Heteroorganic betaines

Photolysis and thermal decomposition of betaines R₃P−CR¹R²−SiR³R⁴−S⁻ (1) follows two main pathways: (a) a Corey—Chaykovsky type reaction with elimination of Ph₃P and generation of silathiirane (2) and (b) a retro-Wittig type reaction accompanied by elimination of R₃P=CR¹R² and generation of silanethione R³R⁴Si=S (3). Highly reactive compounds2 and3 undergo subsequent transformations to give derivatives of tetrahydro-1,4-dithia-2,5-disilin, 1,3-dithia-2,4-disilolane, and phosphonium salts ofsymm-tetraorganodisilthiane dithiolates Ph₃P⁺CHR¹R²]₂(R³R⁴SiS⁻)₂S]. The structures of the compounds obtained were established by X-ray diffraction analysis and multinuclear NMR spectroscopy. For part 3, see Ref. 1. The betaines Et₃P⁺CHMeSiMe₂S⁻ and Et₃P⁺CHMeSiPh₂S⁻ with alkyl groups at the phosphorus atom are distinguished by high thermal stability; their spectral characteristics do not change during storage of solutions of these compounds in pyridine-d₅ or metastable solutions in benzene-d₆ for 1–2 years at −20°C in sealed evacuated tubes or on heating (150°C) for 15 h. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1594–1603, September, 2000.