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.     

A new method for generating organosilanones

A new method for the generation of organosilanones by the reaction of betaines, R₃P⁺-CR¹R²-SiR³R⁴-S^–, with (Et₃Sn)₂O was suggested.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2246–2247, December, 1994.This study was financially supported by the Russian Foundation for Basic Research, Project No. 94-03-09710.     

Electron-transfer induced change of direction of interannular haptotropic isomerization of fluorenyltricarbonylchromium anions

It has been shown by cyclic voltammetry in a THF medium in the temperature range from –70 °C to +20 °C that one-electron electrochemical reduction of (⁶-C¹³H¹⁰)Cr(CO)₃ (1) to the corresponding 19-electron anion radical (1 ^–) is accompanied by splitting off of a H atom to form the 18-electron carbon-centered anion (⁶-C₁₃H₉)Cr(CO)₃ (^–2 ), which at room temperature undergoes intramolecular haptotropic isomerization to the metal-centered (⁵-C₁₃H₉)Cr(CO)₃ ^– (^– 3) anion. The reversible one-electron reduction of3 ^– to the corresponding 19-electron radical dianion3 ^2.– induces ^{5 6} interannular isomerization. In contrast to the equilibrium shift to the ⁵-isomer in 18-electron complexes 2 and 3, in their 19-electron analogs the equilibrium is shifted to the ⁶-isomer.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 48–53, January, 1994.This work was carried out with financial support from the Russian Foundation for Basic Research (no. 93-03-5209)     

Reactions of triferrocenylchloromethane hydrochloride

Conclusions Triferrocenylchloromethane hydrochloride reacts with nucleophilic reagents (organomagnesium and-sodium compounds, aluminum lithium hydride, sodium methylate, sodium cyanide) to yield the corresponding triferrocenylmethane derivatives.     

Activation of C--H bonds in C1-C3 alkanes by titanium(iv) and zirconium(iv) cationic complexes: a DFT study

A DFT study of a model reaction [(⁵-C₅H₅)₂MCH₃]⁺ + RH [(⁵-C₅H₅)₂MR]⁺ + CH₄ (M = Ti^IV, Zr^IV; R = Me, Et, Pr, Prⁱ) was carried out with the PBE density functional. Exchange of -bonded ligand proceeds through the formation of agostic complexes [Cp₂M(RH)CH₃]⁺ followed by their isomerization into complexes [Cp₂M(CH₄)R]⁺ via an inner-sphere migration of a hydrogen atom. The calculated rate constants for such migrations involving the primary and secondary C--H bonds of propane molecule differ by 930 times for Ti^IV complexes and by 47 times for Zr^IV complexes, which is due to the effect of steric factors.     

Magnetic isotope effect in the photolysis of organotin compounds

Photolysis of organotin molecules RSnMe3 is shown to be a spin selective radical reaction accompanied by fractionation of magnetic, (117,119)Sn, and nonmagnetic, (118,120)Sn, isotopes between starting reagents and products. A primary photolysis process is a homolytic cleavage of the C-Sn bond and generation of a triplet radical pair as a spin-selective nanoreactor. Nuclear spin dependent triplet-singlet conversion of the pair results in the tin isotope fractionation. Experimentally detected isotope distribution unambiguously demonstrates that the classical, mass-dependent isotope effect is negligible in comparison with magnetic, spin-dependent isotope effect.     

The I2(B) predissociation by solving an inverse atoms-in-molecule problem

The valence electronic states of the iodine molecule are analysed by means of a simple atoms-in-molecule model which accounts for the lowest ²P states of iodine atoms and approximates the spin-orbit interaction by its atomic part. For this model, an inverse problem is solved, i.e. non-relativistic potential energy curves and diabatic couplings are determined by a least-squares fit to known relativistic potential energy curves. The resulting adiabatic wave functions are used to calculate the electronic matrix elements responsible for natural, hyperfine and magnetic predissociation of the iodine molecule in the B0⁺ _u: state. The results are in reasonable agreement with experimental data, being stable enough with respect to the variation of input relativistic potentials. They also indicate the importance of diabatic couplings between the non-relativistic states of the same symmetry.