Synthesis, Structure, and Photolysis of Germatetrasilacyclopentanes

The five-membered-ring systems germatetrasilacyclopentanes [R 2 Si] 4 GeR‘ 2 ( 1 ) ( 1a, R = i-Pr, R‘ = Me 3 SiCH 2; 1b, R = i-Pr, R‘ = Ph; 1c, R = t-BuCH 2, R‘ = Ph) were synthesized and characterized. The structures of 1b, c have been determined by X-ray crystallography. The Si 4 Ge rings of 1b, c form an envelope and a distorted half-chair conformation, respectively. The photolysis of 1 using two kinds of light sources (low- and high-pressure mercury lamps) was carried out. The photochemical decomposition of 1a afforded two types of four-membered-ring products, cyclotetrasilane (Si 4; main) and germatrisilacyclobutane (Si 3 Ge; minor), with extrusion of germylene (Ge:) and silylene (Si:), respectively. Compounds 1b, c gave, besides the four-membered-ring products as in 1a, two types of three-membered products, cyclotrisilanes (Si 3 ) and disilagermiranes (Si 2 Ge), with extrusion of silagermene (Si Ge) and disilene (Si Si), respectively. This is the first case in which the unusual decomposition of five-membered rings into three-membered rings and dimetallenes has been found.