An isolable NHC-stabilized silylene radical cation: synthesis and structural characterization

The silyl-substituted silylene-NHC complex bis(tri-tert-butylsilyl)silylene-(1,3,4,5-tetramethylimidazol-2-ylidene) [((t)Bu(3)Si)(2)Si:←NHC(Me), 2] was synthesized and isolated as air- and moisture-sensitive orange crystals by reductive debromination of the dibromosilane ((t)Bu(3)Si)(2)SiBr(2) (1) with 2.0 equiv of KC(8) in the presence of NHC(Me). In addition, the silylene-NHC complex 2 cleanly underwent one-electron oxidation with 1.0 equiv of Ph(3)C(+)·Ar(4)B(-) (Ar(4)B(-) = tetrakis[4-(tert-butyldimethylsilyl)-2,3,5,6-tetrafluorophenyl]borate) in benzene to afford the NHC-stabilized silylene radical cation [((t)Bu(3)Si)(2)Si←NHC(Me)](?+)·Ar(4)B(-) (3). The radical cation 3 was isolated as air- and moisture-sensitive yellow crystals and structurally characterized by X-ray crystallography and electron paramagnetic resonance spectroscopy, which showed that 3 has a planar structure with a π-radical nature.     

Kinetic model for formation of DMPO-OH in water under ultrasonic irradiation using EPR spin trapping method

The rate of the formation of the 2-hydroxy-5,5-dimethyl-1-pyrrolidinyloxy (DMPO-OH) radical in water during ultrasonic irradiation was evaluated both experimentally and theoretically. The hydroxyl radical (OH radical) was indirectly detected using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as the spin trapping compound, and the generated DMPO-OH by the reaction between the OH radical and DMPO was measured by an electron paramagnetic resonance. The rate of change in the concentration of the DMPO-OH decreased with time, suggesting that not only the formation reaction of DMPO-OH but also the degradation reaction would take place by ultrasonic irradiation. The formation rate of the DMPO-OH was higher with ultrasonic power intensity and lower with reaction temperature. Based on the experimental results, a kinetic model for the formation of the DMPO-OH was proposed by considering the formation reaction, the ultrasonic degradation, and spontaneous degradation of DMPO-OH. The model well described the effect of the ultrasonic power intensity and the reaction temperature on the formation rate of DMPO-OH. The rate of the formation of the DMPO-OH was evaluated with the aid of the kinetic model.     

Ethylene Epoxidation in Cylindrical Dielectric Barrier Discharge: Effects of Separate Ethylene/Oxygen Feed

The effects of separate C₂H₄/O₂ feed and C₂H₄ feed position on the ethylene epoxidation reaction in an AC cylindrical dielectric barrier discharge reactor were investigated. The highest EO selectivity of 34?% and EO yield of 7.5?%, as well as the lowest power consumption of 1.72?×?10^?16 Ws/molecule of EO produced, were obtained at a C₂H₄ feed position of 0.25, an O₂/C₂H₄ feed molar ratio of 1/4, an applied voltage of 13?kV, an input frequency of 550?Hz, and a total feed flow rate of 75?cm³/min. The results demonstrated, for the first time, that the separate feed of C₂H₄ and O₂ could provide better ethylene epoxidation performance in terms of higher EO selectivity and yield, and lower power consumption, as compared to the mixed feed. All undesired reactions including C₂H₄ cracking, dehydrogenation, oxidation, and coupling reactions are lowered by the ethylene separate feed because of a decrease in opportunity of ethylene molecules to be activated by generated electrons.     

Ligand dependence of pi-complex character in disilene-palladium complexes

The synthesis and structures of new 16-electron disilene palladium complexes with 2,6-dimethylphenyl isocyanide and phenyldimethylphosphine ligands [L(1)L(2)Pd{(t-BuMe(2)Si)(2)Si=Si(SiMe(2)Bu-t)(2)}, where L(1) = L(2) = PhMe(2)P; L(1) = (cyclohexyl)(3)P, L(2) = 2,6-dimethylphenyl isocyanide; L(1) = L(2) = 2,6-dimethylphenyl isocyanide] are described. Comparison of the X-ray structural parameters around the disilene moiety among these complexes and related bis(trimethylphosphine)(disilene)palladium and 14-electron (tricyclohexylphosphine)(disilene)palladium revealed that the pi-complex character is sensitive to the residual ligands and increases with decreasing the strength of sigma-donation from the ligands.     

Reactions of nitrophenide and halonitrophenide ions with acrylonitrile and alkyl acrylates in the gas phase: addition to the carbonyl group versus Michael addition

Gas-phase reactions of isomeric nitrophenide ions and p-halonitrophenide ions with acrylonitrile, methyl acrylate, and ethyl acrylate have been studied using mass spectrometry and computational methods. Depending on the structure of the α,β-unsaturated compound, formation of adducts to the carbonyl group of the acrylate (for methyl acrylate and ethyl acrylate) and β-adducts (adducts of p-halonitrophenide ions to α,β-unsaturated compounds in β position) was observed. Further transformations of these adducts lead to the products of elimination of an alcohol molecule and the anionic products of intramolecular substitution of a halogen atom, respectively.     

Migration mechanism of bases and nucleosides in oil-in-water microemulsion capillary electrophoresis.

The electrophoretic behaviors of five bases and corresponding nucleosides in the oil in water (o/w) microemulsion capillary electrophoresis, microemulsion electrokinetic chromatography (MEEKC), were examined in comparison with those in normal capillary zone electrophoresis (CZE). The microemulsion systems were composed of heptane, sodium dodecyl sulfate (SDS), 1-butanol and 10 mM phosphate buffer (pH 7.0) or toluene, SDS, 1-butanol and 5 mM carbonate buffer (pH 10.0). CZE was carried out in the range of pH 9.7-10.9, and the dissociation constants, pKa, of the bases and nucleosides and the electrophoretic mobilities of the anionic forms were determined. The electrophoretic behaviors of the solutes in the microemulsion systems were analyzed from their pKa, the electrophoretic mobilities of the anions determined by CZE, and the distribution constants, K(D), of the neutral forms between the microemulsion droplets and the outer aqueous phase. The importance of adsorption mechanism in MEEKC system was suggested from the correlation between log K(D) and log P.