An Original Redox-Responsive Ligand Based on a π-Extended TTF Framework Stefan Dolder, ² Shi-Xia Liu,* ,² Franck Le Derf, ‡ Marc Salle ´,* ,‡ Antonia Neels, § and Silvio Decurtins ² Departement fu ¨r Chemie und Biochemie, UniVersita ¨t Bern, Freiestrasse 3, CH-3012 Bern, Switzerland, Laboratoire de Chimie, Inge ´ nierie Mole ´ culaire et Mate ´ riaux d’Angers, CNRS UMR 6200, UniVersite ´ d’Angers, 2 Bd LaVoisier, 49045 Angers, France, and Institut de Microtechnique, UniVersite ´ de Neucha ˆ tel, Rue Jaquet Droz 1, CH-2002 Neucha ˆ tel, Switzerland liu@iac.unibe.ch; marc.salle@uniV-angers.fr Received June 26, 2007 ABSTRACT The synthesis of the first π-extended tetrathiafulvalene (TTF) ligand featuring a furanoquinonoid spacer and pyridyl functional groups is described. This compound shows an unprecedented electrochemical sensing behavior and excellent coordinating properties toward selected divalent metal ions. Solid-state structures of the free ligand and its Ni(II)Cl 2 complex are described. The search for molecular organic metals based on tetrathi- afulvalene (TTF) derivatives has triggered the development of π-extended analogues. 1,2 It has been demonstrated that the extension of the TTF core not only leads to stabilized oxidized states and easy access to polycation states due to a diminution of Coulombic repulsion and mesomeric effects but also gives rise to an energetically narrower HOMO- LUMO gap. 1 Moreover, it can enhance the dimensionality in materials by increasing the number of π-π and/or chalcogen‚‚‚chalcogen interactions. 2 As a consequence, a variety of π-extended TTF derivatives have been prepared. However, to the best of our knowledge, no π-extended TTF systems which incorporate binding sites for the complexation of transition-metal ions have been reported yet. On the other hand, plenty of TTF derivatives, which act as ligands toward metal ions, have been studied in the fields of redox-active sensors, multifunctional materials, artificial antenna systems, and single-component molecular metals. 3 Almost all reported systems are based on TTF derivatives with an unaltered central TTF core. In the context of recognition of metal ions in redox-active sensors, a large amount of work has mainly focused on TTF crown ether derivatives, 4 while other systems ² Universita ¨t Bern. ‡ Universite ´ d’Angers. § Universite ´ de Neucha ˆtel. (1) Bendikov, M.; Wudl, F.; Perepichka, D. F. Chem. ReV. 2004, 104, 4891. (2) Fre `re, P.; Skabara, P. Chem. Soc. ReV. 2005, 34, 69. (3) (a) Segura, J. L.; Martı ´n, N. Angew. Chem., Int. Ed. 2001, 40, 1372. (b) Chem. ReV. 2004, 104, special issue on molecular conductors. (c) Jia, C-Y.; Liu, S-X.; Tanner, C.; Leiggener, C.; Neels, A.; Sanguinet, L.; Levillain, E.; Leutwyler, S.; Hauser, A.; Decurtins, S. Chem. Eur. J. 2007, 13, 3804. (d) Jia, C-Y.; Liu, S-X.; Tanner, C.; Leiggener, C.; Sanguinet, L.; Levillain, E.; Leutwyler, S.; Hauser, A.; Decurtins, S. Chem. Commun. 2006, 1878. (e) Goze, C.; Leiggener, C.; Liu, S-X.; Sanguinet, L.; Levillain, E.; Hauser, A.; Decurtins, S. ChemPhysChem 2007, 8, 1504. (4) (a) Trippe ´, G.; Levillain, E.; Le Derf, F.; Gorgues, A.; Salle ´, M.; Jeppesen, J. O.; Nielsen, K.; Becher, J. Org. Lett. 2002, 4, 2461. (b) Nielsen, M. B.; Lomholt, C.; Becher, J. Chem. Soc. ReV. 2000, 29, 153. (c) Le Derf, F.; Levillain, E.; Trippe ´, G.; Gorgues, A.; Salle ´, M.; Sebastian, R. M.; Caminade, A. M.; Majoral, J. P. Angew. Chem., Int. Ed. 2001, 40, 224. (d) Trippe ´, G.; Le Derf, F.; Lyskawa, J.; Mazari, M.; Roncali, J.; Gorgues, A; Levillain, E.; Salle ´, M. Chem. Eur. J. 2004, 10, 6497. ORGANIC LETTERS 2007 Vol. 9, No. 19 3753-3756 10.1021/ol7015127 CCC: $37.00 © 2007 American Chemical Society Published on Web 08/14/2007