<i>N,N</i>-bis-(dimethylfluorosilylmethyl)amides of <i>N</i>-organosulfonylproline and sarcosine: synthesis, structure, stereodynamic behaviour and <i>in silico</i> studies

(O→Si)-Chelate difluorides R3R2NCH(R1)C(O)N(CH2SiMe2F)2 (9a–c, R1R2 = (CH2)3, R3 = Ms (a), Ts (b); R1 = H, R2 = Me, R3 = Ms (c)), containing one penta- and one tetracoordinate silicon atoms were synthesized by silylmethylation of amides R3R2NCH(R1)C(O)NH2, subsequent hydrolysis of unstable intermediates R3R2NCH(R1)C(O)N(CH2SiMe2Cl)2 (7a–c) into 4-acyl-2,6-disilamorpholines R3R2NCH(R1)C(O)N(CH2SiMe2O)2 (8a–c) and the reaction of the latter compounds with BF3·Et2O. The structures of disilamorpholines 8a,c and difluoride 9a were confirmed by an X-ray diffraction study. According to the IR and NMR data, the O→Si coordination in solutions of these compounds was weaker than that in the solid state due to effective solvation of the Si–F bond. A permutational isomerisation involving an exchange of equatorial Me groups at the pentacoordinate Si atom in complexes 9a–c was detected, and its activational parameters were determined by 1H DNMR. In silico estimation of possible pharmacological effects and acute rat toxicity by PASS Online and GUSAR Online services showed a potential for their further pharmacological study

Four independent structures of a pentacoordinate silicon species at different points on the Berry pseudorotation pathway

A new pentacoordinate silicon species containing two chelating ligands has been synthesized. The structures of four independent cations of the same compound correspond to different points on the Berry pseudorotation pathway. The percentage of square planar character varies between 19% and 40%

Effect of Liquid Viscosity and Flow Orientation on Initial Waves in Annular Gas–Liquid Flow

The complex wave structure of annular gas&ndash;liquid flow with disturbance waves and liquid entrainment is a result of the evolution of high-frequency initial waves, appearing at the very inlet of the flow, prior to the hydrodynamic stabilization of liquid film. This stage of flow evolution is studied experimentally, using a shadow technique, and theoretically, using a linear stability analysis of the Orr&ndash;Sommerfeld equation in both phases. The present work is focused on the comparison of earlier results obtained in air&ndash;water downward flow with the new results obtained in upward flow and with more viscous liquids. The flow orientation affects the shape of the liquid film prior to stabilization; the initial film area is thicker but shorter in upward flow. Upward flow orientation also leads to a lower frequency and the increment of growth of initial waves. The viscosity effect is found to be weak if flow rates of both phases are the same. The model is mostly able to reproduce the qualitative trends, but the quantitative agreement is not reached. Experimental observations indicate that the liquid flow within the initial area is significantly different from the stabilized flow of gas-sheared liquid film, which is used in the model. This difference could explain the discrepancy; further development of the model should be aimed at taking into account the evolution of the velocity profile inside the liquid film during the stage of hydrodynamic stabilization

Synthesis and hydrolysis-condensation study of water-soluble self-assembled pentacoordinate polysilylamides

Polysilylamides (n = 1-8) with a Si-Cl functionality containing pentacoordinate silicon in the backbone were produced in high yield by transsilylation of bis(chloromethyOmethylchlorosilane and the trimethylsilyl derivative of diketopiperazine. Pentaco ordinate 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 (n = 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 N'-(dimethylfluorosilylmethyl))-N'-methyl-N-(organosulfonyl)prolinamides RSO2-Pro-N(Me)CH2SiMe2F (2a-f, R = Me (a), Ph (b), 4-MeC6H4 (c), 4-ClC6H4 (d), 4-BrC6H4 (e), 4-NO2C6H4 (f)) were synthesized from the corresponding disiloxanes 1a-f using Et2O•BF3. According to the NMR and IR data, the extent of dimerization of fluorosilanes 2a-f 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 angstrom) that is 0.02-0.11 angstrom 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 N-(dimethylsilylmethyl) and N-(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 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