Selective metal-cation recognition by [2.2]ferrocenophanes: The cases of zinc- and lithium-sensing

The synthesis, electrochemical, optical and cation-sensing properties of [2.2]ferrocenophanes, in which the two ferrocene subunits are linked through two aldiminic or iminophosphorane moieties, are reported. The new compounds show remarkably selective cation-sensing properties due to the presence of redox-active units (ferrocene) and aza-unsaturated functionalities that are able to act as putative cation-binding sites. In this structural motif, the aldimine groups act as a highly selective binding site for Zn2+ cations, whereas the iminophosphorane bridges display an unusually strong binding affinity towards Li+ cations, which could be explained by an additional Li-Fe interaction. The X-ray structure of the complex 4·Li+ as well as detailed NMR spectroscopic studies, both in solution and in the solid state, support this assessment. Experimental data and conclusions about the cationsensing capabilities of this family of compounds are supported by DFT calculations. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA. Weinheim.