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Pd(OAc)2 in CH3CN–water formed various complexes, including
1ꢁPd (m/z 657). In the presence of excess of 1, we also observed
12ꢁPd (m/z 1209) whereas with Pb(NO3)2 1ꢁPb (m/z 759) was
formed. Titration of Pd(OAc)2 with 1 in chloroform (by UV-vis)
afforded a binding constant of (1.3 ꢂ 0.8)107. Titration of HgCl2
with 1 in chloroform (using 1H NMR) revealed a weaker binding
constant of (1.2 ꢂ 0.3)103 (see ESI†). The multiple binding
stoichiometries and different metal affinities suggest that the
multifarenes offer non-trivial binding geometries, which could
arise from the tangential rather than diametrical orientation of
the sulfur lone pairs.
In conclusion, the multifarenes presented here are synthetic
macrocycles constructed of alternating building blocks. These
new molecules are conveniently accessible by three alternative
synthetic approaches that provide modularity, generality and
scalability. With increasing ring size, multifarenes exhibit
increased flexibility, adopting multiple conformations with
induced fit to their guest molecules. Expectedly, these new
cavitands can bind metals at their heteroatom portals. Work is
Scheme 2 Synthesis of multifarenes 16, 18 and 19. (a) 8 (1 eq.), 2-
imidazolidinone (1 eq.), (CH2O)n (5 eq.), PTSAꢁH2O (50 mol%), toluene,
60 1C, 2d. (b) 7 (1 eq.), 17 (1 eq.), (CH2O)n (2.1 eq.), PTSAꢁH2O (50 mol%),
toluene, 70 1C, 3d. (c) 13 (1 eq.), CDI (3.3 eq.), dry THF, RT, 2.5 h.
another interesting case of induced fit, the molecule is folded currently underway in our labs to explore their host–guest
around its guest molecule, ethyl acetate. The guest itself adopts a chemistry and unique metal binding properties, which can
less favored syn-gauche conformation, fitting into the host cavity. find useful applications, including catalysis, metal ion extrac-
This conformation is dictated by the four pairs of hydrogen-bonded tion, surface chemistry and nanoparticle coating.
thiocarbonyl and phenol groups with S–O distances of 3.15, 3.26,
EK is the incumbent of the Benno Gitter & Ilana Ben-Ami
3.19, and 3.26 Å, and minimization of the molecular dipole Chair of Biotechnology. GP acknowledges the Schulich Scholarship
moment. The centroids of the four aromatic rings are positioned program and the Israel Ministry of Science and Technology for the
at the vertices of a distorted tetrahedron with the six edges being Eshkol scholarship.
7.36, 7.96, 7.66, 7.30, 7.93 and 9.20 Å. The elongation of the latter
edge corresponds to the presence of a methyl group of the host at
that specific edge. Another distorted tetrahedron is defined by
the centroids of the pentagonal imidazolidinethione rings with
Notes and references
1 (a) J.-M. Lehn, Angew. Chem., Int. Ed. Engl., 1988, 27, 89–112;
measured edges of 7.64, 7.21, 7.20, 7.56, 8.05 and 9.95 Å, again with
the ethyl group of the guest corresponding to the main distortion.
As is the case for 2, the H NMR data suggest that the solution
(b) D. J. Cram, Angew. Chem., Int. Ed. Engl., 1988, 27, 1009–1020;
(c) C. J. Pedersen, Angew. Chem., Int. Ed. Engl., 1988, 27, 1021–1027.
2 (a) Comprehensive Supramolecular Chemistry, ed. G. W. Gokel,
Pergamon, Oxford, 1996, vol. 1; (b) Molecular Recognition: Receptors
1
¨
structure of 3 at room temperature averages multiple conforma-
tions of similar energy.
for Molecular Guests, ed. F. Vogtle, Pergamon, Oxford, 1996, vol. 2;
(c) Comprehensive supramolecular chemistry: supramolecular technology,
ed. D. N. Reinhoudt, Pergamon Press, New York, Oxford, 1996, vol. 10;
(d) Modern Supramolecular Chemistry, ed. F. Diedrich, P. J. Stang and
R. R. Tykwinski, Wiley VCH, Verlag, 2008.
3 (a) Calixarenes Revisited, ed. C. D. Gutsche, The Royal Society of
Chemistry, Cambridge, 1998; (b) Calixarenes, ed. M.-Z. Asfari,
All three of the above-described synthetic approaches to
multifarenes offer three significant advantages. First, the ability
to construct them either via single-step or multi-step synthesis
allows for easy diversification and heterogeneity, a task that is non-
trivial for the common cavitands, which are usually made in a
single step. Second, the mild synthetic conditions are compatible
with a broad variety of functional groups. Finally, these synthetic
approaches are simple, inexpensive and scalable.
We demonstrated these advantages by the convenient synthesis
of heterogeneous multifarenes (Scheme 2). For example multifarene-
[4,3S,1O], 16, was prepared in 56% yield by the reaction of precursor 8
with 2-imidazolidinone. Alternatively, an element of chirality could
be incorporated into the multifarene skeleton by using an enantio-
merically pure unit. For example, the chiral multifarene[3,3], 18, was
prepared in 82% yield by the reaction of oligomer 7 with (R,R)-17.
Furthermore, the synthesis of multifarene[2,2O], 19, was accom-
plished in 49% yield simply by using 1,10-carbonyldiimidazole
(CDI) in the reaction with polyamine 13.
¨
V. Bohmer, J. Harrowfield and J. Vicens, Kluwer, Dordrecht, 2001.
4 (a) P. Timmerman, W. Verboom and D. N. Reinhoudt, Tetrahedron,
1996, 52, 2663–2704; (b) G. Mann, E. Weinelt and S. Hauptmann,
J. Phys. Org. Chem., 1989, 2, 531–539; (c) H.-J. Schneider and
U. Schneider, J. Inclusion Phenom. Macrocyclic Chem., 1994, 19,
67–83.
5 (a) J. L. Sessler, W.-S. Cho, D. E. Gross, J. A. Shriver, V. M. Lynch and
M. Marquez, J. Org. Chem., 2005, 70, 5982–5986; (b) P. A. Gale,
´
J. L. Sessler and V. Kral, Chem. Commun., 1998, 1–8.
6 (a) N. L. Strutt, R. S. Forgan, J. M. Spruell, Y. Y. Botros and
J. F. Stoddart, J. Am. Chem. Soc., 2011, 133, 5668–5671; (b) M. Xue,
Y. Yang, X. Chi, Z. Zhang and F. Huang, Acc. Chem. Res., 2012, 45,
1294–1308.
7 (a) J. Lagona, P. Mukhopadhyay, S. Chakrabarti and L. Isaacs, Angew.
Chem., Int. Ed., 2005, 44, 4844–4870; (b) J. W. Lee, S. Samal,
N. Selvapalam, H.-J. Kim and K. Kim, Acc. Chem. Res., 2003, 36,
621–630.
8 (a) Clathrate Compounds, Molecular Inclusion Phenomena and Cyclo-
dextrins, ed. J. L. Atwood, J. E. Davies, T. Osa and D. Reidel,
Michigan, 1984; (b) J. Szejtli, Chem. Rev., 1998, 98, 1743–1754.
9 Multifarious (adjective): having or occurring in great variety, The
Merriam Webster Dictionary, Springfield, online edition, 2013.
Expectedly, multifarenes bind metal ions, as evidenced by
NMR, UV and LCMS. For example, LCMS showed that 1 and
2496 | Chem. Commun., 2014, 50, 2494--2497
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