pubs.acs.org/Organometallics Published on Web 07/13/2009 r 2009 American Chemical Society Organometallics 2009, 28, 4431–4437 4431 DOI: 10.1021/om900277u Dendritic and Ion-Pairing Effects in Oxo-anion Recognition by Giant Alkylferrocenyl Dendrimers C atia Ornelas, Jaime Ruiz, and Didier Astruc* Institut des Sciences Mol  eculaires, UMR CNRS No. 5255, Universit e Bordeaux 1, 33405 Talence Cedex, France Received April 10, 2009 Dendrimers containing 3 nþ2 long tethers (n=generation number from 0 to 7: G 0 -G 7 ) terminated by alkylferrocenyl termini were used for the redox recognition of the oxo-anions H 2 PO 4 - and ATP 2- by cyclic voltammetry (CV) in order to investigate the ion-pairing and dendritic effect in the absence of a functional group attached to the ferrocenyl termini. Such groups were previously assumed to play an essential role in the magnitude of redox recognition due to their supramolecular interaction with the anion perturbing the ferrocenyl potential. Titration in CH 2 Cl 2 solution of these metallo- dendrimers with the n-Bu 4 N þ salt of the oxo-anion provided a new CV wave at less positive potential, while the intensity of the initial ferrocenyl CV wave decreased. Whereas ferrocene and the reference monometallic compound Fc(CH 2 ) 11 OC 6 H 4 OH, 1 (Fc = ferrocenyl), undergo only reversible ion-pairing interaction with H 2 PO 4 - , the reaction of oxo-anions with the ferrocenyl dendrimers is fast and complete (1 equiv oxo-anion per ferrocenyl branch). The difference of wave potential ΔE 1/2 between the initial CV wave and the new CV wave observed with the dendrimers is ΔE 1/2 =120 ( 10 mV from G 0 (9 alkylferrocenyl tethers) to G 3 (243 alkylferrocenyl tethers) without significant differences in this series. Strong adsorption of high-generation dendrimers G 6 and G 7 was favorable for the fabrication of modified Pt electrodes that recognized the oxo-anions. 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