Synthesis of non-symmetric viologen-containing ditopic ligands and their Pd(ii)/Pt(ii)-directed self-assembly.

We present here an efficient method for the preparation of non-symmetric viologen-containing ditopic ligands, as well as the Pd(ii)/Pt(ii)-directed self-assembly of some of these into metallacyclic receptors. The designed synthetic route, that implies the sequential alkylation and the Zincke reaction of activated bipyridinium salts, allowed us to substantially improve the yield in the preparation of three previously reported ligands. The versatility and efficiency of the method have also been tested for the preparation of four new viologen-containing ligands with very different structural features. Furthermore, the self-assembly of the new ligands around Pd(ii) and Pt(ii) centers has been tested, yielding mononuclear rectangular-shaped metallacycles of different dimensions and electronic characteristics.