Tetsuo Yatabe

Cage Compounds of Si and Ge: Synthesis and Structures

Abstract Syntheses, characterization, and reactions of octasilacubane Si8R8 (R = 2,6-diethylphenyl), octagermacubane Ge8R8 (R = 2,6-diethylphenyl), hexasilaprismane Si6R6 (R = 2,6-diisopropylphenyl), and hexagermaprismane Ge6R6 (R = 2,6-diisopropylphenyl) are reported.

1,1,2,2,9,9,10,10-Octamethyl-1,2,9,10- tetragerma[2.2]paracyclophane: the first [2.2]paracyclophane bridged by two GeGe bonds

Abstract Tetragerma[2.2]paracyclphane, the first [2.2]paracyclophane bridged by two GeGe bonds, has been prepared by the reductive coupling reaction of 1,4-bis(chlorodimethylgermyl)benzene with sodium. The molecular structure, determined by X-ray crystallography, and spectroscopic properties of the new cyclophane are described. Interesting comparisons of the structural features with those of tetrasila[2.2]paracyclophane and [2.2]paracyclophane are made.

Synthesis and Mesomorphism of α,ω-Diphenylpermethyl-oligosilanes

Abstract α,ω-Diphenylpermethyloligosilanes, Ph(SiMe2)nPh where n = 12 (3), and 13 (4), showed the mesophases in the range of 126–139 and 127–155°C, respectively. In the mesophases, the silicon chains adopted the all-trans conformation and were perpendicular to the layer plane and hexagonally ordered within the layer. Furthermore, the phenyls at both ends of the silicon chain were interdigitated between the neighboring layers.

Structural Studies of Vacuum-Deposited Thin Film of Permethyloligosilanes with Phenyl End Groups

Thin films of permethyloligosilanes with phenyl end groups, Ph(SiMe2)nPh (n = 10, 12), were prepared by vacuum deposition at various temperatures. The deposited thin films were investigated by X-ray diffractometry in terms of multilayered structures and varying incident-angle absorption spectroscopy in terms of their molecular orientations. The interlayer spacings in the multilayered structures are reasonably well explained by assuming interdigitated structures with the molecules oriented normal to the substrates. When the films were deposited onto cold substrates, another structure appeared, in which molecules are oriented parallel to the substrate. Introduction of phenyl end groups was found to reduce the domain sizes in thin films.

Synthesis and Mesomorphism of 1,10-Dialkylpermethyl-Decasilanes

Abstract 1,10-dialkylpermethyldecasilanes, R[Si(CH3)2]10R where R = C2H5 1b, C3H7 1c, and C4H9 1d, were prepared from 1,6-dichloropermethylhexasilane in a three-step reaction. Decasilanes 1b-d show the enantiotropic mesophase in the range of 50–105, 22–87, and 23–69 C, respectively. The molecular alignment for the decasilanes in the mesophase were investigated by X-ray diffraction method. These oligosilane molecules are hexagonally ordered to form a multilayer interdigitated structure. The alkyl and silicon chains of these oligosilanes adopt almost all trans conformations and are perpendicular to the layers. These decasilanes show absorption bands with maxima at 293–294 nm in the mesophase. These absorption maxima are red-shifted by 12–14 nm, comparing with those in the liquid state and in solution.