ISMSC 2007 - Università degli Studi di Pavia

PSA 13
Halide anion interactions with dicopper(II) and dicobalt(II) bistren cryptates
Greta Bergamaschi, Valeria Amendola, Luigi Fabbrizzi, Antonio Poggi
Dipartimento di Chimica Generale, Università di Pavia, 27100 Pavia, Italy
Homodimetallic bistren cryptates include polyatomic anions, displaying size and shape
selectivity. [1] The dicopper(II) complex of cryptand 1, containing 2,5-dimethylfurane spacers,
forms very stable inclusion complexes with halides, in an aqueous solution buffered at pH 5, the
event being signalled by the development of an unusually intense charge transfer band,
responsible for the bright yellow colour. [2] A slight pH increase (to 7) induces halide extrusion,
which is replaced by an hydroxide ion, with a colour change to seawater green.
The crystal and molecular structure of the [Cu2 II (1)(Cl)] 3+ inclusion complex is shown in the
Figure above. In order to avoid OH competition, interaction of halides with [Cu2 II (1)] 4+ has been
now investigated in an aprotic solvent (e.g. MeCN) through spectrophotometric titration
experiments. On chloride addition to a cryptate solution, the following species form in sequence:
(i) {[Cu2 II (1)]Cl[Cu2 II (1)]} 7+ , in which a Cl ion bridges two Cu II centres of two distinct cages; (ii)
the [Cu2 II (1)(Cl)] 3+ inclusion complex; (iii) [Cu2 II (1)(Cl)2] 2+ , in which each metal centre has its own
Cl coordinated. Noticeably, the strong absorption band at 410 nm ( = 8000 M 1 cm 1 ) and the
intense yellow colour are observed only with the {[Cu2 II (1)] Cl[Cu2 II (1)]} 7+ and [Cu2 II (1)(Cl)] 3+
species, thus specifically involving the Cu II ClCu II fragment. Similar behaviour was observed
on titration with Br and I .
Also cobalt(II) forms a stable dimetallic cryptate complex with 1, whose anion inclusion
tendencies have been investigated in MeCN solution. On halide addition the two ‘bridged’
species form {[Co2 II (1)]X[Co2 II (1)]} 7+ and [Co2 II (1)(X)] 3+ but no intense charge transfer
band develops. Moreover, on further halide addition, Co II ions are abstracted from the cage. In
any case, for both Cu II and Co II cryptates, thermodynamic constants of anion inclusion equilibria
are higher than 10 5 and cannot be determined exactly through spectrophotometric titrations.
Ligand 1 was then reacted with an excess of C16H33Br, to give the hexa-cetylated derivative 2,
which afforded the formation of the dimetallic species [Cu2 II (2)] 4+ in apolar media (n-hexane,
toluene).
[1] M. Boiocchi, M. Bonizzoni, L. Fabbrizzi, G. Piovani, A. Taglietti, Angew. Chem., Int. Ed.,
2004, 43, 3847-3852.
[2] V. Amendola, E. Bastianello, L. Fabbrizzi, C. Mangano, P. Pallavicini, A. Perotti, A. Manotti
Lanfredi, F. Ugozzoli, Angew. Chem., Int. Ed., 2000, 39, 2917-2920.
Dynamic Combinatorial Chemistry – a Selection Based Approach to
Catalysis
Enda Bergin, a David Lewis, b Zoe Pikramenou b and Sijbren Otto. a
a
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW,
UK.
b
School of Chemistry, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
Dynamic Combinatorial Chemistry is proving to be a tremendously rich and fruitful field,
combining the fast screening of combinatorial chemistry with the variety and ease of synthesis
associated with a chemically dynamic system.[1] Disulfide exchange has previously been
successfully used in the search for macrocyclic molecular receptors,[2] and proof-of-principle
results have been achieved in the search for catalysis, both for the Diels Alder reaction[3] and
acetal hydrolysis.[4] In this work we attempt to extend this methodology by the use of thiol
containing compounds capable of binding metal ions, in the expectation that these will produce
more active catalysts. A number of thiol-containing ligands have been synthesised (1-3), and
their behaviour under disulfide exchange conditions, in the presence of d- and f- block metal
ions, has been explored.
HO 2C CO 2H
N
N
HN O
CO
O NH
2H
N
SH SH
HS
R 1
R 2
N N
OH HO SH
NH
N
NH HN
1 2 3
PSA 14
[1] Corbett, P. T.; Leclaire, J.; Vial, L.; West, K. R.; Wietor, J.-L.; Sanders, J. K. M.; Otto, S.
Chem. Rev. 2006, 106, 3652-3711.
[2] For recent examples see (a) Vial, L.; Ludlow, R. F.; Leclaire, J.; Perez-Fernandez, R.; Otto,
S. J. Am. Chem. Soc. 2006, 128, 10253-10257. (b) Rodriguez-Docampo, Z.; Pascu, S. I.; Kubik,
S.; Otto, S. J. Am. Chem. Soc. 2006, 128, 11206-11210.
[3] Brisig, B.; Sanders, J. K. M.; Otto, S. Angew. Chem., Int. Ed. 2003, 42, 1270-1273.
[4] Vial, L.; Sanders, J. K. M.; Otto, S. New. J. Chem. 2005, 29, 1001-1003
SH