
mixture was added with 50 mL of 2 M Na2CO3 and then
extracted twice with CH2Cl2 (50 mL). The combined organic
layers were dried over anhydrous MgSO4 and evaporated to
Acknowledgment. This work was supported by an
Earmarked Research Grant (HKBU2019/02P) from the
Research Grants Council, Hong Kong. We grate-
fully acknowledge Dr. Y. Tao at NRC, Canada, for the
MALDI-TOF mass spectroscopy measurements.
Supporting Information Available: General experimen-
tal details, spectra data, and synthesis of boronic acids;
selected fluorescent titration data; 1H NMR spectra of boronic
acids, compounds 2a-5a, 2b-5b, and 5c; and MALDI-TOF
MS spectra of 4a‚Ag+ and 4b‚Ag+ complexes. This material is
available free of charge via the Internet at http://pubs.acs.org.
(19) Ugliengo, P., Viterbo, D., Chiari, G. Z. Kristallogr. 1993, 207,
9-23.
(20) Because of the limited solubility of Hg(OAc)2 in neat chloroform,
the determination of the association constant in this solvent is not
possible.
(21) Delaigue, X.; Hosseini, M. W.; Kyritsasakas, N.; De Cian, A.;
Fischer, J. J. Chem. Soc., Chem. Commun. 1995, 609-610.
JO048545P
J. Org. Chem, Vol. 70, No. 7, 2005 2819