Bis-cobaltocenium receptor

Anion receptors incorporating cobaltocenium have been studied extensively due to the combination of an accessible redox couple and potential favourable electrostatic interactions of the cationic organometallic metallocene complex with anions. The first anion receptor based on this species was reported by Beer and co-workers in 1989 [6]. The macrocyclic bis-cobaltocenium receptor 1 was shown to bind (via electrostatic interaction) and to electro chemically sense bromide in acetonitrile solvent media. 

Beer. P.D. Hesek, D. Kingston. J.E. Smith, D.K. Stokes, S.E. Drew, M.G.B. Anion recognition by redox-responsive ditopic bis-cobaltocenium receptor molecules including a noVel calix[4]arene derivative that binds a dicarboxylate dianion. Organometallics 1995. 14. 3288. 

The first redox-active receptor for anions was the bis-cobaltocenium macrocylic ester 17 reported by Beer and Keefe in 1989.25 FAB-MS and FT-IR evidence indicates that 17 can bind anions in the oxidized state. Reduction of the cobaltoceniums to the zero state would be expected to weaken this interaction, and indeed a modest 45 mV j/2 shift is observed in acetonitrile upon addition of 4 equivalents of Br. ... 

Molecules 73-75, in which a ferrocene-1,1 -bis-amide is bridged across the upper rim of a calix[4]arene, show similar anion-sensing properties to the cobaltocenium analog 60, described previously.NMR studies in GD3GN demonstrate that these receptors preferentially bind carboxylate anions (acetate and benzoate) over H2P04 and GP. 

Beer. P.D. Drew, M.G.B. Hesek. D. Shade. M. Szemes, F. Anion recognition properties of new upper-rim bis [rhenium bipyridyl. ruthenium(II) bis(bipyridyl), cobaltocenium] calix [4] arene receptors dictated by lower-rim substituents. Chern. Commun. 1996, 18, 2161. 

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