Synthesis and Properties of Branched Hydrogenated Nonasilanes and Decasilanes.

Branched higher silicon hydrides Si nH2 n+2 with n > 6 were recently found to be excellent precursors for the liquid phase deposition of silicon films. Herein we report the gram-scale synthesis of the novel nona- and decasilanes (H3Si)3Si(SiH2) nSi(SiH3)3 (2: n = 1, 5: n = 2) from (H3Si)3SiLi and Cl(SiPh2) nCl by a combined salt elimination/dephenylation/hydrogenation approach. Structure elucidation of the target molecules was performed by NMR spectroscopy and X-ray crystallography. 2 and 5 are nonpyrophoric and exhibit a bathochromically shifted UV absorption compared to neopentasilane and the structurally related octasilane (H3Si)3SiSi(SiH3)3. TG-MS analysis elucidated increased decomposition temperatures and decreased ceramic yields for branched hydrosilanes relative to cyclopentasilane. Otherwise, very similar thermal properties were observed for hydrosilane oligomers with linear and branched structures.