984
T. Nakagaki et al. / Tetrahedron 66 (2010) 976–985
1,3-dimethoxy- (1.15 V vs Fc/Fcþ; lmax 370–390 nm) and 1,3,5-trime-
thoxybenzenes (1.14 V vs Fc/Fcþ; lmax 375 nm) suggested their similar
magnitude of the CT interactions (Table 5). Thus the large Ka value of
1,3,5-trimethoxybenzene@1 may be attributable to the multipoint
1,3,5-trimethoxybenzene, and CV traces for guest molecules. CCDC
reference number 718293, 718294 and 724380. Supplementary data
associated with this article can be found in the online version, at
interactions such as C–H/p, C–H/O, van der Waals, electrostatic in-
teractions along with CT interactions.
Based on the crystal structures of dimethoxybenzene@1, the
smaller Ka value of 1,2,3-trimethoxybenzene (1.8 Mꢀ1) may be as-
cribed to the fact that the 1,2,3-trimethoxybenzene cannot take
a suitable structure in the cavity of 1, which enables the CT, elec-
trostatic, and C–H/O interactions effective since the structure, in
which all the methoxy groups are located in the same plane of the
benzene ring, would be unfavorable due to the steric hindrance of
References and notes
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the three consecutive methoxy groups. The B3LYP/6-31G calcula-
*
tions19–23 most optimized the conformation with two coplanar
methoxy groups (Fig. 15). Deviation of a methoxy group from the
plane of the benzene ring would inhibit insertion of 1,2,3-trime-
thoxybenzene into the cavity of 1. Irrespective of the significantly
strong electron-donating ability of 1,2,3,5-tetramethoxybenzene,
the low Ka value (1.6 Mꢀ1) similar to that of 1,2,3-trimethox-
ybenzene was obtained probably due to similar steric reasons.
3. Conclusions
The parallel-conformation of 1 was observed in the crystal
structure of dimethoxybenzene@1 and this conformation was
expected to be the most stable one by MO calculations. In the
electrochemical study, the effective distance of the electronic re-
pulsive interactions between the radical anion and dianion was
expected to be ca. 7.3 Å, which is longer than those between the
radical anion and neutral species of the imide moieties (ca. 5.0 Å).
Although quantitative analysis of the responsible weak molecular
interactions is impossible at present, we found that 1 can recognize
polymethoxybenzenes by the multipoint interactions such as CT,
6. (a) Odell, B.; Reddington, M. V.; Slawin, A. M. Z.; Spencer, N.; Stoddart, J. F.;
Williams, D. J. Angew. Chem., Int. Ed. Engl. 1988, 27, 1547; (b) Ashton, P. R.; Odell,
B.; Reddington, M. V.; Slawn, A. M. Z.; Stoddart, J. F.; Williams, D. J. Angew.
Chem., Int. Ed. Engl. 1988, 27, 1550; (c) Fujita, M.; Yazaki, J.; Ogura, K. Tetrahedron
Lett. 1991, 32, 5589; (d) Ferguson, S. B.; Seward, E. M.; Diederich, F.; Sanford, E.
electrostatic, van der Waals, the C–H/O, and C–H/p interactions
in organic solvent. Thus molecular recognition of poly-
methoxybenzenes has been accomplished by the neutral host 1 in
nonpolar organic solvent, CHCl3. The synthesis of organic molecular
tubes by the stepwise connection of the functionalized host 1 is in
progress and the result will be reported elsewhere.
´
M.; Chou, A. J. Org. Chem. 1988, 53, 5595; (e) Ferrer, M.; Gutierrez, A.; Mounir,
M.; Rossell, O.; Ruiz, E.; Rang, A.; Engeser, M. Inorg. Chem. 2007, 46, 3395.
7. Cooke, R. G.; Johnson, B. L.; Owen, W. R. Aust. J. Chem. Soc. 1960, 13, 256.
8. Bushby, R. J.; Gooding, D. J. Chem. Soc., Perkin Trans. 2 1998, 1069.
9. In the MO calculations, the hexyloxy groups were replaced with methoxy
groups in 1, and sum of electronic and zero-point energies were calculated to
be ꢀ1863381.421 (parallel-10) and ꢀ1863379.711 (syn-10) kcal/mol,
respectively.
Acknowledgements
10. Even in solution, the parallel-conformer of 1 was expected to be a dominant
conformer by the comparison of the 1H NMR spectra of 1 and 9. The chemical
shifts of the proton signals of 1 and 9 are similar except for the inner naph-
thalene proton signals Hb, which showed the upfield shift in 1 (Dd¼0.41 ppm)
compared to that in 9. This upfield shift due to the ring current effect of the
pyromellitic diimide moieties was ascribed to the preferred parallel-confor-
mation of 1. While the optimized structure of 90 based on MO calculations
The computation was mainly carried out in the computer fa-
cilities at Research Institute for Information Technology, Kyushu
University. We thank Dr. Yoshihiro Watanabe (Kyushu University)
for the M.O. calculations. T.N. is grateful for the partial financial
support by the Front Researcher Development Program from the
Graduate School of Sciences, Kyushu University. We wish to thank
the Theme Project (Professor Tahsin J. Chow), Institute of Chemis-
try, Academia Sinica, Taiwan R.O.C., for the financial support of this
study. We also gratefully thank the financial support by a Grant-in-
Aid for Scientific Research on Innovative Areas (No. 21106015) from
the Ministry of Education, Culture, Sports, Science and Technology,
Japan.
(Gaussian 03, B3LYP/6-31G ) assumes a twisted conformation in which the Hb
*
protons are hardly influenced by the ring current effect of the pyromellitic
diimide moieties. In the MO calculations, the hexyloxy groups were replaced
with methoxy groups in 9.
11. (a) Viehbeck, A.; Goldberg, M. J.; Kavac, C. A. J. Electrochem. Soc. 1990, 137, 1460;
(b) Carroll, J. B.; Gray, M.; McMenimen, K. A.; Hamilton, D. G.; Rotello, V. M. Org.
Lett. 2003, 5, 3177.
12. This is also supportedby MO calculations (B3LYP/6-31G ). The LUMO energy level
*
of 1 is ꢀ2.977 eV, which is similar to that of 2 reported in Ref. 5b (ꢀ3.004 eV). The
coordinate of the X-ray crystal analysis was used in these calculations.
13. (a) Benesi, H. A.; Hildebrand, J. H. J. Am. Chem. Soc. 1949, 71, 2703; (b) Person,
W. B. J. Am. Chem. Soc. 1965, 87, 167.
Supplementary data
14. The Ka values of 1 with 1,2-, 1,3-, and 1,4-dimethoxybenzenes as well as 1,3,5-tri-
methoxybenzene obtained by the 1H NMR titration method in CDCl3 by using
nonlinear curve fitting with the 1/1 model were comparable to those obtained by
theUV–vistitrationmethod:Ka¼4.57ꢃ1.61 Mꢀ1, R¼0.998(1,2-dimethoxybenzene),
General experimental methods, 1H and 13C NMR spectra of 1, 7, 8,
and 9, UV–vis spectra 1 and 1 plus guest molecules, UV–vis spectra 2
and 2 plus guest molecules,1H NMRobservations of 1 and 2 recorded
in CDCl3 in the presence of guest molecules, structural data for the X-
ray analyses, calculated coordinate and total energies of optimized
structure of parallel-10, syn-10, 90, 1,2,3-trimethoxybenzene, and
1,3,5-trimethoxybenzene@10, calculated coordinate of 1,2-dime-
thoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, and
9.54ꢃ1.21 Mꢀ1
,
R¼0.999 (1,3-dimethoxybenzene), 3.36ꢃ2.03 Mꢀ1
R¼0.997
,
(1,4-dimethoxybenzene), and 32.1ꢃ5.15 Mꢀ1, R¼0.999 (1,3,5-trimethoxybenzene).
15. The electron-donating ability of the guests was estimated by the oxidation po-
tentials and the wavelengths of the CT bands obtained by the CV measurements
and UV–vis spectra, respectively. Based on these data, the electron-donating
ability of 1,4-dimethoxybenzene was the strongest in dimethoxybenzenes and
1,2,3- and 1,3,5-trimethoxybenzenes.