Bicyclo[1.1.0]but-1(2)-ene (BBE), one of the smallest bridgehead alkenes and C 4 H 4 isomers, exists theoretically as a reactive intermediate, but has not been observed experimentally. Here we successfully synthesize the silicon analogue of BBE, tetrasilabicyclo[1.1.0]but-1(2)-ene (Si 4 BBE), in a base-stabilized form. The results of X-ray diffraction analysis and theoretical study indicate that Si 4 BBE predominantly exists as a zwitterionic structure involving a tetrasilahomocyclopropenylium cation and a silyl anion rather than a bicyclic structure with a localized highly strained double bond. The reaction of base-stabilized Si 4 BBE with triphenylborane affords the [2 þ 2] cycloadduct of Si 4 BBE and the dimer of an isomer of Si 4 BBE, tetrasilabicyclo[1.1.0]butan-2-ylidene (Si 4 BBY). The facile isomerization between Si 4 BBE and Si 4 BBY is supported by theoretical calculations and trapping reactions. Structure and properties of a heavy analogue of the smallest bridgehead alkene are disclosed.

A platinum(0) complex, bearing a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (DVTMS) and an isolable dialkylsilylene ligand, was successfully synthesized by the reaction between the dialkylsilylene and Karstedt's catalyst. The downfield-shifted 29 Si NMR resonance, the smaller 1 J Si,Pt value, and the longer Si−Pt distance in this complex relative to the corresponding parameters in related bis(phosphine)coordinated silylene-platinum complexes suggest weaker πback-donation from the Pt center to the silylene, which is, however, still significant when compared to related DVTMS-ligated Pt complexes bearing N-heterocyclic carbenes, Nheterocyclic two-coordinate silylenes, or base-stabilized three-coordinate silylenes. The title complex displays excellent catalytic activity in the hydrosilylation of terminal olefins that contain functional groups such as epoxide and amine moieties.

We have developed new C 1-symmetric, chiral bis-phosphoric acids with an electron-withdrawing group as one of the two substituents. This C 1-symmetric, chiral bis-phosphoric acid with a pentafluorophenyl group performs exceptionally well in the asymmetric Diels–Alder reaction of acrolein, methacrolein, and α-haloacroleins with substituted amidodienes. Control over the atropisomeric catalyst structure, enhancement of the catalytic activity, and differentiation of the asymmetric reaction space is possible by the remote control of the pentafluorophenyl group. Furthermore, we have conducted theoretical studies to clarify the roles of both intra- and intermolecular hydrogen bonds in the C 1-symmetric chiral environment of chiral bis-phosphoric acid catalysts. The developed strategy, C 1-symmetric catalyst design through hydrogen bonding, is potentially applicable to the development of other chiral Brønsted acid catalysts.

A platinum(0) complex bearing a cyclic (alkyl)(amino)silylene and a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane (DVTMS) was synthesized and isolated in the form of colorless crystals. The single-crystal X-ray diffraction analysis of this complex in combination with theoretical calculations indicated that the Pt→Si π-back-donation in this complex is weaker than that in the corresponding cyclic-dialkylsilylene-ligated Pt complex. The performance of this complex in the catalytic hydrosilylation of (MeSiO)MeSi-H with various terminal alkenes that contain functional groups was comparable to that of the corresponding cyclic dialkylsilylene/DVTMS Pt(0) complex.

Molecular silicon clusters with unsubstituted silicon vertices (siliconoids) have received attention as unsaturated silicon clusters and potential intermediates in the gas-phase deposition of elemental silicon. Investigation of behaviors of the siliconoids could contribute to the greater understanding of the transformation of silicon clusters as found in the chemical vapor deposition of elemental silicon. Herein we reported drastic transformation of a Si 8 R 8 siliconoid to three novel silicon clusters under mild thermal conditions. Molecular structures of the obtained new clusters were determined by XRD analyses. Two clusters are siliconoids that have unsaturated silicon vertices adopting unusual geometries, and another one is a bis(disilene) which has two silicon-silicon double bonds interacted to each other through the central polyhedral silicon skeleton. The observed drastic transformation of silicon frameworks suggests that unsaturated molecular silicon clusters have a great potential to provide various molecular silicon clusters bearing unprecedented structures and properties.

An anthryl-substituted exocyclic silene, 3-silylene-2-silaaziridine, was synthesized by isomerization of the corresponding disilacyclopropanimine. The UV-vis spectrum of the silene shows a distinct intramolecular charge transfer (ICT) transition from the π orbital of the Si═C double bond to the π* orbital of the anthryl moiety. The relatively high-lying π(Si═C) orbital of the 3-silylene-2-silaaziridine moiety and the low-lying π* orbital of the anthryl group would be responsible for the distinct ICT band.

Although the oxidative coupling of disilenides, i.e., the disilicon analogues of vinyl anions, represents a promising route to extend the conjugation between SiSi double bonds, previously reported synthetic routes to disilenides involve strongly reducing conditions. Herein, we report a novel synthetic route to disilenides from stable disilenes via the selective cleavage of Si­(sp2)–Si­(sp3) bonds under milder reaction conditions. Using this method, a 1,4-bis­(trimethylsilyl)­tetrasila-1,3-diene (5) was synthesized from the corresponding silyl-substituted disilene. Moreover, Et3Si-substituted tetrasila-1,3-diene 7 was synthesized via tetrasila-1,3-dien-1-ide 6, which is the first example of a functionalized tetrasila-1,3-diene.

Treatment of 1,3-di­(t-butyldimethylsilyl)-1,3-disilabicyclo­[1.1.0]­butane 1a with excess lithium in THF provided 1,3-dilithio-1,3-disilabicyclo[1.1.0]­butane 2 via reductive cleavage of the exocyclic Si–Si bonds at the bridgehead silicon atoms. In the single crystals obtained by recrystallization in the presence of 1,2-dimethoxyethane (DME), 2 exists as a solvent-separated ion pair, and its anionic part forms an aggregate that contains three lithium atoms sandwiched by two 1,3-disilabicyclo[1.1.0]­butan-1,3-diide units. Treatment of 2 with chlorotri­isopropylsilane provided triisopropylsilyl-substituted 1,3-disilabicyclo[1.1.0]­butane 1b. The structural characteristics of 1b are close to that of the short-bond isomer, which is consistent with previous theoretical predictions concerning the steric effects of the bridgehead substituents on the structure of silabicyclo[1.1.0]­butane.