ISMSC 2007 - Università degli Studi di Pavia

Cucurbit[n]uril Molecular Containers
Simin Liu, Wei-Hao Huang, Pritam Mukhopadhyay, Lyle Isaacs*
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland,
20742, USA.
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Interest in the cucurbit[n]uril family[1] of molecular containers has accelerated dramatically in
recent years due to the availability of a homologous series of hosts (CB[n], n = 5, 6, 7, 8). In
this contribution we discuss our recent progress in the synthesis of new CB[n] compounds and
the elucidation of some of the unique aspects of their recognition behavior. We highlight
several key results from these projects including:
• CB[7] forms remarkably tight host guest complexes with adamantane ammonium ions with
binding constants exceeding 10 12 M -1 in water.[2]
• The CB[6]•cyclohexanediammonium ion complex has a dissociation rate constant of 10-9 s-1
which is 100-fold slower than Avidin-Biotin.[3]
• Cucurbit[10]uril can be isolated as a stable compound with a cavity volume of 870 Å 3 . CB[10]
displays much interesting host-guest chemistry including act as a host for a cationic calixarene
1 and controlling the folding of triazene-arylene oligomers.[4]
• Inverted CB[n] (n = 6, 7) form as kinetic intermediates during the synthesis of CB[n].[5]
• Nor-seco-CB[10] with its two intimately connected cavities forms ternary complexes with
allosteric control based on guest size.[6]
[1] J. Lagona, P. Mukhopadhyay, S. Chakrabarti, L. Isaacs, Angew. Chem. Int. Ed. 2005, 44,
4844-4870.
[2] S. Liu, C. Ruspic, P. Mukhopadhyay, S. Chakrabarti, P. Y. Zavalij, J. Am. Chem. Soc. 2005,
127, 15959-15967.
[3] P. Mukhopadhyay, P. Y. Zavalij, L. Isaacs, J. Am. Chem. Soc. 2006, 128, 14093-14102.
[4] S. Liu, P. Y. Zavalij, L. Isaacs, J. Am. Chem. Soc. 2005, 127, 16798-16799.
[5] L. Isaacs, S.-K. Park, S. Liu, Y.-H. Ko, N. Selvapalam, Y. Kim, H. Kim, P. Y. Zavalij, G.-H.
Kim, H.-S. Lee, K. Kim, J. Am. Chem. Soc. 2005, 127, 18000-18001.
[6] W.-H. Huang, S. Liu, P. Y. Zavalij, J. Am. Chem. Soc. 2006, 128, 14744-14745.
Biphenylthioureas as organocatalysts for electrochemical reductions
Ana M. Costero, Gemma M. Rodríguez-Muñiz, Salvador Gil, Pablo Gaviña
Departamento de Química Orgánica. Universidad de Valencia. Dr. Moliner, 50. 46100-
Burjassot. Valencia. Spain
Over the past years an increasing interest toward the so called organocatalysts has arised [1].
Organocatalysts are organic molecules that can be used as efficient catalysts for different type
of reactions. These catalysts do not contain any metals and for this reason they are very
convenient from the environmental point of view. Among the different interactions that can be
established between the catalyst and the substrate, hydrogen-bonding has demonstrated to be
very useful [2]. Thus, the potential of N,N-disubstituted (thio)ureas to serve as active metal-free
organocatalysts for a wide range of synthetically useful reactions susceptible to the influence of
general acid catalysis has been recognized [3]. Although, urea and thiourea derivatives have
been successfully used for a variety of
diatereo- and enantioseltive reactions, to the
A1
A1
best of our knowledge no examples of
catalysis in electrochemical reactions of
C 1
C1
C3
O 2N N
organic compounds have been described
being the described examples related to
cation oxidation have been reported [4].
We now report the catalytic activity exhibed by the biphenyl thiourea derivatives 1-3 [5] (Chart 1)
in the electroreduction of some carboxylates.
The effect on the CV of addition of p-methoxybenzoate anions to DMSO solutions of the ligands
is illustrated in Figures 2 for the case of 1. Here, an additional cathodic peak (C3) near to -600
mV precedes the peaks C1 corresponding to the reduction of the nitrobiphenyl moiety of the
ligand previously described. On increasing the concentration of the anion, the peaks C3
monotonically increase as the anion concentration increases, whereas the peak C1 remains
essentially unchanged. The voltammetry of the ligand plus anion could be interpreted on
assuming that the anion coordinates to the ligand via hydrogen bond formation between the
amide groups of the ligand and the carboxylate group of the anion. However the increment in
the current as the concentration of anion increases only can be rationalized on considering the
electrochemistry of the anion that experiment an electroreduction giving rise to 4.4’dimethoxybenzyl.
[1] For reviews on organocatalysts, see; (a) P. I. Dalko and L. Moisan, Angew. Chem., Int. Ed.,
2001, 40, 3726–3748; (b) P. I. Dalko and L. Moisan, Angew. Chem., Int. Ed., 2004, 43, 5138–
5175; (c) Acc. Chem. Res. 2004, 37, 487–631; (d)
[2] P. R. Schreiner, Chem. Soc. Rev. 2003, 32, 289-296.
[3] (a) T. R. Kelly and M. K. Kim, J. Am. Chem. Soc., 1994, 116, 7072–7080; (b) F. P.
Schmidtchen and M. Berger, Chem. Rev., 1997, 97, 1609–1646; (c) B. R. Linton, M. S.
Goodman and A. D. Hamilton, Chem.–Eur. J., 2000, 6, 2449–2455. S. J. Connon, Chem.- Eur.
J. 2006, 12, 5419-5427.
[4] A. Nosal-Wiercinska, G. Dalmata, Electroanalysis 2002, 14, 1275-1280.
[5] A.M. Costero, P. Gaviña, G. Rodríguez-Muñiz and S. Gil Tetrahedron 2006, 62, 8571-8577.
S
H
Chart 1
N
R
H
1 R=C 6H 5
2 R=Et
3 R= 4-NO 2-C 6H 4
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