Masafumi Unno

Synthesis of Octacarboxy Spherosilicate

feasible new preparation was reported for an octacarboxylphenyl functionalized spherosilicate, octakis[(pcarboxyphenyl) dimethylsilyl]silicate, which was a versatile monomer leading to other functional spherosilicate derivatives. The synthesis was started from octakis[dimethyl(p-methylphenyl)silyl]silicate. Octakis[dimethyl(pmethylphenyl) silyl]silicate was brominated by NBS to produce octakis[dimethyl(4-tribromomethylphenyl)silyl]silicate. Finally, octakis[dimethyl(4-tribromomethylphenyl)silyl]silicate was hydrolyzed in the presence of AgNO3 and formic acid to give the desired compound. Octakis[(pcarboxyphenyl) dimethylsilyl]silicate was fully characterized by FTIR, 1H NMR, 13C NMR, 29Si NMR spectra, ESI-MS, and elemental analysis.

Syntheses, structures, and properties of ladder oligosilanes and ladder oligogermanes

Abstract Annelated silicon ring systems have received extensive investigation as interesting targets that provide access to physical and chemical properties that are difficult to achieve with the corresponding carbon systems. The aim of this article is to describe the results of our investigation on the chemical and physical properties of the ladder oligosilanes and the ladder oligogermanes, such as bicyclo[2.2.0]hexasilane, tricyclo[4.2.0.02,5]octasilane, tetracyclo[4.4.0.02,5.07,10]decasilane, pentacyclo[6.4.0.02,7.03,6.09,12]dodecasilane, bicyclo[2.2.0]hexagermane, and tricyclo[4.2.0.02,5]octagermane systems. Such compounds can be prepared by the reductive coupling of the appropriate polychlorosilanes or polychlorogermanes with lithium or magnesium. The X-ray structural analyses of these compounds provide intriguing information about the stereochemistry of the multifused ring systems; each cyclotetrasilane ring or cyclotetragermane ring is not planar but folded, leading to a helical structure of the ladder frameworks of the anti type. The ladder oligosilanes and oligogermanes show absorption in the UV–vis region and have considerably low oxidation potentials. The following examples of the reactions of the ladder compounds are described: the ring-opening chlorination, mono- and polyoxidation, and reduction with alkali metals leading to stable radical ions. In addition, chiral symmetry breaking in the anti-tricyclo[4.2.0.02,5]octasilane is described. For the reactions of ladder oligosilanes, the comparison with octasilacubanes is also discussed.

Tip-substituted cage and cyclic silanols

Synthesis of novel cage and cyclic silanols bearing Tip (2,4,6-triisopropylphenyl) groups was performed. Tip-substituted silanetriol, TipSi(OH) 3 ( 1 ) was prepared from TipSiCl 3 , and can be handled without special care in the air. The versatility of this silanol is amply demonstrated as a starting material of various silanols with novel frameworks. Thus, the condensation of 1 using 2-chloro-1,3-dimethylimidazolinium chloride as a dehydrating agent afforded (TipSi) 5 O 7 OH ( 2 ) in 45% yield. When 1 was treated with (TipSiCl 2 ) 2 O, cis , trans -cyclotrisiloxanetriol ( 3 ) as well as a novel incompletely condensed silsesquioxane, (TipSi) 4 O 5 (OH) 2 ( 4 ) were obtained. In addition, the dehydrochlorinative condensation of (TipSiCl 2 ) 2 O and (TipSi(OH) 2 ) 2 O afforded 4 as single product. The structures of all these novel silanols were determined by X-ray crystallography, and their unique structures (hydrogen-bonded aggregates or intramolecular hydrogen bonding) were demonstrated.

Oxaoctasilahomocubane and dioxaoctasilabishomocubane: novel silicon ring systems

Abstract The novel silicon ring systems, 9-oxaoctasilahomocubane ((SiThex) 8 O, 2) and 5,10-dioxaoctasilabishomocubane ((SiThex) 8 O 2 , 3) (Thex = 1,1,2-trimethylpropyl) were obtained by the photo-induced reaction of octasilacubane, (SiThex) 8 (1) with dimethylsulfoxide. A significant distortion of the framework is revealed by X-ray crystallography; the SiSi bond distances vary from 2.423(4) and 2.559(4) A.

Synthesis, structures, and properties of novel aminodisilanes bearing bulky substituents: 1,2-bis(1,1,2-trimethylpropyl)-1,1,2,2-tetrakis(diethylamino) disilane and 1,2-di-tert-butyl-1,1,2,2-tetrakis(diethylamino) disilane

Abstract Two novel tetraaminodisilanes, 1,2-bis(1,1,2-trimethylpropyl)-1,1,2,2-tetrakis(diethylamino)disilane ( 1 ) and 1,2-di-tert-butyl-1,1,2,2-tetrakis(diethylamino)disilane ( 2 ) were synthesized and X-ray crystallography analyses of these compounds were carried out. Reflecting the steric congestion, the SiSi bonds are very long: 2.539(2) A for bis(1,1,2-trimethylpropyl)disilane, and 2.4764(9) A for di-tert-butyl-disilane. UV spectra and oxidation potentials of several tetraaminodialkyldisilanes are compared and discussed. In addition, in the chlorination of 1 with HCl, 1,1,2,2-tetrachloro-1,2-bis(1,1,2-trimethylpropyl)disilane ( 6 ) was obtained with a 72% yield.

Hexakis(2,4,6-triisopropylphenylsilsesquioxane)

Hexasilsesquioxanes bearing bulky Tip (2,4,6-triisopropylphenyl) groups were synthesized and the structure was determined. The X-ray crystal analysis revealed that the enantiomer pair originating from the restricted rotation of the bulky Tip groups was included in the single lattice. In solution, evidence for the rapid interconversion of both enantiomers was encountered in 1H NMR. Thus, variable temperature NMR indicated peak broadeningupon warming the sample, with a coalescence temperature of 38 ° C. Kinetic parameters of the rotation were also calculated.

Refractive Indices of Silsesquioxanes with Various Structures

In order to provide reliable encapsulants for a high-performance LED, silsesquioxane is one of the most promising materials. However, the refractive indices of conventional silicone materials are relatively low and improvement is necessary. For the aim of developing silicone materials with high refractive index, we investigate the relationship of structures and refractive indices. In this paper, a series of alkyl-substituted silsesquioxanes with various structures (linear, cyclic, ladder, and cage) were newly synthesized and spectral and optical properties were investigated. Thus, linear and cyclic siloxanes were prepared from respective silanols. Two novel tricyclic laddersiloxanes (ladder-type silsesquioxanes with defined structure) were synthesized from cyclic silanols. Cage octasilsesquioxanes with same substituents were also prepared by applying the new method. The structures of the products were identified and their refractive indices were measured. As a result, cyclic siloxanes showed slightly higher values than linear or monomeric siloxanes. By adding more rings, refractive index values increased. Among the compounds we investigated, a tricyclic laddersiloxane comprising 6,8,6-membered rings showed the highest refractive index and Abbe number.

Nonacyclic Ladder Silsesquioxanes and Spectral Features of Ladder Polysilsesquioxanes

Laddersiloxanes, that is, ladder silsesquioxanes with defined structures, could be obtained by stepwise synthesis starting from cyclic silanols. These compounds were shown to have high thermal stability. As an extension of the previous work, the first nonacyclic ladder silsesquioxanes were synthesized by the reaction of bicyclic silanol with tricyclic tetrachloride, which were obtained from cyclic silanols. The structure was confirmed by spectral measurements, and the spectral features of a series of ladder polysilsesquioxanes with determined structures were analyzed.

Chiral Crystallization of anti -Dodecaisopropyltricyclo[4.2.0.0 2,5 ]octasilane

The aim of this article is to describe the results of our investigation on the chiral crystallization of anti-tricyclic ladder polysilane, anti-dodecaisopropyltricyclo [4.2.0.0(2,5)] octasilane (1). In solid state, the silicon framework of 1 adopts twisted conformation in which the Si4 rings are puckered in the same direction. Crystallization of 1 afforded a large conglomerate crystal in high yield. X-ray crystallography revealed that the crystal consists of either right-handed (P) or left-handed (M) molecules. The ultraviolet and circular dichroism spectra of the chiral crystals of 1 reveal two absorption bands in the 400-250 nm region.

A Novel Alkoxysilyl Azobenzene Dye Photosensitizer with Alkylamino Group for Dye-Sensitized Solar Cells

A newly designed alkoxysilyl azobenzene dye with alkylamino group, 4-diethoxyphenylsilyl-4′-dimethylaminoazobenzene, was synthesized and examined as the photosensitizer for a dye-sensitized solar cell (DSSC). The novel azobenzene dye exhibited a strong absorption band in the visible region, and the solar cell using the dye as the sensitizer showed an incident monochromatic photon-to-current conversion efficiency (IPCE) value of 66 % at 440 nm and a light-to-electric energy conversion efficiency of 2.2 % under simulated sunlight irradiation of AM-1.5G one sun condition. The energy conversion efficiency obtained here is the highest value among those reported so far for azobenzene-sensitized solar cells, indicating the potential of alkoxysilyl dyes as photosensitizers for DSSCs.