Heteroorganic betaines

The structures of three silicon-containing organophosphorus betaines containing the⁺P−C−Si−S⁻ fragment were established by X-ray diffraction study. Due to the attractive electrostatic interaction between the anionic and cationic centers, the main chain adopts agauche conformation, whereas this chain in theS-ethyl derivative of the phosphonic salt Ph₃P⁺−CMe₂−SiMe₂SEt]Br⁻ adopts atrans conformation. The changes in the geometric parameters of betaines depending on the substituents at the phosphorus, carbon, and silicon atoms were analyzed. The P−S bond can in principle be formed, resulting in the closure of the four-membered ring provided that additional steric hindrances at the silicon atom occur.