ISMSC 2007 - Università degli Studi di Pavia

PSB 3
Enhanced kinetic inertness in the electrochemical interconversion of Cu(I)
double helical to Cu(II) monomeric complexes
Piersandro Pallavicini, a Massimo Boiocchi, b Giacomo Dacarro a and Carlo Mangano a
a: Dipartimento di Chimica Generale, Università di Pavia, v.le Taramelli, 12 – 27100 Pavia, Italy;
e-mail psp@unipv.it;
b: Centro Grandi Strumenti, Università di Pavia, via Bassi, 21 – 27100 Pavia, Italy
Three new ligands made of two imino-quinoline halves separated by an R,R-trans-1,2cyclohexyl
spacer have been synthesized. These ligands feature –OR functions appended in
the 8-positions of the quinoline rings (R = n-alkyl).
The ligands display a behaviour similar to that of their analogues that contain unsubstituted
quinolines, forming a bistable system with copper.[1] [Cu2L2] 2+ helicates are obtained with Cu(I)
and [CuL] 2+ monomers with Cu(II), as shown by UV/Vis titrations, determination of complexes
formation constants, mass and NMR measurements, and X-ray crystallographic analysis. The
OR groups are found to be non-coordinating, but due to the closed and intertwined nature of the
complexes, the additional –OR groups sterically hinder the disassembling step and make slow
the electrochemical interconversion of [Cu2L2] 2+ into [CuL] 2+ . In particular, oxidation of [Cu2L2] 2+
gives a reversible two steps profile in Cyclic Voltammetry esperiments, due to the formation of
the Cu 2+ helicate [Cu2L2] 4+ , that does not evolve into [CuL] 2+ in the CV experiment time scale..
[1] a) V. Amendola, L. Fabbrizzi, L. Linati, C. Mangano, P. Pallavicini, V. Pedrazzini and M.
Zema, Chem. Eur. J., 1999, 5, 3679; b) V. Amendola, L. Fabbrizzi and P. Pallavicini, Coord.
Chem. Rev., 2001, 216-217, 435; c) V. Amendola, L. Fabbrizzi, L. Gianelli, C. Maggi, C.
Mangano, P. Pallavicini and M. Zema, Inorg. Chem., 2001, 40, 3579; d) V. Amendola, L.
Fabbrizzi, P. Pallavicini, E Sartirana and A. Taglietti, Inorg. Chem., 2003, 42, 1632-1636
PSB 4
Lanthanide Ion Binding Properties of Homooxacalixarene Diethylamide
Derivatives
Paula M. Marcos a, c , José R. Ascenso b , Manuel A. P. Segurado c , Peter J. Cragg d
a Fac. Ciências Univ. Lisboa, Dept. Química / CCMM, Edifício C8, 1749-016, Lisboa, Portugal
b Instituto Superior Técnico, Complexo I, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
c Fac. Farmácia Univ. Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal
d School of Pharmacy and Biomolecular Sciences, Univ. Brighton, Brighton BN2 4GJ, UK
The ability of calixarenes bearing carbonyl groups at their lower rims to bind metal ions has
been extensively studied [1]. We have been synthesising homooxacalixarene derivatives
containing carbonyl groups at the lower rim and studying their binding properties towards alkali,
alkaline earth, transition and heavy metal cations [2, 3]. In the course of these studies, we have
now extended our research into lanthanide cations.
In the present work we report the binding properties of p-tert-butyldihomooxacalix[4]arene
tetra(diethyl)amide (1) [4] and of p-tert-butylhexahomotrioxacalix[3]arene tri(diethyl)amide (2) [5,
6], both in the cone conformation, towards lanthanide cations (La 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ ,
Eu 3+ , Gd 3+ , Dy 3+ , Er 3+ and Yb 3+ ). This has been assessed by extraction studies with the
corresponding lanthanide picrates from aqueous solutions into dichloromethane. Further
information on some cation binding behaviour of derivatives 1 and 2 was obtained by proton
NMR titration experiments. Variable amounts of La, Eu and Yb triflates were added into the
NMR tubes containing the ligands, and the proton spectra recorded after each addition.
Tetraamide 1 is a very good phase transfer agent, displaying extraction percentages between
60-90 %. The results obtained with triamide 2 range from 20-30 %. These lower percentages
should mainly reflect the higher conformational flexibility of derivative 2.
t -Bu
t-Bu
OR
OR
1
OR
OR
t-Bu
O
t - Bu
t-Bu
R = CH 2 CON(Et) 2
t-Bu
O OR O
OR RO
[1] Calixarenes 2001, Z. Asfari, V. Böhmer, J. Harrowfield and J. Vicens (Eds.), Kluwer
Academic Publishers, Dordrechet, 2001.
[2] P. M. Marcos, S. Félix, J. R. Ascenso, M. A. P. Segurado, J. L. C. Pereira, P. Khazaeli-
Parsa, V. Hubscher-Bruder, F. Arnaud-Neu, New J. Chem., 2004, 28, 748-755.
[3] P. M. Marcos, J. R. Ascenso, P. J. Cragg, Supramol. Chem., 2007. (in press)
[4] S. Félix, J. R. Ascenso, R. Lamartine, J. L. C. Pereira, Tetrahedron, 1999, 55, 8539-8546.
[5] H. Matsumoto, S. Nishio, M. Takeshita, S. Shinkai, Tetrahedron, 1995, 51, 4647-4654.
[6] P. J. Cragg, M. G. B. Drew, J. W. Steed, Supramol. Chem., 1999, 11, 5-15.
O
2
t-Bu