title: A Tetraferrocenyl-Resorcinarene Cavitand as a Redox-Switchable Host of Ammonium Salts.
abstract: Tetraannulation of a resorcinarene-octaamino cavitand with ferrocenecarboxaldehyde allows the preparation of a tetrabenzimidazole-resorcinarene cavitand with four ferrocenyl moieties directly linked to the C2 atom of the imidazole units. Oxidation of the four ferrocenyl moieties produces important structural modifications of the molecule, as indicated by DFT calculations performed for the neutral and tetraoxidized forms of the cavitand. By means of (1) H NMR spectroscopic analysis, the encapsulating properties of the new tetraferrocenyl-resorcinarene cavitand toward a series of ammonium salts were evaluated, and a clear cutoff point in binding affinity with respect to size was observed. Cyclic voltammetric studies allowed us to estimate the relative association constants for the neutral and oxidized forms of the cavitand, thus indicating that the guest was bound to the neutral (reduced) state of the cavitand and was released from the oxidized form. These redox-addressable conformational and binding properties of the resorcinarene-tetraferrocenyl cavitand constitute all the necessary features of a redox-switchable molecular gripper. By means of mass-spectrometric analysis, we could unambiguously confirm the molar stoichiometry of the host-guest complex (1:1) and assess the strong guest encapsulation, as indicated by triggering the covalent coupling between host and guest in the gas phase.
authors.affiliation: Institute of Advanced Materials (INAM), Universitat Jaume I, Avda. Sos Baynat. 12071 Castellón (Spain), Fax: (+34) 964387522.
authors.forename: Sheila
authors.initials: S
authors.lastname: Ruiz-Botella
authors.affiliation: Departament de Química, Universitat Autónoma de Barcelona, 08193 Cerdanyola del Vallès, Catalonia (Spain).
authors.forename: Pietro
authors.initials: P
authors.lastname: Vidossich
authors.affiliation: Departament de Química, Universitat Autónoma de Barcelona, 08193 Cerdanyola del Vallès, Catalonia (Spain). gregori@klingon.uab.es.
authors.forename: Gregori
authors.initials: G
authors.lastname: Ujaque
authors.affiliation: Serveis Centrals d'Instrumentació Científica, Universitat Jaume I, Avda. Vicente Sos Baynat, 12071 Castellón (Spain). barrera@sg.uji.es.
authors.forename: Cristian
authors.initials: C
authors.lastname: Vicent
authors.affiliation: Institute of Advanced Materials (INAM), Universitat Jaume I, Avda. Sos Baynat. 12071 Castellón (Spain), Fax: (+34) 964387522. eperis@uji.es.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Peris
keywords: calixarenes; cations; cavitands; ferrocene; host-guest systems