Multi-Ferrocene-Containing Silanols as Redox-Active Anion Receptors

The ability of diferrocenylsilanediol, Fc(2)Si(OH)(2) (5), and 1,1,3,3-tetraferrocenyldisiloxane-1,3-diol, Fc(2)(HO)Si-O-Si(OH)Fc(2) (6), to act as new electroactive anion receptors for either acetate or chloride anions has been investigated in solution, in the solid state, and in the gas phase. H-1 NMR spectroscopic titrations with anions reveal that the binding interaction causes chemical-shift perturbations not only in the Si OH hydrogen-bonding donor motif but also in the ferrocenyl protons of receptors 5 and 6. Square-wave voltammetric studies evidence that multiferrocenyl silanols 5 and 6 exhibit higher ability for electrochemical sensing of acetate than chloride, since the corresponding half-wave potentials (E-1/2) for the successive ferrocene oxidations display a higher cathodic shift in the presence of such an anion. Furthermore, single-crystal X-ray diffraction analyses of the tetrabutylammoinum salts of complexes [Fc(2)Si(OH)(2)center dot CH3COO](-) (8), [Fc(2)Si(OH)(2)center dot Cl](-) (9), [Fc(2)(HO)Si-O-Si(OH)Fc(2)center dot CH3COO](-) (10), [{Fc(2)(HO)Si-O-Si(OH)Fc(2)}(2)center dot CH3COO](-) (11), and [Fc(2)(HO)Si-O-Si(OH)Fc(2)center dot Cl](-) (12) confirm that redox-active silanol receptors 5 and 6 can bind the acetate and chloride anions in the solid state. Electronic structure calculations were carried out for 5 to explore the intrinsic ability of the silanediol group to bind these anions in a vacuum.