Conformations of Cyclohexasilanes

The aim of the project lies in the conformational analysis of cyclohexanes and cycloheptanes with backbones composed of third or fourth row elements silicon, phosphorus and germanium. Variable temperature vibrational Raman spectroscopy (-100C to +100C) will be used to identify various conformations in the liquid state. Extensive quantum chemical calculations of equilibrium geometries and their energies, barriers as well as vibrational frequencies will be performed to support the interpretation of the experimental results. Parent cyclohexasilane Si 6 H12, germapentasilacyclohexane Si 5 H10GeH 2 , phospha-pentasilacyclohexane Si 5 H10PH as well as cycloheptasilane Si7H14 will be investigated first, and the results will then be used in the investigation of the methylated compounds.

In the project, the bi(cyclohexasilanyls) Si6H11-Si6H11 und Si6Me11-Si6Me11, which are composed of two Si6 - rings, were investigated with quantum chemical calculations as well as vibrational Raman Spectroscopy. The research focused on the energetic sequence of the possible conformers, which result from the combination of ring conformations and internal rotation around the SiSi-bond connecting the two rings. The results were supported by an investigation of the bi(silacyclohexyls) C5H11SiX-SiXC5H11 with X = H, F, Cl, Br, I und Ph. These compounds, which are characterized by a single SiSi-bond, have not yet been described in the literature and were synthesized during the project for the first time. Silicon- Sulfur six-membered ring were also investigated in the project. All these ring systems are characterized by a large number of possible conformations, resulting in complicated conformer equilibria at room temperature.