Synthesis of <i>gem</i>-Difluorinated Nitroso Compounds

A method for the synthesis of <i>gem</i>-difluorinated nitroso compounds is described. The reaction involves interaction of organozinc reagents with (bromo­difluoro­methyl)­tri­methyl­silane followed by nitrosation of difluorinated organozinc species with an <i>n</i>-butyl nitrite/chloro­trimethyl­silane system

Synthesis of <i>gem</i>-Difluorinated Nitroso Compounds

A method for the synthesis of <i>gem</i>-difluorinated nitroso compounds is described. The reaction involves interaction of organozinc reagents with (bromo­difluoro­methyl)­tri­methyl­silane followed by nitrosation of difluorinated organozinc species with an <i>n</i>-butyl nitrite/chloro­trimethyl­silane system

Difluoromethylene Phosphabetaine as an Equivalent of Difluoromethyl Carbanion

A method for nucleophilic difluoromethylation of reactive Michael acceptors, aldehydes, and azomethines is described. The reaction is performed using the readily available and air-stable reagent difluoromethylene phosphabetaine. The process involves interaction of an electrophilic substrate with in situ generated difluorinated phosphonium ylide followed by hydrolysis of the carbon–phosphorus bond under mild conditions

Geminal Silicon/Zinc Reagent as an Equivalent of Difluoromethylene Bis-carbanion

A new difluorinated reagent, [difluoro­(trimethylsilyl)­methyl]­zinc bromide, bearing C–Zn and C–Si bonds is described. The reagent is conveniently prepared by cobalt-catalyzed halogen/zinc exchange. It can be coupled with two different C-electrophiles in a stepwise manner (with allylic halides for C–Zn bond and aldehydes for C–Si bond) affording products containing a difluoromethylene fragment

Dihydrogen Bond Intermediated Alcoholysis of Dimethylamine–Borane in Nonaqueous Media

Dimethylamine–borane (DMAB) acid/base properties, its dihydrogen-bonded (DHB) complexes and proton transfer reaction in nonaqueous media were investigated both experimentally (IR, UV/vis, NMR, and X-ray) and theoretically (DFT, NBO, QTAIM, and NCI). The effects of DMAB concentration, solvents polarity and temperature on the degree of DMAB self-association are shown and the enthalpy of association is determined experimentally for the first time (−Δ<i>H</i>°_assoc = 1.5–2.3 kcal/mol). The first case of “improper” (blue-shifting) NH···F hydrogen bonds was observed in fluorobenzene and perfluorobenzene solutions. It was shown that hydrogen-bonded complexes are the intermediates of proton transfer from alcohols and phenols to DMAB. The reaction mechanism was examined computationally taking into account the coordinating properties of the reaction media. The values of the rate constants of proton transfer from HFIP to DMAB in acetone were determined experimentally [(7.9 ± 0.1) × 10^–4 to (1.6 ± 0.1) × 10^–3 mol^–1·s^–1] at 270–310 K. Computed activation barrier of this reaction Δ<i>G</i>^‡theor_298 K(acetone) = 23.8 kcal/mol is in good agreement with the experimental value of the activation free energy Δ<i>G</i>^‡exp_270 K = 21.1 kcal/mol

Synthesis and Hydrolysis–Condensation Study of Water-Soluble Self-Assembled Pentacoordinate Polysilylamides

Polysilylamides (<i>n</i> = 1–8) with a Si–Cl functionality containing pentacoordinate silicon in the backbone were produced in high yield by transsilylation of bis­(chloromethyl)­methylchlorosilane and the trimethylsilyl derivative of diketopiperazine. Pentacoordinate polysilylamides were highly soluble in water as a result of silicon water coordination (Si←OH₂) from hydrolysis of the Si–Cl group in each repeat unit. Interestingly, the water silicon coordination in polysilanolamides was stable toward self-condensation and found to contain pentacoordinate silicon even in water, thus avoiding siloxane (Si–O–Si) bond formation. In the gas phase the polysilanolamides underwent intramolecular stepwise hydrolysis–condensation possibly as a result of CC double-bond formation at each monomer unit, as observed by MALDI-TOF MS. Low-intensity peaks of macrocyclic polysilanolamides (<i>n</i> = 2–5) were also observed that contain water molecules. For a better understanding of the hydrolysis–condensation process of the polysilylamide, new model compounds of pentacoordinated silicon derivatives of pyridones were synthesized, characterized, and compared with the polysilanolamides using NMR and X-ray crystallography. X-ray analysis of the model compounds revealed insight into the silicon water coordination in each repeat unit and the mode of packing within the polymers that contain these monomer units. It is found that the partial hydrolysis of the model pentacoordinate chlorosilanes gives water-coordinated pentacoordinate silicon species that resemble an intermediate in the aqueous hydrolysis of pentacoordinate polysilylamides

Synthesis, Structures, and Stereodynamic Behavior of Novel Pentacoordinate Fluorosilanes: Fluorosilyl Derivatives of Proline

The (O→Si)-chelate <i>N</i>′-(dimethylfluorosilylmethyl))-<i>N</i>′-methyl-<i>N</i>-(organosulfonyl)­prolinamides RSO₂-Pro-N­(Me)­CH₂SiMe₂F (<b>2a</b>–<b>f</b>, R = Me (<b>a</b>), Ph (<b>b</b>), 4-MeC₆H₄ (<b>c</b>), 4-ClC₆H₄ (<b>d</b>), 4-BrC₆H₄ (<b>e</b>), 4-NO₂C₆H₄ (<b>f</b>)) were synthesized from the corresponding disiloxanes <b>1a</b>–<b>f</b> using Et₂O·BF₃. According to the NMR and IR data, the extent of dimerization of fluorosilanes <b>2a</b>–<b>f</b> in solution is negligible, while the O→Si coordination in solution is weaker than that in the solid state. Comparative CP/MAS NMR and X-ray diffraction studies revealed that in solution the coordination Si–O bond length varies in a narrow range (2.22–2.24 Å) that is 0.02–0.11 Å longer than in the crystalline state. Dynamic NMR (DNMR) studies of the fluorides revealed a fine structure of the ¹⁹F signals in the 0–20 °C temperature range, which was related to the structural features of the coordination set in these complexes. The temperature dependence of the SiMe₂ signals in the ¹H DNMR spectra was attributed to a permutational isomerization process involving a positional exchange of equatorial ligands. The narrow range of activational barriers of the process (23–24 kcal mol^–1 and more) and high negative values of the entropy of activation are similar to those observed earlier for Si-substituted <i>N</i>-(dimethylsilylmethyl) and <i>N</i>-(methylphenylsilylmethyl) amides and lactams, which suggests similar permutational processes in all cases. Gas-phase quantum chemical studies demonstrate that the solvation of F^– reduces the activation barrier

Synthesis, Structures, and Stereodynamic Behavior of Novel Pentacoordinate Fluorosilanes: Fluorosilyl Derivatives of Proline

The (O→Si)-chelate <i>N</i>′-(dimethylfluorosilylmethyl))-<i>N</i>′-methyl-<i>N</i>-(organosulfonyl)­prolinamides RSO₂-Pro-N­(Me)­CH₂SiMe₂F (<b>2a</b>–<b>f</b>, R = Me (<b>a</b>), Ph (<b>b</b>), 4-MeC₆H₄ (<b>c</b>), 4-ClC₆H₄ (<b>d</b>), 4-BrC₆H₄ (<b>e</b>), 4-NO₂C₆H₄ (<b>f</b>)) were synthesized from the corresponding disiloxanes <b>1a</b>–<b>f</b> using Et₂O·BF₃. According to the NMR and IR data, the extent of dimerization of fluorosilanes <b>2a</b>–<b>f</b> in solution is negligible, while the O→Si coordination in solution is weaker than that in the solid state. Comparative CP/MAS NMR and X-ray diffraction studies revealed that in solution the coordination Si–O bond length varies in a narrow range (2.22–2.24 Å) that is 0.02–0.11 Å longer than in the crystalline state. Dynamic NMR (DNMR) studies of the fluorides revealed a fine structure of the ¹⁹F signals in the 0–20 °C temperature range, which was related to the structural features of the coordination set in these complexes. The temperature dependence of the SiMe₂ signals in the ¹H DNMR spectra was attributed to a permutational isomerization process involving a positional exchange of equatorial ligands. The narrow range of activational barriers of the process (23–24 kcal mol^–1 and more) and high negative values of the entropy of activation are similar to those observed earlier for Si-substituted <i>N</i>-(dimethylsilylmethyl) and <i>N</i>-(methylphenylsilylmethyl) amides and lactams, which suggests similar permutational processes in all cases. Gas-phase quantum chemical studies demonstrate that the solvation of F^– reduces the activation barrier

Synthesis, Structures, and Stereodynamic Behavior of Novel Pentacoordinate Fluorosilanes: Fluorosilyl Derivatives of Proline

The (O→Si)-chelate <i>N</i>′-(dimethylfluorosilylmethyl))-<i>N</i>′-methyl-<i>N</i>-(organosulfonyl)­prolinamides RSO₂-Pro-N­(Me)­CH₂SiMe₂F (<b>2a</b>–<b>f</b>, R = Me (<b>a</b>), Ph (<b>b</b>), 4-MeC₆H₄ (<b>c</b>), 4-ClC₆H₄ (<b>d</b>), 4-BrC₆H₄ (<b>e</b>), 4-NO₂C₆H₄ (<b>f</b>)) were synthesized from the corresponding disiloxanes <b>1a</b>–<b>f</b> using Et₂O·BF₃. According to the NMR and IR data, the extent of dimerization of fluorosilanes <b>2a</b>–<b>f</b> in solution is negligible, while the O→Si coordination in solution is weaker than that in the solid state. Comparative CP/MAS NMR and X-ray diffraction studies revealed that in solution the coordination Si–O bond length varies in a narrow range (2.22–2.24 Å) that is 0.02–0.11 Å longer than in the crystalline state. Dynamic NMR (DNMR) studies of the fluorides revealed a fine structure of the ¹⁹F signals in the 0–20 °C temperature range, which was related to the structural features of the coordination set in these complexes. The temperature dependence of the SiMe₂ signals in the ¹H DNMR spectra was attributed to a permutational isomerization process involving a positional exchange of equatorial ligands. The narrow range of activational barriers of the process (23–24 kcal mol^–1 and more) and high negative values of the entropy of activation are similar to those observed earlier for Si-substituted <i>N</i>-(dimethylsilylmethyl) and <i>N</i>-(methylphenylsilylmethyl) amides and lactams, which suggests similar permutational processes in all cases. Gas-phase quantum chemical studies demonstrate that the solvation of F^– reduces the activation barrier

Synthesis, Structures, and Stereodynamic Behavior of Novel Pentacoordinate Fluorosilanes: Fluorosilyl Derivatives of Proline

The (O→Si)-chelate <i>N</i>′-(dimethylfluorosilylmethyl))-<i>N</i>′-methyl-<i>N</i>-(organosulfonyl)­prolinamides RSO₂-Pro-N­(Me)­CH₂SiMe₂F (<b>2a</b>–<b>f</b>, R = Me (<b>a</b>), Ph (<b>b</b>), 4-MeC₆H₄ (<b>c</b>), 4-ClC₆H₄ (<b>d</b>), 4-BrC₆H₄ (<b>e</b>), 4-NO₂C₆H₄ (<b>f</b>)) were synthesized from the corresponding disiloxanes <b>1a</b>–<b>f</b> using Et₂O·BF₃. According to the NMR and IR data, the extent of dimerization of fluorosilanes <b>2a</b>–<b>f</b> in solution is negligible, while the O→Si coordination in solution is weaker than that in the solid state. Comparative CP/MAS NMR and X-ray diffraction studies revealed that in solution the coordination Si–O bond length varies in a narrow range (2.22–2.24 Å) that is 0.02–0.11 Å longer than in the crystalline state. Dynamic NMR (DNMR) studies of the fluorides revealed a fine structure of the ¹⁹F signals in the 0–20 °C temperature range, which was related to the structural features of the coordination set in these complexes. The temperature dependence of the SiMe₂ signals in the ¹H DNMR spectra was attributed to a permutational isomerization process involving a positional exchange of equatorial ligands. The narrow range of activational barriers of the process (23–24 kcal mol^–1 and more) and high negative values of the entropy of activation are similar to those observed earlier for Si-substituted <i>N</i>-(dimethylsilylmethyl) and <i>N</i>-(methylphenylsilylmethyl) amides and lactams, which suggests similar permutational processes in all cases. Gas-phase quantum chemical studies demonstrate that the solvation of F^– reduces the activation barrier