Siegel der Universität zu Köln
 
University of Cologne
Faculty of Mathematics and Natural Sciences
Department of Chemistry - Inorganic Chemistry
Dr. Sait Elmas
email: nsaid(at)gmx(dot)de

PhD Thesis:
"Neuartige Komplexe von Oxo-Pincer-Liganden mit späten Übergangsmetallen"

Abstact

During my reserach work a series of so-called Oxo-Pincer ligands was synthesized and fully characterized by NMR, single crystal X-ray diffraction and further analytical, as well as spectroscopic methods. The ligands are classified in two types of Oxo-Pincer ligands. The first type of the these ligands is based on 2,6-disubstituted pyridinediols RR'pydimH2 where also chiral ligands could be obtained. The second type of ligands are 2,6-difuranyl-4-aryl-pyridines difap. In this case the Oxygen donors are involved in an aromatic ring.
The ligands of the type RR'pydimH2 form stable complexes with the late transition metals Co(II), Ni(II), Cu(II), Zn(II), Pd(II) and Pt(II). Their variable structures have been studied in solution and in the solid state by various spectroscopic methods and XRD. The monodentate square-planar Pd(II) and Pt(II) complexes [(RR'pydimH2)MCl2(L)] (L = ligands as dmso or RR'pydimH2) as well as the hexacoordinated Co(II), Ni(II), Cu(II) and Zn(II) complexes [(RR'pydimH2)2M]2+ are stable in any of the applied solvents. The pentacoordinated complexes [(RR'pydimH2)MCl2] undergo a "coordination disproportionation" in polar solvents to the hexacoordinated complexes and the corresponding tetrachlorometallates. In most of the cases, the type of the obtained structural motive could be controlled by preparation procedure. All complexes were fully characterized by elemental analysis, NMR spectroscopy and UV/Vis/NIR spectroscopy and for selected samples by EPR spectroscopy. A big number of the compounds could be characterized by XRD.

The coordination of the ligands of the type difap to Pd(II) and Pt(II) leads to cis and trans isomers cis/trans-[(difap)MCl2(L)] (L = ligands as dmso, dms or difap). The ratio of the isomers can be controlled by the preparation procedure and depends on the ligand. However the coordination occurs only on the pyridine donor function. Pincer coordination (ONO) for Pd(II), Pt(II) or Cu(I) can be forced by abstracting the halogene ligands or using very labile ligands in the corresponding precursor complexes. Also here, all new complexes where characterized by elemental analysis and NMR spectroscopy.