Homologous series of the PdCl2 and PtCl2 complexes of maleonitrile-dithiacrown ethers: synthesis, crystal structures, NMR spectroscopy and mass spectrometry

The chelate complexes of maleonitrile-dithiacrown ethers mn-12S2O2–mn-21S2O5 (mn=maleonitrile) and of the acyclic ligand mn-S2 with salts, respectively, of Pd(II) and Pt(II) were studied in the solid state, in solution and in the gas phase. The structures of [MCl2(mn-S2On)] (n=2–5) (M=Pd, Pt) were investigated experimentally by X-ray analysis, mass spectrometry and 1D and 2D NMR spectroscopy in solution; the complex formation was studied by 1H, 13C and 195Pt NMR titration experiments. As techniques the fast atom bombardment (FAB), desorption ionization (DEI) and electrospray mass spectrometry (ESMS) have been applied. The results of the extraction investigations of the maleonitrile-dithiacrown ethers prove the stability of the complex [PdCl2(mn-S2O2)] to be much higher than that of the other ligands with the same metal ion (H.-J. Holdt, K. Gloe, H. Bukowsky, H. Stephan, Chem. Eur. J. in preparation). The explanation for the preferred complexation of mn-S2O2 regarding the salts PdCl2 and PtCl2 is given. For the ligands with smaller ring sizes, mn-12S2O2 and mn-15S2O3, one sulfur atom was found in R and the second sulfur atom in S-configuration. In the complexes of the larger macrocycle ligands as well as that of the acyclic ligand mn-S2, both sulfur donor atoms have the same configuration. These differences in the configuration at the S-donor atoms of the complexes and the free ligands depending on the ring size have been never described before.