Synthesis and characterization of functional cyclopentasilanes

Cleavage of the exocyclic Si-Si-bond of phenyldimethysilylnonamethylcyclopentasilane 3 by sodium ethoxide followed by chlorination with acetyl chloride leads to the monofunctional chlorononamethylcyclopentasilane 5. Subsequent hydration gives hydrononamethylcyclopentasilane 6, which can be easily converted to the corresponding bromo and iodo derivatives 7, 8. Fluorononamethylcyclopentasilane can be prepared upon treatment of 7 with ZnF2. A different but convenient synthetic pathway to the halononamethylcyclopentasilanes has also been achieved employing the corresponding trifluoromethanesulfonic acid ester 11. The halogen derivatives—as expected—show a strong influence on the physical properties of the compounds. These functionalized cyclopentasilanes may serve as useful synthetic tools in building larger oligosilane ring systems.