5998
K. C. Gowri Sreedevi et al. / Tetrahedron Letters 52 (2011) 5995–5999
meso-carbon just by altering the Grignard reagent of interest. Fur-
ther, the anion binding abilities of these compounds were evaluated,
which shows relatively high binding affinity toward fluoride ions
with respect to the other anions analyzed. The role of diaryl func-
tionality at the meso-position of the dipyrromethane in the binding
process is discussed, which can influence the design of novel macro-
cycles and supramolecular systems in future. Work is currently
underway in this direction in our group.
Acknowledgments
Dr. A.S. thanks DST, New Delhi and NWP-23 for the financial
support. K.C.G.S. thanks CSIR for the fellowship. We thank Dr. C.
S. Purohit, Faculty, SCS, NISER-Bhubaneswar for solving the crystal
structure of 7. We gratefully acknowledge Viji and Adarsh, NIIST-
CSIR, for recording the FAB and NMR spectra.
Supplementary data
Supplementary data (experimental procedures, 1H, 13C and FAB
mass spectra for all the new compounds, crystal data for 7 in CIF for-
mat, Anion Binding studies of 5–8) associated with this article can be
Figure 4. Optimized geometry for 1:1, 1:2 and 2:1 complexes of 7 and FÀ. All bond
References and notes
lengths are given in Å.
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C.-H.; Lindsey, J. S. Tetrahedron 1994, 50, 11427–11440; (c) Sessler, J. L.; Tomat,
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Table 2
The binding constants [MÀ1] of 5–9 in CD3CN at 298 K
Compound
FÀ
C6H5COOÀ
H2POÀ4
5
6
7
8
9
61
37
17
36
16
12
13
10
<10
14
<10
12
a
b
b
—
—
—
a
Could not be obtained due to deprotonation.
No binding. Errors estimated to be within 5%.
b
The binding energy for the different modes are calculated by
5. (a) Dubé, T.; Gambarotta, S.; Yap, G. P. A.; Conoci, S. Organometallics 2000, 19,
115–117; (b) Ganesan, M.; Gambarotta, S.; Yap, G. P. A. Angew. Chem., Int. Ed.
2001, 40, 766–769; (c) Freckmann, D. M. M.; Dubé, T.; Bérubé, C. D.;
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taking 7 as a model compound and the value obtained is 15.3,
12.3, and 9.9 kcal/mol for 1:1, 1:2, and 2:1 modes of binding,
respectively. Even though the values obtained for 1:1 and 1:2 com-
plexes are comparable, calculation of binding energy per fluoride in
1:2 complex is only 6.15 kcal/mol which is less than half of the 1:1
complex. Further, entropy will favor more the formation of 1:1
complex than three component 1:2 or 2:1 complexes. Optimized
structures of 1:1, 1:2, and 2:1 modes are given in Figure 4. The
association constants were calculated for all the 1:1 complexes
using Benesi Hildebrand equation and summarized in Table 2.
The binding constants calculated for compound 5–8 with FÀ ion
are lower compared to the dialkyl and monoaryldipyrromethanes
(170 MÀ1),16 and is expected by considering the stronger repulsive
interaction between the anion and the two aryl rings, where as the
binding constants with the oxoanions are found to be too low. The
observed decrease in the binding constants from 5–7 with FÀ can
be correlated with the increased positive inductive effect from
9. Hafner, K.; Pfeiffer, K. Tetrahedron Lett. 1968, 9, 4311–4314.
10. Crystal data for 7 (from CH2Cl2/hexane): C23H22N2O2, Mw = 358.43, monoclinic,
a = 15.328, b = 11.964, c = 12.157 Å,
V = 1890.0 Å3, T = 293 (2) K, space group C12/C1, Z = 4, Dc = 1.260 mg/m3,
(Mo-K 17159 reflections collected, 2340 unique
) = 0.081 mmÀ1
a
= 90.00, b = 122.03,
c = 90.00°,
l
a
,
(Rint = 0.0312), R1 = 0.0523, wR2 = 0.1363, GOF = 1.093 {I > 2r(I)}.
11. See the Supplementary data.
12. Coles, S. J.; Frey, J. G.; Gale, P. A.; Hursthouse, M. B.; Light, M. E.; Navakhun, K.;
Thomas, G. L. Chem. Commun. 2003, 568–569.
phenyl to anisoyl group, which strongly affects the
p-cloud of
the system with an increase in the electron density, thereby desta-
bilizing the hydrogen bond formed by FÀ with NH of pyrrole.
In conclusion, we have demonstrated a two-step synthesis of
meso-diaryldipyrromethanes by using easily available and stable
precursor in comparatively shorter reaction time with high yield.
The synthetic methodology adopted here is simple and straightfor-
ward due to the absence of side products and hence easier for
purification. Also, we could tune the functional groups at the
13. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Montgomery, J. A.; Vreven, J. 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.;