The structure and chemical transformations of betaines Me2E14(-)-CH2-(+)E15Me3 (E14 = Si, Ge, and Sn and E15 = P and As) and the reaction between 1,3-Di(ter-butyl)-2,3-dihydro-1H-1,3,2-diazasilol-2-ilidene and trimethylmethylenephosphorane

The structure and chemical transformations of model organometallic betaines Me2E14(-)-CH2-((+)EMe3)-Me-15 (E-14 = Si, Ge, and Sn and E-15 = P and As) were studied by density functional theory. The process most favorable thermodynamically for betaines with E-14 = Si and Ge and E-15 = P was isomerization into ilides Me2HE14-CH=(EMe3)-Me-15. For betaines with E-14 = Si and Ge and E-15 = As, the decomposition to etheneelement compounds Me2E14 = CH2 and phosphine (arsine) was found to be most probable. Betaines Me2Sn(-)-CH2-((+)EMe3)-Me-15 (E-15 = P and As) correspond to the global minima of the corresponding potential energy surfaces. It was shown theoretically that betaines L(t-BuN)(2)Si(-)-CH2-PMe3(+) formed in reactions of cyclic silylenes L(t-BuN)(2)Si: (L = CH=CH and CH2-CH2) with Me3P=CH2 should decompose under gas-phase kinetic control conditions to produce phosphine Me3P and silenes L(t-BuN)(2)Si=CH2, although the process most favorable thermodynamically is isomerization to silylated ilides L(NBU-t)(2)Si(H)-CH=PMe3. It was found experimentally that the reaction between silylene L(t-BuN)(2)Si: and Me3P=CH2 in tetrahydrofuran solution at room temperature yielded ilide L(NBu-t)(2)Si(H)-CH=PMe3 (L = CH=CH).