9 research outputs found

    Pentasila-1,4-diene: Homoconjugation between Siî—»Si Double Bonds via a SiMe<sub>2</sub> Unit

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    Although the synthesis of several bis­(disilenes) has already been reported, the number of reported conjugation modes between the SiSi double bonds remains limited. Herein, we report the properties of the stable pentasila-1,4-diene <b>1</b>, which was obtained from the reaction of two equivalents of disilenide <b>4</b> with dichlorodimethylsilane. The π­(SiSi)→π*­(SiSi) absorption band of <b>1</b> is considerably broadened and red-shifted compared to those of the corresponding monodisilene and hexasila-1,5-diene, but blue-shifted relative to those of typical tetrasila-1,3-dienes. The bathochromic shift and the broadening of the absorption band in <b>1</b> should be attributed to the homoconjugation between SiSi double bonds through the SiMe<sub>2</sub> unit

    Redox Reactions of a Stable Dialkylphosphinyl Radical

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    A stable dialkylphosphinyl radical, 2,2,5,5-tatrakis­(trimethylsilyl)-1-phosphacyclopentan-1-yl (R<sup>H</sup><sub>2</sub>P<sup>•</sup>), showed both irreversible one-electron oxidation and reduction peaks at −0.24 and −2.29 V vs ferrocene/ferrocenium couple. One-electron reduction of R<sup>H</sup><sub>2</sub>P<sup>•</sup> with KC<sub>8</sub> in the presence of 18-crown-6 (18-c-6) or [2.2.2]­cryptand (crypt-222) gave the corresponding phosphides [K­(18-c-6)]<sup>+</sup>[R<sup>H</sup><sub>2</sub>P]<sup>−</sup> and [K­(crypt-222)]<sup>+</sup>[R<sup>H</sup><sub>2</sub>P]<sup>−</sup>. Whereas [K­(18-c-6)]<sup>+</sup>[R<sup>H</sup><sub>2</sub>P]<sup>−</sup> exists as a contact ion pair, [K­(crypt-222)]<sup>+</sup>[R<sup>H</sup><sub>2</sub>P]<sup>−</sup> exists as a solvent-separated ion pair in the solid state. Reaction of R<sup>H</sup><sub>2</sub>P<sup>•</sup> with AgOTf afforded an unexpected product, a silver­(I) phosphaalkene complex

    New Isolable Dialkylsilylene and Its Isolable Dimer That Equilibrate in Solution

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    The new isolable dialkylsilylene <b>3</b> bearing a bidentate alkyl substituent was synthesized. Recrystallization of silylene <b>3</b> gave yellow crystals of <b>3</b> and orange-red crystals of tetraalkyldisilene <b>4</b>, a dimer of <b>3</b>. In the solid state, <b>3</b> exists as a monomer with a closest distance of 6.745 Å between dicoordinate silicon atoms, while disilene <b>4</b> has a remarkably long SiSi double bond distance of 2.252 Å. An equilibrium between <b>3</b> and <b>4</b> in solution was observed by NMR and UV–vis spectroscopies, and the thermodynamic parameters of the equilibrium were estimated to be Δ<i>H</i> = −36 ± 3 kJ mol<sup>–1</sup> and Δ<i>S</i> = −170 ± 15 J mol<sup>–1</sup> K<sup>–1</sup>. Analysis of the percent buried volume, a measure of the steric demand around the divalent silicon, showed that the flexible steric bulkiness of the alkyl substituent of <b>3</b> and <b>4</b> allows the reversible dimerization of silylene <b>3</b> to disilene <b>4</b> and the isolation of both species

    Anthryl-Substituted 3‑Silylene-2-silaaziridine Obtained by Isomerization of Disilacyclopropanimine: An Exocyclic Silene Showing a Distinct Intramolecular Charge Transfer Transition

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    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

    Anthryl-Substituted 3‑Silylene-2-silaaziridine Obtained by Isomerization of Disilacyclopropanimine: An Exocyclic Silene Showing a Distinct Intramolecular Charge Transfer Transition

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    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

    New Isolable Dialkylsilylene and Its Isolable Dimer That Equilibrate in Solution

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    The new isolable dialkylsilylene <b>3</b> bearing a bidentate alkyl substituent was synthesized. Recrystallization of silylene <b>3</b> gave yellow crystals of <b>3</b> and orange-red crystals of tetraalkyldisilene <b>4</b>, a dimer of <b>3</b>. In the solid state, <b>3</b> exists as a monomer with a closest distance of 6.745 Å between dicoordinate silicon atoms, while disilene <b>4</b> has a remarkably long SiSi double bond distance of 2.252 Å. An equilibrium between <b>3</b> and <b>4</b> in solution was observed by NMR and UV–vis spectroscopies, and the thermodynamic parameters of the equilibrium were estimated to be Δ<i>H</i> = −36 ± 3 kJ mol<sup>–1</sup> and Δ<i>S</i> = −170 ± 15 J mol<sup>–1</sup> K<sup>–1</sup>. Analysis of the percent buried volume, a measure of the steric demand around the divalent silicon, showed that the flexible steric bulkiness of the alkyl substituent of <b>3</b> and <b>4</b> allows the reversible dimerization of silylene <b>3</b> to disilene <b>4</b> and the isolation of both species

    Siloxy-Substituted Cyclopentadiene Showing Aggregation-Enhanced Emission: An Application of Cycloaddition of Isolable Dialkylsilylene

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    Cycloaddition of an isolable dialkylsilylene converted nonemissive 2,3,4,5-tetraphenylcyclopentadienone to an emissive siloxycyclopentadiene, which shows aggregation-enhanced emission behavior with a light blue fluorescence (λ<sub>em</sub> = 474 nm, Φ<sub>F</sub> = 0.11) in the solid state rather than in solution

    Siloxy-Substituted Cyclopentadiene Showing Aggregation-Enhanced Emission: An Application of Cycloaddition of Isolable Dialkylsilylene

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    Cycloaddition of an isolable dialkylsilylene converted nonemissive 2,3,4,5-tetraphenylcyclopentadienone to an emissive siloxycyclopentadiene, which shows aggregation-enhanced emission behavior with a light blue fluorescence (λ<sub>em</sub> = 474 nm, Φ<sub>F</sub> = 0.11) in the solid state rather than in solution

    Hydrogen Bonds-Enabled Design of a <i>C</i><sub>1</sub>‑Symmetric Chiral Brønsted Acid Catalyst

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    We have developed new <i>C</i><sub>1</sub>-symmetric, chiral bis-phosphoric acids with an electron-withdrawing group as one of the two substituents. This <i>C</i><sub>1</sub>-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 <i>C</i><sub>1</sub>-symmetric chiral environment of chiral bis-phosphoric acid catalysts. The developed strategy, <i>C</i><sub>1</sub>-symmetric catalyst design through hydrogen bonding, is potentially applicable to the development of other chiral Brønsted acid catalysts
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