Harald Stüger

Permethylheteroatomcyclopolysilane mit Heteroatomen der VI. Hauptgruppe. Darstellung und spektroskopische Eigenschaften

Abstract Group VI permethylheterocyclopolysilanes (SiMe 2 ) n X with n = 4,5,6 and X ue5fb O, S, Se have been synthesized from α,ω-dichloropolysilanes and Li 2 S/Li 2 Se or by simple hydrolysis. From UV spectroscopic results considerable contributions of the heteroatom lone pair electrons to low-energy electron transitions can be derived. Siue5f8Si NMR coupling constants satisfactorily correlate with heteroatom electronegativities, indicating dominant Fermi contact contributions to the magnitude of the corresponding coupling constants.

Oligosilane mit Fe- oder Mo-Komplexsubstituenten

Abstract Oligosilanes (n = 2, 3, 4) with Dicarbonylcyclopentadienyliron and Tricarbonyimethyleyclopentadienylmolybdenum (n = 2) in terminal positions were prepared by salt elimination and characterized by means of NMR, IR, MS. The 29Si-data are discussed in detail.

Darstellung und Reaktivität von Phenylthiosubstituierten Oligosilanen

Abstract Phenylthio substituted oligosilanes are obtained from the reaction of oligomeric silicon halides with alkali metal thiophenolates M1SPh (MI = Li, Na, K). Si—Si bonds are formed when phenylthiooli-gosilanes are reacted with alkali metal silicon compounds. Alkali metal thiophenolates, the second reaction products can be separated easily. Quite similarly, Fe—Si-bonds are obtained from phenyl-thiosilanes and Na[Fe(CO)2Cp]. In contrast to the related alkali metal halide elimination reactions of organohalooligosilanes, transmetallations are never observed in the thiophenolate reactions.

PE and UV spectra of linear and cyclic polysilanes and assignment by AB initio calculations

Abstract Ab initio calculations have been performed on linear and cyclic polysilanes including permethylsubstituted compounds. Koopmans approximation was used for assigning experimentally obtained PE and UV spectra. The PE spectrum of octamethylcyclotetrasilane and the UV spectra of cyclopenta and cyclohexasilane are presented for the first time.

1,4-Dihydroxyoctaphenyltetrasilane, a stable polysilane-α,ω-diol

Abstract 1,4-Dihydroxyoctaphenyltetrasilane is obtained in 60% yield by treating a solution of 1,4-dichlorooctaphenyltetrasilane in THF with dilute HCl. Spectroscopic properties of the title compound are reported together with an X-ray structure determination, which shows that there is an intramolecular hydrogen bond between the 2 OH groups. This structural feature accounts for the ease with which the compound loses water to form the heterocyclic siloxane octaphenyloxacyclopentasilane.

Synthese 1,4-disubstituierter tetrasilane durch selektive spaltung von Si-phenyl-bindungen

Abstract Just two of three Siue5f8Ph bonds per silicon atom are cleaved by excess HBr under pressure. Thus, pentaphenyldisilane reacts with HBr at room temperature to give 1-phenyl-2,2,3,3-tetrabromodisilane. Subsequent coupling with bis-(t-butyl)-mercury yields 1,4-diphenyloctabromotetrasilane, which can also be obtained directly from 1,4-dichlorooctaphenyltetrasilane and HBr. Reduction of 1,4-diphenyloctabromotetrasilane with LiAlH 4 affords 1,4-diphenyltetrasilane, which can be converted to the corresponding 1,4-dihalo derivatives by HCl or HBr.

The crystal structure of decaphenyl-1-oxacyclohexasilane·0.5 C6H6 solvate

Abstract The crystal structure of decaphenyl-1-oxacyclohexasilane·0.5 C6H6 solvate is reported. This is the first crystal structure determination for an example of the little known class of polycyclohexasilanes containing a heteroatom. The conformation of the molecule is close to the 1,4-boat form with the oxygen and a silicon atom on the same side of the least-squares plane of the remaining atoms. Two types of Siue5f8Si bonds were found, related by the mirror-symmetry of the ring, with mean bond lengths of 2.391(1) [(O)ue5f8Siue5f8Siue5f8(Si)] and 2.373(2) A [(Si)ue5f8Siue5f8Siue5f8(Si)]. The Siue5f8Oue5f8Si valence angle is 146.0(5)° and the mean Siue5f8C bond distance 1.877(3) A.

PHOTOELECTRON SPECTRA AND QUANTUMCHEMICAL CALCULATIONS OF PERCHLOROCYCLOPOLYSILANES

Abstract He(I)-PE-spectra of perchlorocyclopolysilanes (SiCl2)4, (SiCl2)5 and (SiCl2)6 are recorded and interpreted by semiempirical PM3 calculations. HOMOs may be described by antibonding π∗ interactions of σ{SiSi)3p and (Cl)3p lone pair orbitals. First ionization potentials appear near 9 eV and increase in the order Si4 < Si6 < Si5. HOMO-LUMO studies suggest, that intramolecular charge transfer might be responsible for the unusual low energy of UV absorption bands.

Group VI Heteroatomcyclopolysilanes Syntheses and NMR Properties

Abstract Group VI heterocyclopolysilanes have been synthesized from α, ω-dichloropolysilanes and Li2S/Li2 Se or by simple hydrolysis. Si-Si NMR coupling constants correlate satisfactorily with electronegativities of the heteroelements indicating dominant Fermi contact contributions.

Ab initio calculation of the molecular structure and conformational composition of dihalotetrasilanes

Abstract The ab initio Hartree-Fock pseudopotential DZ+POL method was employed to optimize the structures of 2,3- and 1,4-dihalotetrasilanes. The dihedral angles of the Si4 skeleton were fixed at selected values. The most stable conformers of 2,3-dichloro- and dibromotetrasilane exhibit Ci symmetry, with maximum separation of the halogen atoms and the terminal SiH3 groups. The relative stability of different conformers of the 1,4-dihalotetrasilanes can be described by dipole-dipole interaction between the polar terminal silicon-halogen bonds. Self-consistent-reaction-field (SCRF) calculations predict a reversed sequence of the two lowest energy conformers in solution relative to that found in the gas phase. Compared with their carbon analogues the barriers to internal rotations in tetrasilanes are considerably lower.