Hypercoordinated Oligosilanes Based on Aminotrisphenols.

The hypercoordinated silicon chlorides ClSi[(o-OC6H4)3N] (3) and ClSi[(OC6H2Me2CH2)3N] (5) were used for the synthesis of catenated derivatives (Me3Si)3SiSi[(o-OC6H4)3N] (9), (Me3Si)3SiSiMe2SiMe2Si(SiMe3)2Si[(o-OC6H4)3N] (11), and (Me3Si)3SiSi[(OC6H2Me2CH2)3N] (13) in reactions with (Me3Si)3SiK·THF (7) or (Me3Si)3SiK·[18-crown-6] (8). It was found that the nature of the (Me3Si)3SiK solvate determines the product of interaction, resulting in the formation of (Me3Si)3Si(CH2)4OSi[(OC6H2Me2CH2)3N] (12) or 13. Compounds obtained were characterized using multinuclear NMR and UV-vis spectroscopy and mass spectrometry. The molecular structures of 3, 9, and 11-13 were investigated by single-crystal X-ray analysis, featuring hypercoordinated Si atoms in a trigonal-bipyramidal coordination environment with O atoms in the equatorial plane. The structure of the side product [N(CH2C6H2Me2O)3Si]2O (6) was also studied, indicating highly tetrahedrally distorted trigonal-bipyramidal environment at the Si atoms, which was confirmed by crystal density functional theory calculations indicating the very weak Si ← N interaction. The Si···N interatomic distances span a broad range (2.23-2.78 Å). The dependence of structural and NMR parameters for hypercoordinated catenated compounds from the type of the ligand was established.

Using Functionalized Silyl Ligands To Suppress Solvent Coordination to Silyl Lanthanide(II) Complexes.

The reaction of the potassium 1,3-trisilanediide Me2Si[Si(Me3Si)2K]2 with SmI2 and YbI2 was found to give the respective disilylated complexes Me2Si[Si(Me3Si)2]2Sm·2THF and Me2Si[Si(Me3Si)2]2Yb·2THF. Desolvation of coordinated solvent molecules in these complexes made their handling difficult. However, using a number of functionalized silanide ligands, complexes with a diminished number or even no coordinated solvent molecules were obtained ((R3Si)2Ln(THF)x (x = 0-3)). The structures of all new lanthanide compounds were determined by X-ray single-crystal structure analysis. NMR spectroscopic analysis of some Yb-silyl complexes pointed at highly ionic interactions between the silyl ligands and the lanthanides. This bonding picture was supported by DFT calculations at the B3PW91/Basis1 level of theory. Detailed theoretical analysis of a disilylated Eu(II) complex suggests that its singly occupied molecular orbitals (SOMOs) are very close in energy to the ligand silicon lone pairs (HOMO), and SQUID magnetometry measurements of the complex showed a deviation from the expected behavior for a free Eu(II) ion, which might be due to a ligand-metal interaction.

Tuning the Si-N Interaction in Metalated Oligosilanylsilatranes.

Most known silatrane chemistry is concerned with examples where the attached silatrane substituent atom is that of an element more electronegative than silicon. The current study features silylated silatranes with a range of electropositive elements attached to the silyl group. The resulting compounds show different degrees of electron density on the silatrane-substituted silicon atom. This directly affects the Si-N interaction of the silatrane which can be monitored either by 29Si NMR spectroscopy or directly by single crystal XRD analysis of the Si-N distance. Within the sample of study the Si-N distance is increased from 2.153 to 3.13 Å. Moreover, the bis(trimethylsilyl)silatranylsilyl unit was studied as a substituent for disilylated germylene adducts.

Electron Transfer and Modification of Oligosilanylsilatranes and Related Derivatives.

Several silatranyl -substituted oligosilanes were prepared starting from bis(trimethylsilyl)silatranylsilanide. Electrochemical and theoretical investigations of some oligosilanes revealed that electrooxidation occurs by formation of a short-lived cation radical. This species undergoes structural relaxation to form a pair of conformers, with endo and exo relationships with respect to the Si-N interaction. Reaction of a 1,4-disilatranyl-1,4-disilanide with 1,2-dichlorotetramethyldisilane gave a mixture of cis and trans diastereomers of a cyclohexasilane with the trans isomer showing a diminished Si-N distance.

Synthesis of indium nanoparticles at ambient temperature; simultaneous phase transfer and ripening.

The synthesis of size-monodispersed indium nanoparticles via an innovative simultaneous phase transfer and ripening method is reported. The formation of nanoparticles occurs in a one-step process instead of well-known two-step phase transfer approaches. The synthesis involves the reduction of InCl3 with LiBH4 at ambient temperature and although the reduction occurs at room temperature, fine indium nanoparticles, with a mean diameter of 6.4 ± 0.4 nm, were obtained directly in non-polar n-dodecane. The direct synthesis of indium nanoparticles in n-dodecane facilitates their fast formation and enhances their size-monodispersity. In addition, the nanoparticles were highly stable for more than 2 months. The nanoparticles were characterised by dynamic light scattering (DLS), small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared (FT-IR) spectroscopy to determine their morphology, structure and phase purity.

σ-Bond Electron Delocalization in Oligosilanes as Function of Substitution Pattern, Chain Length, and Spatial Orientation.

Polysilanes are known to exhibit the interesting property of σ-bond electron delocalization. By employing optical spectroscopy (UV-vis), it is possible to judge the degree of delocalization and also differentiate parts of the molecules which are conjugated or not. The current study compares oligosilanes of similar chain length but different substitution pattern. The size of the substituents determines the spatial orientation of the main chain and also controls the conformational flexibility. The chemical nature of the substituents affects the orbital energies of the molecules and thus the positions of the absorption bands.

Oligosilanylsilatranes.

Oligosilanes with attached silatranyl units were obtained by reactions of potassium oligosilanides with a silatranyl triflate. Interaction between Si and N atoms was observed in the 29Si NMR spectra (upfield-shifted SiO3 resonances) and in the solid-state structures (Si-N distances between 2.29 and 2.16 Å). The Si-N interaction can be "switched off" either by protonation of the nitrogen lone pair or by potassium silanide formation caused by trimethylsilyl group cleavage in the presence of potassium tert-butoxide.