Metal- and Ligand-Centered Chirality in Square-Planar Coordination Compounds

Abstract

Chirality is an ubiquitous phenomenon in nature and fundamental for the principle of life we know. One part of this thesis explores the self-assembly and the host-guest chemistry of novel chiral coordination compounds based on chiral organic bispyridyl ligands and Pd(II) metal centers. The structure and the properties of the assemblies are the result of a combination of variables like the temperature, the counter ions, the solvent, the shape and the flexibility of the ligand. The cavity provided by these structures is of high interest, as it can provide a chiral environment for guests to mimic chiral biological systems. The chiral environment can be used as enantioselective sensor or for enantioselective catal-ysis. Therefore, the preparation of chiral ligands and assemblies is described. The struc-tures are characterized by NMR, ESI-MS, UV-Vis, CD and X-ray techniques. The variety of the formed three-dimensional structures includes monomeric cages, interpenetrated double cages, rings and catenanes. The conditions for the selective formation have been studied and even the enantiomeric excess of the used ligand was shown to have a tre-mendous effect on the structure and the properties of the assembly. Host guest experi-ments showed the potential of the provided chiral cavity as sensor, as a chiral helicene-based cage showed different binding affinities towards enantiomeric guests that could be monitored via NMR. Another part of this thesis explores chiral cyclometalated Pt(II) complexes. Cyclomet-alated Pt(II) complexes are heavily studied for their interesting photophysical properties and their use in OLEDs. In contrast to luminescent octahedral complexes, the number of reported chiral Pt(II) complexes is comparable low. In octahedral complexes, where chi-rality is often the result of the assembly, the square planar coordination sphere needs a special design of achiral ligands for the formation of a chiral complex. A new kind of ligand motif for luminescent Pt(II) complexes is reported in this thesis. The synthesis of the achiral trans-chelating ligand and the formation of several chiral Pt(II) complexes is shown. The complexes are characterized by NMR, ESI-MS, UV-Vis, CD and X-ray tech-niques and the photoluminescent properties are reported, which showed circularly polar-ized luminescence for this new kind of binding motif.