Robert Zink

Synthese und eigenschaften funktioneller Tetrasilane und Hexasilane

Abstract The methylphenylsilanes Ph2Si(SiMe3)2, SiMe3SiPh2SiPh2SiMe3, SiMe3SiPh2SiPh2SiPh2SiMe3, PhSi(SiMe3)3 and (SiMe3)2SiPhSiPh(SiMe3)2 have been prepared by dehalogenation of mixtures of Ph2SiMe2/ClSiMe3 and PhSiCl3/ClSiMe3 with sodium-potassium alloy or by reductive coupling of appropriate triflated silanes with lithium. The reactions of the silanes with HX/AlX3 (X = Cl, Br, I) as well as triflic acid have been investigated and the crystal structure of the tetrasilane Me3SiSiPh2SiPh2SiMe3 has been determined.

CMe3SiX3 and SiMe3SiX3 (X=H, F, Cl, Br, I): a combined ab initio and vibrational spectroscopic study

Abstract The infrared and Raman vibrational spectra of the tert-butylsilanes CMe3SiX3 and disilanes SiMe3SiX3 (X=H, F, Cl, Br, I) have been measured and assigned with the help of normal coordinate analyses and potential energy distribution analyses employing ab initio optimized geometries and ab initio symmetry force constants. Scaled theoretical SiX and SiSi force constants are smaller than values estimated by extrapolation from spectroscopic force constants of related disilanes. The synthesis of the novel compound SiMe3SiI3 and the residual disilanes SiMe3SiX3 (X=H, F, Cl, Br) is described.

Rotational isomerism of 1,2-dichlorotetramethyldisilane studied by Raman spectroscopy and ab initio quantum chemical calculations

Abstract The Raman vibrational spectra of 1,2-dichlorotetramethyldisilane recorded at various temperatures prove that two rotamers, gauche and anti, are present in the liquid state due to restricted rotation of the SiMe2Cl groups. The solid is composed of the anti rotamer exclusively. From a van’t Hoff plot, the enthalpy difference ΔH=Hgauche−Hanti has been determined as 1.01±0.2 kJ mol−1, the anti rotamer being more stable. Ab initio SCF-HF calculations of equilibrium geometries, harmonic vibrations and harmonic force fields have been performed for both rotamers and the vibrational spectra have been assigned employing these results.

Gauche, ortho, transoid and anti conformations of the tetrasilanes SiMe3SiX2SiX2SiMe3 (X=H, F, Cl, Br, I): a computational and vibrational spectroscopic study.

The energy profile for rotation around the central Si-Si bonds of the tetrasilanes SiMe3SiX2SiX2SiMe3 (X=H, F, Cl, Br and I) were examined by ab initio calculations and temperature-dependent Raman spectroscopy. Ethanelike intrinsic barriers to rotation were found for X=H, Cl, Br and I. MP2 calculations predict for SiMe3SiF2SiF2SiMe3 the existence of a gauche minimum with backbone dihedral angle ω≈64° and a twisted minimum with ω≈115°, as shown in the picture (solid line=HF, dashed line=MP2). The curious 115° local minium can be accounted for by a unique intrinsic barrier to rotation superimposed by electrostatic interactions involving strongly polar SiF bonds.

1,1,2-Tri-tert-butyldisilane, But2HSiSiH2But: vibrational spectra and molecular structure in the gas phase by electron diffraction and ab initio calculations

The molecular structure of 1,1,2-tri-tert-butyldisilane, But2HSiSiH2But, has been determined in the gas phase by electron diffraction (GED) and ab initio molecular-orbital calculations. Vibrational spectra are consistent with a vapour consisting of one conformer, identified by the structural study as a syn arrangement in which each of the butyl groups eclipses an Si–H bond. Important structural parameters (ra) for the conformer are: Si–Si 236.3(8), Si–C (mean) 191.1(3), C–C 154.5(1), C–H 112.4(1) pm, Si(1)–Si(2)–C(21) 116.0(8), Si(2)–Si(1)–C(11) 111.2(10), Si(2)–Si(1)–C(12) 108.7(9), C(11)–Si(1)–C(12) 121.1(11) and C(21)–Si(2)–Si(1)–H(13) –6.2(11)°, where C(11), C(12) and C(21) are the central carbon atoms of the three tert-butyl groups. These experimental observations are supported by theoretical predictions obtained at the D95*/MP2 level, which also identify two higher-energy conformers.

Molecular structure of ButCl2SiSiCl2But in the gas phase by electron diffraction and ab initio calculations. Molecular structures of the compounds ButX2SiSiX2But (X = Cl, Br or I) by vibrational spectroscopy, X-ray crystallography and ab initio calculations

The series of compounds ButX2SiSiX2But (X = Cl, Br and I) have been studied by X-ray crystallography, vibrational spectroscopy and ab initio calculations. The solids were all found to be anti and the vibrational spectra are consistent with this observation. The molecular structure of 1,2-di-tert-butyltetrachlorodisilane, ButCl2SiSiCl2But, has also been determined in the gas phase by electron diffraction (GED) and ab initio molecular-orbital calculations. The conformation is distorted slightly from the fully staggered arrangement, with ϕ(CSiSiC) 167.7(11)°. Important structural parameters (ra) include: Si–Si 238.0(7) pm, Si–C 187.2(7) pm, C–C 154.3(2) pm, C–H 114.2(4) pm, Si–Si–C 119.8(6)°, Cl–Si–Cl 105.5(8)° and C–Si–Si–C 167.7(11)°. These experimental observations are supported by theoretical predictions obtained at the MP2/6-31G* level.

1,2-Di-tert-butyltetrafluorodisilane,ButSiF2SiF2But: vibrationalspectra and molecular structure in the gas phase by electron diffractionand ab initio calculations

The molecular structure of 1,2-di-tert-butyltetrafluorodisilane, Bu t SiF 2 SiF 2 Bu t , has been determined in the gas phase by electron diffraction (GED) and ab initio molecular orbital calculations. Together with infrared and Raman studies, GED shows that only a single conformer (anti, C 2h symmetry) is present in the gas phase. From normal coordinate analysis, the Si–Si stretching force constant is 179 N m -1 , within the range previously observed for other related compounds. Important structural parameters (r a ) are: Si–Si 234.6(6), Si–C 187.2(3), Si–F 160.0(2), C–C 153.7(3), C–H 113.5(2) pm, Si–Si–C 114.6(7), Si–Si–F 108.7(3) and F–Si–F 107(2)°. This geometry is supported by theoretical predictions obtained at the 6-31G*/SCF level.