Partial and Complete Replacement of the Phenyl Group(s) of 1,1,3,3-Tetraphenyl-2,2,4,4-tetrakis(trimethylsilyl)cyclotetrasilane by Chlorine Atom(s).

The four phenyl groups of 1,1,3,3-tetraphenyl-2,2,4,4-tetrakis(trimethylsilyl)cyclotetrasilane were partially replaced by chlorine atom(s) by successive treatment with trifluoromethanesulfonic acid and lithium chloride. The replacement of all phenyl groups was carried out with hydrogen chloride in the presence of aluminum chloride. The structural features of the resulting mono-, di-, and tetrachlorocyclotetrasilanes were compared by X-ray crystallography.

Cooperation of σ-π and σ*-π* Conjugation in the UV/Vis and Fluorescence Spectra of 9,10-Disilylanthracene.

In 1996, we reported that silyl groups of 9,10-disilylanthracenes significantly affect the UV/Vis and fluorescence spectra. Although the results indicate that the silyl groups have strong electronic effects on anthracene, the details of the mechanisms responsible for this have not yet been clarified. This article describes the analysis of the UV/Vis and fluorescence spectra of 9,10-bis(diisopropylsilyl)anthracene by theoretical calculations.

Silicon-silicon π single bond.

A carbon-carbon double bond consists of a σ bond and a π bond. Recently, the concept of a π single bond, where a π bond is not accompanied by a σ bond, has been proposed in diradicals containing carbon and heteroatom radical centers. Here we report a closed-shell compound having a silicon-silicon π single bond.

A Six-Coordinate Silicon Dihydride Embedded in a Porphyrin: Enhanced Hydride-Donor Properties and the Catalyst-Free Hydrosilylation of CO.

The catalyst-free hydrosilylation of CO under mild conditions remains limited. Herein, we report the synthesis, characterization, and reactivity of 5,10,15,20-tetraphenylporphyrinato(dihydrido)silicon(IV) (1) as a six-coordinate silicon dihydride. The Si-H moiety of 1 reacts with polar double bonds and CO in the absence of a catalyst to afford hydrosilylated products.

Synthesis and structures of lithium alkoxytris(dimethylphenylsilyl)borates.

The reactions of trialkyl borates B(OR) (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 B and Si 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.

Decasilahexahydrotriquinacene and Decasilaisotwistane: σ Conjugation on a Bowl Surface.

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.

The Radical Anion of Cyclopentasilane-Fused Hexasilabenzvalene.

The radical anion of cyclopentasilane-fused hexasilabenzvalene was synthesized by the reduction of the corresponding neutral compound. X-ray crystallographic analysis showed a more trans-bent structure of the disilene moiety than the neutral compound. Theoretical calculations showed that the highly trans-bent structure is attributed to the hexasilabenzvalene structure.

An Isolable Radical Anion of an Organosilicon Cluster Containing Only σ Bonds.

The radical anion of octa-tert-butyloctasilacubane was generated and isolated. The EPR spectrum showed the satellites due to the tertiary (13)C nuclei of the eight tert-butyl groups. The X-ray crystallographic analysis showed that the Si-Si bonds are shortened and the Si-C bonds are elongated compared with those of octa-tert-butyloctasilacubane.

Tetrasilane-bridged bicyclo[4.1.0]heptasil-1(6)-ene.

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.

Two pentasilahousanes fused together.

The organosilicon cluster 1 with two pentasilahousanes fused together was synthesized by the reduction of 1,1,3-trichlorocyclotetrasilane. This reaction involves dimerization and rearrangement of the silicon skeleton. The structure and properties of 1 were studied by X-ray crystallographic and spectroscopic analyses.

Silylation improves the photodynamic activity of tetraphenylporphyrin derivatives in vitro and in vivo.

The effects of silyl and hydrophilic groups on the photodynamic properties of tetraphenylporphyrin (TPP) derivatives have been studied in vitro and in vivo. Silylation led to an improvement in the quantum yield of singlet oxygen sensitization for both sulfo and carboxy derivatives, although the silylation did not affect other photophysical properties. Silylation also improved the cellular uptake efficiency for both sulfo and carboxy derivatives, enhancing the in vitro photodynamic activity of the photosensitizer in U251 human glioma cells.

Cyclopentasilane-fused hexasilabenzvalene.

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.

A ladder polysilane as a template for folding palladium nanosheets.

Although discrete nano-sized compounds consisting of a monolayer sheet of multiple atoms have attracted much attention, monolayer transition metal nanosheets are difficult to access. Here we report a template synthesis of the folding metal nanosheet (2) consisting of 11 palladium atoms by treatment of a ladder polysilane, decaisopropylbicyclo[2.2.

anti-2,2,3,3,6,6,7,7,10,10,11,11,14,14,15,15-Hexadeca-methyl-2,3,6,7,10,11,14,15-octa-silapenta-cyclo-[10.4.2.2(4,9).0(5,8).0(13,16)]icosa-1(17),4,8,12(18),13(16),19-hexa-ene.

The title compound, C28H52Si8, was synthesized by condensation of two mol-ecules of 1,2,3,4-tetra-kis-(chloro-dimethyl-sil-yl)benzene with lithium. The 3,4-disila-1,2-benzocyclo-butene rings in the centrosymmetric molecule are bridged by 1,1,2,2-tetra-methyl-disilanylene chains with an anti conformation. The benzene rings are deformed by fusion with a 3,4-disilacyclo-butene ring resulting in a slight boat conformation.

1,1,3,3-Tetra-tert-butyl-2,2-diisopropyl-4,4-diphenyl-cyclo-tetra-silane.

The molecule in the structure of the title compound, C34H60Si4, lies on a twofold rotation axis that passes through the two Si atoms, resulting in a planar cyclo-tetra-silane ring. The dihedral angle between the cyclo-tetra-silane ring and the phenyl ring is 68.20 (5)°.

An organosilicon cluster with an octasilacuneane core: a missing silicon cage motif.

Cagey silicon: A silicon cluster, consisting of sixteen silicon atoms and composed of an octasilacuneane core (red, see picture) fused with cyclotetrasilanes (orange), was synthesized by reductive tetramerization of tetrachlorocyclotetrasilane. Analytical and theoretical studies reveal the unique structural and electronic features of this organosilicon cluster.

1,1,4,4-Tetra-tert-butyl-1,4-dichloro-2,2,3,3-tetra-phenyl-tetra-silane.

The title compound, C(40)H(56)Cl(2)Si(4), was synthesized by the coupling of 1,1-di-tert-butyl-1,2-dichloro-2,2-diphenyl-disilane with lithium. The asymmetric unit contains one half-mol-ecule, which is completed by an inversion centre. In the mol-ecule, the tetra-silane skeleton adopts a perfect anti conformation and the Si-Si bonds [2.

Synthesis and properties of 5,10,15,20-tetrakis[4-(alkoxysilyl)phenyl]porphyrins: an application of selective deprotection of benzaldehyde diethyl acetals in the presence of alkoxysilyl groups.

Selective deprotection of 4-(alkoxysilyl)benzaldehyde diethyl acetals 1a-1c in the two-solvent system of hydrochloric acid and chloroform gave 4-(alkoxysilyl)benzaldehydes 2a-2c in good yields. Under these conditions, undesired hydrolysis of the alkoxysilyl group was minimized. The reaction of benzaldehydes 2a and 2b with pyrrole in the presence of boron trifluoride diethyl etherate led to 5,10,15,20-tetrakis[4-(alkoxysilyl)phenyl]porphyrins 3a and 3b.

Chiral crystallization of anti-dodecaisopropyltricyclo-[4.2.00.0(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.