Si-Backbones with SiP and SiAs Double Bonds

The project envisages the synthesis of molecules with backbones composed of up to 10 silicon atoms which are connected by single bonds and of phosphorus or arsenic atoms which are bonded to silicon by double bonds. For this purpose, suitable precursor molecules with SiP and SiAs single bonds will be synthesized which in a second step are expected to form the double bonds by salt elimination reactions. To stabilize the double bonds kinetically, large organic substituents such as 2,4,6-trimethylphenyl or 2,4,6-tri-tert-butylphenyl groups will be introduced at the phosphorus and arsenic atoms. By this way, the synthesis of conjugated systems such as 1,4-diphospha-2,3- disilabutadiene will also be attempted. The synthetic work will be complemented by quantum chemical ab initio calculations of equilibrium geometries, NMR chemical shifts and isomerization barriers. Furthermore, the influences of the substituents on bond strengths, electron delocalisation and isomerization barriers will be investigated.

In the present project, open-chain and cyclic dihalooligosilanes Me 14Si 7 X2 und Me 16Si 9 X2 with X = flourine, chlorine, bromine und iodine were synthesized and characterized with single crystal X-ray crystallography.These oligosilanes were furtheron reduced with alkali metals and also treated with lithiumphosphides RPHLi. The reduction of the heptasilanes Me 14Si 7 X2 led to silylenes which trimerized forming cyclotrisilanes. The reduction of the cyclic oligosilanes Me 16Si 9 X2 led to a stable cyclic silylene which was characterized with 29Si-NMR spectroscopy. The reactions with lithium phosphides led to the formation of a SiP bond with atom arrangement HP-SiX, which was used furtheron for the generation of SiP double bonds.