Cyclic silicon-selenium compounds

Cyclic silicon-selenium compounds can be prepared by an insertion-type reaction of a cyclic organosilicon compound with selenium e.g., 2,2-dibutyl- 1-selena-2-silacyclopentane (774) is the product of the reaction of 1,1-dibutylsilacyclobutane (773) with selenium (equation 403)443. 

Photolysis of cyclic silicon-selenium ring systems (analogs of D3, (Me2SiO)3) apparently generated compounds with silicon-selenium double bonds these were trapped with hexamethylcyclotrisiloxane to yield the two-atom insertion products158 (equation 100). 

All studied model compounds can distinctly be divided into three groups (Table VII). The first group is composed of substances in which the sulfur, selenium or cyclopentadienyl anion acts as an anionic center. They exist only in open betaine forms, and their PES do not contain local minima corresponding to cyclic isomers. The second group contains compounds with arsonium cationic and oxide anionic centers and silicon and germanium betaines with arsonium and amide centers. They exist as cyclic isomers and their PES have no local minima corresponding to the open forms. Finally, the third group consists of six studied compounds with phosphonium cationic and oxide or amide anionic centers and arsonium-imide betaine. Their PES have minima for both cyclic and open forms separated by low barriers. 

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