Macrocyclic dithiomaleonitriles for an efficient PdCl2 coordination

We have synthesized a set of new unsaturated macrocyclic dithioethers with an increasing number of flexible methylene units 1–7 (Scheme 2) to investigate the correlation between the ring size of these ligands, the chelation effect and the consequences for an efficient PdCl2 coordination. The dithioethers 1–7 and the complex [PdCl2(4)]·CHCl3 were characterized by X-ray diffraction analysis. The crystal structures of 1–7 show that 2–7 are better preorganized chelating ligands for an exocyclic PdCl2 coordination than 1. The chelation effect of 1–7, the orientation of the sulfur atoms and the S⋯S donor distances, are influenced by the flexibility of the methylene units. In this series the unsaturated macrocyclic ligands 5 and 6 are the best chelating ligands for an efficient PdCl2 coordination. Comparative solvent extraction experiments with mn-12S2O2 (mn = maleonitrile) reveal that the low interface activity of the new ligands reduces the extraction rate. However, a comparison with open-chain dithiomaleonitriles shows the impact of the macrocyclic effect of 4 and 5 on the extraction yield.