One-electron reduction of kinetically stabilized dipnictenes: synthesis of dipnictene anion radicals

The redox behavior of kinetically stabilized dipnictenes, BbtE=EBbt [E = P, Sb, Bi; Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl], was systematically disclosed using cyclic voltammetry and theoretical calculations. It was found that they showed reversible one-electron redox couples in the reduction region. The anion radical species of the Bbt-substituted diphosphene and distibene were successfully synthesized by the reduction of the corresponding neutral dipnictenes (BbtP=PBbt and BbtSb=SbBbt). Their structures were reasonably characterized by ESR, UV-vis, and Raman spectroscopy, and the distibene anion radical was structurally characterized by X-ray crystallographic analysis.     

Synthesis and properties of a new kinetically stabilized digermyne: new insights for a germanium analogue of an alkyne

The reduction of an overcrowded (E)-1,2-dibromodigermene, Bbt(Br)Ge=Ge(Br)Bbt (2) [Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl], with KC8 afforded a stable digermyne, BbtGe[triple bond]GeBbt (1). The Ge[triple bond]Ge triple-bond characters of 1 were revealed by the X-ray crystallographic analysis and spectroscopic studies (UV/vis and Raman spectra) together with theoretical calculations. The Ge[triple bond]Ge bond lengths of the two nonidentical molecules of 1 observed in the unit cell were shorter than that of the previously reported digermyne, Ar'Ge[triple bond]GeAr' (Ar' = 2,6-Dip2C6H3, Dip = 2,6-diisopropylphenyl).     

Crystal-like periodic mesoporous organosilica bearing pyridine units within the framework

Periodic mesoporous organosilica with densely packed pyridine units within the framework and crystal-like molecular-scale periodicity was synthesized. The framework pyridines were chemically active and fully accessible for protonation and Cu(2+) adsorption.     

Prototype of Low Thermal Expansion Materials: Fabrication of Mesoporous Silica/Polymer Composites with Densely Filled Polymer inside Mesopore Space

A prototype of novel low thermal expansion materials using mesoporous silica particles is demonstrated. Mesoporous silica/polymer composites with densely filled polymer inside the mesopore space are fabricated by mechanically mixing both organically modified mesoporous silica and epoxy polymer. The mesopores are easily penetrated by polymers as a result of the capillary force during the mechanical composite processing. Furthermore, we propose a new model of polymer mobility restriction using mesoporous silica with a large pore space. The robust inorganic frameworks covering the polymer effectively restrict the polymer mobility against thermal energy. As a result, the degree of total thermal expansion of the composites is drastically decreased. From the mass‐normalized thermal mechanical analysis (TMA) charts of various composites with different amounts of mesoporous silica particles, it is observed that the coefficient of thermal expansion (CTE) values gradually increase with an increase of the polymer amount outside the mesopores. It is proven that the CTE values in the range over the glass‐transition temperatures (T_g) are perfectly proportional to the outside polymer amounts. Importantly, the Y‐intercept of the relation equation obtained by a least‐square method is the CTE value and is almost zero. This means that thermal expansion does not occur if no polymers are outside the mesopores. Through such a quantative discussion, we clarify that only the outside polymer affects the thermal expansion of the composites, that is, the embedded polymers inside the mesopores do not expand at all during the thermal treatment.     

Non-stereospecific ring expansions of 5-membered heterocyclic sulfoxides

Non-stereospecific ring expansion reactions of 5-membered heterocyclic sulfoxides, 1,3-benzoxathiole sulfoxides, 1,3-benzodithiole sulfoxides, and 1,3-dithiolane sulfoxides having a heteroatom at β-position to the sulfinyl group with acetic anhydride or p-toluenesulfonic acid are described together with thier reaction mechanism involving a sulfonium ion intermediate.     

Electroactive supramolecular self-assembled fibers comprised of doped tetrathiafulvalene-based gelators

New electroactive supramolecular fibers have been formed by self-assembly of the derivatives of tetrathiafulvalene (TTF) in liquid crystals. These derivatives are designed and prepared by introducing the TTF moiety to the scaffold derived from amino acids such as L-isoleucine whose derivatives function as organogelators. These TTF-based gelators form stable fibrous aggregates in liquid crystals. These fibers are the first example of hydrogen-bonded one-dimensional aggregates having electroactive moieties whose electrical conductivities were measured after doping. Their electronic states have also been characterized by spectroscopic methods. Unidirectionally aligned fibers are formed in the oriented liquid crystal solvents on the rubbed polyimide surface for further functionalization of the fibers.     

Stable 2H-azasilirene and 2H-phosphasilirene: Addition reaction of an overcrowded silylene to a nitrile and a phosphaalkyne

In this paper, we present the reaction of an overcrowded silylene bearing a 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt) group with pivalonitrile and t-butylphosphaalkyne to give the corresponding [1+2] cycloadducts, 2H-azasilirene and 2H-phosphasilirene derivatives. This is the first exampleof the isolation of a stable 2H-azasilirene derivative, and the X-ray crystallographic analysis unambiguously revealed its three-membered ring structure in the solid state. In addition, DFT calculations supported three-membered ring character in the structures of the 2H-azasilirene and 2H-phosphasilirene.     

Simultaneous determination of anthraquinones, their 8-beta-D-glucosides, and sennosides of Rhei Rhizoma by capillary electrophoresis

The simultaneous separation and determination of major anthraquinones (emodin, chrysophanol, rhein and their glucosides, aloe-emodin, sennoside A, and sennoside B) of Rhei Rhizoma were achieved by cyclodextrin modified capillary zone electrophoresis. The running electrolyte used in this method was 0.005 M alpha-cyclodextrin in 0.03 M borate buffer (pH 10.0) containing 20% acetonitrile, with an applied voltage of 20 kV.     

Synthesis and characterization of functionalized ferrocenylsilanes bearing a bulky substituent

Several types of overcrowded ferrocenylsilanes, Tbt(Fc)SiX₂(Tbt=2, 4, 6-tris[bis(trimethylsilyl)methyl]phenyl, Fc=ferrocenyl, X = H, OH, and Br) were synthesized and characterized. In addition, DFT calculations for ferrocenylsilanediol systems indicated the existence of the intramolecular hydrogen bonding between the Fe atom and H–O moiety in Tbt(Fc)Si(OH)₂. Dedicated to Professor Mitsuo Kira on the occasion of his 2005 Wacker Awardy     

Synthesis and structure of a distorted octahedral palladium(II) complex coordinated with a tetrathioether ligand tethered with bulky substituents

A new type of an o-phenylene-bridged tetrathioether ligand tethered with extremely bulky substituents, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt) groups, at its terminal sulfur atoms, TbtS[(o-phenylene)S]3Tbt (1), was synthesized by taking advantage of the coupling reaction of thiols with iodobenzenes using Cu2O in 2,4,6-trimethylpyridine. Complexation of 1 with Na2PdCl4 gave the corresponding dichloropalladium(II) complex, [PdCl2(1)] (7). The X-ray structural analysis of 7 indicated that the central palladium metal is in a distorted octahedral environment, where the two inner sulfur atoms of 1 and the two chlorine atoms form a square planar arrangement around the palladium metal and the two terminal sulfur atoms of 1 weakly coordinate to the palladium center at the axial positions. In addition, a phenyl analogue of 1, PhS[(o-phenylene)S]3Ph (2), was synthesized by a method similar to that for 1. Reaction of 2 with Na2PdCl4 gave the corresponding dichloropalladium(II) complex, [PdCl2(2)] (8). X-ray crystallography of 8 showed a type of the structure different from the distorted octahedral structure in 7, i.e., a square planar arrangement around the central palladium atom with the one terminal sulfur atom of 2, its neighboring sulfur atom, and the two chlorine atoms. The results of the NMR studies on 8 in a CDCl3 solution were not consistent with the results of the X-ray crystallography and suggested the coordination of the two inner sulfur atoms of 2 to the palladium metal, although a possibility of the existence of the rapid interconversion among isomers could not be excluded.