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The synthesis and characterization of thermally stable monosubstituted thiophene 1-oxide and 1-imides stabilized by EMind (1,1,7,7-tetraethyl-3,3,5,5-tetramethyl-s-hydrindacen-4-yl) group on the 3-position are described. In addition to the molecular structures determined by X-ray crystallography, inversion barriers at the three-coordinated sulfur atoms have been determined by a coalescence method using diastereotopic C-3 and C-5 indacene carbon atoms as a 13C NMR probe.

Kinetic stabilization with sterically bulky substituents or ligands has played a pivotal role in exploring a large variety of unsaturated compounds or low-coordinated complexes. This article descri...

Monomeric diaryliron(II) complexes, Fe(Rind)2, have been obtained by introducing fused-ring bulky “Rind” groups. For Fe(Eind)2, a significant orbital contribution of the Fe(II) ion due to the linea...

Unlike π-electron chromophores, the peralkylated n-tetrasilane σ-electron chromophore resembles a chameleon in that its electronic spectrum changes dramatically as its silicon backbone is twisted almost effortlessly from the syn to the anti conformation (changing the SiSiSiSi dihedral angle ω from 0 to 180°). A combination of UV absorption, magnetic circular dichroism (MCD), and linear dichroism (LD) spectroscopy on conformationally controlled tetrasilanes 1-9, which cover fairly evenly the full range of angles ω, permitted a construction of an experimental correlation diagram for three to four lowest valence electronic states. The free chain tetrasilane n-Si4 Me10 (10), normally present as a mixture of three enantiomeric conformer pairs of widely different angles ω, has also been included in our study. The spectral trends are interpreted in terms of avoided crossings of 1B with 2B and 2A with 3A states, in agreement with SAC-CI calculations on the excited states of 1-7 and conformers of 10.

Diphosphenes stabilized by the fused-ring bulky 1,1,3,3,5,5,7,7-octa-R-substituted s-hydrindacen-4-yl (Rind) groups have been obtained as orange crystals by the reduction of the corresponding dichlorophosphines, (Rind)PCl2, with lithium naphthalenide (LiNaph). The molecular structures of (Eind)PCl2 and the diphosphenes, (Eind)PP(Eind) and (EMind)PP(EMind), having the bulky Eind and the less bulky EMind groups, have been confirmed by X-ray crystallography. The formation of the PP bond has been fully characterized by spectroscopic methods.

The bulky Eind-based aryllithium, (Eind)Li (Eind = 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl), reacted with BF3·OEt2 in Et2O to form the corresponding aryldifluoroborane (Eind)BF2 (1), along with a trace amount of the sterically congested diarylborane, (Eind)2BH (2). The reaction of 1 with LiAlH4 in THF led to the isolation of the corresponding lithium trihydroborate [Li(thf)]2[(Eind)BH3]2 (3), which can be transformed into the diborane(6), (Eind)HB(μ-H)2BH(Eind) (4), with treatment with Me3SiCl. The Eind-based lithium trihydroaluminate [Li(OEt2)]2[(Eind)AlH3]2 (5) has been synthesized by the reaction of (Eind)Li with LiAlH4 in Et2O. The subsequent addition of Me3SiCl to a solution of 5 in toluene produced the dialumane(6), (Eind)HAl(μ-H)2AlH(Eind) (6), the heavier congener of 4. The dialumane(6) 6 reacted with lithium metal in a mixed solvent of Et2O and toluene to give the diarylalumane, (Eind)2AlH (7), via a disproportionation reaction along with the cleavage and recombination of the Al–C bond. The discrete monomeric structures of 1, 2, and 7 and dimeric structures of 3, 4, 5, and 6 have been determined by X-ray crystallography.

(Z)-1,2-Di(1-pyrenyl)disilene containing bulky 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl (Eind) groups has been obtained as purple crystals by the reductive coupling reaction of the corresponding dibromosilane with lithium naphthalenide. An X-ray crystallographic analysis revealed an Eind- and pyrenyl-meshed molecular gear around the disilene core adopting the Z configuration, in which the two pyrenyl groups intramolecularly interact through the π–π stacking with a distance of 3.635 A between the centers of the two pyrene rings. The disilene π-system exhibits a π(Si–Si) → π*(pyrene) intramolecular charge-transfer (ICT) fluorescence at room temperature, whose wavelengths depend on the solvent polarity. The photophysical properties are theoretically supported by computational studies including excited-state calculations.

A series of neutral and cationic Au(I) complexes incorporating π-conjugated phosphasilene ligands stabilized by the bulky 1,1,3,3,5,5,7,7-octa-R-substituted s-hydrindacen-4-yl (Rind) groups have been synthesized. X-ray crystallographic studies show the η1-coordination mode of the phosphasilene ligand, accommodating the linear trans two-coordinate geometry around the gold center. While the metal coordination slightly enhances the intensity of the strong π–π* absorption of the phosphasilene chromophores, the phosphashilene π-conjugation is not extended through the Au atom.

Diborane(6) as a H-bridged dimer of monoborane can be converted cleanly by two-electron reduction into diborane(6) dianion, which is isoelectronic with ethane, through B-B σ-bond formation when each boron atom has a bulky ligand on it. The existence of the B-B σ bond is supported by the X-ray molecular structure [B-B bond length of 1.924(3) Å], NMR studies, magnetic susceptibility measurements, and DFT calculations. Stepwise hydride abstraction reactions of the diborane(6) dianion produce the corresponding H-bridged diborane(5) anion and doubly H-bridged diborane(4) without B-B bond scission.

The cyclobutadiene (CBD) molecule C(4)H(4) deviates from a high-symmetry square geometry to compensate for its antiaromatic electronic structure. Here, we report a CBD silicon analog, Si(4)(EMind)(4) (1), stabilized by the bulky 1,1,7,7-tetraethyl-3,3,5,5-tetramethyl-s-hydrindacen-4-yl (EMind) groups, obtained as air- and moisture-sensitive orange crystals by the reduction of (EMind)SiBr(3) with three equivalents of lithium naphthalenide. X-ray crystallography reveals a planar and rhombic structure of the Si(4) four-membered ring, with alternating pyramidal and planar configurations at the silicon atoms. The large (29)Si chemical shift differences (Δδ > 350 parts per million) in the solid-state nuclear magnetic resonance spectra suggest a contribution of an alternately charge-separated structure. The rhombic-shaped charge-separated singlet state of compound 1 thus stabilizes its cyclic 4π-electron antiaromaticity in a manner that contrasts sharply with the bond-length alternation, characterizing the rectangular distortion of carbon-based CBD.

The first isolable diborane(4) containing terminal B–H bonds, protected by the bulky 1,1,7,7-tetramethyl-3,3,5,5-tetrapropyl-s-hydrindacen-4-yl (MPind) groups, was synthesized as air- and moisture-...

An air-stable emissive di(1-naphthyl)disilene protected by the bulky Eind groups (Eind: 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl) has been obtained by reducing the corresponding dibromosilane (...

Recent progress in the chemistry of π-conjugated phosphasilenes stabilized by bulky protecting groups based on a fused-ring octa-R-substituted s -hydrindacene skeleton (Rind groups) is reviewed. The phosphasilenes with a variety of aryl substituents at the silicon atom are covered in detail. The X-ray crystallography analysis showed the highly coplanar π-framework reinforced by the perpendicularly-fixed Rind groups. Strong π–π* absorptions have been observed, demonstrating the extension of π-conjugation over the skeleton. The DFT calculations indicated that the LUMO involves significant contribution by the 3pπ*(Si–P)–2pπ*(carbon π-electron system) conjugation. The preparation of the gold(I) complexes of the π-conjugated phosphasilenes is also included.

Some synthetically useful transformations of organosilicon compounds have been developed since the mid 1970s, based on the new concept that the silicon-carbon bonds are activated toward electrophilic cleavage via the formation of penta- and hexa-coordinate species. This review mainly consists of the following aspects: (1) a general concept for the activation of the silicon-carbon bond via penta- and hexa-coordinate species, (2) synthetic application of hexa-coordinate organopentafluorosilicates, and (3) development of the H(2)O(2) oxidation of the silicon-carbon bond and its synthetic applications via the intramolecular hydrosilylation, silicon-tethered intramolecular radical cyclization and Diels-Alder reaction, and some silicon-containing organometallic reagents for nucleophilic hydroxymethylation and hydroxyallylation synthons.(Communicated by Hitosi NOZAKI, M.J.A.).

We have investigated the photophysical properties of the oligosilane-bridged zinc porphyrin-fullerene[60] dyads. Dependence of the rate of the relaxation processes of the singlet-excited state of the ZnP moiety of the dyads on the oligosilane linker was mostly ascribable to the conformational differences of the silicon chain. The charge-separated state with sub-microsecond lifetime was observed in the time-resolved absorption measurements of benzonitrile solution of the dyads. The lifetime of the radical-ion pair scarcely depended on the length and little on the conformation of the oligosilane linkage, which suggests that the super-exchange mechanism disciplines the charge recombination process.

A series of zinc porphyrin–[60]fullerene dyads linked by conformation-constrained tetrasilanes and permethylated tetrasilane have been synthesized for the evaluation of the conformation effect of the tetrasilane linkers on the photoinduced electron transfer. The excited-state dynamics of these dyads have been studied using the time-resolved fluorescence and absorption measurements. The fluorescence of the zinc porphyrin moiety in each dyad was quenched by the electron transfer to the fullerene moiety. The transient absorption measurements revealed that the final state of the excited-state process was a radical ion pair with a radical cation on the zinc porphyrin moiety and a radical anion on the fullerene moiety as a result of the charge separation. The charge separation and charge recombination rates were found to show only slight conformation dependence of the tetrasilane linkers, which is characteristic for the Si-linkages.

A series of oligo(p-phenylenedisilenylene)s (Si-OPVs 1-4), silicon analogues of oligo(p-phenylenevinylene)s, up to the tetramer have been synthesized and isolated by the introduction of a newly developed protecting group [(HexO)MEind] for improving their solubility. The experimental and theoretical studies of the Si-OPVs 1-4 demonstrate the fully extended π-conjugation of the Si-OPV main chains. Single crystal X-ray analyses of the monomer 1 and the dimer 2 revealed the highly coplanar Si-OPV backbones facilitating the effective extension of the π-conjugation, which has further been validated by the significant increases in the absorption maxima from 465 nm for the monomer 1 to 610 nm for the tetramer 4. The absorption maxima exhibit an excellent fit to Meier's equation, leading to the estimation of an effective conjugation length (ECL) of 9 repeat units (nECL = 9) and the absorption maximum of 635 nm for the infinite chain (λ∞ = 635 nm). In sharp contrast to other nonemissive disilenes, the Si-OPVs 2-4 show an intense fluorescence from 613 to 668 nm at room temperature with the quantum yields up to 0.48. All the data presented here provide the first evidence for the efficient extended π-conjugation between the Si═Si double bonds and the carbon π-electron systems over the entire Si-OPV skeleton. This study reveals the possibility for developing the conjugated disilene π-systems, in which the Si═Si double bonds would be promising building blocks, significantly optimizing the intrinsic photophysical and electrochemical properties of the carbon-based π-conjugated materials.

Kinetic stabilization with sterically bulky substituents or ligands has played a pivotal role in exploring a large variety of unsaturated compounds or low-coordinated complexes. This article descri...

A variety of 9-phospha-10-silatriptycenes (PSiT) and some derivatives, such as the phosphine selenides and cis-platinum complexes, have been prepared in order to study their structures and characteristics as a phosphine ligand. The 1J(P−Se) NMR coupling constant of the phosphine selenides demonstrate the large s character of the lone pair orbital on the phosphorus atom, attributable to the small C−P−C bond angles of the PSiT framework, as confirmed by X-ray crystallography. The strong trans influence of PSiT has been determined from the 1J(Pt−C) coupling constant measurements of the cis-[PtMe2(psit)2], which is due to the increase in the P−Pt−P angle in the complexes derived from the steric repulsion between the two bulky PSiT ligands. Both the substituent on the silicon and the bridging benzene rings affect the electronic character. Electron-withdrawing substituents on the silicon atom slightly increase the s character of the phosphorus lone pair orbital, and the isopropoxy groups on the bridging benzene...

Protic and Lewis acid-induced dephenylation reactions of bis(tetramethylene)-tethered bicyclic 1,3-diphenyltrisilane 1 have been found to be accompanied by a facile skeletal rearrangement that forms the ring-contracted silyl-substituted bicyclic disilanes. For the reaction with a protic acid (HX), such as HCl/AlCl3 and trifluoromethanesulfonic acid (TfOH), the protonation of the ipso-carbon of the phenyl group would be followed by the nucleophilic attack of X− on the central silicon atom that induces the skeletal rearrangement. In the case of the reaction with boron trichloride, the same rearranged product was obtained as well, although the reaction mechanism is not clear.

A zinc porphyrin–fullerene dyad with a disilane as a σ-conjugated linker has been newly synthesized to evaluate the electron transfer ability of the oligosilane chain. Its photoinduced processes ha...

Several configurationally constrained cis- and trans-1,2-diaryl-1,2-dimethyl-1,2-disilacyclohexanes (3a–e) have been synthesized in order to measure their photophysical properties, such as UV absor...

The cross-coupling reaction of fluorobenzene with an aryl Grignard reagent has been reinvestigated which revealed that the reaction readily proceeds under ordinary conditions using a catalytic amount of NiCl 2 (dppp) even at room temperature. The use of nickel catalysts and Grignard reagent is essential for the activation of the carbon-fluorine bond. The palladium catalyst is also effective for the 1,2-difluorobenzene and trifluorobenzenes to selectively produce the corresponding mono-coupled products while the nickel-based catalyst system affords a mixture of the mono-coupled product and di- or tri-coupled product.

Various types of main group element-containing π-electron systems have been synthesized using silole, dibenzoborole, or bis-silicon-bridged stilbene as the key building units. In these π-electron s...

The palladium-catalyzed cross-coupling reaction of 1-aryltriazenes with aryl- and alkenyltrifluorosilanes occurs readily at room temperature to yield the corresponding biaryl and stilbene products in moderate to good yields. In contrast to the previous results for the reaction with areneboronic acids, in which an additional Lewis acid such as boron trifluoride is essential for the activation of the 1-aryltriazenes, the Lewis acidity of organotrifluorosilanes seems to be strong enough to directly activate the triazene moiety to enter into the palladium-catalyzed cross-coupling reaction without an extra Lewis acid.

π-Conjugated polymers containing the bis-silicon-bridged stilbene (5,10-dihydro-5,10-disilaindeno[2,1-a]indene) skeleton in the main chain have been synthesized. Our synthesis uses 3,8-dimethoxy derivatives (2) and 3,8-difluoro derivatives (3) of the bis-silicon-bridged stilbene as the key precursors. Thus, their regioselective ortho-metalation reactions with appropriate bases (sec-butyllithium for 2 and LitBu2ZnTMP for 3) followed by quenching with electrophiles afford various 2,7-difunctionalized bis-silicon-bridged stilbenes. By using the 2,7-difunctionalized derivatives as starting materials, a series of π-conjugated polymers, including homopolymers of the bis-silicon-bridged stilbene skeleton and copolymers between the bis-silicon-bridged stilbene unit and other types of monomer units, such as bithiophene and diethynylbenzene, have been synthesized by cross-coupling methodologies. While all the homopolymers of the bis-silicon-bridged stilbene skeleton exhibit an intense blue to greenish-blue emission...

Sulfur-substituted silyllithiums were prepared for the first time, and their thermal stability was investigated. [(Mesitylthio)dimesitylsilyl]lithium (4) was prepared by a tin−lithium exchange reac...

We have prepared anti,cisoid-alternating oligosilanes up to Si22 comprising bis(tetramethylene)-tethered bicyclic disilane units end-capped with n-alkyldimethylsilyl groups to measure their UV absorption and MALDI-TOF mass spectra. It was confirmed that the absorption maximum wavelength due to the σσ* transition remains constant in the present anti,cisoid-alternating oligosilanes irrespective of elongation of the chain length, providing the generality of the suppression effect of σ-conjugation by a cisoid turn.

Transient absorption spectra of ion radicals were observed for tetrasilanes with rigid syn or anti Si units by electron beam pulse radiolysis. Two transient absorption bands at 4.1 and 2.8 eV were clearly resolved for the anion radical of syn-tetrasilane, while for anti-tetrasilane, the anion radical produced a broad absorption band at 4.4 eV. Cation radicals of the tetrasilanes gave similar optical transitions at 3.6 and 2.1 eV for the syn form, and 3.8 eV for the anti form. The spectra for the ion radicals of anti-tetrasilane are identical to those of ion radicals of permethylated pentasilanes or hexasilanes, suggesting that the ion radicals of oligosilane without configurational constraint take an anti conformation. The unique spectra of ion radicals of syn-tetrasilane reflect the large gap between the second and third HOMO (LUMO) of neutral molecules, which is also induced by the configurational constraint.

The Disilane Chromophore: Photoelectron an dElectronic Spectra of Hexaalkyldisilanes and 1, (n+,)-Disila[n.n.n]propellanes

A gold cluster, Au(41)(S-Eind)(12), was synthesized by ligating the bulky arenethiol 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacene-4-thiol (Eind-SH) to preformed Au clusters. Extended X-ray absorption fine structure, X-ray photoelectron spectroscopy, and the fragmentation pattern in the mass spectrometry analysis indicated that formation of gold-thiolate oligomers at the interface was suppressed, in sharp contrast to conventional thiolate-protected Au clusters.

Various types of silole-containing π-conjugated oligomers and polymers, including the silole–pyrrole cooligomers, silole–diethynylarene copolymers, silole–arene alternating copolymers such as the silole–thiophene copolymer, and 2,5-diarylsiloles, have been synthesized by the combination of the new intramolecular reductive cyclization of bis(phenylethynyl)silanes with the well-established transition metal complex-catalyzed cross-coupling reactions. The silole-based π-electron systems thus prepared have unique photophysical properties due to the unusual electronic structure of the silole ring. Some of them have been applied as new materials for organic electroluminescent devices.

This mini-review traces the initial ideas, discoveries and significant features of the cross-coupling reaction between Grignard reagents and C(sp2)-halides such as aryl and alkenyl halides in the presence of a nickel–phosphine complex as a catalyst, which was first reported by Kohei Tamao, Koji Sumitani, and Makoto Kumada in 1972.

We have explored a new possibility of controlling the properties of the main group element π-electron compounds based on a change in the coordination states of the elements. In a series of trianthryl derivatives of boron, silicon, and phosphorus, various control modes of the properties have been achieved depending on the element. Thus, in the case of the Group 13 boron, the change from tri-coordinate tri(9-anthryl)borane to the corresponding tetra-coordinate fluoroborate results in a significant change in the absorption property associated with the color change from orange to colorless. In the case of the Group 14 silicon, the change from tetra-coordinate tri(9-anthryl)fluorosilane to the corresponding penta-coordinate difluorosilicate causes a significant enhancement in the fluorescence of about 20 fold for the quantum yield. In the case of the Group 15 phosphorus, the fluorescence property is changed in multi-stages from tri-coordinate tri(9-anthryl)phosphine to the corresponding tetra-coordinate phosphonium salt and phosphine oxide, and to the penta-coordinate difluorophosphorane. These results demonstrate the significant potential of the present approach as a new molecular design for the functional main group element compounds.

Photoelectron spectra of conformationally constrained methylated tetrasilanes 1−5 were measured, extending to the full 0−180 ° range the previously available 0−80° region of SiSiSiSi dihedral angle...

Divalent silicon species bearing an 8-amino- or 8-phosphino-1-naphthyl group have been shown to behave as nucleophilic sila-ylides in the presence of diphenylacetylene to afford zwitterionic intermediates containing alkenyl anion and ammonium or phosphonium cation moieties. The reaction pathways of these zeitterionic intermediates have been clarified to be highly dependent on the character of the cationic center such as N and P.

Recent theoretical and experimental studies on conformational dependence of the oligosilane chromophore are described. CIS/3-21 G* calculations suggested that a tetrasilane has four transitions into valence excited states. Two of them are of B symmetry, one at lower and one at higher energy. It is not so much the excitation energies as the oscillator strengths of these transitions that are functions of the SiSiSiSi dihedral angle ω (avoided crossing model). This model has been confirmed by experimental efforts such as spectral separation of n-Si4Me10 conformers in low temperature matrices and measurements on conformationally constrained tetrasilane compounds, e.g.., tetrasilanes incorporated into five-to-eight-membered carbosilane ring systems and ones composed of configurationally constrained bicyclic disilane unit (s). In addition to tetrasilanes, three hexasilane conformers were investigated as well. The examination revealed that incorporation of a syn-segment into an anti chain raises the excitation energy of the first transition.

[4+2]-Coordinate disilanes containing two 8-dimethylamino-1-naphthyl (8-Me2N-1-Np) groups on the same silicon atom, (8-Me2N-1-Np)2XSi-SiMe3, where X=F, OH, OEt, and H, are prepared. The X-ray structures of the two derivatives, X=F and OH, show that one of the coordinated dimethylamino groups is anti to the electronegative X group, while the other is anti to the trimethylsilyl group. The [4+2]-coordinate disilanes (X=F or OEt) are found to be thermally stable under these conditions such that the corresponding [4+1]-coordinate disilanes (8-Me2N-1-Np)XMeSi-SiMePh2 (X=F or OEt) readily undergo degradation. In the presence of Pd(PPh3)4 as a catalyst, the [4+2]-coordinate disilane (X=F) undergoes degradation to generate naphthylsilane (8-Me2N-1-Np)-SiMe3, the reaction pathway being different from that of the [4+1]-coordinate disilane (X=F) which affords the fluorosilane, F-SiMePh2.

The boron-containing pi-conjugated systems, including tri(9-anthryl)borane (1) and tris[(10-dimesitylboryl)-9-anthryl]borane (2), have been investigated as a new type of fluoride chemosensor. Upon complexation of 1 with a fluoride ion, a significant color change from orange to colorless was observed and, in the UV-visible absorption spectra, the characteristic band of 1 at 470 nm disappeared and new bands around 360-400 nm assignable to pi-pi transitions of the anthryl moieties were observed. This change can be rationalized as a result of the interruption of the pi-conjugation extended through the vacant p-orbital of the boron atom by the formation of the corresponding fluoroborate. The binding constant of compound 1 with the fluoride ion was quite high [(2.8 +/- 0.3) x 10(5) M(-1)], whereas 1 only showed small binding constants with AcO- and OH- of around 10(3) M(-1) and no sensitivity to other halide ions such as Cl-, Br-, and I-, thus demonstrating its selective sensing ability to the fluoride ion. In contrast to the monoboron system 1, compound 2 having four boron atoms showed multistage changes in the absorption spectra by the stepwise complexation with fluoride ions.

We have already reported that 2,5-di(2-pyridyl)silole (PySPy) has high performance as an electron-transporting material (ETM) for organic electroluminescent devices (OELDs). For the purpose of developing more practicable ETMs, we have now prepared three new 2,5-diarylsilole derivatives, PPySPyP, PyPySPyPy, and PyPSPPy, having 6-phenyl-2-pyridyl, 6-(2-pyridyl)-2-pyridyl, and 3-(2-pyridyl)phenyl as the aryl groups, respectively, and have studied their structure−properties relationships. These derivatives have higher glass transition temperatures when compared to PySPy. Among these compounds and tris(8-hydroxyquinolino)aluminum (Alq), the bipyridylsilole derivative, PyPySPyPy, showed the highest electron-transporting abilities. The efficiency of a device consisting of ITO/triphenyldiamine derivative/Alq/PyPySPyPy/MgAg reached 2.2 lm/W at 3.4 V. Furthermore, the half-life time of a device consisting of ITO/triphenylamine dimer derivative/Alq/PyPySPyPy/LiF/Al was nearly 3 times longer than that of the control ...

Several types of nitrogen-, oxygen-, and sulfur-functionalized silyllithiums have been prepared as the first members of stable and/or well-characterizable functionalized silyl anions. These functionalized silyllithiums can be obtained mainly by tin-lithium exchange reaction of the corresponding silylstannanes with butyllithium and/or by reaction of the corresponding chlorosilanes with lithium. Described herein are also the general aspects of (1) high stability of[(amino) silyl]lithiums, (2) low stability of [(alkoxy)silyl]lithiums, behaving as silylenoid species, (3) low stability of [(arylthio)silyl]lithiums, affording silylenes, (4) structure analyses of the [(amino)silyl]lithiums in solution and in the solid state, (5) [2, 3]-sila-Wittig rearrangement and cyclopropanation reaction of [(allyloxy)silyl]lithiums and the chirality transfer during these reactions, (6) functionalized oligosilane synthesis using [(amino)silyl]lithiums, and (7) synthetic application of (aminosilyl)lithiums as a hydroxy anion equivalent by a combination with the oxidative cleavage of the Si-C bonds.

The pentacoordinate disilanes bearing an 8-chalcogeno-1-naphthyl group and an ethoxy group (or a fluorine atom) on the same silicon center are found to be thermally stable, in sharp contrast to the thermal lability of the analogous disilanes coordinated by the group 15 elements, such as nitrogen and phosphorus, to α-elimination of the ethoxysilane (or fluorosilane) to generate the base-coordinated silylenes. As the reasons for this different behavior, two possibilities are pointed out as follows: (1) the nitrogen-coordinated disilanes are destabilized due to the distortion of the naphthyl moiety, and (2) silylenes are more stabilized by coordination with the group 15 elements than with the group 16 elements. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:392–397, 2001

A series of tris(phenylethynylduryl)boranes (R-C(6)H(4)-Ctbd1;C-duryl)(3)B with various substituents R have been prepared as air-stable solids owing to the steric protection of the boron atom by the three bulky duryl groups. These compounds show unique photophysical properties due to the p(pi)-pi conjugation through the p-orbital on the boron atom. In particular, a push-pull type derivative with R = NMe(2) exhibits a significant solvatochromism of fluorescence from blue to orange colors.

Poly(1,1-silole)s were synthesized for the first time in 1999, by us and by West and his coworkers, as a new type of polysilane which is expected to have a low-lying LUMO due to the σ*–π*conjugation characteristic of the silole ring. Summarized herein are the development of new synthetic methodologies and the structural aspects, photophysical properties and a unique reactivity of the resulting oligo- and poly(1,1-silole)s.