The first bowl-shaped oligosilane, hexadecamethyldecasilahexahydrotriquinacene (1), and a related oligosilane, hexadecamethyldecasilaisotwistane (2), were synthesized, and their structures and properties were studied. The results revealed importance of σ conjugation on a bowl surface: the HOMOs of 1 are σ orbitals delocalized on the bowl surface, whereas the LUMO is a pseudo π* orbital on the convex and concave sides of the bowl surface.

•Alkoxylation of a hydrooligosilane has been accomplished without SiSi bond cleavage.•[RuCl2(p-cymene)]2 is the most effective catalyst.•Various alcohols can be used in this alkoxylation.Transition metal-catalyzed synthesis of alkoxydisilanes via dehydrogenative coupling of a hydrodisilane with alcohols is reported. During the reaction, the SiSi bond is preserved effectively when [RuCl2(p-cymene)]2 is used as a catalyst. Various alcohols can be used in this alkoxylation.

AbstractDithienosiloles bearing 2,4,6-triisopropylphenyl (Tip) and mesityl (Mes) groups at the 2,6-positions have been synthesized, and their structures and electronic properties have been examined. X-ray crystallography showed that the bulky aryl groups have a nearly perpendicular orientation to dithienosilole. In the UV/Vis spectra, the lowest energy absorption bands of these dithienosiloles are shifted bathochromically compared to that of the hydrogen-substituted analog. Theoretical calculations showed that the electronic effect of the bulky aryl groups can be explained by the σ–π and σ*–π* conjugation between the σ and σ* orbitals of the C−C bonds of the perpendicular benzene rings and the π and π* orbitals of the dithienosilole moiety. Furthermore, these dithienosiloles show intense blue fluorescence with high fluorescence quantum yields, as an effect of the perpendicular bulky aryl groups.

Dithienosiloles bearing 2,4,6-triisopropylphenyl (Tip) and mesityl (Mes) groups at the 2,6-positions have been synthesized. Although the bulky aryl groups have a perpendicular orientation to dithienosilole, they affect UV/Vis and fluorescence spectra. For example, these compounds show more intense fluorescence than the hydrogen-substituted dithienosilole. The electronic effects of the perpendicular aryl groups are discussed. The cover graphic shows that intense blue fluorescence is emitted from the Tip-substituted dithienosilole when it is excited with UV light. The hydrogen-substituted dithienosilole is also shown for comparison. More information can be found in the Full Paper by Akihiro Tsurusaki, Atsushi Kobayashi, and Soichiro Kyushin on page 737 in Issue 6, 2017 (DOI: 10.1002/ajoc.201700058).

The reactions of trialkyl borates B(OR)3 (R = Me, i-Pr) with dimethylphenylsilyllithium gave lithium alkoxytris(dimethylphenylsilyl)borates 1a,b. X-ray crystallographic analysis showed that 1a,b were obtained as a contact ion pair and a solvent-separated ion pair, respectively. The 11B and 29Si chemical shifts as well as the Si–B and B–O bond lengths of 1a,b and related compounds largely change, depending on the numbers of silyl and alkoxy substituents.

Tetrasilane-bridged bicyclo[4.1.0]heptasil-1(6)-ene 1 was synthesized by the reduction of 1,1,2,2-tetrachlorocyclohexasilane 2 in 12% yield as red-orange crystals. The structure and properties of 1 were studied by spectroscopy, X-ray crystallography, and theoretical calculations. The linkage of the cyclotrisilene moiety with two tetrasilane chains with tert-butyl groups remarkably affects its structure and 29Si NMR spectrum.

The detailed structure of poly(dimethylsilylene) was analyzed by 29Si and 13C CP/MAS NMR spectra and theoretical calculations. The end groups were assigned to methoxy and hydroxy groups. This assignment was also supported by the NMR measurement of model compounds. Branched structures are not present. A trace amount of siloxane bonds is contained. The degree of polymerization was estimated to be ca. 580–750 by the 29Si CP/MAS NMR spectra.

Cyclopentasilane-fused hexasilabenzvalene 1 was synthesized by the reduction of tetrachlorocyclopentasilane 6 in 19% yield as a green powder. The molecular structure and properties of 1 were studied by spectroscopic and X-ray crystallographic analyses. Theoretical calculations of the model and real molecules of 1 and their structural isomers 12–16 suggest that the linkage of the central hexasilabenzvalene moiety with trisilane chains and the introduction of tert-butyl groups affect their relative energies.

Transition metal-catalyzed monoreduction of dichlorooligosilanes with Grignard reagents is reported. Among the examined catalysts, group 4 metal chlorides such as TiCl4 and Cp2TiCl2 gave the highest reactivity and good selectivity. The reducing power is effectively controlled by changing the catalysts and Grignard reagents to achieve sufficient selectivity depending on the oligosilane substrates.

9-Phenyl-9,10-disilatriptycene (2) was synthesized by the reaction of bis(2-bromophenyl)silane (1) with magnesium in THF. On conventional heating, 2 and cis-9,10-diphenyl-9,10-dihydro-9,10-disilaanthracene (cis-3) were obtained in 31% and 36% yields, respectively. However, the yield of 2 was significantly increased to 71% on microwave irradiation. Theoretical calculations suggest that the intermediary Grignard reagents generated from trans- and cis-9,10-diaryl-9,10-dihydro-9,10-disilaanthracenes have quite different reactivity for construction of the 9,10-disilatriptycene skeleton. The bridgehead Si–H moiety of 2 was readily functionalized to give several 9,10-disilatriptycene derivatives.

The reactions of trialkyl borates B(OR)3 (R = Me, i-Pr) with dimethylphenylsilyllithium gave lithium alkoxytris(dimethylphenylsilyl)borates 1a,b. X-ray crystallographic analysis showed that 1a,b were obtained as a contact ion pair and a solvent-separated ion pair, respectively. The 11B and 29Si chemical shifts as well as the Si–B and B–O bond lengths of 1a,b and related compounds largely change, depending on the numbers of silyl and alkoxy substituents.